Neonicotinoids may not be the cause of declines in bee populations, according to a University of Sussex study.
Flowering crops, such as oilseed rape, are an important source of forage for bees, but the scientists behind the Sussex research said this benefit had often been overlooked by previous field studies.
As a result, they chose to explore the ‘net impact’ of neonicotinoids on bees by looking at the combined benefits and costs of oilseed rape grown from thiamethoxam-treated seeds.
The team found 36 colonies of honey bees and bumble bees near fields of treated oilseed rape, and another 36 colonies several kilometres away from the fields, but in the same ecosystem.
They then measured the effect of the location on the bee colonies during the flowering period of the plants, looking at hive weight, the number of bees and the survival of queen bees.
The results showed the colonies of bumble bees were not significantly affected by their distance from the oilseed rape, and the researchers attribute this to the fact that any negative effects of the insecticide could be offset by improved food supply – a finding backed up by other research.
The survival of the honey bee colonies and queen bees were also unaffected, though there was a small negative effect on the colonies’ weight gain and honey contamination.
Dr Chris Hartfield, senior regulatory affairs adviser at the NFU, said: “The NFU has always called for a more balanced assessment of benefits and costs.
“Back in the summer, the landmark Centre for Ecology and Hydrology study showed only beneficial effects for bees from neonicotinoid use in German field study sites and the researchers suggested this was due to good quality forage resulting in healthier bees.
“This study makes a similar finding, that the benefits of plentiful food, such as from a mass-flowering crop of oilseed rape, can counteract any harmful impacts of neonicotinoid use on the crop.
“This also reinforces a key concern beekeepers often raise with us, which is without neonicotinoids to control pests, farmers are planting less oilseed rape and the resulting loss of this crop as a foraging resource will have more impact on their bees than neonicotinoids ever did.”