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Invasive Species: A Continuous Problem?

September 26, 2001

The continuous promotion to regulate pesticide use as a result of the Food Quality Protection Act (FQPA) and the widespread cultivation to implement integrated pest management (IPM) programs ignore the fact that the greatest economic and ecological threat to agriculture, particularly the ornamental industry, is the introduction of exotic (that is, invasive) species of insects, weeds, and diseases. Although several destructive diseases (Dutch elm disease and American chestnut blight) and exotic weeds (purple loosestrife and leafy spurge) have been introduced into this country, this article, for the sake of brevity, focuses mainly on the impact of exotic insects.

Many insect pests we see today did not originate here; this includes fire ants (Argentina), Africanized honeybees (South America), Formosan termites (Asia), Mediterranean fruit fly (Tropics), Japanese beetle (Japan), Asian longhorned beetle (China), and Gypsy moth (Europe). When these insects entered the United States, they became a problem mainly because they had no natural enemies. In the country of origin, natural enemies "naturally" maintain populations at levels where they are not a significant concern or pest.

Some insect pests were introduced with good inten-tions. For example, Gypsy moth was brought from Europe by the French naturalist Leopold Trouvelot for silk production. However, during a storm in Massachusetts (1869), several caterpillars escaped. As a result, the Gypsy moth became established throughout the Northeast and the Midwest and has continued to migrate westward. In the past 20 years, Gypsy moth has destroyed over $16 million worth of trees.

Another example is the multicolored Asian lady beetle, introduced into the Southeast in the late 1980s to deal with plant-feeding insects such as aphids on fruit trees. Without its natural enemies, it quickly spread into other parts of the country. As a result, it is a seasonal nuisance pest in late summer through early fall, when the adult beetles enter buildings to overwinter, and again in spring, when the adults leave the indoors to search for food. Lady beetle adults feed on fruits, including apples, raspberries, and grapes.

An increase in wide-scale international trade and the impact of globalization will most likely lead to a greater probability of exotic or introduced insects making their way into the United States. Exotics may be introduced by tourists bringing in undeclared plants, fruits, and vegetables. Wide-scale international trade has also led to an increase in urban-type arthropod pests, such as bed bugs. As people travel, bed bugs can "hitch a ride" in luggage, especially on secondhand items bought in other countries. This is not the only reason for the increase, as bed bugs are also parasites of birds and often enter homes via birds nesting or roosting on houses.

Exotic or invasive species are a problem for vari-ous reasons. First, many are small, allowing them to go undetected at border checkpoints. Second, many (though not all) have a very high reproductive potential, giving them superior colonizing ability. Insects are opportunistic and once inside our borders they do whatever it takes to survive.

As a result of the concern regarding exotic pests, then-President Clinton established the Invasive Species Council. The 2001 federal budget included $28.8 million for programs to deal with exotic pests.

It has been estimated that invasive pests (including diseases and weeds) cost the country around $137 bil-lion a year. However, it is hard to assess long-term costs. For example, it has been mentioned that if the Asian longhorned beetle were to become established and spread, it would cost about $500 million a year. Besides economic costs, there are ecological costs. The consequences of exotic insect pest introductions are that they can out-compete or displace native species, which may impact the length of time pests are a problem or result in degradation of wildlife habi-tats, thus impacting endangered species. For example, accidental introduction of the Argentine ant, mainly into California, may have been responsible for the de-cline or disappearance of native ant species there. Another ecological consequence of introducing exotic pests is the erosion of genetic integrity, where native species interbreed with exotics, which may impact the survivability or competitiveness of native species. In addition, exotic, plant-feeding insects may change the existing flora and fauna of an ecosystem over a short- or long-term period. Regardless, the consequences may be devastating and irreversible.

The best and primary strategy in dealing with exotic insect pests is prevention. This is accomplished by the USDA through the Animal and Plant Health Inspection Service (APHIS), with over 1,200 inspectors at entry ports across the country making an esti-mated 230,000 interceptions of exotic arthropods per year. Materials coming through entry ports are in-spected and, if necessary, quarantined, which helps to prevent establishment of an insect pest.

If an exotic insect pest is discovered in the country, then the strategy is an elaborate system of scouting (monitoring) using traps and then control. If insect pests are detected in traps, then a plan to eradicate the insect pest is implemented. Another strategy used against exotic insects already established, such as the Gypsy moth, is to "slow the spread" (STS) by dealing with localized infestations that establish themselves in areas ahead of the main infestation front.

An alternative, long-term strategy being advocated by researchers for managing exotic pests is is biological control. This approach involves travelling to a pest’s country of origin and locating natural enemies (parasitoids, predators, and/or pathogens), which are then brought back and released: Not, however, before being evaluated through strict quarantine procedures.

What can be done to "stem the tide" of invasive insect species? First, it is important to educate the public on the short- and long-term economic costs and ecological impacts of exotics establishing in the United States. Second, we must abide by regulations designed to prevent their entry. Finally, it is important to prevent free movement of plant species that may allow insect pest to enter—particularly plants with soil. The continuous increase in international trade and globalization has increased the permeability of borders, which then leads to a greater probability of exotic or invasive insect species entering and becoming a problem.

Author: Raymond A. Cloyd


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