Different biological mechanisms allow bumblebee queens to survive for several days in spring, when the ground where they spent the winter thaws and becomes waterlogged due to rain, researchers at the University of Ottawa have found.
The work of Professor Charles-Antoine Darveau’s team has demonstrated that queens can survive immersion for more than a week, a real feat for a terrestrial insect.
However, we do not know the limits of these survival mechanisms. We therefore cannot know whether bumblebees will be able to survive if climate change causes earlier melting and more abundant rain.
“It seems contradictory, but several insects that live on land are capable of breathing underwater, even if generally it is the insects that are linked to the aquatic environment,” said Professor Darveau.
“But it sure is surprising to see a queen bumblebee that is able to survive underwater. (…) When the spring conditions arrive, they are not yet ready to come out, they are still immobile in the ground, and that is where all this stuff becomes an important arsenal.
Until now, it was assumed that queen bumblebees ― a species very closely related to honey bees, in evolutionary terms ― that did not wake up in time would simply drown. Instead, researcher Sabrina Rondeau discovered, entirely by chance, that they are able to survive underwater.
While pursuing her doctoral studies at the University of Guelph, Ms. Rondeau noticed that a freezer had leaked water onto containers containing four hibernating queen bees ― and which, to her amazement, were still alive.
Mr. Darveau, Ms. Rondeau and student Skyelar Rojas immersed fifty queen bumblebees in a state of diapause, the equivalent of hibernation in insects, into a container filled with water. They then measured, over eight days, the tiny amounts of CO2 that rose to the surface, which shows that the insects manage to “breathe” underwater, possibly by surrounding their bodies with a thin layer of oxygen.
“We were able to demonstrate in this study that these queens are consuming oxygen and producing CO2 throughout the period during which we studied them, that is to say for eight days,” summarized Professor Darveau.
The researchers found that submerged queens produced 75% less CO2 than queens diapausing outdoors, indicating a significant slowdown in their metabolism. The longer the experience continued, the more the phenomenon amplified.
Insects have also partly shifted to anaerobic metabolism, as evidenced by a fifteen-fold increase in lactate levels in the bees’ bodies.
The queens survived the experiment and woke up after being taken out of the water. However, their breathing then increases by a factor of ten for a few days, the time to get rid of the waste that has accumulated in their body.
“What is new is the combination of possibilities that they have exploited,” said Professor Darveau. We know that animals are capable of producing lactate when there is no oxygen, we know that some insects are capable of breathing underwater, but putting it all together for a queen to survive in these conditions for so long is really the amazing part. A week, eight days… it’s still quite impressive when you see them come back to life.”
It remains to be seen what impact climate change will have on bumblebees, especially since we can assume that what affects bumblebees also affects other species of bees, adding to the threats that already hang over pollinators on a planetary scale.
Some laboratory experiments show, for example, that climate warming could accelerate their metabolism during diapause, which could harm their fertility.
We also don’t know how bumblebees will react if their environment were to be flooded earlier and for longer in the spring, Professor Darveau warned.
If spring spells start to be more frequent and rainfall and flooding are greater, that could impact the success of these insects when spring arrives and the new season begins, he said.
“How long can they last, but also how many flood cycles can they endure? With what we have discovered, and also the costs associated with recovery, we realize that if we have a certain amount of fuel on board available, but each time we use it, how far can we go until we reach the point of no return? These are questions that will follow from these studies,” concluded Professor Darveau.
The findings of this study were published in Proceedings of the Royal Society B: Biological Sciences.
