"Poison Pill" Dooms Pesky Caterpillars

Hiding a bitter pill in a dollop of jelly can make some medicines more palatable to reluctant kids. Scientists are employing a similar trick so destructive caterpillars will eat a "poison pill" that makes them deadly ill.

Such trickery could eventually offer a natural way to control crop-ravaging larvae of beet armyworms, cabbage loopers and other pesky moths. Normally, farmers combat them with chemical insecticides. Agricultural Research Service scientists in Beltsville, Md., envision poisoning them with a natural insect virus. It's known as the Anagrapha falcifera nuclear polyhedrosis virus.

The virus liquefies the pests' tissues, but poses no danger to beneficial insects, humans or wildlife.

To make sure pest larvae ingest lethal doses of virus sprayed as a biopesticide, ARS entomologist Robert Farrar, Jr., and colleagues tested it with powerful insect feeding stimulants. One of these concoctions contains cottonseed oil, sucrose and other ingredients irresistible to certain caterpillars like the beet armyworm. This pest attacks corn, cotton and cole crops.

In greenhouse studies aimed at tickling the armyworm's taste buds with deadly intent, scientists sprayed collard plants with virus alone or in a mix with a feeding stimulant. Of 378 larvae placed on the plants to feed, 43 percent survived the virus spray alone. Only 22 percent survived when the spray also included the feeding stimulant.

In related experiments, scientists sprayed formulations containing fluorescent brighteners. Brighteners help prevent ultraviolet light from degrading the virus before a caterpillar can ingest a lethal dose. Brighteners also bolster the virus' killing power. Seventy-four percent of armyworms died after feeding on collard leaves in outdoor plots sprayed with virus and brightener. Without the brightener, the virus killed only 48 percent.

The scientists plan tests combining all three ingredients--virus, feeding stimulant and brighteners. ARS is the chief scientific arm of the U.S. Department of Agriculture.

Scientific contact: Robert Farrar, Jr., ARS Insect Biocontrol Laboratory, Beltsville, Md., phone (301) 504-5689, fax (301) 504-5104, [email protected].