Gen Eng (Bt) corn

Hector Valenzuela (hector@hawaii.edu)
Mon, 6 Jan 1997 19:11:57 -1000

For your interest, an article from Penn State dealing with transgenic
corn,to fuel the ongoing discussion in this area. Aloha, Hector

Hector Valenzuela
Univ. Hawaii, Horticulture
hector@hawaii.edu

SOURCE:
FIELD CROP NEWSLETTER, Department of Agronomy, Penn State University,
Website Address:
http://www.cas.psu.edu/docs/casdept/agronomy/extension/fcn/fcnindex.html,
December 9, 1996, Vol. 96:13

Bt Corn
By Steve Spangler and Dennis Calvin

This was the first commercial year of Bt hybrid availablility for corn
growers in the U.S. Bt corn is a "transgenic" crop, that is, the plants
have a gene from the bacterium Bacillus thuringiensis, inserted into their
own genetic material. This new gene produces a protein which kill insects
after the protein is ingested. The results so far indicate that dramatic
new levels of corn borer control can be acheived: well over 90%, compared
to an average effectiveness of about 60% for a typical insecticide. In
addition, with these transgenic crops, there is no cost of scouting or
application of a pesticide to a crop, so the only additional cost will be
the premium placed by the company on a bag of seed. Several companies
have developed and patented the technology for these transgenic lines, and
are working with several seedcorn companies. Ciba and Mycogen marketed Bt
corn in Pennsylvania in 1996, and NK had full registration in August 1996.
In 1997, several other seed companies will be using the Bt gene from
Monsanto in some of their hybrid lines. Economic analysis indicates that
the economic benefit in Pennsylvania from using these trangenic corn
hybrids will range between $6 to $26 per acre, depending on the
conditions. There will be about a $7/acre premium on transgenic corn
hybrids. Therefore the economic returns per acre will vary between $0 and
$21 per acre. On average most corn fields will benefit economically from
a trangenic corn hybrid.

But, there is an important assumption to this analysis which states that
Bt corn will pay off in 50-80% of the corn fields in the U.S., and this is
that the Bt hybrids have equal yield potential of the non-Bt hybrids. Put
simply, it is quite possible that a superior non-Bt hybrid will still
out-perform an inferior Bt hybrid. In the end, yield of the corn hybrid
will be some combination of having a good yielding hybrid to begin with,
and having the addition of the Bt gene, or for that matter future gene
insertions which may give protection for other insects (we are told that
corn rootworm transgenics are just around the corner!). Thus, hybrid
trials are still as important as ever.

A major concern with these transgenic crops is the potential for
development of resistance of corn borer to the Bt toxin if they are over
used. Most insect populations, if they are exposed to a toxin
excessively, can develop resistance, making pest control products less
effective. Any potato grower knows of this problem with Colorado potato
beetle. Resistance is also common in many other crops, including cotton
and apples. Also, there have been two documented cases of resistance of
insects in the field to Bt products: diamondback moth in cole crops, and
indian meal moth in stored grain. Fortunately, however, corn borer has not
shown resistance to any chemicals to date. It is everyone's interest -
biotechnology companies, growers, and corn agriculture in general - to
maintain the usefuleness of this valuable technology, so resistance
management needs to become part of everyone's thinking. You may be
hearing a new word in our vocabulary from now on: "refugia".
Specifically, seed companies will probably be specifically recommending
that you not plant all your acres to transgenics. Planting too many acres
to transgenic corn may lead to resistance. However, leaving a small
portion (probably 4-20%) of your acres as non-Bt corn will maintain insect
susceptibility to the Bt corn, in others words, you will more likely
retain the effectiveness of this exciting new technology.