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Attempts to find a new generation of pesticides to replace neonicotinoids have been dealt a potential blow.

Neonicotinoids are the most commonly used insecticide in the world, but had been linked to bee declines.

Studies suggest a new type of pesticide seen as an alternative to the chemicals, which have been banned in many countries, may have similar risks.

The new insecticides may reduce bumblebee reproduction in the wild, according to a study by UK scientists.

The alternatives had been sought because of the evidence linking neonicotinoids to declines in bee populations - leading to the bans and restrictions on their use.

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A study, published in journal, looked at how one of the new class, known as sulfoxaflor, impacts on healthy, wild bumblebees.

Exposed bees had fewer offspring when released into the wild compared with unexposed bees.

"Our results show that sulfoxaflor can have a negative impact on the reproductive output of bumblebee colonies under certain conditions," said study researcher Harry Siviter of Royal Holloway, University of London.

What are the new insecticides?

The new insecticides, based on a chemical known as sulfoximine, have a different chemistry from neonicotinoids and have been seen as a likely successor.

The chemicals kill insect pests by disrupting their nervous system.

They have been approved for use in China, Canada and Australia, with applications underway in many other countries.

Sulfoximine pesticides are not currently licensed in the UK.

What are the implications of the research?

The researchers are calling for regulatory bodies to look at non-lethal effects on bees before issuing a license for new products.

They say we need to know more about what levels of insecticides bees will be exposed to in the wild in order to be able to determine the true risk.

"Our study highlights that stressors that do not directly kill bees can still have damaging effects further down the line, because the health of the colony depends on the health of its workforce," said Dr Ellouise Leadbeater of Royal Holloway, University of London.

What about neonicotinoids?

Scientific studies have linked their use to the decline of honeybees, wild bees and other pollinators.

Other factors also cause bee declines, including habitat loss and disease.

Manufacturers and some farming groups have opposed moves to restrict their use, saying the science remains uncertain.

The campaign group Friends of the Earth said the upcoming ban on neonicotinoids is great news for bees - but the government must ensure that alternative pesticides don't harm pollinators too.

"This study shows that replacing one harmful pesticide with another is not the solution to protecting our crops," said pesticides campaigner, Sandra Bell.

The NFU, which represents British farmers, said farmers need "an effective crop protection toolbox available to combat pests and allow them to produce food for the public".

Senior plant health adviser Emma Hamer said many farmers follow methods to keep the use of plant protection products to a minimum.

"All the products farmers do use have to go through a stringent approval process before they can be registered for use to ensure they pose no unacceptable risk to people or the environment, and are applied in a highly controlled, highly regulated way."