APPENDIX II-CH:  Wilson, et al, “Overkill: Why Pesticide Spraying for West Nile Virus in California May Cause More Harm Than Good,” Pesticide Watch, August, 2003.


This appendix is copied from:


Pesticide Watch

Matt Wilson, Toxics Action Center

Will Sugg, The Maine Environmental Policy Institute

Jasmine Vasavada, Pesticide Watch

August 2003


Why Pesticide Spraying for

West Nile Virus in California

May Cause More Harm

Than Good


The most important person to acknowledge

in this paper is Rachel Carson. Her

book Silent Spring is the wellspring from

which this continuing work to protect the

public from toxic pesticides flows.

This report is heavily indebted to earlier

editions that described problems with

pesticide spraying for West Nile Virus

control in Maine and Massachusetts. The

Maine Environmental Policy Institute

board of directors (Kevin Mattson, Tom

Federle, Matt Scease, and Susie O’Keefe)

supported the first edition, which benefited

from the careful review of Heather

Spalding, Rob Baldwin, Mitchel Cohen,

Sharon Tisher, RusselI Libby, Kathleen

McGee, George and Laura Appell, Paul

Donahue, Mitch Lansky, Will Everitt,

Kim DeFeo, and Elizabeth Spalding.

Without their advice and generosity this

report would not have been possible.

Dr. David Ozonoff, Rachel Zegerius,

Sue Phelan, Stephen Seymour, Ellie

Goldberg, Sarah Little, Monica Garlick,

and Aimee Qui provided significant insights

and review of the report’s Massachusetts


Pesticide Watch gratefully acknowledges

Gina Solomon, M.D., M.P.H.,

Natural Resources Defense Council for

her review and comments, Dave Henson

of the Occidental Arts and Ecology

Center for his insights, and Cornell

“We should no longer accept the counsel of

those who tell us that we must fill our world with

poisonous chemicals; we should look about and

see what other course is open to us.”

Rachel Carson, Silent Spring, 1962

University Professor David Pimentel for

helping navigate the scientific literature.

Also, thanks are due to Tony Dutzik and

Brad Heavner of the Frontier Group of

the State PIRGs who provided keen editorial


Some groups and resources stand out

as being particularly valuable to anyone

researching this issue, and to us in particular:

the No Spray Coalition of New

York; Northwest Coalition for Alternatives

to Pesticides; Pesticide Action Network

of North America; Extension

Toxicology Network; Environmental

Risk Analysis Program (ERAP) of

Cornell University Center for the Environment;

and Rachel Massey and Peter

Montague of the Environmental Research


In addition, we would like to acknowledge

numerous scientists and public education

staff at California mosquito and

vector control agencies who provided

Ê timely, localized information about

preparations for West Nile Virus already

ongoing in the state. In researching this

report, we found that these men and

women, on the front lines of protecting

public health from West Nile Virus in

California, are highly sensitized to the

risks entailed by indiscriminate pesticide

spraying, and are working hard to educate

and activate the public to help take

preventative measures before the virus

arrives in the Golden State.

Thanks also to Harriet Eckstein

Graphic Design.

This report was made possible by the

generous support of Pesticide Watch’s

citizen members. The recommendations

are those of Pesticide Watch, who alone

bears responsibility for any factual errors.

© 2003 Pesticide Watch Pesticide Watch is a grassroots non-profit organization dedicated to turning the toxic

tide of pesticide use in California while pioneering new strategies for empowering communities to protect themselves

and their local environment from the hazards of pesticides.

Table of Contents

Executive Summary 5

Introduction 7

Background 9

Transmission of West Nile Virus 9

The Westward Spread of West Nile Virus 10

The Public Health Impact of West Nile Virus 10

Preparing for West Nile Virus in California 13

West Nile Virus in California? 13

California’s West Nile Virus Surveillance and Response Plan 15

California’s Pesticide Spray Policy 18

Federal Guidelines 18

The Role of Local Agencies in Mosquito Control 19

Pesticide Spraying May Do More Harm Than Good 21

Pesticide Spraying Is Not Proven Effective in Curbing

Human Infection Rates 21

Effectiveness of Spraying in Controlling Mosquito

Populations Is Limited 22

Pesticide Spraying Could Make West Nile Virus Worse 23

Pesticides May Kill Off Natural Mosquito Predators 24

Pesticides Can Make Animals More Susceptible to WNV Infection 25

Pesticide Spraying May Reduce Participation in Other

Important Public Health Measures 26

Pesticide Spraying Entails Significant Risk of Public Exposure 26

Known Health and Environmental Impacts

of Pesticides Approved for Use in California 27

Pyrethroids 27

Organophosphates 29

Larvicides 34

Biopesticides 36

Unknown Health Impacts of Mosquito Control Pesticides 38

“Inert” Ingredients Escape Public Disclosure 38

Pesticides Are Not Proven Safe 39

Balancing the Risks 41

Principles for Safe, Effective Mosquito Control Measures

on the State and Local Level 43

Give Public Health, Not Pesticides, the Benefit of the Doubt 43

To Protect Public Health, Prioritize Alternatives

to Pesticide Spraying 43

Steps Individuals Can Take 45

Appendix: California Mosquito Control Contacts 49

Endnotes 55

4 Overkill: Pesticide Spraying in California

Introduction 5

Executive Summary

Since its emergence in New York City

in 1999, West Nile Virus (WNV)

has spread rapidly across the United

States. The disease, borne by wild birds

and transferred to humans by bird-biting

mosquitoes, is likely to reach California

shortly. If and when WNV does

arrive, California communities must be

prepared to respond in a manner that prevents

harm to human health and the environment.

In doing so, California can

and should avoid the massive pesticide

spraying programs that have been triggered

in other states at the first sign of

West Nile Virus.

Broadcast pesticide spraying, by truck

or aerial application, has not been

proven effective in curbing WNV:

• The Centers for Disease Control and

Prevention have stated that ground

and aerial spraying targeted at adult

mosquitoes is one of the least effective

mosquito control techniques.

• Northeastern communities (Boston,

NYC) that first responded to WNV

with massive spraying subsequently

scaled back their use of adulticides,

prioritizing preventative measures

and establishing stricter criteria to

limit adulticide spraying.

• Despite three years of widespread

spraying to control WNV, no scientific

studies have demonstrated that

such spraying has effectively reduced

the human risk of infection.

Spraying may cause more harm than


• Pesticide spraying may actually

increase the number of mosquitoes

by killing off insect predators such as

dragonflies that feed on mosquitoes

and their larvae.

• Pesticide spraying may increase

infection rates by leading mosquitoes

to develop resistance, live longer,

exhibit more aggressive biting

behavior, and become more susceptible

to infection by WNV.

• Pesticide spraying may create a false

sense of security, diminishing public

participation in preventative public

health measures that are necessary

to effectively reduce the risk of

6 Overkill: Pesticide Spraying in California

contracting WNV. Such measures

include wearing protective clothing

and helping reduce mosquito habitat

by eliminating stagnant water that

serves as a breeding ground for


Pesticide spraying will expose human

beings and nontarget organisms to

chemicals known to affect human

health and the environment:

• For spraying to be effective at all, it

must be timed during the hours

when the mosquitoes are most active

(for most species, the early evening).

However, these same times entail the

greatest risk of exposure to the

general population.

• The chance of any one individual

becoming seriously ill from exposure

to West Nile may be significantly

lower than an individual’s chance of

becoming ill from pesticide exposure.

For example, in 1999 there were 59

known cases of meningitis due to

WNV infection in New York City,

and 187 individuals who reported

experiencing illness after malathion


California’s current West Nile Virus

Response Plan is overly permissive of

dangerous and ineffective pesticide


• Current pesticides approved for

mosquito control in the state include

organophosphates (malathion) and

pyrethroids (Pyrethrin, Sumethrin,

Resmethrin) known to have serious

human health impacts.

• Human health risk assessment

studies, conducted to show these

pesticides are theoretically "safe" if

applied correctly, routinely fail to

account for errors in application

rates and vulnerability of certain

populations, such as infants and the


To ensure minimal environmental and

human health impact, and maximum

effectiveness in mosquito control, the

state plan should be revised to:

• Include strict parameters limiting

the use of health-threatening


• Include specific benchmarks to help

promote public outreach, communication,

and education activities

essential for a preventative public

health strategy.

In addition, local mosquito and vector

control agencies, which will have significant

decision-making power to choose

among mosquito control options, should

immediately initiate a public process in

which concerned community members

can be involved in outreach and education

about mosquito prevention activities

as well as the establishment of strict

local thresholds to reduce or eliminate

the use of pesticide sprays in mosquito


Introduction 7


If and when West Nile virus hits

the West Coast, officials are

prepared to pull out the big

guns. California mosquito

control, now quelling larvae

with environmentally

compatible hormones and

bacteria, would expand to

include air and ground spraying

with insecticides to kill adult

mosquitoes, a state health

official said.

Wall Street Journal Aug 13, 20021

The mosquito-borne West Nile Virus

has traveled across the nation as

far as the Rockies and Washington

State, and is expected to eventually reach

California. When it does, local leaders

and mosquito vector control districts may

be sorely tempted to “pull out the big

guns,” supplementing normal mosquito

control programs with widespread aerial

and ground spraying of toxic pesticides.

Considering the toxicity of such pesticides

to human beings, the ecological

damage they may cause, and their lack of

proven effectiveness in curbing West

Nile, mounting such an offensive may

pose a greater threat to public health than

the West Nile Virus itself.

As the disease has spread rapidly

throughout the nation, states and municipalities

have been forced to scramble to

develop emergency control plans for

mosquitoes. Too often, this crisis management

has relied on spraying entire

neighborhoods, fields, and water bodies

in an attempt to wipe out adult mosquitoes.

Only after the initial crisis has subsided

have health officials and local leaders

8 Overkill: Pesticide Spraying in California

taken time and resources to develop effective

control plans emphasizing mosquito

surveillance, prevention, and public

education—and ensuring a response appropriate

to the level of risk that West

Nile Virus actually poses to most people.

Fortunately, California communities

are in a unique position to avoid the overkill

that has characterized the response

to West Nile Virus in so many parts of

the country. California has had time to absorb

the lessons from WNV control in

the northeastern and Gulf states. Furthermore,

California has a robust infrastructure

in place to prevent mosquito-borne

diseases, several of which are endemic to

the Golden State.

More than 50 mosquito control districts

have been established throughout

the state, with budgets ranging from several

hundred thousand to several million

dollars. These districts rely on guidelines

from the California Department of

Health, which has designed a West Nile

Virus response plan focused on preventative

measures that limit the need for

pesticide spraying—prioritizing elements

of an ideal strategy to effectively control

mosquito populations while minimizing

the spraying of harmful (and largely ineffective)


While the state plan includes guidance

about how to determine when pesticide

spraying is appropriate, local agencies are

left to decide when and where to do so.

Ultimately, community leaders, health

experts, and concerned citizens will need

to work on the local level to ensure that

the agencies, and the public, are not

forced to make a false choice between

“doing something” to stop WNV by

spraying pesticides, or allowing West Nile

to spread by not using pesticides. Rather,

the true choice is between addressing

West Nile Virus with rational control

measures that have been proven effective

or spraying pesticides that may do more

harm than good.

Background 9


The 2002 WNV epidemic in the

U.S. was the largest arboviral

meningoencephalitis epidemic

documented in the Western Hemisphere

and the largest reported

WNME [West Nile Meningoencephalitis]

epidemic. Epizootic and

epidemic activity was most intense

in the central U.S., especially in the

Great Lakes region, and extended

to the West Coast [indicating]

complete transcontinental

movement of WNV within 3 years.

Centers for Disease Control, Morbidity

and Mortality Weekly, December 20, 2002

Figure 1. West Nile Virus Transmission Cycle

Transmission of WNV

Mosquitoes transmit WNV to humans

after biting infected birds, the primary

hosts of WNV. In addition to humans,

horses, bats, and other small mammals

can all serve as alternate hosts. There is

some evidence that amphibians such as

frogs can host WNV as well.2 The WNV

transmission cycle is depicted in Figure 1.

WNV is in a family of arboviruses (arthropod-

borne viruses). It is closely related

to Western Equine encephalitis and

St. Louis encephalitis, mosquito-borne

diseases for which many states have already

developed mosquito control programs.

10 Overkill: Pesticide Spraying in California

Indicates verified human disease case(s)

Verified avian, animal, or mosquito

infections during 2003

Figure 2. West Nile Virus in the United States as

of July, 2003

The Westward Spread

of West Nile Virus

WNV originated in Africa, from which

it spread to the Mediterranean, the

Middle East, and parts of Asia. In 1999,

it emerged in the Western Hemisphere

for the first time in New York City. Infected

wild birds carried the disease up

and down the Eastern Seaboard, then

westward through the Gulf States and up

to the Rockies.4 By the end of 2002,

WNV had been detected in 2,289 counties

in 44 states across the US, an increase

from 359 counties in 27 states and Washington,

D.C. in 2001.5

Experts now believe WNV will never

be eradicated from the United States but

rather will become endemic throughout

the country in areas where related illnesses

such as Western Equine encephalitis

and St. Louis encephalitis are found.

According to the Centers for Disease

Control and Prevention (CDC), from

1964 to 1998, there were 122 confirmed

human St. Louis encephalitis cases in


Over the past three years, WNV has

demonstrated its ability to adapt to different

types of mosquitoes — the vectors

that transfer the virus from one host to

another — allowing WNV to thrive in

Illinois’ long summer days as well as the

hot, humid weather of Louisiana, Mississippi

and Texas.6 The map in Figure 2

depicts states where infected birds, mosquitoes,

or animals have been discovered

as of July 2003.

