"It's easier for an insect to develop resistance to a single toxin," said Shelton. "If an insect gets a jump on one toxin, then it becomes more rapidly resistant to that same toxin in a dual-gene plant. And when one line of defense starts to fail, it puts more pressure on the second toxin in a pyramided plant to control the insect," Shelton added.
While single-gene Bt plants are most prevalent, industry trends suggest that pyramided plants may be favored in the future. In Australia, the use of single-gene Bt cotton was discontinued two years after farmers began planting dual-gene cotton in 2002. In the United States, companies introduced dual-gene cotton in 2003, but single-gene varieties remain on the market.
"Single-gene Bt plants have provided good economic and environmental benefits, but from a resistance management standpoint they are inferior to dual-gene plants. U.S. regulatory agencies should consider discontinuing the use of those single-gene plants as soon as dual-gene plants become available," Shelton said. "And industries should be encouraged to create more dual-gene plants."
Along with effective insect control, pyramided plants have an added advantage of requiring a smaller refuge -- a part of the field where non-Bt plants are grown. Refuges create opportunities for Bt-resistant insects to mate with other insects that do not have resistance. The offspring of such a mating will be susceptible to the toxins.
"Having a refuge is a good management strategy, but it is not suitable for small farmers in China and India," said lead author Jian-Zhou Zhao, a senior research associate in entomology at Cornell. "Th
Source:Cornell University News Service