THE GEOGRAPHICAL-DISTRIBUTION OF THE QUEENSLAND FRUIT-FLY, BACTROCERA(DACUS) TRYONI, IN RELATION TO CLIMATE

CLIMEX is used to analyse the potential distribution of the Queensland fruit fly in relation to long-term average meteorological data. Diffe rent hypotheses on the mechanisms limiting the distribution of this sp ecies are examined. The analyses indicate that different CLIMEX models discriminate between locations in different ways. In particular, the models describing the limiting effects of cold stress yield substantia lly different estimates of the areas that can support overwintering po pulations. With the threshold temperature model of cold stress, extrem e low temperatures exclude flies from high-altitude areas, but fail to exclude them from areas known not to support overwintering population s. These areas can only be rendered unfavourable by using the degree-d ay model of cold stress, which prevents sufficient thermal accumulatio n above the developmental threshold to maintain basic metabolic proces ses for long periods. In contrast, 2 models describing different modes of heat stress accumulation provide similar results and are interchan geable. Our analyses also indicate the potential for agricultural prac tices, such as irrigation, to alter quite dramatically the suitability of an area for Queensland fruit fly, and impact upon its geographical distribution and the pattern of activity.