A PHYSIOLOGICALLY-BASED MODEL OF PEST-NATURAL ENEMY INTERACTIONS

The population dynamic processes in aphids and mites are very similar, because the two groups show strong similarities in their biology. Res ource limitation, density-dependent emigration and natural enemies are major factors controlling aphid and mite populations, but an assessme nt of their relative importance has proven difficult. We used a physio logically based simulation model to investigate the relative impact of the three factors on aphid pest populations. The present simulation m odel includes winter wheat, three aphid species, Metopolophium dirhodu m (Wlk.), Rhopalosiphum padi (L.) and Sitobion avenae (F.) (Hom.: Aphi didae) and three parasitoids, Aphelinus abdominalis Dalman (Hym.: Aphe liniidae), Aphidius rhopalosiphi De Stefani-Perez and Praon volucre (H al.) (Hym.: Aphidiidae). We derived and parameterized the model from l iterature data and validated it against independent field data. The st udy showed that resource limitation and density-dependent alate produc tion restricts aphid numbers in the field. The mortality due to parasi toids increased late in the season and reduced the peak aphid numbers only moderately. The modelling approach we used is appropriate for sim ulating other pest-natural enemy systems, such as the spider mite-pred atory mite system. Using an object-oriented modelling framework as a t emplate, acarologists can now efficiently develop the simulation model of their choice.