(1st Place) Within-plant distribution of Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) eggs on soybeans

Helicoverpa zea Boddie or corn earworm is a major pest of soybean in the southeastern USA. Information on the within-plant distribution of eggs is needed to support scouting techniques and to improve insecticide targets. Two soybean varieties were selected within the same relative maturity, one with a determinate growth habit (5220R2X/S) and one with an indeterminate growth habit (AG52X9). Soybeans with a determinate growth habit finish most of their vegetative growth before flowering begins, while soybeans with an indeterminate growth habit continue vegetative growth after flowering begins. Both varieties were planted during 2022 in North Carolina. Adult moths were caged in the field and allowed to oviposit during various soybean development stages (R1-R2, R2-R3, R4-R5, R5-R6) in a 2x5 factorial design. Soybean plants were divided into upper, medium, and lower parts. The total number of eggs was counted in the upper part of the leaf, the bottom part of the leaf, newly emerged trifoliate, stems, flowers, pods, auxiliary buds, and petioles. Additionally, leaf biomass and leaf area were measured to determine their relationship with egg distribution in soybeans. Most eggs were laid in the upper part of the canopy on soybean leaves, and H. zea oviposited more eggs at the beginning of the flowering stage (R1-R2). Also, there was a positive correlation between soybean leaf area and biomass in contrast with the total number of eggs laid. These results will assist our understanding of H. zea sampling techniques, adoption of integrated pest management, and potentially improve control.