Some effects of dimethoate on arthropods in winter wheat.
The application of dimethoate to winter wheat to control cereal aphids caused changes in the numbers of the non-target arthropod fauna. The total number of non-target arthropods in the treated area was 15% of that in the untreated area 7 days after treatment and 40% after 2 weeks. There were still differences in both the equitability of phytophagous species and the diversity of predatory species two months after treatment. Adults and the immature stages of many arthropod predators were reduced; for example, Araneae were reduced by 90% 7 days after treatment and predatory Carabidae by 76% during the 6-week-period after treatment. Many dead adult and larval Coccinellidae and Syrphidae were found in the field after treatment. Chrysopa carnea (Chrysopidae) appeared to be the most resistant `aphid specific' species. The widespread use of insecticides, such as dimethoate, on cereal crops could possibly exacerbate pest problems, not only in cereals but also in other crops.