Larval Population Dynamics of Culicoides variipennis (Diptera: Ceratopogonidae) in Southern California

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Abstract
Larval Culicoides variipennis (Coquillett) were sampled weekly for 18–24 mo in two dairy wastewater ponds in southern California. Numbers of larvae were lowest in January–April and highest in July–November. As many as 7,616 larvae were recovered from a single 30-ml aliquot of shoreline mud in early October. Overall, recoveries of first to fourth instars composed ca. 3, 13, 34, and 50% of the total, and relative instar recoveries were similar for both cool and hot seasonal periods. Water-levels fluctuated irregularly throughout the year, but numbers of larvae could not be related directly to changes in water level. Most first instars were collected under conditions of rising water, however. Under stable shoreline and water-level conditions, most eggs and first and second instars were recovered at or above waterline, whereas most third and fourth instars were recovered below waterline. Time series analysis techniques were applied to separate the cyclical fluctuation due to voltinism from background variation. Approximately 9–11 discrete generations were found per year, with an average interval of 4.8–6.5 wk. A time-varying cosine function model was developed to account for the yearly pattern in larval abundance and seasonal variability in the generation interval. During summer and fall (peak bluetongue virus transmission period), the generation interval was 3.0–4.5 wk.