Heating obsolete insecticide can restore its mosquito-killing power: Study

Researchers have found the best way to restore an insecticide’s mosquito-killing power—just microwave it! Microwaving the insecticide deltamethrin has been found to rearrange its crystal structure, effectively renewing its ability to kill mosquitoes that have developed resistance to the chemical, according to a recent study published in the Malaria Journal on April 21.

Path-breaking research on insecticides

The research team, led by Bart Kahr, a crystallographer at New York University, discovered that heating deltamethrin altered its crystal structure, resulting in improved efficacy. Kahr noted that modifying crystal arrangements is a well-established method of giving drugs new properties. However, this approach had not been previously explored in the context of insecticides. The team's findings revealed the potential of crystal rearrangement in revitalising insecticides, shedding light on a previously untapped area of research.

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To investigate further, Kahr and his colleagues heated a chalk formulation of deltamethrin known as D-Fense Dust using both an oven and a microwave. While precise temperature control was possible in the oven, the researchers were curious to test the effectiveness of the microwave, as deltamethrin is a consumer product. Surprisingly, the microwave yielded similar results to the oven, but Kahr cautioned against using the same microwave for heating food and insecticides.

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Then, the researchers collaborated with entomologists to assess the impact of the rearranged crystals on five strains of Anopheles mosquitoes from West Africa, which were resistant to deltamethrin. Encouragingly, the altered crystals successfully killed the resistant mosquitoes.

Big boost to mosquito population control efforts

Insecticide resistance poses a significant challenge to mosquito population control efforts and hampers the fight against malaria transmission. Janet Hemingway, a geneticist at the Liverpool School of Tropical Medicine in England who was not involved in the study, emphasised the severity of the issue, stating that almost nowhere in Africa is fully susceptible to insecticides anymore.

Researchers working to put the findings to use

Kahr's team is actively working on integrating the heat-treated deltamethrin crystals into bed nets. Although liquid sprays are not feasible due to the crystals' inability to retain their structure when mixed with water, spraying the heated chalk is a potential alternative.

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However, Kahr acknowledged the need to consider social and cultural factors, as homeowners may not like having chalky walls. Kahr says, “There are all kinds of social and cultural things that you could propose from a scientific perspective that wouldn’t be welcomed by a community of homeowners.”

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