Seasonal Microdistribution of Immature Culicoides variipennis (Diptera: Ceratopogonidae) at Saltville, Virginia

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Abstract
Spatial distribution of immature Culicoides variipennis (Coquillett) within the littoral habitat in Saltville, Va., changed throughout the year. During warmer months of the year most larvae were found to inhabit the surface mud at or near the waterline. Pupae were found above the shoreline. Insects overwintered in the larval stage, mostly as third instars. During autumn, larvae began to burrow into the shoreline mud. In winter, when the pond and underlying mud froze, most larvae were recovered far from the shoreline in the ice/mud interface. Although overwintering larvae possessed elevated levels of glycerol, marked declines in larval density occurred within the habitat after periods of abrupt freezing and thawing. In early March, most larvae molted to fourth instars and migrated above the shoreline in preparation for pupation and adult emergence in April. Larvae collected during summer were smaller than those collected during autumn and winter. This was attributed to higher temperatures, lower organic content of ingested mud, and possible effects of crowding during summer.