TILLER COUNTING OR TOTAL PLOT HARVEST - HOW EXACT ARE PREDATOR COUNTSIN WINTER-WHEAT

Methodical investigations on predator recording in winter wheat were p erformed at 3 sites in Middle Germany (Flaeming, Magdeburger Boerde, M iddle German dry region near Halle/S.) in 1994 to 1996. In 13 field st udies tiller counts (5 x 6 m drill row with corresponding soil surface ) were compared with the total plot harvest (an ''absolute method'', c ombination of D-VAC suction sampling and vegetation harvest within a 1 m(2)-cage, laboratory determination of arthropods). The U-test analys is of each survey according to MANN and WHITNEY shows only 8 significa nt differences in 55 comparisons. There were no clear trends. Consider ing the average predator densities in 13 investigations, the following relative densities (and significances using t-test) were calculated f or field counts in comparison with the total plot harvest: coccinellid adults - 0.88 (P>0.10), coccinellid larvae - 0.88 (P>0.10), syrphid l arvae - 0.92 (P>0.10), chrysopid larvae - 0.84 (P>0.10), adult carabid s - 0.24 (P=0.054), adult staphylinids - 0.14 (P=0.002) and adult spid ers - 0.48 (P=0.058). The important underestimation of polyphagous pre datory arthropods in field counts is discussed.