West Nile Virus and Mosquito Control


    In a 2004 paper, West Nile Virus and Mosquito Control, PhD entomologist David Pimentel of Cornell University writes that "Widespread ULV 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." 

    As to proper control, Pimentel writes "The prime method of control is the elimination of the breeding habitats for larval mosquitoes, such as water accumulating in bird baths, flowerpots, old tires, and other containers."

    Note that he writes "For effective mosquito control, at least 90% of the adults must be killed. Only a few scientific studies of the effectiveness of spraying for mosquito control have been reported. These results are relatively discouraging. For example, in Greenwich, CT, only a 34% mosquito population reduction was reported after ground spraying, and in Houston, TX, only a 30% reduction occurred after spraying.[6] Then in Cicero Swamp, FL, populations of disease-carrying mosquito populations increased 15-fold after spraying,[6] when the mosquito population was measured 11 days after spraying. However, it is doubtful that the insecticide spray caused the increase in the mosquito population, but clearly the insecticide provided insufficient adult mosquito control. . . . Also to be considered are the serious public health and environmental problems associated with the application of insecticides from aircraft"

    Vector control officials and people taking measurements in this area are reporting 35% to 40% kill rates in cages, and lower results are expected in the natural habitat.  They clearly are not getting anywhere near the 90% figure Pimentel notes they must get for effective mosquito control.


    In an email note he wrote the following when he sent a copy of this paper.  We had called his attention to the Carney study by California Department of Public Health Officials:

"Thanks for your letter and the additional information.  I have a few comments concerning this paper.  First, before I comment I should  emphasize that I am not opposed to the careful use of insecticides.  My concern is that we use insecticides carefully and we know what we are doing when we use insecticides and other pesticides.
My comments concerning this paper are:
1)  No mosquito population counts were made 5 days before and 5 days after spraying to assess the effectiveness of the spraying.    
2)  Aircraft spraying is more effective than ground spraying . . .  It should be emphasized that only 10% to 25% of the insecticide applied by aircraft reaches the target area, up to 90% drifts away from the target area and into the environment at large.  Clearly, the serious public health and environmental problems associated with the application of insecticides need to be considered.  There was no mention of these problems in the report.
3)  I am not a statistician, but would like to know the type of statistical analysis they used because they had only 1 control and 2 treatments.  The 1 control is especially troubling.

. . .  this is not a highly scientific assessment of the use of insecticides in West Nile virus control.  Mosquito control and control of the diseases transmitted by mosquitoes is extremely difficult.  Pesticide treatments cost a great deal of money and are hazardous to public health and the environment.  Thus, great care needs to be exercised to make sure that public health and the environment benefit from any insecticide treatment that is made."