Beekeepers and researchers nationally are reporting growing evidence that a powerful new class of pesticides¹ may be killing² off bumblebees. Now, research at the University of Pittsburgh points toward another potential cause: metal pollution from aluminum³ and nickel. Published in the journal Environmental Pollution, the Pitt study finds that bumblebees are at risk of ingesting toxic⁴ amounts of metals like aluminum and nickel found in flowers growing in soil that has been contaminated by exhaust from vehicles, industrial machinery⁵, and farming equipment. The Pitt study finds that bumblebees have the ability to taste -- and later ignore -- certain metals such as nickel, but can do so only after they visit a contaminated flower. Therefore, the insects are exposed to toxins⁶ before they even sense the presence of metals.

 

"Although many metals are required by living organisms in small amounts, they can be toxic to both plants and animals when found in moderate to high concentrations," said Tia-Lynn Ashman, principal investigator⁷ of the study and professor and associate chair in Pitt's Department of Biological Sciences in the Kenneth P. Dietrich School of Arts and Sciences. "Beyond leading to mortality, these metals can interfere⁸ with insect taste perception, agility⁹（敏捷，灵活）, and working memory -- all necessary attributes for busy bumblebee workers."

 

Ashman and George Meindl, coauthor of the study and a PhD candidate in Ashman's lab, studied bumblebee behavior using the Impatiens capensis, a North American flower that blooms in summer. Its flowers are large, producing a high volume of sugar-rich nectar each day -- an ideal place for bumblebees to forage¹⁰. The blooms were collected from the field each morning of the two-week study and were of a similar age, color, and size.

 

To determine whether nickel and aluminum in the flowers' nectar（花蜜，甘露） influenced bumblebee behavior, Ashman and Meindl used two groups of uncontaminated flowers, one group of flowers contaminated by nickel, and another contaminated by aluminum. When a bumblebee visited a flower in an array, the entire visitation was recorded as well as the time spent (in seconds) foraging¹¹ on each individual flower. This included monitoring whether the bee moved from a contaminated to a noncontaminated flower, whether the bee moved to the same group it had just sampled, or whether the bee left the flower group without visiting other individual blooms. Following each observed visit, all flowers in the array were replaced with new flowers, to ensure accurate results.

 

"We found that the bees still visited those flowers contaminated by metal, indicating that they can't detect metal from afar," said Ashman. "However, once bumblebees arrive at flowers and sample the nectar, they are able to discriminate¹² against certain metals."

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