T. TUSKA, J. KISS
Szent István University, Department of Plant Protection, H-2100 Gödöllö, Hungary
C.R. EDWARDS
Purdue University, Department of Entomology, 1158 Smith Hall, West Lafayette, IN 47907-1158, USA
Z. SZABÓ, I. ONDRUSZ, P. MISKUCZA, A. GARAI
State Stud-Estate Corporation, Mezõhegyes, H-5820 Hungary

Economic larval damage caused by western corn rootworm (WCR) to corn root systems has been reported from Europe. However, little is known about silk feeding damage caused by WCR adults and its impact on production of corn hybrids and commercial corn in Europe. Silk feeding by WCR adults on inbred lines was tested and economic thresholds developed in the USA by Culy, Edwards, and Cornelius, 1992. The build-up of the WCR population in Europe requires that tests be conducted to determine the potential effect of WCR adult silk clipping on hybrid and commercial corn production.

The study was conducted on two inbred corn lines (one early and one late) and on one commercial corn hybrid under field production conditions in Mez?hegyes, Hungary, in 2001. Seed corn plots were established with male and female plants arranged in a 1:2 and 2:4 planting configuration for early and late lines, respectively. Four densities of WCR adults (0, 3, 6, and 9 per ear) were placed into individual, cylindrical nylon bridal veil ear cages (40 by 25 cm, with 1 mm openings) at the plant growth stage R1. WCR beetles were randomly collected from a nearby cornfield 2-3 days prior to beginning the study. Two control treatments (0 beetles), one with ear cages and one without were included in the study to assess the impact of the bridal veil ear cages on pollination. Each treatment (beetle density) for each inbred line or commercial hybrid was replicated 16 times.

Presence of WCR adults was observed and silk length was measured daily at the same hour until silks dried. The WCR population density over the field was determined by counting beetles on 4x25 corn plants and on 12 Pherocon AM traps. Cages were removed after pollination and the ears were allowed to mature. Ears were harvested, dried, and stored for further testing.

Data on silk length, cob length, kernel number, thousand-kernel weight (inbred lines and commercial corn), and kernel fraction (inbred lines) will be correlated with beetle densities.

First-year preliminary results indicate that the economic threshold for WCR adults is between 3-6 adults/ear for inbred lines and above 9 adults/ear for commercial corn. (The authors thank Dr. Mike Culy, Dow AgroSciences, Indianapolis, IN, USA, for information supporting this study.)