The Public Health Impact

of West Nile Virus

Rates of Human Infection by WNV

As the disease has spread across the country,

the number of people infected by

West Nile has also steadily increased.

From 1999 to 2001, the CDC confirmed

149 cases of human illness and 18 deaths

attributed to WNV. Last year, as the disease

traveled to the Midwest and South,

the number of laboratory-confirmed

human infections grew to 4,156, including

284 deaths.7

In 2002, the Midwest was especially

hard hit by WNV. A provisional analysis

by the CDC estimated that 5 states experienced

64% of the nation’s known

WNV illness in 2002: Illinois, Michigan,

Ohio, Louisiana, and Indiana. The first

four of these states, together with Texas,

accounted for 67% of reported meningitis

resulting from West Nile infection.8

The data show that WNV poses a

small but real risk to the general population.

In New York State, where the disease

first emerged, studies showed that

less than one-tenth of one percent of

people bitten by infected mosquitoes

evinced any symptoms of the disease, and

even fewer exhibited serious symptoms

such encephalitis or meningitis, in which

the brain or its casing becomes inflamed.9

A Louisiana study found that in St.

Tammany Parish, eight people in 100,000

showed any WNV symptoms (also less

than one-tenth of one percent), but of

Background 11

those, a significant number developed

encephalitis, and the risk of death was 4

in 1 million.10

In general, elderly and immuno-compromised

individuals face the greatest risk

of serious illness associated with a West

Nile infection. According to a CDC

analysis of WNV cases from January

through November 2002, the median age

of WNV-infected people was 55 years,

and the median age of people who experienced

meningitis was 59 years. Of the

2,354 people with meningitis, 199, or 9%,

died; in addition, 2 elderly people (more

than 80 years old) died of the normally

less-serious West Nile Fever. The median

age of those who died from West Nileassociated

illness was 78 years.11

Many believe that these infection rates

will subside as West Nile Virus becomes

“endemic” to the United States, and will

be characterized by low baseline infection

rates interrupted by sporadic outbreaks.

In Africa, where West Nile Virus

has been recognized for more than sixty

years and where it is widespread, very few

human epidemics have been identified.

The same has been observed in the

United States with related infections,

such as St. Louis encephalitis and Eastern

equine encephalitis, where 30 or more

years may pass between human outbreaks.

New York City’s Experience with

WNV and Mosquito Control

In the summer of 1999, a physician noted

a cluster of patients in Queens, New York

City, who were thought to be infected

with St. Louis encephalitis. This was later

determined to be WNV, the first known

emergence of the disease in the United


City officials, lacking a robust mosquito

control plan, followed CDC recommendations

to embark on an aerial

insecticide spraying program. A $5 million

program of repeated aerial applications

of malathion, a pesticide related to chemicals

developed for military use in World

War II, ensued. Some neighboring counties

sprayed heavily as well, some even in

the absence of confirmed human infection.

Other counties did not spray.

This emergency management measure

occurred with minimal assessment of the

relative risks to human health associated

with exposures to the sprayed insecticides

versus those of contracting WNV. Indeed,

little was known about WNV or

whether the outbreak could be limited

geographically by intensive aerial spraying.

During the first spray season, 187

people reported health symptoms associated

with malathion exposure to New

York City’s Poison Control Center.13

In 2000, after significant public opposition

to aerial spraying and hundreds of

complaints from people reporting pesticide

exposure, the NYC Health Department

switched from its aerial campaign

to largely ground-based spraying of Anvil,

a pyrethroid.14 A private contractor

hired by the city sprayed this pesticide

(which consists of the active ingredients

sumithrin and piperonyl butoxide) in a

two-mile radius around places where

WNV infections or infected dead birds

were reported.

By 2001, new data indicated that spraying

should be further restricted to a onemile

radius, and even then only as a “last

resort.” Furthermore, city officials

switched to an emphasis on prevention.

“While last year we had a formulaic and

somewhat reflexive approach . . . this year

we’re going to look very carefully to determine

where the greatest risk to people

is,” City Health Commissioner Dr. Neal

Cohen told a New York Post reporter.15 In

a separate interview with the New York

Times, city officials stated: “To reduce the

reliance on pesticides in the battle against

West Nile virus, the city will use a more

conservative, concentrated approach to

spraying this summer.”16

12 Overkill: Pesticide Spraying in California

Infection Rates Case Study:

A Closer Look at NYC

Surveys of blood samples taken from New

Yorkers have revealed that many people

infected with the virus never evinced any

symptoms. A New York City Health Department

survey of blood samples taken

from people who lived in northern

Queens, the epicenter of the 1999 outbreak,

showed that 19 out of 677 tested

positive for the virus, but none had become

seriously ill, and all either reported

no symptoms or mild illness, such as a

low-grade fever.

The survey’s statistical analysis concluded

that between 1.2 percent and 4.1

percent of the 46,000 residents (533 and

1,903 people) in that three-square-mile

area had probably been infected. Of the

infected group, four people in the sample

had non-specific aches, pains or fever.

The others presented no symptoms.17

However, some people did become ill

from WNV, and some deaths were recorded.

Out of New York City’s population

of more than 7 million, 62 people —

or less than .0009% — became ill with

the virus, and 7 died (one in one million).

While this is a real and quantifiable

public health impact that should not be

dismissed, one must question whether the

pesticide spraying campaign that New

York City embarked upon was an appropriate

response to the West Nile threat.

A comparison of WNV infection rates

to rates of influenza in New York City in

1999 can provide some context, revealing

that 2,474 individuals in New York

City died from influenza or pneumonia

in 1999, representing 400 times the number

of WNV mortalities.18

Preparing for WNV in California 13

WNV in California?

Given the rapid spread of WNV in the

three years since its introduction on the

East Coast, it is likely that WNV will

arrive here this summer.

To date, no wild birds, sentinel chickens,

or mosquito pools have tested

positive for WNV in California. One

known instance of human infection has

been documented. However, since the

person lived near Los Angeles International

Airport and no other tests have

revealed the presence of WNV, this infection

is generally attributed to a bite

from an infected mosquito that arrived

on board an airplane.

California is home to more than 40

mosquito species. The state’s urban areas,

coastal bays and wetlands, and the drainage

ditches and irrigation canals of the

Central Valley provide a range of potential

habitats. Laboratory experiments have

indicated that several California species

are likely to transmit West Nile Virus.

While mosquitoes are found in all parts

of the state, officials have noted that

southern areas, such as the Imperial Valley

and Riverside County, have been most

Preparing for WNV in California

We fully expect that, over time,

the virus will make it to the West

Coast. What the timing of it will

be is unknown at this time. It’s

unknown whether the virus

will make it to California or the

West Coast this year or next

year or the year after that. It’s

completely a matter of conjecture.

Dr. Peterson, Medical Epidemiologist,

CDC Center for Infectious Diseases19

14 Overkill: Pesticide Spraying in California

Figure 4: Culex pipiens, the house


Figure 3: A NASA-funded study mapped

satellite imagery of temperature and

vegetation to help predict where West

Nile virus will spread.

Photo: Courtesy of CDC

Photo courtesy of NASA

Culex pipiens, the “house


In residential and urban areas, the common

house mosquito, C. pipiens, is expected

to play a significant role as well.

C. pipiens has been the primary WNV

vector in much of the nation, and breeds

in stagnant, standing fresh water. It can

be found in high concentrations at

sewage treatment plants and often lives

underneath buildings, in storm drains,

and in catch basins. It bites primarily in

the evening and after dark, and is not active

in daylight. Because C. pipiens rarely

travels distances greater than a half mile,

local efforts to eliminate breeding sites

can play a major role in controlling human

health impacts.

Ochlerotatus squamiger

The salt marsh mosquito, Ochlerotatus

squamiger, inhabits coastal regions from

Sonoma County down to the Baja peninsula.

Unlike Culex species, this mosquito

breeds in brackish tidal waters. A

strong flyer, it easily reaches nearby cities

during its early morning and late afternoon

flights, and is considered a

significant nuisance in cities like San

Francisco.24 Preliminary studies show it

is not as readily infected with WNV as

C. pipiens. However, it is of concern due

to its abundance and more aggressive biting


vulnerable to other forms of mosquitoborn

encephalitis, and are therefore likely

to be most vulnerable to WNV as well.20

Culex tarsalis, the “encephalitis


In the western United States, Culex

tarsalis is the primary carrier of Western

Equine encephalitis and St. Louis encephalitis,

and is therefore expected to be

a significant vector of WNV should it

arrive in California. This mosquito,

which bites mostly between sunset and

midnight, has been shown in laboratory

experiments to readily become infected

by and transmit WNV.

C. tarsalis is especially abundant in the

Central Valley and coastal regions. It can

live in all but the most polluted waters,

ranging from wetlands and salt marshes

to puddles and containers. In most places

C. tarsalis is most active in the spring and

fall, but in Southern California it is active

all winter long.21 After years of intense

efforts to keep this endemic species

under control, vast populations in the

Central Valley have become resistant to

nearly all the common chemical insecticides.


In populated areas, other species such

as Culex quinquefasciatus and Culex pipiens

are also expected to play a significant role

in the transmission of WNV.23

Preparing for WNV in California 15

“‘Carpet bombing, like what some states have done, would be our last resort,’ and only

‘if the powers that be agree that it’s necessary to protect human life.’”

Ted Toppin, Spokesperson, Mosquito and Vector Control Association of California, Boston Globe April 3, 200325

Mosquito Surveillance: Because mosquitoes

are the vectors of viruses like West

Nile Virus, monitoring mosquitoes provides

a somewhat accurate estimate of the

immediacy of risks to humans. Mosquitoes

are tested using fixed trap sites. These

sites provide information regarding

mosquito numbers, virus prevalence and

estimation of WNV risk. More intensive

mosquito trapping will be employed in

response to increased virus activity in specific


Sentinel Chickens and Wild Bird

Surveillance: WNV is fatal to birds, with

a particularly high mortality rate in

American crows. Therefore, dead birds

are potential indicators of virus activity

in an area, and bird reporting and testing

will be an important component of

California’s efforts. Approximately 200

chicken flocks, known as “sentinel chickens,”

are strategically placed throughout the

state and are tested routinely during the

mosquito season to detect evidence of

infection from West Nile and other related


In addition, the California Animal

Health and Food Safety Laboratory

screens dead wild birds and sends tissue

samples to UC-Davis and the Department

of Health Services for testing.25

Equine Surveillance: Because many

horses are vaccinated against viruses

borne by mosquitoes, they are not the

ideal species to study to keep track of the

spread of these viruses. Veterinarians are

contacted annually by DHS and the

California Department of Agriculture

(CDFA) to ensure that horses are vaccinated

and to describe diagnostic services


West Nile Virus Surveillance

and Response Plan

Following the West Nile outbreak in

New York in 1999, California leaders recognized

the need to update the state’s

mosquito control strategy to ensure

detection and prevention of the spread

of WNV.

The state plan was developed in a joint

effort of the California Department of

Health Services (DHS), the Mosquito

and Vector Control Association of California

(MVCAC), and the University of

California at Davis and Berkeley. It provides

guidelines for local agencies to use

in responding to the WNV threat.

This plan, available on the Web at, emphasizes

public education, prevention, and monitoring

as critical strategies to effectively

reduce the risk of WNV while minimizing

the use of harmful pesticides. However,

the plan does not rule out or set strict

thresholds to limit the systematic broadcast

of pesticides to kill adult mosquitoes.

Mosquito Monitoring and


Monitoring and surveillance are the first

line of defense against mosquito-borne

illnesses. California’s mosquito control

plan includes an extensive monitoring and

surveillance network to ensure prompt

detection and identification of WNV.

Such surveillance can play a critical role

in helping towns and counties avoid

unnecessary spraying. California’s surveillance

plan includes the following:

16 Overkill: Pesticide Spraying in California

Figure 5: Mosquitofish feed on mosquito


Biological Controls

Biological control entails the intentional

use of natural predators or parasites to

control mosquito populations. According

to the state Surveillance and Response

Plan, the most widely used biological

control agent in California is the

Mosquitofish, which can be released

annually in rice fields, small ponds, and


In addition, Bti and Bacillus sphaericus,

two microbial control agents, are

recommended for use in larval control.

Since these biological agents are applied

to treat water bodies in a manner similar

to chemical pesticides, they are discussed

further in the following section on chemical


Chemical Control

In addition to physical and biological control

measures, the State Mosquito Control

Plan explicitly lists a range of pesticides

“approved for use” in California. These

pesticides include adulticides, usually pesticide

sprays, which target adult mosquitoes,

and larvicides, generally liquids that

are applied to the pools of water where

mosquitoes breed. Many of these insecticides

are chemicals known to have significant

impacts on human health and

other organisms in the environment. A

partial list of pesticides “approved” for

use in California can be found in Table 1.

that are available in the event of a suspected

case of WNV or related diseases,

such as western equine encephalitis.

Human Surveillance: Specimens from

clinical human cases of encephalitis will

be screened in order to determine the

possible cause of infection. In addition,

hospitals will be contacted in the geographic

areas of increased virus activity.


The Mosquito-Borne Virus Surveillance

& Response Plan notes the importance

of public education in teaching people

how to protect themselves, and others,

from WNV. It refers to the important

role of residents, farmers, and duck club

owners in eliminating standing water, and

the need for education of the medical

community. The plan does not make specific

prescriptions of how such education

should be conducted, however.

Mosquito Control Measures

There are three general kinds of mosquito

control articulated in California’s plan:

environmental management, biological

control, and chemical control.

Environmental Management

Physical control measures discussed in

the California plan include water management

and vegetation management.

These include measures that increase the

water disposal rate through evaporation,

recirculation, or drainage, as well as restricting

growth of vegetation to decrease

habitat availability for immature mosquitoes.

