www.checkbiotech.org ; www.raupp.info ; www.czu.cz

Mike Gray, University of Illinois Extension entomologist, has monitored two
trends in the last decade that seem to be interrelated, January 2006 by
Daniel Grant.

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.

[farmweek.ilfb.org]

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