Genome-wide markers reveal temporal instability of local population genetic structure in the cotton fleahopper, Pseudatomoscellis seriatus (Hemiptera: Miridae)

Authors: RASZICK, TYLER - Texas A&M University; Suh, Charles; DICKENS, C - Texas A&M University; SWORD, GREGORY - Texas A&M University

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/15/2019
Publication Date: 8/15/2019
Citation: Raszick, T.J., Suh, C.P., Dickens, C.M., Sword, G.A. 2019. Genome-wide markers reveal temporal instability of local population genetic structure in the cotton fleahopper, Pseudatomoscellis seriatus (Hemiptera: Miridae). Pest Management Science. 76:324-332. https://doi.org/10.1002/ps.5518.
DOI: https://doi.org/10.1002/ps.5518

Interpretive Summary: A major pesticide development company recently developed a new genetically-modified line of cotton that produces a Bt toxin intended for Lygus plant bugs, but the toxin also has shown activity against the cotton fleahopper. As the case for other insect pests on Bt crops, development of resistance to the toxin is a major concern. Consequently, before this new Bt cotton can be released commercially, refuge requirements and other Insect Resistance Management (IRM) strategies to prevent or at least delay the development of cotton fleahopper resistance to the new toxin will have to be established as mandated by EPA regulations. Working in cooperation with the company, we examined the genetic population structure and numbers of cotton fleahoppers produced in cotton fields and nearby weed hosts. We found that patches of wild weed hosts produced enough cotton fleahoppers to mate with potentially resistant cotton fleahoppers throughout the growing season. Our genomic data also revealed a high level of intermixing among cotton fleahopper populations in cotton and wild weed hosts, particularly at the end of the growing season when woolly croton, a preferred weed host of cotton fleahoppers, becomes available in late summer. Based on the abundant numbers of cotton fleahoppers found in nearby weed hosts and the high level of intermixing among cotton fleahopper populations in weed hosts and cotton fields throughout the growing season, our findings suggest the planting of non-Bt cotton plants (refuge) in the proximity of the new Bt cotton is not necessary; instead, nearby wild weed hosts could serve as a natural refuge for the new Bt cotton.

Technical Abstract: BACKGROUND: The cotton fleahopper, Pseudatomoscelis seriatus (Reuter) (Hemiptera: Miridae), is a pest of upland cotton, Gossypium hirsutum L. (Malvales: Malvaceae), that attacks pre-floral buds (squares), leading to abscission and yield losses. In the Brazos Valley cotton production area of Texas (USA), P. seriatus exhibits a seasonal pattern of host use. In spring, eggs hatch from the overwintering host, woolly croton, Croton capitatus Michx. (Malpighiales: Euphorbiaceae). During the growing season, individuals feed on a variety of host plants, including cotton. Adults return to woolly croton at season end to oviposit. We investigated if genetic differentiation occurs between populations infesting cotton and those infesting alternative hosts, and whether woolly croton serves as a year-end site of admixture that could be suitable as a natural refuge for the purposes of insect resistance management. We combined high-throughput DNA sequencing with fine-scale spatio-temporal sampling to test (1) whether a population genomic approach would recover patterns of genetic variation consistent with earlier studies,and (2) if local genetic population structure was robust to seasonal changes in local habitat over time. RESULTS: We found high gene flow among populations of P. seriatus collected from different host plants in the Brazos Valley. We identified mid-season turnover of local genotypes in cotton and alternative host plants that carried into the following season, indicating that population genetic structure may be labile to time. CONCLUSION: We support the status of woolly croton as a natural refuge that promotes year-end gene flow between genotypes infesting cotton and those infesting alternative hosts.