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2-Plants: Transgenic corn rootworm hybrid stumbles in Urbanaexperiment



                                  PART I
-------------------------------- GENET-news -------------------------------

TITLE:  Transgenic Corn Rootworm Hybrid Stumbles in Urbana Experiment
SOURCE: the Bulletin, University of Illinois, USA
        by Kevin Steffey and Mike Gray
        http://www.ipm.uiuc.edu/bulletin/article.php?issueNumber=22&issue
        Year=2004&articleNumber=1
DATE:   2 Sep 2004 

------------------- archive: http://www.genet-info.org/ -------------------


Transgenic Corn Rootworm Hybrid Stumbles in Urbana Experiment;
Some Producers Also Report Severe Lodging with YieldGard Rootworm Hybrids
in Commercial Fields

On February 25, 2003, Monsanto Company received a conditional
registration under the Federal Insecticide, Fungicide, and Rodenticide
Act (FIFRA) section 3(c)(7)(C) from the U.S. Environmental Protection
Agency for the sale of YieldGard Rootworm-protected corn (MON 863,
Cry3Bb1). The U.S. Environmental Protection Agency judged that the use of
transgenic hybrids for corn rootworm larval control would serve the
public interest by replacing or reducing the use of soil insecticides
(particularly organophosphates) deemed to be of greater risk
(environmental, human health, and safety). In addition, the use of
transgenic hybrids for corn rootworm control was judged to have
"comparable or greater efficacy than current chemical alternatives." As
the 2004 growing season revealed, this recombinant technology is still
relatively new with respect to corn rootworm control, and we have much to
learn.

As we stated last year in an article in issue no. 1 of the Bulletin
(March 20, 2003), producers should anticipate finding numerous corn
rootworm adults in their fields of YieldGard Rootworm corn. These adults
are immigrants from other cornfields as well as survivors from YieldGard
Rootworm corn. Different from the poor survival of European corn borers
on Bt hybrids used to control them (hybrids resulting from high-dose
transgenic events), some rootworms survive after feeding on the roots of
current transgenic hybrids for control of corn rootworm larvae. Why? The
MON 863 event is a non-high-dose product. In August 2002, the EPA's FIFRA
Scientific Advisory Panel believed it was not necessary to distinguish
between low- and moderate-dose events. Regardless of the precise
characterization of the YieldGard Rootworm event (low dose vs. moderate
dose), it remains certain that corn rootworm survivorship is evident. In
2001, we placed adult emergence cages over transgenic plants (MON 863)
that were planted on May 10. The cages were checked for adult emergence
every 2 days. A total of 96 emergence cages were used in this replicated
split-plot experiment. Based on the number of adults emerging into these
cages, we projected that 2,450 male western corn rootworm adults would
emerge per acre from the MON 863-event corn. The number of females
emerging per acre from the transgenic corn was 25,320. Overall, we
projected that 27,770 adults would have emerged from 1 acre of transgenic
corn (MON 863, Cry3Bb1), and 91% of these were females. Emergence of
males and females also from the transgenic corn rootworm hybrid was
delayed when compared with emergence from the non-transgenic isoline.
Delayed emergence and survivorship data such as these have been reported
by other entomologists from land-grant institutions. Although MON 863 is
a non-high-dose event, root protection afforded by this technology in
university research plots had been exceptional.


Adult corn rootworm emergence cage..

In 2003, we established three corn rootworm product efficacy trials in
trap-crop settings located near DeKalb, Monmouth, and Urbana. Average
root-injury ratings (1-to-6 scale) in our untreated check plots (DeKalb
60-15 hybrid) were 4.06 (one node destroyed), 5.75 (2-3/4 nodes
destroyed), and 5.45 (2-1/2 nodes destroyed), respectively. Planting
dates in 2003 for DeKalb, Monmouth, and Urbana were May 28, May 16, and
May 13, respectively. In 2003, corn rootworm larvae began hatching by May
29 across much of central Illinois. Despite the intensity of larval
feeding, the DeKalb YieldGard rootworm hybrid offered excellent root
protection at each experimental site: at DeKalb, the average root rating
was 1.45; at Monmouth, 2.05; and at Urbana, 1.35.

