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. Different hypotheses on the mechanisms limiting the distribution of this species 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 substantially different estimates of the areas that can support overwintering populations. With the threshold temperature model of cold stress, extreme low temperatures exclude flies from high-altitude areas, but fail to exclude them from areas known not to support overwintering populations. These areas can only be rendered unfavourable by using the degree-day model of cold stress, which prevents sufficient thermal accumulation above the developmental threshold to maintain basic metabolic processes for long periods. In contrast, 2 models describing different modes of heat stress accumulation provide similar results and are interchangeable. Our analyses also indicate the potential for agricultural practices, 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.