Genetic diversity of Brazilian boll weevil populations based on morphometric characteristics and ISSR molecular markers
The boll weevil, Anthonomus grandis (Curculionidae) is the main pest of cotton culture. To establish more efficient forms of control, it is important to understand its genetic structure and the diversity of its populations. We examined the genetic diversity of various populations of boll weevils, collected from several Brazilian locations, through morphometric and molecular analyses. Flower buds were collected from cotton plantations in three municipalities in the Caatinga region and seven municipalities in the Brazilian Cerrado region. Fifty specimens from each population (municipality) were randomly selected for morphometric characterization and 15 specimens, among the 50 insects characterized morphometrically, were randomly selected for molecular characterization. In the analysis of the principal components, based on 13 morphometric characteristics, the variables that had the most impact on the first two eigenvectors of males and females were total body length and maximum prothorax width. Based on the band count obtained from the ISSR markers, and subsequent construction of the binary matrix, the averages of the number of loci, percentage of polymorphic bands and expected heterozygosity were 71, 53%, and 0.126, respectively. The genetic variation within and between populations was 42.69 and 57.30%, respectively. Using the unweighted pair group method, formation of two population groups was observed after adopting the 95% cut-off point; the clusters formed using molecular data were different from the clusters of males and females formed using morphometric data. The low genetic diversity and the weak geographical structure of the boll weevil in Brazil is apparently due to its being an exotic pest that has been recently introduced, composed of a small portion of the population of origin. The low diversity also indicates that geographically closer populations are not necessarily genetically similar.