Indian farmers spending more on insecticides for Bt cotton

"Now farmers in India are spending more on seeds, more on fertilizer and more on insecticides," said researcher Glenn Davis Stone from Washington University in the US.

"Our conclusion is that Bt cotton's primary impact on agriculture will be its role in making farming more capital-intensive -- rather than any enduring agronomic benefits," Stone added.

According to the study, published in the journal Nature Plants, genetically modified (GM) Bt cotton produces its own insecticide.

The seeds were introduced in India in 2002 and today account for 90 per cent of all cotton planting in the country.

Bt cotton is now the most widely planted GM crop on small farms in the developing world. In India, Bt cotton is the most widely planted cotton crop by acreage, and it is hugely controversial.

"Bt cotton is explicitly credited with tripling cotton production during 2002-2014. But the largest production gains came prior to widespread seed adoption and must be viewed in line with changes in fertilisation practices and other pest population dynamics," Stone said.

According to the researcher, there are two particularly devastating caterpillar pests for cotton in India, and, from the beginning, Bt cotton did control one of them: the American bollworm.

"It initially controlled the other one, too -- the pink bollworm -- but that pest quickly developed resistance and now it is a worse problem than ever," Stone said.

Bt plants were highly vulnerable to other insect pests that proliferated as more and more farmers adopted the crop.

Farmers are now spending much more on insecticides than before they had ever heard of Bt cotton and the situation is worsening, according to Stone.

"Yields in all crops jumped in 2003, but the increase was especially large in cotton," Stone said.

"But Bt cotton had virtually no effect on the rise in cotton yields because it accounted for less than 5 per cent of India's cotton crop at the time," Stone added.