ECOLOGICALLY-BASED MANAGEMENT OF INSECT PESTS OF CORN, WITH EMPHASIS ON CORN BORERS, ROOTWORMS, AND CUTWORMS
Location: Corn Insects and Crop Genetics Research
Title: Population structure and genetic diversity of the boll weevil, Anthonomus grandis (Coleoptera: Curculionidae), on Gossypium in North America
Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 2, 2012
Publication Date: November 1, 2012
Citation: Kuester, A.P., Jones, R.W., Sappington, T.W., Kim, K., Barr, N.B., Roehrdanz, R.L., Senechal, P., Nason, J.D. 2012. Population structure and genetic diversity of the boll weevil, Anthonomus grandis (Coleoptera: Curculionidae), on Gossypium in North America. Annals of the Entomological Society of America. 105(6):902-916.
Interpretive Summary: The boll weevil, a severe insect pest of cotton, has nearly been eradicated from the U.S. It invaded the U.S. about 120 years ago from Mexico and is still a constant threat to reinvade the U.S. Reintroductions of boll weevils are detected by a monitoring system of traps so that they can be eliminated early-on before populations can build. Different races or varieties of boll weevils that prefer different host plants seem to exist in Mexico, and at least one, the Thurberia weevil, does not attack cultivated cotton. However, sampling in Mexico is difficult and relationships of different populations to one another remain cloudy. It would be useful to determine the status of these races so that genetic identification of captured weevils (which cannot be distinguished visually) will allow appropriate responses by pest management and eradication personnel. In this study, extensive sampling and genetic analyses identified two distinct races, one east and one west of Mexico's central mountain range. These are different than the three races previously hypothesized. One of the races includes the type commonly known as Thurberia. This information will be used by university and government scientists in Mexico and the U.S. to better understand the threats to cultivated cotton posed by the different races. Furthermore, the markers can be used to improve the system of boll weevil race identification.
While the boll weevil, Anthonomus grandis, has been identified as one of the most devastating pests in U.S. history, its origin and activity in Mexico, both on wild and cultivated cotton hosts (genus Gossypium), is poorly understood. Three forms (geographical or host-associated races) of A. grandis have been distinguished in the past based on morphological differences and host plants. Also, the extent to which populations on wild hosts are genetically distinct and contribute to infestations on domesticated cotton (G. hirsutum) is unclear. We sequenced one mitochondrial and four nuclear genes to evaluate the identity and evolutionary relationships among North American boll weevil forms and their distributions on wild and domesticated cotton hosts. We found that the genetic data do not support the traditional classification of boll weevils into Southeastern (from G. hirsutum in the southeastern United States and northeastern Mexico), thurberia (southern Arizona and northwestern Mexico), and Mexican (the remainder of Mexico and Central America) forms in all loci but the Intertranscribed Spacer II. Likewise, we find little support for the classification of two subspecies, Anthonomus grandis grandis and A. grandis thurberiae. Instead, two well-differentiated groups are indicated by our genetic data: an eastern group comprising the Southeastern form and the Mexican form east of the Sierra Madre Occidental, and a western group comprising the thurberia form and the Mexican form west of this mountain range. Based on these results, we recommend a new classification of the boll weevil consisting of two geographically distinct forms, each of which utilizes multiple host species.