SUBLETHAL EFFECTS OF DELTAMETHRIN RESIDUES ON THE WITHIN-CROP BEHAVIOR AND DISTRIBUTION OF COCCINELLA-SEPTEMPUNCTATA

The behaviour and distribution of adult Coccinella septempunctata L. ( Coleoptera: Coccinellidae) were recorded in two plots of winter wheat infested with the cereal aphids Sitobion avenae (E) and Metopolophium dirhodum (Walk.) (Homoptera: Aphididae). One plot was sprayed with the pyrethroid insecticide deltamethrin at a rate of 6.25 g a.i./ha and t he other was left unsprayed. Single ladybird beetles were released seq uentially on the ground at the centre of the sprayed and unsprayed plo ts and their behaviour and position in the crop canopy were recorded a t 30 second intervals for a total of 15 min per beetle. Assessments, w ith fresh beetles, continued for four days after spray application wit h a total of eighty ladybird beetles observed. The 15 min period was s elected to avoid lethal effects and no ladybird beetles were killed or knocked down as a result of exposure to deltamethrin residues during this period. Significant differences were found between the overall be haviour patterns of C. septempunctata in the untreated and deltamethri n treated plots up to three days after the spray application. Ladybird beetles exposed to deltamethrin residues were observed to walk and gr oom significantly more frequently and to rest significantly less frequ ently than those in the unsprayed plot. Significant differences were a lso found between the observed distribution of ladybird beetles in the sprayed and unsprayed crop canopies, with higher numbers of observati ons towards the bottom of the crop canopy and on the ground in the del tamethrin treated plot than in the untreated plot during the first two days after deltamethrin application. Upon the foliage itself, ladybir d beetles were observed significantly more frequently on the abaxial l eaf surface in the deltamethrin treated crop compared with the untreat ed crop. The results are discussed in terms of possible evidence for t he repellency of deltamethrin to C. septempunctata and also the implic ations for integrated pest management of changes in predator behaviour and crop distribution resulting from sub-lethal uptake of insecticide s.