Potential for grain sorghum as a trap and nursery crop for Helicoverpa zea and its natural enemies and dissemination of HearNPV into cotton

Authors: CALVIN, WILFRID - University Of Arizona; GORE, JEFFREY - Mississippi State University; GREENE, JEREMY - Clemson University; Perkin, Lindsey; KERNS, DAVID - Texas A&M University

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/11/2024
Publication Date: 8/13/2024
Citation: Calvin, W., Gore, J., Greene, J., Perkin, L.C., Kerns, D.L. 2024. Potential for grain sorghum as a trap and nursery crop for Helicoverpa zea and its natural enemies and dissemination of HearNPV into cotton. Agronomy Journal. 14(8). Article 1779. https://doi.org/10.3390/agronomy14081779.
DOI: https://doi.org/10.3390/agronomy14081779

Interpretive Summary: Genetically engineered plants that produce multiple insecticidal toxins are primarily used to manage caterpillar pests in cotton, but the bollworm, Helicoverpa zea, has already developed resistance to some of the toxins. Thus, alternative strategies are critically needed to manage this insect pest in cotton or to at least delay the development of resistance to the toxins. We examined the effectiveness of using HearNPV treatments, a viral pesticide developed for caterpillar pests, in combination with interplanting sorghum in cotton fields to serve both as a trap crop for bollworms and as a nursery crop for beneficial arthropod populations. Based on the results of our two-year study, sorghum interplanted with cotton and applications of HearNPV did not consistently increase beneficial arthropod densities or reduce bollworm densities and feeding damage in cotton. However, based on molecular analyses, we did detect HearNVP in several groups of beneficial arthropods such as ants, ladybugs, lacewings, and spiders, suggesting that these arthropods may play a key role in maintaining and spreading this viral pesticide throughout fields.

Technical Abstract: Experiments were conducted in 2020 and 2021 in College Station, TX; Stoneville, MS; and Blackville, SC, to evaluate the potential of grain sorghum to serve as a trap crop for H. zea, a nursery crop for natural enemies of H. zea, and source of HearNPV for H. zea management in cotton. The experiments consisted of 3 treatments, including cotton-only, non-treated cotton-sorghum, and HearNPV-treated cotton-sorghum. Variables, including percentage of damaged fruiting forms, parasitized H. zea larvae, egg density, H. zea larval density, beneficial arthropod numbers, and HearNPV prevalence, were compared between treatments. Growing cotton in an intercropping system with grain sorghum did not result in a consistent increase in H. zea control and beneficial arthropod density relative to the cotton-only treatment. Additionally, our results did not show sufficient evidence that grain sorghum interplanted with cotton can serve as a source of HearNPV that can favor H. zea control in cotton. However, we found that, if maintained in the cotton canopy, HearNPV may favor some level of H. zea suppression in cotton. Based on our PCR analyses, insects in the families Chrysopidae, Coccinellidae, Pentatomidae, Reduviidae, Formicidae, Anthocoridae, and spiders appeared to be carrying HearNPV. The virus was detected consistently in specimens of coccinellids, pentatomids, and reduviids across both years of the study. We suggest that further investigation on virus efficacy against H. zea in cotton using the sorghum-cotton system as well as the ability of grain sorghum to serve as a H. zea trap crop and source of H. zea natural enemies be considered in future studies.