In 2004, we again established corn rootworm product efficacy plots in our
three standard experiments in trap-crop settings. Our trap crop consists
of late-planted, mixed-hybrid corn interplanted with pumpkins. Planting
dates for DeKalb, Monmouth, and Urbana were April 28, April 27, and April
19, respectively. These planting dates were considerably earlier in 2004
than the corresponding planting dates in 2003: 1 month earlier in DeKalb,
19 days earlier in Monmouth, and 24 days earlier in Urbana. Corn rootworm
larval hatch in central Illinois was estimated to be about 1 week to 10
days earlier in 2004 than in 2003. In 2004, we planted a Golden Harvest
(H-8588 RW) YieldGard Rootworm hybrid and its isoline (Golden Harvest H-
8799). Root injury (1-to-6 scale) in the untreated checks was severe at
each location and averaged 5.0 (2 nodes destroyed), 5.75 (2 3/4 nodes
destroyed), and 5.8 (nearly 3 nodes destroyed) at DeKalb, Monmouth, and
Urbana, respectively. Root evaluations were conducted for each of these
locations on July 21, July 15, and July 10, respectively. Average root
ratings for the Golden Harvest YieldGard Rootworm hybrid at DeKalb,
Monmouth, and Urbana were 2.35, 1.80, and 3.15 (pruning occurred,
considerably less than 1 node), respectively. The level of root injury to
the YieldGard Rootworm hybrid in the Urbana experiment was greater than
anticipated. Plants from our trials near DeKalb, Monmouth, and Urbana
were checked (by Monsanto personnel) for expression of the Cry3Bb1
protein, and the results were positive (i.e., the roots were expressing
the protein).

On July 13, a severe storm swept across central, north-central, and east-
central counties of Illinois. High winds and torrential rains
characterized this impressive storm. Within a few days, we began to
receive telephone and e-mail inquiries concerning severely lodged corn,
including concerns from some producers who had planted YieldGard Rootworm
hybrids. We visited some of these producers' fields. In some cases, root
injury was greater than expected. In others, the level of root pruning
was minimal in theYieldGard Rootworm fields, yet the fields were severely
lodged and harvestability was seriously compromised. Not long after these
observations from commercial cornfields became more common, Ron Estes
(insect management and insecticide evaluation program manager, Department
of Crop Sciences, University of Illinois) noted that the YieldGard
Rootworm hybrid (Golden Harvest H-8588RW) in our Urbana experiment was
severely lodged. At that point, we elected to take more root-injury and
lodging evaluations from this treatment at all three of our experiments.


Lodged YieldGard Rootworm plants, Urbana experiment, August 2004.

During the first week of August, we extracted 40 roots (10 per
replication) from the YieldGard Rootworm plots in the Urbana experiment
and rated them for larval damage (1-to-6 root-rating scale). Slightly
more than 3 weeks had elapsed since our original ratings on July 10.
Average root ratings per replication were 3.6, 3.4, 3.6, and 3.8 (overall
average = 3.6). The range in root injury was 3 to 4 (60% of the roots
were rated 4.0). None of the roots was assigned a root rating of 1 or 2
during the root evaluations in August. To quantify the level of pruning
on these roots more precisely, we also used the 0-to-3 rating scale for
node injury developed at Iowa State University. Root-injury ratings per
replication were 1.43 (nearly 1-1/2 nodes destroyed), 1.08 (1 node
destroyed), 1.64 (slightly more than 1-1/2 nodes destroyed), and 1.24
(slightly more than 1 node destroyed). The node-injury rating for
YieldGard Rootworm corn in the Urbana experiment was 1.35 (1-1/3 nodes
destroyed). The level of injury we observed in August was much greater
than what we observed in July.


Injured YieldGard Rootworm roots, Urbana experiment, August 2004.

In addition to the root evaluations, we measured the level of lodging
that occurred in the YieldGard Rootworm corn. The percentage of plants
lodged in each of the replications (four-row plots) was 40%, 79%, 61%,
and 39%.

Because of our experience with YieldGard Rootworm corn in our Urbana
experiment, we took additional root ratings (August 12) and lodging
counts in our DeKalb and Monmouth experiments. Average root ratings (1-
to-6 scale) in the DeKalb experiment (by replication) were 2.6, 2.3, 2.3,
and 2.2 (overall average = 2.35). The range in root ratings in our DeKalb
experiment was 2 to 5. None of the YieldGard Rootworm corn plants was
lodged in the DeKalb study. Average root ratings (1-to-6 scale) in the
Monmouth experiment (by replication) were 2.5, 2, 2.7, and 2.2 (overall
average = 2.35). The range in root ratings was 2 to 4. The percentage of
plants lodged in each replication (four-row plots) was 29%, 3%, 9%, and 0%.

