#varroa

[ Image description: a photograph of a V. destructor mite on honeycomb(1).  It is a hairy ovoid creature, brownish-red in color, with hair little legs sticking out along one of its long sides.  It is such a small little beast that the hexagonal shape of the comb is not apparent in the photograph. End ID. ]

Varroa destructor is a mite that arrived in Europe in the 1970s, and made its way to the US in force in the late 1980s(2).  By 2007, it was established in the entire United States, including all of the islands of Hawai’i(3).  This is important, because a lot of the beekeeping practices that are based on the natural lives of the honeybees (such as the Warré Hive) were developed prior to the mite’s arrival. 

I myself am passionate about the importance of knowing how bees live in the wild if you’re going to have an apiary -- I know not all beekeepers are like this, for various reasons (e.g., if you’re a commercial beekeeper who’s working with orchard growers to pollinate trees under contract, you need to both have a lot of bees, and you need to be able to transport them, so you’re going to necessarily have different needs & a different perspective than, say, a hobbyist like me).  I think it’s okay: the important thing is: we need bees.  And we need to understand what Varroa’s doing to our bees.

Varroa evolved with a different species of honeybee: Apis cerana, or the Asian honeybee.  In the west, the primary species that beekeepers keep is Apis mellifera.  This means that the Varroa was able to hop right on over onto a species that had not evolved defenses to it.  The results have been devastating -- let me tell you why.

Until very recently, most researchers would tell you (and probably still will) that Varroa feed on the bees’ hemolymph -- their version of blood.  In 2019, a number of researchers demonstrated that this is not the case: what the Varroa are feeding on is a honeybee organ called the fat body(4).  The fat body is something akin to our liver, in that it (among many other things) functions as a filter, which is why I jokingly call these little bastard mites “the Hannibal Lecters of the honeybee”.  But the fat body does a lot more: it both acts as an energy store, which I probably don’t need to tell you is important, is a major piece of the bees’ immune system, and it produces a complex called Vitellogenin (I’m gong to refer to it as “Vg” for short).

Vg is critically important to the honeybee.  It is has a three-in-one function: as a protein complex, it contains proteins, but it also lipids and carbs.  It’s vital to the bee’s ability to synthesize proteins, it supports the immune system’s response, and it is what determines a honeybee’s longevity: a queen bee, who lives for 2-3 years, is packed with it, whereas your regular honeybee worker doesn’t have a lot, and conversely lives for 45-60 days. 

Who else has a relatively high level of Vg?  Winter bees, which is why Dr. Ingrao refers to them as the fourth honeybee caste: in addition to workers, drones, and the queen, you have these “winterover” bees with their high Vg level.  What’s their purpose?  To live.  In particular, to live for 4-6 months during the winter, when they’ll have no access to food outside the hive, and during which time they’ll be keeping the nest (and queen) alive by keeping it warm.  They do this by clustering tightly (insulation) and shivering (thermoregulation), which requires a lot of energy.  So they need that fat body both for its energy stores, as well as for the Vg so that they live long enough to keep the colony alive (they also eat honey, of course, which is why it’s important for beekeepers to leave honey in place, and also to leave honey in certain places, since the cluster will not expand in cold temperatures, so they’ll never get to honey stored too far away from the center).

This is why Varroa mites are so awful: they eat that fat body away to practically nothing.  The little bastards grow at an exponential rate: in the beginning of the season, their numbers are low enough that they’re not going to have a lot of impact on the bees.  But if a beekeeper does nothing, their population will explode in the months of August and September. This is precisely when the colony is beginning to develop the generation of winter bees it’s going to need to make it through the cold.  That explosion of mites gets into the brood of baby winter bees and feeds on the larvae’s fat bodies, so when the winter bees finally emerge, their fat bodies are fatally compromised: they haven’t developed the necessary levels of Vg, meaning they won’t live very long.  Their immune system is compromised, leaving them vulnerable to the many myriad viruses that the Varroa mite carries.  Because their energy system is compromised, they can’t thermoregulate effectively.*** And their fat body can’t filter environmental toxins(5), making them more vulnerable to pesticides such as neonicotinoids**, which are most likely in the honey that’s been put away for the winter. 

** This family of pesticides is in fact banned in Europe because of their impact on pollinators (but, sadly, not yet across the US).

*** I believe that this is not helped by thin-walled beehives.  But that’s a topic for another article.

With all this in mind, it’s absolutely no wonder that Colony Collapse Disorder occurs, and that whole colonies die before the winter is out (and sometimes in the middle of summer).

What to do?  Well, there’s been some stellar work in breeding Varroa-resistant strains of Apis mellifera, which is great news for beekeepers.  Also, Dr. Thomas Seeley discovered that evolution is working as it should in Cornell Universty’s Arnot Forest, a research preserve in New York State, as he recounts in The Lives of Bees.  However, this resistance has game at the cost of a mitochondrial bottleneck, though fortunately overall genetic diversity had increased -- while the number of queens had been drastically reduced, the dying colonies had apparently still produced enough drones to spread their genes throughout the forest’s bee populations(6).  But critically, his research pointed towards the evolution of the mites versus the bees (in other words, the mites’ overall success depended on them becoming less lethal to the bees)(7).  At any rate, some beekeepers advocate doing nothing: just let the bees sort it out on their own, and develop resistance through evolutionary processes.

