Metal Toxicity Contributing To The Decline In Bumblebee Population

Bees play a vital role in the pollination within the global food chain. Pollination is the process in which pollen is transferred from plant to plant, stimulating fertilization and reproduction. Bees accomplish this when hopping from flower to flower, drawing nectar.

The pollen collects on the bee’s body and is topically transferred, allowing for the germination of okra, kiwi, onions, broccoli, mustard, watermelons, blueberries, raspberries, strawberries, cocoa, sesame, tomatoes, guava, and countless other consumables.

Loss of pollinators – a phenomenon known as pollinator decline or colony collapse disorder (CCD) – has a significant economic and ecologic impact. Colony collapse is significant economically because many agricultural crops worldwide are pollinated by bees; and ecologically because of the major role that bees play in the reproduction of plant communities in the wild.

The American Institute of Biological Sciences reports that native insect pollination saves the US agricultural economy an estimated $3.1 billion annually. Natural pollination produces some $40 billion worth of products annually in the US alone.

Bees have also been shown to be an important resource in medical research. A Washington University School of Medicine study recently determined a component in bee venom may lead to potential therapies for treating or eliminating HIV.

The drastic decline in honeybee and bumblebee populations in recent years has scientists, apiculturists (bee keepers), and environmentalists scouring for potential culprits.

Habitat destruction, pesticides and insecticides such as neonicotinoids, malnutrition, environmental changes, migration stress, along with parasitism and diseases have been found to contribute to the decimation of bee colonies.

Neonicotinoids are a class of neuro-active insecticides chemically related to nicotine. The pervasive use of clothianidin and imidacloprid and other pesticides have been linked to the rise in bee deaths since 2005, as the compound attacks the insects’ central nervous systems.

Several independent studies have been published demonstrating the causational link between neonicotinoids and the waning bee population.

Previously undetected, the toxic exposure affected bees through dust, pollen, and nectar; subnanogram toxicity concentrations resulted in the failure of bees returning to the hive.

In addition, controlled reproductive studies revealed an 85 percent decline in queen production in bees exposed to pesticides.

Imidacloprid is one of the most toxic insecticides to the western honeybee, Apis mellifera. Research studying sub-lethal effects in adult bees found when bees were exposed to low-levels of imidacloprid (sub-lethal doses of 1-24μg/kg and 0.1 – 20 ng) navigation, foraging, and feeding behavior was impaired. In higher doses, bee mobility and communication capacity was affected.

These alarming results provoked a formal 2013 peer review by the European Food Safety Authority. It was declared neonicotinoids posed an impermissible high risk to bees, and that the industry-sponsored science upon which regulatory agencies’ “claims of safety” relied on was flawed.

In more recent research, published in the journal Environmental Pollution, a University of Pittsburgh study has determined bumblebee populations may be suffering from exposure to high concentrations of metal pollution.

The study suggested bees are ingesting plants contaminated with toxic levels of aluminum and nickel, absorbed from the soil – put there through expanding industrial areas, mine tailings, improper disposal of high metal wastes, application of fertilizers and animal manures, sewage sludge, pesticides, wastewater irrigation, combustion residues, vehicle exhaust, and spillage of petrochemicals.

Tia-Lynn Ashman – the principal investigator 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 – explained how metals like copper, lead, selenium, iron, zinc, arsenic, and nickel do exist naturally, and some are required by living organisms in small amounts.

However, ingesting moderate to high amounts of the aforementioned metals can be lethal. In regards to insects, heavy metal toxicity can “interfere with insect taste perception, agility, and working memory –all necessary attributes for busy bumblebee workers,” according to Ashman.

According to Science Daily, Ashman and co-author George Meindl studied bumblebee behavior for two weeks at a nature reserve in Western Pennsylvania during August and September in 2012. They used the Impatiens capensis or an Orange Jewelweed, a tri-lobed North American flower that blooms in summer and produces copious amounts of nectar as part of the experiment. Orange Jewelweeds are commonly found in bottomland soils areas of ditches and along creeks. The blooms were collected daily, of similar morphologies.

Metal Toxicity in Soil and Flowers Contributing To The Decline In Bumblebee Population

Researchers divided the flowers into groups of uncontaminated, contaminated by nickel, and contaminated by aluminum. When a bumblebee visited a flower in the assortment, the entire visitation was recorded as well as the time spent at each individual flower.

Examiners especially watched for whether the bees moved from a contaminated to a non-contaminated flower, if they moved within the same group, or if the bees abstained from a particular flower. Blooms were replaced before each test.

The data revealed bees visited both the contaminated and non-contaminated samples, but after tasting the nectar were able to differentiate the existence of nickel and discriminate against those particular blooms. Although bees were able to taste and later ignore metal contaminated flowers, they first had to come into contact with the offending element in order to do so. The bees were incapable of discerning between aluminum and non-contaminated nectar.

Meindl and Ashman were unable to explain exactly why the bees were unable to sense aluminum, but suggested the possibility of a preexisting tolerance to the presence of aluminum over nickel, as they found aluminum was naturally higher in concentration.

The paper, “The Effects of Aluminum and Nickel in Nectar on the Foraging Behavior of Bumblebees,” mentioned the implementation of phytoremediation – an environmentally friendly approach to decontaminating soil of toxic pollutants.

Funding was provided by the Carnegie Museum of Natural History’s Powdermill Nature Reserve in Rector, Pennsylvania, a Botany-In-Action Fellowship from the Phipps Botanical Garden and Conservatory in Pittsburgh, an Ivey McManus Predoctoral Fellowship to Meindl, and a National Science Foundation grant (DEB 1020523) to Ashman.

[Image of Orange Jewelweed from Wikicommons/Feature image via Wikicommons]