The Whitefly Plan: A Five-Year Update
A one-sixteenth-inch long Silverleaf whitefly, Bemisia argentifolii.
In 1992, scientists with the U.S. Department
of Agriculture, universities, state departments of agriculture, and
industry adopted a national 5-year plan of research and action against the
silverleaf whitefly, Bemisia argentifolii. This millimeter-long insect,
also known as biotype B of sweetpotato whitefly, B. tabaci, has left a
multibillion-dollar dent in U.S. agriculture.
What have scientists delivered to help growers?
"Several new technologies are in growers' hands, and a lot of new
possibilities have opened up," says Robert M. Faust. He is the
Agricultural Research Service's national
program leader for field and horticultural crop entomology at Beltsville,
Maryland. "Crop and related economic damage have been reduced
somewhat," Faust says. "But big challenges remain."
It is easy to see the contrast between silvery leaves and netted veins of sugar
pumpkin infested with silverleaf whiteflies (foreground) and the darker green,
normal leaf behind.
In the United States, the white sap-sucking insect first appeared on
poinsettias in Florida greenhouses in 1986. It spread quickly. Many scientists
and growers believed they recognized the culprit as the sweetpotato whitefly,
known in this country for a century. But the new pest attacked more crops,
reproduced more rapidly, inflicted more damage, and seemed more resistant to
By 1990, it had spread to dozens of crops in vital, year-round farming
regions of Florida, Texas, California, and Arizona. Losses, roughly $100 to
$500 million a year, have probably reached several billion dollars since then.
There isn't room here to summarize all the important contributions of
scientists through the research and action plan. But a sampling suggests the
scope of their achievements in helping growers get new technology to cope with
A Spreading Contagion
Along with the new whitefly's appearance in Florida, puzzling and
devastating viruses, plant disorders, and diseases began rising. One disorder,
tomato irregular ripening, makes the fruit worthless. But since most commercial
tomatoes are picked green, the problem often wasn't noticed until buyers
discovered the fruit's distorted, incomplete ripening.
Another disorder, not seen before, was marked by silver-colored streaks and
blotches on leaves of squash and other plants. Called squash silverleaf, it
often affected entire fields.
In early studies, entomologists Raymond Yokomi, Kim Hoelmer, and Lance
Osborne proved that only nymphsan immature stageof the new pest
could produce the symptoms. The adult insect could not. Nor could nymphs or
adults of the familiar strain of sweetpotato whitefly.
Whiteflies proliferate on cotton plants near Blythe, California.
"The powerful systemic nature of this and similar disorders has helped
stimulate new research on the regulatory mechanisms of plant development,"
says Yokomi. He is with ARS' Crops Pathology and Genetics Research Unit at
Davis, California. At the time, he and Hoelmer were based at ARS'
Research Laboratory in Orlando, Florida. The studies also confirmed why
squash silverleaf is now recognized worldwide as a sign of the new pest.
In 1995, the disorder even lent its name to the new insect. Thomas Perring
and Thomas Bellows at the University of California (UC) Riverside identified
the pest as a new species, B. argentifolii, and named it
But the insect's identity is still in some doubt. Some scientists conclude
that it is one of many, perhaps hundreds, of strains of a B. tabaci
species complexand that its important genetic distinctions are only
beginning to be revealed. What is clear is that its genetics endow it with
capabilities that frustrate growers and scientists alike.
Silverleaf whiteflies wreak havoc simply by feeding on leaves and stems.
Worse yet, they are prodigious spreaders of plant viruses.
Virus particles wind up in a whitefly's saliva if it feeds on an infected
plant. When the insect moves to healthy plantsin the same field or miles
awayso does the virus.
Many viruses these insects transmit have not been seen in this country
before. At ARS laboratories in Salinas, California, plant pathologists James
Duffus and Gail Wisleralong with other ARS colleaguesare unlocking
secrets about the viruses and the whiteflies. They'll use the findings to build
strategies for protecting crops.
