Ensuring the bollworm resistance is futile

Cotton industry works to ensure bollworm remains susceptible to Bt toxins


Cotton
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It's completely counter-intuitive, but cotton producers are being urged to keep a small patch of cotton plants where bollworm can thrive.

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Sharon Downes, CSIRO, has been researching bollworm resistance to Bt toxins for 15 years.

Sharon Downes, CSIRO, has been researching bollworm resistance to Bt toxins for 15 years.

IN ORDER to produce profitable cotton crops, Australian producers should grow varieties with absolutely no resistance to bollworm and let the pests roam free and decimate the crop.

Sounds ridiculous doesn’t it? But as counter-intuitive as it sounds allowing bollworm numbers to build up on varieties without the Bt gene containing the bacteria toxic to the worm could play a critical role in managing resistance to the Bt technology which has revolutionized Australia’s cotton industry.

Sharon Downes, principal research scientist at CSIRO, explained that there had been a rise in bollworm resistance to the Bt toxin across the world in recent years.

Resistance levels in Australia remain relatively low, despite the detection relatively high starting levels of resistance in some insects in Australia to two of the three toxins that are in the current types of Bt cotton, with the resistance yet to spread widely.

To this end, Dr Downes, who has been studying bollworm resistance to Bt over the past 15 years, said ensuring insects were not bred specifically for resistance was key.

This is where the non-Bt varieties come in.

Dr Downes said the strategy was to get cotton growers to set aside areas among their crops where they grow cotton plants that don’t have in-built toxins.

In these areas, susceptible insects are able to thrive and in turn has a muting effect on resistance because the resistant insects interbreed with susceptible insects.

Keeping the efficacy of the Bt varieties is critical to the Aussie cotton industry.

The overwhelming majority of cotton varieties now grown in Australia are Bt, which is genetically modified to include strains of the bacterium Bacillus thuringiensis, which produce over 200 different Bt toxins poisonous to bollworm.

This breakthrough revolutionised the industry and allowed farmers to cut pesticide use by at least 85 per cent, and improved local eco-systems by limiting detrimental impacts on beneficial animals such as pollinators.

By preserving susceptibility to Bt cotton farmers can continue to apply virtually no insecticide sprays to control the cotton bollworm in this crop.

This has the flow on effect of also preserving beneficial insects, like spiders and parasitoids, insects whose larvae kill their hosts, which can further help to control the bollworm and a range of other crop pests.

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