Nav: Home

Researchers use big-brother tech to spy on bumblebees

February 17, 2017

By tagging individual bumblebees with microchips, biologists have gained insights into the daily life of a colony of bumblebees (Bombus impatiens) in unprecedented detail. The team found that while most bees are generalists collecting both pollen and nectar over the course of their lifetime, individual workers tend to specialize on one of the two during any given day, dedicating more than 90 percent of their foraging sorties to either pollen or nectar. The observations also revealed that individual bumblebee workers differ vastly in terms of their foraging activity.

Just like their domesticated cousins, the honey bees, bumblebees play important roles as pollinators, thus helping in agriculture and fruit production. But despite the ecological services they provide, many aspects of their biology still remain a mystery. By outfitting each bumblebee with a radio frequency identification, or RFID, tag -- similar to the ones used to protect merchandise from shoplifters -- the researchers were able to keep tabs on them at all times and log the data automatically instead of relying on human observations limited to certain times.

"The way these studies have typically been done requires a human observer sitting in front of a hive entrance and taking notes all day, and nobody wants to do that," says Avery Russell, the lead author of the study. Russell is a doctoral student in entomology and insect in the lab of Daniel Papaj, a professor in the University of Arizona's Department of Ecology and Evolutionary Biology. "With the RFID chips, we can track every nectar and pollen collection trip made over each worker's lifespan and a portion of the colony's lifespan."

The researchers then used this data to determine how patterns of specialization on each food type differed at timescales of a day or over a lifetime. The results are published in the journal Scientific Reports.

Once a bumblebee queen has mated, she burrows into the ground and overwinters. The following spring, she emerges and starts a hive that lasts until the fall. A typical bumblebee colony grows to about 75 workers, with about 40 to 50 going out and foraging on flowers for nectar and pollen. After the colony's growth phase, the colony produces unfertilized eggs that hatch into males. The male bumblebees then disperse in search for other unmated queens to begin the cycle anew.

"Each individual bee only lives between two weeks to a month at the most," Russell says, "and even though they behave as generalists over their lifetime, our study showed that they tend to specialize on one food source over the course of a foraging day."

The researchers were surprised to find a vast difference in efficiency, with the most active foragers making 40 times the number of trips each day as the least active workers.

"Interestingly, when we studied the morphology between very active foragers and workers that barely leave the hive, we found that bees with more sensitive antennae foraged more," Russell said.

Similar variation has been in observed in honey bees and other eusocial species, where some workers are much more active than others, but no one had seen it to this extreme due to the limits of human observations.

"If you watch a bee only for an hour or so, you can't say what it will do over the course of a few days or over its whole life," Russell says. "We don't yet know why, but it could be that workers that forage less do so because they aren't quite as skilled at foraging as others and make themselves useful by doing more around the hive."

To track the bees' behavior, the team superglues tiny RFID tags to the backs of the bees. Each tag weighs only 2 to 3 percent of the bee's weight. A Y-tube connects the hive to two arenas, one that offers pollen and one that offers nectar. When a bee leaves the hive to forage, it can choose to go to the pollen chamber or the nectar chamber. Two RFID readers mounted at the entrance keep track of the bees going in and out and help the researchers collect a wealth of data.

"This setup gives us information about directionality," Russell explains. "Is the forager leaving or returning from foraging? We also get an idea of whether a bee goes from one chamber to the other, or whether it makes repeated trips to only one chamber, and we get to know how long the trips were."

Since the team was especially interested in the sequence of the foraging trips over the course of the day, some heavy lifting was needed to make sense of all the data. To do this, Russell enlisted the help of Sarah Morrison, a doctoral student in the UA's Lunar and Planetary Laboratory, who studies orbital dynamics and the evolution of solar systems.

"Each RFID reader only spits out timestamps and the identity of the bee, so if you want to know what the bees are doing, you need to parse all that information and turn it into things we can understand," Russell says. "For example, how many trips a forager makes per day."

While honey bees are known to be very consistent and tend to stick to one species of plant and often one type of reward over a day, a phenomenon known as floral consistency, bumblebees were thought to be more generalist. The present study came somewhat as a surprise in that Russell's team found the bees tend to make strings of foraging runs for the same reward on a given day.

