Assessment of the relative impact of different natural enemies on population dynamics of the grain aphid Sitobion avenae in the field

1. A detailed population dynamics model was devised to provide a tool for i ntegrated pest management against the cereal aphid Sitobion avenae on winte r wheat. 2. This model allowed investigation of the relative impact of different nat ural enemies on aphid population dynamics. 3. The output of the model was compared with a set of data collected in the western part of France from 1976 to 1986. 4. Fungal diseases accounted for 75% of the reduction in peak aphid density and were the key factor acting on aphid dynamics in this region. 5. This study highlights the importance of detailed population dynamics mod elling of keystone species, like aphids, for elucidation of the relations b etween the keystone species and other species associated in the ecosystem.