THE TOXICITY OF APHICIDE RESIDUES TO BENEFICIAL INVERTEBRATES IN CEREAL CROPS

The toxicity of dimethoate, deltamethrin and pirimicarb residues to Bembidion lampros and Coccinella septempunctata was evaluated by confining groups of insects to winter wheat foliage and soil for 24 h at different times after treatment in the field. Flag leaf residues were found to be more toxic than first leaf residues: soil residues were the least toxic with pirimicarb showing virtually no soil toxicity. In general, dimethoate and deltamethrin showed similar levels of foliar toxicity with flag leaf toxicity on the first day after treatment being in the range 60-80% for B. lampros; deltamethrin was however, less toxic than dimethoate at ground level. Both of these products were more toxic than pirimicarb. The long-term exposure of insects, surviving the 24 h bioassays, to treated soil at different times following application resulted in further mortality and provided estimates of the maximum levels of mortality that populations of predators might suffer migrating into the crop at different times following application. Dimethoate was shown to be particularly harmful at the current recommended field application rate and reduced doses were proposed to limit the severity of the initial effects.