Bionomics of Anopheles stephensi Liston in the malarious area of Hormozgan province, southern Iran, 2002.

Anopheles stephensi Liston is an important malaria vector in Hormozgan province, where it is the most prevalent anopheline mosquito. It shows two annual activity peaks, one in spring and another in the autumn. In mountainous areas the second peak starts earlier than in coastal regions. Adults are endophilic and endophagic, but in the hot season when people sleep outside buildings they frequently bite outdoors. Larvae are found in a wide-range of habitats, both natural and man-made. All three biological forms of the species, occur in the province, i.e. An. stephensi stephensi (type form), An. stephensi mysorensis, and the intermediate form. An. stephensi mysorensis is found only in rural-mountainous areas, whereas the type and intermediate forms occur in urban-coastal regions and the rural plains, with the type form predominant. The presence of the type form in urban areas and mysorensis in rural areas is consistent with the available epidemiological data for malaria in the region and with the finding in India that the type form is an efficient malaria vector inhabiting urban areas whereas mysorensis is rural and has a lower vectorial capacity. Insecticide susceptibility tests on field collected adult mysorensis and adults from laboratory strains of the type and intermediate forms were carried out according to WHO standard methods. These showed that all three forms are susceptible to bendiocarb, propoxur, malathion, fenitrothion, deltamethrin, permethrin, cyfluthrin, and lambdacyhalothrin, but are resistant to DDT and show low level of tolerance to dieldrin. Examination of the larvicidal activity of malathion, fenitrothion, temephos and chlorpyrifos at diagnostic doses showed that these stephensi forms are susceptible to all larvicides except fenitrothion. Irritability tests to pyrethroid insecticides showed high levels of irritability to permethrin and lambdacyhalothrin, but low irritability to cyfluthrin and deltamethrin. The importance of these findings for the epidemiology and control of malaria in the region are discussed.