SPATIAL CHANGES IN INVERTEBRATE PREDATION RATE IN WINTER-WHEAT FOLLOWING TREATMENT WITH DIMETHOATE

Experiments were conducted in 1989 and 1990 to investigate the mechani sm underlying patterns of invertebrate population recovery in winter w heat following treatment with the broad-spectrum insecticide dimethoat e. Predation of Drosophila pupae and artificially induced aphid popula tions was monitored at different distances into plots treated with dim ethoate. An initial drop in predation was recorded in all positions fo llowing treatment. Predation rate then showed a period of recovery, wh ich 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 Lin yphiidae. The results are discussed in terms of mechanisms to explain observed patterns of recovery of invertebrate 'prey' groups such as ap hids. It is concluded that the ranking of pesticides by their toxicity alone would fail to take into account ecological processes that deter mine the different patterns of population change following treatment.