Silvana Vieira Paula-Moraes

Helicoverpa zea Boddie (corn earworm or bollworm) is a primary target of transgenic crops expressing insecticidal Cry and Vip3Aa proteins from Bacillus thuringiensis (Bt). Widespread resistance to Cry toxins has increased reliance on Vip3Aa. We evaluated Vip3Aa susceptibility in 71 field populations of H. zea collected across the southeastern USA from 2018 through 2025 using diet-overlay bioassays of F₁ progeny. Vip3Aa1 was used in 2018 and Vip3Aa39 from 2019 through 2025. Median lethal concentrations (LC₅₀) were estimated and resistance ratios calculated relative to two susceptible laboratory colonies, a field-collected susceptible and the commercially available Benzon colony. Resistance ratios depended strongly on the susceptible reference used. Three populations evaluated in 2018 had resistance ratios ≥ 10 relative to the field-collected susceptible colony, whereas all Benzon-referenced resistance ratios were 50 values showed no temporal trend from 2019 through 2025, when all populations were evaluated with Vip3Aa39. These results provide no evidence of a sustained regional decline in Vip3Aa susceptibility in this region, but they highlight the importance of stable susceptible benchmarks, protein quality control, and complementary approaches for long-term resistance monitoring.

Migration plays an important role in the ecology of insect pests, including Helicoverpa zea , a major pest of multiple crops across the U.S. The long-standing “pied piper” hypothesis proposes that H. zea populations migrate northward each summer to exploit seasonal resources but because cannot overwinter in the lethal winter conditions, populations of this pest fail to continue to be established in higher latitudes in North America. This study investigated the natal origins and migratory connectivity of H. zea moths collected across Florida between 2017 and 2024 using stable hydrogen isotope analysis of wing tissues. Through this approach, we traced the origins of 249 individuals, revealing that most late-season moths originated locally or from southern U.S. regions. However, a distinct subset exhibited isotopic signatures indicative of long-distance migration from northern areas, including the upper Midwest and Corn Belt. Estimated flight distances for these northern migrants ranged from 1,375 to 1,725 km, with dispersal patterns showing a predominant northwest-to-southeast orientation. These findings provide evidence that H. zea populations engage in bidirectional migration. This H. zea reverse migration has critical implications for integrated pest management (IPM) and insect resistance management (IRM) to insecticides and Bt traits, considering the risk of gene flow of populations under continuous selection for resistance in both Cotton and Corn Belts.

BACKGROUND: The recent evidence of ‘northward/southward’ migratory behavior of Spodoptera frugiperda in North America underscores the crucial need for comprehensive area‐wide insecticide susceptibility data to effectively manage this pest. This study investigated the susceptibility of 24 field populations of S. frugiperda from corn, sorghum and grasses/rice across seven southern U.S. states to four common insecticides: λ‐cyhalothrin, diflubenzuron, methoxyfenozide and chlorantraniliprole. RESULTS: Relative to a laboratory‐reared susceptible strain, 82.6% and 60.9% of the field populations demonstrated a resistance ratio (RR) of >10‐fold to λ‐cyhalothrin (≤2289‐fold) and diflubenzuron (≤674.9‐fold), respectively. Additionally, 10 (or 41.7%) populations had >10‐fold (≤67.6‐fold) resistance to chlorantraniliprole. Resistance to methoxyfenozide was less common with four (or 16.7%) populations having a RR of >10 (≤24.0‐fold). No correlations were observed in the insect susceptibility among the four insecticides. Significant variations in mean susceptibility were found between geographical locations for λ‐cyhalothrin and between sampling years for methoxyfenozide. CONCLUSIONS: Spodoptera frugiperda populations in the southern U.S. have evolved extensive and pronounced resistance to λ‐cyhalothrin and diflubenzuron. Low‐to‐moderate levels of resistance to chlorantraniliprole are common, whereas resistance to methoxyfenozide is still relatively low. The documented insecticide susceptibility/resistance status in the southern U.S. provides helpful insights into the expected continued selection pressure for resistance on a regional scale, and thus resistance management programs can be improved based on the updated information generated from the present study. © 2025 Society of Chemical Industry.

Beet armyworm, Spodoptera exigua Hübner, is a sporadic pest of cotton (Gossypium hirsutum L.) that was once widespread in the crop across much of the US Cotton Belt. During 2021, we collected beet armyworm larvae from a field in North Carolina of transgenic cotton producing the Cry1Ac + Cry2Ab2 + Vip3Aa19 insecticidal proteins with unexpected injury to the plants. In diet-based bioassays with Vip3Aa39 protein, the colony collected from cotton in North Carolina displayed 813-fold resistance to Vip3Aa compared to a field-collected colony from Florida. We then performed reciprocal crosses and bioassays, which determined that the resistance was autosomal, recessive, and monogenic. Furthermore, the resistance likely had fitness costs, supported by the loss of resistance through rearing in the laboratory, requiring re-selection to restore it. Although beet armyworm is not currently a threat to Bt cotton in the United States, our finding of Vip3Aa resistance demonstrates that this pest has the capacity to evolve resistance under field conditions. This finding highlights the potential for beet armyworm to re-emerge as a significant pest if agronomic or climatic conditions shift to favor its establishment and spread. Moreover, the emergence of resistance in this historically sporadic pest should serve as a broader warning that Bt resistance can evolve and persist in non-target or secondary pests.

