Insecticide drift deposition on noncrop plant surfaces and its impact on two beneficial nontarget arthropods, Aphidius colemani viereck (Hymenoptera, Braconidae) and Coccinella septempunctata L. (Coleoptera, Coccinellidae)

Drift of the pyrethroid insecticide X-cyhalothrin into field margins bordering wheat and its effect on nontarget arthropods was investigated under field conditions. Insecticide deposition on leaf surfaces of broad beans exposed within field margins at 1-, 2-, and 3-m distance from the field edge and directly within the crop was quantified using a fluorescent tracer. The toxicity of leaf deposits to the aphid parasitoid Aphidius colemani Viereck (Hymenoptera: Braconidae) and to larvae of the ladybird Coccinella septempunctata L. (Coleoptera: Coccinellidae) was estimated. Mean corrected mortalities of A. colemani were < 50% (I m) and < 30% (2 and 3 m), and mortalities of C septempunctata larvae were <= 80% (1 m), <= 67% (2 m), and <= 52% (3 m) 12 and 24 h postexposure to drift deposits. High positive correlation coefficients proved the relationship between leaf deposits and mortalities of test organisms. The connection of drift deposit measurement and exposure bioassay provides a promising approach to determining effects of insecticide drift on nontarget arthropods. However, due to the patchiness of drift deposition on noncrop plant surfaces, risks to nontarget arthropods at defined distances from the sprayed crop are not highly predictable.