To use the sterile insect technique against mosquitoes, females must be removed from the lab-raised populations before release. For species in the genus Anopheles, such as Anopheles stephensi (shown here), separation is difficult because male and female larvae and pupae “show negligible differences in body size and pupation timing.” However, a new study shows that adult female mosquitoes’ taste for blood can be used against them by lacing a bloodmeal with insecticide, significantly accelerating the sex-separation process before sterile males can be released. (Photo by Jim Gathany via CDC Public Health Image Library)

By Ed Ricciuti

Ed Ricciuti

A group of researchers in China has put a new spin on “spiking a drink,” in this case to fight mosquitoes. Their study published in June in the Journal of Medical Entomology describes how slipping a dose of lethal drugs into blood imbibed by female mosquitoes eliminates what they call “a longstanding bottleneck” that has limited the use of an environmentally friendly and effective weapon against Anopheles mosquitoes.

Known as the sterile insect technique (SIT), the method is, in effect, is a form of birth control for insect pests and increasingly incorporated into integrated pest management. The concept is simple, although its application is not: Male insects of the targeted species are raised en masse in a laboratory, sterilized by radiation, and then released to mate with females in the wild. Eggs from such mating are not viable, suppressing the population of the species.

Sterile insect technique eradicated the New World screwworm fly (Cochliomyia hominivorax) from North America in the late 20th century. It is now being deployed again to stop a new invasion, feared since the fly was detected in Texas in June.

When SIT is used with flies, males and females raised in the lab aren’t separated; the sterilized females released with the males are harmless and produce no offspring. However, for use of SIT with mosquitoes, males must be separated from females after propagation and before release, because female mosquitoes bite and are thus capable of further spreading vector-borne disease. The rub is that, with some mosquito species, separating males and females is easier said than done. Although SIT has suppressed populations of the Asian tiger mosquito (Aedes albopictus) and the yellow fever mosquito (Aedes aegypti), it’s been a bust when tried against the genus Anopheles, which includes species that are the sole vectors of malaria. For Anopheles, in fact, SIT is barely possible, at least at an operational level.

With Aedes mosquitoes, for instance, sexes can be sorted by automation because female pupae and larvae are larger than males, each sex passing through different sized slits in a glass separator. But some females are smaller, so the technique is not foolproof, even if mostly effective.

Because Anopheles larvae and pupae of both sexes are similar in size and look, on the other hand, they must be sorted manually, maxing out at about 500 an hour, not nearly enough for SIT.

To feed mosquitoes a bloodmeal in a lab, researchers use an apparatus that consists of a temperature controller and six blood feeding units, each with a flexible membrane that covers the blood to mimic human skin conditions. (Image originally published supplemental to Zhu et al. 2026, Journal of Medical Entomology)

“Physical sex sorting relying on pupal size disparity works well for Aedes mosquitoes, yet Anopheles males and females show negligible differences in body size and pupation timing, rendering mechanical sex separation impractical,” says Dongjing Zhang, Ph.D., of Sun Yat-Sen University in Guangzhou, China, a co-author of the new study. “Manual sorting is extremely slow and cannot support large-scale field releases.”

The key to solving the problem—removing all females before release—is that females feed on blood while males don’t. “Our approach leverages a fundamental biological distinction: only female mosquitoes take blood meals, whereas males never feed on blood,” says Zhang.

When a spiked blood meal is offered, the females feed and drop like proverbial flies, while males ignore the blood and survive. The technique does not kill quite enough females to meet the threshold of less than 1 percent for direct release of mosquitoes, but it makes manually sorting out the few survivors a breeze.

The researchers screened, tested and evaluated 11 different chemical brews on the Asian tiger mosquito (Aedes albopictus) then verified its effectiveness in Anopheles stephensi. They compared how various chemicals impacted blood feeding , taking into account factors such as temperature, frequency and duration of feeding, and age of the mosquitoes involved. Surviving males were rigorously evaluated for how well they flew, longevity, capacity to mate, and how effectively they competed for females.

Screening of candidate chemical compounds was exhaustive and strict. The deadly cocktail that worked best was a mix of deltamethrin, a synthetic version of chrysanthemum pyrethrins that attacks the insect nervous system. The brew is made even more lethal by the addition of piperonyl butoxide, which blocks the action of an insect’s metabolic defenses that detoxify pyrethrins.

The feeding supplement ATP was added to what the researchers term their “tailored pesticide cocktail” because female mosquitoes possess highly sensitive chemoreceptors specific to the compound on their mouthparts. It makes females ravenous, so they gorge on large amounts of blood, boosting their intake of deadly pesticides.

After females are eliminated, say the researchers, highly precise additional sorting, powered by artificial intelligence and genetics, can fine tune the batch so that it contains almost exclusively males.

“Though this protocol has not yet attained the female contamination threshold mandatory for direct SIT release, it serves as a highly efficient pre-processing step with substantial practical value for mosquito SIT programs,” says Zhang.

Ed Ricciuti is a journalist, author, and naturalist who has been writing for more than a half century. His most recent book is called Bears in the Backyard: Big Animals, Sprawling Suburbs, and the New Urban Jungle (Countryman Press, June 2014). His assignments have taken him around the world. He specializes in nature, science, conservation issues, and law enforcement. A former curator at the New York Zoological Society, and now at the Wildlife Conservation Society, he may be the only man ever bitten by a coatimundi on Manhattan’s 57th Street.