more about Bt in Agricultural Research
Cotton Farmers Bt Investment
By Jan Suszkiw
February 12, 2001
Helping cotton farmers prolong
Bacillus thuringiensis (Bt) effectiveness as a natural
pesticide against crop-damaging caterpillars is the aim of
Agricultural Research Service studies in
There, at ARS's
Insect Management Research Unit, Dick Hardee and Doug Sumerford are
monitoring the ability of tobacco budworms and bollworms to feed and grow on
artificial diets containing insecticidal Bt proteins used in transgenic
cotton. In U.S. cotton crops, these caterpillar pests cause up to $300 million
annually in damages and control costs.
Since 1996, cotton varieties engineered with Bt genes for making the
protein have offered growers a way to reduce insecticides. Bt cotton is
now grown on 2 million-plus U.S. acres. Because of such extensive plantings of
cotton and other Bt crops, there is concern that natural selection will
favor insects having traits for Bt resistance.
The researchers have sought to quantify this in budworms and bollworms by
obtaining caterpillar specimens from cotton fields across the nation and
rearing them to adulthood on Bt- free diets. Once theyve mated,
the insects offspring are reared on Bt diets and compared with the
labs control colonies. This allows scientists to check the insects
Bt tolerance levels. The more tolerant a caterpillar is, for example,
the faster it grows on the Bt diet and the bigger it gets. A sensitive
assay also enables scientists to compare genetic differences among
Bt-fed insects, based on these physiological cues.
Hardee, Sumerford and John Adamczyk also are:
- Monitoring Bt insect control differences based on environmental
factors, such as soil salinity, and accidental mixing of Bt and non-Bt
- Comparing Bt expression among different cotton varieties, as well
as in different parts of these transgenic plants.
- Testing cotton having two Bt genes.
Since starting the program, the scientists have noticed no change in their
budworm collections Bt tolerance. A bollworm assessment is pending
more data from the Cotton Belt. A longer story is in Agricultural Research magazine.
ARS is the U.S. Department of
Agricultures chief scientific research agency.
Scientific contact: D.D. Hardee, ARS Southern Insect Management
Research Unit, Stoneville, Miss., phone (662) 686-5231, fax (662) 686-5421,