Relative importance of predators and parasitoids for cereal aphid control

Martin H. Schmidt, Andreas Lauer, Tobias Purtauf, Carsten Thies, Matthias Schaefer, Teja Tscharntke

Abstract

Field experiments with manipulations of natural enemies of plant–feeding insects may show how a diverse enemy group ensures an important ecosystem function such as naturally occurring biological pest control. We studied cereal aphid populations in winter wheat under experimentally reduced densities of: (i) ground–dwelling generalist predators (mostly spiders, carabid and staphylinid beetles); (ii) flying predators (coccinellid beetles, syrphid flies, gall midges, etc.) and parasitoids (aphidiid wasps), and a combination of (i) and (ii), compared with open controls. Aphid populations were 18% higher at reduced densities of ground–dwelling predators, 70% higher when flying predators and parasitoids were removed, and 172% higher on the removal of both enemy groups. Parasitoid wasps probably had the strongest effect, as flying predators occurred only in negligible densities. The great importance of parasitism is a new finding for aphid control in cereal fields. In conclusion, a more detailed knowledge of the mechanisms of natural pest control would help to develop environmentally sound crop management with reduced pesticide applications.