Insecticide resistance in some Zika mosquitoes

One of the most common insecticides used in the battle against the Aedes aegypti mosquito—which carries the viruses that cause Zika, dengue fever, and yellow fever—has no measurable impact when applied in communities where the mosquito has built up resistance to it, a new study finds.

The study is the first to show how vital insecticide-resistance monitoring is to controling the Aedes mosquito. "The results are striking," says lead author Gonzalo Vazquez-Prokopec, a disease ecologist in Emory's Department of Environmental Sciences and assistant professor in environmental health at Rollins. "If you use the insecticide deltamethrin in an area with high-deltamethrin resistance, it's the same as if you didn't spray at all."

The results of the randomized, controlled trial are important because some public health departments in places where Zika and dengue viruses are endemic do not necessarily monitor for insecticide resistance.

"The recent epidemic of the Zika virus has raised awareness that we need to focus on what really works when it comes to mosquito control," Vazquez-Prokopec says. "The data from our study makes a bold statement: Any mosquito-control program involving spraying insecticides needs to be based on knowledge of the current levels of insecticide resistance of the local mosquitoes."

It's a natural biological process for mosquitoes to mutate in response to insecticide exposure.

Even more worrying are so-called "superbug" mosquitoes that show resistance to more than one insecticide. "You can't stop evolution," Vazquez-Prokopec says. "That's why it's important for countries to have resistance-monitoring systems at both local and national levels to help manage the use of insecticides more efficiently and effectively."—Carol Clark