Identity, Distribution, and Hosts of Aphidius matricariae Haliday, an Important Parasite of the Green Peach Aphid, Myzus persicae (Hymenoptera: Aphidiidae — Homoptera: Aphidoidea)1

The widespread aphid parasite Aphidius matricariae Haliday is shown to be conspecific with: A. cirsii Haliday, arundinis Haliday, polygoni Marshall, lychnidis Marshall, valentinus Quilis, affinis Quilis, renominatus Hincks (all from Europe), phorodontis Ashmead, and nigriteleus Smith (both from North America). Rearing records from 40 aphid species are given, and Myzus persicae (Sulzer) is shown to be the most common and most important host. The rather sudden appearance of this parasite in field populations of M. persicae in California in 1957, its activity and distributional patterns up to 1960, the probability of its accidental introduction into North America at least 75 years ago in greenhouses, and its recent establishment outside of greenhouses are discussed.