Potential for Grain Sorghum as a Trap and Nursery Crop for Helicoverpa zea and Its Natural Enemies and Dissemination of HearNPV into Cotton

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 Helicoverpa zea (Boddie), a nursery crop for natural enemies of H. zea, and a source of Helicoverpa armigera nucleopolyhedrovirus (HearNPV) for H. zea management in cotton. The experiments consisted of three treatments, including cotton-only, non-treated cotton–sorghum, and HearNPV-treated cotton–sorghum. Variables, including percent injury to fruiting forms, parasitized H. zea larvae, egg density, H. zea larval density, beneficial arthropod numbers, and HearNPV prevalence, were compared between the 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 HearNPV infection analyses using PCR, chrysopids, coccinellids, pentatomids, reduviids, formicids, anthocorids, 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.