North American bumblebees have been significantly decreasing in recent decades. This is attributed to a host of factors including fading availability of flowers that attract bees. Bumblebees are essential pollinators for both native and agricultural plants. Their ability to fly in colder temperatures makes them especially important pollinators at high elevation.
A study has identified the flowers most frequently nibbled by bumblebees as part of research to improve the pollination of critical plants as bee species face declines nationwide.
Published last Tuesday in the journal Environmental Entomology, researchers captured bumblebees on more than 100 plant species across more than 400 plots in the Plumas National Forest in California which is a mountainous, meadowy area with wildlife habitats near running water and where bumblebees are abundant.
The most popular flowers among the bees were found to be Oregon checker-mallow and mountain pennyroyal flowers.
The decline in population was evident between April 2015 and April 2016 when beekeepers in the U.S. lost 44% of their colonies.
The authors compared which species of flowers the bees used relative to the availability of each flower species across the landscape.
According to Dr. Jerry Cole, a biologist with the Institute for Bird Populations, it is essential to consider the availability of plants when determining the preference of bees.
Not all flowers are utilized equally by bumblebees, and not all flowers are equally available to them.
Recognizing which flowers are favored by bumblebees can help scientists understand which plants they need, but putting that choice in the context of what is available to bees across a landscape provides a more accurate idea of which flowers are highly valued.
Learning bumble bees' flower preferences will support the conservation of declining bee species.
According to Helen Lofland, "This kind of information can actually enhance the effectiveness of restoration for bumblebees and in a method that's comparatively straightforward and cost-effective to implement."
The results found that each bumblebee species in the study selected a different assortment of flowers, even though the bees were foraging across the same landscape. This can be convenient for land managers who are restoring or managing meadows and other riparian habitats for native bumblebees.
When a bee was captured on a flower, the biologists estimated the number of those flowers in a given plot of forest, the study said.
Reasons behind the declines were: transfer of parasites from honey bees to bumblebees, loss of floral resources, competition with other insect species, or a mismatch between the phenology of plant species and the phenology of bumblebee species, Jerry Cole, lead author of the research and biologist at the Institute for Bird Populations in California, said.
The synchronicity between plants and animals is important, as our food supply depends on the timing of phenological events.
Other studies merely use the proportion of captures on a plant species alone to determine which plants are most important to bees.
According to Cole, without comparison to how available those plants are, a plant might be mistaken to be preferentially selected by bees, when it is only very abundant.
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