Implications of potential global warming on agricultural pests in Australia1

The potential influence of climate warming on the future status of agricultural pests in Australia is discussed in terms of the possible effects that changes in temperature, rainfall and weather patterns will have on the future distribution, numbers, fluctuations and movements of pest populations. Event-driven outbreaks are distinguished from rate-driven processes in pest populations. The future severity and frequency of pest outbreaks will depend on changes in the frequency of extreme weather events, some of which are related to the El Niño/Southern Oscillation phenomenon. Three scenarios are presented for geographical changes to rate-driven and to event-driven processes: little change (displacement of agroecosystems and their associated pests to new climatic optima); expansion of tropical pests, contraction of Mediterranean (winter rainfall) pests; increased pest multiplication in geographically fixed agroecosystems such as irrigation schemes and some animal production systems. There is considerable uncertainty about the future severity of outbreaks and chronic infestations because of our current difficulties in forecasting and realistically simulating population changes in agroecosystems. This probably results from the complex feedback mechanisms involving natural enemies and other factors. In Australia the overall expansion of areas affected by tropical pests portends an overall worsening of agricultural pest problems.