This item is one of the news releases and story leads that ARS Information
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www.ars.usda.gov/is/pr/thelatest.htm.
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From: "ARS News Service"
To: "ARS News List"
Subject: Tobacco Budworm Resistance to Bt
Date: Thu, Mar 8, 2001, 6:44 AM
STORY LEAD:
Mechanism of Tobacco Budworm Resistance to Bt Proposed
___________________________________________
ARS News Service
Agricultural Research Service, USDA
March 8, 2001
Sharon Durham, (301) 504-1611, sdurham@ars.usda.gov
___________________________________________
How does a tobacco budworm develop resistance to Bt? An Agricultural
Research Service scientist may be closer to answering that question, based
on tests she conducted on budworm cells.
ARS research physiologist Marcia Loeb of the Insect Biocontrol Laboratory in
Beltsville, Md., used tobacco budworm gut cells, cultured in the laboratory,
to help understand how this insect--a major caterpillar pest of cotton,
soybeans and tomatoes--becomes resistant to the natural toxin produced by
the bacterium Bacillus thuringiensis (Bt).
Bt has been one of the most promising biocontrol products of recent years in
combating pests that attack a variety of crops. But some subgroups of
tobacco budworm (Heliothis virescens) are becoming resistant to Bt.
Bt toxin causes mature budworm gut cells to swell, burst and die. In
culture, Loeb found that as the toxin kills, remaining cells produced
cytokines, substances that signal budworm gut stem cells to multiply and
rapidly differentiate to form new mature cells. If a low dose of Bt is
present, more new cells will be produced than those killed.
In Loeb's experiments, when the Bt toxin was washed from the cultured gut
cells exposed to low doses of Bt, the ratio of cell types returned to normal
and the culture recovered. According to Loeb, this suggests that if an
insufficient dose of Bt is "washed out" of the insect's gut during normal
evacuation, the insect's gut will heal and the insect will survive.
This could explain why low doses of Bt toxin don't kill insects. To be
effective, the dose of Bt must be high enough that the cell replacement
process can't be completed before the insect dies. If the insect is able to
produce high enough numbers of new gut cells to replace those that have been
killed, the insect will survive.
This information will be useful to applicators of Bt toxin for pest control,
as well as other scientists studying this toxin.
ARS is the chief scientific research agency of the U.S. Department of
Agriculture.
___________________________________
Scientific contact: Marcia Loeb, ARS Insect Biocontrol Laboratory,
Beltsville, Md., phone (301) 504-8103; fax (301) 504-5104;
mloeb@asrr.arsusda.gov.
___________________________________________
This item is one of the news releases and story leads that ARS Information
distributes on weekdays to fax and e-mail subscribers. You can also get the
latest ARS news on the World Wide Web at
www.ars.usda.gov/is/pr/thelatest.htm.
* Feedback and questions to ARS News Service via e-mail: isnv@ars-grin.gov.
* ARS Information Staff, 5601 Sunnyside Ave., Room 1-2251, Beltsville MD
20705-5128, (301) 504-1617, fax (301) 504-1648.
