Southern Limits of Distribution and Abundance of the Biting-Midge Culicoides-Brevitarsis Kieffer (Diptera, Ceratopogonidae) in Southeastern Australia - an Application of the Growest Model

Abstract

Field surveys established that C. brevitarsis has a megathermic distribution. The GROWEST model of Nix was modified to reflect the temperature requirements of the midge, and a data bank was created of daily rainfall over 20 years, 1965-84, from 130 localities scattered across New South Wales. The environmental indices calculated were correlated with extensive field data on seasonal abundance of C. brevitarsis collected from 11 localities, and further checked against survey data collected from 1963 to 1984. The seasonal and annual distributions of potentially suitable environments for the midge, derived from the model, agreed well with field observations. Areas suitable for summer multiplication and winter survival were identified, and regions favourable for survival of breeding population, defined as being enclosed within 'brevitarsis lines', were determined for the spring of each year. In the wet years, 1973-78, these regions increased in size to the west and southwards along the coastal plains. In the drought, 1979-83, they conrracted to the upper Darling Basin and coast. The model enables extensions in the distribution in the summer to be analysed to determine whether they are due to local or long-distance dispersal, and has considerable application in analyses of epidemics of arboviruses of which C. brevitarsis is a vector.