Signs of Fall 9: Time is Honey

Photo by I.Tsukuba, Flickr

The title of this week’s post is taken from Bernd Heinrich’s remarkable book Bumblebee Economics (full quote: “to a bee, time is honey”). I was reminded of this quote when I read an article published a few weeks ago (Oct 7, 2016) in the New York Times (“Six Scientists, 1000 miles, One Prize: The Arctic Bumblebee”).  But, I will get back to that in a minute!

Over the past eight years I have written about both domesticated and wild bees a dozen or more times. There are many reasons why I frequently return to this topic: 1. Bees are most people’s favorite insect (in fact, bumblebees have been called the “pandas of the insect world!” (They are big and fuzzy and cute and move slowly enough for us to clearly see them (and, if necessary, to get out of their way!)), 2. Bees are vital in the production of human food (they not only use their “time” to make honey but also (according to Dr. Gabriola Chavarria the former Director of the Natural Resources Defense Council’s Science Center and a Science Advisor to the Director for the U. S. Fish and Wildlife Service) pollinate 30 percent of the world’s crop plants and 90 percent of the world’s wild plants (as E. O. Wilson once said, we should say “thank you” to a bee after every third bite of our food), and 3. Bees are in serious trouble (due to climate change, pesticide poisoning, loss of natural habitats, and rapidly spreading parasites and pathogens).

These three big points energize the scientific discussion of bees! Many studies are being conducted that explore the biology and ecology of these incredible insects, and many papers are published each year describing new aspects of or new perspectives on their lives. I keep a file folder on my desk top entitled “Bees” into which I put new articles that I find in both scientific journals and also major newspapers. When it fills up, I feel compelled to write!

Which cycles us beautifully back to the arctic bumblebee and the brilliant article about it from the Times!

Photo by USFWS (Public Domain)

In the arctic many insects rely on long, extended and frequently interrupted life cycles by which they eke out their existences and finally accumulate enough resources and energy to accomplish reproduction in the harsh environment and extremely short individual growing seasons of the far north. Arctic bumblebees, though, do not have the luxury of stretching out their life phases over several truncated growing seasons. These bees must accomplish all of the energy gathering, growth, and reproduction in the limited weeks of a single, arctic spring and summer!

So up on the northern rim of the world, these bees have had to develop ways to generate and retain body heat even when the outside temperatures are near freezing. Many of these adaptations are very logical: metabolically they can generate a vast amount of body heat from the contractions of their muscles (an arctic bumblebee can get its body temperature up to 95 degrees F and can then engage its flight muscles even when it’s 32 degrees F outside!) The overwintering queen arctic bumblebee (who is able to survive brutally cold sub-zero temperatures throughout the long arctic winter) uses this same metabolic-muscle engine to stimulate ovulation so that the retained sperm (from her pre-hibernational mating back in the fall) can fertilize her ova. Further, the arctic bumblebee is larger than our temperate bumblebee so it has a reduced surface area to volume ratio that helps to slow down heat loss. It is also covered with a thick coat of highly insulating hair. The dark color of the arctic bumblebee also helps it absorb heat from the, admittedly weak, arctic sun.

So why did this group of six scientists drive a thousand miles through Alaska to search for this arctic bumblebee? Think about global warming changing the climate and then the flora and fauna in lower latitudes. One hypothesis is that mobile species (like bumblebees) will move north as the climates of their traditional ranges get warmer. But, if this happens, where will the bees at the very edge of northern world go? What will happen to all of the wild plants that specifically rely on them for pollination? These were the big questions these bee hunters were asking.

Photo by Trounce, Wikimedia Commons

In another bee paper published this past summer in Plos Pathogen (August 11, 2016) , scientists from Cambridge University found that tomato plants infected with the cucumber mosaic plant virus attracted more bumblebees (their primary pollinator) than non-infected plants. The consequence of this increased pollinator attention was that the infected tomato plants even though they were energy stressed by their viral loads produced just as many fruits and seeds as uninfected plants. The virus made the tomato plant “more visible” to the pollinating bumblebee! Possibly the positive, reproductive impacts of this viral infection will eventually out-weigh its negative, physiological effects on the plant! This infection response may be the first step in a co-evolutionary symbiosis between the virus and the tomato!

In another bee paper (published in the July 27, 201 Proceedings of the Royal Society B) scientists in New Zealand found that honeybees exposed to neonicotinoid pesticides had less viable and less active sperm than unexposed honeybees.  Previous studies have shown that both honeybees and bumblebees are strongly attracted to plant nectars that contain neonicotinoid pesticides so this impact could be quite significant. Neonicotinoid pesticides are used for insect control on many type of crops but have been linked to significant bee damage in many studies (The European Union, in fact, has recently banned these chemicals because of their links to high levels of bee mortality. Bills have been proposed in the US Congress to restrict the use several of these pesticides, but these bills were sent to committee and no definitive action was taken). Possibly this inhibition of reproductive efficiency is one of the mechanisms by which so much bee damage is mediated. In a related study published in Nature Communications (August 16, 2016) the use of these neonicotinoid pesticides on oilseed rape fields in England over an 18 year time period had significantly negative impacts on 62 species of wild bees.

Photo by H. Zell, Wikimedia Commons

And, finally, in a paper just published in Current Biology (October 6, 2016): a South African flower (Ceropagia sandersonii) was found to synthesize a mixture of scent molecules that mimicked the alarm and distress pheromones produced by a wounded honeybee (Apis mellifera). These scent molecules attracted predatory Desmometopa flies to the flowers (these flies feed avidly on honeybees that have been captured or wounded by spiders (or other predators) in these flowers). These flies are also the primary pollinators of C. sandersonii! So, by ringing an olfactory dinner bell for the flies, the flower gets more focused and more frequent pollinator visits and a much more efficient overall rate of pollination!

So bees are being pushed to the edge of the world. They are also participating in ongoing co-evolutionary transformations, are being sterilized by pesticides, and are indirect participants in elegant chemical ecological systems. No wonder we keep talking about them!