F. TÓTH, T. TUSKA, J. KISS
Szent István University, Department of Plant Protection, H-2103 Gödöllö, Hungary

Hybrid seed corn is more sensitive to biotic and abiotic factors affecting its silk than commercial corn. Silk clipping is the main damage of Diabrotica virgifera virgifera adults in corn. Therefore, silking hybrid seed corn can be a sensitive indicator of the actual and potential predatory pressure on D. v. virgifera adults. Theridion impressum was found to be the most important spider predator of D. v. virgifera in Hungary in our earlier studies (Tóth et al. 1998, 1999, 2000).

The present study aimed to determine the ability of T. impressum to decrease the silk clipping of D. v. virgifera in hybrid seed corn.

The study was conducted in Mez?hegyes, in 2001 (see Tuska et al. this volume). 80 corn ears were isolated with ear cages and 48 corn plants with whole-plant cages. The isolated ears were infested with 0, 3, 6 or 9 D. v. virgifera adults, and were treated with 0 or 1 T. impressum adult female in the latter case (9 beetles/ear) 1-2 days prior to silking (R1). The isolated whole plants were infested with 0 or 9 beetles and were treated as above. Number of replicates was 16 in each case. Silk length was measured daily until the end of silking. Other quantitative and qualitative parameters of the ears and kernels will be measured after harvest in October.

Both the cage types and treatments had a considerable and statistically significant effect on silk length. Theridion impressum females could decrease but not terminate silk clipping. Effect on yield parameters and methodological consequences are going to be discussed in details.

This study was partly supported by OTKA F32957 and F. Tóth was a Bolyai Research Grant fellow.