France said it plans to ban a pesticide made by Swiss agro-chemical group Syngenta that is widely used to treat rapeseed crops after scientists suggested it could pose danger to bees.

A sharp decline in bee populations across the world in recent years, partly due to a phenomenon known as Colony Collapse Disorder, has prompted criticism of pesticide use, although research has yet to show clearly the causes of falling bee numbers.

France intends to withdraw the permit of the Cruiser OSR pesticide used for coating rape seeds, pending a two-week period during which Syngenta can submit its own evidence, Agriculture Minister Stephane Le Foll said on Friday.

The decision was based on a report from French health and safety agency ANSES, which went along with recent scientific findings suggesting that a sub-lethal dose of thiamethoxam, a molecule contained in Cruiser, made bees more likely to lose their way and die.

"To protect rapeseed plants there exist alternatives to coating seeds that are already widely used. If the withdrawal of the authorisation (for Cruiser OSR) is confirmed, farmers will therefore have solutions to call on," Le Foll said in a statement.

Syngenta rejected the move as based on a single study and not backed up by field observations.

"Currently in France you have 650,000 hectares that are cultivated (with Cruiser-treated rapeseed), and there are no cases of bee mortality identified as being linked to Cruiser," Laurent Peron, head of corporate communication for Syngenta France, told Reuters.

This crop area amounts to nearly half of about 1.5 million hectares of rapeseed sown in France. In Europe, more than 3 million hectares of rapeseed use Cruiser, including in Germany, Peron said.

France seeks EU review

France is the largest crop producer in the European Union and with Germany is the leading EU grower of rapeseed, used for making vegetable oil and biodiesel fuel.

The French ban on the pesticide will take effect before the start of the next rapeseed sowing campaign in late summer, a farm ministry official said, stressing that it would not affect versions of Cruiser used for other crops such as maize (corn).

France also has asked the European Commission to reconsider its criteria for authorising Cruiser for rapeseed ahead of the next sowing campaign, Le Foll said.

In its report, ANSES said while exposure of bees to thiamethoxam in actual field conditions was lower than in the recent study on bee navigation, a similar level could not be excluded in some circumstances.

More research is needed at European level on the impact on bees as well as a broader review of the neonicotinoid family of substances to which thiamethoxam belongs, it said.

In a separate opinion published on Friday, the European Food Safety Authority said doses of neonicotinoids tested in the bee research were above the highest residue levels actually recorded in plant nectar, adding that more studies were needed to evaluate exposure in different field situations.

Dave Goulson of Stirling University in Scotland, who led another recent study on risks to bees from neonicotinoids, said there was growing evidence that these chemicals may play a role.

"It would be massively oversimplifying to say that these chemicals are the only cause of bee decline, although it is clear they are a part of the problem," he told Reuters.