Spatial and temporal effects of dimethoate use on populations of Carabidae and their prey in winter wheat.

Abstract

1. 1. Following pesticide use, populations often undergo two phases of numerical change: an initial rapid reduction, followed by a gradual increase - the recovery.
2. A field trial was conducted in a 40 ha field of winter wheat in southern England to investigate the mechanisms of such recovery of Carabidae and their prey, following treatment with the broad spectrum organophosphate insecticide dimethoate.
3. Carabids exhibited what has been termed 'invasion mediated recovery', with numbers increasing from the edges to the centre of the treated area.
4. Aphididae and symphypleone Collembola showed the opposite recovery patterns, with the largest post-treatment numbers occurring at distances furthest into the treated area 27-74 days after treatment.
5. Cumulative totals of carabids following treatment showed a highly significant (P<0.00l) inverse relationship with the rate of change of aphid numbers.