Submitted to: Insect Molecular Biology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/17/2004
Publication Date: 6/1/2004
Citation: Kim, K.S., Sappington, T.W. 2004. Genetic structuring of boll weevil populations in the U.S. based on RAPD markers. Insect Molecular Biology. 13:293-303. Interpretive Summary: The boll weevil is an insect pest of cotton, which originally invaded the U.S. from Mexico a little over a century ago. Tremendous effort and resources are being invested in eradicating the weevil from the U.S., and the threat of weevils flying into eradication zones from neighboring areas that are still infested is of great concern. Very little is known about how far a weevil is likely to migrate, and it is a difficult problem to investigate. To obtain information on weevil migration patterns, we used a molecular technique called "RAPD analysis" to study variation in DNA from weevils collected across eight U.S. states and northeast Mexico. We found that migration is fairly frequent up to distances of 300-400 km, but estimates of the numbers of weevils that migrate are much lower than in a previous study which used a different technique. The current estimate is judged to be more reliable, but more studies are underway to clarify this issue. These results provide critical information that can be used by Boll Weevil Eradication personnel to develop appropriate regional and national regulatory policies for preventing reinfestation.
Technical Abstract: The boll weevil (Anthonomus grandis, Boheman) (Coleoptera: Curculionidae) is a serious pest of cotton in the United States. An understanding of boll weevil dispersal behavior is essential to characterizing and responding to the threat of migration into eradication zones. Randomly amplified polymorphic DNA (RAPD) analysis was performed to make inferences on the magnitude and pattern of genetic differentiation among boll weevil populations from 18 location across 8 U.S. states and northeast Mexico. Sixty-seven reproducible bands from six random primers were analyzed for genetic variation within and between weevil populations. Genetic and geographic distances among all populations were positively correlated, reflecting a pattern of isolation by distance within a larger metapopulation. Genetic diversity was greatest in samples from Mexico and was generally greater in southern than northern populations, consistent with the historical boll weevil range expansion into the southern U.S. from Mexico. Phylogenetic and principal component analysies revealed that genetic differentiation between eastern and western populations is pronounced, and that south-central populations occupy an intermediate position between them. Gene flow between south-central, western and eastern regions is limited, but migration between locations within regions appears to be relatively frequent up to distances of ~300-400 km. However, estimates of effective migration were much lower than those estimated from mtDNA-RFLP data reported previously.