Control of malaria vectors with the insect growth regulator pyriproxyfen in a gem-mining area in Sri Lanka

The study was conducted in eight adjacent villages in central Sri Lanka where there are many shallow pits dug by gem miners that Fill with water. These become breeding places of the main malaria vector Anopheles culicifacies, and of the second most important vector Anopheles subpictus. but not of Anopheles varuma. the third most important vector, With the help of local volunteers. data on the adult populations or these three species was collected by various standard methods., and data on the incidence of malaria cases was collected by two clinics set Lip for the project and through the existing hospitals. Prevalence of malaria infection in symptom-less people was investigated by mass blood surveys. On the basis of a year's pre-intervention data the villages were stratified into four with high levels of malaria transmission and four with lower transmission. Within each stratum two villages were randomly assigned for mosquito control by treating all the gem pits, as well as river bed pools, with a granular formulation of the insect growth regulator pyriproxyfen at a target dose of 0.01 mg a.i./litre. The intervention caused significant reductions in the adult populations of An. culicifacies and Ali. subpictus. Similarly, incidence of malaria was reduced in the intervention villages to about 24% (95% c.l. 20-29%) of that in the controls. Prevalence of parasitaemia also declined significantly. It is concluded that in this situation where. with active community participation, the breeding sites of the main vectors could be located: vector control by a highly active and persistent insect growth regulator can be a very effective means of malaria control. (C) 2001 Elsevier Science BN. All rights reserved.