The two hop cultivars “Hallertauer Magnum” (HM) and “Spalter Select” (SE) are regarded by growers as extremely different in their susceptibility to the damson-hop aphid Phorodon humuli (Schrank). To investigate these anecdotal observations, spring migration and initial population development of P. humuli were monitored on the two cultivars in 1998 and 1999 in an experimental hop garden. Numbers of migrant aphids on SE were significantly lower, comprising 18.8 and 30.2% as compared to HM in 1998 and 1999, respectively. Population development of apterous aphids on these two cultivars differed significantly. At the end of the monitoring period numbers of aphids on SE were 7.5 and 14.2% as compared to HM in 1998 and 1999, respectively. In behavioral studies of P. humuli alates released on glasshouse plants, those on SE spent significantly more time in motile behavior patterns than aphids on HM. In the glasshouse, population development also differed significantly and the number of aphids developing on SE was 12.9% of that on HM after 28 days. It is concluded that SE exhibits a certain repellent effect on P. humuli and, compared to HM, is possibly nutritionally less suitable to the aphid.