Missouri turns to imported weevils to kill invasive plant

KANSAS CITY — An alien plant species has invaded Missouri and is threatening to overrun crops and livestock pastures.

To combat the scourge weed, officials are deliberately releasing two alien insect species to destroy its roots and seeds.

What could possibly go wrong?

History shows that bioengineering projects can have unintended consequences. But agronomists and entomologists say there’s nothing to worry about here.

The root weevil and the flower head weevil being introduced in Missouri will feed only on the noxious spotted knapweed plant, they say, and even if the alien insects reproduce into the millions, they will not disrupt the ecology, except in ways that we want them to.

“They are not going to become pests in themselves,” said Ben Puttler, professor emeritus of entomology at the University of Missouri.

However safe the knapweed weevils may be, the record of deploying one species against another is spotted with repercussions that often are not understood for years or even decades. Some alien species can end up attacking native plants or disrupting the food chain in complicated ways:

•An alien parasite introduced in the U.S. in 1906 to kill gypsy moths did not stop that invasive species from spreading. Instead, it now attacks more than 180 native species of North American butterflies and moths.

•Asian ladybugs introduced in the 1970s to control aphids in pecan groves became so prolific they are now crowding out — and even eating — native ladybugs. They also invade households and stink.

•Parasitic wasps introduced in Hawaii before 1950 to control sugar cane beetles are attacking native caterpillars, which are a food source for birds.

•An alien weevil introduced in the 1970s to control musk thistle, another noxious weed in Missouri and elsewhere, is now threatening some native thistles in Nebraska with extinction, according to a university ecologist.

But there are many cases in which biocontrol of pests has been successful without side effects, going back to the 1880s, when an Australian beetle was released to combat a pest afflicting California citrus crops.

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