Vertical distribution of European corn borer (Lepidoptera: Crambidae) egg masses on sweet corn

Within-plant height (leaf position) of European corn borer, Ostrinia nubilalis (Hübner) egg masses were analyzed in four sweet corn hybrids planted across four planting dates from 1994 to 1996. From the five-leaf to 15-leaf vegetative stages, the mean leaf position of an egg mass was typically at the midpoint of available (nonsenescent) leaves. The mean leaf position of egg masses gradually increased from early to late leaf stages as new leaves were added, and continued to increase during the first reproductive stage (green tassel). The increase in vertical position during vegetative stages was modeled as y = -0.766 + 0.653(x), where y = nodal leaf position, and x = total leaves expanded (r² = 0.94). However, when the mean egg mass position was expressed as the mean position within available (expanded and nonsenescent) leaves, no relationship was found. These data indicate that during vegetative stages the mean egg mass position increases relative to ground level, but remains near the midpoint of available (nonsenescent) leaves. Mean egg position during the next four reproductive stages (anthesis, green silk, brown silk, and postharvest) stabilized at ear height, or within the immediate two leaf positions above the ear. The distributions of egg masses among leaf positions during the vegetative and reproductive stages generally exhibited normal distributions: where sample sizes were sufficient, 80% (17/21) of the comparisons (having sufficient sample sizes) did not deviate from normality. This study represents the most detailed examination to date on vertical distribution of European corn borer egg masses in corn. Implications of the study in ovipositional ecology and pest management are discussed.