Signs of Spring 8: More on Bees!

Bumblebee. Photo by Alvagaspar, Wikimedia Commons

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In the fourteen years that I have been writing this blog I have written twenty-four essays dedicated to bees. They are the most frequently presented topic in my 400 + posts! I keep a folder on the desktop of my computer where I put articles I find about bees. When the folder gets full I write about them! So, in honor of all of those past blogs about bees, here’s is #25!

Bumblebees gather nectar from flowers by drinking it at the flower source, transporting it in their stomachs back to their colonies, and regurgitating it into wax containers called “honey pots.” These honey pots are communal food sources from which other members of the colony can feed and from which the nectar and pollen mixture for the bumblebee larvae is made.

When bumblebees evaluate a nectar source, they take into consideration a wide range of variables: how far is the nectar source from their colony? Is the energy cost of transporting a belly-full of nectar paid back by the energy content of the sugar in the nectar? What color and shape are the flowers of the nectar producing plants? (Certain species of plants are better sources of nectar than others). And, what is the sugar content of the nectar?

At first glance the sugar content of the nectar should be positively correlated with bumblebee preferences: higher sugar content nectars contain more energy and should, thus, be preferred over more dilute nectars.

Researchers at Oxford University, though, in a paper published in the Journal of the Royal Society Interface (January 22, 2020) found that lower sugar content nectars were actually preferred by foraging bumblebees. High sugar content nectars are very viscous which makes them hard to swallow (thus significantly increasing the time the bumblebee has to stay on each flower) and, possibly more importantly, the thick nectar fluids are hard to regurgitate back at the bumblebee’s nest (which greatly increases the time the bumblebee must remain in its home filling its honey pot. A stomach full of a 35% sugar solution, for example, is regurgitated by a bumblebee in four or five seconds. A similar stomach full of a 65% sugar solution, though, takes the bumblebee nearly 30 seconds to regurgitate.

Bernd Heinrich’s bumblebee economics slogan comes to mind: “time is honey!” The increased time efficiency in gathering the weaker nectar sources more than offsets the lower, milliliter by milliliter sugar content of the more dilute nectars!

Fossil bee nests, Photo by J. Genise

In a January 29, 2020 article in PlosOne fossils from Argentina were described that indicate that modern bees were present one hundred million years ago and that they were evolving right along with flowering plants. The fossils consisted of a set of tunnels with numerous clusters of small, ovate chambers densely packed around them. These fossilized tunnels resembled the very distinctive nest tunnels of bees in the family Halicitidae (the “sweat bees”). These finding push back the evolutionary origin of modern bees by five to ten million years!

Honeybee. Photo by C.J.Sharp, Wikimedia Commons

Researchers at Penn State (Penn State News, January 21, 2020) explored the specific impact of “oral based” agricultural insecticides (insecticides that are in the nectars and pollen of insecticide treated plants) on honeybees. They determined that although honeybee populations are being damaged all across the United States (an average 9% increase in oral based insecticide toxic load over the past twenty years) , certain areas of the country are being affected more severely than others. In particular, honeybees in the area classified as the “Heartland” of America (Iowa, Illinois, Indiana, Missouri and parts of five adjacent states) had a 121% increase in  oral based toxic load, and honeybees in the “Northern Great Plains” (North Dakota and parts of South Dakota, Nebraska, Colorado, Wyoming, Montana and Missouri) had a 53% increase in their oral based toxic load.

The toxic oral based insecticides particularly include neonicotinoids that are directly applied as coatings to seeds prior to planting. Corn and soybeans are two major crops whose seeds are commonly treated with insecticide coatings. The environmental impacts of these treatments are severe, but previous research has shown that the benefit of these seed coatings on crop production is negligible. Stopping the coating of these seeds seems like a logical move to reduce the insecticide load in and ongoing decline of these important pollinators!

Honeybee with attached Varola mite. Photo by USDA

In a January 31, 2020 article in the journal Science researchers at the University of Texas at Austin reported that they have genetically modified a common, honeybee gut bacterium. This modified member of the honeybee’s gut microbiome stimulates the bee’s immune system to kill both varroa mites and also a pathogenic virus that these mites carry.

Varroa mites are exotic invasive parasites of honeybees that were introduced to North America (initially in Maryland and then Wisconsin and Florida) from mainland Asia and Japan in 1987. They have spread to all fifty states and are a major component of Colony Collapse Disorder (CCD) which has caused North American honeybee populations to drastically decline (over the past 50 years the number of honeybee hives in North America has gone from six million to just two and a half million). Honeybees all around the world have declined similarly due to impacts of this complex syndrome.

It is hoped that the reduction of varroa mite stress on honeybees will enable them to better tolerate all of the other stresses that contribute to CCD.

Bumblebee. Photo by Trounce, Wikimedia Commons

And finally, in a February 7, 2020 paper published in Science examined the changes in the distribution of sixty-six bumblebee species in North America and Europe over the past one hundred and nineteen years. Observations of bumblebees were down 46% in North America and 17% in Europe. The declines at each observation site were correlated with both overall rises in temperature  and especially with the periodic occurrence of extreme heat events!

Bumblebees are very well insulated. Their fuzzy bodies prevent the loss of the considerable metabolic heat generated by their flight muscles. This feature enables bumblebees to live about the Arctic Circle and also allows them to emerge from hibernation quite early in the spring. This insulation layer, though, can be detrimental when a bumblebee is exposed to very warm temperatures. Their inability to disperse their metabolic heat in these instances coupled with heat absorption from their environment can actually lead to metabolic dysfunction and even death.

In our climate changing world, bumblebees are having difficulties finding environments within which they can function and live!