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The majority of field corn, Zea maysL., in the southeastern United States has been genetically engineered to express insecticidal toxins produced by the soil bacterium, Bacillus thuringiensis(Bt). Field corn is the most important mid-season host for corn earworm, Helicoverpa zea(Boddie) (Lepidoptera: Noctuidae), which has developed resistance to all Cry toxins in Bt corn. From 2020 to 2023, corn earworm pupae were collected from early- and late-planted pyramided hybrids expressing Bt toxins and non-Bt near-isolines in North and South Carolina (16 trials). A total of 5,856 pupae were collected across all trials, with 55 and 88% more pupae collected in later-planted trials relative to early plantings in North and South Carolina, respectively. Only 20 pupae were collected from hybrids expressing Cry1F + Cry1Ab + Vip3A20 across all trials. Averaged across trials, Cry1A.105 + Cry2Ab2 hybrids reduced pupal weight by 6 and 9% in North and South Carolina, respectively, relative to the non-Bt near-isoline. Cry1F + Cry1Ab hybrids reduced pupal weight on average by 3 and 8% in North and South Carolina, respectively, relative to the non-Bt near-isoline. The impact of the Bt toxins on pupal weight varied among trials. When combined with data from 2014 to 2019 from previous studies, a significant decline in the percent reduction in pupal weight over time was found in both states and hybrid families. This study demonstrates a continued decline in the sublethal impacts of Bt toxins on corn earworm, emphasizing the importance of insect resistance management practices.

The corn earworm, Helicoverpa zea(Boddie) (Lepidoptera: Noctuidae), is a cosmopolitan pest in the field crop landscape in the southeastern United States. Field corn (Zea maysL.) is the most important midseason host for H. zeawhere intensive selection pressure occurs for resistance to insecticidal toxins from Bacillus thuringiensis(Bt). Because spatial patterns of H. zeain field corn have not been extensively studied, field corn was sampled for H. zealarvae and injury in 2021 and 2022. Patterns of spatial aggregation were identified in a number of fields in both larval populations and injury. Aggregation of H. zealarvae was less common at R5 than at R2. Associations between the spatial patterns of H. zeaand the variability in crop phenology were identified in some fields, with positive associations between plant height and H. zealarvae, indicating that ovipositing H. zeamoths avoid areas with reduced plant height and delayed reproductive maturity. Additionally, negative spatial associations between stink bug ear injury and H. zealarvae and their injury were found in a small number of cases, indicating some spatial interactions between the two pest complexes and their injury. Results from these studies provide valuable insight into the spatial patterns of H. zeain field corn. An understanding of the local dispersal and population dynamics of H. zeacan be used to help further improve integrated pest management and insect resistance management programs for this major polyphagous pest.

A complex of stink bugs, primarily the brown stink bug, Euschistus servus(Say) (Hemiptera: Pentatomidae) , and the southern green stink bug, Nezara viridula(L.) (Hemiptera: Pentatomidae) , are the most damaging insect pests of field corn, Zea maysL., in the southeastern United States. Characterizing the spatial patterns of these highly mobile, polyphagous pests is critical for developing efficient and effective sampling plans. In 2021 and 2022, stink bugs and their injury were assessed biweekly from emergence through R2 in 20 corn fields. The spatial analysis by distance indices (SADIE) showed that aggregation patterns were identified primarily in adult populations of both E. servusand N. viridula, and in nymphal populations of both species to a lesser extent. Aggregation patterns were also identified in early vegetative injury, but not in ear injury assessed at R2. The spatial association of stink bugs and their injury varied with corn phenological stage. A lack of spatial association between stink bug populations early in the season and vegetative injury suggests a need for intensive sampling, particularly in fields with increased residue from cover crops. Results of this study illustrate the variability in spatial patterns of stink bugs in corn, which can help to improve sampling plans for decision-making in IPM programs.