Many questions have arisen from producers regarding performance issues
relative to some YieldGard Rootworm hybrids and severe lodging that has
occurred in certain commercial cornfields. The observations from our
experiments will hopefully begin to help us find answers to many of these
perplexing questions. Most notably, why was the level of injury in our
Urbana experiment much greater than we had anticipated? The following set
of questions and answers is designed to help improve our understanding of
this issue.


Has resistance toYieldGard Rootworm hybrids already occurred?

We don't believe so. Keep in mind that YieldGard Rootworm hybrids were
released commercially for the first time in 2003. It does not seem
probable that rootworm resistance to the Bt protein has occurred this
quickly. The FIFRA Scientific Advisory Panel (August 2002) suggested that
the likelihood of resistance development within the first 3 years of
commercialization is unlikely, regardless of refuge size. In April 2003,
the U.S. EPA issued a document titled "Event Mon863 Bt Cry3Bb1 Corn
Biopesticide Registration Action Document". The authors clearly point out
many of the assumptions underlying model predictions for potential
resistance development. If these models have underestimated the actual
initial resistance allele frequency, then resistance development could
proceed more rapidly. We simply don't have the required data to answer
this question.


What steps should be taken if unexpected damage or suspected resistance
does occur?

The FIFRA Scientific Advisory Panel (August 2002) specifically
established four steps a registrant should follow to confirm whether
resistance may have developed:
1. "Request the grower check planting records."
2. "Rule out damage from nontarget insects, weather, or other
environmental factors."
3. "Conduct tests to verify MON 863 was planted and that the correct
percentage of plants are expressing."
4. "If plants are MON 863 and damage approaching a 0.5 (node-injury
scale) is found on any expressing plant, evaluate roots from the
corresponding refuge."

The following paragraph from the April 2003 EPA document (page IID 11) is
of particular interest with respect to resistance confirmation.

"Resistance should be confirmed by a standard diet bioassay or evaluation
of root node injury. An insect diet bioassay with the Cry3Bb1 protein
that results in a LC50 that exceeds the upper limit of the 95% confidence
interval of the LC50 established from baseline measurements of
susceptible populations could be used to confirm resistance.
Alternatively, resistance may be confirmed when one or more root nodes of
at least 50% of Cry3Bb1 plants grown in the laboratory are destroyed.
[Recall that 60% of the roots evaluated from the YieldGard rootworm
treatment in Urbana rated 4.0 (1 node destroyed)]. A discriminating
concentration bioassay may also be used to confirm resistance; however,
this method may take a long time to develop. The August 2002 SAP also
recommended investigating the potential of using samples of populations
surviving on Bt corn or an evaluation of larval root tunneling to confirm
resistance."

Resistance confirmation must be reported to the U.S. EPA within 30 days.


What other explanations may account for the loss of performance with the
YieldGard Rootworm hybrid in the Urbana experiment?

In 2003 (root rating in the untreated check = 5.45) and 2004 (root rating
in the untreated check = 5.8), we had severe corn rootworm larval injury
in our Urbana trials. So the explanation for the reduced efficacy of the
YieldGard Rootworm hybrid in 2004 cannot be blamed solely on severe corn
rootworm larval pressure. However, considerable differences in planting
dates occurred between the two growing seasons. In 2003, the Urbana
experiment was planted on May 13 (late by today's standards). In 2004,
the Urbana study was planted on April 19, more than 3 weeks earlier than
the 2003 planting date. We, as well as other researchers, have determined
that development and emergence of rootworms are delayed by the MON 863
event. Is root protection compromised significantly when certain factors
converge, such as (1) early planting (early to mid-April), (2) delayed
corn rootworm development resulting from larvae feeding on MON 863
hybrids, and (3) intense larval pressure (root ratings in the untreated
check of two or more nodes of roots destroyed)? Might these factors
explain the compromised efficacy in our Urbana experiment as well as in
some producers' fields?


Other questions to ponder:

Does the expression of the Cry3Bb1 protein diminish as the season
progresses, compromising root protection in late July and early August?

Are there critical differences in expression of the Cry3Bb1 protein
across hybrids?

Are some hybrids with less than satisfactory root characteristics poor
candidates for the YieldGard Rootworm technology?

As indicated at the outset of this article, we still have much to learn
about transgenic hybrids and their role in an overall corn rootworm
management program. One thing seems certainthere continues to be no
silver bullet that can be directed at this impressive and resilient
insect pest of corn.