Plant pathologist Gail Wisler examines dot blots of nonradioactive probes that
help identify both tomato infectious chlorosis and cucurbit yellow stunting
disorder that are spread by whiteflies.
Lettuce chlorosis is among the newly emerging viruses carried by silverleaf
whiteflies. It afflicts lettuce and sugarbeets in California and Arizona.
Another, tomato chlorosis, attacks Florida tomato crops. These pathogens, known
as closteroviruses, typically don't kill plants. But they reduce yield and can
Closteroviruses can escape accurate diagnosis, partly because symptoms of
one virus can resemble those of another. Or a virus-infected plant can look
identical to one with a different problem, such as a nutrient shortage. To
speed accurate detection, Salinas researchers and a team led by Bryce Falk at
UC Davis are developing diagnostic tests. When ready, these could be used at
labs that scrutinize sickly plants sent by worried growers.
The tests could also help researchers detect virus-infected cropsand
weeds that can be viral reservoirs. Gary Simone and Jenny Knight at the
University of Florida are trying the Salinas lab's new test for tomato
chlorosis. To reveal susceptibility to a different virus, lettuce chlorosis,
Rebecca Creamer of UC Riverside has used other diagnostic tests, in
collaborative studies with ARS entomologist Steven Castle at Brawley,
ARS experiments at Salinas are also determining how longonce it's been
picked up by a silverleaf whiteflya virus remains able to infect other
plants. Lettuce chlorosis virus stays active for 4 days in whitefly saliva;
tomato chlorosis, only 2 or 3 days. "These basic biological
characteristics," says Wisler, "are simple yet important clues for
diagnosing the new viruses."
Related work has exposed silverleaf whitefly as a prime culprit in spreading
pathogens belonging to another virus family, the geminiviruses. Each
geminivirus particle has twin compartments sharing one circular,
single-stranded piece of viral DNA.
One geminivirus, tomato mottle, has appeared in every major tomato-producing
region of Florida, say Ernest Hiebert and Jane Polston, who are at the
University of Florida.
Another, tomato yellow leaf curl, has clobbered tomatoes in the Dominican
Republic and Cuba. Hiebert's team and Douglas Maxwell's group at the University
of Wisconsin are waging war on this virus. Robert Gilbertson of UC Davis is
probing other new geminiviruses in Mexico and South America, as well.
In Salinas, California, where plant virus transmission by whiteflies is being
studied, postdoctoral researcher Ruhui Li adjusts a video display showing
infectious chlorosis virus RNA.
Judith Brown at the University of Arizona is pursuing geminiviruses of
vegetables and cotton in Mexico along with Arizona, Texas, the Caribbean basin,
and Central America. She is producing databases with DNA sequences of the
pathogens and their whitefly vectors.
"It's all part of trying to know who and where the enemy is," says
Brown. She collaborates with the Biological Control Center of USDA's Animal and
Plant Health Inspection Service (APHIS) in Mission, Texas; other USDA agencies;
and scientists at Texas A&M and other universities.
"Whitefly-transmitted geminiviruses are emerging pathogens with
enormous impact in many areas of the world," Brown says. "I've often
seen geminivirus spread from a few plants to an entire field within a couple of
As for her whitefly genetics studies, she says, "A given whitefly
population may have an important genetic difference that a parasitic wasp can
detect--but human eyes can't. Knowing this difference could help biocontrol
workers select the most appropriate parasites for field releases."
Sticking It to Cotton
Whiteflies cost cotton growers money, even after the crop is harvested and
trucked to the gin. The insects survive by sucking the sugary sap from plants,
and they excrete a sticky waste called honeydew.
Since whitefly densities on leaves may reach thousands per square inch,
there are plenty of opportunities for microscopic droplets of honeydew to fall
onto open bolls of cotton fibers. The sticky fibers gum up high-speed machinery
in cotton gins and textile mills. Processors lose money in down time and
cleaning costs. They pay growers much less for sticky cotton, and the problem
extends to the export market.
