Seasonal life history, abundance and biology of the parasitoids of the pea aphid, Acyrthosiphon pisum (Harris) in Manitoba. A survey of the parasitoids of the pea aphid was conducted in alfalfa and field peas in the Red River Valley area of Manitoba during 1981-85. Five primary parasitoids and twelve secondary parasitoids were collected. The five primary parasitoids, all aphidiids, were: Praon occidentale Baker, Praon pequodorum Viereck, Aphidius ervi Haliday, Aphidius pisivorus Smith and Aphidius smithi sharma and Subba Rao. P. pequodorum and A. ervi comprised most of the primary parasitoids each year. A. smithi was not found prior to the introduction of this parasitoid in Manitoba in 1983. The twelve secondary parasitoids, including 8 identified to the species level, were: five pteromalids, Asaphes lucens (Provancher), Coruna clavata Walker, Pachycrepoideus vindemiae (Rondani), Pachyneuron siphonophorae (Ashmead), Pachyneuron sp.; three alloxystids, Alloxysta victrix (Westwood), Alloxysta megourae complex, Phaenoglyphis ambrosiae (Ashmead); three megapilids, Dendrocerus carpenteri (Curtis), Dendrocerus sp. a. Dendrocerus sp. and one encyrtid, Aphidencyrtus aphidivorus (Mayr). A. lucens was the most abundant secondary parasitoid collected each year. The percentage parasitism of the pea aphid by the primaries was determined for 1983-85 by both rearing and dissecting aphids collected from stem samples in the field. The relative abundance of the adult primary parasitoids for 1981-85 was determined from D-Vac collections, and for both the primary and secondary species from emergence from field-collected mummies. Seasonal changes in the abundance of the parasitoids are discussed.