ECOLOGICALLY-BASED MANAGEMENT OF INSECT PESTS OF CORN
Location: Corn Insects and Crop Genetics Research
Title: Temporal changes in genetic variation of boll weevil (Coleoptera: Curculionidae) populations, and implications for population assignment in eradication zones
Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 2, 2011
Publication Date: July 1, 2011
Citation: Choi, S., Kim, K., Lee, H., Adamczyk Jr., J.J., Greenberg, S.M., Westbrook, J.K., Sappington, T.W. 2011. Temporal changes in genetic variation of boll weevil (Coleoptera: Curculionidae) populations, and implications for population assignment in eradication zones. Annals of the Entomological Society of America. 104(4):816-825.
Interpretive Summary: Boll weevils are a serious pest of cotton in the south-central U.S. They have been eradicated from much of the Cotton Belt, but the eradication is ongoing in some areas, especially southern and eastern Texas. Because boll weevils can fly long distances, potential reinvasion of weevil-free areas is monitored closely with traps. When a boll weevil is captured unexpectedly in an eradication zone, the response of eradication personnel depends in part on where they think the weevils came from and how they arrived. By comparing variation in the DNA of captured weevils to that of weevils captured in surrounding locations, scientists can determine the most likely origin of the invaders. DNA variation can change over time at a location for a number of reasons, so periodic updating of the database for samples making up the comparative populations is important. We found that only one of the populations tested had changed significantly since it was first sampled. This means that the old and new DNA data for each of the other locations can be combined, making future population assignment tests statistically more powerful. We also added two new locations to the database. This information will be of use to eradication officials and scientists at the USDA-Animal and Plant Health Inspection Service, the Texas Department of Agriculture, and the Texas Boll Weevil Eradication Foundation as they strive to finally eliminate this pest from Texas, and to prevent reinvasions of U.S. cotton growing regions.
Genetic differentiation among 10 populations of boll weevil, Anthonomus grandis grandis, sampled in 2009, in Texas and Mexico, was determined using ten microsatellite loci. In addition, temporal changes in genetic composition were examined in the eight populations for which samples were available from previous years. Because the existing microsatellite genotype database is used in population genetic assignment analyses of boll weevils captured in eradication zones, it is important to update it in case of changes in genotype frequency at any of the locations over time. Such changes could be caused by drift, immigration, or population bottlenecks. There was little change in genetic variation over time at seven of the eight locations tested. For those seven locations, genotype and allele frequency data can be pooled over the two sample dates, lending more statistical power to future population assignment tests involving those locations. The low magnitude of change adds confidence to the future use of older data from populations for which new samples in 2009 could not be taken because of low population levels. In the case of Ojinaga, there has been a substantial change in genetic variation since 2004, and the genotype data collected in 2009 should be substituted for the older data in future analyses. Finally, two new locations, Brownsville and Lockhart, have been sampled, genotyped, and added to the database. The addition of Lockhart is particularly important given its surprisingly high isolation from all other populations in the database, including those relatively nearby, namely Cameron and Uvalde.