2-Plants: Background information about rootworm-resistant Bt-corn
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-------------------------------- GENET-news --------------------------------
TITLE: Operation rootworm
SOURCE: Farm Journal, by Andrew Burchett
edited and sent by Agnet, Canada
DATE: November 1, 2001
------------------ archive: http://www.gene.ch/genet.html ------------------
Despite bad publicity and huge costs to the food industry following the
StarLink debacle, genetically enhanced corn may soon earn its keep. The
much-anticipated release of a Bt corn variety that controls corn rootworm
may happen in time for limited 2002 planting, pending regulatory approval
in the United States and Japan. Every year corn rootworm gobbles a billion
dollars of farm profits through yield loss or control cost, reports USDA.
That's a big round number for such a little larva, and it's growing as the
western corn rootworm (Diabrotica virgifera virgifera) adapts to foil corn-
soybean rotations that once starved generations that hatched in soybeans
every other year.
"We started seeing this variant of corn rootworm in 1993," explains John
McFerson, Corn Technology Development manager for Monsanto. Each year, the
resistant beetles appear another 150 miles west and 50 miles east from hot
spots in Illinois and Indiana. They may be in Iowa. The devilish pests
evolve to hatch in corn, mature, mate and move to soybean fields to lay
eggs so when farmers rotate from beans into corn, the next generation
hatches in corn.
Northern corn rootworm (Diabrotica barberi) has started beating the
rotation strategy with extended diapause, or eggs that hatch a year later
when field rotations return to corn. That's a huge worry for central Corn
Belt growers. Many don't have the equipment to apply the various soil
insecticides used for years by western Corn Belt producers to control
rootworm in continuous corn.
The current leader in Bt corn technology is Monsanto, with the Cry3B(b)
protein, which destroys the mid-gut lining of the voracious larva, killing
it or repelling it until it starves. A joint effort by Dow AgroSciences and
Pioneer HiBred International is a year or so behind, using a pair of
proteins from the Bt strain PS149B1. If test plot data are an indicator,
both products give better, more consistent control than available soil-
Assuming that a root rating of 3.0 (on a scale of 1.0 to 6.0) is the
economic threshold at which it pays to use corn rootworm control,
Monsanto's data shows Cry3B(b) is 100% consistent in keeping root damage
under a 3.0 rating, based on academic trials at 21 locations this year. The
average root damage ratings for corn containing Cry3B(b) was 1.7, where
untreated corn averaged a 3.9. Root damage to corn in those plots treated
with leading insecticides averaged 2.3 to 2.9.
Farm feedback. It's not tough to sell farmers on corn rootworm control in
seed. "I've seen some of the Bt corn in test plots and it looks every bit
as good as what is treated with granular insecticide," says Yuma County,
Colo., farmer Steve Sears. His fields of continuous corn and sandy loam
soils provide perfect habitat for corn rootworm. "Putting control in the
plant gives season-long control no matter when the corn is planted or eggs
hatch." Sears is ready to cut back on insecticide use for environmental
reasons, as well as his own health.
Bill Northey of Spirit Lake, Iowa, has had problems with northern corn
rootworm in recent years, and he doesn't want to buy insecticide
application equipment. "It would be a lot easier if control was in the
seed," he says. "I have one field where extended diapause is a bigger
problem than others. I'd like to plant Bt varieties there." For producers
like Sears and Northey, Bt corn that controls rootworm is worth more than
Bt corn for corn borer. "Corn borers are not always around in sufficient
numbers to justify cost," says John Babcock, field development biologist
for Dow AgroSciences. "The rewards of corn rootworm control will be more
And the Environmental Protection Agency has reason to look favorably on the
new Bt corn. It could greatly reduce the insecticide that's used on 20% to
25% of corn acres each year, says Monsanto's McFerson. The organophosphate
and carbamate active ingredients used in some insecticides are on the EPA's
Food Quality Protection Act hit list, and farmers don't like to handle
them. Environmental and handler safety of Bt technology is a big plus, says
Kay Kuenker, global marketing specialist for traits and germplasm licensing
at Dow AgroSciences. She sees potential for the new Bt technology to get
favorable response from environmental groups. For a product that seems to
have everything going for it, there is uncertainty.
