At an ARS experimental plot near Weslaco, Texas, technician
Joel Garza applies a whitefly-killing fungus, Beauveria bassiana, to
Whitefly Fungus on Its Way to
A natural fungus that kills sweet potato whiteflies could start providing
relief this fall lo growers of melons, cucumbers, cole crops, tomatoes, and
other vegetables in the Southwest and Florida. Vegetables, citrus, cotton,
alfalfa, and other crops have been ravaged by a new whitefly biotype.
With the fungus, vegetable growers may be able to control whiteflies with
less reliance on chemical insecticide, says entomologist Raymond I. Carruthers.
He is with USDA's Agricultural Research Service in Weslaco, Texas.
In 1992, Carruthers began evaluating 40 fungus strains under a cooper-alive
research and development agreement, or CRADA, with Mycotech Corp. of Butte,
Montana. Lab and field tests point to "GHA," a Mycotech strain of
Beauveria bassiana, as the most promising first candidate for
Carruthers and Mycotech entomologist Steven Wraight conducted tests at
Weslaco's Subtropical Agricultural Research Laboratory. Carruthers heads the
lab's Biological Control of Pests Research Unit. In spring and fall of 1994,
the GHA fungus killed up to 90 percent of immature white-flies in small field
plots of cantaloupe, cucumber, and tomato.
Many B. bassiana strains have been isolated from soils and insects
around the world. For whiteflies, Mycotech plans to market GHA in a wettable
powder, as Mycotrol-WP. The company has other GHA formulations for
grasshoppers, Mormon crickets, and locusts.
"Originally," says Mycotech vice president Clifford Bradley,
"we had testedand planned to registerthe GHA fungus against
grasshoppers. We spent $500,000 on toxicology tests on its safety to people and
the environment. Luckily, the same strain consistently kills whiteflies."
In March 1995, the U.S. Environmental Protection Agency approved commercial
use of Mycotrol. Supplies will be limited until a larger production plant goes
on line as planned next year, Bradley adds.
To spray Mycotrol-WP, farmers would mix the powder with water and a welling
agent that helps fungus spores stick to leaves.
When the spores touch a whitefly, they germinate, releasing natural
chemicals that poke holes through its skin. Fungi invade and release enzymes
that dissolve the insect's fat reserves. Fungal cells feed on this material.
The insect soon stops eating, weakens, and dies a few days later,
Beauveria-infected whiteflies look like brownish bits of rust.
First found in Florida, biotype B of sweet potato whitefly, also called the
silverleaf whitefly, began tormenting American farmers in 1986.
The insect attacks hundreds of plants, including dozens of field crops and
ornamentals. It sucks juices from leaves, sapping a plant's vitality. It
transmits viruses and resists insecticides. Spending much of its time on leaf
bottoms, it is partly shielded from insecticide. Biotype B is prolific and can
breed all year where mild climate allows fall- and winter-planted vegetables to
bracket the summer season of plants like cotton. Carruthers has seen whitefly
densities as high as 500 per square centimeter. "In the air over a heavily
infested field, whiteflies look like aerial plankton," he says.
Huge losses -- in crop value, sales, employment, and other indirect
lossesare blamed on the whitefly. Arizona, California, Florida, and Texas
have the worst damage. In California's Imperial Valley, for example, county
officials charge whiteflies with annual losses that averaged $320 million and
more than 5,000 jobs from 1991 through 1993.
In 1992, scientists at ARS. other agencies, and universities began a
coordinated attack plan. [See "Get The Whitefly SwattersFast!"
Agriculture Research, November 1992, pps. 4-13.] Carruthers and Wraight
began lab bioassays that year with 40 Beauveria and Paecilomyces
strains. Their main questions: Which strains killed whiteflies most
consistently and quickly? Which ones were hardiest? Which multiplied fastest?
Meanwhile, Mycotech scientists determined which strains the company could
most economically mass-produce at high quality.
With the best candidates from their lab bioassays, Carruthers and Wraight
then ran outdoor tests in plots about 8 rows wide and 30 feet long. "We
sprayed live fungus spores mixed with water and a wetting agent,"
The fungus performed as well as or better than insecticide. It consistently
reduced numbers of nymphsimmature whitefliesby 80 to 90 percent or
"We think most growers may need to use insecticide to knock down the
first whitefly populations infesting spring-planted melons and other
vegetables," Carruthers says. "Then they would spray just the fungus
about every week or so, depending on how severe the infestation is."
The fungus is undergoing larger field tests this year in Arizona,
California, and Texas. The primary aim is to refine integrated pest management
strategies for using it on vegetable crops. IPM doesn't always eliminate
chemical pesticide, but it can dramatically reduce the number of applications.
In an ARS lab test at Weslaco, Texas, insect pathologist
Stephen Wraight sprays fungal pathogens on immature whiteflies.
To help adjust IPM strategies, Weslaco scientists are using computers to
simulate life cycles of the pest and its natural enemies. Will spraying fungus
instead of insecticide leave fields with larger natural populations of whitefly
enemies such as parasitic wasps? "So far, small field studies at Weslaco
show the fungus has little effect on field populations of biocontrol
insects," Carruthers says. "We'll examine this more closely."
Scientists are also combining fungus sprays and a biocontrol-release tactic
called augmentation in which quantities of a natural enemy of a crop pest are
introduced into an area. In one test, begun this spring in Parker, Arizona,
they will release 100,000 to 200,000 Serangium parcesetosum beetles in
commercial cantaloupe and honeydew melon fields. They're also spraying fungus.
Insecticide will be a last resort.
USDA's Animal and Plant Health Inspection Service is conducting the Parker
test in cooperation with the Arizona Cotton Research and Protection Council,
ARS, and Mycotech. "Besides finding out if this can control whiteflies in
melon fields, we want to see if it can reduce the number of whiteflies
switching to nearby cotton soon after the melon harvest," says Robert
In Phoenix, Arizona, Staten directs APHIS' Methods Development Center, which
is lab-rearing the beetles. Their ancestorsfrom Indiawere collected
by Lawrence Lacey and Alan Kirk at ARS' European Biocontrol Research Laboratory
in Montpellier, France, and colleagues.
At Weslaco, scientists will investigate why the fungus so far has killed
more whiteflies on some varieties of cotton than on others. Tests using about a
half-dozen cotton varieties will be run by scientists at the Weslaco lab,
Mycotech, and ARS' Area-wide Pest Management Research Unit in College Station,
"We think this fungus has wide-ranging potential," Carruthers
notes, "and some other fungi may be as good or better."
One is a strain of Paecilomyces fumosoroseus. Carruthers and Wraight
included it in bioassays after it caused a natural epidemic in whiteflies in
Texas broccoli fields. And ARS researchers in West Virginia and New York are
cooperating with Mycotech and university scientists to see if the Mycotrol
fungus can control Russian wheat aphid and pear psylla. By Jim De
Agricultural Research Center, 2413 East Highway 83, Bldg. 200, Weslaco TX
78596; phone (956) 447-6301, fax (956) 447-6345.
"Whitefly Fungus on Its Way to Growers" was
published in the May
1995 issue of Agricultural Research magazine.