It's Invaders vs. Invaders as Scientists Target Alien Species

February 22, 2006

Empowered by a lack of natural enemies, invasive species often overwhelm the regions they infiltrate.

But some scientists are fighting invaders with invaders, importing natural enemies from the problem species' native regions. (Related photos: invasive species in the United States.)

"What happens when we introduce an organism to a new range is that we often leave behind the natural enemies that keep it under control," said Mark Lonsdale in a Pulse of the Planet radio program broadcast today. Lonsdale is an ecologist with the Commonwealth Scientific and Industrial Research Organization (CSIRO) in Canberra, Australia. (Pulse of the Planet and this news story are sponsored by a grant from the National Science Foundation.)

The trick is to select and introduce natural enemies that will not cause additional damage to the ecosystems.

"There is a very long, extensive, and strict process of review" undertaken before any organism is released into a new environment, John Scott said. Scott is an entomologist and colleague of Lonsdale at CSIRO.

Scott added that Australia has a century-long tradition of using so-called biological controls, or biocontrols, in the battle against invasive weeds. Some 200 insects, mites, and fungi have been successfully and safely introduced, he says.

Bridal Creeper

According to Scott, the latest biocontrol success story is the implementation of a fungus and two insects against bridal creeper, an invasive weed introduced to Australia from South Africa in the 19th century.

Bridal creeper was introduced as a garden plant, but is now considered one of the worst weeds in the bushland of southern Australia, where its climbing stems and foliage smother native plants.

Unlike most other invasive plants, the creeper has seeds that can germinate on soil that isn't stirred up. The creeper can therefore spread more quickly, particularly in undisturbed habitats, such as nature reserves. This makes the plant a primary cause of ecological change in some pristine habitats, Scott said.

"And because it's in areas of nature conservation, our only option we have to control it is to use biological control," since chemical methods are banned in these areas, he added.

The first biocontrol approved for release was the bridal creeper leafhopper, a 0.08-inch-long (2-millimeter-long) insect that sucks photosynthetic cells from the creeper's leaves. (Plants rely on photosynthesis to convert light into energy.)

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