CAN ANYTHING BE DONE TO MAINTAIN THE EFFECTIVENESS OF PYRETHROID-IMPREGNATED BEDNETS AGAINST MALARIA VECTORS

Pyrethroid-treated bednets are the most promising available method of controlling malaria in the tropical world. Every effort should be made to find methods of responding to, or preventing, the emergence of pyr ethroid resistance in the Anopeles vectors. Some cases of such resista nce are known, notably in An. gambiae in West Africa where the kdr typ e of resistance has been selected, probably because of the use of pyre throids on cotton. Because pyrethroids are irritant to mosquitoes, lab oratory studies on the impact of, and selection for, resistance need t o be conducted with free-flying mosquitoes in conditions that are as r ealistic as possible. Such studies are beginning to suggest that, alth ough there is cross-resistance to all pyrethroids, some treatments are less likely to select for resistance than others are. Organophosphate , carbamate and phenyl pyrazole insecticides have been tested as alter native treatments for nets or curtains. Attempts have been made to mix an insect growth regulator and a pyrethroid on netting to sterilize p yrethroid-resistant mosquitoes that are not killed after contact with the netting. There seems to be no easy solution to the problem of pyre throid resistance management, but further research is urgently needed.