Sticky whitefly residue on cotton fiber strands causes processing problems and
reduces grower prices.
"The industry uses reliable methods that evaluate several fiber
qualities of every bale of cotton produced each year, in a matter of seconds
per bale," says Frank Carter, who is with the National Cotton Council in
Memphis, Tennessee. "But we don't have such a tool to rapidly measure
stickiness of every bale. As a result, we may unintentionally ship sticky bales
to our overseas customers. While we work with those processors to minimize
their production problems, we have to wonder about customer loyalty."
Next year, growers may be using commercial enzymes to dissolve the
The tactic began taking shape a few years ago in Phoenix, Arizona. Plant
physiologist Donald Hendrix at ARS' Western Cotton Research Laboratory
pinpointed the basic chemistry of more than 30 complex sugars, called
oligosaccharides, in whitefly honeydew. He and colleagues searched chemical
catalogs for enzymes that might break them down. None worked well.
"Then we obtained one from Genencor International [of Elkhart, Indiana]
and were pleased with the results," says Hendrix. "Their chemists
suggested another enzyme that turned out even better." It cut stickiness
80 percent in tests at ARS'
Research Station at Clemson, South Carolina.
In field tests, the Arizona researchers experimented with spray nozzles
attached to cotton picking machines. But some bolls got too much spray, some
In October, ARS scientists tested a different approach with 15 tons of
freshly harvested cotton. They sprayed 1 to 3 pounds of the Genencor enzyme per
1,000 pounds of cotton, using equipment first developed by Wayne Coates of the
University of Arizona. Some treatments reduced stickiness 90 to 100 percent.
Using ultraviolet light fluorescent dye, plant physiologist Donald Hendrix
identifies enzyme spray coverage on cotton. The spray shows up as pink dots in
In this approach, growers would apply the enzyme before shipping the crop.
"This would be fine with most growers. They can wait up to 4 weeks while
the enzyme breaks down the saccharides," Hendrix says.
"The enzyme is very effective andbest of allvery
environmentally friendly," says O.J. Lantero of Genencor. "It's a
protein that poses no threat to workers and can't contaminate soil or water
After a final analysis this summer by ARS scientists in South Carolina,
growers may have guidelines for the 1998 crop, says Tom Henneberry, director of
the Phoenix laboratory.
Whitefly Count Tells When To Begin Control
How can a grower know when to strike against the whitefly?
"Growers want to hold off as long as possible," Henneberry says,
"so they don't hasten development of insect resistance or waste money on
chemicals they don't need. But if they wait too long, the insects may inflict
In cottonfields, "turning leaves over and inspecting for adult insects
is the most reliable and cheapest method we have for determining whitefly
densities," says entomologist Steven Naranjo at the Phoenix lab.
Plant physiologist Donald Hendrix (left) and entomologist Thomas Henneberry
compare samples of sticky cotton (left) and clean cotton.
The sampling procedure he designed takes only about 10 minutes per field.
It's now used in Arizona, California, Texas, and in other countries including
Mexico, Israel, Pakistan, and Egypt. ARS researchers tested and implemented it
in cooperation with University of Arizona scientists Peter Ellsworth and
Sampling methods and thresholds are still needed for other crops, Henneberry
Getting Around Resistance
"When only one or a few insecticides are used over time, some insects
may prove to be unaffected," says David Akey, ARS entomologist at Phoenix.
"It takes only a few resistant whitefly pairs out of millions of
susceptible ones to negate years of research development." Silverleaf
whiteflies have this capability to an unusual degree, partly because they can
produce a new generation about every 3 weeks.
But Nick Toscano and Nilima Prabhaker Castle of the University of
California, Riverside, and ARS' Steve Castle lead a project that is helping
growers delay this resistance.
