Like nicotine for humans, certain pesticides seem to hold an addictive attraction for bees, which seek out tainted food even if it may be bad for them, research showed Wednesday (22 April).
Not only did bees show no signs of avoiding neonicotinoid-laced food in lab tests, they seemed to prefer it, said a study in the science journal Nature.
“We now have evidence that bees prefer to eat pesticide-contaminated foods,” said study author Geraldine Wright of Newcastle University.
This suggests, she said, “that like nicotine, neonicotinoids may act like a drug to make foods containing these substances more rewarding”.
Neonicotinoids are lab-synthesised pesticides based on the chemical structure of nicotine. They are widely used to treat crop seeds – designed to be absorbed by the growing plant and attack the nervous system of insect pests.
Previous research, however, has linked them to scrambling memory and navigation function in bees, affecting the little pollinators’ ability to forage.
Bees have been hit in Europe, North America and elsewhere by a phenomenon called “colony collapse disorder”, which has alternatively been blamed on mites, a virus or fungus, pesticides, or a combination of factors.
Bees account for 80% of plant pollination by insects – a function estimated to be worth at least $153 billion (€142 billion) a year globally.
Pending clarity on the safety of neonicotinoids, a topic that is fiercely debated among scientists, environmentalists and agrochemical producers, the European Commission has restricted their use in bee-attracting plants for two years, since 1 December, 2013.
A second study carried out by Nature on Wednesday found further evidence of risk for some bee species from neonicotinoids, which come in three types: clothianidin, imidacloprid and thiamethoxam.
Scientists in Sweden sowed eight fields with clothianidin-treated canola seeds, while another eight were untreated.
“The most dramatic result that we found was that bumble bee colonies almost didn’t grow at all at the .. treated sites compared to the control sites,” said project coordinator Maj Rundloef of Lund University.
There were also fewer wild bees in the contaminated sites, but honeybee colonies did not appear to be affected.
‘Like a drug’
In the other study, Wright and her team used hundreds of bumble bees and thousands of honeybees in lab experiments – allowing them to feed freely from either a sucrose solution with a neonicotinoid added in concentrations found in floral nectar in nature, or one without.
“Foraging-age bees of both species did not avoid any of the concentrations of any of the three neonicotinoids,” Wright told AFP by email.
“Instead, they chose to feed on tubes containing either imidacloprid or thiamethoxam,” she said.
Bees did not exhibit a preference for the third type, clothianidin.
“I believe that the experiments show that these compounds have a pharmacological effect on the bee’s brain,” she said.
This meant that even if alternative food is provided for bees in areas where pesticides are used, a solution suggested by some, the insects may prefer to forage on the contaminated crops anyway.
The European Crop Protection Association (ECPA), a trade group representing pesticide makers in Europe, contested the science behind the study published in Nature.
"Conducted in the laboratory – with a range of concentrations including some which are environmentally irrelevant – Kessler et al make the claim that bees have preference for forage treated with neonicotinoids; implying that this places bees at greater risk. However, a close inspection of the results of this study shows that bees experience no negative health effects when exposed to realistic amounts of these crop protection products," ECPA said in a statement.
ECPA was equally critical of the second study, by Rundlöf et al, saying the conclusions drawn on the risk posed to wild bees were questionable. "The very high pollen and nectar residues reported have not been seen in any other oil seed rape field studies. Likewise, as there are no benchmarks for wild bees it’s hard to put the findings into context."
"These studies are the latest exercises attempting to show negative effects of neonicotinoid pesticides on bees. The highly emotive discussion around the health of bees should be informed by studies which help people understand what’s really happening," ECPA said in a statement.
The Pesticide Action Network Europe (PAN), an environmental pressure group, said the Nature study added to a growing body of evidence that neonicotinoids are highly toxic to pollinators.
PAN urged the European Commission to take these studies into consideration when reviewing its partial ban on neonicotinoids later this year but said it was concerned that the process will be delayed by a pending impact assessment requested by Commission Vice-President Frans Timmermans.
Hans Muilerman, PAN Europe’s chemical officer said: “The European Commission is under enormous pressure from lobby groups such as ECPA and COPA-COGECA who fight
to maintain the use of neonicotinoids. It constantly shuts its eyes on all the derogations provided by Member States (Finland, Germany, Romania, Latvia in 2014). We feel citizen’s long term interest and environment protection are less important that financial interest of companies.”
The European Commission has launched a rescue plan for Europe’s dwindling honeybee colonies.
In January 2013, it adopted a 24-month ban on three widely-used neonicitinoid pesticides that the European Food Safety Authority (EFSA) says pose “high acute risks” to pollinators.
Around 16% of Europe’s honeybee colonies disappeared between 1985 and 2005 – with greater losses recorded in England, the Czech Republic, Germany and Sweden – according to the EU-funded Status and Trends of European Pollinators (STEP) project.
Insects such as honey bees and wild bees help pollinate around 84% of Europe’s 264 crop species and 4,000 vegetable varieties, contributing an estimated €22 billion to the EU's economy, STEP says.
The EU-funded STEP project recommends several ways farmers can protect bee populations:
- Try to avoid those pesticides known to have negative impacts on bees;
- Reduce the use of herbicides which suppress flowering plants;
- Leave uncultivated flower rich patches in farmland where pollinators can benefit from flowers and nesting resources;
- Plant mass-flowering crops (oilseed, clover and field beans) as part of rotations to provide extra nectar and pollen for bees and other insects.
- By 1 Dec. 2015: EU Commission to review ban on clothianidin, imidacloprid and thiametoxam
- European Commission: Bees & Pesticides: Commission goes ahead with plan to better protect bees
- European Food Safety Authority: EFSA identifies risks to bees from neonicotinoids (16 jan. 2013)
- European Environment Agency: Neonicotinoid pesticides are a huge risk – so ban is welcome, says EEA (2 May 2013)
Business & industry
- Copa-Cogeca: Statement on EFSA report (16 Jan. 2013)
- European Seed Association: EFSA states high level of uncertainty in its evaluations of neonicotinoids and their impact on bee health (16 Jan. 2013)
- European Crop Protection Association (ECPA): EFSA acknowledges high level of uncertainty in its negative evaluation of the risk of neonicotinoids to bees (16 Jan. 2013)
- Pesticide Action Network Europe: Save the honey bees