Bumblebees Threatened By Metal Toxins In Flowers
April 3, 2013

Toxin-Laced Flowers May Be Killing Off Bumblebees

April Flowers for redOrbit.com - Your Universe Online

Across the US beekeepers and researchers have been reporting that a powerful new class of pesticides may be killing off bumblebees. A new study, led by the University of Pittsburgh, pinpoints another potential cause: metal pollution in flowers from aluminum and nickel.

The study findings, published in the journal Environmental Pollution, reveal that bumblebees are at risk of ingesting toxic amounts of metals such as nickel and aluminum. These trace elements are found in flowers growing in soil that has been contaminated by exhaust emissions from vehicles, industrial machinery and farming equipment.

According to the researchers, bumblebees have the ability to taste and then ignore these dangerous metals. However, they are only able to do so after they visit a contaminated flower, meaning that the bees are first exposed to the toxic metals before they are able to detect them.

"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," explained Tia-Lynn Ashman, professor and associate chair in the university´s Department of Biological Sciences in the Kenneth P. Dietrich School of Arts and Sciences.

"Beyond leading to mortality, these metals can interfere with insect taste perception, agility, and working memory — all necessary attributes for busy bumblebee workers."

Working with Impatiens capensis, a North American summer-blooming flower, the team studied bumblebee behavior. Impatiens flowers are large and produce high quantities of sugar-rich nectar every day, making them ideal foraging sites for bumblebees. Each morning during the two week study, the researchers collected blooms of similar age, color and size.

Ashman and her colleague George Meindl, a PhD candidate in Ashman's lab, used two groups of uncontaminated flowers — one contaminated by nickel and the other by aluminum — to determine whether the metals in the flowers' nectar influenced bee behavior. When one of the flowers was visited by a bumblebee, the entire visitation was recorded. The amount of time that the bees spent foraging  at each flower was also recorded.

The scientists tracked 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.“¯To ensure accurate results, all flowers in the array were replaced with new flowers following each observed visit.

"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 discriminate against certain metals."

The study found that bees were able to taste, recognize and then abandon those flowers that contained nickel. This did not appear to be true, however, for flowers that contained aluminum, as the bees foraged on these contaminated flowers for time periods equal to that of uncontaminated flowers.

"It's unclear why the bees didn't sense the aluminum," said Meindl. "However, past studies show that the 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 study findings have implications for environmental efforts to decontaminate soil, especially with a method called phytoremediation, which involves growing metal-accumulating plants on polluted soils to absorb and remove the contaminants. This approach should be considered with caution, Ashman warns, because the bees observed in the study foraged on some metal-rich flowers. Further research will be needed to identify plants that are ecologically safe and will not pose threats to local, pollinating animals.