Tests for possible effects of selection by domestic pyrethroids for resistance in culicine and anopheline mosquitoes in Sichuan and Hubei, China.

Resistance tests, by conventional methods and by observing the time for knockdown, showed no evidence for any build up of resistance to deltamethrin in malaria vectors from areas where millions of bednets have been treated with this compound annually for up to 7 years. However, a strain of Culex quinquefasciatus which had been bred in a factory in which volatile pyrethroids are handled had developed unequivocal resistance to deltamethrin. Observation of the time for knockdown gave clearer discrimination between resistant and susceptible strains than did observation of percentage mortality after a standard exposure time.