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Alien Invasion

 
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Nature Vs. Nature 4 pages: | 1 | 2 | 3 | 4 |

Still at Large

Photo of Loosetrife
 
Innocent in appearance, purple loosestrife is one of America's best-known alien invaders.

Another native of Europe, the infamous purple loosestrife is a familiar site along highways all over North America. It arrived in the eastern United States in the 1800's, either as an ornamental plant or as an unwanted hitchhiker in the ballast of ships. Covering nearly half a million acres of land in North America, the perennial poses a serious threat to endangered wetland habitats. The hardy purple weed edges out native plant species, as well as the insects, fish, amphibians, birds and animals adapted to feed and live among them.

Though more than one hundred insects feed on purple loosestrife in its native Europe, these natural enemies had to be screened carefully before being released in North America. "Feeding trials" began in 1987, exposing the candidate insects to native wetland species and important agricultural species to ensure that an introduced insect would not itself become a problem invasive species.


Though more than one hundred insects feed on purple loosestrife in its native Europe, these natural enemies had to be screened carefully before being released in North America.


After rigorous testing, the United States and Canada approved the release of five species of beetles in 1992. As of 1996, three insect species have been released in 25 U.S. states and in seven Canadian provinces. One species feeds on the foliage, another lays its eggs in the stem and the third eats the plant's roots. Though scientists expect the insects to reduce purple loosestrife populations by up to 80%, they don't expect to see this reduction for at least another ten to twenty years. The verdict is still out, therefore, on the overall success of this program. However, there have been local successes at insect release sites in New York, Minnesota, Ontario and Illinois- where the insects reduced the loosestrife populations by 97% within three years of release.

Looking Ahead

Photo of Beetle
 
Loosestrife-munching beetles may be the only way to control this prevalent weed.

Seven thousand alien species currently live in the United States, some of which can have severe negative economic and ecological consequences if allowed to thrive unchecked.

"Invasive species aren't like a wild fire that blows up in your face," says Noah Poritz of Biological Control of Weeds, Inc. "It's a quiet fire burning with equally devastating effects."

Biological control has obvious advantages over other forms of control. It's cheaper and less toxic than pesticide use, and it's far less labor intensive than removing offending foreigners by hand; however, biological control is not a magic bullet.


"Invasive species aren't like a wild fire that blows up in your face," says Poritz. "It's a quiet fire burning with equally devastating effects."


For one thing, ecologist Daniel Simberloff of the University of Tennessee at Knoxville estimates biological control works just one time out of ten. And it can require years of careful research and thoughtful planning in order to avoid creating a bigger problem than the one it's meant to solve.

"Biological control should be the method of last resort, rather than first," says Simberloff. "Its reputation as an environmentally friendly means of control is largely undeserved."

In many cases, some combination of biological control, mechanical removal and pesticides will work best to eradicate unwanted species. But, for now, the most effective way to avoid the ecological and economic devastation caused by invasive species is to keep them out in the first place.

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4 pages: | 1 | 2 | 3 | 4 |

Photos: Corey Lindgren, Manitoba Purple Loosestrife Project


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