The effect of dimethoate and cypermethrin on soil-dwelling beetles under semi-field conditions

The effect of cypermethrin and dimethoate exposure on soil-dwelling beetles, in spring barley at different growth stages, of doses of up to eight times maximum field application rate has been investigated. Doses up to eight times maximum field application rate of cypermethrin did not have any acute effects on larger beetles, such as P. melanarius and C. erratus. Small beetles (A. bilineata, A. dorsale, B. lanpros, B. obtusum) were not harmed by doses up to two times maximum field application rate. T. hypnorum was affected at maximum field rate. Dimethoate at maximum field application rate harmed all species, but in particular the smaller species. When dimethoate was applied in high foliage density fields in the summer, very severe acute effects on spring breeding beetles were found. In the autumn, when only a low crop cover existed, this very high effect was not observed. The severe effect in the summer may be explained by the mode of action of dimethoate on 'old beetles'. The observed high toxic effect of dimethoate on spring breeders in the summer is expected only to have limited effect on the population, because the spring breeders at this time of the year have finished their egg depositing in the soil.