Culicoides (Diptera: Ceratopogonidae) biting midge is a genus of small hematophagous flies that can transmit multiple disease-causing pathogens to animals and humans. In southern California, Culicoides sonorensis is the only known vector of the bluetongue virus, which is of great concern worldwide due to its rapid spread and high morbidity/mortality in ruminant animals. Investigating the diel host-seeking activity of C. sonorensis as a function of environmental conditions and exploring the overwintering mechanism of BTV will increase our knowledge of BTV transmission. It is observed that the host-seeking activity pattern of C. sonorensis varies among days and most activity starts near sunset though sometimes it starts before sunset during winter periods. The host-seeking activity pattern is influenced by weather, moon, and seasons. The relatively mild winter in southern California allows C. sonorensis to be active throughout the year, but virogenesis requires a certain temperature. Therefore, it remains unclear which mechanisms BTV is utilized for overwintering and needs further investigation. While C. sonorensis is recognized as the main vector of BTV in the southern California dairies, other Culicoides species may be important vectors of BTV to wild ruminants (e.g., bighorn sheep) in the desert regions of California. However, correct identification of these species becomes an obstacle for investigating Culicoides species-related topics in the desert area. Therefore, I develop molecular techniques combined with traditional morphological methods to identify Culicoides species in the southern California desert, which contributes to the global Culicoides taxonomy and biology. Moreover, studying the Culicoides diversity and their host preferences in the inland desert area of southern California may shed light on the relationship between Culicoides species and hemorrhagic diseases among wild ruminants and will facilitate studies of the epizootiology of hemorrhagic diseases in the area. Evaluating different trap methodologies increases the knowledge about the appropriate trapping method for targeting different Culicoides species and Culicoides of different physiological statuses in the desert region. With the sequence information, identification of immature midge species becomes easier and the abundance variation of midge species at two locations will assist future research on immature ecology.