For the project, yellow sticky cards are sprayed with one or a combination
of insecticides growers use. Knowing how many whiteflies are killed by each
treatment lets scientists monitor changes in chemical resistance over time.
They conduct the monitoring biweekly in three California valleysImperial,
Palo Verde, and San Joaquinand report the mortality data via newsletters,
news media, and the Internet.
Chemical engineer Don Brushwood prepares to insert a cotton sample, called a
web, into an experimental sticky cotton thermodetector. Developed at Clemson,
south Carolina, the device can measure stickiness in up to 20 webs an hour, for
120 to 160 cotton samples in an 8-hour day.
As a result, growers and pest control advisers can quickly respond with more
effective strategies. This includes avoiding spraying the same insecticide more
than twice consecutively and, instead, rotating to a different insecticide
classfor example, from a pyrethroid to an insect growth regulator.
In 1996, Imperial County adopted a new trap for whitefly monitoring.
Chang-Chi Chu of ARS' Phoenix lab developed and tested it in cooperation with
ARS colleagues Henneberry and Allen Cohen and Kai Umeda of the University of
Arizona. ARS is planning to patent the technology.
The new trap allows more accurate population estimates, largely because it
doesn't get overloaded with massive numbers of whiteflies and traps only the
adults. And since it isn't sticky, it can be reused, so it's more economical.
Breeding is a traditional tool for reducing crop loss from pests. Scientists
have identified varieties or lines of cotton, alfalfa, tomato, soybean, and
other crops on which whiteflies inflict less damage. But it takes years for
improved breeding lines to reach growers as commercial varieties.
To determine whitefly population density in a cottonfield, entomologist Steve
Narango inspects the undersides of plant leaves.
Alfalfa lines with some whitefly resistance have been developed by Larry
Teuber at UC Davis. Imperial Valley growers are helping fund the alfalfa
studies at UC's Desert Research and Extension Center in Holtville.
The earliest cotton harvested in the United States for the past 2 years was
a new commercial variety that offers some whitefly protection. The Texas 121
variety is derived from lines developed by Charles Cook at ARS'
Subtropical Agricultural Research
Laboratory in Weslaco, Texas. The plants mature earlier, so they escape
some of the whitefly's late-season buildup in south Texas.
Organophosphates and pyrethroids remain common chemical choices of growers
battling whiteflies. But alliances among growers, scientists, and industry have
widened the options. For example, a federal-state-industry team cooperated to
seek an emergency exemption from the U.S. Environmental Protection Agency (EPA)
allowing use of two insect growth regulators, or IGR's, on Arizona cotton in
1996. [More on IGR's in "Forum" article: click
Whitefly researchers have focused mainly on natural or nature-based
controls, including quite a number of fungi, insects, and plant compounds.
Wasps: Sting Operations at Home and Abroad
ARS' European Biological Control Laboratory in Montpellier, France, has been
the primary source of whitefly natural enemies imported from abroad. From 1992
to 1996, Montpellier entomologist Alan Kirk and insect pathologist Lawrence
Lacey (now with ARS' Yakima
Agricultural Research Laboratory in Wapato, Washington) explored 25
countries in Africa, Asia, Europe, and South America. They sent U.S. colleagues
over 100 shipments of more than 30 species of parasitic and predatory insects
and hundreds of isolates of whitefly-killing fungi.
Nearly all the insect shipments went first to APHIS' Biological Control
Center in Mission, Texas.
Since 1993, the APHIS workers have reared 46 species or populations of
exotic whitefly parasites and predators. The center has distributed over 28
million beneficial insects to dozens of scientists for lab and field studies.
Hibiscus plants growing in isolation harbor parasitic insects that will be
shipped to whitefly researchers around the country. Biological aide Pat Lasby
logs their progress.
