MODELS OF INTERMEDIATE COMPLEXITY IN INSECT-PATHOGEN INTERACTIONS - POPULATION-DYNAMICS OF THE MICROSPORIDIAN PATHOGEN, NOSEMA-PYRAUSTA, OFTHE EUROPEAN CORN-BORER, OSTRINIA-NUBILALIS

Nosema pyrausta is an important microsporidian pathogen of the Europea n corn-borer, Ostrinia nubilalis (Pyralidae), a major pest of corn (ma ize). The population dynamics of the interaction between the moth and its pathogen have been studied previously using simple models phrased as coupled differential equations, and using large simulation models c ontaining over 150 000 coupled equations. A middle approach is adopted here and the interaction studied using an age-structured model writte n as a system of delay-differential equations. Although the model cont ains twenty four parameters, estimates for twenty of these were availa ble in the literature. Our model provides a good qualitative match to observed within and between season dynamics and suggests which aspects of the interaction are most important in determining the nature of th e system's population dynamics. More generally, we argue that in the a bsence of better data on insect-disease interactions in natural habita ts, valuable insights can be gained by studying equivalent systems in agro-ecosystems. We also argue that models of intermediate complexity that incorporate considerable detail about the natural history of indi vidual interactions, but which are derived from the classical models o f animal ecology and epidemiology, offer the most profitable way of mo delling insect-pathogen interactions in the wild.