These measures can be considered

“source reduction,” since they decrease

the number of breeding sites for mosquitoes.

According to the CDC, such measures

are the most effective and

economical methods of providing longterm

mosquito control in many habitats.26

Photo courtesy of CDC

Preparing for WNV in California 17

Table 1: Pesticides Approved For Use In California Mosquito Control Larvicides


Bacillus thuringiensis israelensis

(BTI: e.g. Vectobac, Teknar)

Bacillus sphaericus (e.g. Vectolex)

Methoprene (e.g. Altosid)

Diflurobenzamide (e.g. Dimilin)

Larviciding oils (e.g. Golden Bear 1111,

BVA Chrysalin)

Monomolecular Films (e.g. Agnique




a. Malathion (e.g. Fyfanon)

b. Naled (e.g. Dibrom, Trumpet EC)

Pyrethrins (natural pyrethrin products:

e.g. Pyrenone Mosquito Spray, Pyrocide)

Pyrethroids (synthetic pyrethrin products

containing resmethrin or permethrin:

e.g. Scourge)

Use: Approved for most permanent

and temporary bodies of water.

Use: Approved for most permanent

and temporary bodies of water.

Use: Approved for most permanent

and temporary bodies of water.

Use: Impounded tailwater, sewage

effluent, urban drains and catch basins.

Use: Ditches, dairy lagoons, floodwater.

Effective against all stages, including


Use: Most standing water including

certain crops.

Use: May be applied by air or ground

equipment over urban areas, some

crops including rice, wetlands.

Use: Air or ground application on

fodder crops, swamps, floodwater,

residential areas.

Use: Wetlands, floodwater, residential

areas, some crops.

Use: All non-crop areas including

wetlands and floodwater.

Note: Many Cx. tarsalis populations in the Central Valley are resistant to label organophosphate

application rates.

The plan acknowledges that some pesticides,

such as organophosphates, should

be used infrequently because of their impact

on non-target organisms and the

environment, but does not expressly

limit the use of these pesticides, beyond

stating that adulticides in particular are

used “when larval control is not possible

or has been used to the fullest extent


18 Overkill: Pesticide Spraying in California

California’s Pesticide

Spray Policy

The California Surveillance and Response

Plan identifies three levels of

mosquito control in response to three

levels of threat: normal season, emergency

planning, and epidemic conditions.

The plan states that adulticide spraying

“may be recommended” as an appropriate

response in the “emergency planning”

stage, as determined by the following


• Snow pack and rainfall above


• Significant increase in adult

mosquito populations;

• One or more WNV isolations

from mosquitoes;

• One to three chickens carrying

the virus antibodies per flock of

10 birds;

• One or two equine cases;

• One human case statewide;

• Viral activity in small towns or

suburban area; and

• Evidence of recent infection in

wild birds.

However, the plan does not set a strict

threshold that must be reached in a community

before a mosquito control district

can decide to spray. In the absence of such

thresholds, California mosquito control

districts may be vulnerable to politicallymotivated

calls for spraying, potentially

resulting in unwarranted application of

hazardous pesticides. They do not have

to prove that there is a public health

threat to conduct widespread spraying.

Like the federal guidelines, the state

plan leaves this decision in the hands

of local mosquito and vector control


Federal Guidelines

On the federal level, the Centers for Disease

Control and Prevention, Division of

Vector-Borne Infectious Diseases, has

developed West Nile Virus response

guidelines for individual states to use.27

These federal guidelines for surveillance,

prevention, and control of WNV

have changed with time, raising the

threshold at which pesticide spraying

should be considered and placing more

emphasis on preventative measures.

In 2000, for example, the guidelines

recommended chemical control (pesticide

spraying) of adult mosquitoes within

approximately a 2-mile radius around the

area where a WNV-positive dead bird or

infected mosquitoes were found.28 By the

following year, however, the CDC had

removed this direct recommendation of

broadcast spraying of adulticides. The

guidelines now state, “Control activity

should be initiated in response to evidence

of virus transmission [to humans],

as deemed necessary by local health departments.”


These revisions acknowledged the fact

that there is no truly objective evidence

to determine when and if spraying should

occur. “There is no simple formula for

determining how large an area to treat

around a positive surveillance indicator

or a suspected or confirmed human case

of WNV. Nor is there adequate information

to determine the degree of vector

population suppression that must be attained,

or for how long this suppression

must be maintained to reduce risk of disease.”

In the absence of scientific evidence to

support a specific spray policy, the revised

federal guidelines give state and local

officials significant flexibility in determining

how large an area to treat around a

positive surveillance indicator or a suspected

or confirmed human case of

WNV, or even whether to spray at all.

Preparing for WNV in California 19

East Bay vector control districts already are doing their part.

Wednesday, a team of all-terrain vehicles sprayed a flooded

pasture in Bethel Island, while a helicopter dropped insecticide

pellets into blackberry thickets and other hard-to-reach areas.

News report on March 14, 2003 in Contra Costa Times30

Figure 6. Organizational Flow Chart of a Mosquito Control District


The Role of Local Agencies

in Mosquito Control

In California, mosquito control is conducted

by more than 70 local agencies.

This includes 53 mosquito and vector

control districts, servicing areas inhabited

by 80% of the state’s population, and

dozens of environmental health and

county health departments. In areas without

defined vector-borne disease control

programs, the California Department of

Health Services provides oversight.

These local mosquito control districts

have significant leeway to decide to defer

pesticide spraying even if “Emergency

Conditions” specified by the state plan

are met. Conversely, these agencies have

significant leeway to increase use of

chemical pesticides even before a known

threat has emerged. Many of these districts

routinely spray pesticides to control mosquito

populations, even in the absence of

an “emergency” situation.

Mosquito Control Districts operate

under Sections 2200-2398 of the Health

and Safety Code of California. They develop

mosquito control plans based on

guidelines developed by the CDC and the

California Department of Health Services,

which outline acceptable mosquito

control practices and pesticide usages.

They also report pesticide use to the

County Agricultural Commissioner each


Mosquito control districts typically

cover half a dozen or more municipalities,

and many have a county-wide jurisdiction.

They are governed by boards of

trustees comprised of representatives appointed

from each member city and the

county at large. In most districts, the

Board of Trustees oversees the fiscal administration

of the organization but

leaves day-to-day operation and decisionmaking

in the hands of the District Manager.

(See Figure 6.) Funding is provided

by a combination of property taxes and

other special taxes authorized by local

voters. For a complete listing of California

Mosquito Control Districts and contact

information, see Appendix A.





Support Staff

Environmental Specialist

Equipment & Facilities Specialist

Entomological Specialist

Systems Specialist

Control Staff

Assistant Mosquito Control Technician, Mosquito Control Technician, Vector Biologist

Board of Trustees

One from each incorporated city and one from the County

20 Overkill: Pesticide Spraying in California

Local districts have considerable

decision-making power in choosing to

use, or refrain from using, pesticides. The

Alameda County Mosquito and Vector

Control District (CMVCD) is particularly

open about its decision-making process,

which is outlined in the Control Plan

posted on its Web site.

In 2002, the Alameda CMVCD reported

“regularly using” methoprene and

larvicides, and “occasionally using” the

adulticides pyrethrins, resmethrin, and

permethrin. In fact, adulticides, totaling

less than 1 ounce, were only applied on

two occasions in that year.

The following is an excerpt from their

control plan, available on the web at

The District uses a phased approach

to pesticide treatments. In the choice of

material to use District personnel will

use the material with the least impact

to control larvae and as a last resort,

localized adulticiding may be chosen.

In general this progression of choices

would be:

2Bti, Duplex (Bti + methoprene),

Methoprene, Oil or Agnique, Pyrethroids

Decisions on where and when to

treat are based on thresholds....These

thresholds are meant to be guidelines

since each site is different and other

factors play a role in the levels of

mosquitoes that can be tolerated. Some

of these factors are as listed:

• The proximity of homes or heavy

human use areas to the source.

• The age and distribution of the

immature mosquitoes in a source.

• The number of mosquito service

calls attributed to the source from

previous seasons.

• The expected weather conditions

and the season of the year.

• The accessibility to the source

(including special restrictions).

• The pest or disease significance of

the mosquito to be controlled in

the source.

• The size of the source (staff and

equipment needs increase with


• The sampling method used to

check the source.

• The number of active sources and

available personnel and equipment.

We surveyed Web sites of 20 mosquito

control districts, finding that control

plans are generally not posted on their

Web sites. However, these plans are public

information and should be available

upon request.

Pesticide Spraying 21

Pesticide Spraying May Do

More Harm Than Good

Pesticide Spraying

Not Proven Effective

In Curbing Human

Infection Rates

Does spraying pesticides to kill mosquitoes

have a significant impact on the

transmission rates of the West Nile Virus?

Does spraying prevent more illness than

unintended pesticide exposures cause?

Despite three years of potential data,

in which pesticide spraying was used in

an attempt to stop the spread of WNV,

these are critical questions that have not

been answered by scientific study. At the

moment, given the relative lack of knowledge

about WNV, the Centers for Disease

Control and Prevention are not

conducting the statistical analysis necessary

to identify the effect of insecticide

spraying on infection rates in communities

throughout the country. In fact, few

studies have even been conducted to answer

a simpler question: How effective is

spraying at killing targeted mosquitoes?

The average person thinks the

way you control mosquitoes is you

spray for them. That’s absolutely

not true. Spraying is a last, last


Dr. Wayne J. Crans, Director of Mosquito

Research and Control at Rutgers University,

New York Times, Sept 8, 199931

22 Overkill: Pesticide Spraying in California

Effectiveness of Spraying in

Controlling Mosquito

Populations is Limited

One study conducted by the Connecticut

Agricultural Experiment Station in

2002 found that mosquito populations

did not drop notably after trucks sprayed

pesticides in the cities of Greenwich and

Stamford.33 However, very few studies

have been conducted to document the

effectiveness—or lack of effectiveness—

of pesticide spraying in curbing mosquito

populations under real-word conditions.

Most studies on the impact of pesticide

spraying are performed under outdoor

“lab” type conditions. In such

studies, caged mosquitoes are placed at

measured distances from spraying, at differing

pesticide potencies. Some cagetrap

experiments in residential areas have

shown a reduction in mosquito populations

of about 30 percent after a spraying.34

Such studies, however, may overestimate

the effectiveness of spraying since

they do not take into account the many

variables that are involved in ground

spraying. Real-world mosquitoes are not

trapped in one place. Rather, they can

hide under leaves and in vegetation. As a

result, extrapolating the efficacy numbers

from cage or trap studies to actual spraying

programs is questionable.

“In order to work, the insecticide must

hit the mosquito directly,” Cornell University

researcher Dr. David Pimentel

reported in a November 2000 interview

with Newsday. “But since spray trucks are

only fogging the street side of buildings,

I doubt that more than one-tenth of 1

percent of the poison is actually hitting

its target. And you have to put out a lot

of material to get that one-tenth of a

percent onto the mosquito.”35

In fact, scientists have estimated that

less than 0.0001% of ULV (Ultra Low

Volume) pesticide sprays actually reach

the target insects.36 So for every droplet

that reaches a mosquito, hundreds of

thousands more droplets circulate pointlessly

in the environment.37

The CDC has also noted that, “ground

applications are prone to skips and patchy

coverage in areas where road coverage is

not adequate or in which the habitat contains

significant barriers to spray dispersal

and penetration.”38

In a 1998 study, it took two to three

times more insecticide to kill 90% of the

mosquitoes in residential settings than it

took to kill 90% of the mosquitoes in

open areas. Spraying high enough levels

of insecticide to kill most of the mosquitoes

in residential areas would require violating

current labeling safety guidelines.39

Many factors decrease the effectiveness

of pesticide spraying in urban areas. For

example, the West Nile Virus Advisory

Group to Cambridge, MA has pointed

out the following factors:

• Most mosquitoes prefer to bite birds,

particularly birds at rest, of which

there are few in the street and

building-front areas at the time the

spray is applied.

• Mosquitoes may be located in

roosting areas that are higher than

the reach of the spray.

There’s not enough evidence that all this spraying has changed the dynamic of the

outbreak, and that’s in part because the studies really haven’t been done to find out.

Michael Hansen, the chief pesticide researcher at Consumers Union, which publishes Consumer Reports magazine,

Newsday, November 7, 200032

Pesticide Spraying 23

You’re going to see a resistant strain of these insects. It’s like every time you get the sniffles,

you don’t use an antibiotic. We’re running out of those. You want to use the worst treatment

for the worst cases—you don’t want to use the extreme approach if the risk is not that high.

Sheldon Krimsky, Professor of Urban and Environmental Policy, Tufts University42

• Buildings and trees close to the street

may block the spray from spreading

to reach mosquito habitat.

• Backyard roosting areas are not

effectively reached because close

spacing of buildings limits penetration

beyond the buildings.

• The period that the spray is effective

and airborne is of relatively short


Furthermore, in many places mosquitoes

may already be resistant to pesticides

applied at health-protective label rates.

California’s Mosquito Control Plan notes

that mosquitoes in the Central Valley

have now developed sufficient resistance

to organophosphates like malathion that

spraying at the levels permissible under

current labeling requirements is ineffective.

Too often, agencies will assume a high

rate of effectiveness from spraying that is

never backed up with experimental verification.

For example, Deputy Commissioner

Carl Johnson of the New York

State Department of Environmental

Conservation, which regulates pesticide

use around the state, told reporters that

local governments had anecdotally reported

“60 to 80 percent reductions” after


Yet although New York City Health

Department researchers told reporters in

November, 2000, that they were conducting

studies to determine the effectiveness

of pesticide spraying in WNV control,

such studies have not been released to the

public. As of June 6, 2003, a health department

official told Pesticide Watch

that the data were still being analyzed,

and may be available to the public in four

to six weeks. Three weeks later, the same

official reported that the principal investigator

had resigned, delaying the study’s

release indefinitely.41

Pesticide Spraying Could

Even Make WNV Worse

Spraying pesticides for mosquito control

may be worse than ineffective—it may

even make the West Nile virus situation

worse, contributing to higher infection rates.

