Effects of Insecticide Application to Winter Wheat and Subsequent Tillage on Groundbeetle Communities (Coleoptera: Carabidae)

Abstract

Four plots of about 5 hectares' size each were marked off in a large wheat field near Magdeburg, Germany, for a simple comparison of variants. Two plots (IP, IK) were treated with the insecticide Karate (lambda-cyhalothrin) once at growth stage BBCH 69, while the other two (CK, CP) served as untreated controls. Several surveys were performed, including pitfall trapping (n=10) to elucidate groundbeetle activity and diversity. Plots IP and CP were ploughed in autumn, whereas plots IK and CK were conservatively tilled. Pitfall trapping was again performed in the succeeding crop (sugar beets) on all four plots exactly one year after insecticide application. The plots varied significantly with respect to activity densities (sums, dominant species) within three weeks of treatment, that is, activity was higher in the controls (SAS, t-test, P<0.05). These differences vanished later on and in autumn. Surveys in the succeeding crop (sugar beets) showed no indication that ploughing might be an additional stress factor in the treated plots, because the number of Groundbeetles trapped in the treated and ploughed plot (IP) was the same as in the untreated and unploughed plot (CK). Most beetles were found in the untreated and ploughed plot (CP), which differed significantly from IP and CK. The results did not indicate any sustained or synergistic effects of insecticide treatment or tillage. They are discussed relative to species and other study findings.