I spend more time thinking about varroa than anything else in beekeeping and I’m stepping up the monitoring. I’ve just shook- swarmed a colony with higher varroa levels than any of the others, even though there were only 3 mites in a 300 bee sample in April. Uncapped drone brood revealed a lot of mites inside the cells. The colony was strong but there were several bees out front with deformed wing virus. I’d been planning to change all the combs anyway but this meant that I have now dealt with 3 things in one move; varroa, old comb, and swarm control, Shook Swarm for Apiary Hygiene and Swarm Prevention/Control. (beelistener.co.uk)
Until I discovered this new website, www.varroaresistant.uk , I was going to buy a tool to pin-kill brood and test for hygienic behaviour in my quest to promote varroa resistant bees, but this is only half the story. Hygienic behaviour is good and when brood are killed/die the faster they are removed by worker bees the better. They remove any dead brood but this doesn’t demonstrate varroa resistance. This is where Steve Riley comes in to explain the difference. Steve is an expert on this subject and one of the leaders in the field of developing varroa resistant bees and showing beekeepers just how successfully it can be done. Instead of the pin-kill tool, I will be buying a strong magnifying glass. Thank you, Steve, once again for taking the time to share your expertise and knowledge with us here.
Steve is currently the Chair and Education Officer at Westerham Beekeepers’ Association. He has written previously for Beelistener readers on how to reduce chemical varroa treatments and enable the honey bee colonies to manage varroa by themselves and stay healthy, Developing Varroa Resistant Bees: Steve Riley’s Guest Blog. (beelistener.co.uk)
Honey bees repurposing hygienic behaviour against Varroa.
Honey bees have already developed complex hygienic behaviours to deal with wax moth, chalkbrood, and AFB, which allow the bees to detect and remove dead and diseased larva and pupae. Work from Professor Marla Spivak’s group [Spivak et al., 2003] has uncovered the role of different workers in the process and changes in brain chemistry of specialised detector worker bees. Thus, the honeybees already have a mechanism, but just need time to learn to associate the unique smell coming from mite-infested cells with the presence of Varroa (Mondet et al., 2021). This explains why testing using pin-prick or freeze-kill methods are inaccurate for identifying Varroa infestation, as they test for the ability of the honey bee to detect dead or dying larvae or pupae, rather than mite presence.
For over 30 years, since Varroa arrived in the UK (and longer in mainland Europe), the beekeeper solution has been to reduce mites through various varroacides and biotechnical methods. Where there has been no involvement by beekeepers, honey bees found ways to control mite populations to levels that were not injurious to the colony. Varroa resistance occurred in unmanaged (or feral) colonies in places around the UK, France, Oslo, the Netherlands and in the Arnot Forest, USA – all confirmed by scientific research. In countries where there was a policy of not using varroacides or they couldn’t be afforded (throughout sub-Saharan Africa, Brazil, Central America, Mexico and Caribbean Islands), widespread resistance to Varroa occurred after a period of initial losses.
Can beekeepers ‘catch up’ with the honey bees on Varroa?
Some are already there. A website (www.varroaresistant.uk) was launched at the BBKA Spring Convention in April 2023 by Professor Stephen Martin and a small team of beekeepers. This combines the latest scientific research, together with beekeeper case studies and suggestions for those looking for Varroa resistant traits in their own bees. The case studies come from various parts of the UK and from beekeepers on different scales, including commercial. Beekeepers from north west Wales are featured, as a group of 100 beekeepers with around 500 colonies has the UK’s largest population of Varroa resistant bees. In this and many other examples, Varroa resistance has spread from unmanaged honey bee colonies in buildings or trees.
The other route towards finding resistant bees is for beekeepers to look for the mechanisms that honey bees deploy to control their mite populations. Nurse bees have learnt to detect the unique odour coming from infested worker cells. This leads to several actions that can be observed and measured by beekeepers, which are covered in depth on the recently launched website.
The diagram and accompanying explanation below summarise beekeepers’ actions to identify resistant traits in their bees: –
Identifying Resistant Traits.
1 Uncapping is easy to see during inspections and mostly occurs at the white to purple eyed stage of the worker development. Recapping of these cells by the bees is more difficult to identify, although a quick photo of sealed worker brood, blown up later, will help to spot the disturbed surfaces.
Uncapping and recapping can occur many times as part of the inspection process by the bees and none of this harms the developing bees.
2 Chewing out infected pupae stops Varroa reproduction. The offspring die and whilst the mother mite escapes, she can only lay eggs on 2-3 occasions in her life and eventually becomes infertile. Beekeepers can observe the evidence of chewing-out behaviour from white exoskeleton on an insert board under an open mesh floor.
3 Low mite counts, over the season, are the result. This is the main indicator of whether there is sufficient hygienic activity by your bees.
Low mite numbers = low levels of Deformed wing virus = healthy colony.
Understanding the interruption to Varroa’s reproduction cycle.
Worker brood is where most reproduction opportunities occur for Varroa, which is available from January to November in the south east of England. During the c.12 days that the worker cell is sealed, uncapping / recapping / chewing-out activity by the bees is normally observed at the white to purple-eyed stage of the pupae.
By overlaying the reproduction cycle of Varroa, it can be seen that the interruption occurs ahead of the son and daughter mites being sexually mature (indicated by the blue & magenta arrows). Mite reproduction is stopped by the bees’ actions.
Uncapping: wax moth or “bald brood”?
Where uncapping occurs in straight lines, beekeepers rightly associate this behaviour with wax moth. Uncapping & recapping for Varroa occurs in clusters (Grindrod & Martin 2021); the difference can be seen in the pictures below.
“Bald brood” (ie; uncapped cells) was historically seen as a common disorder but not understood. We now know this is more likely to be the bees’ hygienic behaviour against Varroa.
Now that the hygienic behaviour underpinning how honey bees control their Varroa populations is largely understood, it’s over to beekeepers to select for these traits in their colonies. Otherwise, we are breeding from bees with no or low defences against Varroa.
It is a fascinating new area of beekeeping where we are privileged to observe adaption occurring in nature. For more information go to www.varroaresistant.uk .
Hygienic behaviour in the honey bee (Apis mellifera L.) and the modulatory role of octopamine Spivak, M. Masterman, R. Ross, R. Karen A. Mesce, KA (2003) Journal of Neurobiology 55 (3),341-354. https://doi.org/10.1002/neu.10219
Chemical detection triggers honey bee defense against a destructive parasitic threat. Fanny Mondet et al. (2021) https://doi.org/10.1038/s41589-020-00720-3
Spatial distribution of recapping behaviour indicates clustering around Varroa infested cells; Isobel Grindrod & Stephen J. Martin (2021) , Journal of Apicultural Research, 60:5, 707-716, DOI: 10.1080/00218839.2021.1890419 To link to this article: https://doi.org/10.1080/00218839.2021.1890419
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Thank you, Ann 🐝