In 1999, Executive Order 13112 defined an invasive species as one that is:

• Nonnative, alien, or exotic to the ecosystem under consideration, and
  
  
• One whose introduction causes, or is likely to cause, economic or environmental harm or harm to human health.

In addition, the definition considers the costs and benefits, or net damages, of an alien species, because the benefits exceed the costs of some nonnative species, including some crops, livestock, and ornamental plants.

Growing potential and actual economic threats to U.S. agriculture and other sectors of the economy have generated renewed interest in policies to address the threats from invasive species.

Other factors pointing to the need for new research on invasive species policy include:

• Exponential growth in USDA's emergency eradication expenditures
• Expansion in the flow of imported goods and travelers into the U.S.—important pathways for invasive species introduction
• Increased vulnerabilities from the changing structure of livestock and crop production in the U.S.
• Increased likelihood of invasive species survival during transit from faster modes of transport for people and goods
• Growing concern for adverse impacts of species on native ecosystems
• Increased restrictions on traditional chemical control options.

The ERS PREISM program focuses on economic issues related to nonnative pests of agricultural significance or that fall under USDA programs, a subset of invasive species. These species, sometimes called exotic or alien pests, include nonnative weeds, insects, fungi, bacteria, viruses, and other disease-causing agents that can affect production or trade of poultry and livestock animals (including zoonotics that can cause disease in animals and humans) or crops, including food, feed, and fiber crops, ornamentals, and pasture and range. While such pests affect agricultural production or trade, some can affect nonagricultural systems as well. The ERS program focuses on pests that have entered the U.S. (or have moved outside their natural range in the U.S.) and potential pests that have not entered the U.S.

Some species originally from other countries can damage U.S. agriculture by reducing crop and livestock production or threatening export potential, with impacts on U.S. prices, consumers and trade. International trade is a potentially important way for pests to move between countries. The presence of some pests in the U.S. can cause some countries to stop importing U.S. products or require special inspections or practices before entry.

In addition, there are the costs that U.S. producers, other businesses, APHIS, and State governments incur to prevent or reduce such losses. So, an important economic issue is the allocation of resources between exclusion, surveillance, control, or mitigation programs to address pests that could affect U.S. agriculture and natural resources.

Important economic questions for APHIS and State governments include:

• The choice of what pests to control
  
  
• When and where to control them
  
  
• The type of control approach to use (such as monitoring, eradication, containment, or long-term areawide management programs)
  
  
• The type of control practice to use (such as a pesticide, biological control, or other practice)
  
  
• When to terminate the control program or practice

Information about potential economic consequences of pests and the costs and benefits of programs to control them are important to making decisions about public programs. Some species have special potential for damage because, once introduced in the U.S., their populations can increase and spread without control from natural enemies to levels that are difficult to eradicate. Complicating decisions about such species are uncertainties, or lack of knowledge, about important variables: the likelihood of pests entering and establishing damaging populations, how rapidly the populations can grow, how far they can spread, and the damages they can cause to agriculture and ecosystems.

for more information, contact: Craig Osteen
web administration: webadmin@ers.usda.gov
page updated: March 17, 2003