CHANGES IN ABUNDANCE AND BEHAVIOR OF VECTOR MOSQUITOS INDUCED BY LAND-USE DURING THE DEVELOPMENT OF AN OIL PALM PLANTATION IN SARAWAK

Surveys a ere conducted of adult and immature mosquitoes in an area un dergoing oil palm development in north Sarawak. Point prevalence data from 2 sites were collected annually, coinciding with annual phases of forest clearing, burning/cultivation, and maintenance. Major habitat perturbation during the forest/clearing transition shifted the major m osquito faunal equilibrium in terms of species composition, relative d ensity and occurrence. Analyses of variance showed that the mean numbe rs of 4 species of Anopheles decreased significantly after forest clea ring. Relative densities of immature stages decreased after forest cle aring, but A. letifer and Culex tritaeniorhynchus remained relatively unchanged after the second year. Comparisons with the pre-development forest stage showed that the reductions in person-biting rates, adult survival and combined entomological inoculation rates (EIR) of A. dona ldi and A. letifer decreased the risk of malaria transmission by 90% o ver the 4 years period. Concomitant reductions in EIR and annual malar ia incidence were also correlated. This study highlighted the 'law of unintended consequences', since 2 contrasting effects were observed: r eduction of malaria vectors but concomitant increase of dengue vectors .