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Synthesis/Regeneration 31   (Spring 2003)

Pyrethroids and Living Creatures

by Wilma Kennell, Gateway Green Alliance

The total effectiveness of any vector control program is a function not just of the short-term effect on the target insects. One must consider the consequences for all living creatures, including humans. Pyrethroids (such as permethrin) are toxic to all insects.

These include predator insects, like dragonflies. Some are even more sensitive than the target insect. For example, black flies are pests. The black fly predator, caddisfly, is susceptible to permethrin at concentrations lower than those necessary to kill black flies. The same is true for spider mite predators and the mite pests. [1] Bees are extremely sensitive to pyrethroids with LD50 (half of population killed) as low as 0.03 microgm/bee. Water surface insects, crustaceans, including lobster and shrimp, as well as most fish are killed by pyrethroids. [2, 3]

These animals consume millions of mosquito larvae.

…resistant mosquitoes can quickly become the predominant members by selection…

It is difficult to quantify the extent that pesticides kill humans because it would take massive epidemiological studies to prove that such deaths were initiated by pesticide exposure. However, such correlations can be made with more certainty from autopsies of animals killed in the wild. Recently, the New York Department of Wildlife performed autopsies on 80,000 dead birds to determine causes of death. Only 11% died from WNV while 25% (more than twice as many) died from pesticide poisoning. The remainder died from other toxins. [4]

We upset the normal checks and balances that have evolved by natural selection over billions of years of evolution and create far greater long-term problems through pesticide use. Not only is there more destruction of beneficial life, but it doesn’t take long for the highly adaptable microorganisms or insects to develop resistance. For example, culex pipiens mosquitoes can become resistant to pyrethroids by a single point mutation (one nucleotide change) in the knockdown resistance (kdr) gene (leucine to phenylalanine). [5] These resistant mosquitoes can quickly become the predominant members by selection—requiring higher doses or use of more toxic pesticides. This never-ending cycle provides continuing riches for the chemical industry and increasing peril to humans and our environment.

Note. This is from a statement made by the author to the St. Louis County Council on October 22, 2002. The author has done graduate work in biological sciences at Yale University and the University of California at Berkeley.


1. Hill, I.R. 1985. Effects on non-target organisms in terrestrial and aquatic environments. In J.P. Leahey (ed.). The pyrethroid insecticides. London, UK: Taylor & Francis.

2. Subcommittee on Pesticides and Industrial Organic Pesticides. National Research Council of Canada. 1986. Pyrethroids: Their effect on aquatic and terrestrial ecosystems. NRCC No. 24376. Ottawa, Canada.

3. Smith, T.M., & G.W. Stratton. 1986. Residue Reviews. 97:93–120.

4. New York Department of Wildlife. 2002, personal communication.

5. Martinez-Torres, D., C. Chevillon, A. Brun-Barale, J.B. Berge, N. Pasteur, & D. Pauron. 1999. Voltage-dependent Na+ channels in pyrethroid-resistant Culex pipiens L mosquitoes. Pesticide Science. 55:1012–1020.

[21 apr 03]

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