Current Trends in Destructive Insect and Disease Invasion of North America.

Invasions by non-native insects and diseases represent one of the greatest threats to the stability of forest ecosystems world-wide.  In the United States these species have established at a rate of one species every two years, a rate that has remained essentially constant since 1900.  The two most important pathways by which forest insects and disease enter are solid wood (e.g., packing) and live plants (e.g., plants for planting).  Efforts are underway to limit both pathways, but given trends of increasing global trade, these efforts are not likely to completely stop the influx of new species.  Alien forest pests have arrived and established in the northeastern US at a higher frequency than elsewhere in the country. This trend appears to be the result of the greater diversity of host trees in the region.  Invasions by forest pests have caused the virtual elimination of several important tree species, have disrupted many important ecological processes in forest land and caused billions of dollars worth of damage to trees in urban settings.