"The most widely used strategy to delay resistance is to set aside refuges," he explained, "patches with regular, non-Bt cotton where the pest can feed without ingesting the Bt toxin."
"If you plant Bt crops with no refuges, the vast majority of the caterpillars will die, but a tiny fraction will be resistant. These rare resistant survivors will emerge as adults and mate with each other."
The result is obvious: an exploding population of resistant insects.
The refuges ensure a substantial population of non-resistant insects will be around, fluttering about in search for mates. Given the abundance of non-resistant insects relative to the scarce resistant ones, chances are slim that two resistant moths will mate with each other. Instead, most, if not all, resistant moths will mate with a susceptible partner. When resistance is inherited as a recessive trait, the hybrid offspring produced by mating between resistant and susceptible moths are also susceptible.
While the refuge concept has worked reasonably well at keeping the pests at bay, it is incompatible with eradication, Tabashnik pointed out.
"Refuges are a way of managing pest populations, so you have to accept the permanent presence of the pest," he said. "You don't get rid of them. You maintain susceptibility by promoting survival of the susceptible insects."
So, rather than relying on susceptible moths from refuges to thwart resistance, the eradication program staff reared large numbers of pink bollworms, sterilized them, and released the sterile moths into cotton fields where they could block reproduction of the wild insects.
"When a sterile moth mates with a fertile wild moth, the progeny won't be fertile,
|Contact: Daniel Stolte|
University of Arizona