Getting Mosquitoes to Poison Their Own Larvae

Henry Fountain, The New York Times 19 Jun 09;

Controlling the mosquito that’s largely responsible for infecting people with the dengue fever virus isn’t easy. That’s because the bug, Aedes aegypti, has evolved in parallel with humans, living around them and breeding in even the smallest puddles of water — rainwater in a discarded can, say, or the saucer under a flower pot.

With so many potential breeding sites, spreading pesticide can be a painstaking, door-to-door activity. But Gregor J. Devine of Rothamsted Research, an agricultural institute in Britain, had a different idea: why not let the mosquitoes do the work?

Building on laboratory studies that showed that adult mosquitoes could pick up an insecticide and transfer it, he and his colleagues conducted field experiments in Iquitos, Peru, using pyriproxyfen, a compound that kills larvae but is not harmful to adult mosquitoes (or to people, either, in the amounts used).

After getting a meal of blood from a human, a female A. aegypti likes to find a dark, damp spot to rest while its eggs develop, buzzing off later to find water to deposit the eggs in. Dr. Devine said their work, described in The Proceedings of the National Academy of Sciences, took advantage of this routine.

He and his team set up “dissemination stations,” consisting of dark, damp cloths dusted with pyriproxyfen, in the nooks and crannies of above-ground tombs in a cemetery. When a female rested on the cloth, its legs picked up some of the pesticide, which came off when it later landed in a breeding pool. The researchers found that putting stations in as little as 3 percent of the available spots in the cemetery resulted in coverage of almost all the breeding habitats in the immediate area, and mortality of up to 98 percent of the mosquito larvae.

Dr. Devine said the technique may be useful for controlling A. aegypti in conjunction with other eradication methods and may also help control mosquito species that spread other diseases, like malaria.