Effects of pirimicarb, dimethoate and benomyl on natural enemies of cereal aphids in winter wheat

Abstract

The insecticides, pirimicarb and dimethoate are commonly applied to cereal crops in the UK and when this study was begun the fungicide benomyl was also regularly used. The effects of these chemicals on natural enemies of cereal aphids were examined in replicated plots of winter wheat.Benomyl did not affect any of the groups examined but it was applied early in the season (April/May) when most natural enemies were few or absent from the crop. Numbers of carabid beetles, staphylinid beetles and spiders, sampled using pitfall traps and a vacuum net sampler, were all reduced by dimethoate but not by pirimicarb, although these effects were only detected by pitfall traps when the small plots were surrounded by polyethylene barriers to prevent inter-plot movements. Parasitic Hymenoptera were decreased by both insecticides, partly due to direct toxicity and partly to host removal. Data on the aphid predators, Coccinellidae, Syrphidae and Chrysopidae were inconclusive because there were very few in the crop due to the scarcity of aphids.Ways in which pesticides can affect natural enemy populations other than by direct mortality and the dangers associated with routine, prophylactic pesticide applications are discussed.

Predator–Prey Relationships in a Two-Species Toxicity Test System

“…It is a broad-spectrum insecticide with pronounced effects on the arthropod fauna at the recommended dose level (Frampton, 1988;Powell et al, 1985;Vickerman and Sunderland, 1977). Dimethoate (Cheminova Argo A/S, 400 g/l EC) was dissolved in the soil inoculate and was added to the soil in an exponential range of concentrations, which is given in the description for each experiment.…”

Toxicity of Dimethoate to Some Soil Animal Species in Different Soil Types

“…It has been found to have adverse effects on terrestrial in the earthworm storage boxes and thus originates from the invertebrates, even at recommended dose levels (e.g., Vick-same field as the earthworms. erman and Sunderland, 1977;Powell et al, 1985;Frampton, 1988;Unal and Jepson, 1991), but there was only little infor-Earthworm Test mation available about the toxicity of dimethoate to soil The earthworm test was carried out mainly according to animals. It has been chosen as a reference pesticide in the the OECD earthworm test (OECD, 1984).…”

Laboruntersuchungen zum einfluss von insektiziden auf getreideschädlinge und deren antagonisten

“…A true ecological advantage of substances protective for beneficial arthropods is the reduction of insecticide-related selective pressure in agrobiocoenosis. (Powell et al, 1985;Poehling, 1987;Karg et al, 1987;Al Hussein und Wetzel, 1990;Heimbach, 1991;Al Hussein et al, 1991). Zusammenfassende Ubersichten zur okologischen Bewertung verschiedener Pflanzenschutzmittel sind auch aus Ripper (1956) von der mortalen Konsequenz einer Blattlausbekampfung zu betrachten.…”