Biocontrol Duo Gang up on Armyworms

Double trouble may loom ahead for beet armyworms that ravage cotton plants.

Scientists with USDA’s Agricultural Research Service are teaming a natural insect virus with a parasitic wasp to put the kibosh on the pest.

The virus, called a nuclear polyhedrosis virus, liquefies the bodies of beet armyworm caterpillars it infects. But it doesn’t harm people, animals or beneficial bugs.

The parasitic wasp, Cotesia marginventris, is a native U.S. insect that lays its eggs in the worm. Wasp larvae hatch from the eggs and feed on the pest’s innards.

In small field plots, spraying the virus on cotton plants killed over 50 percent of the worms in 4 days. Researchers then released about 500 Cotesia wasps; they doomed half the survivors. In all, the virus-wasp combo killed three-fourths of the beet armyworms.

Currently, growers fight the beet armyworm by spraying insecticide. But using its natural enemies instead would spare helpful predators like big-eyed bugs that keep other pests in check.

In the studies, researchers used--with equal success--a commercial virus product registered as Spod-X and an ARS-developed strain. Special techniques were used to mass-rear the wasps.

Scientific contact: P. Glynn Tillman, USDA-ARS Biological Control and Mass Rearing Unit, Mississippi State, Miss., phone (601) 323-2230, fax (601) 323-0478, pgt2@ra.msstate.edu.