Pattern of mitochondrial DNA variation between and within Anopheles stephensi (Diptera: Culicidae) biological forms suggests extensive gene flow.

Anopheles stephensi Liston is the most prevalent anopheline species and plays an important role in malaria transmission in Indian subcontinent and Middle East including southern parts of Iran. It exists as three biological forms; "type", "intermediate", and variety mysorensis. The type form is reported to be an efficient vector of urban malaria, whereas mysorensis and intermediate are considered to be rural species and poor vectors. Moreover, differences in cuticular hydrocarbon and chromosomal characters have been described between urban and rural forms. However, the genetic structure of the biological forms remains unclear. This study was conducted to determine the genetic structure of the An. stephensi biological forms in south of Iran where all three forms are present. Live specimens were collected from the field and transferred to insectaries, reared, and identified based on egg morphological characters. Genetic structure of the biological forms was studied using PCR-RFLP of 1512 bp of mitochondrial DNA (mtDNA) cytochrome oxidase subunit I and II (COI-COII) and sequence of about 712 bp of COI and 562 bp of COII genes. Sequence analysis showed that except for a few substitutions in COII, all three forms and populations were nearly identical. The high homology of COI and COII sequence of An. stephensi forms indicates extensive gene flow between populations and forms in the region. This data will serve as first report on the sequence of mDNA COI-COII of biological forms of An. stephensi, which could be used as a diagnostic tool to identify vector/non-vector, gene flow, and geographical exchanges.

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.