China warns of Bt cotton dangers

Bt cotton kills cotton pest, bollworm, without any insecticides. But, the absence of chemical sprays increases the occurrence of other non-target pests, which in turn not only damage cotton but also other crops.

This has been observed by scientists from the Chinese Academy of Agricultural Sciences who monitored vast Bt cotton landscape in six cotton growing areas in northern China for ten years 1998 to 2009 and found a steady growth in the population of mirid bugs, a non-target pest, everywhere.

Field trials show that mirid bugs have acquired pest status in cotton and other multiple crops. Bt cotton has become a source of mirid bugs and that their population increase is related to the drop in insecticide use in this crop, it was reported in the journal “Science” on Friday.

Conventional farming

Mirid was never an important cotton pest in the Chinese cotton system. Though the bugs have many host crops like Chinese dates, grapes, apple, peach and pear, they prefer cotton in June. In conventional cotton farming, when farmers sprayed chemicals to kill bollworms, the same insecticides also killed mirids. But introduction of Bt cotton in China in 1997 has changed the agriculture practice.

After Bt cotton adoption, farmers do not need to use insecticide to control cotton bollworm in June. This gives a space for mirid population increase in cotton fields. The bugs then move to other host crops as source, Kongming Wu, principal investigator of the research told Deccan Herald. The first confirmed report of landscape-level emergence of non-target pests with the adoption of Bt cotton which led to reduction in sprays, is worrying  Indian cotton researchers who want to do a stock taking at the earliest.

“We are yet to study the occurrence of these species on other crops in India, but must do it immediately to evaluate the broad implications of Bt cotton in India. We will take up the study on priority. These are lessons for tomorrow,” said K R Kranthi, director, Central Institute of Cotton Research in Nagpur. Asked about the prevalence of mirid bugs in India, he said three species of mirid bug population have been occurring in Indian cotton for the last five to six years and have been causing economic damage. These species were never reported to be of any economic significance  in India.

These insects are difficult to be noticed by non-experts and may have been ignored on other crops, said Kranthi who also heads the nation-wide monitoring network for Bt cotton.