Black fly larval diversity and community structure in rural streams of northern Thailand: associations with environmental factors

Although black fly (Diptera: Simuliidae) ecology has been extensively studied in forest ecosystems, knowledge from rural landscapes-where human and livestock interactions are frequent-remains limited. This study investigated the diversity, community structure, and environmental associations of black fly larvae in rural streams of Mae Rim district, Chiang Mai province, northern Thailand. Larvae and pupae collected monthly from three types of study areas were evaluated. Environmental variables were recorded in situ. A total of 3,649 last instar larvae representing 19 species across three subgenera were identified. Dominant species included Simulium nodosum (15.2%), S. chiangmaiense (14.1%), S. wangkwaiense (11.9%), S. asakoae (10.3%), and S. fenestratum (9.5%). Four human-biting species-S. asakoae, S. chamlongi, S. nodosum, and S. doipuiense complex-were identified, with the first three predominantly found in village sites. Species richness and diversity were higher in sites without human intervention (forest without human activity) compared to those in forest with human activity and villages. Canonical Correspondence Analysis (CCA) revealed that conductivity, stream width, water velocity, and salinity were significantly associated with species composition (χ2 = 1.53, P < 0.01). Notably, human-biting species were associated with wider, warmer, fast-flowing streams with elevated conductivity-conditions typical of disturbed village sites. These findings underscore the ecological significance of stream conditions in shaping black fly communities and provide critical insights for vector surveillance and control in human-impacted landscapes.