Pesticide spraying may build

resistance, leading to resurgence

of mosquito-borne disease

Ecologist Garret Hardin has stated that

“every biocide selects for its own failure.”

This means that mosquitoes can and will

become resistant to chemical efforts to

destroy them. Overuse of pesticides may

create resistant super-mosquitoes that

require ever increasingly toxic chemicals

to kill them.43

Few studies have been conducted to

document the actual impact of aerial and

ground adulticide spraying for West Nile

Virus control on mosquito resistance.

However, there is documentation that

spraying may have contributed to a global

resurgence in mosquito-borne disease

over the last twenty years. The year before

West Nile emerged in the United

24 Overkill: Pesticide Spraying in California

Figure 7. Pesticide spraying can increase populations of harmful pests.

States, a CDC researcher, Dr. Duane

Gubler, wrote that while the factors contributing

to this resurgence are complex,

“the technical problems of insecticide and

drug resistance, as well as too much emphasis

on insecticide sprays to kill adult

mosquitoes, contributed greatly to the

resurgence of diseases such as malaria and

dengue.” Furthermore, according to Dr.

Gubler, the lack of emphasis on preventative

measures “and emphasis on hightech

solutions to disease control have led

most physicians, health officials, and the

public to rely on ‘magic bullets’ to cure

an illness or control an epidemic.”44

Such “magic bullet” spraying targeted

at Aedes aegypti, the mosquito species responsible

for spreading dengue fever, has

been ineffective at both controlling the

mosquito population and influencing the

course of dengue epidemics. Though this

may be due to features of Aedes aegypti

natural ecology not shared by all other

mosquito species, the fact that spraying

programs of long standing were ultimately

found futile indicates that pesticide

efficacy (not the simple of efficacy of killing

exposed mosquitoes but the broader

efficacy of controlling populations and

curtailing disease) is an open question with

each new climate/mosquito species/disease

combination that arises.

Pesticides May Kill Off

Natural Mosquito Predators

Spraying can increase mosquito populations

by killing off natural predators (fish,

other arthropods, birds, etc.) of the mosquitoes

and their larvae, thereby removing

natural checks on population levels.

A 1997 study looked at trends in populations

of a mosquito primarily responsible

for transmitting eastern equine

encephalitis (EEE) among birds. Over a

period of eleven years, Cicero Swamp in

central New York State was sprayed fifteen

times with the insecticide Dibrom

(naled). Instead of declining, the mosquito

population grew fifteen-fold during

Photo: Courtesy of CDC

Pesticide Spraying 25

this period. The study suggests that the

pesticides may have altered the ecological

balance of the swamp, killing organisms

whose presence would ordinarily

help limit the mosquito population.45

Other studies have shown that spraying

malathion, another pesticide approved

for mosquito control in

California, may have similar results. For

example, in California in the early 80s,

widespread aerial applications of malathion

were used in attempts to eradicate

the Mediterranean Fruit Fly, an agricultural

pest. An observed increase in the

population of another pest, Old Black

Scale, was attributed to the effect of the

pesticide spray on beneficial insects. In

Florida, where malathion was also used

in an attempt to control Medfly infestations,

the spraying did not kill mosquito

larvae but did kill the larvae of an important

mosquito predator, the dragonfly.46

Populations of scale insects on citrus

trees exploded following medfly eradication

sprays in California. This occurred

because parasitoids that normally keep

scale populations under control were

killed by the malathion spray.

Pesticides Can Make

Animals More Susceptible

to WNV Infection

Low level chemical exposures to pesticides

can decrease the quality of animals’

immune system function, leading some to

speculate that wildlife with compromised

immune systems may be more susceptible

to becoming infected by encephalitis

when bitten by an infected mosquito.

This in turn would increase the numbers

of formerly healthy mosquitoes

developing encephalitis (since their

chance of biting encephalitis infected

wildlife has also increased), contributing

to the spread of the illness.

Studies have shown that impurities and

by-products present in malathion can

further disrupt immune system function.

47 Immunosuppression may enhance

susceptibility of mammalian systems to

bacterial, viral, or parasitic infection or

possible increased tumor formation.48

Use of these pesticides for WNV mosquito

control could actually end up suppressing

human and avian immune

systems in the areas sprayed, putting each

species at greater risk than before of

spreading, contracting, and becoming

seriously ill from WNV.

Another theory, still untested, is that

mosquitoes that are sprayed but not killed

may themselves experience genetic damage

that would increase their infection

rates—by weakening a stomach barrier

known to play a role in preventing ready

infection by the virus, for example.

Pesticide researcher Richard Pressinger

advanced this theory to help explain

observed increases in rates of encephalitis

infection among sentinel chickens in

Florida counties over the past decade.

“Every time a mosquito spray plane or

truck sprays these proven genetically

damaging pesticides over the area, they

are very likely increasing the amount of

subtle genetic damage in the mosquito

population, and hence, increasing the

number of mosquitoes with genetic flaws

which could in theory, allow the encephalitis

virus to take hold and grow more

rapidly,” he surmised.49

Some scientists have disputed Pressinger’s

theory.50 Clearly, more research

is needed to explain the increasing infection

rates despite widespread pesticide


Another way spraying can contribute

to increased infection rates is simply by

aggravating biting behavior. In an interview

with the New York Public Interest

Research Group, Dr. Ray Parsons, who

heads the Harris County Mosquito Control

Division in Houston, observed that

26 Overkill: Pesticide Spraying in California

pesticides or other chemicals. Furthermore,

many pesticides continue to be

widely used, despite large volumes of

clinical and laboratory evidence that exposure

to these pesticides can have severe,

sometimes fatal, human health


The Centers for Disease Control have

noted, “For adult mosquito control, insecticide

must drift through the habitat

in which mosquitoes are flying in order

to provide optimal control benefits.” This

kind of drift inevitably entails exposure

to human populations if spraying is conducted

in urban areas. Furthermore, since

most mosquitoes are active nocturnally,

spraying must occur during the evening

hours, times of maximum exposure to

those living in residential areas, for the

spraying to have the desired impact on

the targeted mosquitoes.

Although public notification efforts

such as television broadcasts or reverse

911 calls may caution listeners to remain

indoors during spraying, the time of

spraying at any one location can be difficult

to predict and many people cannot

or choose not to remain indoors all day

on the announced day of spraying. Furthermore,

it is not easy to keep these pesticides

from entering people’s homes.

Indeed, outdoor air pollutants tend to accumulate

at higher levels indoors than


Widely used adulticides such as

malathion (an organophosphate) and the

synthetic pyrethroids sumithrin (Anvil)

and resmithrin (Scourge) have significant,

well-documented, human health impacts

that are discussed in the following pages.

malathion may actually aggravate Culex,

causing an increase in aggressive biting

behavior for an hour or two after spraying.51

Pesticide Spraying May

Reduce Participation in

Other Important Public

Health Measures

When cases of WNV show up in California,

citizens may understandably want

government officials to “do something”

to prevent them from being bitten by

WNV-carrying mosquitoes. A massive

spraying campaign runs the risk of giving

residents a false sense of security, encouraging

them to think they are less likely to

be bitten after the spraying, and less likely

to implement non-toxic preventative


Pesticide Spraying Entails

Significant Risk of Public


Aerial and ground spraying of pesticides

in urban and residential areas is of particular

concern due to the heightened

risks of exposure to the general population.

Whenever these pesticides are broadcast,

there are unintended impacts on human

health and the environment. Even pesticides

with relatively low acute toxicity to

adults may pose a significant threat to

young children with immature nervous

systems, asthmatics, the elderly, and other

individuals with unusual sensitivities to

Health & Environmental Impacts 27

Known Health and Environmental

Impacts of Pesticides

Approved for Use in California


Pyrethroids” are a class of chemicals

modeled on natural insecticides derived

from chrysanthemum flowers, called

“pyrethrins.”52 Synthetic pyrethroid compounds

vary in their toxicity, as do the

natural pyrethrins.

Many health effects of pyrethroid exposure

have been well documented. The

Cornell University Program on Breast

Cancer and Environmental Risk Factors

in New York State lists over 125 journal

studies on the health effects of pyrethroids

on its Web site.53

Acute pyrethroid insecticide poisoning

can result in tremors, salivation, hyperexcitability,

choreoathetosis (involuntary

movements), and seizures, as well as

numbness and tingling in exposed body

parts, and gastrointestinal irritation when


Despite these known human health

impacts, synthetic pyrethroids such as

resmethrin (sold under the trade name

Scourge), sumithrin (sold under the trade

name Anvil), and permethrin (sold under

the trade names Ambush or Pounce) have

been widely used in mosquito control.

New Yorkers exposed to sumithrin

when the compound was sprayed to

control for WNV reported symptoms

typical of pyrethrum inhalation, including

asthmatic breathing, sneezing, nasal

stuffiness, headache, nausea, poor coordination,

tremors, convulsions, facial

flushing and swelling, and burning and

itching sensations. The most severe

poisonings have been reported in infants.


A report in the New York Daily News

told the story of a woman who was

sprayed directly on the street in Manhattan

with sumithrin who ended up in the

emergency room after experiencing

blurry vision, nausea, itching, coughing,

choking and a swollen tongue. “I threw

up three days in a row, I really thought I

was going to die,” said the unidentified

woman. In the story, a New York City

Health Department spokesperson stated

that this incident was one of 200 complaints

from people who called the city’s

pesticide hotline in 2000 reporting illness

due to pesticide spraying.56

Inert ingredients are often added to

delay the enzyme action in pyrethroids

28 Overkill: Pesticide Spraying in California

so a lethal dose is assured. These inerts

may include toxic organophosphates, carbamates,

or other synergists. The inerts

in resmetherin (sold under the trade name

Scourge) include piperonyl butoxid and

petroleum distillates. Piperonyl butoxide

has been shown to cause liver tumors in

rats and mice.16

Natural Pyrethrins

Natural pyrethrins are contact poisons

that quickly penetrate the nerve system

of the insect. A few minutes after application,

the insect cannot move or fly away.

Natural pyrethrins can be swiftly detoxified

by enzymes in the insect. Thus, some

pests will recover.

Links between pyrethroids and

hormonal disruption

Numerous studies have indicated that

pyrethroids disrupt the endocrine system

by mimicking the effects of the hormone

estrogen, which can cause breast cancer

in women and lowered sperm counts in


A Mount Sinai School of Medicine

study examined four pyrethroid pesticides,

including sumithrin. It concluded

that pyrethroids “should be considered

to be hormone disruptors, and their potential

to affect endocrine function in

humans and wildlife should be investigated.”


A study at the Roger Williams General

Hospital of Brown University on

pyrethroids concluded, “chronic exposure

of humans or animals to pesticides

containing these compounds may result

in disturbances in endocrine effects.”59

A Cambridge University report issued

in June 2000 by the Royal Society in England

called for international cooperation

to deal with the dangers posed by endocrine-

disrupting chemicals, including

pyrethroids, and recommended reducing

human exposure to these chemicals.60

Links between pyrethroids and

childhood brain cancers

Studies have found nervous-system damage

from pyrethroids to be comparable

to damage from DDT.61

A report of pesticides and childhood

brain cancers published in Environmental

Health Perspectives revealed a strong

relationship between brain cancers and

pyrethroids used to kill fleas and ticks.

The study concludes, “The specific

chemicals associated with children’s brain

cancers were pyrethrins and pyrethroids

(which are synthetic pyrethrins, such as

permethrin, tetramethrin, allethrin,

resmethrin and fenvalerate) and

chlorpyrifos (trade name: Dursban).”62

Links between pyrethroids and

neurological damage

A study conducted by the Physiological

Institute at Ludwig Maximilians University

in Munich, Germany, found that neurological

effects of pyrethroid poisoning

were still seen in patients after more than

two years.

Among these long-term symptoms


1) reduced intellectual performance

with 20%-30% reduction of

endurance during mental work;

2) personality disorders;

3) visual disturbances and tinnitus

(ringing in the ears);

4) sensomotor-polyneuropathy,

most frequently in the lower


5) increased heat-sensitivity and

reduced exercise tolerance due to

circulatory disorders.63

This has been corroborated by Swedish

lab studies showing that low-dose exposure

to pyrethroids “resulted in irreversible

changes in adult brain function in the

mouse” when exposed during

Health & Environmental Impacts 29

the growth period. This occurred at levels

of exposure less than what was found to

affect adult mice. The study also found

“neonatal exposure to a low dose of a

neurotoxic agent can lead to an increased

susceptibility in adults to an agent having

a similar neurotoxic action, resulting

in additional behavioral disturbances and

learning disabilities.”64

Links between pyrethroids

and thyroid damage

A pesticide study conducted on rats concludes,

“[E]xposure to organochlorine,

organophosphorus, and pyrethroid insecticides

for a relatively short time can suppress

thyroid secretory activity in young

adult rats.” The study also said a decrease

in body weight seen “suggests that pyrethroid

insecticides can inhibit growth

rate.”65 “We tested four frequently encountered

pyrethroids, fenvalerate,

sumithrin, d-trans allethrin, and permethrin,

for estrogen and progesterone

agonist/antagonist activities. Through

these hormonal pathways, exposure to

certain pyrethroids may contribute to

reproductive dysfunction, developmental

impairment, and cancer.”66

Wildlife impacts

All pyrethroids are extremely toxic to

beneficial insects, including bees. They

are also extremely toxic to aquatic life,

such as bluegill and lake trout, while

slightly toxic to bird species, such as mallards.

