Bt loving insects

February 2011 
Photo: pink bollworm emerging from damaged cotton ball. Image Wiki Commons
 When Indian cotton farmers started to complain that their GM, supposedly insecticidal, crops were being eaten by pink bollworm, toxin and all, Monsanto was quick to lay the blame on the growers and regulators. 
“Apparently, the pink bollworm resistance problem is due to farmer ignorance: failure to plant non-Bt crop refuges, failure to procure non-Bt seed for the refuges, failure to scout the crop for pest emergence, failure to switch to Monsanto's Bollguard II which has had two Bt genes inserted, over-use of pesticides, failure to manage the infected crop residues and unopened bolls after harvest, poor tillage and inadequate grazing of cattle on the GM stubble, and previous illegal planting of unsuitable Bt cotton crops.” (Bt RESISTANCE RIGHT ON CUE – March 2010)
Up until that point, Bt cotton had been a runaway success story in India. Before GM, widespread and regular outbreaks of bollworm infestation had led to a steady increase in pesticide applications along with increasing cost of production. Between 2002 when commercial Bt cotton cultivation started in India and 2008, pesticide applications dropped by almost 50% principally due to the reduction in bollworm, and productivity jumped from 302 to 567 kg/ha. For this triumph to continue, it's important that the grubs remain susceptible to the Bt toxin. Recent research has suggested that the emergence of new Bt-resistant insects could just be a matter of time.

One prime reason for the evolution of Bt-munching insects was not mentioned by Monsanto. It's now established that there's a considerable variation in the quantity of Bt produced in different parts of the plant and at different times during the growing season: exposure to low levels of any toxin is a guaranteed way to generate resistance.

When Indian agricultural scientists studied the bollworm they found on their experimental plots of cotton, they made a number of disturbing observations:
  • the grubs not only weren't dying or even failing to thrive, but were quite able to develop into adults and produce healthy offspring
  • contrary to the biotech theory that pests would have trouble evolving resistance to two different pesticides at the same time, the presence of both Cry1Ac and Cry2Ab Bt genes in one experimental crop posed no obstacle.
If the Bt resistant pests come to form a majority on Bt crops, there's no reason why they shouldn't breed together and build a resistant population. The specified 'refuges' of non-GM crops would then have limited impact.

The authors did not establish to what extent the resistance found was already present in the background pest population. However, their test plots did not suffer from any of the effects of farmer ignorance invoked by Monsanto as the cause of Bt-resistance elsewhere.

Entomologists commented that eight years is a very short space of time for Bt resistance to develop and puts a question mark on the wisdom of relying so heavily on GM pesticidal plants. They stress that multiple strategies are needed to combat pests sustainably. GM crops should, they argue, be used in tandem with Integrated Pest Management (IPM).

Unfortunately, IPM is another highly technical modern approach to cultivation. It requires regular, at times even daily, monitoring of pests in the field, and a calibrated response to the pest populations found. This may be beyond the resources and expertise of smaller farmers just as much as the miracle GM cotton is turning out to be.


Sounds like a good case for organic cotton growing in India. All it needs is for you to create the demand (see ASKING TO CHANGE THE WORLD – News, February 2011)

  • Ranjith et al., 2010, Survival and reproduciton of natural populations of Helicoverpa armigera on Bt-cotton hybrids in Raichur, India, Current Science 99:11, December 2010
  • Worms eat into GM crop myth – Insects expected to drop dead thrive on cotton plants, Telegraph (India), 11.12.10

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