Although Monsanto has the new trait available in several commercial
hybrids, they are still awaiting full U.S. regulatory approval. Acceptance
by export customers is just as important. Monsanto's requirement of
Japanese approval--even before selling limited quantities to growers the
first year--is self-imposed. Losing an extra year of sales is worth
avoiding the risk of growers' being stuck with a product the market doesn't
want. Hence the wait for Japan's approval, anticipated in time for a 2002
product launch. European import authorization is not expected anytime soon.
Reeling in resistance. Concerns about resistance management have also
The Bt corn for corn borer control recently underwent an extended comment
period as part of its re-registration process. Any changes in registration
requirements could affect corn containing Cry3B(b) and other new Bt
products. "We anticipate a lot of these products will be stacked with the
corn borer product," says Paula Davis, Pioneer's technology specialist
manager. "Consistency [in resistance management plans] will be important."
The goal of insect resistance management (IRM) is maintaining the
durability of insect control tools for growers. In addition to technical
considerations, developing a single refuge plot requirement that works for
both corn borer and rootworm Bt products is an industry goal in order to
avoid confusion and increase compliance. That's reflected in the fact that
Monsanto's interim proposed refuge plan for YieldGard Rootworm is identical
to that of YieldGard Corn Borer. It recommends a 20% refuge of non-Bt corn
within half a mile of Bt varieties.
Finding a single solution for two species can be a challenge. "Corn
rootworm beetles are generally thought to not travel long distances before
mating," says Babcock. "That's the major criticism of the 80-20 plan."
Other concerns have been expressed by NCR-46, a committee of research and
Extension entomologists considered national authorities on corn rootworm.
Among the committee's concerns is the fact that Cry3B(b) expressed in
Monsanto's transgenic corn is a lower dose for the corn rootworm than
Cry1A(b) is for the European corn borer.
The apparent survival of some corn rootworms to adulthood on corn roots
expressing Cry3B(b) could be a problem if the adult beetles are fit enough
to reproduce and pass on resistance traits. The committee suggests that
using the 80-20 refuge plan as a one-size-fits-all resistance management
solution might not be advisable.
There's more to be learned about the Bt dose and pest biology, says
McFerson. Monsanto continues to work with academic experts to gather
additional data, he adds. "It's far from being an exact science, but we've
been successful with YieldGard Corn Borer and Bollgard cotton," he points
out. Mixed bag. For integrated pest management proponents, the fact that
corn rootworm Bts only hurt corn rootworm and leave non-target species
unharmed is a boon. However, those farmers who buy insecticides primarily
to control corn rootworm also get broader spectrum help with wireworm,
seedcorn maggot and other secondary pests not controlled by Bt corn.
Seed treatments will likely be used to make up the difference, says Kelly
Fleming, Monsanto's global product manager for corn rootworm. "A low level
of seed treatment takes care of secondary pests with little or no effect on
non-target species." Both Monsanto, and the Dow-Pioneer project would like
to stack corn rootworm and corn borer control in a single seed. Dow plans
to offer trait stacking with Cry1F, the Bt protein in the Herculex I brand,
to add control of black cutworm and fall armyworm to that of corn borer and
rootworm. Seed treatment and stacked traits will add something to the cost,
of course. Until products are registered, companies can't share price
information. However, it's understood that prices will have to be
comparable to current insecticide treatments on a per-acre basis.
In the case of Dow, there will be some cannibalization of products such as
its own Lorsban 15G. "This is inevitable with the potential of the new Bt
technology," says Kuenker. "But there will always be a continued fit for
traditional insecticides for IRM and refuge acre requirements."
-------------------------------- GENET-news --------------------------------
TITLE: Stalking the supreme survivor
SOURCE: Farm Industry News, by Gil Gullickson
edited and sent by Agnet, Canada
DATE: October, 2001
------------------ archive: http://www.gene.ch/genet.html ------------------
STALKING THE SUPREME SURVIVOR
If producers of the television show "Survivor” ever run short of
contestants, they can always turn to the lowly corn rootworm. Each year,
this pest costs U.S. farmers $1 billion in lost yields and control
measures. Yet, corn rootworm survives and thrives despite widespread use of
crop rotation and aerially applied and soil insecticides. But soon farmers
should have the best chance they've ever had to bludgeon this bug. Pending
federal approval, Monsanto aims to market Bt hybrids resistant to corn
rootworm in 2002. Dow AgroSciences and Pioneer Hi-Bred International also
are jointly researching a corn rootworm-resistant product that federal
regulators should approve in 2003 or 2004. And Syngenta Seeds also plans to
develop similar transgenic hybrids in several years.
