Larval survey of surface water-breeding mosquitoes during irrigation development in the Mahaweli Project, Sri Lanka

A survey of ground water-breeding mosquitoes was done during 1986-1987 in an area undergoing irrigation development in the Mahaweli Project of Sri Lanka. Forty-nine species were collected during the 12-mo phase of humans settlement and infrastructure construction, and 42 species during the succeeding 12-mo period under irrigated rice culture. Development resulted in the elimination of some preexisting breeding habitats, the modification of others, and the creation of new habits. The overall change from uninhabited forest to settled irrigated rice sharply increased the prevalence of Anopheles annularis van der Wulp, An. peditaeniatus (Leicester), Aedeomyia catasticta Knab, Mimomyia hybrida (Leicester), Mansonia uniformis (Theobald), and Culex tritaeniorhynchus Giles. Equally sharp decreases occurred in the prevalence of An. barbirostris van der Wulp, An. barbumbrosus Strickland & Choudhury, Ae, jamesi (Edwards), Ae. vittatus (Bigot), Ae. pseudomediofasciatus (Theobald), Cx. halifaxii Theobald, Cx. malayi (Leicester), Cx. minutissimus (Theobald), Cx. nigropunctatus Edwards, Cx. fuscocephala Theobald, and Cx. mimulus Edwards. Other species that showed smaller positive or negative changes included An. nigerrimus Giles, An. culicifacies Giles, An. jamesii Theobald, An. subpictus Grassi, An. vagus Donitz, An. varuna Iyengar, Mi. chamberlaini (Ludlow), Ma. annulifera (Theobald), Cx. bitaeniorhynchus Giles, Cx. gelidus Theobald, and Cx. pseudovishnui Colless. Irrigation development led to reduced breeding by the majority of species; however, most species that did increase in prevalence were potential vectors of human disease. Components of the irrigation system such as reservoir and canal margins, seepages, and rice fields provided increased breeding sites for some of these species.