Losing resistance

THE Bt cotton varieties, which have the transgene Bacillus thuringiensis, are claimed to be resistant to the deadly American bollworm. But a recent study by the scientists Dr. K. Chandrasekar and Dr. G.T. Gujar from the entomology division of the Indian Agricultural Research Institute found that the American bollworm (Helicoverpa armigera) developed resistance to the toxin "cry1ac" and increased it 31-fold within six generations.

This is not the first study to prove Bt resistance by bollworm. A study done in 2000 by scientists at the Central Institute for Cotton Research in Nagpur showed that bollworm can develop 76-fold resistance within 10 generations.

According to the recent study, published in the Indian Journal of Experimental Biology (Vol 42, February 2004), the bollworm also develops cross-resistance to two more toxins, "cry1aa" and "cry1ab". The study found that the resistance developed against `cry 1ac' was both in terms of mortality and growth.

According to the study, the expected life of Bt crops may be 7-10 years. And that too only in farms that have more than 70 per cent of their area under Bt crops (where non-Bt or refuge is less than 30 per cent).

According to scientists, the findings cannot be ignored because they indicate that resistance can appear in the fields. The tests, according to them, highlight the importance of adapting strategies to avoid or delay the emergence of resistance.

Are there strategies to stall resistance? Yes, say scientists. There are two doable strategies. One, the dual gene system, which ensures that if one toxin is unable to kill pests, the other one would. Two, planting adequate amounts of refuge that prevent pests from developing resistance. The resistant insects breed with their susceptible counterparts surviving on the non-Bt crops so that the resistant trait gets diluted in the next generations.

The first strategy is expensive, but the second is a viable option. However, farmers may be tempted to discard the refuge and grow Bt crops in all the land available to them to counter the high cost of cultivating these crops. Scientists say it is crucial to create awareness among farmers about the importance of refuge. However, Greenpeace India scientific adviser Ashesh Tayal asks: "How can one expect the authorities to spread awareness about refuge when they have not even done the mandated field studies to compute the frequency of resistant genes among insects?"

According to Rajeswari S. Raina, a scientist with the New Delhi-based National Institute of Science, Technology and Development Studies, before sanctioning further commercialisation of Bt crops, officials should ensure adequate management of the fields currently under transgenic crops (Down To Earth, April 15, 2004). "Despite a major scientific breakthrough, biotechnology may not go very far in India if the current state of affairs continues," she says. To begin with, India needs a biotechnology policy, apart from a foolproof regulatory process and transparency in approving Bt crops.