These hybrids control corn rootworm with a Bt protein, Cry3Bb, inserted
into their chromosomes. In biotech jargon, this is called an "event,” and
the protein differs from that used in Bt hybrids resistant to European corn
borer (ECB). Rootworm larvae die when they chomp into the hybrids' roots.
To control corn rootworm, all farmers will need to do is load their
planters with these transgenic seeds and go.
No longer will farmers be limited to corn rootworm insecticides, the
leading chemical control option. Because of their toxicity, insecticides
require special application, calibration and disposal equipment.
Inconsistent corn rootworm control also results. "There are situations
where soil-applied insecticides can and do fail,” says Larry Bledsoe,
Purdue University research and extension entomologist. "Excessively dry or
wet conditions can impact performance.”
Because transgenic seed contains the fatal corn rootworm protein, control
does not hinge upon weather conditions. "They're a more foolproof control
tactic than insecticides,” says John McFerson, Monsanto corn technology
development manager for market development. Insecticides also do little to
curtail corn rootworm numbers. "Under high populations, rootworm larvae
will remove almost all of the root tissue,” Bledsoe says. "When this
happens, few rootworms survive and most starve. "But when you use a soil
insecticide, you create a zone of protection around the center part of the
root system that prevents excessive feeding. As the protected rootball
extends roots into the soil outside the zone, rootworms feed on it. This
can support lots of rootworms.” Because they die when they ingest roots of
resistant hybrids, fewer corn rootworm larvae emerge as adults than when
soil insecticide treatments are used.
The Monsanto transgenic hybrids, which the company will market and license
under the YieldGard Rootworm brand, also give excellent root protection,
McFerson says. In Monsanto tests, root protection for the resistant hybrids
exceeded that of leading soil insecticides, he adds. University tests
concur. "Rootworm kills with the Monsanto event are slightly higher than
what we see with the best insecticides,” says Ken Ostlie, University of
Minnesota extension entomologist. Nor has any yield drag surfaced in three
years of Monsanto tests, McFerson says. For these reasons, corn rootworm-
resistant hybrids may sell faster than cold beer on a sultry summer day.
"It sure makes you drool when you compare them to conventional hybrids
under high rootworm pressure,” says Steve Sodeman, a Trimont, MN, crop
consultant. "Farmers will latch onto them pretty fast.”
Rootworm-resistant corn still faces several hurdles. The United States,
European Union (EU) and Japan have not yet approved Monsanto's event,
Mon863. Environmental, food and feed approval will likely occur early in
2002 in the U.S. and Japan, says Kelly Fleming, Monsanto's corn rootworm
launch team leader. But the EU is not likely to approve the product for
next year. "EU approval is something we are eager to have, but the EU has
not approved any new biotech products since early 1998,” Fleming says.
Thus, farmers and grain merchandisers will have to segregate any YieldGard
Rootworm corn from EU-approved corn.
Some scientists also question the event's impact upon nontarget organisms.
Earthworms may be vulnerable to Cry3Bb endotoxins under stressful
conditions such as drought, says Charles Benbrook, president of Benbrook
Consulting Services, Sand Point, ID. Although U.S. federal regulators may
clear the technology, Cry3Bb's impact upon nontarget organisms may cause
European regulators to reject it. "They take so much more seriously the
consequences of adverse impacts on nontarget species,” says Benbrook, who
submitted comments to the EPA for the Union of Concerned Scientists, a
group critical of ag biotechnology. however, Monsanto studies show that
Cry3Bb activity is specific to corn rootworm. Thus, the risk of nontarget
organism exposure is low, McFerson says.
Benbrook is also concerned that allergen issues that plagued StarLink corn
in 2000 may resurface in transgenic rootworm hybrids. YieldGard Rootworm
corn kills rootworm larvae through its roots, which contain high levels of
Cry3Bb protein. However, the protein also resides in the plant's grain.
With the exception of the protein Cry9c in StarLink corn, Mon863's grain
protein levels are at least 50 times higher than in other Bt events,
Benbrook says. "StarLink caused a lot of problems because of an allergen
issue due to high expression levels in the grain,” Benbrook says. "The
pattern of expression in the Cry3Bb is fairly close to that of StarLink.”
