Assessment of Diel Emergence in Culicoides variipennis123

In northeastern Colorado, Culicoides variipennis (Coquillett) (Diptera: Ceratopogonidae) exhibited a bimodal diel periodicity of adult emergence. The principal peak of activity followed sunset; a 2nd peak occurred 3–5 h after sunrise; and there was little or no activity between these periods. In the hour following sunset more males emerged than females (60% of total); in the morning sexes emerged in equal numbers. Emergence traps were modified to alleviate moisture and gas accumulation. A method for trap placement was devised that limited the temperature differential after 1 h to no more than 1°C between substrate exposed to direct sunlight and substrate beneath the trap.