Spraying can make WNV worse!(West Nile virus)

• Author: Fitz, Don

It is not entirely correct to say "Spraying has no effect on West Nile Virus (WNV)." There is good reason to believe that spraying can make WNV worse in three ways:

* Spraying can cause a long-term increase in mosquito populations.

* Spraying may result in an increased prevalence of WNV in mosquitoes.

* Spraying can make it more likely that humans will develop encephalitis from WNV.

Most of us learned when we took our first biology course that insects develop resistance to pesticides within a few years. Even if a spray kills 99%, the 1% that survive will pass resistance genes to their offspring. The attempt to overcome the inevitable by using more and deadlier pesticides has come to be known as the "pesticide treadmill."

Recent facts indicate that pesticide spraying can also increase the mosquito population. Pesticides can kill mosquito predators that have a longer life span than mosquitoes. (See "Belly-Up Goldfish.")

Less well known is the effect that spraying can have on a "sympatric" species that occupies the same ecological niche. John Howard and Joanne Oliver collected data on spraying the pesticide naled near New York's Cicero and Toad Harbor Swamps for mosquitoes which carry eastern equine encephalitis (EEE). Though there were short-term reductions after sprayings, from 1984 to 1994 there was a 15-fold increase in the number of mosquitoes. The researchers also discovered a large decrease in a different species of mosquitoes; living in the same area. When the populations of non-EEE carrying mosquitoes were killed off, the EEE-carrying mosquitoes took their place. The authors concluded that the increase in disease-spreading mosquitoes "discredits the rationale that preventive applications of naled reduce the risk of EEE."

A major cause of growth in mosquito-borne diseases is global warming and the real solution is massive reduction of greenhouse gases. The cover article in the August, 2000 Scientific American by Harvard Medical School's Paul Epstein predicts that global warming will lead to large growth of mosquito-borne diseases such as malaria, dengue fever, yellow fever and several kinds of encephalitis. He explains that warmer weather creates more breeding grounds, lengthens the time of year that mosquitoes are active, allows them to "proliferate faster and bite more," and speeds up the rate of viral reproduction inside the mosquitoes. Spraying pesticides while ignoring global warming is like being on an airplane heading towards a...