For a process so simple in nature--a seed germinates in the soil and grows
into a fruitful plant--getting a healthy crop up and keeping it going can be an
astonishingly complex task.
That's because crop plants have a multitude of enemies, seen and unseen. The
most obvious enemies are the bugs--everything from borers that burrow into a
plant's stem and wreak havoc from the inside out, to grasshoppers whose
appetites have been known to extend to fenceposts and tractor tires.
Perhaps even more baffling are the "new"enemies--viral and fungal
culprits that our farming ancestors could see only in terms of the devastation
they left behind.
Of course, many of our new crop enemies aren't new at all. Potato farmers in
recent years have been again battling Phytophthora infestans, the most
destructive disease of potatoes worldwide. P. infestans is an ancient
foe; it's the same fungus that repeatedly wiped out the Irish potato crop in
the 18th and 19th centuries.
Sometimes the enemy changes just enough to confound control efforts--again, P. infestans comes to mind. Recently, a new, more virulent
strain of late blight, the disease caused by P. infestans, has invaded
the United States.
Agricultural Research Service
scientists at Albany, California, are using the latest biotechnology to study a
new experimental potato hybrid that might carry genes for resistance to the
fungus. If the researchers can pinpoint and clone the gene behind the hybrid's
disease resistance, they intend to transfer it to commercial potato varieties.
Cloning and moving genes are just a few pieces in the big picture of
biocontrol--finding ways to protect plants other than with chemicals. Many
times, nature provides a promising weapon in the form of natural enemies--from
bacteria to wasps--that can do battle against insect pests, crop pathogens,
and weeds, if only we can discover the most effective ways to use those
One of the most destructive crop pests ever to arrive in America is the
silverleaf whitefly, Bemisia argentifolii, also known as biotype B of
sweetpotato whitefly, Bemisia tabaci. This sap-sucking pest first
appeared on poinsettias in Florida greenhouses in 1986. Within just 4 years, it
had spread to dozens of crops in year-round farming regions of Florida, Texas,
California, and Arizona. Losses caused by this tiny insect now run as high as
$500 million per year.
Now a fungus called Beauvaria bassiana has proven highly effective at
stopping the whiteflies. In tests in Weslaco, Texas, ARS scientists showed that
B. bassiana killed up to 90 percent of the immature pests in small
vegetable plots. Today B. bassiana is available commercially in a
product called Mycotrol, the result of a cooperative research and development
agreement between ARS and Mycotech Corp. of Butte, Montana.
In this issue, you'll read how ARS scientists across the country are pitting
their ingenuity against crop pests. In North Carolina, the focus is on
Cercospora fungus, which attacks a wide range of crops from corn to
soybeans. ARS scientists have found that Cercospora carries around a
vital internal defense--a gene that protects the fungus from its own poison.
Those scientists are now pursuing whether that protective gene can be put to
work in crop plants.
You'll also read about ARS researchers in California who've come up with one
of the most unusual defensive maneuvers of all--actually flinging beneficial
insects into fields aboard lightweight disks that degrade naturally in rain or
irrigation water to unload their predacious passengers.
The battle to protect crops without chemicals has taken researchers down
roads undreamed of only a few decades ago. One of the biggest challenges of
pitting beneficial insects against crop pests has been producing great enough
numbers of the beneficials.
Key to these efforts is a diet that will sustain and nourish beneficials,
such as the Edovum puttleri parasitic wasps that attack Colorado potato
beetles. ARS scientists in Colorado have cooked up an artificial diet that
mimics the potato beetle eggs that are the favored snack of Edovum wasps
and their offspring.
A special ingredient of that diet is hemolymph--insect blood. The ARS
scientists are now searching for a cheap, off-the-shelf substitute for
hemolymph, which harbors critical substances that trigger the wasp larvae's
metamorphosis into adult insects.
If the scientists succeed, the benefits could be tremendous, both for
farmers and the environment. In trials where 2,000 Edovum wasps were
released weekly in eggplant fields, growers only had to spray chemicals 4 times
during the growing season to combat potato beetles--down from the average 14
"Chef to the bugs"was probably not on any ARS researcher's
original list of career goals. But it's this kind of innovative approach to
biocontrol-based crop protection that, in the long run, is going to ensure that
all of us (and others around the world) have enough to eat.
Sandy Miller Hays
"Forum" was published in the August 1998
issue of Agricultural Research magazine. Click here to see this
issue's table of contents.