Reduced dose insecticide use in cereals : effects on insect pests and predators

Abstract

The insecticides deltamethrin, dimethoate and Studies investigated the intrinsic toxicity of pirimicarb to Rhopalosiphum padi (Walk) (Homoptera: Aphididae) in the laboratory on a simple glass substrate. The dose-response data generated was used to predict reductions of cereal aphid populations in the field using reduced dose insecticide rates. The predicted reductions were initially tested under semi-field conditions and the results showed that above a certain dose threshold the predictions fitted well for deltamethrin. When predictions were tested in the field, predicted and observed population reductions were found to correlate well for deltamethrin and aphid control using reduced rate insecticide doses was not significantly different to a full field rate application. Temperature was shown to influence the toxicity of topically applied X-cyhalothrin and dimethoate to the cereal aphids R. padi and Sitobion avenae (Homoptera: Aphididae). The toxicity of A-cyhalothrin was negatively and dimethoate positively correlated with temperature. S. avenae was more susceptible than R. padi to topical applications of both insecticides. Residual exposure to ?L-cyhalothrin and dimethoate affected their toxicity to the aphids R. padi and S. avenae at different temperatures. A negative temperature coefficient was shown for 1-cyhalothrin whilst that of dimethoate was more complicated. Altering the route of exposure affected the susceptibility of the aphids to the insecticides. Laboratory exposure of aphids to deposits of l-cyhalothrin applied in the field showed the same trends as X-cyhalothrin applied in the laboratory. sub-lethal The application of padi individuals affected measurements of their growth and development. Development time, adult weight, number of nymphs produced, mrgr and rm values of the aphids were significantly different from untreated aphids when reared at an ambient temperature of 12°C. There were no differences between measurements of aphid growth and development at ambient temperatures of 18 and 25°C. 1-cyhalothrin to R. doses of Substrate type affected the residual toxicity of laboratory applied doses of deltamethrin and dimethoate to carabid beetles (Goleoptera: Carabidae). Application of insecticide dose-rates similar to those used for aphid control were toxic on glass but relatively harmless on soil. The exposure to an insecticide by topical or residual application affected aphid consumption of carabid beetles in the laboratory. Presenting carabid beetles with insecticide contaminated aphids reduced the beetles consumption of the aphids compared to controls. When the contaminated prey were removed aphid consumption returned to that of the controls. The potential and limitations of reduced dose insecticide rates for iPM in cereals are discussed.

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