Beet armyworm (BAW), Spodoptera exigua (Hübner), is a polyphagous and migratory lepidopteran pest that causes damage to a broad range of host plants, including row crops and vegetables, with increasing reports of insecticide-resistant populations. Understanding its movement ecology is essential for integrated pest management (IPM) and insect resistance management (IRM) programs. We investigated the population dynamics and migratory origins of BAW during the 2024 cropping season in two counties of the Florida Panhandle, USA. Larval sampling and adult pheromone trapping were conducted in commercial peanut fields, and hydrogen stable isotopes were used to infer the probable geographic origins of moths. Across the season, the presence of BAW accounted for 7.1% of all individuals collected, with infestation occurring only in July and August. Moth captures were significantly higher in the eastern Florida panhandle than in the western Florida Panhandle. Stable isotope analysis revealed four distinct migratory patterns, with most BAW likely originating from South Florida, the Caribbean, or the central and southern United States, indicating northward movement. Our findings provide critical insights into the movement ecology of BAW and highlight its implications for outbreak forecasting, resistance management, and regional IPM/IRM strategies in the southeastern United States.

The two-spot cotton leafhopper, Amrasca biguttula (Ishida, 1913) (Hemiptera: Cicadellidae), is a polyphagous pest native to the Indian subcontinent, where it is a significant pest of cotton (Gossypium spp.), okra (Abelmoschus esculentus, Moench), and other crops. At adult and immature stages, they feed on leaf cell contents, causing characteristic “hopperburn” symptoms and yield losses of up to 40% in cotton in its native range. In July 2025, A. biguttula was detected for the first time during the cotton growing season in commercial and experimental fields across multiple counties in Alabama, Florida, Georgia, and South Carolina. Identification was confirmed through morphological examination of diagnostic external features and male genitalia. Within four weeks, the pest was found in 101 counties, with injury symptoms ranging from mild chlorosis to severe necrosis and defoliation. Given the southeastern United States’ average of 979,339 hectares of cotton valued at USD 1.7–USD 2.8 billion annually, the potential for economic impact is considerable. Rapid symptom development, broad host range, and multiple generations per year underscore the need for coordinated monitoring and research to determine preliminary control measures and to identify potential alternative hosts. This report documents the first confirmed occurrence of A. biguttula in U.S. cotton and highlights its potential as an established recurring pest threat in the region.

Spodoptera eridania (Stoll, 1781) (Lepidoptera: Noctuidae) is an important pest with a broad host range and growing relevance due to its high dispersal capacity, recent invasions into Africa and Asia, and documented resistance to biological insecticides. Here, we assessed S. eridania flight phenology and seasonal dynamics in the Florida Panhandle, using pheromone trapping data to evaluate population trends and environmental drivers. Moths were collected year-round, showing consistent patterns across six consecutive years, including two distinct annual flight peaks: an early crop season flight around March, and a more prominent flight peak during September–October. Moth abundance followed a negative quadratic relationship with temperature, with peak activity occurring between 15 °C and 26 °C. No significant relationship was found with precipitation or wind. These results underscore the strong influence of abiotic factors, particularly temperature, on seasonal abundance patterns of this species. Our findings offer key insights by identifying predictable periods of high pest pressure and the environmental conditions that drive population increases. Understanding the flight phenology and behavior of this species provides an ultimate contribution to the development of effective IPM and insect resistance management (IRM) programs, promoting the development of forecasting tools for more effective, timely pest management interventions.

Soybean looper (SBL), Chrysodeixis includens (Walker) (Lepidoptera: Noctuidae: Plusiinae), a major pest native to the Americas, poses considerable management challenges. Sex pheromone trapping in IPM programs represents a tool to detect initial infestations and promote timely management decisions. However, commercial formulations of sex pheromone for SBL are non-specific, leading to the cross-attraction of morphologically similar plusiines, such as cabbage looper (CBL), Trichoplusia ni (Hübner), and gray looper moth (GLM), Rachiplusia ou (Guenée). Current identification methods of plusiine adults are laborious, expensive, and thus inefficient for rapid detection of pests like SBL. This study explores the use of deep learning models and visualization techniques to explain the learned features from forewing patterns as an identification tool for SBL and differentiation from morphologically similar plusiines. A total of 3,788 unique wing images were captured from specimens collected from field and laboratory populations with validated species identification. Five deep learning models were trained on lab-reared specimens with high-quality wing patterns and evaluated for model generalization using field-collected specimens for three classification tasks: classification of SBL and CBL; male and female SBL and CBL; and SBL, CBL, and GLM. Our results demonstrate that deep learning models and the visualization methods are effective tools for identifying plusiine pests, like SBL and CBL, whose wing patterns are difficult to distinguish by the naked human eye. This study introduces a novel application of existing deep learning models and techniques for quickly identifying plusiine pests, with potential uses for pest monitoring programs targeting economic plusiine pests beyond SBL.

Fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith, 1797) (Lepidoptera: Noctuidae), is a major pest in the U.S. and has spread globally, causing severe agricultural losses in different countries. Due to its high mobility and potential for long-distance dispersal, understanding FAW migration is a key tool for forecasting outbreaks and implementing timely management measures. Recent studies using stable hydrogen isotopes indicated reverse (southward) migration of Helicoverpa zea Boddie (Lepidoptera: Noctuidae). Here, we tested the reverse migration hypothesis for FAW in North America. Estimation of the hydrogen isotopic ratio on 324 samples collected in Florida, an intermixing zone at the edge of the continental U.S., indicated evidence of reverse migration in samples of FAW moths. They showed a high probability of origin from the U.S. Corn Belt, with a greater probability of origin in Nebraska, South Dakota, Minnesota, Kansas and Wisconsin. This southward movement provides new insights into the risk of spreading pesticide resistance alleles in this species to southern regions and contributes to the improvement of integrated pest management and insect resistance management programs.