Beyond workers: mating and overwintering bumble bees


In WPC’s Bumble Bee Conservation Lab, we raise bumble bee colonies in captivity with queens we collect during our spring surveys. You can learn all about the conservation breeding lab and the colonies we raised this year in a previous blog here. We monitor these colonies throughout the summer, and into the fall. Throughout the summer colonies produce workers, but in the fall towards the end of their colony cycle, they begin to produce males and gynes (new queens).

Part of our bumble bee conservation breeding program includes running mating trials in the fall. This year, mating trials were conducted for eight weeks, between August and October. So, how does it work? Each day we set up a mesh tent outdoors and inside are 4-12 pairings of bumble bees set up in individual enclosures. Each pairing consists of two males and a single gyne from different colonies. Bees are often marked with different coloured oil-based paint markers to help us identify what colony they came from and help us keep track of how old they are.

A peek inside the mating tent. Photo: E. Richard

This year we were trying three different types of enclosures to see which works best, since it’s been found previously that some bumble bee species prefer certain sized areas for mating. Enclosures range in size from smaller boxes, into which we install spring queens, to large flight cages, and each gyne was given a chance to mate in each of the enclosure types. In the enclosures, we provided them with nectar and pollen so that they have everything they need to be comfortable!

Bees were left out for roughly eight hours during the day, and our staff regularly observed them throughout the day, recording any activity that we saw. We didn’t witness any direct mating events this year, but we did have some close calls! We think we potentially saw some post-mating behaviour that would indicate our bees successfully mated, even if we didn’t directly observe it.

A look at the three different types of enclosures trialed for mating in 2021. 1) Flight cage, 2) Colony Box (box we move colonies to after they grow too large for the initial box), and 3) Queen Starter Box (the box we initially put queens in after being collected in the field). Photo: T. Harrison

This demonstrates the type of behaviour we look for and record – close interactions such as male on top of gyne. This is not evidence of mating but close. Males are denoted with colour markings. Photo: E. Richard

After we’ve attempted to mate a gyne three times, or they reach 11 days old, an age at which they are less likely to successfully mate, they move along to the next step…overwintering!

In nature, mated bumble bee gynes will hibernate over the winter in spaces such as underground burrows and beneath leaf litter, before emerging the following spring and initiating a colony. In our conservation breeding lab, it is important to simulate this same overwintering process.

To do this, we move our gynes into individual small boxes and put them in a fridge of 8°C for 12-24 hours before transferring them to an even cooler fridge of 4°C  to simulate a transition into snug overwintering conditions. Inside the fridges we are trying out the use of terra cotta discs (the same material used in orange clay pots) which we hope will help maintain a higher level of humidity.

As of early November, we have 93 queens (17 common eastern and 76 brown-belted) cozied up in our overwintering fridge. Each week over the winter months, our team will be checking in and weighing each of our overwintering queens to monitor their weight loss throughout the winter, because just like bears, bees need fat stores to survive through the winter.

We wish them a peaceful slumber!

A peek inside the overwintering fridge where queens are stored in boxes. Photo: T. Harrison

Weighing an overwintering queen.
Photo: T. Harrison

Tiffani Harrison

Conservation Outreach and Field Biologist – Native Pollinator Initiative

Tiffani joined WPC as a bumble bee conservation field technician in 2017 and fell in love with the work. Since then, she has worked a variety of roles leading monitoring surveys, research projects, and community outreach both in Ontario and Alberta. Currently she manages the field work and outreach components of the Bumble Bee Recovery Program. Tiffani completed her MEnvSc in Conservation and Biodiversity at the University of Toronto and comes from a background of ecology and conservation biology.

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