Hyperparasitoids from Pea Aphid Mummies, Acyrthosiphon pisum (Homoptera: Aphididae), in North America

The pea aphid, Acyrthosiphon pisum (Harris), seems under biological control in North American alfalfa, primarily as a result of attacks by parasitoid wasps. Of the 10 known primary parasitoids, an introduced aphidiid, Aphidius ervi Haliday, seems most important in Iowa and elsewhere in the East. Mummies of A. pisum collected in central Iowa during five seasons produced four species of hymenopterous hyperparasitoids, although eight additional species are known from other studies elsewhere. The Iowa species in descending order of abundance were: Asaphes lucens (Provancher) (Pteromalidae), Dendrocerus carpenteri (Curtis) (Mesaspilidae), Alloxysta victrix (Westwood) (Alloxystidae), and Pachyneuron siphonophorae (Ashmead) (Pteromalidae). Keys and descriptive notes are presented to allow identification of all known North American A. pisum hyperparasitoid species in their adult stages, and the known primary and hyperparasitoids by means of evidence left on or in vacated aphid mummies. Hyperparasitoids constituted a smaller proportion (17.8%) of the insects successfully emerging from Iowa A. pisum mummies than expected. Speculations about the reason for the low level of hyperparasitism and its implications for biological control are provided.