Scientists have created a new crystal form of the pyrethroid pesticide deltamethrin that is up to 12 times more effective against mosquitoes. Insecticides such as deltamethrin and DDT can prevent the spread of diseases carried by mosquitoes and are often sprayed indoors and on bed nets. When mosquitoes step on insecticide crystals, it is absorbed through their feet and kills the mosquitoes. In their PNAS study , the researchers heated the commercially available form of deltamethrin to 110°C/230°F for a few minutes and let it cool to room temperature; this resulted in a new crystallized form of deltamethrin, composed of long, tiny fibers radiating from a single point.When tested on Anopheles quadrimaculatus and Aedes aegypti mosquitoes--both of which transmit malaria--and fruit flies, the new crystal form of deltamethrin worked up to 12 times faster than the existing form. Moreover, less of the new form would need to be used to achieve the same effect, potentially lowering the cost of mosquito control programs and reducing environmental exposure to the insecticide.