Effect of planting dates and Bacillus thuringiensis corn on the populationdynamics of European corn borer (Lepidoptera : Crambidae)

Field studies were conducted to determine how field corn. Zea mays L., phen ologies in combination with transgenic Bacillus thuringiensis Berliner (Bt) corn and non-Bt (near isogenic) corn could affect egg laying by female Eur opean corn borer, Ostrinia nubilalis (Hubner), and subsequent larval injury . Transgenic Bt (events 176 and Btll) and non-Bt corn was planted at three different times to assess the use of early- and late- planted Bt corn as a means for egg recruitment to these targeted planting dates. Plant growth st ages, egg densities, and stalk tunneling was recorded at four locations in southwestern, central, and northern Iowa for three summers (1996-1998). No significant differences in egg densities were observed between Pt and non-B t corn during the first and second generation for all three years. Signific ant differences did occur among planting dates. Between 50 and 100% of the eggs were laid in the early planting during the first generation. In additi on, between 40 and 65% of the eggs were laid in the late planting for the s econd generation. Correlations between egg density and larval tunneling wer e inconsistent from year to year. Additional inconsistencies stemming from yearly phenological differences among sequential plantings and variable O. nubilalis populations increases the difficulty in recommending planting dat e adjustments as a practical management tool for European corn borer and Pt corn.