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2-Plants: Are Bt hybrids taking bite out of borer population?



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TITLE:  Are Bt hybrids taking bite out of borer population?
SOURCE: FarmWeek, Illinois Farm Bureau, USA
        http://farmweek.ilfb.org/viewdocument.asp?did=8744
DATE:   27 Jan 2006

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Are Bt hybrids taking bite out of borer population?

Mike Gray, University of Illinois Extension entomologist, has monitored
two trends in the last decade that seem to be interrelated.

Gray told participants of the U of I Corn and Soybean Classic in
Bloomington last week that as the use of Bt corn hybrids reaches all-
time highs, the number of European corn borers monitored by the U of I
remains historically low.

The latest corn borer survey, conducted across the state in the fall of
2005, found an average of just 0.34 corn borers per stalk and an
infestation level of 24 percent, well below the long-term historic
averages of 1.15 corn borers per stalk and an infestation level of 49 percent.

In fact, each annual count of corn borers has totaled less than the
historic averages since Bt corn was introduced in 1996 -- with the
exception of 1997-98 when the U of I did not conduct the annual fall survey.

"The numbers (of corn borers) are very low post Bt," Gray said. "The
question is -- are we going to see corn borer populations again rival the
1980s, the early 1990s, or even the 1940s?"

Gray said 1949 represents the high-water mark of corn borer infestation
with an average of 4.2 borers per stalk. He said some farmers at that
time resorted to deep plowing or burning stalks in an attempt to
eradicate the pest.

After that, infestation levels continued a cyclical pattern until 1996,
when Bt corn was introduced. Since then, the number of corn borers has
plummeted to an average of just 0.5 borers per stalk.

While it would seem Bt corn is having a favorable impact on reducing the
number of corn borers, Gray said it will take more time to accurately
make that determination.

"One of the things that is very clear is corn borer populations
fluctuate over time, largely due to environmental conditions," Gray said.

"We need to stretch the survey another four or five years to see if
(corn borer) numbers rebound."

In the meantime, Gray expects farmers to plant more transgenic varieties.

Bt hybrids were planted on 28.6 million acres in 2005, accounting for 35
percent of all U.S. corn acres, according to the National Agricultural
Statistics Service. The use of Bt hybrids for corn rootworm control
increased from 400,000 acres in 2003 to 2.1 million acres in 2004.

But, while the technology has provided some benefits to farmers in its
first decade of use, Gray cautioned that over-use of Bt and other
transgenic hybrids could have negative consequences.

"If we squeeze this insect (the corn borer) enough, it will adapt," Gray
said. "And I've become particularly nervous about squeezing the
rootworm, which has proven to be a very adaptable animal. Ultimately, it
could have negative consequences."

Farmers who use Bt corn are required to plant 20 percent refuge areas of
non-Bt varieties in order to reduce the chance of developing a resistant
insect population. -- Daniel Grant

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