Solitary bees thrive in flowering oilseed rape

Some species of native wild bees are thriving in the UK, largely thanks to the increase in oilseed rape area and the adoption of intensive minimal tillage cultivation techniques by growers.

Speaking at a meeting of leading oilseed rape growers in the Cotswolds earlier this month, independent entomologist and bee specialist, Mike Edwards, highlighted that where the short life-cycle of a solitary mining bee species coincided with the crops’ flowering, the wealth of food resource had helped to support and, in some cases, significantly increase their numbers.

Furthermore, with the mining bees nesting and laying their eggs in a network of holes beneath the ground, they were undisturbed by minimal cultivations at a shallow depth and could safely emerge in the following year – when the next season’s oilseed rape was again in flower.

“Although the oilseed rape typically moves from field to field in the farm’s rotation, solitary bees are remarkably adept at seeking out the good food resources. If the subsequent nesting sites are undisturbed, be that in the field or dedicated habitat areas, there is real chance for bee numbers to increase,” he said.

Belinda Bailey
Belinda Bailey

Mr Edwards highlighted that the solitary mining bee species, Andrena cineraria, one that had increased in line with the increase in the in area of oilseed rape crops over the past two decades, since its six-week adult life cycle was predominately over the crops’ flowering period.

Reports of bee monitoring on the National Biodiversity Network website, exclusively provided by the Bees, Wasps and Ants Recording Society (BEWARS), have highlighted the increase in A. cineraria distribution across the UK between 1970 to 1990, compared to 1990 to 2010 – which mirrors the increase in oilseed rape area.

Furthermore, Mr Edwards reported monitoring has shown Andrena haemorrhoa could now be found in almost every oilseed rape crop across southern England, with A. scotica, A. chrysosceles and A. nigroaenea among the half a dozen or so Andrena species typically observed in over half of all rape fields. Importantly, these solitary bees have increasingly been recognised as especially efficient pollinators of oilseed rape and other crops.

Mike Edwards & Mason bee in flowering rape trial
Mike Edwards & Mason bee in flowering rape trial

“Unlike the honey bee and most of the bumble bee species, which build up a colony over the season and require a long supply of food resources, the solitary bees typically need a focussed flowering over a short period to complete their life-cycle.

“Flowering crops and fruit can provide the essential food, which can be importantly supplemented and extended by the creation of wildflower margins and areas. This also serves to provide nesting sites for all the bee species, along with vital habitat for a vast array of other insects and farm biodiversity,” he advised.

Also speaking at the meeting, Syngenta UK Operation Pollinator Manager, Belinda Bailey, advised that specific habitat creation by farmers could play an important role in further increasing pollinator numbers across a range of bee species. “Research has shown that, by establishing good quality flowering habitats, the levels of many pollinating insects increase. Not only is this good for wildlife, but it also brings the potential for better quality and yields for crops which benefit from insect pollination.

“The quality of the habitat created has a particularly positive effect on wild bees and recent work looking at pollination in OSR suggests that the solitary bees are the most effective at carrying out the pollination in the crop,” she said. Additionally, the Operation Pollinator initiative can play an important role in increasing overall farm biodiversity, protecting soil and water resources and meeting the objectives of Government and EU environmental schemes, as well as improving the public perception of farming.