Impacts of neonicotinoid use on long-term population changes in wild bees in England

This study tested whether commercial use of neonicotinoids on oilseed rape (OSR) crops in England can be linked with bee declines in the wild at a national scale. Laboratory and field tests have demonstrated both lethal and sublethal effects from neonicotinoid exposures. Yet, these studies are unable to determine whether neonicotinoids are linked to bee declines at timescales relevant to population level processes.

Using 18 years of information from a wild bee distribution dataset and relating it to pesticide use survey data, this correlational study was the first to evaluate the long-term impact on wild bee populations from neonicotinoid use in OSR. The researchers found evidence that sublethal impacts of neonicotinoid exposure is linked to large-scale population extinctions for wild bees in England. More specifically, the study demonstrated that exposure to neonicotinoids from use of coated OSR seeds can impact the population persistence of wild bee communities. Still, the reductions have not led to population extinctions on a national scale.

The effects of neonicotinoids are strongest for, but not limited to, species known to forage on OSR. The negative association was 3 times greater for the species that foraged on OSR compared to bee species not known to forage on OSR. The researchers also found a positive association between OSR cover with the distribution of OSR foraging bees. Yet, the benefits of OSR cover do not compensate for the negative effects of neonicotinoid exposure.

Researchers also evaluated the impact of foliar applications of insecticides. Foliar applications of insecticides, including neonicotinoids, had little or no negative consequences on the persistence of wild bee populations. It was hypothesized that the lack of a correlation could be due to management decisions that minimize exposure during foliar applications.

While not studied, the findings suggest that other mass flowering crops (e.g., sunflowers) could similarly provide a route of exposure to neonicotinoids, thus negatively impacting wild bee population persistence. Finally, researchers point out the need for further study on the capacity of bees to recover from the effects of neonicotinoid exposure.

Further information is available in an article on the blog of the Centre for Ecology and Hydrology, at: http://www.ceh.ac.uk/news-and-media/blogs/wild-bees-neonicotinoids-defining-decline.