Response of Culicoides variipennis (Diptera: Ceratopogonidae) to water level fluctuations in experimental dairy wastewater ponds.

Water levels were fluctuated in experimental dairy wastewater ponds in southern California to study the response of Culicoides variipennis (Coquillet). Immatures consistently were found in surface mud at the water's edge in ponds where the water level was stable. In ponds where the water level was fluctuated, immatures did not relocate to the new, lower waterline when the water quickly receded 3 m in horizontal distance. Younger larvae apparently were stranded above the waterline and were killed by heat or desication, or both; pupae and late fourth instars emerged as adults at the old waterline. A larvae were recovered from fairly dry mud up to 19 d after the water level receded. Substantial oviposition occurred at the lower waterline following the water level decrease, and adults began to emerge 14-18 d later. Immatures relocated to the higher waterline 3 h to 2 d after a rise in water level. Densities of this species were slightly, but not significantly, reduced in the fluctuated ponds under this water management regime. Water level fluctuations at 1-wk intervals might be expected to reduce substantially C. variipennis production from these habitats.