Vertical and temporal distribution of Helicoverpa zea (Lepodoptera: Noctuidae) larvae in determinate and indeterminate soybean

Authors: REISIG, D. D. - North Carolina State University; COOK, D.J. - Mississippi State University; GREENE, J. - Clemson University; CAPRIO, M. A. - Mississippi State University; GORE, J. - Mississippi State University; MUSSER, F. - Mississippi State University; REAY-JONES, F. - Clemson University

Submitted to: Entomological Research Bulletin of
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/27/2020
Publication Date: 9/18/2020
Citation: Reisig, D., Cook, D., Greene, J., Caprio, M., Gore, J., Musser, F., Reay-Jones, F. 2020. Vertical and temporal distribution of Helicoverpa zea (Lepodoptera: Noctuidae) larvae in determinate and indeterminate soybean. Entomological Research Bulletin of. 111:282-288. https://doi.org/10.1017/S0007485320000619.
DOI: https://doi.org/10.1017/S0007485320000619

Interpretive Summary: Helicoverpa zea (Boddie) is one of the costliest and widely distributed insect pests of US soybean, Glycine max (L.) Merr., especially in the southern USA. Abundance of H. zea in soybean is influenced by different cultural practices, which can have an impact on the growth habit of soybean plants. H. zea larval populations are generally greater in open canopy between soybean rows. The vertical distribution of H. zea larvae in determinate and indeterminate varieties was evaluated, hypothesizing that larval distribution in the canopy would vary between these two growth habits and over time. This hypothesis was tested in a naturally infested replicated field experiment and two experimentally manipulated cage experiments. In the field experiment, flowering time was synchronized between the varieties by manipulating planting date, while infestation timing was manipulated in the cage experiments. Larvae were recovered using destructive sampling of individual soybean plants, and their vertical distribution by instar was recorded from three sampling points over time in each experiment. While larval population growth and development varied between the determinate and indeterminate varieties within and among experiments, we found little evidence that larvae have preference for different vertical locations in the canopy. This study lends support to the hypothesis that larval movement and location within soybean canopies do not result entirely from oviposition location and nutritional requirements.

Technical Abstract: Most oviposition by Helicoverpa zea (Boddie) occurs near the top of the canopy in soybean, Glycine max (L.) Merr, and larval abundance is influenced by the growth habit of plants. However, the vertical distribution of larvae within the canopy is not as well known. We evaluated the vertical distribution of H. zea larvae in determinate and indeterminate varieties, hypothesizing that larval distribution in the canopy would vary between these two growth habits and over time. We tested this hypothesis in a naturally infested replicated field experiment and two experimentally manipulated cage experiments. In the field experiment, flowering time was synchronized between the varieties by manipulating planting date, while infestation timing was manipulated in the cage experiments. Larvae were recovered using destructive sampling of individual soybean plants, and their vertical distribution by instar was recorded from three sampling points over time in each experiment. While larval population growth and development varied between the determinate and indeterminate varieties within and among experiments, we found little evidence that larvae have preference for different vertical locations in the canopy. This study lends support to the hypothesis that larval movement and location within soybean canopies do not result entirely from oviposition location and nutritional requirements.