Bees, bumblebees, and variety of wild pollinating insects, have seen their numbers dropping considerably in recent years. Most recent research has found a strong connection between these declines and the use of of certain pesticides, loss of wild habitat/deforestation, and growing urban/agricultural areas. And now, another major cause of decline has been discovered, metal pollution, especially aluminum and nickel pollution.
Toxic metals such as aluminum and nickel are present in many soils located near human development, primarily as a result of exhaust from vehicles, industrial machinery, and farming equipment, but also power plants and industrial plants. Bumblebees are at particular risk of ingesting significant and toxic quantities of metals, such as aluminum and nickel, when they feed on flowers growing in contaminated soil.
What the new research from the University of Pittsburgh found, is that while bumblebees have the ability to “taste” certain metals such as nickel, and subsequently leave that flower, they can only detect the contaminant after visiting the flower and being exposed to it.
“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 and professor and associate chair in the University of Pittsburgh’s Department of Biological Sciences. “Beyond leading to mortality, these metals can interfere with insect taste perception, agility, 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 forage. The blooms were collected from the field each morning of the two-week study and were of a similar age, color, and size.”
In order to better understand the effects that the presence of nickel and aluminum in the flowers’ nectar was having on bumblebee behavior, the researchers “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 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 discriminate against certain metals.”
The research found that the bees are capable of “tasting” and discriminating against 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 noncontaminated 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.”
Soil contamination is a growing problem throughout much of the world. Metal pollution, including heavy metals, is ubiquitous throughout most “developed” and “developing” regions of the world. If were to sample pretty much any of the soil located near the roads in your city you would be likely to find significant levels of lead among other contaminants. Which is one of the primary reasons why if you are growing your own food that it is highly recommended that you don’t simply use the soil already present in your yard. It is very likely to contain significant levels of contaminants. The problem seems to a more significant one for insects such as bumblebees than it is for humans though. Worth noting is that without wild pollinators such as bumblebees, large-scale human agriculture would more or less collapse, very quickly. And wild pollinating insect numbers have been dropping at a significant rate in recent years.
The new research was just published in the journal Environmental Pollution.
Image Credit: University of Pittsburgh, Bumblebee via Wikimedia Commons