Evaluation of reverse migration and morphological adaptations of Helicoverpa zea across North America using stable hydrogen isotope analysis

Insect migration is a key driver of population dynamics and gene flow. However, the full extent and ecological implications of reverse (southward) migration in major agricultural pests remain poorly understood. This study evaluated the patterns, routes, and morphological adaptations associated with the bidirectional migration of Helicoverpa zea (corn earworm) across North America, using stable hydrogen isotope analysis of 421 moths collected from Canada, the United States, and the Caribbean between 2017 and 2024. Hydrogen isotope ratios (δ²H) of moth wings were analyzed to infer natal origins, revealing strong evidence for both northward spring/summer migration from southern overwintering sites and reverse southward migration in late summer and fall. Northward migrants accounted for up to 100% of individuals in northern regions, while reverse migrants were detected in Florida, Texas, and Arizona, with distinct isotopic signatures indicating long-distance return journeys. Morphological analysis revealed that migratory individuals had significantly larger wing areas than local moths, with the largest wings observed in northward migrants, supporting the hypothesis that enhanced flight morphology facilitates long-distance movement. These bidirectional movements promote extensive gene flow and the persistence of resistance alleles, complicating localized pest management strategies. The integration of isotopic and morphological data provides robust evidence for the ecological and evolutionary significance of reverse migration in H. zea, highlighting the need for continent-wide approaches to insect resistance management. This study advances the understanding of migratory connectivity in pest insects and underscores the importance of considering both directions of movement in ecological research and agricultural policy.