C.K. GERBER
Purdue University, Department of Entomology,
1158 Smith Hall, West Lafayette, IN 47907-1158, USA
C.R. EDWARDS
Purdue University, Department of Entomology,
1158 Smith Hall, West Lafayette, IN 47907-1158, USA
J. KISS
Szent István University, Department
of Plant Protection, H-2100 Gödöll?, Hungary
Adult western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte, sampling methods were tested in soybean fields, and larval damage was evaluated in first-year cornfields located in northwest Indiana from 1997-2000. The sampling methods included Pherocon® AM unbaited sticky traps, cucurbitacin vial traps, Pherocon® CRW (corn rootworm) non-lure traps, and a 14.5cm diameter sweep net. Calculations for the minimum sample size required for 15% and 25% level of precision was determined for each sampling method using Southwood's formula n = (s/Em)2. Corn root damage was compared with analysis of variance procedures and mean separation using Fisher's protected LSD test. Economic thresholds also were determined by regressing the number of WCR adults collected with Pherocon AM and Pherocon CRW traps in soybean during 1998 and 1999 with corn root damage in fields the proceeding years, 1999 and 2000. Damage to corn root systems was significantly higher in untreated plots than treated plots in 1997-2000. The Pherocon AM traps and Pherocon CRW traps, at the 25% precision level, required the least number of traps (4.39 and 5.32, respectively) to determine the estimated adult WCR population in soybean fields. The regression equations developed by adult collections using the Pherocon CRW traps revealed R2 values of 0.067 and 0.008 in 1998-1999 and 1999-2000, respectively. Adult collections using Pherocon AM traps during the same time period revealed R2 values of 0.579 and 0.360. An R2 value of 0.460 was determined when the Pherocon AM trap data was combined for both trapping cycles. Although a range of thresholds resulted from this experiment, the economic threshold, as estimated by a root damage rating of 3.5, has been determined as eight WCR adult beetles per Pherocon AM trap per day.