Acalypha ostryifolia: a natural refuge for Chloridea virescens and Helicoverpa zea (Lepidoptera: Noctuidae) in the Southern United States

Authors: Allen, Clint; Elkins, Blake; Little, Nathan

Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/6/2023
Publication Date: 11/16/2023
Citation: Allen, K.C., Elkins, B.H., Little, N. 2023. calypha ostryifolia: a natural refuge for Chloridea virescens and Helicoverpa zea (Lepidoptera: Noctuidae) in the Southern United States. Annals of the Entomological Society of America. https://doi.org/10.1093/aesa/saad034.
DOI: https://doi.org/10.1093/aesa/saad034

Interpretive Summary: The tobacco budworm and corn earworm have had a intertwined relationship with regards to their importance as pests in agricultural production systems in the Southern U.S. Previous studies have examined the impacts of early-season wild host plants on local populations and numbers of these two insects on cultivated crops such as cotton and soybean. Additional studies have examined the importance of wild host plants which act as a refuge of these insects from insecticides. In the current study, we examined the importance of hophornbeam copperleaf as a host plant for mid-late season populations of tobacco budworm and corn earworm. Patches of hophornbeam copperleaf were sampled along roadsides and the edges of fields from 2014-2020 in the MS Delta to examine population density, species composition, and parasitism of these two insect pests on this wild host plant. Insects were collected from hophornbeam copperleaf from the end of June through October during some years. The largest densities (based on the number of caterpillars per sweep) of were over one caterpillar per sweep. Overall, 49.5% of the collected caterpillars were determined to be tobacco budworm. Parasitism rates increased throughout the season. Overall densities of caterpillars encountered on hophornbeam copperleaf were greater than densities reported for most other wild host plants. Hophornbeam copperleaf appears to be an important natural refuge for both insect populations from plants with insecticidal toxins or synthetic insecticide applications.

Technical Abstract: The tobacco budworm, Chloridea virescens (F.), and corn earworm, Helicoverpa zea (Boddie) (heliothines) have had a long-intertwined relationship with regard to their importance as pests in agricultural production systems. Previous studies have examined the impacts of early-season wild host plants on local population density and distribution of these two insects on cultivated crops such as cotton, Gossypium hirsutum L., and soybean, Glycine max L. Additional studies have examined the importance of wild host plants, which act as a refuge of non-exposed populations of C. virescens and H. zea to insecticidal toxins from the soil bacterium, Bacillus thuringiensis Berliner, (Bt) or synthetic insecticide applications. The current study examined hophornbeam copperleaf, Acalypha ostryifolia Riddell, as a host plant for mid-late season populations of C. virescens and H. zea. Patches of A. ostryifolia were sampled along roadsides and the edges of fields from 2014-2020 in the MS Delta to examine larval density, species composition, and parasitism of heliothines on this wild host plant. Insects were collected from A. ostryifolia from the end of June through October for some years. The largest densities (based on the number of caterpillars per sweep) of heliothines were over one larva per sweep. Overall, 49.5% of the collected caterpillars were determined to be tobacco budworms. Parasitism rates ranged from approximately 1 to 30 percent, but generally increased throughout the season. Overall, densities of heliothines encountered on A. ostryifolia were greater than densities reported for other wild host plants. Hophornbeam copperleaf appears to be an important natural refuge for both heliothines from Bt toxins and synthetic insecticide applications.