More than 100 species of benign microbes have been intentionally introduced for processing wine, beer, cheese, and other foods. In addition, about 50 microbes have been introduced for the biological control of pest insects, particularly Bacillus thuringiensis (BT). Many more have crept in without notice, including those that cause fatal human diseases. Only the bad actors attract attention--and usually when it is too late.

As history has proved, it is especially difficult to protect against infectious disease--a single afflicted traveler can wreak devastation. The two non-indigenous diseases having the most impact at the present time are AIDS and influenza. In 1993, the Centers for Disease Control had counted 103,533 cases of AIDS with 37,267 deaths. The cost of treatment averages about $6 billion a year. Meanwhile, new strains of influenza from the Far East quickly spread to the U.S., where flu may account for five to six percent of deaths. Hospitalization costs for a single outbreak of type A influenza can top $300 million.

Plants get sick as well. According to the Cornell study, an estimated 121 species of microbes, mostly introduced inadvertently with seeds and other parts or host plants, have become major crop pests in the U.S. Nearly 65 percent of the $36 billion in crop losses attributed to plant pathogens--or about $23 billion per year--can be blamed on non-indigenous species. An additional $500 million is spent on the control of these imported pathogens. Damage to lawns, gardens, and golf courses amounts to $2 billion each year.

Image: University of Wisconsin

In forests more than 20 non-indigenous species of plant pathogens attack woody plants. Two of the most serious plant pathogens are the chestnut blight fungus (Cryphonectria parasitica) and Dutch elm disease (Ophiostoma ulmi). Before the introduction of chestnut blight (image left), approximately 25 percent of eastern U.S. deciduous forest consisted of American chestnut trees. Removal of dead and dying elm trees continues to cost about $100 million a year. Annual losses in forest products by non-indigenous pathogens is estimated to be $2.1 billion.

Data: Excerpted from Environmental and Economic Costs Associated with Non-indigenous Species in the United States

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