Wildlife

Neonic pesticide link to long-term wild bee decline

The large-scale, long-term decline in wild bees across England has been linked to the use of neonicotinoid insecticides by a new study. Over 18 years, researchers analysed bees who forage heavily on oilseed rape, a crop widely treated with "neonics".

The scientists attribute half of the total decline in wild bees to the use of these chemicals while industry sources say the study shows an association, not a cause and effect.

In recent years, several studies, conducted in the lab and in the field, have identified a negative effect on honey bees and bumble bees from the use of neonics. But few researchers have looked at the long term impacts of these substances.

This new paper examined the impacts on populations of 62 species of wild bees across England over the period from 1994-2011. The team, from the Centre for Ecology and Hydrology (CEH), used distribution data on wild bees, excluding honey and bumblebees collected by the bees, ants and wasps recording scheme. They were able to compare the locations of these bees and their changing populations with growing patterns of oilseed rape across England over 18 years. The amount of this crop being sown has increased significantly over the period of the study, from around 500,000 hectares in 1994 to over 700,000 in 2011.

A key innovation was the commercial licensing of neonicotinoid insecticides for the crop in the UK in 2002. Seeds are coated with the chemical and every part of the plant becomes toxic to pests.

Manufacturers hailed the development as a major advance, reducing the need for leaf spraying with other insecticides. Around 85% of the oilseed rape crop in England now uses this method for pest protection.

But this new work suggests, for the first time, that the detrimental impacts seen in the lab can be linked to large scale population extinctions of wild bees, especially for those species of bees that spend longer foraging on oilseed rape.

There was a decline in the number of populations of 10%, attributable to neonicotinoids, across the 34 species that forage on oilseed rape. Five of the species showed declines of 20% or more, with the worst affected declining by 30%. Overall, half the total decline in wild bees could be linked to the chemicals.