A Metapopulation Approach to Modelling the Long-Term Impact of Pesticides on Invertebrates

Two simulation models are presented which predict the impact of local and episodic applications of pesticide on the dynamics of invertebrate metapopulations. Both models assume that invertebrates disperse at particular rates over a matrix of fields and that each field experiences a specific pesticide regime. Model 1 investigates the population dynamics of a polyphagous predator which experiences direct mortality from pesticide exposure but is unaffected by the availability of the targeted pest. Model 2 investigates a similar system but also considers the dynamics of the pest, which is influenced both by predation and by pesticide exposure. Using stability diagrams and isocline portraits we characterize the likely long-term effects of factors such as the frequency and extent of spraying, factors which have hitherto not been widely considered in general pesticide models