Cry Toxin Expression in Bt -Cotton Hybrid Seeds:Impact on ‘refuge-in-Bag’ Strategy for Managing Resistance in Bollworms

A key strategy for delaying the deve-lopment of resistance among cotton bollworms to the Bt toxins is ‘refugia’. This refers to the cultivation of a small proportion of non-Bt-cotton alongside Bt-cotton, in order to maintain a consi-derable population of bollworm adults that are not selected for by the Bt toxins^1–3 . The unselected population of bollworm adults, by means of mating with, if any, a small number of selected individuals, is expected to reduce the rate of resistance development^4,5 . Thus, with the purpose of implementing the refugia strategy, farmers purchasing Bt-cotton seeds have been provided with a prescribed quantity of non-Bt seeds for simultaneous planting. However, Indian cotton farmers, most of whom are small or marginal, have barely taken the risk of planting non-Bt seeds, thus leading to gross non-compliance of the pre-scribed refuge requirement. This non-compliance has been attributed to the development of resistance recorded among the bollworms against the Bt toxins ^6–8 .