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Insects Developing Resistance to GM Bt Crops

Immediate release (10 Nov 2011)

Calls to: Pete Riley 07903 341065

GM Freeze today published a review of insect resistance to Bt toxins in GM maize and Bt cotton crops around the world. It shows how, contrary to promises from GM companies, pesticide use is increasing to keep up with insects in GM crops. [1]

Scientists have confirmed five incidents of insects evolving resistance to Bt toxins in the field to date: Bt cotton in India (2010) and US (2008), moth pests in maize in Puerto Rico (2007) and South Africa (2007) and a beetle pest in maize in the US (2011).

Reasons for resistance developing are:

  • Failure to provide adequate non-GM refuges in GM crops to ensure non-resistant adult insects can survive to breed with resistant ones so that the resistance gene does not become dominant. Refuges are required by US laws that are widely flouted.
  • Levels of Bt toxin in the crops too low to deliver lethal doses to pests. Sub-lethal doses mean resistance can develop as pests survive, mate and pass on the resistance gene. If the number of resistant individuals is high they can multiply quite rapidly and become dominant.

Monsanto has admitted the failure of their Bt cotton to control the pink bollworm has caused widespread damage in crops in Gujarat, but has tried to shift the blame onto farmers. [2] Pesticide costs on infested crops are reported to have risen by a nearly a third.

In Iowa in 2011 the first beetle pest resistance to a Bt toxin was confirmed, in western corn rootworm, which has caused “severe rootworm feeding injury to Bt maize”. [3] The problem appears to be emerging in other key maize producing states.

Commenting Pete Riley of GM Freeze said:

There are two confirmed cases where GM resistance to major crop insect pests has broken down and widespread damage to crops has occurred. Biotech companies are not liable, so farmers have no recall when infestations are economically damaging.

Strategies to prevent pests becoming resistant are either not being correctly implemented, are failing, or are suffering from a combination of both. The result is more pesticide use rather than less. Throwing more GM at the problem may work in the short term, but the history of artificial pest control in agriculture has repeatedly shown the pests will win over the longer term.

The sooner we switch to agroecological farming techniques, such as avoidance of monocultures, long rotations and the use of natural predators to control pests, the better.



[1] See GM Freeze briefing Insect Resistance to Bt Toxins in GM Insect Resistant Crops

[2] See Sharma, Dinesh, 6 March 2010. “Bt Cotton Has Failed Admits Monsanto.” India Today.


Monsanto, 5 May 2010. “Cotton in India”.

[3] Gassmann AJ, Petzold-Maxwell JL, Keweshan RS, Dunbar MW, 2011. “Field-Evolved Resistance to Bt Maize by Western Corn Rootworm”. PLoS ONE 6(7): e22629. doi:10.1371/journal.pone.0022629