Insecticide treated nets: impact on vector populations and relevance of initial intensity of transmission and pyrethroid resistance.

Insecticide treated bednets locate a deposit of a quick-acting insecticide of low human toxicity between a sleeper and host-seeking mosquitoes. Thus a chemical barrier is added to the often incomplete physical barrier provided by the net. Treated nets may be considered as mosquito traps baited by the odour of the sleeper.

Deltamethrin impregnated bednets against Anopheles minimus transmitted malaria in Assam, India.

Of the 20 Anopheles species caught in villages in Sonapur, Assam, only An. minimus was incriminated as a malaria vector by finding sporozoites in the salivary glands. It was found to be endophagic and endophilic in Assam and because its biting peaked after midnight it was a suitable target for insecticide impregnated bednets.

Laboratory studies of pyrethroid-netting combinations to kill mosquitoes.

Bioassays of cotton or synthetic netting, impregnated with one of two formulations of deltamethrin or a formulation of lambda-cyhalothrin, showed that the order of merit of these insecticides varied significantly with the type of netting used. Washing reduced the insecticidal power of all combinations of insecticide and netting. Halving the time of exposure and doubling the dose tended to increase the mortality.