Toxicity increases with higher water

temperatures and acidity.67 EPA

warnings on the pesticide labels include

restrictions that prohibit the direct application

of products to open water or

within 100 feet of lakes, streams, rivers

or bays. Because most pyrethroids were

registered with the EPA before 1984,

when comprehensive health assessment

reviews were first required, EPA has

scheduled such a review of pyrethroids

for 2004.68



In response to WNV, New York City

embarked on a control program relying

on malathion, one of the most widely

used organophosphate insecticides in the

United States and throughout the world.

Eradication programs for pests such as

mosquitoes and fruit flies have exposed

thousands of people to malathion applied

in aerial applications, in many cases

provoking citizen complaints of allergic

reactions and flu-like symptoms.69

Proponents of malathion use often refer

to the chemical’s relatively low acute

mammalian toxicity. But like DDT and

other pesticides that have been found to

cause irreparable damage to human and

environmental health, malathion may

pose a greater risk than the product label

would lead one to believe.

Shown to be mutagenic; a possible carcinogen;

implicated in vision loss, reproductive

and learning problems, immune

system disruption and other negative

health effects in human and animal studies;

damaging to non-target organisms;

and containing highly toxic impurities,

malathion has a legacy of serious problems.70

Acute Malathion Poisoning

Numerous incidents of acute poisoning

have been documented for this widelyused

pesticide. For example, in June 2001,

the Glens Falls Post-Start reported that 37

fourteen and fifteen year-old girls became

ill at a softball game after being exposed

to malathion, which was being applied to

an area adjacent to the field.

Organophosphates such as malathion

are in the same chemical class as the nerve

gas Sarin. These chemicals act as neurotoxins,

disrupting the nervous system by

inhibiting the enzyme cholinesterase.

High exposures can produce fatal poisoning.


30 Overkill: Pesticide Spraying in California

Symptoms of






Respiratory arrest

Pulmonary edema

Loss of reflexes

Flaccid paralysis

Symptoms of moderate

or severe poisoning

Tightness in chest

Difficult breathing






Abdominal pain






Heavy salivation

Profuse sweating


Blurred vision

Pinpoint pupils

Poor concentration


Memory loss

Common early or mild





Muscle weakness



Table 2: Symptoms of Organophosphate Insecticide Poisoning73

In laboratory animals, malathion exposure

has caused stomach ulcers, testicular

atrophy, chronic kidney disease,

increased liver and kidney weights, adverse

gastrointestinal tract effects, and

changes in the adrenal glands, liver, and

blood sugar levels.72

Table 2 lists symptoms of organophosphate

exposure compiled by the United

States Environmental Protection Agency.

Link between malathion and

blood disorders

During a malaria mosquito eradication

spray program in Pakistan in 1976, 2,800

people became poisoned from malathion

and five died.79 Physicians at Travis Air

Force Base Medical Center in California

have observed seven children with bone

marrow disorders over the past eight

years. The physicians believe organophosphate

pesticides caused the blood

disorders in all cases. All blood disorders

occurred shortly after exposure to the

pesticides DDVP/propoxur and


Malathion and reproductive


Juvenile male rats exposed to daily doses

of malathion had decreased numbers of

sperm forming cells.81 In sheep,

malathion exposure of pregnant ewes resulted

in an increase in aborted fetuses,

stillbirths, and low birth weight babies.

Longer duration and earlier initiation of

malathion exposure resulted in more severe


Health & Environmental Impacts 31

Case Study: Malathion Spraying to Control Medflies in California

Despite strong public opposition, malathion spraying was repeatedly (and

ultimately unsuccessfully) used in California from 1980 through the early

1990s in an attempt to eradicate an agricultural pest called the Mediterranean

fruit fly, commonly known as the Medfly.

An infestation of this pest, which can feed on and damage more than 200

species of fruit and vegetables, first appeared in California in 1975, but quickly

subsided. However, a bigger infestation in 1980 led the United States Department

of Agriculture to order an unprecedented campaign of widespread aerial

malathion spraying. Citizen and local government opposition, including city

council resolutions, helped stave off the spraying for nearly a year, when the

governor authorized an all-out aerial assault. From July 10, 1981, through September

1982, more than 1,300 square miles of land were subjected to aerial

spraying each week, resulting in several deaths due to accidental poisoning.74

Similar waves of infestation and aerial malathion spraying occurred despite

public opposition throughout the 80s and early 90s. Often, the aerial spraying

occurred in populated areas, exposing thousands of residents in Santa Clara

County in 1983 and 1984, and 1.6 million people in the Greater Los Angeles

area over a six-month period in 1989 and 1990.75

Dr. Jorge Mancillas, a neurobiologist at UCLA and professor

at the UCLA School of Medicine, calculated that during the

Los Angeles spraying, a 50-pound child exposed to malathion

on a surface equivalent to that of a dollar bill would have been

subjected to an exposure exceeding the EPA’s “acceptable daily

intake level.” Although in theory the spray levels were set low

enough to be “safe” (amounting to 1.4 milligrams per square

foot) the actual rate of deposition of the chemical exceeded the

predicted rates by 40% or more, resulting in clearly unsafe exposure


In 1990, Ventura County successfully filed an injunction to

prevent malathion spraying, helping end the aerial campaign. In 1992, one study

of aerially applied malathion for Medfly control in California found an association

between malathion exposure during the second trimester of pregnancy and

the occurrence of gastrointestinal abnormalities in infants.76 By that time, 10%

of residents in affected areas refused to allow access to their backyards for spraying.


After nearly a decade of repeated aerial bombardments, communities finally

won an end to the aerial spraying program, which was replaced by release of

sterile Medflies to prevent any introduced Medflies from mating successfully.

According to a senior economic entomologist with the Medfly Prevention Release

Program based in Orange County, since the shift to a preventative sterile

release program in 1996, “there has been only one minor infestation of Medflies

within the boundaries of the program.”78 After years of harmful spraying,

the preventative approach turned out not only to be the least threatening to

public health, but also the most effective in controlling the pest.

“. . . a 50-pound child exposed

to malathion on a surface

equivalent to that of a dollar bill

would have been subjected to an

exposure exceeding the EPA’s

acceptable daily intake level.”

32 Overkill: Pesticide Spraying in California

Malathion and vision disorders

Between 1957 and 1971, Japanese school

children experienced a tremendous increase

in cases of myopia (nearsightedness),

which correlated with the increased

use of organophosphate insecticides, including

malathion.83 Reduced visual

keenness was discovered in 98 percent of

the children examined from Saku, an agricultural

area where malathion was regularly

applied. Other examples of what is

now called “Saku disease” in both children

and adults were reported throughout

Japan where organophosphate

pesticides were applied.

In California, one incident involved a

15-year-old boy who was declared legally

blind after being outside while helicopters

were spraying malathion. An ophthalmologist

and a pesticide expert both

agreed that the boy may have Saku disease.84

Malathion and immunosuppression

Impurities and by-products present in

malathion can further disrupt immune

system function.85 Immunosuppression

may enhance susceptibility of mammalian

systems to bacterial, viral, or parasitic

infection or possible increased tumor


Ironically, use of these pesticides for

WNV mosquito control could actually

end up suppressing human and avian immune

systems in the areas sprayed, putting

each species at greater risk than

before of spreading, contracting, and becoming

seriously ill from WNV.

Link between malathion and cancer

In April 2000, a U.S. Environmental Protection

Agency (EPA) committee reviewed

a series of studies on mice and rats

exposed to malathion. Based on this review,

the committee concluded that there

was “suggestive evidence of carcinogenicity.”

87 For the moment, malathion remains

listed by EPA as “not classifiable”

with regard to carcinogenicity.88 However,

recent evidence suggests that organophosphates

such as malathion can cause

Non-Hodgkin’s Lymphoma (NHL).89

Use of malathion by farmers in Iowa and

Minnesota has recently been linked to an

increased risk of one type of NHL.90

Wildlife impacts

Malathion is lethal to beneficial insects,

snails, microcrustaceans, fish, birds, amphibians,

and soil microorganisms. Sublethal

exposure of these species can cause

a variety of behavioral and physiological


Naled and Related Pesticides

Naled (trade name Dibrom) is an organophosphate

with many of the same characteristics

and concerns as malathion.

Naled can cause cholinesterase inhibition

in humans; that is, it can overstimulate

the nervous system causing nausea,

dizziness, confusion, and at high exposures,

can cause respiratory paralysis and


Dichlorvos: toxic byproduct of naled

One of the byproducts of degradation of

naled is dichlorvos, another registered

organophosphate.92 Researchers at the

Cornell University Program on Breast

Cancer and Environmental Risk Factors

in New York State prepared a fact sheet

reviewing several studies on dichlorvos.

They found the following:

• Female mice that were fed high doses

of dichlorvos over a long period of

time had a higher frequency of

stomach cancers than untreated


• High doses of dichlorvos fed over

two years caused an increase in the

number of male rats that had

pancreatic tumors and leukemia.

Health & Environmental Impacts 33

Naled can cause cholinesterase inhibition in humans; that is, it can overstimulate the

nervous system causing nausea, dizziness, confusion, and at high exposures, can cause

respiratory paralysis and death.”

• A higher number of leukemia cases

were reported in one study among

male farmers who used dichlorvos

for more than ten days per year,

compared to those who had not

used dichlorvos.

• A higher number of childhood brain

cancer cases were reported among

families that used dichlorvos than

among families that did not.93

In addition, Russian researchers found

fish exposed to dichlorvos demonstrated

slower growth rates. Researchers believe

it may be due to the subtle neurotoxin

actions of the pesticide and its effects

upon the areas of the brain involved in

feeding or food search mechanisms.94

Trichlorfon: ingredient in naled

The pesticide trichlorfon is a common

ingredient in the mosquito pesticide

Dibrom (naled). In one study, trichlorfon

was found to cause a “severe reduction”

in brain weight (and shape) in test

animals exposed. The timing of exposure

to the developing offspring appeared to

be the key factor in determining neurological

damage (known as the “critical

brain growth period”). It occurred when

the chemical was administered between

40-50 days gestation for the guinea pig,

which scientists say, correlates with the

brain growth spurt period for the animal.95

Wildlife impacts

Naled is characterized as very highly toxic

to bees and aquatic invertebrates. It is

moderately to highly toxic to fish and

slightly toxic to upland game birds and

waterfowl.96 There is potential for

chronic risk from naled to estuarine invertebrates.



Temephos (Abate) is an organophosphate

insecticide used to control mosquito,

midge, and black fly larvae. It is used in

lakes, ponds, and wetlands. It also may

be used to control fleas on dogs and cats

and to control lice on humans. The compound

is sometimes found in mixed formulations

with other insecticides

including trichlorfon. As an organophosphate,

it has many of the same concerns

and characteristics as malathion and


Symptoms of acute exposure to

Temephos are similar to other organophosphates

and may include nausea, salivation,

headache, loss of muscle

coordination, and breathing difficulties.98

Some studies show that Temephos may

greatly increase the observed toxicity of

malathion when used in combination

with it at very high doses.99

Wildlife impacts

Tests with various wildlife species indicate

that the compound is highly toxic to

some bird species. The compound is also

highly toxic to bees.100 Temephos shows

a wide range of toxicity to aquatic organisms,

including salmon.101 Freshwater

aquatic invertebrates such as amphipods

are very highly susceptible to temephos,

as are some marine invertebrates.102

Temephos is very highly toxic to saltwater

34 Overkill: Pesticide Spraying in California

species such as the pink shrimp, and presumably

to lobsters as well.

Temephos has the potential to accumulate

in aquatic organisms. In one study,

the bluegill sunfish accumulated 2,300

times the concentration present in the



Larvicides applied to mosquito breeding

pools are generally considered to have

lesser impacts on public health than

adulticide sprays. For this reason, many

mosquito and vector control programs

rely on larviciding as the primary intervention

strategy to limit mosquito populations.

Indiscriminate use of larvicides,

however, may have harmful impacts on

wildlife and contaminate drinking water



Methoprene is applied to water bodies

such as sewers, wetlands, ditches, and

ponds for the purpose of killing mosquito

larvae. According to EPA human toxicity

ratings, the larvicide methoprene

(Altosid) is considered to be practically

nontoxic to humans.104

Interrupting the normal life cycle of

an insect, methoprene prevents larvae

from maturing to the adult stages, and

thus prevents them from reproducing. To

be effective, it is essential that this growth

inhibitor be administered at the proper

stage of the target pest's life cycle.

Methoprene is not toxic to the pupal or

adult stages. Treated larvae will pupate

but adults do not hatch from the pupal


Methoprene may be the larvicide of

choice in many mosquito control districts,

due to the fact that one application

remains effective for significantly

longer than a single application of biological

agents such as Bti, discussed in the

following section. This can reduce the

labor costs of ongoing larviciding by

more than fifty percent. Methoprene

mimics the action of an insect growth

regulation hormone. However, application

of methoprene may have significant

ecological impacts.106

Wildlife impacts

Studies have documented methoprene to

be slightly toxic to birds and slightly to

moderately toxic to fish.107 Methoprene

residues may have a slight potential for

bioconcentration in bluegill sunfish and

crayfish.108 Methoprene is very highly

toxic to some species of freshwater, estuarine,

and marine invertebrates.109

Methoprene harms shrimp development.

110 Studies at the laboratory of researcher

Charles McKenney have shown

that methoprene inhibits the metamorphic

success of larval estuarine shrimp and

crabs with exposure to concentrations

used in killing salt marsh mosquitoes.111

Methoprene and birth defects

in vertebrates

Some researchers have hypothesized that

methoprene may cause birth defects and

deformities that have been observed in

frogs throughout the United States.112

The larvicide methoprene has been

linked to frog deformities, particularly

extra limbs growing from various parts

of a frog’s body or head.113 These deformities

are thought to result from exposure

to methoprene acid, a chemical that

is formed when methoprene breaks down.

