A field trial with Lambda-cyhalothrin (ICON) for the intradomiciliary control of malaria transmitted by Anopheles darlingi root in Rondonia, Brazil

A two stage field trial comparing the effects of Lambdacyhalothrin (ICON) and DDT when used as residual sprays on the inside surfaces of houses, was conducted in the Machadinho and Jaru areas of Rondonia, Brazil, in 1987 and 1988. In 1987 houses along two 16 km contiguous stretches of a main and a side road were sprayed and the effects on malaria vectors monitored for the succeeding year. In the second stage approximately 55 000 houses in both districts were sprayed with ICON and the effect on malaria incidence measured by passive case detection. Of the eleven species of Anopheles caught in indoor and peridomicilliary collections A. darlingi was the commonest and is recognised as the most important vector in Brazil. ICON at either of two concentrations in bioassays killed more mosquitoes than DDT at each test from seven to twelve months after spraying. A rise in the number of A. darlingi collected eight months after spraying with DDT was so marked in the ICON areas. Side effects of the insecticide were limited. The number of reported Plasmodium falciparum cases in the second phase declined 76% in Machadinho after spraying with ICON to 2851 cases. In Jaru there was a 28% reduction. The observed efficacy of the insecticide, its ready acceptance by the local populace, and its cost effectiveness make it a more useful insecticide for anti-malaria campaigns than DDT.