The Nasci Report.
In his report, which we have not seen published in a scientific journal, of work conducted in the Ft. Collins area of Colorado in 2003, Dr. Nasci draws the two conclusions that 1) "Adulticide caused a measurable decline in vector mosquito density," and 2) "The number of new human cases in Ft. Collins with onsets after adulticide applications declined relative to other communities in the region."
Some scholars have challenged Nasci's conclusions, however, on the grounds that there were serious deficiencies in the data that fail to support the conclusion that adulticiding resulted in a dramatic reduction of adult mosquito populations. Martin Walter, Professor of Mathematics at the University of Colorado, who studied the presentation and discussed the issues with colleagues, has written that:
"The Nasci presentation does not in any way show that the number of cases of West Nile were reduced by spraying. (While there definitely was a risk to the environment posed by the pesticide.) The City of Boulder did not spray and had better results (as measured by number of West Nile cases) than any of the communities around it that did spray. I would have to agree . . . that spraying has a large component of politics mixed in with it. If you spray you are visibly 'doing something.' Unfortunately, the only thing we know we are doing for sure when we spray is that we are adding poison to our environment." [See Walter Note ]
The "Louisiana Papers."
We wanted to read the actual papers and
contacted Dr. Kramer, who faxed us a copy of one paper with the
references omitted. The title of the paper is “Impact of
West Nile Virus Outbreak upon St. Tammany Parish Mosquito
Abatement District,” and it appeared in the Journal of the
American Mosquito Control Association, 21(1):33-38, 2005.
The important question is whether adulticide
reduces transmission of WNV as compared to doing nothing or to
treating with larvicides and using other methods only. What
is the decrease in effective WNV transmission when adulticide is
used? This paper cannot possibly answer those questions, as
it was not a comparative study. It was not a study in any
way, shape or form; there were no alternative approaches examined;
there were no controls. Rather this is a documentation of
what one district did and the impacts upon that district.
The goal of the district was to prevent new WNV cases, yet it had
no marker against which to gauge success or failure, there was no
comparison of treatment methods, and there were no control areas
Our district officials did not answer the
question if they had done models to show effectiveness, and this
paper they rely on does not even discuss spraying vs. not
spraying. While the numbers went down, this might have been
from the increased larvaciding, and it might have happened in
spite of any control measures as the numbers went down naturally
anyway. No conclusions about the efficacy of adulticiding
can be drawn from this administrative report, yet it was cited as
one of the two best pieces of evidence in August of 2005.
The DHS "Report."
In 2006 Vector Control officials cite a report by DHS officials as
evidence. This report has significant problems,
however. The first one to note is that the arithmetic in the
chart is flawed. We suspect that DHS officials can do simple
arithmetic, so we suspect that this report was not checked before
it was published. It has other flaws, but no conclusions
whatsoever can be drawn with the incorrect arithmetic.
Please see a full critique here.
We made several Public Record Act requests to
get all information associated with that report, but full
information was never supplied. In May of 2008 authors from
the CDPH published the final version of their report. It is
fatally flawed, however.
These papers and the report were the best that
the head of the California Department of Health Services, Vector
Borne Diseases Section, and the SYMVCD could come up with to
justify the use of aerial ULV spray of populated areas. They
have no evidence, no models, no scientific studies.
Actual Scientific Evidence -- as
to Inefficacy -- the Reddy, Bowman, and Pimentel papers.
In a 2006 paper
resulting from a study led by the Harvard School of Public Health,
Michael Reddy and the other authors conclude “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 simulating the major outcomes of such treatments indicates
that they are unlikely to reduce the force of transmission of such
an arbovirus." The model to which they refer appears in
another paper, and its abstract
states that "The model indicates that ULV has little impact on
disease incidence, even when multiple applications are made,
although the peak of the epidemic may be delayed. Decreasing the
carrying capacity of the environment for mosquitoes, and thus the
basic reproduction rate of the disease, by source reduction or
other means, is more effective in reducing transmission." If the
peak of the epidemic is delayed, this could necessitate more
"treatments," which is why some experts insist that the best thing
to do is to eschew adulticiding altogether and allow the disease
to run its course and move into chronic endemicity.
spoke about the Bowman paper at length during PBR's "Insight"
on July 31, 2007, but neither David Brown nor Glennah Trochet
asked for a reference or to see it. We can only conclude
that they do not wish to see any information that might show that
spraying adulticides is not effective.
of the Alliance for Informed Mosquito Management (AIMM) states
succinctly that "In too many municipalities across the country,
there are inadequate mosquito management policies in place.
In some cases, a coherent management plan does not even
exist. As a result, there is often a heavy reliance on mass
spraying of pesticides to kill adult mosquitoes. This method
of mosquito management is widely considered by experts to be the
least effective and most risky response to this important public
health concern. There is
no credible evidence that spraying pesticides used to kill adult
mosquitoes, also known as adulticides, reduce or prevent WNV
incidents or illnesses. In fact, communities that do not generally use
adulticides as part of their mosquito control often have lower
cases of WNV than their neighbors that do.
Pesticides used in the battle against mosquitoes have been linked
to numerous adverse health effects including asthma and
respiratory problems, dermatological reactions, endocrine
disruption, chemical sensitivities, and cancer. Adulticides
can also be harmful or fatal to nontarget wildlife. There
are much safer and more effective ways to manage mosquitoes and
protect the public from mosquito-borne illnesses like WNV than the
spraying of adulticides." (emphasis ours)
It is also important to note that Shawnee Hoover of Beyond Pesticides has indicated to us that she advised Dr. Kramer of the serious problems with the Nasci study well before August 23, 2005.
Given that the current evidence is strongly
against the effectiveness of spraying, it is important to note
that effective alternatives exist, revolving around the concept of
integrated pest management. Such alternatives can involve
larviciding, use of mosquito fish, implementing more safe and
effective biological controls,
eliminating standing water, discovering hot spots and treating
them aggressively, and extensive public education. The success of
the Boulder, Colorado, program
is a good example. Without good evidence of effectiveness,
there is simply no reason to spray adulticides no matter what
level any of the District's triggers reach.
We address safety concerns elsewhere on these
pages. Actually, at the time of the debut of this webpage the U.S. EPA was roughly halfway
through the process to reevaluate the registration of pyrethrins
and PBO for use in pesticides. The docket (OPP-2005-0042 and
OPP-2005-0043) revealed that the preliminary risk assessment
indicated new areas of concern and that there was significant
evidence that this assessment had to be revised since it
underestimated the risk of harm.
1. Paula Macedo, Jerome Schlier III, Marcia Reed, Kara Kelley, Gary Goodman, David Brown and Robert Peterson, "Evaulation of Efficacy and Human Health Risk of Aerial Ultra-low Volume Applications of Pyrethrins and Piperonyl Butoxide for Adult Mosquito Management in Response to West Nile Virus Activity in Sacramento County, California," Journal of the American Mosquito Control Association, 26(1):57–66, 2010.
2. Dia-Eldin Elnaiem, K. Kelley, Stan Wright, Rhonda
Laffey, Glenn Yoshimura, Maria Reed, Gary Goodman, Tara Thiemann,
Lisa Reimer, William Reisen, and David Brown, "Impact of aerial
spraying of pyrethrin insecticide on Culex pipiens and Culex tarsalis (Diptera: Culicidae) abundance
and West Nile virus infection rates in an urban/suburban area of
Sacramento County, California." Journal
of Medical Entomology 45: 751-757, 2008.