This byproduct may function as a retinoid,

a compound that stimulates gene

transcription in vertebrates.114 Changes

in exposure to retinoids during certain

critical stages can cause birth defects in

all vertebrates, including humans, and

may be contributing to the global epidemic

of skeletal deformities in frogs.115

A recent controlled study published in

Aquatic Toxicology demonstrated that

Health & Environmental Impacts 35

Spraying to Kill Mosquitoes and Killing Lobsters Instead

In 1999, immediately after Hurricane Floyd hit the eastern seaboard,

lobstermen who fish in the Long Island Sound noticed a sharp decline in the

local lobster population.

By the following year, experts estimated that more than 10 million lobsters,

or 90% of the stock, had died off in the western part of the Long Island Sound.116

President Clinton declared the Sound a natural resource disaster area, and Congress

appropriated $13.9 million for research and financial assistance to licensed


The lobstermen, arguing that the lobster had survived polluted

runoff in the past, believe that WNV spraying in the summer of

1999 was the cause for the decimation of their fishery, and filed a

$125 million putative class action lawsuit against insecticide manufacturers.


This hypothesis is potentially bolstered by studies that have documented

that exposure to pyrethroids used in mosquito control can

kill lobsters and shrimp.119 Although shellfish appear very different

from mosquitoes, they share many life characteristics and a common

evolutionary history with insects. Insects, for example, an external

skeleton and development from a larval stage through a series of molts.

Some scientists, such as those studying the lobsters at the University

of Connecticut, have hypothesized that insecticides may have

been indirectly responsible for the lobster die-off. For example, pesticide

exposure may have lowered their immune system, allowing a

parasitic infection to overwhelm the population.

The EPA has launched an investigation into the cause of the lobster crash.

Scientists estimate it will take at least 10 years for the population to recover.

Research is still being conducted to determine the effects that mosquito control

pesticides might have on lobsters, particularly sub-lethal effects at low levels. If

lobstermen are right and widespread use of mosquito control pesticides was responsible

for the crash in Long Island’s lobster population, California’s lobster

industry could be similarly imperiled.120

California’s Lobster Industry

Recently, the California lobster harvest has rebounded to the highest levels

in over fifty years, totaling over 950,000 pounds. The economic value of

California’s fishing industry to the state is estimated at more than $800

million annually. The industry ranks among the top 5 seafood-producing states

in the U.S. (472 million pounds in 1999).121

It is not clear how the California lobster and shellfish industry could be damaged

if pesticides are used more widely to control mosquito populations. However,

it would be irresponsible and shortsighted to introduce these chemicals onto

land or water bodies without knowing the effects they might have on lobsters.

“This hypothesis is

potentially bolstered

by studies that have

documented that

exposure to pyrethroids

used in mosquito

control can kill lobsters

and shrimp.”

36 Overkill: Pesticide Spraying in California

Figure 8. Some researchers have

hypothecized that methoprene may

breakdown into compounds that cause

deformities in vertebrates.


Biopesticides have emerged as important

alternatives to traditional chemical pesticides

with fewer known human health

impacts. However, they, too, should be

used sparingly. Like traditional chemical

pesticides, significant research needs to

be done on the ecological effects of

biopesticides. What non-target invertebrates

that are important in the food

chain are also affected by their use? How

will a potential decrease in this part of

the food chain affect fish and amphibians,

and the birds and animals that feed on

them? Many unanswered questions make

it difficult to estimate the potential risk

of biopesticide use.

Bacillus thurengiensis israelensis (Bti)

and Bacillus sphaericus

Bti is a biological pesticide that contains

naturally occurring soil bacteria in different

strains that target specific insects.

It is not known to be toxic to animals,

birds, humans, fish or beneficial insects.

Bti is required to have EPA warning and

caution labels, as is the requirement by

law for any registered pesticide.123

Based on extensive testing, no harmful

effects to the public are expected to

occur when biopesticide products are

applied according to label directions.

Because there is the potential for skin and

eye irritation, applicators are warned to

avoid direct contact with the granules or

a concentrated spray mix. Various tests

revealed no expected harm to non-target


Biopesticides closely related to Bti are

widely used in organic farming. Some

trade names are Aquabac, Teknar, and

LarvX. Bacillus sphaericus (VectoLex) is

another naturally occurring biopesticide.

It was registered in 1991 for use against

mosquito larvae, which ingest the bacteria

and die after the toxin in the bacteria

disrupts their gut function.

Photo: Laboratory of Joe Kiesecker, Penn State University

frog embryos exposed to high concentrations

of methoprene did not show any

developmental defects. However, the

study found that methoprene can degrade

into other compounds that do cause developmental

toxicity at concentrations

significantly higher than those expected

to result from proper application of the


The U.S. Environmental Protection

Agency risk assessment for methoprene

did not include an evaluation of its chemical

breakdown products, retinoids. This

illustrates a common failure of the

agency’s risk assessments, which do not

evaluate the breakdown by-products of the

chemical pesticides under consideration.

Health & Environmental Impacts 37

If Bti and variants are too widely used,

insects may develop immunity to these

pesticides, thereby limiting their effectiveness

for mosquito control and for use

by organic farmers. The University of

California Working Group on Organic

Farming has estimated that this industry

has a value exceeding $225 million in the

state of California alone.125

The Threat to Agriculture

All of the aforementioned chemicals are

designed to kill insects, many of which

are responsible for pollinating wild and

cultivated plants in California. The future

of agriculture depends on pollinators.

Insect pollination is a necessary step in

the production of most fruits and vegetables

we eat and in the regeneration

of many forage crops utilized by livestock.

California growers of almonds, apples,

and many other crops depend on insect

pollinators — both managed and wild —

to produce fertile seeds and full-bodied

fruit. Recent surveys document that more

than thirty genera of animals — consisting

of hundreds of species of floral visitors

— are required to pollinate the 100

or so crops that feed the world. Domestic

honey bees service only 15% of these

crops, while at least 80% are pollinated

by wild bees and other wildlife.126

Researchers have estimated severe revenue

losses to both almond growers and

honey producers in California resulting

from a pesticide-induced decline in the

numbers of pollinators where pollination

by honeybees alone is valued at over

$14.6 billion.127

Organic crops are also at risk, should

the state choose the method of aerial or

ground spraying of pesticides. It is unlikely

that sprayed farms will lose their

certified status, but sprayed crops and

plant material may not be able to be marketed

as ‘organically produced.’128

38 Overkill: Pesticide Spraying in California

it to mean “harmless.” Since neither the federal

law nor the regulations define the term

“inert” on the basis of toxicity, hazard or risk

to humans, non-target species, or the environment,

it should not be assumed that all

inert ingredients are non-toxic.129

Since the technical (chemically pure)

grade of a pyrethroid is usually formulated

(mixed with carriers, solvents, synergists,

etc.) for use in commercial pest control,

the toxicity of these other ingredients

must be taken into consideration when

assessing the toxicity of a formulated

product. Researchers found a ten-fold

difference in toxicity between formulations

with the same active ingredient, but

with different carriers, solvents, etc.130

Some mixtures of Anvil are made up

not only of 10% artificially manufactured

Sumithrin but 10% piperonyl butoxide

(PBO), a suspected carcinogen, and 80%

“inert” ingredients such as polyethylbenzene,

which is listed by the EPA

as being “potentially toxic.”131

PBO is added to make the pyrethroids

more effective. It acts by inhibiting naturally

occurring enzymes that would otherwise

degrade the insecticide. PBO breaks

“Inert” Ingredients Escape

Public Disclosure

The true nature and health threat of a

pesticide is difficult to analyze, since many

of its ingredients may never be made public.

The Federal Insecticide, Fungicide,

and Rodenticide Act (FIFRA), the

nation’s primary pesticide control law,

classifies pesticide ingredients into two

categories—active and inert. The active

ingredients are those designed to kill pests

while the inerts are added to make the

active ingredient more potent and easier

to use. Inert ingredients can make up a

significant percentage of the material that

is actually sprayed. Yet these inerts, which

are often highly toxic, are often classified

as “trade secrets” under law and are not

listed on the label. In September 1997, U.S.

EPA issued a memo encouraging pesticide

manufacturers to voluntarily substitute

the term “inert ingredients,” with the

term “other ingredients,” noting that:

Many of these compounds are potentially

harmful, even more so than the active ingredient

in the pesticide. Many consumers are

misled by the term “inert ingredient”, believing

Unknown Health Impacts

of Mosquito Control Pesticides

Unknown Health Risks 39

Current policies such as risk assessment and cost-benefit analysis give the

benefit of the doubt to new products and technologies, which may later

prove harmful. And when damage occurs, victims and their advocates

have the nearly-impossible task of proving that a particular product or

activity was responsible.135

Peter Montague, Environmental Research Foundation

Although they may be off the public

radar screen, inert chemicals may have

significant impacts on public health and

the environment.

Pesticides Are

Not Proven Safe

Many people assume that a pesticide is

safe to use if it has been approved for use

and is available on the store shelves at

their local hardware store. However,

thousands of chemicals on the market lack

adequate testing to demonstrate that they

will not harm human health or the environment.

Pesticides are routinely approved before

their health consequences have been

accurately determined, as evinced by the

fact that nearly 100 pesticides have been

banned or severely restricted by the EPA

since their introduction.136 As recently as

June 8, 2000 the EPA announced a ban

on virtually all uses of Dursban (chlorpyrifos)

in residential and commercial buildings.

Diazinon, one of the most widely

used pesticides in the United States, will

be phased out of home and garden use

by 2004 because of health concerns.

Yet it can be years or even generations

before a dangerous compound is banned

or its use restricted. Consider the examples

of lead in paint and gasoline,

through the insect’s defense, making the

insecticide more powerful. The EPA’s

Office of Pesticide Programs suspects

PBO of being a carcinogen. The National

Institute for Occupational Safety and

Health’s Registry of Toxic Effects of

Chemical Substances lists it as a suspected

gastrointestinal or liver toxicant, and a

suspected neurotoxicant. It has also been

reported as a suspected reproductive toxicant.

132 In addition, there is some evidence

that PBO-pyrethroid mixes can

affect the human immune system.133

Polyethylbenzene (PEB), a heavy aromatic

solvant also known as naphtha, is

widely used in pesticides. PEB is listed on

the EPA Office of Pesticide Programs’

Inert Pesticide Ingredients List No 2,

which is a list of 64 substances the EPA

“believes are potentially toxic and should

be assessed for effects of concern. Many

of these inert ingredients are structurally

similar to chemicals known to be toxic;

some have data suggesting a basis for concern

about the toxicity of the chemical.”

PEB, for example, is related to ethylbenzene,

which is listed as a suspected

reproductive toxicant and a suspected

respiratory toxicant by the EPA. White

mineral oil, also known as hydro-treated

light paraffinic petroleum distillate, is

also listed on the EPA’s Inert Pesticide

Ingredients List No. 2 of potentially toxic


40 Overkill: Pesticide Spraying in California

Risk assessments may be designed and

conducted to prove that a pesticide spray

program is safe. Yet, significant uncertainties

often underlie these assessments. A

working group of the U.S. Environmental

Protection Agency identified the

following uncertainties in current knowledge

which limit regulators’ “ability to

make decisive assessment conclusions and

take fully informed actions to prevent or

mitigate pesticide problems:”

• What is the efficacy of spraying,

especially ground spraying without


• What should agencies do when

public health comes head-to-head

with environmental risks?

• Communication of risk of disease

vs. risk of control.

• What are effects of multiple

spraying (risks)?

• More measurements of (outdoor and

indoor) pesticides via spraying.

• Is turning air-conditioning off

effective in reducing exposure; what

about restarting?

• When is it safe to allow children and

pets out after spraying?

• What are the results of environmental

spraying and implications to the

lower end of food web/chain?137

Only rarely will risk assessments performed

to justify proposed spraying programs

clearly delineate the above


DDT in pesticides, and DES and thalidomide

for pregnant women.

This demonstrates a faulty system in

which pesticides, not public health, are

given the benefit of the doubt in regulatory

decision-making. The risk assessment

models used by the state to evaluate

the chemicals, although they enjoy widespread

use in the regulatory community,

are often inadequate in determining

whether the introduction of these compounds

into the environment will adversely

affect humans, wildlife, and entire


In order to protect public health and

the environment, pesticides should be

subjected to standards like those used by

the Food and Drug Administration, in

which a product is considered harmful

until it is proven safe.

Risk assessments are used to demonstrate

the relative safety of using a given

toxic chemical when exposure is limited

to a certain level. The officials and applicators

will assure the public, based on

their risk assessments, that the levels of

chemicals they will be exposed to will be

so low, and so infrequently applied, that

there will be no effect on the environment

and human health, or that the

compound’s toxicities quickly degrade.

These assessments may be unreliable

for a number of reasons. First, many of

these chemicals may have significant to

subtle negative health and environmental

effects at extremely low levels. Secondly,

pesticides are never applied under ideal

conditions as planned. There will always

be mistakes, spills, and oversprays. The

compounds, although analyzed for safety

and degradation characteristics under

ideal laboratory conditions, will be applied

by real people in the real world.

Balancing the Risks 41

Balancing the Risks

If we’re just spraying all over and

not doing a damn bit of good,

then this is a waste of time and

money, and it’s also a hazard.

Dr. David Pimentel, Professor of Entomology,

Cornell University, Newsday, November 7, 2000

As Michael Gochfeld, Professor of Environmental

and Community Medicine at

the Robert Wood Johnson Medical

School and School of Public Health,

Rutgers University has written:

In weighing the risks and benefits of mosquito

control, we should consider the disease

itself and the risk to the human population.

