Potential vectors of bluetongue in Australia.

Bluetongue has only been isolated as yet from species of biting midges of the genus Culicoides, initially from Culicoides pallidipennis in South Africa by du Toit (1944) and then from C. variipennis in the United States of America by Price and Hardy (1954). More recently it has been isolated from C . pallidipennis, C . milnei and C . tororoensis in Kenya (Walker and Davies 1971), and from C. pallidipennis in Israel (Braverman and Galun 1973). It is for this reason that studies at the McMaster Laboratory have concentrated on biting midges, but not to exclusion of other groups of blood-sucking insects which attack stock. Bluetongue is a disease of sheep, goats and cattle, and there is increasing evidence of other ungulates being infected with the virus. Consequently, the intensive studies on the insects which bite cattle, which have been in progress since the ephemeral fever epizootic of 1967-68 (Standfast and Dyce 1972a, 1972b), are as vital to our preparedness for the future as are studies on the insects which bite sheep. Various techniques have been used in Australia to determine which midges bite sheep and cattle, and of them direct collection from sheep and cattle appears to be the most satisfactory (Dyce, A. L. and Muller, M. J., personal communication). Drop traps and tent traps have been used but some species do not enter such traps, and the engorged insects captured might not necessarily have fed on the bait animal within the trap. Truck trap and light trap collections frequently contain engorged females, and the source of the blood meal can be identified by the techniques described by Murray (1970). Species of Culicoides, which bite cattle and buffalo and are likely to be important vectors of arboviruses are C. brevitarsis, C . marksi, C . dycei, C . victoriae, C . schultzei and C. peregrinus (Standfast and Dyce 1972b). The first four species also bite sheep (M. J. Muller, A. L. Dyce and M. D. Murray, unpublished data). There are several other species, such as C . marmoratus and C . mubirnaculutus, which bite sheep and/or cattle, and undoubtedly others will be added to the list in the future. It is the female Culicoides which attacks stock, one blood meal at least being required for the < I