Planet Earth Online

Limiting grass growth could help bees

1 April 2011, by Tamera Jones

Increasing the numbers of wildflowers growing on farmland could encourage bumblebees and butterflies, because they provide the insects with the pollen and nectar they need for their food.

Bumblebees and honeybees pollinate a long list of crops from apples to strawberries, and runner beans to oilseed rape. Honeybees also collect nectar which they turn into honey. Butterflies can pollinate some tropical crops and wildflowers, but they're more important as food for farmland bird species.

Over 70 per cent of the world's major food crops depend on bees for pollination, which is worth an estimated £120 billion.

But worldwide bee declines have led conservationists to claim we're in the middle of a global pollination crisis. And while the disappearance of the honeybee is on most people's radars, the bumblebee hasn't received quite the same attention.

In the last 20 years, one of the UK's 15 species of bumblebee has gone extinct, seven are in decline, and seven are classed as stable.

'The most common bumblebees use lots of different types of habitat, so they're not doing too badly. But the ones that are in trouble are much more specialist and can only feed on nectar from a few different types of flowers,' explains Robin Blake from the University of Reading, lead author of both studies.

On the back of an increasing awareness of the negative effects of intensive farming on biodiversity, the UK government has funded numerous schemes to help restore habitats to support native wildlife.

'Farmers are paid to sign up to these schemes so that their land is managed in an environmentally friendly way,' says Blake.

While there are schemes that encourage farmers to sow wildflower seeds on parts of their land, few farmers have signed up. 'Less than 0.05 per cent of English agricultural land is set aside for schemes which help bumblebees,' says Blake. 'We just don't have enough habitat to support bumblebees and could be doing more.'

But this latest research suggests that sowing wildflowers into existing buffer strips to encourage pollinators isn't enough on its own, because the grasses that grow in these strips are so competitive.

To find out how to help pollinators, Blake and colleagues from the University of Reading, the Centre for Ecology & Hydrology, and Syngenta applied three different treatments to grass buffer strips on two farms in southern England.

In the first, the grass buffer strip was left as it was, so served as a control. In the second treatment, the researchers cultivated a grass buffer strip and sowed wildflower seeds. In the final treatment, they cultivated the strip, treated it with a grass-specific herbicide (called fluazifop-P-butyl) and then sowed nine different types of wildflower seeds. The wildflowers the researchers chose are cheap, easy to get hold of, and are good for bees and butterflies.

They then checked how many bumblebees and butterflies visited the areas over three consecutive years.

Significantly more wildflowers grew on the land that had been cultivated, sown with wildflower seeds and treated with herbicide than in the other two treatments.

Over the three years, the scientists counted 279 bumblebees, with the majority visiting strips that had received the final treatment: over 75 per cent of visits were to red clover and common knapweed flowers.

They also found that many more butterflies visited the treatment three strip compared with the other strips.

'If Natural England and Defra were to implement these treatments, we could see more bees, which would certainly help farmers, and would be better for the economy,' says Blake.

However, he points out that this study only concentrated on two farms in southern England, so is only preliminary. 'We need to rollout this approach to lots of farms across the whole country to see if we get the same result,' he says.

The research is published in Pest Management Science and the Journal of Insect Conservation.

Keywords: Biodiversity, Europe,

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