Missing Enzyme Linked to Bt-Resistance in Insects By
The absence of an enzyme from the gut of certain Indianmeal moths makes
those stored grain pests resistant to the powerful biological control agent Bacillus
thuringiensis (Bt), Agricultural
Research Service scientists report.
ARS researchers at the Grain Marketing
and Production Research Center in Manhattan, Kan., have found that two
strains of Indianmeal moths lack an enzyme that converts Bt protoxins to
activated toxins that kill insects.
In laboratory studies, scientists demonstrated that insects lacking the
enzyme survive when fed Bt diets. The scientists also showed that loss
of the enzyme is genetically linked to insect resistance to Bt.
Bt, a soil bacterium, has been used for 35 years as a safe and
effective alternative to chemical insecticides for controlling moth pests. Its
use either as a spray or through genetic insertion into crops doesn't harm
humans, animals, beneficial insects or other crops. But insect resistance to
Bt is sometimes reported in areas where farmers use Bt
extensively for insect control.
Bt transgenic plants were first used by farmers in 1996 and crop
yields were excellent. This success may lead to increased planting of
transgenic crops, which will lead to increased insect exposure to Bt.
Understanding how insects cease responding to Bt toxins may help to
prolong the use of this safe insecticide.
The researchers are now studying 35 other strains of the Indianmeal moth for
the presence or absence of the enzyme. They are seeking industry collaborators
to help monitor for resistance in insects exposed to Bt transgenic crops
and to search for a similar "missing enzyme" phenomenon in other
insect pests, such as corn earworms and cotton bollworms.
Scientific Contact: Brenda Oppert, ARS-USDA,
Grain Marketing and Production Research
Center, 1515 College Avenue, Manhattan, KS 66502. Telephone: (785)
776-2780; fax: (785) 537-5584, firstname.lastname@example.org.