Susceptibility level of aedes mosquitoes to insecticides in Chiang Mai Province

Abstract

          The susceptibility of Aedes aegypti and Ae. albopictus to various kinds of insecticides was carried out during 2001-2005 using WHO standard susceptibility test. Four communities of Sri Phum (SP). Suthep (ST), Mae Rim district(MR) and Mae Teang district (PMD), Chiang Mai Province, were selected to be study sites. The first two communities were located in Chiang Mai town while the later two were situated in rural areas. The study objective was to monitor the susceptibility level of Aedes aegypti and Ae. albopictus, dengue vectors in Thailand. The information of the study will be useful for considering policy making in selection of insecticides used in the future. Nine insecticides, DDT, Malathion, Permethrin, Delamethrin, Cypermethrin, Cyfluthrin, Bifenthrin, Lamda-cyhalothrin and Propoxur were used to expose vectors to discrimination dosages of insecticides for recommended exposure periods, and the 24-hour mortality was recorded. The results revealed that Aedes aegypti collected from both urban and rural areas had developed resistance to DDT and Proposur with mortality rates of 11-45% and 51-67% respectively. It was found that Ae. aegypti collected from both urban and rural sites had developed resistant tendency with observed reduced mortality rates for Permethrin (63.64-98.00%). Deltamethrin (77-100%). However it was it was still fully susceptible to Malathion with 99-100% mortality rate. In contrast Aedes albopictus collected from rural communities were found fully susceptible to DDT with 100% mortality rate. Moreover urbnan-collected albopictus were still susceptible to Permethrin and Deltamethrin. However, evidence of tolerance was recorded to Bifethrin (67%) and slight increase in tolerance to Cypermethrin (83%) and Lambdacyhalothrin (97%) respectively.