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GM crops that make their own insecticide also deliver benefits for their conventional plant neighbours, a study in China has concluded.

These strains seem to boost populations of natural pest-controlling predators, and this effect spills over to non-transgenic crops, the research found.

Details of the work by a Chinese-French team <link> <caption>appear in the journal Nature</caption> <url href="http://www.nature.com/nature/journal/vaop/ncurrent/full/nature11153.html" platform="highweb"/> </link> .

But one group critical of GM planting described the effect as a spillover "problem", not a "benefit".

Scientists investigated a modified version of cotton grown in China that generates a bacterial insecticide.

The strain has led to a reduction in the use of insecticide to control a major pest, the cotton bollworm.

After the GM cotton was introduced, researchers saw a marked increase in numbers of pest predators such as ladybirds, lacewings and spiders.

At the same time, populations of crop-damaging aphids fell.

The predatory insects also controlled pests in neighbouring fields of non-GM maize, soybean and peanut crops, said the team led by Dr Kongming Wu from the Chinese Academy of Agricultural Sciences in Beijing.

Commenting on the study, Professor Guy Poppy from the University of Southampton, UK, said: "Global food security will require us to sustainably intensify agriculture. Opponents of GM have argued this can't be done through biotechnology, whereas this research challenges this view and demonstrates the wider benefits of using GM plants.

"By reducing the need for insecticides against caterpillars, insect biodiversity is increased and this is shown to have added benefits outside of the GM crop field."

Emma Hockridge, head of policy at the Soil Association, the British campaign group that advocates organic farming, said: "Encouraging predator insects is crucial to managing crop pests sustainably - indeed, that's how organic farmers avoid pesticides, using natural processes to encourage beneficial predators.

"This study finds that Bt cotton is a better habitat for such predators than cotton that has been sprayed with pesticides.

"What it doesn't cover is other recent research in China that has discovered increased insect resistance and increased numbers of pests developing in and around these GM cotton crops."

Previous research by Dr Wu showed that one crop pest - the mirid bug - had <link> <caption>boomed since the introduction of Bt Cotton</caption> <url href="http://www.sciencemag.org/content/328/5982/1151" platform="highweb"/> </link> , as it filled the gap left by other cotton pests. This had driven farmers back to using pesticides.

Professor John Pickett from Rothamsted Research, UK, commented: "Many, including distinguished scientists, have looked for associated problems as the technology has been commercially developed throughout the world and, of course, we should always exercise caution in introducing new technologies.

"However, use of GM-based Bt resistance to pest insects would not have advanced so dramatically without advantages, not least a reduction in use of insecticides against the target lepidopterous insect larvae."