Distribution, Abundance, and a Probability Model for Larval Culicoides variipennis (Diptera: Ceratopogonidae) on Dairy Farms in New York State

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Abstract
Aquatic habitats on New York State dairy farms were sampled to determine the distribution and abundance of larval Culicoides variipennis (Coquillett), and to develop a probability model for the presence of the species. Late-instar larvae were found on five to seven of eight dairies selected randomly in each of seven geographically widespread counties; overall, larvae were present on 46 of 56 (82%) farms. Of 626 substrate samples examined, 294 (47%) contained C. variipennis larvae. Larval density was I to 10, II to 49, and >49 larvae per 150-cm3 sample in 72, l4, and 14% of positive samples, respectively. Larvae occurred in a wide variety of farm habitat “types” and “locations” but were particularly abundant in cattle-modified substrates in pastures and cow yards where the source of water was “spring fed” or “milkhouse effluent.” Only I of 108 samples from 20 dairy manure storage systems contained C. variipennis larvae. Nine variables associated with larval habitats contributed significantly to a stepwise logistic regression equation that predicted the presence or absence of C. variipennis with an accuracy of 80.07%. The “degree of animal access,” “pH,” “nitrate concentration,” “water source = milkhouse effluent,” “phosphorous concentration,” “habitat type = stream,” “water source = spring fed,” and “sample period” were positively associated with the presence of larvae; “percent organic matter” was negatively associated. These findings are discussed in terms of their relevance to Northeast dairy operations.

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