Among the shipments to Mission was a parasitic wasp Kirk and Lacey found in
Spain. The female Eretmocerus wasp deposits an egg under a whitefly
larva. The egg hatches, and the immature wasp feeds on the whitefly, killing
it. Eventually the wasp emerges as an adult and seeks a mate.
In studies, John Goolsby, Matt Ciompernik, Lloyd Wendel, and Don Vacek of
the Mission center and ARS entomologist Walker Jones at Weslaco compared the
Spanish wasp with other exotic and native wasps. The Spanish Eretmocerus
attacked more whiteflies on cantaloupe, kale, and broccoli than did other
parasitic wasps. It was also more tolerant of some pesticides. Jones says this
increases this wasp's potential for situations when insecticide must be used
against other pests.
In 1995, ARS scientist Kirk, Jesusa Legaspi, who is with Texas A&M
University's Research and Extension Center, and Ray Carruthers (now ARS
national program leader for biological control) collected wasps, fungi, and
ladybugs in Thailand, Taiwan, Malaysia, and Indonesia. At Mission, an ARS-APHIS
team evaluated many strains of exotic beneficials on cotton, melons, and
broccoli to determine which strains produced the highest attack rates on each
plant type. APHIS is using the results to plan mass-rearing for field releases.
Exotic Eretmocerus species and strains have been released in many
field trials. APHIS and the UC's Cooperative Extension conducted trials in
spring melon fields in the Imperial Valley. Early-season releases would be a
feasible tool for growers if the wasps become available through commercial
insectaries, says Gregory Simmons of APHIS.
Descendants of Eretmocerus from Spain, India, and Pakistan have
persisted 1 or 2 years after releases near Bakersfield in the San Joaquin
Valley. Charles Pickett of the California Department of Food and Agriculture
and APHIS' John Goolsby and William Abel released the wasps.
With all these wasps to pick from, how can growers know what is the best
six-legged tool for the job in a particular crop?
Hoelmer and Simmons of APHIS found preliminary answers in studies in
California and Arizona. They identified strains of exotic Eretmocerus
and Encarsia wasps that were most prolific in cantaloupe, broccoli, and
alfalfa crops. Mass-rearing and release of standout wasps for field trials is
under way. Wasps that pass muster could join growers' anti-whitefly arsenal.
Fluorescent lighted insectary where lab technicians Arturo Cortez (left), and
John Sears attend to host plants and their whitefly inhabitants.
One complication: Some exotic wasps are very closely related toand
look almost identical tosome native wasps.
"Right now, the only way to know which biocontrol wasp agent is present
is to dissect individual whiteflies and examine each parasite under a
microscope," says ARS entomologist Bruce C. Campbell at ARS' Western
Regional Research Center in Albany, California.
Campbell has identified genetic regions that can distinguish among closely
related wasps. He's working on a field testa few years awaythat
would let scientists quickly check many whiteflies for the presence and
abundance of specific parasites.
Oscar Minkenberg of the University of Arizona showed a native
Eretmocerusfrom Arizona to be valuable in greenhouses. Based on his
early results, some growers began using the wasp in 1993, especially in Europe,
where greenhouse vegetable farming is more common than in this country.
Late in 1995, some of Minkenberg's research funding came from Beneficial
Insectary of Oak Run, California.
"We don't plan to rear this wasp ourselves, because the U.S. market is
not yet big enough to justify it," says Sinthya Penn, the firm's
president. "But at the time, there was no other consistent supply. We just
wanted to be sure the wasp was available so the research could be
Now, three insectaries in Europe are mass-rearing the insect and selling it
there and in the United States.
Predators: Whiteflies on the Menu
Even before imported wasps found U.S. homes, researchers were examining a
different breed of biocontrol: native predators such as
A native predator, this adult Delphastus pusillus beetle feasts on
In Florida in the late 1980's, Hoelmer, Osborne, and Yokomi conducted
studies of Delphastus that led to its commercial development. It is
available from insectaries worldwide, primarily to protect greenhouse crops.
