Oct 23

Pesticides used in farming are killing bumblebees and affecting their ability to forage, putting colonies at risk of failure, according to a new study.

Photo of a buff-tailed bumblebee

Buff-tailed bumblebee on flower

An estimated one-third of all plant-based foods eaten by humans rely on bees for pollination, and bees and other pollinators have been estimated to be worth around $200 billion a year to the global economy. However, bee numbers have been plummeting in recent years, particularly in North America and Europe.

As bees provide around 80% of pollination by insects, it is vital to understand and deal with the causes of these declines.

Colony effects

Recent studies have suggested that pesticides may play a role in bee declines, as pesticide exposure can cause changes in bee behaviour and reduce the production of queens in colonies. However, the overall effects at the colony level are less well understood. Bees are also exposed to a number of different pesticides while foraging, but their combined effects have rarely been investigated.

Photo of honey bee performing waggle dance

Honey bees

In the new study, published in Nature, scientists exposed colonies of bumblebees to the pesticides neonicotinoid and pyrethroid over four weeks, at levels similar to those found in the field.

Most previous studies have focused on honey bees, which are smaller than bumblebees but have much larger colonies, sometimes numbering tens of thousands of individuals. In contrast, bumblebees form colonies of just a few dozen individuals, potentially making them more vulnerable to impacts at the colony level.

Photo of a small garden bumblebee nest

Nest of the small garden bumblebee

The findings showed that long-term exposure to the two pesticides impaired the foraging behaviour of the bees and increased worker mortality, leading to significant reductions in colony success. The researchers also found that being exposed to a combination of more than one pesticide increased the likelihood of a colony failing.

Effects at the individual level can have a major knock-on effect at the colony level. That’s the novelty of the study,” said Richard Gill, the lead author of the study.

Important piece of the jigsaw

According to the researchers, the new findings emphasise the need for wider testing of pesticides. They endorsed the recommendations of the European Food Safety Authority (EFSA) that pesticides should be tested over longer periods and that new protocols should be developed to detect the cumulative effects of multiple chemicals on bees. There should also be separate assessments for different bee species.

Photo of female common carder bumblebee feeding from flower

Common carder bumblebee foraging

Parasites and habitat destruction, leading to a reduction in food supplies, have also been blamed for the decline in bee populations. A number of different factors are likely to be involved, and more research is still needed.

My guess is that the decline of bees is like a jigsaw – there are probably a lot of pieces to put into place. This is probably a very important piece of that jigsaw,” said Gill.

Read more on this story at The Guardian – Pesticides put bumblebee colonies at risk of failure, study finds.

View photos and videos of bees on ARKive.

Liz Shaw, ARKive Text Author

  • Robert Vincin (October 25th, 2012 at 6:10 am):

    Albert Einstien said “if bees disappear mankind has but 4 years left”. Bees also pollinate the clovers and like soil enriching ground cover hence the impact far wider that the above report. These chemicals also impacting on mictrobes. Ancient and informed Farming communities recognise and use weeds as part of the Farm cycle. Many weeds are utilised in medicines and indeed they are C4 photosynthesis pathway sequestering CO2 to store CO2 as carbon. Robert Vincin

  • Hannah (November 3rd, 2012 at 5:14 pm):

    I think bees are seriously underestimated and do not get the treatment they deserve, especially after enabling us to have lovely honey.
    Pesticides are not the only threat to bees.