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Do GMOs accelerate pesticide resistance?

Dr. Greg Copenhaver, UNC Director of Graduate Studies, Biology Department

Dr. Greg Copenhaver, UNC Director of Graduate Studies, Biology Department

Does the “precise” form of genetic modification (as Dr. Greg Copenhaver referred to) accelerate the development of pesticide resistance?

Dr. Copenhaver: No, not necessarily. The method itself neither slows nor accelerates pesticide resistance. Instead, the main determinate of how quickly pest populations develop resistance is the way we use pesticides. Traditional pesticide practices can quickly lead to the development of resistance if not used properly.

For example, various strains of the most important potato pest, the Colorado potato beetle, are now resistant to 52 different chemical insecticides including all the major classes commonly used1. Even the use of “organic” pesticides can contribute to rapid resistance if not used strategically2. There are several agronomic practices that can help mitigate resistance (regardless of what technology you employ) including: stacking pesticides, rotating pesticides, and most importantly using refugia to promote non-resistant survivors. Losses due to pests vary by region and crop but can be as high as 80% in cotton, 50% in wheat and 40% in maize and rice3. Models developed by atmospheric scientists indicate that losses in mid-latitude farms may double by the end of the century due to more favorable climatic conditions for insects4. As a result, use of pesticides is likely to be an unavoidable feature of modern agriculture.

The processes of selection (as described by Darwin and his predecessors) assure us that resistant pests will develop as a result. The problem thus becomes one of understanding and slowing those processes. Critics of genetic engineering will argue that GM crops represent a particularly pernicious form of the problem because the bio-based pesticides (like Bacillus thuringiensis insecticides, or Bt for short) are produced by GM crops on a continual basis and therefore present a strong selective pressure. As I’ve argued above, strong selection is not unique to Bt crops.

Nonetheless, it is a reasonable concern and is an excellent reason to devote effort and resources to improving the technology. Time and tissue specific expression of bio-based insecticides offer one such opportunity. The development of bio-based insecticides that are expressed only when and where they are needed within the plant and only at the minimal levels required to keep pests below economic injury levels (EIL)5 is achievable using currently existing technology.

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1 Alykohin et at. (2008) American Journal of Potato Research 85: 395-413. doi: 10.1007/s12230-008-9052-0
2 Tabashnik(1994) Annual Review of Entomology 39: 47-79.
3 Oerke (2005) The Journal of Agricultural Science 144: 31-43. doi: http://dx.doi.org/10.1017/S0021859605005708
4 Maxmen (2013) Nature 501:S15-S17. doi:10.1038/501S15a
5 Stejskal (2003) Journal of Pest Science 76: 170-172. doi: 10.1007/s10340-003-0015-4

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