A SIMULATION-MODEL FOR THE POPULATION-DYNAMICS OF RICE LEAF-FOLDERS (LEPIDOPTERA, PYRALIDAE) AND THEIR INTERACTIONS WITH RICE

1. A simulation model for the population dynamics of rice leaf-folders (Lepidoptera: Pyralidae) interacting with rice (Oryza sativa L.) is described. It was designed to improve the understanding of the role of rice leaf-folders as elements of the rice ecosystem and to detect crucial knowledge gaps in view of a holistic assessment of their pest status. The model represents a synthesis of experimental results on leaf-folder biology and behaviour. 2. A distributed delay model including attrition was applied to simulate dynamic population changes such as birth, ageing, mortality, migration and growth in terms of numbers and biomass. 3. The host-plant on the one hand is assumed to affect leaf-folder survival, migration and growth rates while leaf-folders on the other hand influence plant growth and development by feeding and folding of leaves. 4. Based on the metabolic pool approach, leaf-folder feeding and hence leaf mass losses to the rice plant were described with a generalized functional response model which is 'source' and 'sink' driven. 5. In a preliminary test with independent field and laboratory data the model predicted the leaf-folder population dynamics and the resulting leaf area losses in rice in a satisfactory manner. 6. The simulation results show minor yield losses due to leaf-folder infestations and suggest that economic injury levels are generally underestimated. Furthermore, the model stresses the influence of adult migration and natural enemies on leaf-folder population dynamics, both significant but poorly investigated aspects of the leaf-folder life cycle.