In winter in Indiana, our soybean aphids (Aphis glycines) are overwintering as eggs on its secondary host, buckthorn. Soybeans, soybean aphid and buckthorn are all non-native plants imported separately from Asia. Buckthorn was introduced as a horticultural plant that became invasive. Thus, when soybean aphid arrived in North America, both its primary and secondary hosts were present.
In late spring, aphids on buckthorn produce wing forms that colonize emerging soybeans. The timing of alate production is important for soybean aphid. The aphids must leave buckthorn before pressure from predators increases. However, leaving before soybeans sprout would result in death. In some areas, phenological timing may limit soybean populations.
In areas of Northeastern China, soybean aphid alates appear on Buckthorn around two weeks prior to appearing on soybean. Are these aphids starving? Investigations by a group of scientists* found a likely “transitional” host for soybean aphid. Metaplexis japonica is a perennial vine, a common weed and often germinates in fields before soybeans sprout. The availability of a suitable transitional host would allow the soybean aphid to successfully transition the period between leaving buckthorn and arriving on soybean.
*Wenpeng Sun · Zhifeng Hu · Lanlan Han · N. B. Sanda · Yuan Hu Xuan · Kuijun Zhao. 2015. Discovery of a transitional host of the soybean aphid, Aphis glycines (Hemiptera: Aphididae), in northeastern China. Appl. Entomol Zool. 50: 361-369.