AFLP, mtDNA, and microsatellite analysis of emerald ash borer population structure from Asia and North America
Emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), is a devastating invasive pest of North American ash trees (Fraxinus spp.) that was first discovered outside of its native range of Northeastern Asia in 2002 (Haack et al. 2002). With the unintended assistance from human movement of infested ash material, EAB spread swiftly from its initial discovery in the Detroit area of Michigan and Windsor, Ontario to currently include 13 states in the United States and two provinces in Canada. Understanding the population biology of an invasive species such as EAB could provide valuable information on geographic origin and location of possible effective biological control agents, estimate host range potential, and provide evidence of the main mode of spread. This study had three main goals: (1) obtain samples from throughout the native and introduced ranges of EAB, (2) characterize the genetic population structure of EAB in its native and introduced range using mitochondrial partial gene sequencing and DNA fingerprinting using amplified fragment length polymorphisms, and (3) develop and characterize microsatellite loci to further assess population dynamics and invasion history. To accomplish the first goal, a network of collaborators, including myself, was developed to obtain samples throughout the native of China, South Korea, and Japan and introduced ranges in the United States, Canada, and western Russia. This effort yielded a collection consisting of 1799 specimens from across 7 states in the United States, 114 in Ontario, Canada, 12 in Moscow, Russia, 274 specimens in China, 17 in South Korea, and 3 in Japan.
To accomplish the second goal, individual insects were characterized with partial mtDNA cytochrome oxidase subunit I sequence (481 bp) and four AFLP primer pair combinations yielding 273 loci. COI sequences detected one common haplotype found in China, South Korea and all samples in N. America, as well three unique haplotypes in China, and four from South Korea differed from the common sequence by 2-4 nucleotides. A single EAB from Japan differed by 22 nucleotide changes (3.7%). The majority of the AFLP genetic variability was within populations and not among populations. Very weak genetic structure was detected. Average pairwise Opt across all populations in N. America revealed the lowest population differentiation between Dagong and Tangshan, China (Opt = 0.0877 and 0.0848, respectively). Over 67% individual beetles from N. America were assigned either to Dagong or Tangshan, China by assignment tests. The final goal to develop and characterize microsatellite loci evaluated 41 primer pair combinations that successfully amplified in EAB, however, none of these loci yielded variation to assess within and between populations in Asia. Microsatellite loci variation of EAB is presented on a subset of samples in this study on two loci developed by a Dr. Jenny Cory (Simon Fraser University, BC, Canada). These data did not provide enough information to distinguish between single or multiple EAB introductions into N. America.