"Poison Pill" Dooms Pesky CaterpillarsBy
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
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,