New Delhi: A 10-year study by Chinese scientists on the long-term impact of Bt cotton shows an increase in a class of cotton pests traditionally considered minor or relatively harmless to Bt cotton.

While the damage to the crop due to these pests is still insignificant, the study’s findings are borne out by similar instances of infestation in India and point to the need for having an effective, long-term insect management strategy rather than have farmers depend entirely on genetically modified (GM) seed to protect their crop.

Bt cotton now occupies over 90% of the country’s cotton acreage and has been credited with tripling the yield and making India a net exporter of the commodity since 2006. It’s largely due to the success of Bt cotton and its acceptance among farmers that several companies and agricultural research institutes have been trying to integrate the Bt gene into food crops in India.

Bug worry: A cotton field in Haryana. A rise in the number of pests will mean more insecticides and may also raise input costs. India’s cotton productivity has fallen over the past three years. Rajkumar/Mint

A rise in different pests could mean more insecticide sprays and an increase in farmers’ input costs.

While the scientists haven’t computed the extent of damage caused by these insects, called mirid bugs, they note that “over the study period, mirid bugs gradually increased population and damage in cotton, and multiple other crops".

Moreover, significant infestation levels were recorded in crops such as grapes, apple, peach and pear and this strongly correlated with the extent of Bt cotton planted, the report added.

Genetically modified cotton today uses one or more genes from a soil bacterium called Bacillus thuringiensis that trigger an insecticidal protein. These toxins are usually fatal only to a bug called the American bollworm, considered the chief cotton pest and, as a result, the target of most insect sprays. Though Bt cotton seeds are costlier than their non-Bt counterparts, its proponents claim that seeds engineered in this way dramatically reduce the sprays—and hence costs—in protecting cotton crop.

According to the study, mirid bugs were on an average three times more prevalent on Bt cotton plants, than non-Bt cotton plants sprayed with pesticides typically used to cull the cotton bollworm.

“Since the advent of Bt cotton, farmers have been spraying less of the insecticides that were traditionally employed to contain the bollworm. It’s that decrease in spraying that strongly relates to the rise in mirid bug population," said Kongming Wu, the lead author of the study and a scientist at the Chinese Academy of Agricultural Sciences, Beijing.

It is estimated that pests cause losses worth $120 billion (Rs5.4 trillion), of which losses worth Rs60,000 crore take place in India. Pesticides worth $8 billion are used every year in India, with cotton accounting for nearly $3.8 billion of this. GM technology is expected to reduce at least 50% of the expenditure on pesticides.

Though previous studies, including some in India, have documented a rise in pests that weren’t the target of Bt toxins, this is the first study to confirm an overall rise in such pests across several locations over a long period.

In 2007 and 2008, cotton farmers in Punjab saw a rise in another cotton pest called the mealy bug that agriculturists say cut production by one-fourth in the state. Jagresh Rana, director, Mahyco-Monsanto Biotech Ltd, said that very often a change in weather conditions triggers a rise in minor pests. “The mealy bug attack was last seen in the 70s. We’ve always maintained that seed alone can’t be a solution for protecting crops and we have to improve integrated pest management strategies," he added.

Previously, Keshav Kranthi, director of the Central Institute of Cotton Research, had pointed out similar concerns over the unforeseen consequences of the widespread adoption of Bt cotton. In a report, he said 90% of the current GM cotton hybrids appear susceptible to mealy bugs and whiteflies (also considered a minor cotton pest) and that insecticide use in cotton, as measured by value, appears to have increased from Rs640 crore in 2006 to Rs800 crore in 2008.

The report also points out that seed companies have produced over 600 GM cotton hybrids, and farmers in cotton-growing districts find themselves having to choose from 150 to 200 hybrids.

Interestingly, India’s cotton productivity has declined over the past three years—from 560kg lint per hectare in 2007 to 520kg lint in 2008 and 512kg lint in 2009. A wrong choice of hybrids, Kranthi had said, may be contributing to this drop. Kranthi wasn’t available for comment on this report’s findings.