Soybean aphid (SBA) spends nine months of the year on a common undergrowth shrub, buckthorn (R. catharica), yet its development is little studied on this host. In fall 2004, small buckthorn shrubs infested with SBA eggs were potted and left out doors during winter outdoors. In February 2005, the potted plants were placed in growth chambers set at a series of constant temperatures ranging from 12-27^oC. Degree day models for hatch, first reproduction, generation time, and first observed alates were developed and related to the development of buckthorn plants. These models were then tested at a field location near Guelph, ON in spring 2005. Growth chamber data predicted a thermal threshold of 9^oC and 55 degree days for hatch, however hatch was observed in the field after only 22 DD. This may be due to microclimate effects related to the heat retaining characteristics of the shrub and the colouration of aphid eggs (black). In both growth chamber and field studies, first observed hatch was simultaneous with buckthorn bud swell. Development of alates and the movement of SBA from buckthorn to soybean were observed under field conditions and related to predictive models.