Host range and habitats of the aphid parasitoid Diaeretiella rapae (Hymenoptera: Aphidiidae) in Washington state

Host aphids of the parasitoid Diaeretiella rapae (M'Intosh,) are defined for Washington Slate, together with a listing of world findings. Specifies are given on host habitats frequented by the parasitoid, comparative population abundance, associated parasitoid species, and host switching. D, rapae is a common parasitoid of Brachycorynella asparagi (Mordvilko), Hayhurstia atriplicis (L), Brevicoryne brassicae (L.), Diuraphis noxia (Kurdjumov), and sometimes Myzus persieae (Sulzer). In total, 19 species of aphids were positively linked with D, rapae and 6 are reported as hosts for the first time-Acyrthosiphon lactucae (Passerini), Phorodon humuli (Sehrank), Dysapphis plantaginea (Passerini), Brachycaudus tragopogonis (Kaltenbach), Uroleucon ivae Robinson, and Braggia sp. D. rapae was shown to switch or alternate successfully between hosts, which suggests that certain host habitats might he used in conjunction with farmlands to enhance host opportunities for the parasitoid and improve its population stability. Two of its primary aphid hosts, B. asparagi and D. noxia, reached pest status shortly after their arrival in Washington but are less problematic today, in part at least because of host switching and acceptance by D, rapae.