Monsanto has evaluated the allergen potential of Cry3Bb through an
extensive search of public and private databases that contain information
on known protein allergens. This search revealed that the amino acid
sequence of Cry3Bb is not similar to that of known protein allergens,
McFerson says. He adds that the EPA considered expression of the gene in
all corn tissue - grain included - before establishing a Cry3Bb tolerance
exemption last May. This exemption gives EPA's assurance that the corn is
safe for both human and animal consumption.
Federal law prevents companies from pricing a product prior to approval.
But if the added seed cost hovers around the $15/acre cost of soil
insecticides, producers may quickly adopt rootworm-resistant corn. "Most
producers, especially those with continuous corn, incorporate soil
insecticides as a standard practice,” says Mike Gray, University of
Illinois integrated pest management specialist. "If transgenic hybrids are
similar in cost to insecticides, many producers could opt for the
convenience of not having to calibrate their planters for soil
If producers forego other control methods and rely solely upon transgenic
hybrids, resistance could develop, Gray adds. Historically, farmers have
overused effective rootworm control tools, including heptachlor and aldrin
in the 1950s and early 1960s. Resistance to these chemicals was common
across the Corn Belt by the late 1960s. Nebraska farmers who aerially
applied methyl parathion (PenncapM) and carbaryl (Sevin XLR) in the late
1970s faced resistant western corn rootworm strains in the late 1990s.
For years, farmers controlled corn rootworm by rotating corn with soybeans.
Larvae that hatched from eggs laid by beetles in corn the previous year
could not survive in soybeans. Now in east-central Illinois, northern
Indiana and southern Michigan, western corn rootworm beetles lay eggs in
soybeans that hatch in corn the following year. Meanwhile, northern corn
rootworm has thumped the corn/soybean rotation in parts of the Dakotas,
Minnesota and Iowa via extended diapause: Eggs laid by adult beetles in
corn lie dormant the next year in soybeans before hatching in corn the
Monsanto initially proposed a YieldGard Rootworm refuge similar to that for
Bt corn that is resistant to ECB. Within one-half mile of each biotech
field, farmers would have to plant 20% of non-biotech first-year corn.
However, university and USDA entomologists disagreed with this proposal,
because mating patterns of the ECB and corn rootworm differ. Currently, no
resistance plan exists. However, one will be in place before Monsanto
markets these transgenic hybrids, McFerson says. Gray proposes a voluntary
prescription plan to prevent resistance. Growers and crop consultants would
monitor fields in summer to estimate adult beetle abundance via beetle
counts on plants or the use of sticky traps. If beetle numbers exceeded a
certain threshold, producers would then plant transgenic hybrids the
What to do
Should you plant rootworm-resistant hybrids? First, consider your rotation.
Although the corn/soybean rotation does not control corn rootworm in some
areas, it still works in most regions of the Corn Belt. Corn rootworm
incidence drops even further if you plant more than two crops in your
rotation. Next, avoid choosing hybrids based solely upon rootworm
resistance. "Getting the trait in the right hybrids is key,” says Rick
McConnell, president of Pioneer. "If you put a trait like this in a second-
rate corn hybrid, all you have is a hybrid that even an insect doesn't
You also should scrutinize how the cost of rootworm-resistant hybrids
compares to that of soil insecticides. "I would find the $15/acre seed
charge a bit prohibitive for our farm,” says Dale Koester, who farms near
Wadesville, IN. "We do invest $12 to $15/acre in insecticides, but I feel
that we get more control of other insects than just corn rootworm.” But
rootworm-resistant hybrids also offer peace of mind. Soil-applied
insecticides sometimes fail, says Erik Petry, a grower from Rochelle, IL.
"However, you know that the seed technology is there and working,” he says.
"Likewise, you cannot put a price on safety from not having to handle
Rootworm-resistant hybrids are a potentially valuable tool to control corn
rootworm, Gray says. "But we have to remember not to use the same tool to
bludgeon corn rootworm over the head time after time. We need to prolong
What's on tap for 2002
Even if federal regulators approve Monsanto's YieldGard Rootworm event,
hybrid numbers will be limited in 2002. "Our goal for the launch year is to
have growers first try the technology,” says Kelly Fleming, Monsanto's corn
rootworm launch team leader. "We will have a number of hybrids for use
across the Corn Belt.” Monsanto will emphasize the trial volumes in
Nebraska, eastern Colorado and Kansas. Pending regulatory approval,
Monsanto also plans to market a stack of rootworm-resistant and European
corn borer-resistant traits in YieldGard Plus hybrids in 2002.
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