Heterogeneity of Culicoides Variipennis Field Populations to Oral Infection with Bluetongue Virus

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Abstract
A standard colonized population (000 line) of Culicoides variipennis (Coquillett) was used as the control for comparing the infection rate (IR) responses of different field populations of the vector to oral infection with several strains of bluetongue virus (BTV) that belonged to four serotypes. Three field populations from Colorado and Oregon tested concurrently in 1969 were differently susceptible to three BTV strains representing three serotypes. The IR's of each of the three populations varied greatly for the three serotypes, and the lowest IR for each of two Colorado populations was for a different serotype. The IR's of different populations to the same BTV strain varied greatly, and the lowest and highest IR's for two serotypes with adequate virus concentration occurred in different populations. Two Kentucky field populations in 1971 were completely resistant to oral infection with a BTV strain; in 1972, one population remained resistant and the other became moderately susceptible. The IR's of different field populations in 1971 to a single BTV strain ranged from 0 to 68%. The IR's of an Idaho population to three BTV strains representing three serotypes showed that a susceptibility rate (SR) could be calculated if the IR's were similar for one and for two infective blood meals. The average SR of this population was 42%; the SR's to each serotype were 32%, 40%, and 54%, with the highest response for the serotype that included the BTV strain collected during the BT outbreak from which the vector population was also collected.