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Weevil May Help Fight Invasive Water Weed

By Marcia Wood
July 1, 1999

Sleek black weevils are being put to work in an east Texas pond, lake, and reservoir to help stop the spread of a fast-growing water weed, Salvinia molesta. If the weevils perform as well in the United States as they have in countries such as Australia, South Africa and India, they might reduce the need for chemical controls.

This week near Jasper, Texas, Agricultural Research Service scientists and colleagues from the Texas Parks and Wildlife Department are freeing about 500 of the one-tenth-inch long weevils known as Cyrtobagous salviniae. Earlier, they set loose about 350 weevils.

Salvinia molesta produces small, oval, green to yellow-green leaves that can form dense mats that crowd out native plants and ruin conditions for fish and wildlife. The mats can also interfere with flood control and irrigation as well as with fishing, swimming, boating, and water skiing.

Native to South America, S. molesta poses a threat to waterways in warm-weather areas of the U.S. Unchecked, it can quickly double its spread in only a few days, according to Ted D. Center, who leads the ARS Aquatic Weed Control Research Laboratory in Ft. Lauderdale, Fla.

The weevil, also native to South America, showed up in Florida several decades ago. It is thought to have a key role in keeping another Salvinia species, S. minima, in check in Florida.

The ARS researchers in Ft. Lauderdale collected the weevils in Florida and are releasing them in Texas with the permission of federal and state regulatory authorities. Weevil adults and young attack primarily the new, nitrogen-rich buds of the plant. The weevils can produce a new generation of hungry young every 3 weeks.

ARS scientists and their Texas associates will monitor the weevils to determine if they can adapt. Winter weather poses the biggest threat to the newcomer insects in Texas. ARS is USDA's chief research agency.

Scientific contact: Ted D. Center, ARS Aquatic Weed Control Research Laboratory, 3205 College Ave., Ft. Lauderdale, FL 33314; phone (954) 475-0541, ext. 103; fax (954) 476-9169,