Pesticides More Perilous To Bees Than Previously Thought
October 22, 2012

Pesticides More Perilous To Bees Than Previously Thought

Lawrence LeBlond for - Your Universe Online

There´s more bad news for bees. Biologists from the University of London say that exposure to pesticides are having a broader, previously unforeseen effect on bumblebee populations.

While pesticides have been blamed for bee decline in the past, studies on the issue have focused mainly on single pesticides at high doses. The new British study is the first to take a more direct look at the effect of a combination of chemicals and at the sort of levels typically seen in rural settings.

London biologists have found that bees exposed to high levels of crop chemicals were more likely to gather less pollen and get lost more often. The researchers also discovered a higher mortality rate in young bees.

The scenario is frightening. Since the 1980s, the British honeybee population has been cut in half due to a number of forces, with colony collapse disorder (CCD) at the forefront of this long-standing calamity. Not only are bees in decline, but three of the UK´s 25 bumblebee species are now extinct.

To probe the issue of crop chemicals, the Royal Holloway team of researchers created 40 controlled colonies of bumblebees. Some of which were exposed to the pesticide Imidacloprid for four weeks, others to a generic crop spray. A third group were exposed to both chemicals, and the last group was kept clear of all pesticides.

In a real world, the researchers said it would have been difficult to calculate the insects´ total exposure to chemicals, partly because these bees get their food from both sprayed crops and wild plants. In the controlled setting, the researchers were able to mimic the real-world by spraying crops with different pesticides at different dosages and at different times.

The team, led by Richard Gill, tagged 259 bees with radio frequency identification (RFID) to monitor their movements, allowing them to see when these bees left home and then returned. The team set up the groups in a way that only three were allowed to access feeder boxes, set up in the path of their nest boxes. The feeder boxes contained a sugary syrup laced with the Imidacloprid insecticide and/or a filter paper laced with another chemical, gamma-cyhalothrin. These bumblebees were not constrained, and were allowed to forage freely in the surrounding landscape for pollen and nectar. The fourth group, the “control,” did not have access to the feeder boxes.

The team found that bees exposed to Imidacloprid foraged more often, yet collected less pollen on their trips and were 55 percent less likely to make it back to their nest. The researchers believed the pesticide caused them to become confused. Furthermore, the researchers found four times as many bees dead in the nest colonies exposed to the crop spray, compared with those who were not in contact with either chemical.

The study was not able to determine, however, if the deaths of young bees in the nest was due to poisoning by pesticide-tainted food, or if exposure to the chemicals led to the worker bees providing less care to their young in the nest.

Study coauthor Nigel Raine said that pesticides are playing a significant role in the decline of Britain´s bumblebees. Other causes include farming, climate change, pollution and disease. “There is an urgent need to understand the reasons behind current bee declines as they are essential pollinators of many agricultural crops and wild flowers,” he warned.

“Our findings have clear implications for the conservation of insect pollinators in areas of agricultural intensification, particularly social bees, with their complex social organization and dependence on a critical threshold of workers,” said the research team, reporting in the journal Nature.

The four-week-long study showed that more research is needed into chemical use on croplands. Currently, guidelines only require pesticides to be tested for up to 96 hours (4 days).

“This new work adds another substantial boulder to the rapidly growing mound of evidence which now points to a significant and worrying impact of these chemicals on our wild bumblebees.,” said Professor David Goulson of the University of Stirling.

“This new study also highlights the threat posed by exposing beneficial insects to mixtures of toxic chemicals, something which all bees face in agricultural environments, but the effects of which are rather poorly understood,” added Goulson, who was not involved in the study.

The Department for Environment, Food and Rural Affairs said it is conducted its own research on the risks of pesticide to bumblebees.

“We are looking at the risks of pesticides to bees, as we take any threat to them very seriously,” said a spokesman for the agency. “However, until we have all the evidence back from our research, we won´t be putting in place any new restriction.”

“We will act if our evidence shows the need,” the spokesman noted.

CCD, a phenomenon that has swept across the globe killing as much as half of all bumblebees, has been blamed on mites, viruses, fungi, pesticides, or a combination of these factors. The issue has experts and apiologists scratching their heads trying to find an answer to end the reign of the deadly condition and bring bee populations back to healthy numbers.

Bees are vital because they account for 80 percent of plant pollination by insects. Without them, many crops around the world would be unable to bear fruit, without the aid of man, stepping in and taking the place of bees as pollinators.

Bumblebees, which were included in the current study, are biologically different from honeybees. As such, the study conclusions cannot be directly compared to other bee populations, including the commercially important honeybee.