Beekeepers and conservationists have called for the continuation of a temporary EU-wide ban on a pesticide that is linked to a decline in pollinating insects, in the wake of the publication of new research.
An international team of scientists, including some at Trinity College Dublin, have found that although they cannot taste them and therefore cannot avoid them, bumblebees and honeybees are actually attracted to nectar that contains the pesticides known as neonicotinoids.
A second paper, also published in the journal Nature, found that in the field the use of neonicotinoid-treated plants has a negative impact on the behaviour and success of some bee species.
The studies back up several other pieces of research, which have found pesticide can have a negative impact on bee foraging and the fitness of colonies, prompting worries about the wider impact on other pollinators.
Bees and other insects are of fundamental importance to the pollination process and the increase in crop yields. Their value is estimated to be €14.6bn a year in Europe alone.
Against the backdrop of these concerns, in 2013 the EU temporarily banned the use of three neonicotinoids used on flowering crops for two years while efforts were made to study their effects on insects.
Some critics of this policy have argued that pesticide exposure could be reduced by planting alternative sources of nectar and pollen, implying that insects may choose to forage on other available flowers.
However, today's study found that when bees are given the choice between sugar solutions containing sucrose alone or sucrose laced with a neonicotinoid, neither honeybees nor bumblebees are repelled by the solutions containing pesticides.
Further experiments indicate that bees cannot taste neonicotinoids but still preferred to drink neonicotinoid solutions, implying that naturally foraging bees would be more likely to seek out flowers with neonicotinoid-laced nectar.
The second paper found that oilseed rape sown from seeds coated in neonicotinoids reduced wild bee density, solitary bee nesting, and bumblebee colony growth and reproduction, demonstrating that these pesticides pose a substantial risk to some bee species under field conditions.
"Our findings imply that even if alternative food sources are provided for bees in agricultural landscapes where neonicotinoid pesticides are used, the bees may prefer to forage on the neonicotinoid-contaminated crops," said Professor of Botany and Principal Investigator in the School of Natural Sciences at Trinity College Dublin, Jane Stout.
"Since neonicotinoids can also end up in wild plants growing adjacent to crops, they could be much more prevalent in bees' diets than previously thought."
The EU ban is coming up for review later this year, and ahead of that a new study was carried out by the independent European Academies Science Advisory Council.
The findings, published two weeks ago, found an increasing body of evidence that widespread use of neonicotinoids has a severe negative effect on non-target organisms, like bees and other insects, which provide ecosystem services, including pollination and natural pest control.
It also found clear evidence that neonicotinoids have sub-lethal effects on the future behaviour or fitness of non-target organisms.
Conservationists and beekeepers say all the findings taken together lend weight to an extension of the ban to allow for further research.
However, farmers in Ireland say that while they are respectful of the environment, the ban is impacting on the viability of certain crop production, particularly oilseed rape (OSR).
The Irish Farmers’ Association says the amount of OSR in production this year looks set to fall to 2009 levels as it struggles to return a viable return to growers.