A new study has linked oilseed rape crops grown from neonicotinoid-treated seed to the long-term decline in wild bee species across the English countryside.
The research, led by the Centre for Ecology & Hydrology, examined changes in the occurrence of 62 wild bee species with oilseed rape cropping patterns across England between 1994 and 2011 - the time period spanning the introduction of wide-scale commercial use of neonicotinoids.
The scientists found evidence suggesting that neonicotinoid use is linked to large-scale and long-term decline in wild bee species distributions and communities.
The decline was, on average, three times stronger among species that regularly feed on the crop such as Buff-tailed bumblebee (Bombus terrestris) compared to species that forage on a range of floral resources.
This indicated that oilseed rape is a principle mechanism of neonicotinoid exposure among wild bee communities.
Field of oilseed rape in flower
Neonicotinoids are a group of insecticide which can be applied to seed prior to planting.
The active compound is expressed systemically throughout the growing plant so can lead to potential ingestion where pollinators feed on the pollen and nectar of treated crops.
These findings add to previous small-scale and short-term exposure studies which have identified negative effects of neonicotinoids on honeybees and a limited number of commercially-bred wild bee species.
For five of the species investigated, including the spined mason bee (Osmia spinulosa) and the furrow bee (Lasioglossum fulvicorne), neonicotinoid use was equivalent to at least 20% of local population extinctions of wild bees
According to the researchers, the data suggest that neonicotinoid use is correlated with wild bee biodiversity losses at a national scales and has implications for the conservation of bee communities in intensively farmed landscapes.
The results add to an extensive body of evidence that will inform the review of the risks neonicotinoid pesticides pose to bees being undertaken by the European Food Standards Authority and anticipated to be complete by January 2017.
'Nullified by effects of neonicotinoids'
Lead author, Dr Ben Woodcock, said: "As a flowering crop, oilseed rape is beneficial for pollinating insects.
"This benefit however, appears to be more than nullified by the effect of neonicotinoid seed treatment on a range of wild bee species.
Dr Woodcock added: "Although we find evidence to show that neonicotinoid use is a contributory factor leading to wild bee species population decline, it is unlikely that they are acting in isolation of other environmental pressures.
"Wild bees have undergone global declines that have been linked to habitat loss and fragmentation, pathogens, climate change and other insecticides."
Paul de Zylva, nature campaigner at Friends of the Earth, said the study "adds a huge new peak to the existing mountain of evidence showing the risk these chemicals pose to our bees".
"This is the strongest ever evidence of harm to bees from neonicotinoid pesticides in British fields," he said.
"If the government genuinely wants to safeguard Britain’s bees, it must keep the ban on neonicotinoid pesticides regardless of what happens with Brexit – and tighten the way pesticides are tested and licensed for use."
Damaging impact
Emma Hockridge, head of policy for farming & land use said the results of the research "are horrifying".
"It adds to the strong and quickly growing body of overwhelming scientific evidence which points to the damaging impact of neonicotinoid pesticides on pollinating insects, including bumblebees and honey bees," Miss Hockridge said.
"There are a range of methods which farmers can use which do not require the use of neonicotinoid pesticides.
"Organic farmers use a system of production which has strong benefits for pollinator populations – for example a meta-analysis from Oxford University showed on average, non-organic farms have 48% more species of pollinators than non-organic farms."
