“Government lab faults Mahyco’s study of pest resistance to Bt cotton” (March 7) is a major setback for Bt cotton. The subject has been studied in depth in the US by the University of Arizona.
The key to Bt cotton’s continued efficacy is the use of refuges — patches of traditional cotton intermingled with the fields of Bt cotton. The refuges ensure that the few pink bollworm moths that are resistant to Bt are most likely to mate with Bt-susceptible pink bollworm moths that grow up in the refuges. The offspring from such mating die when they eat Bt cotton.
In contrast, if all Arizona’s cotton was Bt cotton, only pink bollworm caterpillars that were resistant to the Bt toxin would survive. If resistant pink bollworm moths mated with each other, their offspring would be resistant and could feed on Bt cotton. Bt cotton would then become useless against pink bollworm.
M M Gurbaxani, Bangalore
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