Its use is compatible with parasitic wasps and commercial products made with
oil from seed of the neem tree, Hoelmer says.
In Phoenix, meanwhile, ARS entomologist James Hagler is biochemically
pumping the stomachs of native predators to find out what they eat. He has
developed several quick tests called predator gut content immunoassays. Each
assay uses a custom-built molecule that binds only to a specific
proteinin one case, a protein in whitefly eggs. So it reveals whether the
predator recently had a meal of whitefly eggs.
The same technology is used in home pregnancy test kits and other medical
applications. Hagler and colleagues are first to field-test this approach for
insect predators. Other researchers have adopted it, and APHIS experts are
exploring using it to screen predators of whiteflies and other insect targets.
Studies by Hagler and Naranjo turned up a surprise: the native collops
beetle, Collops vittatus. Not readily abundant in cottonfields, it's
been overlooked as a potential biocontrol. But almost two-thirds of the beetles
tested positive for whitefly eggs.
A predator from India also shows a hearty appetite for whitefly eggs. In an
ARS lab test at Weslaco, immature Serangium parcesetosum beetles all but
ignored eggs of corn earworm and tobacco hornworm. They chowed down whiteflies
instead. Each beetle ate about 600 whitefly eggs and nymphs in 24 hours,
according to Texas A&M's Jesusa and Benjamin Legaspi.
In March 1995, the EPA approved commercial use of Mycotrol, a product made
with a whitefly-killing fungus, Beauveria bassiana. The product grew
from a cooperative research and development agreement (CRADA) between ARS and
Mycotech Corp. of Butte, Montana.
Mycotrol-WP is a powder containing the fungus. Farmers spray it in a mix
with water and a wetting agent. The fungi invade the whitefly and destroy its
A tiny pirate bug, Oris insidiosus, feeds on whitefly nymphs.
In Weslaco, ARS entomologist Ray Carruthers and Stephen Wraight, then with
Mycotech, conducted lab trials that identified the B. bassiana strain as
a candidate for commercialization. In 1994, this Mycotrol strain killed up to
90 percent of immature whiteflies in small vegetable plots. EPA's registration
opened the way to large-scale tests by Mycotech, ARS, APHIS, land-grant
universities, and growers. A Mycotech factory that can produce enough fungus to
treat 500,000 acres a year was scheduled to go on line last month.
Strains of another fungus, Paecilomyces fumosoroseus, also perform
well against whiteflies. Developing a more economical mass-production technique
for it is the goal of another CRADA with Mycotech, in studies led by ARS
researchers at Weslaco and ARS' National Center
for Agricultural Utilization Research in Peoria, Illinois. The new
technique uses liquid fermentation, in which Paecilomyces forms
yeastlike cells called blastospores.
Lacey, Kirk, and David Akey of ARS experimented with using mist irrigation
to apply blastospores of U.S. strains of Paecilomyces in greenhouses.
The fungi killed up to 80 percent of whiteflies on heavily infested tomato and
In experiments at the University of Florida, entomologist Lance Osborne
discovered that a native strain of P. fumosoroseus is highly effective
at killing whiteflies and also kills spider mites, aphids, and diamondback
moths. Under a license from the university, Thermo Trilogy Corp. of Columbia,
Maryland, incorporated this fungus into a commercial product. It will soon be
sold in Europe to control whiteflies and other pests in greenhouses. Thermo
Trilogy has applied to EPA to register the fungus for use in the United States.
Can fungi that kill whiteflies also kill helpful insects? Unfortunately,
they may. To assess the extent of possible damage to beneficials, insect
pathologist Tad Poprawski of Texas A&M University and ARS entomologist
Walker Jones ran cooperative studies at Weslaco with APHIS' Mission facility.
The scientists examined effects of Paecilomyces and Beauveria on
more than two dozen beneficial insects. Results suggest an acceptable level of
compatibility exists between the fungi and most beneficials.
