Armyworm on the march

January 2015

Fall armyworm. Photo from Wikimedia Commons
'Fall armyworm' is a long-distance migratory insect distributed from Argentina to Canada. It is a major pest of both maize and cotton, and has a wide host range of over 80 plant types, including several grasses.
To beat fall armyworm, GM 'Bt' insecticidal crops have been planted since 2001. Despite reports from Puerto Rico of resistance emerging in the pest only three years after first planting the Bt maize (after which the GM crop was banned there), tests for something similar happening in mainland America weren't carried out until 2011.
Researchers were surprised to find very significant levels of Bt resistance genes in fall armyworm collected in non-maize and non-Bt sweetcorn crops in Florida and North Carolina. They presented "compelling evidence"of field-evolved resistance which seems to be geographically extensive in South East America. Based on weather patterns, the authors suggested that the resistant pests had migrated from Puerto Rico.
Worryingly for the biotech industry, the researchers also showed cross-resistance between the original Bt gene type which caused the problem in Puerto Rico and three other insecticidal GM maize strains.
As the authors pointed out, geographic isolation seems not to have been a barrier to the spread of resistance to the GM insecticide. The presence of huge Bt-free natural 'refuges' of alternative host-plants for the fall armyworm doesn't seem to have dented the pests' resistance. Also the resistance gene doesn't seem to come at any cost (such as a physiological weakness or energy-drain) to the insects which would limit the problem.
The lesson is that changes in wildlife quality in response to GM toxins can be permanent and far-ranging, and can spread even in the absence of any continuing "evolutionary pressure" from the presence of the toxin. This points to a fundamental flaw in the whole concept of using genetically engineered insecticidal-producing genes to control pests. It also raises more questions about the assumption that Bt crops will remain effective if farmers plant non-Bt refuges. 
About time we asked for more scientific attention and cash directed at crop management techniques and conventional breeding to reduce pest problems.
  • Fang Huang, et al., 2014, Cry1F Resistance in Fall Armyworm Spodoptera frugiperda: Single Gene versus Pyramided Bt Maize, PLOS ONE 9:11
  • Fall armyworm, University of Florida, reviewed February 2014

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