Changes in within-plant distribution of Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) on soybeans

Within-plant distribution of Helicoverpa zea (Boddie) on soybeans, Glycine max (L.) Merrill, was investigated from 1980 to 1986. The distribution of larvae upon plant parts was evaluated based on the number on each plant part and on the number adjusted for the surface area of each plant-part. Distribution of larvae changed with larval size. The proportion of larvae, based on the number per plant part, was highest on rolled leaves for small larvae, but was highest on open leaves for large larvae. Distribution of larvae adjusted for the area of plant parts was most dense on rolled leaves, flowers, and pods. Plant phenology affected larva distribution because flowers and pods were unavailable in some plant growth stages. Larvae were observed feeding on all plant parts, but larvae found on stems were predominantly moving rather than feeding