Better biological control by a combination of experimentation and modelling

Abstract

Greenhouse whitefly (Trialeurodes vaporariorum) and sweet potato whitefly (Bemisia tabaci) are very common, highly polyphagous pest insects worldwide. Biological control of greenhouse whitefly with the parasitoid Encarsia formosa has been applied with great commercial success during the past twenty years, while natural enemies for the sweet potato whitefly are now evaluated. Modelling has played a role in the process of selecting and improving the efficacy of releases of natural enemies, but often biologically unrealistic simplifications were part of these models which strongly limited their predictive value. We have developed a model which is unique in that it is individual-based and simulates the local searching and parasitization behaviour of individual parasitoids in a whitefly-infested crop. The model includes stochasticity and spatial structure based on location coordinates of plants and leaves. This model comprises several submodels for the parasitoid’s foraging behaviour, the whitefly and parasitoid population development, the spatial distribution of whitefly and parasitoid within and between plants in the crop, and for leaf production. With the model we can simulate temporal and spatial dynamics of pest and natural enemy. The model will allow us to explain why the parasitoid can control whiteflies on some crops and not on others in large commercial greenhouses, to improve introduction schemes of parasitoids for crops where control was difficult, to predict effects of changes in cropping practices (e.g. greenhouse climate, choice of cultivars) on the reliability of biological control and, finally, to develop criteria for the selection of natural enemies.