THE DISPERSAL OF CULICOIDES BREVITARSIS IN EASTERN NEW-SOUTH-WALES AND ASSOCIATIONS WITH THE OCCURRENCES OF ARBOVIRUS INFECTIONS IN CATTLE

Distributions of the vector Culicoides brevitarsis Kieffer (Diptera: C eratopogonidae) (determined from light trap data) and 2 arboviruses (d etermined from seroconversions in sentinel cattle) were studied in eas tern New South Wales in 1993-94. C brevitarsis was recorded progressiv ely from endemic areas on the north coast, to Nowra on the south coast , and westward to Scone, in the Hunter Valley. C brevitarsis also surv ived through winter at Paterson, in the Hunter Valley. Its apparently focal reappearance in this marginal area had no obvious effect on the broad pattern of its progression or the dispersal of Akabane and bluet ongue viruses. These viruses were first recorded from foci near Coffs Harbour, on the mid-north coast. Their first occurrences at different locations were associated with those of C brevitarsis, but not with ea ch other. The viruses were found only within the recorded limits of th e vector's distribution, Delays between the initial occurrence of C br evitarsis and first evidence of virus transmissions at locations range d from 2 to 7 months. The delays decreased away from the points of foc us and were negatively associated with the time of initial occurrence of the vector. Seroconversions to the viruses were related to the pres ence of C brevitarsis. However, the densities of C brevitarsis had no apparent effect on the initial numbers of cattle seroconverting to eit her virus. The results support the conclusion that the progressions of C brevitarsis and Akabane and bluetongue viruses were the result of g radual movements by the vector.