Deltamethin is a pyrethroid insecticide for control of malaria which has been used for a little while. Perhaps inevitably, mosquitoes are developing resistance to it. So what could be done about countering this? Well, perhaps surprisingly, form a polymorph![cite]10.1073/pnas.2013390117[/cite] These crystal structure isomers are often highly undesirable;
Significance The use of deltamethrin, a crystalline contact insecticide and a leading tool in combatting malaria vectors, faces an uncertain future, threatened by developing resistance of mosquitoes. A more active crystalline polymorph of deltamethrin, discovered here, speeds the knockdown of susceptible mosquitoes by a factor of up to 12 compared with the currently used crystalline form. The faster-acting deltamethrin polymorph is predicted to suppress malaria transmission and associated human mortality while reducing environmental exposure because less agent is required to achieve the same effect. The outstanding performance of form II promises increased serviceable use of deltamethrin crystals for indoor residual spraying. Metastable forms of contact insecticides should be considered generally for public health applications.