Source population determination for boll weevil re-infestation events in Texas

Authors: Cohen, Zachary; Perkin, Lindsey; FIFIELD, ADRIANE - Texas A&M University; RASZICK, TYLER - Animal And Plant Health Inspection Service (APHIS); SWORD, GREGORY - Texas A&M University; Suh, Charles

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/2/2025
Publication Date: 6/22/2025
Citation: Cohen, Z.P., Perkin, L.C., Fifield, A.L., Raszick, T.J., Sword, G.A., Suh, C.P.-C. 2025. Source population determination for boll weevil re-infestation events in Texas. Insect Molecular Biology. Article toaf139. https://doi.org/10.1093/jee/toaf139.
DOI: https://doi.org/10.1093/jee/toaf139

Interpretive Summary: The boll weevil has been eradicated from all cotton-growing areas of the U.S., except along the Texas/Mexico border. These remaining populations continue to pose a threat to previously eradicated areas. In 2018 boll weevils were captured throughout the latter half of the growing season in Kingsville, TX, an area that had been free of boll weevils for several years prior to 2018. We obtained boll weevils from that re-infestation and conducted genomic analyses to determine their likely geographical origin and if the re-infestation involved continuous movement of weevils over time or movement of a few weevils followed by reproduction in local fields. Our findings indicate the weevils originated from the Lower Rio Grande Valley production area of Texas, and likely inolved movement of a few weevils into the area followed by reproduction in fields. The analytical methods and information generated from this study will allow eradication programs to make informed regulatory and management decisions to minimize the potential occurences and effects of future re-infestations.

Technical Abstract: The boll weevil, Anthonomus grandis grandis Boheman, is an infamous pest of commercial cotton in the Americas, but it has been successfully eradicated throughout most of the United States. However, endemic populations in the Lower Rio Grande Valley (LRGV) along the Texas-Mexico border persist and continue to threaten U.S. cotton production. When a boll weevil is captured in an eradicated zone, it is not sufficient to just diagnose the threat. Management personnel aim to determine the geographic origin of captured weevils to identify and reduce the risk of similar reintroductions. Here, we determined the likely geographic origin for a 2018 boll weevil outbreak in a previously eradicated region near Kingsville, TX, using independent methods for determining population structure and sample relatedness. We also compared the outbreak population to similar outbreaks in other eradicated areas in previous years as well as individuals throughout the LRGV. Finally, we assessed the reliability of our fine-scale relatedness metrics by empirically validating the method using established genetic lines and crosses of the model insect Tribolium castaneum Herbst. We conclude that the 2018 boll weevil outbreak in Texas likely originated from an independent introduction of individuals from the LRGV. Additionally, fine-scale relatedness patterns among these individuals indicate they were as closely related as first to second degree relatives, e.g. parent-offspring, sibling-sibling, or half siblings. Together, these methods and results illustrate the utility of whole genome sequencing, demographic reconstruction, and pairwise relatedness for non-model insects to enable precise agricultural management and conclusive source estimation.