The genetically engineered Bt cotton, which is designed to produce its own insecticide, appears to have lost its efficacy over its primary target: the rapacious bollworm.
Scientists have discovered that the cotton bollworm, Helicoverpa armigera, thrives on Bt cotton. The parasite has completed its lifecycle and even reproduced. This indicates the larvae's growing resistance to the hybrid crop's self-producing toxins, says a research paper published in the latest edition of Current Science.
Experiments at the University of Agricultural Sciences, Raichur, found that the bollworm feasted on both forms of Bt cotton grown commercially in India: the single gene (Cry1Ac) and the double gene (Cry1Ac and Cry2Ab) varieties.
A proportion of the succeeding generation was also able to complete its lifecycle on the crop, according to researchers M.T. Ranjith and A. Prabhuraj of the UAS, Raichur, and Y.B. Srinivasa of the Institute of Wood Science and Technology, Bangalore.
In the first six years since Bt cotton's commercial introduction in India in 2002, cotton production grew by 135 per cent, from 2.3 million tonnes to 5.4 million tonnes. Concurrently, pesticide use declined by half. However, the primary advantage of the genetic crop — its defence against the destructive pest — could be negated by a new resistant population of bollworm.
“There is a distinct possibility of discovering potentially resistant populations of H. armigera to the Cry toxins in the near future,” the authors cautioned.
While the bollworm has been known to feed on Bt cotton in India, this is the first time that scientists have demonstrated “the ability of these individuals to complete their lifecycle and successfully reproduce using the same host”.
The amount of the toxin produced varies in different parts of the cotton plant and at different times of the growing season, a phenomenon believed to gradually lead to resistance in the pests.Staff Reporter