Population genetics of the soybean aphid in North America and East Asia: test for introduction between native and introduced populations

Understanding the population genetic diversity and structure of recently introduced pest species is important for determining appropriate strategies for pest control. In recent years, the rate of introduction of new invasive insect pests between continents has continued to increase. About a decade ago, the soybean aphid, Aphis glycines Matsumura, was introduced from East Asia (EA) into North America (NA) and is now widely established in NA. To compare soybean aphid populations between the native and invasive regions, we examined 689 individuals obtained from 28 different collections in NA and EA. A total of 8 microsatellite loci were used for population genetics statistics. Genetic differentiations among NA populations were very low compared to those among EA populations. Gene diversity and mean number of alleles in NA populations averaged 0.40 and 2.70, respectively, whereas in EA they averaged 0.55 and 4.32, respectively. Structure analysis of all populations revealed two distinct structures in the invaded and in the native regions. NA populations were divided into two distinct structures consistent with their geographic distribution. Among EA populations, certain Korean populations were genetically closest to NA populations, especially those from Ohio and Delaware. An approximate Bayesian computation test also supports an introduction into NA from Korea. These suggest that Korea is most likely to be the origin of soybean aphids in North America, rather than China or Japan.