I personally have a couple of issues with this: first, unless you are specifically breeding bees for resistance (in other words, you’re artificially speeding up the evolutionary process), this is going to take a long time, and you’re going to lose most of your bees.  Also, if you’re not pursuing the treatment-free process correctly (i.e., monitoring, and then killing the colonies that experience mite explosion, so that only the colonies that are able to control the mite population on their own survive to reproduce), you’re selecting for successful mites instead of successful bees(8).

If you’ve got a ton of money and can afford buying new bee packages every year (at something like $150 to $200 a pop) until you’ve built up an apiary of successful bee colonies, that’s okay, but there is yet another problem: swarming.

This is a colony’s means of reproduction: a strong colony will cast of one or more swarms -- children, sort of***.  This is one of the ways that wild bees actually manage their Varroa loads: the departing bees take a bunch of Varroa with them.  The problem with this for beekeepers is that a) they generally keep steps to prevent bees from swarming, which means more Varroa remains in their really big hives or b) if the bees do swarm, and there are other beekeepers in the area, some of those bees are probably going to make their way into their hives, taking your problem into their apiaries, which imo is not cool unless you absolutely know they’re okay with it, and which means that on top of everything else, you have to be completely invested in swarm control.  It’s a lot of work!

** I say “sort of” because the primary swarm is actually the old queen leaving with a bunch of bees, leaving a bunch of bees in the original nest/hive along with a virgin queen.  It would be roughly analogous, in humans, to the parents of a child moving out of the family home when it’s time for the child to be on their own, and the brand new queen there now has to fly out on a mating flight and successfully make it back to the nest in order for this next generation to survive (in their childhood home).  Subsequent swarms, if the colony is big enough to support them, will consist of yet more bees departing with newly-hatched virgin queens, who not only have to fly their mating flights, but have to establish a completely new household somewhere.

Knowing what Varroa does to bees, I’m personally not at all cool with these parasitic bastards.  They’re awful, and I don’t want to do that to any colonies of mine.  To me, it’d be like not vaccinating a pet for a nasty virus (like FIV for a cat) and then potentially letting that cat run around outdoors where it can not only pick it up, but also spread it to other cats in the neighborhood, all in the name of “letting cats develop FIV resistance naturally”.  It’s just not for me, at least, not right now.

There are, fortunately, a ton of ways to knock down the mite load in honeybees, many of which are natural but all of which you need to actually understand before you utilize.  Some beekeepers will simply treat with one or more method on a regular schedule -- this is called “prophylactic treatment”, and I personally am not a fan of it: I’m concerned that this will allow mites to built up resistance to them.  I’m also not a fan of doing nothing, for the above reasons: potential impact on my neighbors, and I just don’t want to be losing bees all the time.  So if I actually ever set up any hives, I’m going to go for an Integrated Pest Management solution: I’ll monitor my colonies for Varroa, and then treat them with the appropriate treatment when (and only when) the mite load is high enough to call for it (I’ll check 300 bees with either a sugar role or alcohol wash method and if I find 9 or more mites, I’ll treat).

I'd originally been very interested in the Warré Hive for its emphasis on beekeeping that operated in accordance with the bees’ own natural inclinations.  But the need to be able to inspect the hive for pests, particularly Varroa, means that for me at least, I need to have moveable frames.  So I’m probably going to go with a Langstroth-style hive, with some modifications for experimental purposes, which I might talk about later, if I get around to it.

As always, thank you for reading my book!

Citations (unlinked to ensure the post shows up in the applicable tag feeds)

Note: where information, above, is uncited, I’ve obtained it from the “Heroes to Hives” course material.  Most of it’s easily available in the applicable Wikipedia articles.

(1) User Wasp32, “Varroa destructor”. - https://commons.wikimedia.org/wiki/File:Varroa-destructor.jpg

(2) Reid, Brandon.  “Introduced Species Summary Project Varroa Mite (Varroa destructor)” (2004) - http://www.columbia.edu/itc/cerc/danoff-burg/invasion_bio/inv_spp_summ/varroa_destructor.html

(3) Texas Invasive Species Institute, “Varroa Mite” (2014). - http://www.tsusinvasives.org/home/database/varroa-destructor

(4) Ramsey, Samuel, et al. “Varroa destructor feeds primarily on honey bee fat body tissue and not hemolymph” (2019) - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6358713/

(5) Ibid, figure S5 of the supplementary file (page 6).

(6) Seeley, Thomas. The Lives of Bees: The Untold Story of the Honey Bee in the Wild (2019). Princeton University Press.  Also available in the original research paper by Dr. Selley:

(7) Seeley, Thomas, “Honey bees of the Arnot Forest: A population of feral colonies persisting with Varroa destructor in the northeastern United States“ (2007) - https://www.researchgate.net/publication/226076088_Honey_bees_of_the_Arnot_Forest_A_population_of_feral_colonies_persisting_with_Varroa_destructor_in_the_northeastern_United_States