Resistance management under fire
Not all farmers in the USA appear to be complying with the resistance management requirements for genetically modified Bt maize. A consumer protection organisation has evaluated data from the Environmental Protection Agency (EPA) and concludes that the proportion of farmers following the rules has been declining for some years. At the same time, Americans are discussing whether the requirements can be relaxed as new maize varieties are being developed.
In the past, insects have, sooner or later, developed resistance to most of the active substances used to control insects. So it is theoretically possible that large-scale cultivation of Bt maize could lead to a rapid increase in insects that have a survival advantage. So far, however, no maize pests have developed resistance to Bt proteins .
To prevent the development of resistance, farmers in the USA are required to plant fields with non-Bt plants in the vicinity of Bt maize fields. This provides a refuge where non-resistant European corn borers and Western corn rootworms can survive. This can ‘thin out’ any resistances that develop. The refuges have to cover 20 per cent of the total growing area and be planted at set distances from the Bt fields.
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In the USA, these measures have to be supervised by the firms that sell genetically modified seed. They have to train the farmers in resistance management and demonstrate to the EPA that the relevant requirements have been complied with. To do this, the seed companies commission anonymous interviews by telephone and, since 2007, over the internet. Employees also conduct standardised face-to-face interviews on farms. The results of all the surveys are compiled in a joint report each year and submitted to the EPA. The Center for Science in the Public Interest (CSPI), an American consumer organisation, has evaluated the data on resistance management for Bt maize for the years 2003 to 2008. According to the data from face-to-face interviews on farms, up until 2006, around 95 per cent of the farmers surveyed complied with the requirements when growing Bt maize that is resistant to the European corn borer or Western corn rootworm. By 2008 this figure had dropped to around 85 per cent. Similar results were found for maize varieties that are resistant to both pests. The results from telephone and internet interviews were worse, especially for maize resistant to the Western corn rootworm or to both pests. According to this data, the percentage of farmers complying with the requirements fell to less than 75 per cent in 2008. In an open letter addressed to the Director of the EPA, the CSPI has called for reapproval of genetically modified maize varieties, which is due for all GM varieties in the USA in 2010, to be made conditional on firms achieving a significant improvement in compliance with the resistance management measures. |
At the same time, the seed companies are developing new genetically modified maize varieties which they hope will make it possible to relax the resistance management requirements. These maize varieties produce different Bt proteins to combat the same pest, which considerably reduces the probability of resistance developing. The plan is that the new maize varieties will allow the refuges to be reduced to as little as 5 per cent of the cultivation area. However, a report published in November 2009 on the impacts of GM crops on the use of pesticides warns against this course of action. The report says that experience with chemical plant protection agents shows that resistance can take ten to fifteen years to develop. Genetically modified Bt crops have been grown in the USA since 1996. First populations of Bt-resistant pests were found in Bt cotton between 2003 and 2006, and a recently published study shows that the cotton bollworm can develop multiple resistance. Against this background, the report recommends waiting a few years before relaxing the resistance management requirements for Bt maize.
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