A few minutes in the microwave made a common insecticide about 10 times more lethal to mosquitoes in lab experiments.
The toxin deltamethrin is used around the world in home sprays and bed nets to curb the spread of mosquito-borne diseases like malaria — which kills over 400,000 people each year, according to the World Health Organization. But “mosquitoes the world over are showing resistance to deltamethrin and [similar] compounds,” says Bart Kahr, a crystallographer at New York University who has helped develop a more potent form of deltamethrin by heating it.
This form of deltamethrin may stand a better chance of killing insecticide-resistant pests, Kahr and colleagues report online October 12 in the Proceedings of the National Academy of Sciences. Malaria has been essentially eradicated in the United States, but more effective pesticides could be a boon for regions like sub-Saharan Africa, where the disease is a major public health problem.
Kahr’s team increased the potency of commercial deltamethrin dust spray simply by melting a vial of it — either by heating it to 150° Celsius in an oil bath for five minutes or by popping it in a 700-watt microwave for the same amount of time. While the microscopic deltamethrin crystals in the original spray have a haphazard structure, which looks like a jumble of misaligned flakes, the melted deltamethrin crystals solidified into starburst shapes when they cooled to room temperature.
Chemical bonds between deltamethrin molecules in the starburst-shaped crystals are not as strong as those in the original microcrystal structure. “The molecules are intrinsically less happy, or settled, in the arrangement,” Kahr says. So, when a mosquito lands on a dusting of starburst-shaped crystals, it should be easier for deltamethrin molecules to be absorbed into the insect’s body via its feet.
The researchers tested the more potent version of deltamethrin on lab-bred mosquitoes from two species: Anopheles quadrimaculatus, which can spread malaria, and Aedes aegypti, which can transmit other life-threatening diseases, such as Zika and dengue (SN: 1/8/19). Forty mosquitoes of each species were released into petri dishes coated in the original deltamethrin dust spray, and another 40 into a dish covered in the new form of the insecticide.