Pests emerging concern for Bt cotton

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New Delhi, Apr 27: The target pests becoming resistant to Bt cotton has now emerged as a new problem in parts of Gujarat, Andhra Pradesh and Maharasthra. A study done by the Nagpur-based Central Institute for Cotton Research (CICR) has suggested the need for proactive six-pronged insect resistance management (IRM) on Bt cotton fields. “Otherwise the development of insect resistance to Bt cotton can significantly diminish the returns and benefits that are currently being derieved from the technology,” it said.

The Cry 1 Ac gene from soil bacteria, bacillus thuringiensis, was inserted in selected cotton hybrids to protect it from the bollworm, helicoverpa armigera. The team led by the head of the CICR crop protection division, KR Kranthi conducted a study on the population of the major pest, helicoverpa armigera collected from 10 cotton growing districts of north India, 26 districts of central India and 17 districts of south India in the period 2001-07.

“The data did not indicate high levels of resistance in the pest population that may be adequate for significant survival of the pest under field conditions. However, the data indicated that there was a clear decrease in the proportion of susceptible pest population,” said Kranthi.

Other pests like spodoptera litura, mealy bugs, mired bugs, dusky cotton bugs and pink bollworms have increased due to lack of adequate sprays of insecticides.

He said that stochastic model outputs indicated the need to initiate IRM strategies in addition to the currently recommended 5-row non-Bt cotton refuge per acre of Bt cotton. “In light of the facts that the Cry 1 Ac expressed in Bollgard (Bt cotton) does not represent high dose against helicoverpa armigera and also that the allele conferring bollworm resistance to Cry 1 Ac is not extremely rare and is inherited in a semi-dominant manner, it is important to develop IRM strategies appropriate to Indian conditions,” he said.

Kranthi said that Cry 1 Ac has been inserted in 10 crops including cotton, out of which eight were good alternate hosts of helicoverpa armigera and had been serving as naturally occurring refugia area near Bt cotton fields.

“As we go ahead with more and more crops harbouring