United States Department of Agriculture-Animal and Plant Health Inspection Service
Plant Protection and Quarantine-Center for Plant Health Science and Technology

Biological invasion by exotic species can alter ecosystem properties and processes such as productivity, decomposition, and nutrient cycling (Vitousek 1986), and also can have overwhelmingly negative consequences for native species and communities (Elton 1958, Jarvis 1979, Clark et al. 1984), thus changing the biodiversity pattern.

The sevenspotted ladybeetle (Coccinella septempunctata), an introduced aphid predator, has dispersed throughout much of the U.S. (Schaefer et al. 1987). It appears to be outcompeting the native ninespotted ladybeetle (C. novemnotata) and has displaced that species in alfalfa fields (R.D. Gordon, personal communication).

Among phytophagous insects, Lattin and Oman (1983) referred to some immigrant Heteroptera and Lepidoptera that may have adversely affected populations of native species. In addition, an adventive spittlebug (Lepyronia coleoptrata) may be displacing the indigenous L. quadrangularis in roadside vegetation (Wheeler 1991; E.R. Hoebeke, personal communication), and introduced dung beetles (Scarabaeidae) are believed to frequently replace and possibly eliminate native species (H.F. Howden ).

Undoubtedly other examples of this phenomenon exist in the literature, but very little is known about the impact that non-indigenous insects have had on our native fauna (Bates 1956). Turnbull (1967) suggests that some immigrants will have distinct advantages over native species and that displacement is particularly apt to occur "in cases where species that evolved in other associations are introduced to new areas."  We simply cannot say how rare or common such displacement really is.

(All text on this page is from Kim & Wheeler's 1991 report.)