Aphidius ervi (Hymenoptera: Braconidae) was introduced to the United States in the late 1950’s and early 1960’s for biological control of pea aphid [Acyrthosiphon pisum (Hemiptera: Aphididae)], and is now widely distributed in North American alfalfa, often achieving high levels of parasitism. Praon pequodorum (Hymenoptera: Braconidae) is a native aphid parasitoid which also includes the pea aphid in its host range. Prior to the introduction of A. ervi, P. pequodorum was a common parasitoid of pea aphid in alfalfa in the southern part of the State of Wisconsin. Since the establishment of A. ervi in this region, P. pequodorum abundance in alfalfa has decreased dramatically, though we lack information from other habitats and other parts of the state. Here, we examine geographic and habitat variation in the relative abundance of these two parasitoids, and discuss implications for competition and indirect non-target interactions between them.