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New Fungal Strain Spells
Trouble for Caterpillar Pests
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In tests to control caterpillars on vegetable
crops, ecologist Stephen Wraight examines nozzles used to spray
spores of the insect pathogenic fungus Beauveria bassiana.
(K9123-2)
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The future of environmentally
friendly crop insecticides could be brightened by the discovery of a more
effective fungus from which to make mycoinsecticides. Mycoinsecticides are
fungal sprays that work on insect pests from the inside out. Fungal spores
attach to an insect's cuticle, germinate, and then penetrate its body. Spores
from dead insects can survive to infect later pest generations.
A new strain of the Beauveria bassiana fungus known as BB-1200 appears
to be even more effective in curbing lepidopteran—or
caterpillar—pests than its close relative, the commercially available GHA
strain.
In laboratory bioassays, BB-1200 consistently exhibited virulence equal to or
greater than the GHA strain against all lepidopteran pests tested, including
fall armyworm, beet armyworm, black cutworm, corn borer, and cabbage
looper—pests that are not highly susceptible to the GHA strain, according
to ARS ecologist Stephen P. Wraight.
"These lepidopteran defoliators are among the most destructive insect
pests of important crops like corn and cabbage and other vegetables. Each year,
they cause billions of dollars in losses," says ARS entomologist John D.
Vandenberg. |
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A healthy armyworm (right) next to two that were
killed and overgrown by B. bassiana strain Mycotech BB-1200.
(K9122-1)
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Cooperation Leads to Success
While the GHA strain of B. bassiana is effective against some
lepidopteran pests—including diamondback moth—in the field, vegetable
crop damage typically results from the feeding activities of several
caterpillar pest species. Manufacturers of conventional pesticides, however,
are often reluctant to research new controls for these pests because their
hosts are considered to be minor crops and therefore offer limited market
potential.
It was through a cooperative research and development agreement between ARS and
Mycotech Corporation of Butte, Montana, that spores of Beauveria strain
GHA came to be incorporated in two commercial biocontrol products: Mycotrol and
BotaniGard. These products grew out of joint efforts to exploit a
Beauveria strain first discovered by Vandenberg over two decades ago.
Now with ARS at the U.S. Plant, Soil, and Nutrition Laboratory at Ithaca, New
York, Vandenberg collected the GHA strain while he was a graduate student at
Oregon State University—Corvallis in 1977. Originally isolated from a
chrysomelid beetle, the GHA strain was tested extensively against grasshoppers
and whiteflies before its commercial development and patenting by Mycotech.
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Entomologist John Vandenberg examines a culture
of BB-1200, discovered to be highly virulent against a broad range
of caterpillar pests.
(K9124-2)
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The commercial products Mycotrol and
BotaniGard are registered for use in the United States, Mexico, and other
countries for biological control of grasshoppers, whiteflies, aphids, thrips,
and diamondback moths. They can be used on many important agricultural crops,
such as cabbage, broccoli, cucumbers, and greenhouse ornamentals.
"The fungus used in the Mycotrol and BotaniGard products could be said to
originate here at Ithaca," says Wraight. That's because Mycotech
scientists discovered the commercial pest-control potential of the GHA strain
after screening many other strains selected from the ARS Collection of
Entomopathogenic Fungal Cultures (ARSEF) in Ithaca. The GHA strain originated
from Vandenberg's culture, originally deposited as ARSEF-201.
Curated by ARS microbiologist Richard A. Humber, the Ithaca collection includes
about 6,200 cultures of fungi. Specimens are stored at very low temperatures in
liquid nitrogen, and many have undiscovered insect biocontrol properties,
Humber says.
The Search for a Better Fungus
"After the discovery of ARSEF-201, the search intensified for a more
highly virulent, broad-spectrum mycoinsecticide effective against a large group
of lepidopteran pests," says Wraight.
Since the registration of Mycotrol in 1995, its use in the United States has
been largely limited to greenhouse production. Larger markets have been slow to
develop, but vegetable production is one area in which demand for
mycoinsecticides is strong. That's partly because of recent passage of the Food
Quality Protection Act, which regulates insecticide use on certain food crops.
During 1998 and early 1999, ARS scientists at Ithaca tested about 50 strains of
B. bassiana and several of Paecilomyces
fumosoroseus—selected from the extensive culture collections of ARS
and Mycotech—against the diamondback moth, fall armyworm, European corn
borer, and corn earworm. They also tested promising strains against the beet
armyworm, black cutworm, cabbage looper, and imported cabbageworm.
"Many of these strains came from the ARSEF collection, which is a
veritable treasure trove of untapped potential biocontrol fungi," says
Wraight. "But we found no single strain with acceptable mass-production
characteristics that was also highly virulent against more than three pest
species."
Better Than the Rest
Then, in June 1999, Wraight and Vandenberg, who head up the ARS
fungal-screening program at Ithaca, discovered the high virulence and
exceptionally broad lepidopteran host range of the BB-1200 strain.
"Mycotech had received this new isolate—originally taken from a
diamondback moth—from a collaborator and passed it on to the ARS
fungal-screening program for routine study as part of our long-standing
cooperative agreement," says Wraight.
Laboratory testing of the BB-1200 strain is continuing at Ithaca, to further
characterize its host range and virulence and to determine its potential for
use as a biological control agent in the United States, says Wraight. Field and
greenhouse experiments are planned that will compare effectiveness of exposing
moths either to direct sprays of fungal spores or to spores sprayed on plant
foliage.
Meanwhile, researchers at Mycotech are investigating industrial-scale mass
production and shelf life of the new fungal strain. Other Mycotech
collaborators are assessing its efficacy against thrips, whiteflies, and other
major insect pests.
Mycotech has applied to the appropriate regulatory agencies to request permits
for limited field testing in the United States. Preliminary field evaluations
against armyworms and diamondback moths are under way in Mexico and Guatemala.
Results of these studies will determine whether further commercial development
is warranted.
The Ithaca lab's role in future development efforts will focus both on field
testing of new BB-1200 formulations and on laboratory studies to discover
reasons for BB-1200's high level of potency against lepidopteran pests. If
successful, this collaboration could lead to registration, production, and use
of one or more new mycoinsecticides to control lepidopteran pests and better
protect the nation's vegetable crops.—By
Hank
Becker, Agricultural Research Service Information Staff.
This research is part of Plant, Microbial, and Insect Genetic Resources,
Genomics, and Genetic Improvement, an ARS National Program (# 301) described on
the World Wide Web at http://www.nps.ars.usda.gov.
Stephen P. Wraight,
John D. Vandenberg, and
Richard A. Humber are with the USDA-ARS
U.S. Plant, Soil, and
Nutrition Laboratory, Tower Rd., Ithaca, NY 14853; phone (607) 255-2458,
fax (607) 255-1132. |
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"New Fungal Strain Spells Trouble for Caterpillar
Pests" was published in the
November 2000
issue of Agricultural Research magazine.
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