Methodical investigations on predator recording in winter wheat were performed at 3 sites in Middle Germany (Flaeming, Magdeburger Boerde, Middle German dry region near Halle/S.) in 1994 to 1996. In 13 field studies tiller counts (5× 6 m drill row with corresponding soil surface) were compared with the total plot harvest (an „absolute method”, combination of D-VAC suction sampling and vegetation harvest within a 1 m2-cage, laboratory determination of arthropods).
The U-test analysis of each survey according toMann andWhitney shows only 8 significant differences in 55 comparisons. There were no clear trends. Considering the average predator densities in 13 investigations, the following relative densities (and significances using t-test) were calculated for field counts in comparison with the total plot harvest: coccinellid adults −0.88 (P>0.10), coccinellid larvae −0.88 (P>0.10), syrphid larvae −0.92 (P>0.10), chrysopid larvae −0.84 (P>0.10), adult carabids −0.24 (P=0.054), adult staphylinids −0.14 (P=0.002) and adult spiders −0.48 (P=0.058). The important underestimation of polyphagous predatory arthropods in field counts is discussed.