Corn Rootworms Get Juiced
Corn rootworm larva.
Corn rootworms account for more pesticide use on row crops than any other
insect pest in the United States.
Farmers apply pesticides, often as a preventive measure, to between 30 and
40 million acres annually. The insect costs corn farmers about $1 billion a
year in control measures and lost crops.
Now, Agricultural Research Service
scientists from two laboratories at the Beltsville (Maryland) Agricultural
Research Center have concocted a mix that turns the insects' gluttony against
them. The new potion combines a red dye--proven safe for people and animals but
deadly to insects--with the juice from a bitter, mutant watermelon.
While the bitter watermelon juice would gag most human palates, "it
tastes like a hot fudge sundae to rootworms," says Albert DeMilo, who is
now retired from the ARS Insect Chemical Ecology Laboratory. "The insects
gorge on it, taking in plenty of the deadly red dye at the same time."
DeMilo, former postdoctoral fellow Chang-Joo Lee, and Robert Schroder, an
entomologist with the ARS Insect Biocontrol Laboratory, identified the
watermelon ingredient--cucurbitacin E-glycoside--that rings the rootworm's
internal dinner bell. Now they have developed a process for extracting the
juice, which is also a perfect solvent for the lethal dye, DeMilo says. When
formulated, the juice-dye mix sprays uniformly and penetrates to the core of
corn plants, where the adult rootworm beetles hang out.
Farmers normally apply pesticides to the soil to kill the larvae, says
Schroder. But these pesticides can pollute groundwater and surface streams. By
contrast, the watermelon-dye combo zeros in on the adult stage of the insect
and helps to break the reproductive cycle so next year's population is lower.
And it's safe.
The dye, phloxine B, is approved by the Food and Drug Administration as
D&C Red #28 for use in drugs and cosmetics. It's also in the registration
process for controlling fruit flies.
Sunlight activates the dye inside the insects, where it forms a potent
oxidizing agent that attacks their tissues, DeMilo explains. It doesn't take
long before they die. [For more on dye as an insecticide, see "Red Dye,
Updated Traps," Agricultural Research, January 1996, p. 20.]
The new potion held its own against a promising bait-pesticide combo called
SLAM that was developed by industry and ARS researchers in Brookings, South
Dakota. SLAM is expected to cut the quantity of pesticide used for corn
rootworm control by more than 90 percent. [See "Corn Belt Growers Give
Areawide IPM a Try," Agricultural Research, October 1997, p. 5.]
But it's good to have a backup, says Schroder, because insects are notable for
developing pesticide resistance.
In a preliminary field test at the Brookings laboratory last summer, the
watermelon-dye combo actually killed 25 percent more rootworms than SLAM on the
first day of application and equaled SLAM's kill rate after 4 days. A larger
field test is planned for this summer.
DeMilo, Schroder, and Lee applied for a patent on the watermelon-dye combo.
PhotoDye International of Baltimore, Maryland, has signed a cooperative
research and development agreement with ARS, giving the company right of first
refusal to license the patent. Other companies have also expressed interest,
Schroder says.--By Judy
McBride, Agricultural Research Service Information Staff, 6303 Ivy
Lane, Greenbelt, Maryland 20770, phone (301) 344-2861.
Robert F. W. Schroder is at
the USDA-ARS Insect
Biocontrol Laboratory, Bldg. 306, 10300 Baltimore Ave., Beltsville, MD
20705-2350; phone 301-504-8369, fax 301-504-8190.
"Corn Rootworms Get Juiced " was published in the May 1998
issue of Agricultural Research magazine. Click here to see this
issue's table of contents.