"One possible explanation is that foraging for pollen versus nectar requires very different behavioral regimes, so it makes sense for them to focus on one at a time," he says. "Also, in many cases pollen and nectar are not both available from the same plant species."

Researchers still don't know why bees switch between foraging for nectar or pollen.

"It is possible they take cues from the brood," Russell says, "in that they produce pheromones that say 'we need more of this or more of that.'"

Bumblebees that specialize in a task, either over the course of their lifetime or over the course of a foraging day, turned out to be no more active than their generalist peers, however. Neither were they found to be larger, more able foragers -- raising the question as to why they specialize in the first place.

"One of the reasons bees might specialize could be some sort of memory constraint," Russell says. "Rather than having to switch back and forth between dealing with many different floral designs and constructions, it might be more efficient to just stick with one for the duration of a foraging day."

As for the more domestic individuals that were found to forage far less than their more adventurous colleagues, Russell says that this might reflect economics of skill allocation.

"Those that are less good at foraging probably shouldn't go foraging in the first place," he explains, "as that requires a lot of learning how to recognize a flower and how to collect the nectar. Foragers hone their skills over dozens, if not hundreds, of visits until they figure out how to efficiently pry open the lips of a snapdragon flower, for example. Plus, they have to use visual and olfactory cues to learn which are the rewarding and the non-rewarding flowers."
-end-


University of Arizona

Related Bees Articles:

How bees live with bacteria
More than 90 percent of all bee species are not organized in colonies, but fight their way through life alone.
Where are the bees? Tracking down which flowers they pollinate
Earlham Institute (EI), with the University of East Anglia (UEA), have developed a new method to rapidly identify the sources of bee pollen to understand which flowers are important for bees.
Pesticides deliver a one-two punch to honey bees
A new paper in Environmental Toxicology and Chemistry reveals that adjuvants, chemicals commonly added to pesticides, amplify toxicity affecting mortality rates, flight intensity, colony intensity, and pupae development in honey bees.
Bees can count with just four nerve cells in their brains
Bees can solve seemingly clever counting tasks with very small numbers of nerve cells in their brains, according to researchers at Queen Mary University of London.
Trees for bees
Planting more hedgerows and trees could hold the key to helping UK bees thrive once again, a new study argues.
The secret to better berries? Wild bees
New research shows wild bees are essential for producing larger and better blueberry yields - with plumper, faster-ripening berries.
How do flying bees make perfect turns?
Bees adjust their speed to keep turning forces constant, new research from the Queensland Brain Institute, The University of Queensland shows.
Bees on the brink
Using an innovative robotic platform to observe bees' behavior, Harvard researchers showed that, following exposure to neonicotinoid pesticides -- the most commonly-used class of pesticides in agriculture -- bees spent less time nursing larvae and were less social that other bees.
Why do we love bees but hate wasps?
A lack of understanding of the important role of wasps in the ecosystem and economy is a fundamental reason why they are universally despised whereas bees are much loved, according to UCL-led research.
The more pesticides bees eat, the more they like them
Bumblebees acquire a taste for pesticide-laced food as they become more exposed to it, a behavior showing possible symptoms of addiction.
More Bees News and Bees Current Events

Top Science Podcasts

We have hand picked the top science podcasts of 2019.
Now Playing: TED Radio Hour

In & Out Of Love
We think of love as a mysterious, unknowable force. Something that happens to us. But what if we could control it? This hour, TED speakers on whether we can decide to fall in — and out of — love. Guests include writer Mandy Len Catron, biological anthropologist Helen Fisher, musician Dessa, One Love CEO Katie Hood, and psychologist Guy Winch.
Now Playing: Science for the People

#542 Climate Doomsday
Have you heard? Climate change. We did it. And it's bad. It's going to be worse. We are already suffering the effects of it in many ways. How should we TALK about the dangers we are facing, though? Should we get people good and scared? Or give them hope? Or both? Host Bethany Brookshire talks with David Wallace-Wells and Sheril Kirschenbaum to find out. This episode is hosted by Bethany Brookshire, science writer from Science News. Related links: Why Climate Disasters Might Not Boost Public Engagement on Climate Change on The New York Times by Andrew Revkin The other kind...
Now Playing: Radiolab

An Announcement from Radiolab