The effect of spatial scale of treatment with dimethoate on invertebrate population recovery in winter wheat.
The influence of plot size in assessing the impact of pesticide treatment on invertebrate populations in cereal fields was investigated in winter wheat in southern England in which dimethoate (an insecticide used against aphids) had been applied. Recovery was shown to depend on the size of the plot treated. Two contrasting patterns of recovery were identified: (A) recovery progressing from the edge to the centre of treated areas; (B) recovery most rapid in the centre of the large treated areas. Type A recovery was associated with the predatory arthropods Carabidae, Staphylinidae and Linyphiidae, and was consistent with that expected from reinvasion from the surrounding untreated areas. Type B recovery was associated with the prey groups Aphididae and Collembola; recovery seemed to be most rapid in areas with the fewest predators. The results suggest that small-scale within-field pesticide evaluations would in many instances fail to predict the impact of treatment on a commercial scale.