In an ARS lab test at Weslaco, Texas, insect pathologist Stephen Wraight sprays
fungal pathogens on immature whiteflies.
One promising duo is Beauveria and an Eretmocerus wasp native
to south Texas. The researchers' findings suggest that spraying
Beauveria on crops a few days after releasing wasps could increase total
whitefly mortality, because the fungus would kill many whiteflies that escaped
the wasps. Earlier, the scientists found that the fungus doesn't invade a
whitefly already doomed by a developing wasp parasite. So a parasite can safely
develop to adulthood and emerge to seek a mate, spelling more trouble for more
In another cooperative study with APHIS, Poprawski and Wraight controlled
whiteflies in a year-round rotation of broccoli, fall cucumbers, spring
cantaloupes, and cotton. They used Beauveria, parasitic and predatory
insects, and (on the melons) one early-season application of the insecticide
imidicloprid. With this approach, crops wouldn't need several costly sprays of
pyrethroids late in the season, say the scientists.
Scientists also want to learn if beneficial fungi can be harmed by chemicals
used to suppress crop-damaging fungi. In tests on cantaloupe plots, Poprawski
and Wraight found strong clues to which fungicides can be usedand
Chemical Defense Plants
Under a CRADA, ARS evaluated a mixture that Morse Enterprises Limited, Inc.,
of Miami, Florida, designed to boost tomato yield. Besides nutrients, the mix
contains alpha keto acids. A plant can use these acids more readily than the
amino acids from which they are made.
"We had found that the mix also boosted plants' natural defenses,"
says Richard Mayer, director of ARS'
Research Laboratory in Orlando, Florida.
Plants make defense proteins and chemicals when being fed on by whiteflies,
but their normal response is slow and weak. In tests, Mayer and colleagues
sprayed the mixture on tomato plants. They then recommended improvements to the
mixture's formula to further boost the defense substances.
At an ARS experimental plot near Weslaco, Texas, technician Joel Garza applies
a whitefly-killing fungus, Beauveria bassiana, to vegetable crops.
Morse plans to market the mixture in 1997 under the KeyPlex product line. In
other studies, Mayer, biochemist Hamed Doostdar, and entomologist Moshe Inbar
are following clues that silverleaf whiteflies may manipulate a plant's
chemical defenses for their own benefit.
An extract from neem tree seed oil is the key ingredient in three new
biopesticidesTrilogy, Triact, and Rose Defensedeveloped under a
CRADA between ARS and Thermo Trilogy Corp.
In ARS studies at Beltsville led by James Locke, neem seed oil killed
whiteflies and other pests. The oil also protects plants against some fungal
diseases, including powdery mildew and black spot, says Locke. He is in the
Nursery Plants Research Unit of the U.S. National Arboretum.
Other plant defenses with antiwhitefly potential include extracts of leaves
of Nicotiana gossei, a wild Australian relative of tobacco. Leaves of
the plant turn out sucrose esters--sugar molecules with attached fatty
acidsthat kill pests. The extracts killed whiteflies, aphids, pear
psyllas, and other insects in tests at the Floral and Nursery Plants Research
Unit and other locations.
Industry is also looking at synthetic sucrose esters. These were developed
by chemist O.T. Chortyk (retired) at ARS' Richard B. Russell Agricultural
Research Center in Athens, Georgia. Firms testing synthetic esters against
whiteflies or other pests include Rohm and Haas Co. of Spring House,
Pennsylvania; Fuller System, Inc., of Woburn, Massachusetts; and Griffin Corp.
of Valdosta, Georgia.
"All these developments are encouraging, and we may have turned the
corner on this pest," says national program leader Faust. "But we are
far from finished. We need to strengthen our collaboration with growers and
industry so more scientific knowledge and effective strategies can be put in
place." -- By Jim De Quattro, Dennis Senft, and Marcia Wood,
ARS Information Staff.