Mosquito Aerial Spray Programs Endanger Human Health, Don’t Work

Posted on 02 August 2012

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By Kim Glazzard, Organic Sacramento; Samantha McCarthy, Better Urban Green Strategies; Jack Milton, Stop West Nile Spraying Now; Asael Sala, Pesticide Watch

Aerial mosquito spraying over populated areas this year by the local mosquito control district used a more hazardous pesticide than in previous years. While there is no scientific evidence that the spray is effective in stopping the spread of West Nile virus (WNv), there is evidence that the spraying endangers health.
The more dangerous pesticide used this year is an organophosphate. Similar to chemical warfare agents produced during World War II, this chemical adversely affects the human nervous system even at low exposure levels, and ingredients are on California’s Proposition 65 list of chemicals known to cause cancer.

The district justifies its spray protocol by such factors as the number of WNv-infected mosquitoes and birds, but this is a rare human disease. According to the Centers for Disease Control (CDC) only a tiny fraction of the human population becomes infected, and only 1 in 150 of those develop serious symptoms. The total serious human case count for Sacramento and Yolo counties for 2011 and 2012 is 1.

It is well established that it is safer and much more effective to target mosquito larvae before they become biting adults. Although the district uses mosquito fish to some extent, there are other effective larvae predators, such as nematodes (small roundworms) that establish populations for ongoing control and are effective from the very beginning of the mosquito season. These nematodes infect only mosquito larvae so they pose no risk to human health or the environment. Even more effective against the supposed vectors of WNv is a mosquito fungus that has exhibited 95% mosquito mortality and has been shown effective in areas where mosquito fish cannot be used.

Both peer-reviewed scientific research and mathematical modeling demonstrate that spraying is ineffective for WNv control. Cornell University entomologist David Pimentel writes: “Widespread ULV [ultra-low volume] spraying from ground equipment or aircraft for control of mosquitoes and West Nile virus is relatively ineffective, costly, and has been associated with environmental and public health risks.” Also, a Harvard School of Public Health study concludes: “We find that ULV applications of resmethrin had little or no impact on the Culex vectors of WNv, even at maximum permitted rates of application.”

A model widely used for infectious diseases produced two important conclusions when applied to WNv transmission: 1) early, sufficient, treatment for mosquito larvae is the key to control; 2) treatment aimed at adults later in the season cannot possibly eradicate the virus, particularly with the protocol the district uses.

Justifications the district has used to support its aggressive aerial spray program have been very weak at best. In 2005 the district cited a slide show about treatments in Fort Collins, Colorado and a report from a Louisiana parish, but they revealed nothing about the efficacy of spraying. In fact, the Fort Collins spraying, when viewed in context, demonstrates the ineffectiveness of spraying: nearby Boulder did not spray and had better results than surrounding communities that sprayed.

The district cites a purportedly peer-reviewed paper from the CDC website on the efficacy of its 2005 Sacramento spraying; however, the authors did not provide a single review in response to a Public Records Act request. Furthermore, that spray event was not set up as a study and parameters were adjusted after the fact. Additional flaws include: human infection locations were based on a false assumption and the spray was halted for 8 consecutive days by wind, which inhibits mosquito flight and biting behavior. The wind is not even mentioned in the report.  No valid conclusions can be drawn, yet officials continue to cite this report as evidence of efficacy.

The district’s claim that the spray “breaks the transmission cycle” is contradicted by research and the facts – within only 17 days after the June 11-12, 2012 spray the District’s own risk assessment triggered spraying once again, confirming that even the more dangerous pesticide did not work. And, while they have more potent vectors and a humid climate that promotes greater transmission of the virus Washington, D.C. officials do not spray precisely because of spray inefficacy and health risks to residents.
The price tag for this ineffective program is staggering. For example, the district reports that the cost of the 2005 aerial spraying was $701,790.

The district must base its policies on sound science and recognize that its program poses a greater risk to public health than the virus against which the spraying allegedly protects.

For references for these points plus further discussion, see

Thank you for printing this informative piece that lays out the lack of scientific basis for aerial spraying of populated areas for mosquitos, as well as the disturbing news that the Sacramento-Yolo Vector Control District is using ever more dangerous pesticides for this purpose. The fact that the spraying is necessary so often according to the district's own risk assessments, and that the district feels the need to use even more hazardous pesticides because the previous ones were not effective enough, indicates that this approach is not working and not workable. The state needs a new, safe approach that does not entail involuntary mass exposure of the public to hazardous chemicals.

I notice there are a lot less mosquitos when they spary. It is fine with me if they spray...I think the spray is the least of our worries...I am sure the car exhaust will get ya before the once a year mosquito spay. I rather enjoy not haveing mosquito bites, so keep on spraying:)

Thanks Vector Control!

