Pesticides have knock-on effect for bees, study finds

bee
A honey bee robs a comb. Photo by Lynn Ketchum

Chronic exposure to pesticides has a bigger knock-on effect on bees than conventional probes suggest, according to a new study on Sunday touching on the mysterious collapse of bee colonies.

Biologists at the University of London carried out an exceptional field study into exposed to two commonly used agricultural insecticides.

They sought to mimic what happens in a real-life setting, where different crops are sprayed with different pesticides at different dosages and times.

Because get their food both from sprayed crops and , such variations make it hard to calculate the insects' total exposure to the chemicals.

In addition, very little is known about what happens to bees once they return to the colony after foraging, possibly passing on pesticide-laden food to .

A team led by Richard Gill monitored 40 , tagging 259 bees with (RFID) to time exactly when the insects left home or returned.

The colonies were divided into four groups.

Three were allowed to access feeder boxes, set up in the path of their nest boxes, that had a sugary syrup spiked with imidacloprid insecticide and/or a filter paper laced with another agricultural chemical, gamma-cyhalothrin.

The bumblebees were not constrained to visit the treated material—they could forage freely in the surrounding landscape for pollen and nectar.

The fourth group of colonies was a "control" or comparison group that did not have the feeder boxes.

In the colonies exposed to imidacloprid, fewer adult workers emerged from larvae and a higher proportion of foragers failed to return to the nest, the investigators found.

In those exposed to gamma-cyhalothrin, there was a higher death rate among .

And colonies that were exposed to both kinds of pesticides were likelier to fail.

The experiment was exceptionally long and detailed, the scientists say.

It lasted four weeks, whereas current guidelines test pesticides on bees for only up to 96 hours.

In addition, it looked at what happened when bees were exposed to two chemicals at the same time and at the changes in a colony's social structure.

"Our findings have clear implications for the conservation of insect pollinators in areas of agricultural intensification, particularly social bees, with their complex social organisation and dependence on a critical threshold of workers," says the study, published in Nature.

Beekeepers in Europe, North America and elsewhere are worried by so-called colony collapse disorder, a phenomenon which has been blamed on mites, a virus or fungus, pesticides or a combination thereof.

Bees are vital because they account for 80 percent of plant pollination by insects. Without them, many crops would be unable to bear fruit or would have to be pollinated by hand.

Another big concern is for honeybees given their commercial value.

Bumblebees too are important pollinators, but their colonies are far smaller than those of honeybees, usually with just a few dozen workers, which made it far easier for Gill to follow them.

Outside scientists who commented on the study hailed its innovation but noted that bumblebees could not be directly compared with honeybees, as they were biologically different.

"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," David Goulson, a professor of biology at Stirling University in Scotland, told Science Media Centre.

But, he cautioned, the impact remains "rather poorly understood."


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Use of imidacloprid - common pesticide - linked to bee colony collapse

More information: Paper: DOI: 10.1038/nature11585
Journal information: Nature

(c) 2012 AFP

Citation: Pesticides have knock-on effect for bees, study finds (2012, October 21) retrieved 25 April 2019 from https://phys.org/news/2012-10-pesticides-knock-on-effect-bees.html
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Oct 22, 2012
It makes one wonder how much pesticide is in our honey and other foods... and if it's connected with the increasing cancer rate in contemporary society...
...and it makes me want to grow all my own crops and raise my own animals for food... It's about the only way I'll know, for sure, what is and is not in my food.

Oct 22, 2012
It makes one wonder how much pesticide is in our honey and other foods... and if it's connected with the increasing cancer rate in contemporary society...

...and it makes me want to grow all my own crops and raise my own animals for food... It's about the only way I'll know, for sure, what is and is not in my food.


I'm pretty sure the only way you'll know for sure what is and is not in your food is doing chemical analysis on it all, in which case you would have nothing to eat. I don't think growing your own fruit and veg and raising your own animals is going to give you conclusive answers.

Oct 22, 2012
Pesticides are like pissing into one`s pants in cold weather. At first it will feel warm, but soon the negative long term effect will be felt. So the sooner pesticides are banned, the sooner the healing can start. But probably we just continue as usual and move further into the ecosystem destruction.

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