Relative importance of predators and parasitoids for cereal aphid control.
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.
Schmidt
Martin H
MH
Department of Agroecology, Georg-August University, Waldweg 26, D-37073 Göttingen, Germany. m.schmidt@uaoe.gwdg.de
Lauer
Andreas
A
Purtauf
Tobias
T
Thies
Carsten
C
Schaefer
Matthias
M
Tscharntke
Teja
T
D000818:Animals; D001042:Aphids / Q000469:parasitology / Q000502:physiology*; D004463:Ecology; D002523:Edible Grain / Q000502:physiology; D020387:Food Chain; D011156:Population Density; D011157:Population Dynamics; D014863:Wasps / Q000502:physiology