By Joseph Milton

Genetically modified (GM) crops can save farmers using conventional seeds even more money than those using the transgenic varieties, according to an analysis published in Science this week. And ensuring that some fields are kept free of the GM crops seems to be key to the overall success of the transgenic variety.

Researchers, led by entomologist William Hutchison of the University of Minnesota in St Paul, assessed the effects of planting maize (corn) genetically modified to produce Bttoxin, which kills the European corn borer (Ostrinia nubilalis). They found that since the crop was introduced in 1996, US farmers in the key maize-growing states of Iowa, Minnesota, Illinois, Wisconsin and Nebraska (see map below) had saved nearly $6.9 billion. Of that, conventional farmers saved just over $4.3 billion, some 62% of the total.

"We were surprised to find that a higher proportion of the total benefit is actually going to the non-Bt farmers," says Hutchison.

The reason for the conventional farmers' windfall is tied up in the effectiveness of the transgenic crop. Not only does Bt maize suppress the corn-borer population in fields planted with the GM crop, it exerts a 'halo effect', lowering the pest population in conventional maize fields too. As a result, farmers planting non-GM crops benefit from fewer pests, but don't have to pay the higher prices for the GM seeds.

Overall, Hutchison's team found that corn-borer populations have declined by between 27% and 73% across the five states in the 14 years since the transgenic crop was introduced.

"This work provides strong evidence for the reduced pest burden for non- Bt corn caused by the Bt corn, based on a reduction in overall pest-population size," says David Hopkins, director of science at the Scottish Crop Research Institute near Dundee, UK.

Conventional growers also help to stop corn borers becoming resistant to the Bt toxin by hosting pest populations that are susceptible to it, according to the team's research. Hutchison says that another species, the corn earworm (Helicoverpa zea), has evolved resistance to Bttoxin in situations where GM-crop coverage is 100%. But maintaining a mosaic of GM and non-GM fields means pests that develop a tolerance can breed with susceptible populations from conventional fields, slowing the evolution of full-blown resistance.

"Some farmers were very sceptical of entomologists telling them they needed to maintain non-Bt corn so they could grow corn borers," says Hutchison, "but over 14 years it's been very successful."

Conflict concerns

The results are positive news for GM seed producers. But 5 of the 18 authors listed on the Science paper work for big food or agri-business companies, including Syngenta Seeds in Slater, Iowa and General Mills in Le Sueur, Minnesota. Hutchison says that the authors who work for industry provided data about corn borers and were not involved in the financial calculations.

Margaret Mellon, director of the food and environment programme at the Union of Concerned Scientists based in Cambridge, Massachusetts, says that it is preferable if authors of scientific articles that could affect policy decisions don't have either financial or other interests in the outcome of the research. "But," she adds, "I wouldn't go as far as to say it undercuts the findings in this case." "By clearly providing all the affiliations of the authors in the paper, we provide transparency with regard to relationships that could have a bearing on the paper, and allow the reader to consider the affiliations when evaluating the research," says Natasha Pinol, a spokeswoman for Science.