DNA barcoding and study of haplotypes of the chestnut gall wasp, Dryocosmus kuriphilus Yasumatsu, 1951 (Hymenoptera: Cynipidae: Cynipini), in the eastern United States

The chestnut gall wasp (CGW), Dryocosmus kuriphilus Yasumatsu, 1951 (Cynipini, Cynipoidea, Hymenoptera), is a globally invasive pest on chestnuts ( Castanea spp., Fagaceae). Since its first reported occurrence in the state of Georgia in 1974, CGW has been reported to have spread to 16 additional states in the eastern United States. Despite its wide occurrence, investigations of the invasion and colonization history of CGW have not been conducted. To address this shortcoming, we screened one mitochondrial (cytochrome c oxidase subunit 1; COI) and one nuclear gene (internal transcribed spacer 2; ITS2) to examine the genetic variation across four discrete CGW populations from four states (New Jersey, Pennsylvania, Maryland, Tennessee). We tested whether CGW in the eastern U.S. originated from one or multiple introductions followed by subsequent dispersal. Additional insights came from comparing the sequences with two CGW populations sampled from its native range in mainland China, and one population each from Taiwan and Japan. Sequences revealed that both genes exhibit the same haplotype across all sampled specimens of all locations. The COI haplotype in this study is the dominant haplotype recorded in China, while the haplotype of ITS2 has been reported in both Japan and Europe. The uniformity of genetic structure suggests that CGW invasion in the U.S. could have either single or multiple origins, or both, accompanied with the common haplotype on each occasion. Further insights into the invasion history and expansion of CGW in the U.S. will require a combination of sampling more populations and utilizing a next generation sequencing strategy.