Present gains against malaria and other vector-borne infectious diseases are threaten by the evolution of resistance to pyrethroid insecticides embedded in mosquito nets, prompting the World Health Organization (WHO) to call for a return to DDT, which is a contact insecticide that functions when insects contact the crystal surfaces. Curiously, a difluoro analog of DDT, DFDT, developed by German manufacturers during World War II and claimed to be faster acting than DDT, was ignored in the chaos of war. Herein, we characterized and evaluated many solid-state forms of DFDT and MFDT, which is a chiral monofluoro analog of DDT, and their relative thermodynamic stabilities were studied. Comparison on the fruit fly Drosophila revealed the rapid knockdown characteristics of crystalline DFDT and MFDT, while their amorphous states were considerably more active. The efficacy of amorphous DFDT and MFDT was further verified by two infectious disease vectors, Anopheles and Aedes mosquitos. Fast knockdown speeds of insecticides repress mosquito resistance. Our study reveals the applicable value of fast-acting fluoro analogs of DDT for public health. In addition, for each contact insecticide studied here, the lethality is inversely correlated with the thermodynamic stability of its solid-state forms. We suggest solid-state formulation as a practical strategy to improve the lethality of existing contact insecticides, which would reduce the amount of insecticides required for vector control, therefore minimizing environmental effect.

Solid-state form dependent lethality of fast-acting fluoro analogs of the contact insecticide DDT

2019 Fall National Meeting

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