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 has shown.
Not only do bees show no signs of avoiding neonicotinoid-laced food in lab tests, they seem to prefer it, a study in science journal Nature says.
“We now have evidence that bees prefer to eat pesticide-contaminated foods,” said 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 used to treat crop seeds and are absorbed by the plant, but then attack the nervous system of insect pests.
Research, however, has linked them to scrambling bees’ memory and navigation functions, affecting their ability to forage.
Bees have suffered colony collapse disorder, which has been blamed on mites, a virus or fungus, pesticides, or a combination of factors.
Pending clarity on the safety of neonicotinoids – a topic debated by scientists, environmentalists and agrochemical producers – the European Commission restricted their use in bee-attracting plants on December 1, 2013, for two years.
A second study by Nature last week 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. In the other study, Wright’s team used hundreds of bumble bees and thousands of honeybees in lab experiments – allowing them to feed freely from either a sucrose solution with neonicotinoid added-in concentrations from 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,” said Wright.
“Instead, they chose to feed on tubes containing either imidacloprid or thiamethoxam.”
Bees did not exhibit a preference for clothianidin.
“I believe that the experiments show that these compounds have a pharmacological effect on the bee’s brain,” she said.
Even if alternative food was provided where pesticides were used, the insects might prefer to forage on contaminated crops.
*AFP