LAUSR

Abstract We studied the population structure of cotton bollworm (CBW), Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae), in Xinjiang, the largest cotton-growing region in China, using a fragment of cytochrome c oxidase subunit I (COI) gene. Alignments of all 192 COI sequences revealed 28 haplotypes including 23 in southern Xinjiang, 5 in eastern Xinjiang and 13 in northern Xinjiang. Negative and significant values of neutrality tests for the Tajima's D and Fu's FS parameters, combined with the high values of haplotype diversity (Hd), low values of nucleotide diversity (π) and a high number of low frequency haplotypes indicated a recent demographic expansion of Xinjiang CBW populations. Analysis of molecular variation (AMOVA) indicated low and non-significant genetic structure, regardless of geographical scale or crop, with most of genetic variation occurring within local CBW populations. Pairwise FST analyses also indicated low genetic differentiation. This demographic event and high gene flow could be responsible for the low genetic structure currently found. CBW populations in Xinjiang need to be considered as one panmictic unit in its management, especially for the design of refuges to delay the development of resistance by this migratory pest to transgenic Bt (Bacillus thuringiensis) cotton.