Researchers are investigating evidence that pesticides may be killing off bumblebees, but research at the University of Pittsburgh points toward another potential cause: flowers contaminated with metallic pollution.
Appearing in the journal Environmental Pollution, the Pitt study shows that bumblebees are at risk of ingesting toxic amounts of metals like aluminum and nickel found in flowers growing in soil that has been contaminated by exhaust from vehicles, industrial machinery, and farming equipment.
“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 investigator of the study. “Beyond leading to mortality, these metals can interfere with insect taste perception, agility, and working memory – all necessary attributes for busy bumblebee workers.”
The researchers 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 forage.
To determine whether nickel and aluminum in the flowers’ nectar influenced bumblebee behavior, Ashman and co-researcher George 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) foraging on each individual flower. This included monitoring whether the bee moved from a contaminated to a non-contaminated 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.
Ashman reported that the bees were able to taste, discriminate against, and leave flowers containing nickel. However, this was not the case for the aluminum-treated flowers, as the bees foraged on the contaminated flowers for time periods equal to those of the non-contaminated flowers.
“It’s unclear why the bees didn’t sense the aluminum,” said Meindl. “Concentrations of aluminum found throughout blooms tend to be higher than concentrations of nickel. This suggests that the bees may be more tolerant or immune to its presence.”
The new findings also have implications for efforts to decontaminate soil, in particular a method called phytoremediation – a promising approach that involves growing metal-accumulating plants on polluted soil to remove such contaminates. Ashman says this approach should be considered with caution because the bees observed in the study foraged on metal-rich flowers. She states that further research is needed to identify plants that are ecologically safe and won’t pose threats to local pollinators.
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