Rising temperatures may affect pesticide effectiveness

The effectiveness of an important mosquito-fighting insecticide may be impaired by global warming, according to a recent study.

Two researchers from Montana State University, graduate student Shavonn Whiten and Robert Peterson, have shown that permethrin becomes less effective at killing the yellow fever mosquito (Aedes aegypti) as temperatures increase.

These mosquitoes, which are found in the tropics and the subtropics, can transmit viruses that lead to dengue, chikungunya, yellow fever, and other diseases.

"Many of the areas where these insecticides are employed have varying drastic temperature changes," Whiten said.

The researchers exposed adult mosquitoes to varying concentrations of permethrin at a range of temperatures.

They found an inverse relationship between death and temperature from 16 AoC to 30 AoC, which showed the highest negative correlation.

From 30 to 32, there was, however, a positive correlation between mortality and temperature. And from 32 to 34, the negative correlation resumed.

"It probably has something to do with variability and heat stress," said Peterson.

"Once you get to those higher temperatures, there are other things going on regarding stress on the mosquito that cancel out the effect of the pyrethroids (a class of pesticides to which permethrin belongs) working better at lower temperatures and worse at higher temperatures," he explained.

People involved in mosquito-control efforts should take temperature into account when choosing a pest-control product, researchers said.

The study was published in the Journal of Medical Entomology.