A pest overrides Bt

pests can override biotechnology. A recent laboratory test is another confirmation of this debatable fact. During the experiment, Helicoverpa armigera -- a rampant cotton pest commonly known as American bollworm -- evolved 31-fold resistance against a toxin of the Bacillus thuringiensis (bt) gene inserted in crops to help combat pests. The resistance developed against cry1 ac, the toxin, was both in terms of mortality and growth, found G T Gujar, a scientist from the entomology division of the Indian Agricultural Research Institute (iari), New Delhi.

Gujar fed 400 larvae of H armigera 0.5 microgrammes of cry1 ac per gramme of chickpea diet for four days till about 90 per cent of them died. The surviving larvae were then given a normal diet and maintained till pupation. Adults were allowed to lay eggs and the above process of selection was continued for larvae of the next six generations, though the level of toxin exposure was increased for every subsequent generation.

Assessment of the first, third, fourth and sixth generations of H armigera showed that most larvae developed manifold resistance to cry1 ac within six generations. The resistance mechanism was easy to trace -- proteases (enzymes) of resistant insects 'degraded' cry1 ac faster than those of susceptible insects, leading to the unavailability of the toxin in desired quantity.

As per the findings, published in the Indian Journal of Experimental Biology (Vol 42, February 2004, p164), the expected life of bt crops may be 7-10 years, that too in farms having more than 70 per cent of their area under bt crops (where non-bt crops or refuge is less than 30 per cent).

The test is one among many to verify H armigera's tendency to evolve resistance. In 2000, for instance, researchers from the Central Institute for Cotton Research, Nagpur, established that the bollworm can develop 76-fold resistance within 10 generations.
Crucial implications Do these similar experiments make the case of not using bt stronger? No, say experts. "They just warn against what can go wrong if bt is not judiciously managed in the fields," says Rakesh Tuli, coordinator, molecular biology and genetic engineering division, National Botanical Research Institute, Lucknow. "Resistance has not been reported from fields to date. Making a hullabaloo based on experiments is not justified, as insects are encouraged to develop resistance during the tests," asserts K Veluthambi of the School of Biotechnology, Madurai Kamaraj University, Tamil Nadu.

Agrees Raj K Bhatnagar, group leader, insect resistance group, International Centre for Genetic Engineering and Biotechnology, New Delhi. "A 31-fold laboratory resistance is not alarming," he says, adding: "But the findings cannot be ignored because they theoretically indicate that resistance can appear in the fields. The tests highlight the importance of adapting strategies to avoid or delay emergence of resistance."

There are two key strategies: use of dual gene system and planting adequate amount of refuge. Use of dual genes ensures if one toxin is unable to kill pests, the other achieves the desired affect. Refuge, on the other hand, prevents pests from developing resistance -- resistant insects breed with their suspectible counterparts surviving on the non-bt crops, and the resistant trait gets diluted in the next generation.

Usage of two bt genes may prove to be an expensive proposition for farmers already bothered by the high prices of bt seeds having one gene. "The dual gene system works in favour of the company," admits Bhatnagar. The biotech giant Monsanto has already sought permission from Indian authorities to conduct trials of Bollgard ii, which contains two genes.

The use of refuge can be a viable option. But "farmers may to tempted to discard the refuge in favour of the economics of bt crop," states Gujar. To avert a future quandary, Tuli advocates spreading awareness about the importance of refuge. "But can one expect this from authorities who have not even mandated field studies to compute the frequency of resistant allele (genes) among insects?" asserts Ashesh Tayal, scientific advisor of Greenpeace India. To assess the performance of bt crops, calculation of the number of insects having resistant allele is deemed necessary before and after commercialisation.

According to Rajeswari S Raina, a scientist with the New Delhi-based National Institute of Science, Technology and Development Studies, the present state of affairs clearly indicate that biotechnology may not be able to go very far in India, despite being a scientific breakthrough. "Before sanctioning further commercialisation of bt crops, officials should ensure adequate management of fields currently under transgenic crops," she concludes.

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