I can't believe you would print an article without checking some basic facts. The products used by mosquito and vector control districts are not anywhere on the prop 65 list. It's amazing that these pesticide opponents call out vector control professionals who dedicate their lives to studying and implementing strategies to protect public health for utilizing scare tactics, yet in the same article make claims that these products will cause cancer because they're on the prop 65 list. Check the list at I don't see naled or sumithrin on the list, yet these pesticide opponents want everyone to believe that they're going to get cancer because vector control is spraying. Rubbish. I love how these folks pump their own opinions, but where is the link to the vector control study so i can review it for myself. They claim that vector control scares us with WNV yet they don't want to hear the other side of the story. Where is the interview with an actual victim who can give their side of the story. I know two people that got WNV, I don't know anyone who died of pesticide poisoning, which is what they want us to believe. Left wing nuts. You gotta love Ca, everyone has an opinion-keep it to yourself, I'll trust the folks that do this work everyday.

Dibrom, which is being used in aerial spraying by the local vector control district, does contain chemicals that are on California's Prop 65 list. While Naled is one of the chemicals in Dibrom, Dibrom also contains DDVP and Naphthaliene. Number 15 on page 9 of the Material Safety Data Sheet (MSDS) for Dibrom states:

CALIFORNIA (Proposition 65): This product contains chemicals known to the State of California to cause cancer - DDVP, Naphthalene."

If you look on California's Prop 65 list you will see DDVP and Naphthaline listed there as chemicals known to cause cancer.

And, as if cancer isn't bad enough, listed in number 3 on page 2 of Dibrom's MSDS under "Hazards Identification" is this additional warning:

"DANGER! POISON! CORROSIVE! An off-white to straw yellow liquid with a sharp, pungent odor that causes irreversible eye and skin damage. May be fatal if swallowed, inhaled or absorbed through skin and eyes."

How is it possible to avoid inhaling or having skin and eye exposure to chemicals that are being blanket-sprayed in the air over 100,000 acres of a major metropolitan area?

Common sense dictates we should all be concerned about the increasingly toxic soup in which we are swimming. The body of scientific and medical literature easily available to citizens online at the National Library of Medicine at the National Institutes of Health ( will provide thousands of references that delineate why we are at risk from escalating numbers of chemicals, combining in unanticipated compounds, even in infinitesimal dosages, causing devastating human health risks. If you are able to dismiss personal concerns about your increased vulnerability to cancers, neurological disorders such as Parkinson's, and reproductive infertility, please think about the children you know and love. Children, because of their immature neurological and detoxification systems and smaller body size, are eating, drinking, breathing, and absorbing devastating portions of pesticides and other industrial toxins. We can no longer be cavalier. This must stop.

Thanks to the authors for thoroughly outlining just one more example of an opportunity missed to reduce the toxic body burden we each bear daily.

I realize there are more and more toxins in our environment these days, but why not focus on the pollutants from power plants and cars. Who knows there may be some risk at a low level. However, mosquitos are pests they bite and cause infections/illness in humans and our pets. ....I bet the African countries where everyone has to sleep with nets over them if they are lucky to have them would be thrilled to have the number of mosquitos reduced, and it seems to me the benefit outweighs the risk. Plus, this article does not exactly back up the claims it makes either way. So instead of advocate against something that could be a potential health benefit why not seek a different environmental avenue to be passionate about.

It was just reported that an elderly woman died from the disease....based on this group, she was old and was going to die soon anyway. I want the district to do what they can to protect me, my family, and my friends, whether they are old, young, or in between.
West Nile virus clearly endangers human health, and based on the lack of cases in Sacramento, it appears to be working much better than this letter states.

More mosquitoes?
Or a array of other mosquito transmitted diseases?

In 1983 material developed at UCD and the Sutter-Yuba Mosquito Abatement District was furnished to the Colombian Service Eradicacion de Malaria. Colombia had an epidemic that killed 10,000 people in 1983. Between 1982 and 1983 they tripled the application of DDT and malaria doubled to over a million cases and over 10,000 fatalities. These biological agents were employed in a remote region of Choco Provence and the resulting reduction of mosquito populations and malaria transmission was monitored for the next two years. All malaria transmission had ceased in the test area which remained free of malaria for 18 months beyond the single application.There has not been a single fatality due to malaria in this region since 1983 when the alternative project was started..
This convinced the Colombian Health Ministry to discontinue DDT spray. There has been no insecticide applied for vector control in Colombia since 1996. The incidence of malaria is 4% of its 1983 level and there has been no serious outbreak of yellow fever or dengue either since the 1996 change in national public health policy to promote bed nets, rapid delivery of primary health care and water management as the primary vector control programs with the utilization of biological controls where feasible.
Sac-Yolo vector control should be applying these same practices for managing a far less serious disease like WNv.

