TAIUIACorn Rootworms Just Can't Get
Taiuia, Cayaponia bonariensis, growing in the wild.
South American farmers have a word of advice for their counterparts in the
North who are troubled by corn rootwormsand that word is
"taiuia." This plant, like squash and cucumbers, is a member of the
curcurbit family. But it contains a powerful feeding stimulant that could help
farmers control rootworms using less insecticide.
Brazilian farmers have already shared their secret about its powerful
rootwhich looks like an oversized cassavawith
Agricultural Research Service
scientists. By coincidence, two different farmers told two different ARS
scientists about taiuia in the early 1990s.
ARS biologist Willie Cabrera Walsh remembers asking one farmer why he was
placing plastic containers with slices of a root that looked somewhat like
cassava in his field. The farmer explained they were pieces of taiuia laced
with insecticide. The roots lured the corn rootworm adults, and the poison
delivered a mortal blow.
Cabrera Walsh works for ARS' South American Biological Control Laboratory in
Buenos Aires, Argentina. Many pests that plague North American farmers came
from other parts of the world, so having international laboratories to study
foreign pests makes sense. Often, natural predators from the homeland can
become U.S. control agents.
Entomologist Robert F. Schroder also learned about taiuia from a Brazilian
corn grower. Schroder, who is with the ARS Insect Biological Control Laboratory
in Beltsville, Maryland, was in Passo Fundo, Brazil, collecting corn rootworm
biological controls with entomologist Dirceu Gassen, who is with EMBRAPA, the
Brazilian Institute of Agricultural Research.
"We had been using a small, hand-held aspirator to collect the insects.
It was a very exhausting process and not very effective," says Schroder.
"Gassen introduced me to a man known as farmer Louis, who pulled up this
root that had corn rootworms all over it. We didn't know at the time what it
Biologist Willie Cabrera Walsh holds the major part of a taiuia
During the rest of the trip, Schroder and Gassen had no trouble collecting
samples. They just put slices of the root out where they saw a few of the
insects and returned later to collect thousands of them.
Schroder and Cabrera Walsh have been collaborating on their studies of
taiuia's potential. Cabrera Walsh sends taiuia samples to Schroder, who assays
the extracts and determines their usefulness in controlling corn rootworm
Cabrera Walsh devised a corn rootworm taste test. He put out samples of
artificial diets of corn, soybeans, and taiuia. Then, he set loose a group of
corn rootworms, allowing them to pick their favorite. What happened next amazed
"All the insects crowded around the taiuia," he says. "They
wouldn't stop eating, and they wouldn't touch the other samples until the
taiuia was gone."
Cabrera Walsh also did a literature search on the plant. He found Brazilian
scientist Iniberto Hamerschmidt first reported taiuia's alluring powers in
1985. Hamerschmidt wrote that farmers in Brazil's Curitiba area had been using
the plant as a lure since 1979.
Other ARS laboratories are evaluating wild buffalo gourd as a lure, and
Schroder had been working with cucurbitacins from mutant watermelons. [See
"Corn Rootworms Get Juiced," Agricultural Research, May 1998,
p. 11.] But Schroder's lab tests suggest that taiuia is best for luring the
southern corn rootworm, one of the many species of this pest complex.
Adult corn rootworms are actually beetles that feed on the corn's silk
tassels. The immature larval stage feeds on corn roots. Throughout its life
cycle, the pest costs U.S. farmers around a billion dollars each year in crop
losses and overhead expense. They've also been known to attack soybeans,
squash, melons, and other crops.
About 50 percent of all insecticides applied on row crops in the United
States are used against this pestthat's about 20 million pounds a year.
And many of the chemicals used to control corn rootworms will soon be banned
because of environmental concerns.
Part of the problem with current controls is that it is hard for
insecticides to reach the pests, since they lay their eggs in the soil and the
larvae feed underground.
But with taiuia as bait, it might be possible to cut the amount of
insecticide needed to control the pest. Or farmers might use taiuia to boost
the killing power of less effective but environmentally safe pesticides,
because taiuia spurs insects to eat more of the toxin.
Why do these pests love taiuia? It's all a part of evolutionary chess.
Taiuia, over time, developed higher and higher levels of a number of incredibly
bitter compounds called cucurbitacins to keep bugs away. Most plant feeders
couldn't stand the taste.
Corn rootworm adults, however, munch away on taiuia. How is that possible?
It seems they somehow developed a craving for cucurbitacins, which they store
in their own fatty tissues, making them very bitter. This protects the
rootworms from predators. In fact, their colorful body markings may be part of
"Birds are very sensitive to color patterns," explains Cabrera
Walsh. "They have to make the mistake of eating a corn rootworm only once.
They vomit it up and never eat one again."
Taiuia stores cucurbitacins in its bright-red berries and fat, potato-brown
roots that can weigh as much as 25 pounds. Adult beetles feed on the berries,
which helps free up the plant's seeds. In that way, the beetle has made an
evolutionary bargain with what could have been a bitter enemy.
Since corn rootworms don't shy away from plants that carry cucurbitacins,
their once beneficial craving could now become their chief liability. And
there's a bonus: Since taiuia repels beneficial insects, they won't be poisoned
accidentally when it's used as bait.
Trays with small flower pots of Cayaponia bonariensis (foreground) and
Cayaponia spp. seedlings.
The next question is whether taiuia can be grown in the United States as a
crop. It would do best in the southern half of the country, where growing
conditions are warmer and generally more like temperate or subtropical South
Taiuia berries could be harvested instead of having to kill the plant to
harvest the cucurbitacins in its root. Cabrera Walsh says taiuia's agronomic
potential would have to be analyzed, perhaps with the help of an industry
And of course, as with any new plant introduction, USDA's Animal and Plant
Health Inspection Service would have to certify that taiuia poses no threat to
native plant species or wildlife.
Lacking that certification, enterprising South Americans could grow the
plant as a crop and ship the cucurbitacin extract in a liquid or powder form to
U.S. companies that could then use the material to produce new corn rootworm
control products. "With all the good it's doing for South American
farmers, it seems a shame taiuia can't also benefit people in the United States
and Canada," says Cabrera Walsh. By
Jill Lee, Agricultural Research
Service Information Staff.
This research is part of Crop and Commodity Pest Biology, Control, and
Quarantine, an ARS National Program that is described on the World Wide Web at
Guillermo Cabrera Walsh is
with the USDA-ARS South
American Biological Control Laboratory, U.S. Embassy Buenos Aires,
Argentina, Unit 4325 APO AA 34034-0001; phone 54 11 4662-0999 or 54 11
4452-4838, fax 54 11 4452-1882 (Dial 104 after the greeting message).
Robert F. Schroder is
with the USDA-ARS
Insect Biocontrol Laboratory, Bldg. 306, Rm. 322, 10300 Baltimore Ave.,
Beltsville, MD 20705-2350; phone (301) 504-8369, fax (301) 504-8190.
"TAIUIACorn Rootworms Just Can't Get Enough"
was published in the April 1999
issue of Agricultural Research magazine.