Flowers Contaminated With Metal Behind Bumblebee Decline

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More than a little evidence has linked pesticidesto the alarming decrease in the number of bumblebees in the U.S. Now new research from the University of Pittsburgh suggests another factor: metal pollution.

According to a recent study in the journal Environmental Pollution, bumblebees are ingesting metals such as aluminum and nickel in toxic amounts. The metal comes from flowers that have been grown in soil contaminated by exhaust from a combination of motor vehicles, industrial machinery and farm equipment. Modern agriculture practices, in which more and more tasks are mechanized, are contributing to the decline in bumblebee numbers.

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Bumblebees can detect the presence of certain metals in flowers by tasting them, but not from afar - that is, by the time they've identified metal, they've ingested some. The bees are able to ignore some metals and will still forage from contaminated flowers, so moderate to high levels of metals can accumulate in the tiny creatures' bodies over time.

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Tia-Lynn Ashman, a biological sciences professor at Pitt and a PhD student in her lab, George Meindl, studied bumblebee behavior around uncontaminated and contaminated Impatiens capensis. This North American flower provides an "ideal place" for bumblebees to seek out food as it has large blossoms and produces plenty of super-rich nectar daily. The researchers collected fresh flowers for two weeks and observed the bees' behavior in a lab.

Notably, the bees tasted and then left flowers containing nickel. But this was not the case for flowers contaminated with aluminum. The bees foraged on these for as long as they did uncontaminated flowers, adding to the levels of that metal in their bodies.

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Why the bees sensed nickel but not aluminum is not yet known. Meindl cites previous studies that found higher concentrations of aluminum in flowers than of nickel, a suggestion that the bees may actually be "more tolerant or immune" to the presence of aluminum.

40 to 50 percent of the U.S.'s population of honeybees has been wiped out this year. The ramifications for supplies and prices of U.S.-produced honey and of almonds, fruits and vegetables pollinated by honeybees are huge and beekeepers have become more and more aware of the damage pesticides - especially neonicotinoids - can cause. In the case of bumblebees, these powerful chemicals are just one threat. As the Pitt researchers' findings suggest, looking even more closely, and critically, at multiple aspects of modern farming practices and their environmental impacts (pdf) is necessary to ensure their survival.

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