That pink bollworm has developed resistance to Cry1Ac and Cry2Ab (or Bollgard-II) — the two biotech solutions currently available in India to tackle pink bollworm — is no news.
Virulent attack of the pest is destroying the fibre crop on lakhs of acres across the country, particularly in the West, Central and Southern parts.
An American pink bollworm expert says that it is impossible to tackle the menace with the current two Bt toxins being used in the country. “It has gone out of control. It’s too late. Too little,” he points out, when asked about the likely control mechanisms.
“The two genes that are being used in India are now ineffective. The resistance is widespread. There is no way we can set the clock back if we use these two Bt toxins,” Bruce Tabashnik, Head of Department of Entomology at the University of Arizona, who studies pest resistance and has done extensive study on pink bollworm and its resistance to Bt toxins, told BusinessLine .
It, however, is not the end of the road. There is a way out, he asserts. “Use all tools. For now, shorten cotton season, destroy crop residues, go for deep summer ploughing, crop rotation, mating disruption, insecticides based on scouting and thresholds,” he points out.
For the future, he says there are new Bt toxins that could help, including an edited form of Cry1Ac. “You need to engineer cotton to make two or more such new Bt toxins,” he says.
Presence of two genes will make it more difficult for the worm to develop resistance.
Talking to BusinessLine , he recommends a multi-layered approach to address the challenge. Besides deploying a new set of Bt toxins into the seed, two or more at a time, with 20 per cent non-Bt seeds as refugia, and integrated pest management system (IPM) could be an effective solution for cotton in India.
The methods successfully adopted by Arizona (the US) and China to tackle pink bollworm can’t be adopted at this stage in India as “it’s too late and efforts too little.”
Citing the example of Arizona, he said sterile bollworm moths were released in large numbers on the fields, far outnumbering the worms that were resistant to the technology.
This, along with other measures, resulted in the eradication of pink bollworm by October 2018. This strategy, according to Bruce, won’t work in India now as the infestation is widespread and resistance complete.
In China, farmers reversed low levels of pink bollworm resistance to Bt cotton by planting second-generation hybrid seeds from crosses between Bt and non-Bt cotton.
The refuge percentage in seed mixtures of 5-10 per cent declared for India is too low to make a difference. At least 20 per cent non-Bt seed must be planted to substantially delay resistance, he said.