GM corn field studies endorse safety

Studies on the impact of genetically modified (GM) corn (Zea mays) on monarch butterfly caterpillars (Danaus plexippus) in the cornfields of Northern America provide more information on the environmental effects of genetically modified crops. Six papers published simultaneously in the on line early edition of Proceedings of the National Academy of Sciences seem to agree that Bacillus thuringiensis corn (Bt corn) has a negligible impact on monarch larvae populations, although it is suggested that one Bt corn hybrid could have sub-lethal effects on non target insect species. Bacillus thuringiensis was first described in Thuringia, Germany in 1911 and the toxins it produces have been available for pest control in commercial formulations since the 1930s. For many years Bt remained only a minor component of pest management. The bacteria finally received a celebrity status in 1996 when the first genetically engineered Bt corn was cultivated in the US. Bt corn is genetically modified to express a toxin extremely efficient in killing lepidopteran pests. The toxin degrades rapidly and cannot bind in the digestive systems of non-target animals. Following a study published in May 20 1999 Nature suggesting that pollen from Novartis Bt corn could harm monarch butterflies, the US Department of Agriculture (USDA) in conjunction with the Universities of Guelph-Ontario, Iowa, Nebraska and Maryland studied the impact of Bt corn pollen on non-target insect species, represented by monarch butterfly larvae. The results of these trials show that there is a distinct temporal and spatial overlap between monarch larvae and Bt corn pollen (Proc Natl Acad Sci USA 2001, 10.1073/pnas.211234298). But the impact of Bt corn pollen from current commercial hybrids on monarch butterfly populations is largely negligible (Proc Natl Acad Sci USA 2001, 10.1073/pnas.211329998 & Proc Natl Acad Sci USA 2001, 10.1073/pnas.211277798). The lack of Bt pollen effect may be due to the fact that a single rain shower can remove 54–86% of the pollen from leaves on the upper portion of milkweed plants — where monarch larvae tend to feed (Proc Natl Acad Sci USA 2001, 10.1073/pnas.211287498). Richard Hellmich, Assistant Professor at the Department of Entomology, Iowa State University and co-author on behalf of USDA, carried out a series of assays to establish the toxicity of Bt toxins present in various transgenic corn hybrids. His results suggest that pollen from the Cry1Ab (events Bt11 and Mon810), Cry1F, and experimental Cry9C hybrids, have no acute effects on monarch larvae in field settings. But, the pollen in the fields cultivated with the less used Cry1Ab event 176 hybrids consistently affected monarch larvae (Proc Natl Acad Sci USA 2001, 10.1073/pnas.211297698). In another study (not sponsored by the USDA) Zangerl and colleagues at University of Illinois at Urbana-Champaign, also found that the 176 Novartis hybrid had adverse sub-lethal effects on non-target insects (Proc Natl Acad Sci USA 2001, 10.1073/pnas.171315698). Despite their cautionary results, Zangerl et al. point out that even if non-target impacts of GM corn exists, these can be managed by careful selection of the Bt hybrid. The hybrid they identified with potential sub-lethal effects (Novartis event 176) represents less than 2% of GM corn currently planted in US. In addition, the US Environmental Protection Agency has said that it does not anticipate a re-registration for this hybrid. "That there may be non-target impacts of Bt corn is not in itself surprising. There are non-target impacts of any pest management approach. Risks and benefits of Bt corn must be evaluated relative to alternative methods of management," the authors said. The trials published in PNAS all investigate Bt corn pollen in the agricultural land of the US and Canada instead of using pollen 'naturally dusted' on plants in laboratories. Evidence accumulate in this way is clearly of enormous value in the ongoing debate surrounding the safety of GM crops. But, even with this new body of evidence that Bt corn has a negligible impact on the environment, it may still be hard to overcome the generally negative image of GM foods. Although the talk of 'Franken-foods' is often exaggerated and misleading, Governments and the biotech industry have already been forced to respond to many of the concerns of consumer groups and environmentalists. In 1999 Japan started a 5-year trial on GM corn but has a ban in place for the use of all Bt crops for agricultural purposes. Some Japanese companies have already abandoned all their research programmes into GM food. Whether insect tolerant plants can in practice harm non-target insects — and, by extrapolation, birds and mammals — is high on the list of questions for a multi-year farm-scale study currently underway in the UK. The UK government advisers on GM food maintain the view that researchers do not yet know whether the planting of genetically modified crops will make things better or worse. What is clear is that the use of Bt crops considerably reduces the exposure of farm workers to the chemical residues or classical pesticides and may increase profit margins for farmers. US farmers planting Bt corn in 1997 made about $72 million more than from conventional varieties. But the following year, when three times more acreage was planted with Bt corn, growers lost $26 million as pest infestation levels were low, leading to a reduction in pesticide use. "There is a need for maintaining a 'diverse toolbox' for pest management. Careful use of these tools can help to preserve their utility as well as to maintain environmental quality" concluded May Berenbaum, Professor and Head of Department of Entomology at University of Illinois at Urbana-Champaign.

GM corn field studies endorse safety

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