                                  PART II
-------------------------------- GENET-news -------------------------------

TITLE:  2004 Evaluations of Rootworm Control Products
SOURCE: the Bulletin, University of Illinois, USA, by Ron Estes
        http://www.ipm.uiuc.edu/bulletin/article.php?issueNumber=22&issue
        Year=2004&articleNumber=2
        file 200422table01.gif attached
DATE:   2 Sep 2004 

------------------- archive: http://www.genet-info.org/ -------------------


2004 Evaluations of Rootworm Control Products

For many growers, 2004 has been a bumper-crop year for corn rootworms,
and it was no different in our rootworm-control efficacy trials. Each
year, we establish three trials at University of Illinois research and
education centers near Urbana, Monmouth, and DeKalb. We plant our
rootworm-control trials into areas in which a "trap crop" (late-planted,
mixed-maturity corn hybrids + pumpkins) was planted the previous year.
The trap crop attracts egg-laying female rootworms. Consequently, we
usually have considerable rootworm pressure in our trials.

We planted all of our rootworm-control trials in mid- to late April
(Urbana, April 19; Monmouth, April 27; DeKalb, April 28). Two corn
hybrids were used in each of these trials, Golden Harvest H-8588RW (YGRW)
and Golden Harvest H-8799 (nontransgenic isoline). Each treatment plot
was four rows wide and was replicated four times in a randomized complete
block design. Table 1 shows the average root ratings from our rootworm-
control trials at the three locations. These averages are based on 20
roots (five from each replication). The roots were rated on the 1-to-6
scale developed by Hills and Peters (1971). A brief video describing the
rating scale can be found on the IPM Web site.

[table 1: attached]

Because of the abundance of rootworm larvae, injury in our untreated
check plots was severe, resulting in high average root ratings (5.00 at
DeKalb, 5.75 at Monmouth, and 5.80 at Urbana). The economic index used by
many entomologists is a root rating of 3.0 (several roots eaten off to
within 1-1/2 inches of the plant but never the equivalent of an entire
node). Rootworm damage resulting in a root rating above this index could
lead to potential yield loss and be deemed unacceptable. That said, the
average root ratings in the untreated checks well exceeded this
threshold, as did the average root ratings for some rootworm-control products.

The performance of the rootworm-control products varied not only by
location but also by type (liquid, granular, transgenic) and formulation.
Consequently, it is difficult to make many generalities about performance
of products, with the exception of a few products. Empower2 did not
perform well under the intense pressure at Urbana or DeKalb, with average
root ratings above 4.0 at both locations. Likewise, the seed treatments
could not withstand the high pressure at any of the three locations. The
Cruiser and Poncho treatments had average root ratings ranging from 4.15
to 5.10 and 3.95 to 4.10, respectively. In regard to liquid insecticides,
Lorsban 4E provided significantly better root protection than Capture 2EC
at Urbana and DeKalb. YieldGard Rootworm (YGRW) transgenic hybrids had
the lowest average root ratings at Monmouth (1.80) and DeKalb (2.35).
However, the average root rating for YGRW corn was higher than the
average root ratings in plots treated with some traditional insecticides
at Urbana. We had not encountered an average root rating greater than 3.0
for YGRW corn in previous years' efficacy trials, so the average root
rating of 3.15 for YGRW at Urbana raised more than one eyebrow. This
topic is addressed in another article in this issue of the Bulletin,
"Transgenic Corn Hybrid Stumbles in Urbana Experiment; Some Producers
Also Report Lodging with YieldGard Rootworm Hybrids in Commercial Fields."

In closing, I would like to touch on some questions asked at this year's
University of Illinois Crop Sciences Research and Education Center
Agronomy Day (August 19). More than one grower asked questions such as
"My insecticide didn't work. What should I use next year?" and "Why does
product X work in your trials, but it hasn't worked for me or my
neighbors in years?" Unfortunately, I don't have definitive answers for
those questions. My suggestion is to look at product consistency over
time and geography. If our results contradict what you are seeing in your
area, consult results from other land-grant universities. If nothing
else, ask your neighbors what they are using for rootworm control, how
long they have used it, and whether they have been consistently happy
with the results. However, I add a word of caution. If you ask a neighbor
for advice, inquire whether he or she ever left an untreated check strip
to determine what the rootworm pressure really is. If the level of
rootworm pressure is unknown, then the true performance of a product is
unknown as well.




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200422table01.gif;