The media always paired the words “lethal”

or “deadly” with “West Nile” or “encephalitis,”

reinforcing in the public’s mind the danger

from the disease. But it would be equally

propriate to characterize West Nile virus infection

as “unapparent,” “usually asymptomatic,”

or “occasionally serious.” Seven deaths

in a population of over 10 million people over

a one month period is certainly tragic, but

pales beside the number of deaths from many

other diseases that are addressed less aggressively.


Dr. Gochfeld and other experts have

argued further that we have insufficient

evidence to know how to control WNVtype

diseases or how our control measures

may affect them. Filling in these data gaps

will be crucial in assessing the risk

tradeoffs essential to public health decisions

in this area.139

42 Overkill: Pesticide Spraying in California

Why the Push for Pesticide Spraying?

Considering the lack of evidence demonstrating the effectiveness of pesticide

spraying, it may seem surprising at first that the vast majority of government

officials have responded to the emergence of West Nile Virus

with broadcast spraying programs.

The push to spray comes from several very different sources: the urge to do

something highly visible to show that action is being taken to address the health

threat; momentum resulting from the fact that pesticide spraying has been the

dominant approach to such problems for the past thirty or forty years; and the

influence of pesticide manufacturers on local, state, and national decision-making


In states lacking mosquito control plans when WNV first appeared, pesticide

spraying provided a quick and easy solution to a very complicated and multifaceted

problem. Thinking they had to “do something,” most government officials

put their finger firmly on the pesticide trigger, picking the easiest and quickest,

but not the safest, least costly, or most effective response to address the WNV.

These officials could say that they had done “something,” highly visible to the

affected communities, even though their solution may have caused more harm

than good.

In states with more prevalent and long-standing mosquito control problems,

the decision to spray may be based in years of precedent in which spraying has

been the main approach to mosquito control.

There is also big money to be made by spraying pesticides. Pesticide manufacturers

and applicators stand to profit from manufacturing and applying sprays for

WNV mosquito control. In New York City, for example, Clarke Environmental

Mosquito Management, Inc. was paid $650/hour per truck in a $4.6 million New

York City contract.140 (The company’s bid for a three year contract to spray was

in excess of $50 million.141 This bid was rejected by the state, and Clarke was

recently fined $1 million for violating New York State’s

pesticide application laws.)

The corporations who manufacture the pesticides are

often the same entities funding research to document the

effectiveness of those same pesticides. Furthermore, the

line between publicly-funded mosquito control and forprofit

chemical companies is consistently blurred by “public/

private partnerships.” For example, many pesticide

companies have direct links to the California Mosquito and

Vector Control Association’s (MVCAC) website, and are

corporate sponsors or “members” of this governmental

agency. “Sustaining members” who made significant financial contributions to

MVCAC in 2002 include large chemical pesticide manufacturers and distributors,

such as Aventis Chemical Corporation, Clarke Mosquito Control Products,

Inc., Electramist, Inc., Fen-nimore Chemicals, Pigott & Associates, Inc., Valent

Biosciences Corporation, Vopak USA, and Zoecon Professional Products.142

“. . . the line between publiclyfunded

mosquito control and

for-profit chemical companies

is consistently blurred by

“public/private partnerships.”

Balancing the Risks 43

In this sense, the state of knowledge

of WNV control is analogous to the state

of understanding of Medfly control in

California in the mid 1980s (described on

page 31) when there was no clear-cut

technical or scientific evidence to support

a program of ground spraying, aerial

spraying, or the mass application of pesticides

in any form. In the case of the

Medfly infestations, pesticides were given

the benefit of the doubt until exposed

communities organized against the onslaught.

It took more than a decade of

ineffective pesticide spraying before preventative,

nonchemical control programs

were implemented in their place.

This time, communities can be prepared.

In many parts of the country, the

West Nile Virus outbreak has been accompanied

by intensive media coverage,

including daily or near-daily reports highlighting

each additional case discovered

in humans or birds. The impacts of pesticides

on nontarget organisms rarely

have been given comparable attention. An

important first step may be actively working

with journalists in California to ensure

that media representations of WNV

include clear discussion of the risks and

known impacts of pesticides, rather than

simply inflaming public fears of a new

health threat.

Principles for Safe, Effective

Mosquito Control Measures

on the State and Local Level 143

I. Give Public Health, Not Pesticides,

the Benefit of the Doubt

In order to safeguard public health in the

state, a balanced approach to West Nile

Virus must weigh the threats posed by

pesticide use to the general population

against the threat posed by West Nile

Virus. In the absence of evidence demonstrating

that spraying helps limit transmission

of the disease to humans,

pesticide spraying should not be part of

the WNV control plan.

1. Before any decision to use pesticides,

community-specific assessments of

health and environmental hazards of

proposed products that take into

consideration all pesticide ingredients

(including inerts) should be

conducted, with full public input.

2. Reevaluate and eliminate spraying

conducted for nuisance reasons. Such

spraying generally relies on the same

potentially hazardous pesticides used

in WNV control. Furthermore,

indiscriminate use of these pesticides

builds up resistance in mosquito

populations, making targeted use for

disease control even less effective.

II. To Protect Public Health,

Prioritize Alternatives To

Pesticide Spraying

Public education and outreach, behavioral

changes and preventative measures

that reduce mosquito breeding habitat

can effectively minimize risk of WNV

while reducing momentum for dangerous

pesticide spraying programs.

While public outreach and education

of this nature may be a significant part of

a mosquito control district’s strategies for

“An important first step may be to actively work

with journalists in California to ensure that media

representations of WNV include clear discussion of the

risks and known impacts of pesticides, rather than

simply inflaming public fears of a new health threat.”

44 Overkill: Pesticide Spraying in California

Healthy Wetlands Help Control Mosquito Populations

Laboratory studies have shown that salt marsh mosquitoes are unlikely to be

major vectors of West Nile Virus. However, they are among the mosquitoes

most commonly sprayed for nuisance reasons. Restoring degraded wetlands

can help limit both the public health threat and nuisance of mosquito populations.

For example, the Ora Loma Marsh in the San Francisco area was recently

restored for a number of sensitive species, including the endangered salt marsh

harvest mouse. According to a paper by Wes Maffei, the manager of

the Napa County Mosquito Abatement District, the marsh design

“was altered to improve tidal flow, thereby reducing the amount of

stagnant water in which mosquitoes thrive. Although it has only been

a couple of years since the restoration occurred, mosquito breeding

has been markedly reduced and it is quite apparent that the health of

a degraded marsh is now returning.”145

On the flip-side, wetland restoration projects that lack adequate

design controls and funding for ongoing maintenance may actually

undermine attempts at effective mosquito control.

Open Marsh Water Management, or OMWM, was developed to

control mosquitoes by facilitating access of their natural fish predators to areas

on salt marsh where mosquitoes breed.146 Through a system of pools and pannes

connected by radial ditches, small fish that eat mosquito larvae can reach the

larvae during high tide, then retreat to sumps or reservoirs at low tide. Robert

Scheirer, a coordinator with the US Fish and Wildlife Service, has written that

“This has been found to be an effective, long-term method of controlling mosquito

populations without using sprays.”147

“Restoring degraded

wetlands can help limit

both the public health

threat and nuisance of

mosquito populations.”

controlling mosquito populations, the

state plan does not lay out specific parameters

for it. Community leaders and

activists can work with district managers

to ensure that mosquito control resources

are focused on prevention and education,

rather than chemical spraying response.

Focus on source reduction

Source reduction encompasses a broad

range of activities. It can be as simple as

steps taken by individuals where they live,

such as turning over empty containers,

removing used tires and cleaning rain

gutters and bird baths. Source reduction

also encompasses extensive regional water

management projects conducted by

mosquito control agencies or fish and

wildlife officers. Comprehensive source

reduction activities can eliminate or substantially

reduce mosquito breeding and

the need for repeated applications of insecticides

in the affected habitat.

• Stock manmade ponds and other

appropriate bodies of water with

mosquito-eating fish. In some cases,

it may be appropriate to use bacterial

larvicides or mechanical controls

such as vegetable-based oils that

smother mosquito eggs floating on

the surface of the water (see larvicide


• Keep waterways clean so that fish

and other mosquito predators can

survive. Ensure vegetation is cleaned

out of natural sloughs in marshy

areas to keep water flowing, preventing

mosquito habitat from forming.

Balancing the Risks 45

Involve and Engage the Community

• On a municipal or county level, set

up a system for citizens to report

standing water near their homes.148

• Educate the public about what

people can do at home to minimize

mosquito exposure and eliminate

breeding sites through press releases,

Web sites, school presentations,

mailings, and distribution of brochures

in public offices. Public health

education is a good investment of

resources and will pay off better than

quick-fix expenditures on chemical


• Respect public requests not to spray,

both on the individual and municipal


• Hold public hearings that offer

community members the opportunity

for meaningful input into local

mosquito control decisions involving

the use of pesticides.

• Continuously evaluate the effectiveness

of all mosquito control measures.

Steps Individuals Can Take

1. Learn about local mosquito control


Contact your mosquito control district to

obtain a copy of their mosquito control

plan, including information about their

policies regarding pesticide use (what indicators

will “trigger” spraying, how will

they notify the public of their intent to


Find out when there may be opportunities

for public input (e.g. schedule of

mosquito control board meetings.)

2. Reduce standing water and other

mosquito habitat.

• Get rid of any unnecessary items on

your property that can hold stagnant

water, such as old tires. If you use old

tires for farming or gardening, drill

holes in them and empty them


• Empty water from buckets, toys, and

containers, and store them in places

where they will not collect rain.

• Drill holes in the bottoms of recycling

bins and any other containers

that must be kept outdoors.

• Drain the water from bird baths,

fountains, wading pools, plant pots

and drip trays twice a week. Call

your local mosquito control district

to learn whether stocking fountains

or ponds with mosquito fish might

be appropriate.

• Check for other ways water may be

collecting around your house, such as

puddles beneath air conditioners.

• Clean out your gutters and fix gutters

that sag or do not drain completely.

Check for areas of standing water on

flat roofs.

• If you have a swimming pool, outdoor

sauna, or hot tub, make sure

rainwater does not collect on the


• Clear vegetation and trash from any

drains, culverts, ponds or streams on

your property so that water drains


• Keep grass cut short and trim shrubs

to minimize hiding places for adult


• Eliminate standing water in your


3. Report dead birds.

Reports of dead birds can be made to the

California Department of Health Services

Surveillance program by calling

(877) WNV-BIRD or by clicking the

46 Overkill: Pesticide Spraying in California

Mosquito Sources


Swimming pools

Tree holes

Plastic pools


Bird baths

Standing water

Watering troughs

Cooler drains

Street gutter or catch basins

Cesspool or septic tanks

Roof gutters

Irrigated lawns or fields

What to Do to Reduce Mosquitoes

Stock pond with Mosquitofish. Each fish can eat

100 to 500 larvae per day. They play an important

role in mosquito control in ponds, canals, irrigated

fields and some other freshwater sources. The fish

live two to three years; they are live-bearing and

produce 3 to 4 broods each year.

Remove excess vegetation.

Keep water off cover.

Maintain water quality at all times.

Fill hole with sand or mortar.

Drain water when not in use, or cover so

mosquitoes cannot lay eggs.

Empty water.

Store in an inverted position.


Cover so mosquitoes cannot lay eggs.

Change water at least once a week.

Eliminate by draining.

Fill in low areas.

Stock with fish, or change water weekly.

Prevent water from standing.

Keep litter and garden debris out of gutter.

Do not over-water yard.

Seal and cover opening so mosquitoes can’t

lay eggs.

Clean once a year to remove debris.

Avoid over-irrigation.

Drain standing water.

Table 3. Checklist of Possible Mosquito Sources Around the Home149

“Report Dead Bird” link: westnile. Cal DHS will

initiate the pick up of bird specimens.

4. Mosquito-proof your house and body.

• To minimize the likelihood of being

bitten inside your house, make sure

window and door screens fit properly

and replace outdoor lights with

yellow “bug lights.”

• To avoid being bitten outdoors, wear

hats, long sleeves and long pants in

the evenings, when mosquitoes are

most active.

Balancing the Risks 47

What You Should Know

About Personal Protection

and Insect Repellents

The most effective method of personal

protection from mosquito bites is to avoid

places where mosquito densities are high

and to avoid being out-of-doors at times

of the day when mosquito activity is at

its highest. Wearing protective clothing

such as hats, long sleeves and pants can

help limit exposure.

If you choose to use insect repellents,

treat clothing, rather than skin, whenever

possible, and wash off repellents with soap

and water after returning indoors.150


DEET has been demonstrated to be an

effective mosquito repellent. However,

use of DEET may entail the risk of serious

side effects.

A recent study published in the New

England Journal of Medicine found a

formulation containing 23.8 percent

DEET offered complete protection

from mosquito bites for 5 hours, on average,

compared to a soybean-oil-based

repellent (see Bite Blocker/Buzz-Off

section below), which protected against

mosquito bites for an average of 94.6


More than 50 cases of serious toxic side

effects experienced by people using the

insecticide DEET have been documented

in the medical literature. The U.S. Environmental

Protection Agency (EPA)

acknowledges fourteen cases in which

individuals reported seizures associated

with exposure to DEET.152 Twelve were

children, three of whom died.

A press release from Duke University

Medical Center research pharmacologist

Mohamed Abou-Donia, Ph.D., whose

animal studies have shown that DEET

has potential interactions in humans, argues

that “safe is better than sorry.”153

Dr. Abou-Donia recommended:

1. Never use insect repellents on

infants, and be wary of using them

on children in general.

