Background: The basin water supply are responsible to development the larval habitat and increase the mosquitoes density and possible transmission of mosquitoes borne diseases.Objectives: The aim of this investigation was to found the effects of developed larval habitat due to basin water supply on mosquitoes fauna, composition and their distribution in the study areaMaterials and Methods: Three rural areas, Cheheltan, Chashm, Kemroud and Foolad mahaleh villages were selected in Mahdishahr township, Semnan province, northern Iran. Eudominant, dominant, subdominant, rare, and sub rare species were classified based on Heydemann classification method. The Jaccard’s index was used for cluster analysis and the relationship between the categories of the entomological data of selected study areas. Adult and larval stages of mosquitoes were sampled to obtain data required for measuring diversity of mosquitoes Alfa and beta indices were analyzed to compare mosquito diversity Results: Three genera and nine different species were collected and identified including; Anopheles claviger, An. maculipennis, An. superpictus, Culex hortensis, Cx. mimeticus, Cx. perexigus, Cx. pipiens, Cx.theileri and Culiseta longiareolata. Evaluation of dominance structure of species showed that mosquitoes of this area rangelands include various eudominant, dominant, subdominant, rare, and sub rare species. The cluster analysis based on Jaccard’s index indicated the relationship between the categories and indicates that Cheheltan, Chashm and Kemroud are the closest categories in their specific composition in related to more developed larval habitat.Conclusion: It is the first formal biodiversity study due to water supply system which occurs in northeast of
Iran as a historic endemic malarious area. The higher diversity of mosquitoes in Fooladmahaleh with a low degree of interspecific dominance was observed, while Cheheltan, Chashm, and Kemroud recorded the lowest observed diversity and a high degree of interspecific dominance.