The concentration of larval black flies in well-defined aquatic habitats makes knowledge of the breeding sites critical for the efficient management of pest species. Black flies can achieve pest status either as generalists by developing in many types of streams and rivers or as specialists by developing in one or a few types of flowing water, such as large rivers. These two developmental strategies are evident in pest and vector species of the Simulium (Gomphostilbia) varicorne species group in Thailand. Simulium chumpornense is a habitat generalist, whereas S. khelan gense is a habitat specialist, developing in the large Mekong River, where we discovered its immature stages. The first descriptions of the larva and pupa of S. khelangense, along with mitochondrial and nuclear genetic markers, allow accurate identification and comparisons with structurally similar species in the S. varicorne species group, thus aiding the ability to monitor the pest and vector status of black flies in Southeast Asia.
