Biological control of greenhouse whitefly with the parasitoid Encarsia formosa on tomato: An individual-based simulation approach

Biological control strategies of greenhouse whitefly with the parasitoid Encarsia formosa were studied with a simulation model of the parasitoid-host interaction in a crop. The model is based on developmental biology of both insect species and on the searching and parasitization behavior of individual parasitoids, in relationship to host plant characteristics and greenhouse climate. The model includes stochasticity and a spatial structure which is based on location coordinates of plants and leaves. The simulated population increase of greenhouse whitefly in the absence or presence of parasitoids agreed well. with observed populations in a tomato crop. Whiteflies were suppressed rather than regulated by the parasitoids at extremely low densities (<0.3 unparasitized pupae per plant), but did not become extinct. The percentage of black pupae fluctuated between 40 and 70%. According to the model, the parasitoid adults reached high densities of 7.4 per plant, but due to the low whitefly density not more than 1% of the parasitoids were searching on infested leaflets. The degree of whitefly control was strongly affected by variation in giving up time (GUT) of the parasitoids. When variation in GUT was excluded in the model, the whitefly population became almost extinct. Other important parameters of the parasitoid which strongly influenced the level of control were the walking speed and walking activity, the probability of oviposition after encountering a host, the ratio of search times on both leaf sides, and the longevity. The combined effect of these important attributes of a parasitoid can be tested with the model. When comparing successes of E. formosa on different crops, attention should be focused on the same parameters plus the whitefly development duration and the number, size, and production of leaves in the canopy. The model can be used to evaluate a number of release strategies on several crops and under various greenhouse climate conditions. (C) 1997 Academic Press.