GTLAUS - A MODEL OF WHEAT, CEREAL APHID, PREDATOR INTERACTION AND ITSUSE IN COMPLEX AGROECOLOGICAL STUDIES

In this report, GTLAUS (version 3.7), a discrete simulation model of w heat - cereal aphid - predator interaction, which can be used for comp lex ecological studies in a representative tritrophic system of arable farming, is described and presented with selected scenario runs. GTLA US is not a prediction model for practical plant protection, bur a too l for analysis of the interaction of different pest and antagonist den sities and ecological effects of changing climate and other environmen tal conditions. The model contains three submodels: wheat ontogenesis, popular-ion dynamics of the cereal aphid Sitobion avenae (FABR.), and population dynamics and predation of aphid-specific predators, especi ally Coccinella septempunctata L. Several functions for certain featur es, e.g. grain yield loss and aphid mortality due to parasitoids and e ntomopathogenic fungi, were also incorporated into the model. A large number of scenario runs with various initial population densities and different weather regimes were analyzed to quantify aphid population d evelopment under certain conditions and antagonist potential for natur al control. Age structure variation in the initial aphid population le ads to markable differences in population growth race. Temperatures 3K higher than the long-term German mean temperature were found to give especially C. septempunctata a relative predatory advantage compared w ith aphid multiplication. Natural control, therefore, increases even c learly so. The model calculations also showed that the impact of benef icials varies greatly, depending primarily on aphid density and temper ature. Lower temperatures may favour aphids for seasons of prolonged w heat ripening and weaker predator activity.