2. Never combine insecticides with

each other or use them with other

medications. Even so simple a drug

as an antihistamine could interact

with DEET to cause toxic side


Some state Bureaus of Health in the

USA and Health Canada do not recommend

using DEET at all on infants and/

or children under 2, and only 10% (or less)

DEET preparations on kids 2-12. Health

Canada also recommends that adults not

use preparations with over 30% DEET,

and will not register products with a higher

concentration than 30% after 2004.

Plant-Based Insect Repellents

University of California Pest Management

Guidelines note that plant oils such

as those from birch, bluestem grass, geranium,

pine, rosemary, spearmint, yarrow,

lantana, and neem have been shown

to be somewhat repellent to mosquitoes,

but most are not available in commercial

mosquito repellents.154

Two commercially available plant oilbased

repellents are Bite Blocker and

Buzz-Off.155 Studies published in the New

England Journal of Medicine have shown

that repellents containing oil of eucalyptus

provided protection for an average of

two hours, and a product containing soybean

oil (Bite Blocker for Kids, HOMS)

was effective for an average of 90 minutes.156

Citronella repellents and candles are

non-toxic and somewhat effective

Studies show that citronella can be an

effective repellent, but it provides shorter

complete protection time than most

DEET-based products. Frequent reapplication

of the repellent can partially compensate

for this.157

48 Overkill: Pesticide Spraying in California

State Department of Health, April 2003,

downloaded on June 6, 2003)

1. Keep windows closed during and

immediately after spraying. If

possible, also turn off window air


2. Stay inside and keep children and

pets inside during spraying and until

the next morning after spraying.

Pregnant women should take special

precautions to avoid exposure.

3. Bring in or cover portable outdoor

furniture, toys, laundry, pet dishes

and tools.

4. Cover larger outdoor items such as

barbecue grills or sand boxes. Swing

sets and items that cannot be covered

should be rinsed thoroughly after the


5. Cover ornamental fish ponds because

pesticides are highly toxic to fish.

6. Cover vegetable gardens if you can

with plastic sheeting; wash any

exposed vegetables before storing,

cooking or eating.

7. Remove shoes when entering the

home after spraying because

pesticides can be tracked indoors and

remain toxic for months in synthetic

carpet fibers. Pesticides used for

mosquitoes are most easily degraded

in direct sunlight and are sheltered

when inside where they do not

degrade quickly.

8. Hose off window screens, door

handles and hand railings after spraying

occurs to avoid direct contact.

9. If you suffer symptoms such as

dizziness, headache, nausea,

vomiting, weakness, blurred vision,

breathing difficulties, or irritation of

the eyes, nose, lips, mouth or throat,

see your doctor immediately.

Canadian researchers studied, under

field conditions, the efficacy of three citronella-

based products (lotion, milk and

sun block formulations (active ingredients:

10% oil of citronella and 5% terpene

of citronella) to protect against

biting mosquitoes. All of the repellents

“reduced the number of mosquitoes biting

by 95% over the 1st and 2nd 30 minutes

after application.”158

The same group of researchers assessed

the efficacy of 3% citronella

candles and 5% citronella incense in protecting

against mosquito bites under field

conditions. “Although significantly fewer

bites were received by subjects at positions

with citronella candles and incense

than at nontreated locations, the overall

reduction in bites provided by the citronella

candles and incense was only

42.3% and 24.2%, respectively.”159

Avon Skin-So-Soft TM

When tested under laboratory conditions

against Aedes aegypti mosquitoes, this

product was shown to be mildly effective.

However, with a half-life of 30 minutes,

frequent reapplication is necessary to

maintain a protective layer of the oil on

the skin, which works by forming a barrier

that insect mouthparts have difficulty


Mosquito traps

A range of devices are being marketed

that have been shown to trap and kill

measurable numbers of mosquitoes over

a geographic range. Such traps may be

an adjunct to other precautionary measures,

but homeowners should be aware

that depending upon their placement,

such traps may attract more mosquitoes

into an area than they can catch.

If pesticide spraying occurs in your

community, take precautions to limit


(adapted from “Fight the Bite,” New York

Appendix 49


California Mosquito Control Contacts

Public Interest Advocacy Organizations

• Pesticide Watch at (213) 251-3690 ext. 308

• Environment California, at (415) 206-9185

• The Pesticide Action Network of North

America at (415) 981-1771

• Californians for Pesticide Reform at

(888) CPR-4880 or (888) 277-4880

• Your local Mosquito and Vector Control

District or Environmental Health Department.

(See following table.)

Mosquito and Vector Control

Association of California:

California Department of Health Services/

Vector-Borne Disease Section or


The U.S. Environmental Protection

Agency (EPA) Web site:


California Mosquito Control Districts

Who do I contact if

I have more questions

about mosquito control

or pesticide use

in California?

50 Overkill: Pesticide Spraying in California

California Mosquito Control Districts, available on the web at:

Agency Contact Info

Coastal Region

Alameda County MAD 23187 Connecticut St., Hayward,-94545

John R. Rusmisel

510/783-7744 (510/783-3903)

Alameda County VCSD 1131 Harbor Bay Parkway, Alameda, CA 94502

William Pitcher

510/567-6800 (510/337-9137)

Contra Costa MVCD 155 Mason Circle Concord, CA 94520

Craig Downs

925/685-9301 (925/685-0266)

Marin-Sonoma MVCD 595 Helman Lane, Cotati, CA 94931

Jim Wanderscheid

707/285-2200 (707/285-2210)

Napa County MAD Post Office Box 10053, American Canyon, CA 94503

Wesley A. Maffei

707/553-9610 (707/553-9611)

No. Salinas Valley MAD 342 Airport Blvd., Salinas, CA 93905

Peter B. Ghormley

831/422-6438 (831/422-3337)

San Mateo County MAD 1351 Rollins Road, Burlingame, CA 94010

Robert Gay

650/344-8592 (650/344-3843)

Santa Clara County VCD 976 Lenzen Drive, San Jose, CA 95126

Tim D. Mulligan

408/792-5010 (408/298-6356)

Santa Cruz County MVCD 640 Capitola Road, Santa Cruz, CA 95062

Paul Binding

831/454-2590 (831/464-9161)

Solano County MAD 2950 Industrial Court, Fairfield, CA 94533

Jon A. Blegen

707/437-1116 (707/437-1187)

Sacramento Valley Region

Burney Basin MAD Post Office Box 1049, Burney, CA 96013

Michael S. Churney

530/335-2133 (530/335-2663)

Appendix 51

Butte County MVCD 5117 Larkin Road, Oroville, CA 95965

James A. Camy

530/533-6038 (530/534-9916)

Colusa MAD Post Office Box 208, Colusa, CA 95932

David B. Whitesell

530/458-4966 (530/458-0818)

Durham MAD Post Office Box 386, Durham, CA 95938

Aaron A. Amator

530/345-2875 (530/345-1792)

El Dorado Co. V.C.-CSA3 1170 Rufus Allen Road, S. Lake Tahoe, CA 96150

Virginia Huber

530/573-3450 (530/542-3364)

Glenn County MVCD 165 Co. Rd. G, Willows, CA 95988

Richard T. Ramsey 530/934-4025 (530/934-5971)

Lake County VCD Post Office Box 310, Lakeport, CA 95453

Arthur Colwell, Ph.D.

707/263-4770 (707/263-3653)

Oroville MAD Post Office Box, CA 940, Oroville, CA 95965

Jeff Cahn


Pine Grove MAD Post Office Box 328, McArthur, CA 96056

William Clark

530/336-5740 (530/336-6866)

Placer MAD Post Office Box 216, Lincoln, CA 95648

Charlie Dill

916/435-2140 (916/435-8171)

Sacramento-Yolo MVCD 8631 Bond Road, Elk Grove, CA 95624

David Brown

916/685-1022 (916/685-5464)

Shasta MVCD Post Office Box 99033, Redding, CA 96099

William C. Hazeleur

530/365-3768 (530/365-0305)

Sutter-Yuba MVCD Post Office Box 726, Yuba City, CA 95992

Ronald L. McBride

530/674-5456 (530/674-5534)

Tehama County MVCD Post Office Box 1005, Red Bluff, CA 96080

D. Andrew Cox

530/527-1676 (530/527-3353)

North San Joaquin Valley Region

East Side MAD 2000 Santa Fe Avenue, Modesto, CA 95357

Claude L. Watson

209/522-4098 (209/522-7841)

52 Overkill: Pesticide Spraying in California

Merced County MAD Post Office Box 909, Merced 95341

Allan D. Inman

209/722-1527 (209/722-3051)

San Joaquin County MVCD 7759 S. Airport Way, Stockton 95206

John R. Stroh

209/982-4675 (209/982-0120)

Turlock MAD 4412 North Washington Road, Turlock 95380

Jerry M. Davis

209/634-8331 (209/634-4103)

South San Joaquin Valley Region

Coalinga-Huron MAD Post Office Box 447, Coalinga 93210

Ralph Baiza


Consolidated MAD Post Office Box 278, Selma 93662

Steve Mulligan

559/896-1085 (559/896-6425)

Delano MAD Post Office Box 220, Delano 93216

Ralph T. Alls, Ph.D.

661/725-3114 (661/725-3179)

Delta VCD Post Office Box 310, Visalia 93279

Michael W. Alburn

559/732-8606 (559/732-7441)

Fresno MVCD 2338 McKinley Ave, Fresno 93703

David G. Farley

559/268-6565 (559/268-8918)

Fresno Westside MAD Post Office Box 125, Firebaugh 93622

Elizabeth A. Cline

559/659-2437 (559/659-2193)

Kern MVCD 4705 Allen Road, Bakersfield 93312

Robert A. Quiring

661/589-2744 (661/589-4913)

Kings MAD Post Office Box 907, Hanford 93232

Lue Casey

559/584-3326 (559/584-3310)

Madera County MVCD 900 North Gateway Dr., Madera 93637

Kevin Pinion

559/674-6729 (559/674-6004)

Tulare MAD Post Office Box 1476, Tulare 93275

Marshall Norgaard

559/686-6628 (559/686-2013)

West Side MVCD Post Office Box 205, Taft 93268

Don W. Black

661/763-3510 (661/763-5793)

Appendix 53

Southern California Region

Antelope Valley MVCD Post Office Box 1192, Lancaster, CA 93584

Cei Kratz

661/942-2917 (661/940-6367)

Coachella Valley MVCD 43-420 Trader Place, Indio, CA 92201

Donald E. Gomsi

760/342-8287 (760/342-8110)

Compton Creek MAD . 1224 So. Santa Fe Avenue, Compton, CA 90221

Mitchel R. Weinbaum

310/639-7375 (310/639-4768)

Greater L. A. County VCD 12545 Florence Avenue, Santa Fe Springs, CA 90670

Jack Hazelrigg, Ph.D.

562/944-9656 (562/944-7976)

Long Beach -Vector Control Prog 2525 Grand Ave, Rm 220, Long Beach

90815 Donald D. Cillay

562/570-4132 (562/570-4038)

Los Angeles Co. W. VCD 6750 Centinela Ave, Culver City, CA 90230

Robert Saviskas

310/915-7370 (310/915-9148)

City of Moorpark/VC . 799 N. Moorpark Ave, Moorpark, CA 93020

John Brand

805/517-6267 (805/529-0267)

Northwest MVCD 1966 Compton Avenue, Corona, CA 92881

Major S. Dhillon, Ph.D.

909/340-9792 (909/340-2515)

Orange County VCD Post Office Box 87, Santa Ana, CA 92702

Robert Sjogren, Ph.D.

714/971-2421 (714/971-3940)

Owens Valley MAP 207 W. South Street, Bishop, CA 93514

Ernest Poncet

760/873-7853 (760/873-3236)

San Bernardino Co. VCP 2355 E. 5th Street, San Bernardino, CA 92410

Joan Mulcare

909/388-4600 (909/386-5148)

San Gabriel Valley MVCD 1145 N. Azusa Canyon Rd, West Covina, CA 91790

Steve A. West

626/814-9466 (626/337-5686)

Santa Barbara Coastal VCD P.O. Box 1389, Summerland, CA 93067

Mitchell J. Bernstein

805/969-5050 (805/969-5643)

West Valley MVCD 13355 Elliot Avenue, Chino, CA 91710

Min-Lee Cheng, Ph.D.

909/627-0931 (909/627-0553)

54 Overkill: Pesticide Spraying in California

1. Marilyn Chase and Ann Carnns, “Rapid

Spread of West Nile Virus Has Health Officials

on Defensive,” Wall Street Journal, 13 August


2. Kostyukov MA et al., “Experimental infection

of Culex pipiens with West Nile virus by feeding

on infected Rana ridibunda frogs and its subsequent

transmission,” Med Parazitol., 1986;

6:76-8, as cited by VPIRG, “West Nile virus,

Vermont, and Pesticides,” March 2001.

3. California Department of Health Services

Brochure, ‘West Nile Virus,” January 20, 2003.

4. USGS, “West Nile Virus Maps 2002,” found



5. Environmental Risk Analysis Program,

Cornell University, “What’s Going on with the

West Nile Virus: Information, educational

materials, scientific resources about the disease,

its prevention & control,” 13 March 2003.

6. Seth Borenstein, “Science Tracks West Nile

Virus Mutating as it Creeps Across Nation,”

Mercury News, 26 November 2002.

7. CDC, “West Nile Virus 2002 Case Count,”

reviewed 16 May 2003.

8. CDC, “Provisional Surveillance Summary of

the West Nile Virus Epidemic — United States,

January—November 2002” MMWR Weekly,

51(50); 1129-1133, 20 December 2002.

9. Gochfeld, Michael, Professor of Environmen

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