Homes in a Tanzanian village sprayed with a sweet-smelling pesticide saw a sharp drop in the number of mosquitoes inside.

Elison Kemibala

Pesticide-spiked punch lures mosquitoes to their doom

WASHINGTON, D.C.—Sweets are the downfall of many a human. But they may signal an even deadlier risk to mosquitoes, which have their own sweet “tooth.” That’s because scientists recently invented an aromatic cocktail derived from plant nectars that strongly attracts the insects to feed on a pesticide-laced potion. After just 2 weeks, mosquito populations in an initial field trial plummeted by nearly 66%, researchers reported at a meeting here yesterday. If successful in larger trials, the new approach could be commercialized in as little as 1 year.

Every year, approximately 725,000 people die from mosquito-borne diseases like malaria, according to the Bill & Melinda Gates Foundation. Efforts to reduce mosquito populations by spraying insecticides across wide areas or distributing insecticide-containing bed netting have helped in some places. But many mosquitoes have evolved resistance to certain insecticides. To make matters worse, widespread insecticide use has contaminated soils and streams and wreaked havoc on beneficial insects, such as bees and other pollinators.

To avoid these issues, Agenor Mafra-Neto, a chemist and CEO of ISCA Technologies in Riverside, California, wondered whether using a special type of bait might target mosquitoes more directly. He and colleagues from several universities collected a variety of sweet-smelling flowers and other nectar-producing plants. They used a technique known as gas chromatography to separate and identify the odor compounds. They then exposed mosquito antennae to thousands of the compounds to determine which might have a biological effect. At the same time, they eliminated scents that seemed to attract bees. Once they settled on a combination of 20 compounds, they added mosquito-killing insecticides, such as pyrethroids or spinosad, to the mix.

To test their concoction, Mafra-Neto and his colleagues initially placed samples in a mosquito-containing greenhouse in Tanzania that they had used to test other mosquito control agents. Within 2 days, all the mosquitoes in the greenhouse had died from the poison. Next, they moved on to field trials. In four Tanzanian villages of roughly 500 residents in total, they sprayed their formulation under the eaves of houses, where gaps between mud walls and thatched roofs commonly let mosquitoes in. Homes in four other similarly sized villages remained untreated. At this week’s meeting of the American Chemical Society here, Mafra-Neto reported that the number of mosquitoes in the treated homes dropped by two-thirds in just 2 weeks, compared with a spike in mosquito numbers in untreated households (thanks to a period of rain). And they saw no effect on bees or other beneficial insects.

“There’s a lot of promise there,” says Edmund Norris, an entomologist at Iowa State University in Ames, who attended the presentation. Dan Strickman, a vector control program manager at the Gates Foundation here who was also at the meeting, adds that if further trials prove equally successful, the new approach will have a unique advantage: Unlike many mosquito control approaches such as aerial spraying and bed nets, it may work well both indoors and outdoors. Mafra-Neto says his company is working now to get approval for their formulation from the U.S. Environmental Protection Agency, which he says could come in as little as 1 year. However, he adds, countries such as Tanzania that face persistent problems with malaria and other mosquito-borne illnesses may approve of the sweet smelling antimosquito cocktail even sooner. And the company, he adds, has already begun efforts to extend their approach to ticks, another major vector of human diseases.