Assessment of the consequences of the house-spraying of malathion on the interruption of malaria transmission.

Marked female Anopheles culicifacies were released into an enclosed palm-leaf hut at dusk and survivors recovered the following drawn by hand on several occasions before and after spraying with the insecticide malathion. Pre-spray releases yielded only 25-50% recovery which was thought to be due to concealment of resting mosquitoes in the palm-leaf. A mortality of 100% was recorded for over 2 months after spraying the insecticide but after 71 days small numbers of live recoveries were found. The likely effect on malaria transmission of the observed survival rates was assessed theoretically. Although the percentage survival found in the experiment would not seem to prevent the control of malaria the data suggest that the spraying regime would immediately give a great selective advantage to any resistance gene arising in the population.