Competitive displacement between ecological homologues

Competitive displacement among three species of parasitic Hymenoptera which are ecological homologues has occurred in the field in southern California. Aphytis chrysomphali (Mercet) [Hymenoptera: Aphelinidae] was eliminated in 10 years (1948-1958) from nearly all of its former range—an area of some 4,000 square miles—by Aphytis lingnanensis Compere, which was imported from the Orient in 1948. Subsequently, Aphytis melinus DeBach, another exotic from India-Pakistan, virtually displaced A. lingnanensis from about 500 square miles of interior climatic areas in 4 years (1957-1961), but during the same time A. lingnanensis precluded the establishment of A. melinus in the milder intermediate climatic areas of San Diego County. Competitive displacement occurred in places in spite of food [the host scale insect, Aonidiella aurantii (Maskell)] being abundant. Thus food scarcity is not necessary for competitive displacement to occur. Two other species of parasites, Comperiella bifasciata Howard and Prospaltella perniciosi Tower, which attack the same host but are not ecological homologues of the Aphytis spp., continued to coexist with Aphytis spp.