Temperature and humidity limits for flight activity of field-collected Culicoides biting midges (Diptera: Ceratopogonidae) in the United Kingdom under defined laboratory conditions.

Culicoides biting midges are biological vectors of internationally important arboviruses, including bluetongue virus (BTV) and epizootic hemorrhagic disease virus (EHDV), which significantly impact livestock production in Europe. Temperature is a fundamental driver of the transmission of Culicoides-borne arboviruses, regulating virus replication within the insect, vector survival and activity. A key determinant of the spread of Culicoides-borne viruses is vector dispersal through flight activity which is constrained by temperature. Here we determine the temperature and humidity thresholds of flight activity for UK Culicoides vector species. More than 40,000 adult Culicoides were collected from field sites in the southeast of England using CDC light traps during spring, summer, and autumn. Bioassays conducted under laboratory conditions were used to determine temperature and humidity thresholds of Culicoides flight activity by measuring flight phototaxis towards an ultraviolet light source over a 24-h period. The highest flight activity (48%) was observed at temperatures between 20 and 25 °C, with reduced activity above and below this. Flight activity at 10 and 35 °C was reduced, with less than 10% of Culicoides active. Moreover, seasonal variation in low and high temperature thresholds for flight were recorded, with a lower threshold for flight activity recorded in populations caught in spring compared with those caught in summer and autumn. Finally, Culicoides flight activity and survival was significantly reduced under low humidity conditions (<50% rH). The flight response of UK Culicoides vector species to temperature and humidity presented here will facilitate the refinement of existing models used to predict incursion and spread of Culicoides-borne viruses.