Model evaluation of the function of prey in non-crop habitats for biological control by ladybeetles in agricultural landscapes

The availability of alternative prey is considered to be an important factor for the conservation of predators in agro-ecosystems. However, only a limited number of studies have investigated the effect of prey availability in non-crop habitats on predator impact. We studied the potential of the generalist predator Coccinella septempunctata to control pest aphids in wheat fields in landscapes with varying levels of prey in non-crop habitats using a spatially explicit simulation model. Simulations indicate that C. septempunctata reproduction and the associated control of pest aphids is affected by both the availability of non-pest aphids in non-crop habitats and the infestation date of pest aphids in wheat fields. When the infestation of wheat by pest aphids takes place early in the season, prey availability of pest aphids alone is sufficient to allow C. septempunctata to attain its maximal reproduction. However, when the infestation by pest aphids is somewhat delayed, C. septempunctata becomes increasingly dependent on aphids in non-crop habitats. Scarcity of prey may prevent C. septempunctata from reproducing or initiate long distance migration. Therefore, prey availability in non-crop habitats may play a significant part in the conservation of ladybeetles and the related biological control in agro-ecosystems. (C) 2003 Elsevier B.V. All rights reserved.