Vector-borne diseases : Malaria poses a serious public health problem for Colombia . It is estimated that 18 million people live in areas where malaria is transmitted. In 1998, there was an epidemic with 240,000 confirmed cases. In 2000, there were 141,047 confirmed cases - a figure consistent with the endemic level observed over the preceding decade - and 41 deaths. Another serious public health problem in Colombia is dengue. Around 65% of the urban population faces a high probability of becoming infected with dengue and dengue hemorrhagic fever (DHF). In 1998, a total of 57,985 cases were documented, including 5,171 cases of DHF. The dengue-2 and dengue-4 serotypes were circulating simultaneously. In 2000, there were 22,772 reported cases of classic dengue and 1,819 cases of DHF, with 19 deaths. The high index of Aedes aegypti infestation in many municipalities poses a serious risk factor for the urban transmission of yellow fever, and jungle yellow fever continues to be active in Colombia . In the 1990s, there were an average of 4 cases per year.

Wow! Thank you! I continually wanted to write on my blog something like that. Can I take a portion of your post to my website?

I must remark upon comments submitted by "Jim". Since my nickname is also Jim and I was closely involved with a project for the control of epidemic malaria in Colombia from 1982-1987, some persons have assumed that I submitted these remarks.
"Bobby" is right to dispute the claim that no insecticide has been used in all of Colombia since 1996, this is only true for the Pacific Coast region of Choco Provence; not even all of Choco, most of which is on the inland side of the mountains.
He is also right to dispute the claims of malaria reduction for the nation of Colombia since it only rightfully applies to 23 communities in Choco Provence on the Pacific Coast.
Dr. William Rojas's publications about this project can be readily discovered in a number of medical journals starting with the Bulletin of the World Health Organization in 1987:
Rojas, W. Northup, J. et al (1987) Reduction of malaria prevalence after the introduction of Romanomermis culicivorax (Mermithidae:Nematoda) in larval Anopheles habitats in Colombia. Bull. WHO 65(3): 331-337

The results of the extended program post 1996 can be reviewed in this publication:
Rojas, W. Botero, S. and Garcia, HI. (2001) An integrated malaria control program with community participation on the Pacific Coast of Colombia, Cad. Saúde Pública, Rio de Janeiro, 2001, 17(Suplemento):103-113

The citation of no fatalities due to malaria since 1983 in the four communities of the original project is accurate.

It is edifying to compare Dr. Rojas's conclusions with the cited experts in the article linked by "Bobby":

Both experts agree that development is the only effective remedy. “Malaria is an economic, social and cultural problem” which only disappears from areas with industrialisation and better socio-economic conditions, says Agudelo.

Thanks for the clarification....but it does beg the question as to why Columbia has not embraced this project throughout the rest of the country. Do you know why?

I've been asked by a colleague if I might respond to your question.
Your question implies that the idea of alternative measures has not been adopted. This is not exactly the case. While the authors of the article you linked did not mention the program on the coast of Choco, they and the Choco health officials they cited seemed to think that this community development approach is the best way to combat malaria, but that no one was funding it.
If you were to compare the World Health Organization’s 2010 "Role Back Malaria" program with the programmatic proposals in William Rojas’ community development approach you will find a striking similarity. Points one and two are essentially identical; Rojas says “bed nets and primary health care - which means permanent clinics staffed by doctors and supplied with medicine”. The WHO prioritizes bed nets and the distribution of pharmaceuticals. The use of DDT in domiciliar spray programs used to be WHO's number one priority; it now places vector control with domiciliar spray as number three.
There are a number of reasons to adjust away from insecticidal spray but principally it has to do with the vectors’ abil9ty to develop resistance. So far there has not been any well established insect population rendered extinct by directed insecticidal applications. We may have inadvertently damaged non-target insects. In terms of long term amortization the spray approach will always become more costly and fail whereas building and staffing medical clinics goes on to treat many disease situations and becomes less costly after initial investment, albeit more expensive than spray.
I have not been involved in any plenary discussions about malaria control in Colombia for some time so I cannot explain the unwillingness of local and provincial governments to fund such programs. I can say that the special coastal zone in Choco has received a great deal of private charitable funding and grant money as well as the assistance from CINDE’s Casa Promesa Community Cooperative, the Catholic Diocese of Choco and the “Flying Doctors of Medellin”.
I can also tell you that Glen Nimnicht, the co-director of CINDE
until his death in 2004 is the only US citizen or for that matter, non-Colombian, to receive the Colombian Medal of Honor for his philanthropic work on this project.
The epidemiologists from Choco Public Health services who were interviewed in the linked article, indicated that there are three main causes for this resurgent malaria and dengue in Choco and Colombia as a whole: number one, poverty at 73%; number two, the displacement of more than 70,000 of the 800,000 population in Choco by the ongoing civil war; and three, the decentralization of public health services to be the responsibility of local and provincial governments which are not funding public health. They note that while the federal government has supposedly signed on to the WHO initiative, so far no monies have been appropriated.
The experts cited in the article state that economic development including better housing and improved infrastructure for managing water and sewage, greater development of public health services and the increase in living standards is the only solution for dealing with these mosquito vectored diseases.