Invasive Species Vector
The Asian Tiger Mosquito is a serious
vector for many human diseases. (Photo:
U.S. Department of Agriculture)
Invasive species have arrived in the United States through a multitude of means,
including introductions by early human settlers who seek reminders of their
homelands, to importation of ornamental plants, to introductions by government
agencies to combat some other problem (often an agricultural one), to an expanding
global trade enterprise that inadvertently allows the rapid spread of
species. Modern trade has greatly increased the spread of a number of species.
Asian tiger mosquitoes hitchhike into new areas in rainwater pools in discarded
tires and even aboard water-filled depressions on ship structures. This mosquito
is associated with the transmission of many human diseases, including dengue
virus, West Nile virus, and Japanese encephalitis (Global Invasive Species Database
Ship ballast, typically water pumped into a ship's tanks at one port and
pumped out at another, is used to balance the weight and control the steerage of
freight vessels and is a well-documented vector. The most noted species introduced
by ballast is the zebra mussel. Zebra mussels (Dreissena polymorpha) are
native to the Caspian Sea, but long ago began spreading throughout much of Europe.
In 1988, they were detected in the Great Lakes where they had caused serious
problems by out-competing native species for food and damaging harbors,
boats, and power generation plants.
In some cases, the military itself unintentionally may have been responsible for
the spread of invasive species. While it is difficult to pinpoint the precise time, location,
and cause of introduction, there is speculation that the military introduced
the brown tree snake to Guam, African iceplant to the San Francisco Bay area,
black rats to the Midway Islands, and sakosia shrubs (Timonius timon) to Palau.
The military has taken a leadership role to reduce future unintentional introductions.
The Armed Forces Ballast Water Management Program, which requires
DoD vessels to twice flush ballast water at least twelve nautical miles from shore,
should be used as an example to commercial vessels. Transportation policy and
procedures rules already require the washing of vehicles after field operations.
The primary purpose is to extend the life of field equipment, but it also has a secondary
purpose of reducing hitchhiking foreign pests from entering U.S. borders.2
Proceed to Next Section: Federal Guidelines for Invasive Species