Phorodon humuli (Schrank 1801)

(Fig. 4a–f; Fig. 5a–f)

is the hop aphid, adventive and widespread in North America at least since 1863 (Foottit et al. 2006). Apterae of P. humuli can be distinguished from those of P. cannabis by the absence of flabellate setae and by shorter setae on antennal segment III (Fig. 2b and 4b). This species is common and damaging on hops in North America, especially in the Pacific Northwest and is not known from Cannabis. The aphids overwinter on Prunus, particularly ornamental purple leaf plum, Prunus cerasifera Ehrh (Rosaceae) (S. E. Halbert, personal observation).