Have you ever wondered what solitary bees do if they emerge from overwintering into an environment without flowers?
We often worry about how flowering plants would fare without local bees to pollinate them, but what about the other way around?
– = ?
Here’s another question you might not have considered:
What do you do if you’re sent out into the field as an over-eager new graduate student to survey native bee communities, so of course you start in February because you don’t want to miss anything, but then you find yourself just pacing timed transects through barren, drizzly, cold sampling plots?
Let me back up a minute and explain how these two questions are related.
I love fieldwork. I love it for the improvisational, arts & craftsy troubleshooting it brings to the theoretically hard and tidy world of science. I love it because, if you chose wisely, it is beautiful, grungy, exhausting, and full of Vitamin D. And I love it because it brings me back into a place of unstructured wonder about the natural world, and opens the flood gates on a stream of questions I don’t allow myself to daydream about with my giant office whiteboard to-do list looming over me.
My graduate fieldwork involved setting up and then surveying long-term native bee monitoring sites in different habitats across Pinnacles National Park, California. For each sampling event, my lab technician and I spent thirty minutes methodically traversing a football-field-sized area with bee nets, collecting whatever flying Apoids we saw and recording floral hosts. I was (and still am) interested in collecting this data in order to evaluate biodiversity and community ecology patterns describing this protected area rich with native (mostly solitary) bee species. To make sure we captured the full phenology of these seasonal species, we started in February…
Here are some pictures of what Pinnacles looks like in February. Not exactly the sunny, buzzing meadows of pollination wonder you may have been imagining (me either):
A discovery borne of boredom.
Embarking on a mission to document what flowers different bee species are visiting in these pre-bloom habitats for multiple thirty-minute sessions per day can be(e) pretty…boring. But it turns out that spending thirty minutes just observing the nuanced details of your study sites and being open to the unexpected, is not. Sometimes when what you’re looking for isn’t there, you find what you were not looking for. Sometimes when you think you should be looking, you find you should be listening instead. Sometimes when you stop looking for bees on flowers, you hear them buzzing on sugary sticks, and an experiment is borne. Things we lose have a way of coming back to us in the end, if not always in the way we expect. (Ok, that last one was a quote from Luna Lovegood in Harry Potter and The Order of the Phoenix.)
My eagerness to catch the very first bee of the season and record the full story of bee communities at Pinnacles, I’m happy to say, was not a waste of time but instead has resulted in my first lead publication, out in print in The American Naturalist next month, and currently online for your viewing pleasure: http://www.journals.uchicago.edu/doi/10.1086/692437.
In this free, open-access paper, titled “Bees without Flowers: Before Peak Bloom, Diverse Native Bees Find Insect-Produced Honeydew Sugars,” we describe our observation, borne of field boredom, that 42 different species of native, mostly solitary bees visit — you guessed it — honeydew sugars produced by scale insects, similar to aphids, on non-blooming plants. This study is the first to document this non-floral-centric foraging behavior across an entire community of bees, and the first to evaluate the possible mechanisms behind it. We are excited to share the results and hear your reactions.
“Curiosity is not a sin.” –Dumbledore, The Goblet of Fire
So how does this work? How do bees find sugars without flowers to lure them in?
Since the times of Charles Butler researching beekeeping in the 16th century, to the Swiss naturalist Francois Huber writing about bees in the 18th century, to Karl von Frisch winning fame and a Nobel Peace Prize for his work on honeybee perception and communication in the late 19th century, knowledge about bee foraging has centered around their attraction to flowers. Flowers, in turn, are known to have evolved in response to the color, shape, and scent preferences of their bee pollinators. Pollination does not occur on large scales without bee visits to flowers. So what are these bees doing visiting bare, moldy sticks like the one pictured on the left below?
After watching dozens of bees visiting, landing, and appearing to forage on these pre-bloom branches, I broke off a blackened stick and showed it to Utah State University plant pathologist, Dr. Fred Baker. He told me that this ‘sooty mold’ was growing on insect honeydew secretions from scale insects colonized on these plants, barely visible beneath the mold and camouflaged as bark-like growths (middle and right pictures above). Like their better-known cousins, the aphids, scale insects use piercing mouthparts to siphon phloem from the plant, process it through their bodies, and excrete excess carbohydrates onto the surface as sugary insect “honeydew.” Ants are known to feed off this sugar source, even offering aphids protection from predators in exchange. But somehow, though bees have perhaps the most infamous sweet tooth of the entire animal kingdom, Winnie the Pooh excepted, use of honeydew by bee communities had not been studied.
So I designed an experiment to decipher what cues bees were using to find this resource, how widespread this behavior was across the native bee community at Pinnacles, and whether or not they gained some other resource besides sugars from these plants as well. I made sure to include plenty of trips to the craft store, a Go-Pro to record bee foraging behaviors in slow motion, a cool infrared thermometer, and lots of focused staring at non-flowering shrubs with a bee net in hand, sure to confuse the National Park visitors passing us by on the trail. We got up early, mixed up concoctions of sugar and paint and insecticides in spray bottles, and hiked to the far reaches of Pinnacles National Park to explore the spatial and temporal breadth of this novel bee foraging behavior.
I’m not going to ruin the ending, except to tell you that our results by treatment, which looked something like the graph below, were highly significant and that our conclusions involved introducing the concept of “interspecific eavesdropping” as a possible foraging mechanism among solitary bees accessing non-traditional sugars during times of low nectar availability. For more details, you’ll just have to read the paper. Or you can check out the popular science coverage of it by Emily Benson in The New Scientist and by Willy van Strien on her blog, From so simple a beginning.
Thanks for tuning in. Now you know the answer to the title question:
What do bees do when flowers are few?
They find insect honeydew.
Maybe you can help further this research by thinking outside the floral-foraging box and taking some time to stare at bees acting like random weirdos on sticks in your field sites. As my graduate adviser, Dr. Morgan Ernest, would say, it’s interesting because it’s just “sugar on a stick.”
Here’s to mis-adventures in science side projects.
“Let us step into the night and pursue that flighty temptress, adventure.” –Dumbledore, The Half-Blood Prince