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

This is a brief description of the service ... An introduced pest arthropod may affect the economy directly through infesting crops or as a forest pest attacking economically important trees. Additionally, an introduced arthropod may attain pest status through environmentally harmful effects on an ecosystem. Many pests may not be detected until 10-15 years after their presumed arrival (Reynolds et al. 1982), and for the wheat bulb fly (Delta coaractata), several decades passed before its arrival was reported. Some introduced alien species may never be detected if their introduction has a
negligible effect on the ecosystem.

The following table was produced through compilation of NANIAD data on the consequences of the introduction of known arthropods into North America.

• Pest Status # of Individuals % of Total
• Undetermined status 1,052 44%
• No economic importance 299 12%
• Minor pest 258 11%
• Major pest 228 9%
• Beneficial 577 24%
• Total 2,414 100%

Thus we see that of the reported non-indigenous arthropods, 20% are pests, 24% are beneficial (biological control introductions,  pollinators, etc.), and 56% are either not of economic importance or their status has yet to be determined. Intentional importation of biological control agents accounts for many of the non-indigenous beneficial arthropods; however, they may also enter as hitchhikers on imported commodities.

Predicting what insect may become an important pest if it becomes established in the U.S. is difficult and uncertain. McGregor (1973) pointed out that only about one third (73) of 212 invasive alien arthropods that became important pests in the United States were predicted to attain pest status.