Spatial changes in invertebrate predation rate in winter wheat following treatment with dimethoate.

Abstract

Experiments were conducted in 1989 and 1990 to investigate the mechanism underlying patterns of invertebrate population recovery in winter wheat following treatment with the broad-spectrum insecticide dimethoate. Predation of Drosophila pupae and artificially induced aphid populations was monitored at different distances into plots treated with dimethoate. An initial drop in predation was recorded in all positions following treatment. Predation rate then showed a period of recovery, which progressed from the edge to the centre of the treated plots. This pattern of recovery corresponded to the numerical pattern of recovery of the predatory invertebrate groups; Carabidae, Staphylinidae and Linyphiidae. The results are discussed in terms of mechanisms to explain observed patterns of recovery of invertebrate 'prey' groups such as aphids. It is concluded that the ranking of pesticides by their toxicity alone would fail to take into account ecological processes that determine the different patterns of population change following treatment.