So vast is this "bioinvasion" (as some have termed it) that only rough estimates can be made of the numbers of non-native species now in North America, much less the rest of the world. In consequence, agencies whose mission it is to address those risks also are better developed. Some focus on narrowly drawn problems. Threat of Invasive Species

Various abundant invasive species have had severe economic impacts on U.S. industries and the natural environment. Seaports, where many ships exchange ballast water, are at severe risk of invasions: even if only a tiny proportion of newly arriving non-native species survive in busy ports like San Francisco Bay or Chesapeake Bay, the actual number of successful invasive species may be large. In the 19 th century, the railroads over which cattle were transported were a major path for the establishment of new plants. In the 20 th century, zebra mussels quickly escaped the drainage of the Great Lakes (probably via the Chicago Sanitary and Ship Canal) and began an invasion into the Mississippi River drainage, and Asian carp are repeating the process in the opposite direction. The mission of the National Institute of Invasive Species Science is to work with others to coordinate data and research from many sources to predict and reduce the effects of harmful non-native plants, animals, and diseases in natural areas and throughout the United States. What characteristics of seed dispersal, nesting, food and host preferences, etc., are most likely to lead to exuberant proliferation and result in economic and ecological harm? This evidence may be based on experience with the species domestically or in other countries. (For many species, the economic impacts are simply unknown.) These non-native crops and their benefits are not the focus of this report but should not be forgotten in discussions of those imported species that cause serious harm. Quarantines operate basically on either of two strategies: 
investing in strict control at points of entry to prevent organisms from leaving the quarantine area (with the risk that it could be too late to prevent escape) or attempting to control before the organisms arrive in the country (i.e., trying to act on the source or point of export or regulating the pathway of import). Basic Methods of Invasive Species Control

If inspections and quarantines fail to keep an invasive plant or animal out of a region and a species becomes established, the problem shifts to control of the species, which includes preventing its spread between local areas and beyond any established perimeter. Prevention practices vary depending on the species and surrounding environment, and they may include more than one of the methods described below. Biopesticides can be divided into three major classes: biochemical pesticides are naturally occurring substances (e.g., pheromones) that control pests by nontoxic mechanisms (e.g., interfering with finding mates); microbial pesticides contain a microorganism (e.g., a bacterium, fungus, virus, or protozoan) as the active ingredient, such as various types of the bacterium Bacillus thuringiensis (Bt) used to control certain insects harmful to cabbages, potatoes, and other crops; and plant-incorporated protectants are pesticides that plants produce from genetic material that has been added to the plant, as when the gene for the Bt pesticidal protein is introduced into a plant's own genetic material, causing the plant to manufacture the substance that destroys pests. Issues for Congress: Actions and Approaches

Current federal laws concerning invasive species form a patchwork, stronger in certain areas, such as agriculture and ballast water, and weaker or absent in other areas. Congress could choose to address these gaps either by explicitly delegating such authority to the President or by crafting legislation. Specifically, it does not regulate the release of a species into the wild once they have been admitted, unless that species is already designated a noxious weed or disease carrier. Approaches to Regulation: Species-by-Species vs. Pathways

Legislation to address invasive species could take a species-by-species approach, a pathway approach, or a combination of the two. Review of industries dependent on importing and transferring non-native species . While the current 16 teams work primarily on NPS lands, they also may work with adjoining landowners.
For the first few centuries after the arrival of Europeans in North America, plants and animals of many species were sent between the two land masses. The transfer of non-natives consisted not only of intentional westbound species ranging from pigs to dandelions but also of intentional eastbound species such as grey squirrels and tomatoes. And for those centuries, the remaining non-native species crossing the Atlantic, uninvited and often unwelcome, were ignored if they were noticed at all. They were joined by various species arriving deliberately or accidentally from Asia and Africa. The national focus on invasive species arose in the 19th century, primarily owing to losses in agriculture (due to weeds or plant diseases), the leading industry of the time. A few recently arrived invasive species, and estimates of adverse economic impacts exceeding $100 billion annually have sharpened that focus.
Very broadly, the unanswered question regarding invasive species concerns whose responsibility it is to ensure economic integrity and ecological stability in response to the actual or potential impacts of invasive species, and at what cost. As this report shows, the current answer is not simple. It may depend on answers to many other questions: Is the introduction deliberate or accidental? Does it affect agriculture? By what pathway does the new species arrive? Is the potential harm from the species already known? Is the species already established in one area of the country? Finally, if the answers to any of these questions are unsatisfactory, what changes should be made?
The specific issue before Congress is whether new legislative authorities and funding are needed to address issues of invasive species and their increasing economic and ecological impacts on such disparate matters as power-plant operations, grazing lands, and coral fishes. Such legislation could affect domestic and international trade, tourism, industries dependent on importing non-native species, those dependent on keeping them out, and finally, the variety of natural resources that have little direct economic value and yet affect the lives of a broad segment of the public.
In the century or so of congressional responses to invasive species, the usual approach has been an ad hoc attack on the particular problem, from impure seed stocks to Asian carp in the Chicago Sanitary and Ship Canal. A few notable attempts have begun to address specific pathways by which invasives arrive (e.g., ship ballast water), but no current law addresses the broad, general concern over non-native species and the variety of paths by which they enter this country. A 1998 executive order took a step in bringing together some of the current authorities and resources to address a problem that has expanded with both increasing world trade and travel and decreasing transit time for humans and cargo. Multiple bills have been introduced on this subject in recent Congresses.
There are two basic approaches to limiting the spread of invasive species: a species-by-species assessment of the risks or benefits of admitting or excluding species, and a policy based on controlling pathways of entry in which vigilance is maintained on incoming ballast tanks, cargo holds, packing materials, and similar vehicles for unwanted organisms. These two approaches may complement each other. Policymakers also may emphasize prevention over post hoc control or vice-versa, or they may adopt a combination of the two approaches.