Seasonal dispersal and population genetics of soybean aphid (Aphis glycines) occurring in Wisconsin

Soybean aphids depend on long distance, wind-aided dispersal to complete their life cycle. Despite our general understanding of soybean aphid biology, little is explicitly known about dispersal of soybean aphids between winter and summer hosts in North America. A greater understanding of soybean aphid dispersal has become especially important in light of the discovery of soybean aphid “biotypes” capable of overcoming aphid-resistant soybean varieties. This study compared genotypic diversity of soybean aphids sampled from several overwintering sites and soybean fields in Wisconsin and Ohio to test the hypothesis that these overwintering sites are potential sources of soybean colonists throughout the Midwest. In addition, basic trajectory analyses were employed to demonstrate the potential for long distance dispersal events to occur from/to these overwintering sites. Results suggest that soybean aphids from overwintering sites along the Illinois/Iowa border and northern Indiana/Ohio are potential colonists of soybean throughout the Midwest. A level of population structure was also revealed that is not associated with the locations of soybean fields in which aphids occur, but that may be related to specific overwintering environments or simply a relic of the invasion of North America. This, combined with the highly variable nature of their dispersal, presents a serious challenge to the successful management of soybean aphid, especially if Rag virulence or insecticide resistance becomes common. Next to the continued development of aphid-resistant soybean varieties, the most pressing need in soybean aphid research are studies aimed at elucidating the nature of dispersal between buckthorn and soybean in North America.