This week's episode is all about a nasty little parasite that is decimating honey bee colonies all over the globe; the varroa mite. Currently, Australia is the only continent free of this pest.
Sources used for this episode:
Honey Bee Biology and Beekeeping by Dewey M. Caron with Lawrence John Connor.
The Lives of Bees: The Untold Story of the Honey Bee in the Wild by Thomas D. Seeley
The Backyard Beekeeper 4th Edition by Kim Flottum
Various articles by Randy Oliver at his website, Scientific Beekeeping.
'Reproductive Biology of Varroa Destructor in Africanized honey bees (Apis Mellifera)' by Calderon et al, 2009.
What is the varroa mite?
The varroa is a large bodied, reddish-brown mite, visible to the naked eye. It is active on adult bees, burrowing between abdominal segments.
Only the females of this species are parasitic. The males are essentially only there for reproduction.
A mated female mite will enter a cell shortly before it is capped, hiding in the bee food at the base of the cell to avoid detection. Female mites actually lack antenna and eyes so it is believed they use touch, heat, and smell to target their hosts.
Within 60 hrs of entering the cell, the female mite lays her first egg, which is ALWAYS male. Within another 30 hrs, she lays fertile female eggs. These daughter mites then mate with their brother.
The varroa mite prefers drone cells as the longer capped cell period allows her to produce more daughters; up to 5.
The female mites pierce the exoskeleton of the bee pupa and feed off its fat tissue stores. These infected pupa will usually emerge but can suffer such issues as shortened abdomens, misshapen wings and legs, less body weight, and reduced hemolymph volume. A heavily infested pupa might die in the cell, never to emerge.
After the male mite has participated in his disgusting incestuous orgy with his own sisters, he dies. The female mites will eventually emerge from the cell, attach to an adult bee, and go off to infest more pupa, either within the same hive or another (through colony drift).
The puncturing of the bees exoskeleton for the mites to feed either introduces viruses to the bee, or makes them vulnerable to such viruses and diseases. The immune system of the bee is clearly effected.
To quote Thomas D. Seeley (a researcher of honey bees in the US); “when a colony has a high mite load, the worker bees it produces start their lives with such high virus titers that they are too sick to work”.
This leads to colony collapse. Usually identified when you come to your hive and find almost no adult bees and a small amount of brood. This led to the idea of ‘vanishing bees’ before the cause was identified.
Now, the varroa mite originated in mainland Eastern Asia so how did it get transmitted almost globally?
For a concise but detailed history, I looked to Thomas D Seeley’s new book (The Lives of Bees; The Untold Story of the Honey Bee in the Wild), which has a convenient timeline of how the varroa mite came to spread. The following information is all from this book:
As I said, this mite originated in Asia where it had a stable host-parasite relationship with the Asian/Eastern Honey bee (Apis Cerana). In the early 1900s, the European/Western honey bee became a host for this parasite after movement of the European honey bee from Western Russia and Ukraine to the eastern region of Russia. This caused an overlap in range for the two honey bee species, exposing our honey bee friends to this nasty mite.
In the 1950s/60s, Russian beekeepers spread varroa to Europe via shipped queens that were infested, Infestations of varroa were first reported in Bulgaria in 1967, Germany in 1971, and Romania in 1975. From here it spread to North Africa around 1975/6 via 100s of colonies sent as part of a foreign aid program from Romania and Bulgaria.
In 1971 varroa reached S. America due to movement of bees from Japanese beekeepers into Paraguay, Brazil was effected in 1972, although this transmission route isn’t clear.
Varroa entered N.America via two potential routes:
1/ Florida. Mid-80s via smuggling of Brazilian queens, and/or swarms of Africanized honey bees that came off cargo ships. Documents indicate 8 ships came to port with swarms between 1983-1989, and it is recorded that they had varroa mite infestations.
2/ Texas. 1990s, swarms of Africanized honey bees came north via Mexico.
An interesting note about Africanized honey bees. You might be familiar with these bees from various horror stories of them swarming and killing animals, children, and even adults. They are famously aggressive, and Southern states struggle with keeping their genetics out of their colonies. But AHB appear to be more resistant to varroa than our European honey bee.
According to a paper I found: ‘Reproductive Biology of varroa destructor in Afrixanized honey bees’ by Calderon et al (2010), which looked at varroa levels and transmission in tropical areas of S.America, the apiculture of AHB has been minimally affected by this nasty parasite.
AHBs seem to have increased levels of hygienic behaviour; detecting mites even in capped cells and removing them and the infested pupa; but also varroa mites have lower levels of fertility when feeding on AHB, which indicates some level of resistance within the biology of the AHB itself. See link in the source list at the top of this post for the full article.
So you know more about this parasite. What now? What do you do?
Testing/Sampling
Mite testing is recommended from April to October.
Historically, brood sampling was an approved method of testing for infestation. This involves uncapping brood cells, preferably drones, and counting the number of brood with mites present. The problem with this is that the percentage of pupa effected does not correlate to the mite load present so it’s not a reliable method of testing. In fact, I’d never heard of this until I started doing all this research.
Adult sampling is the norm currently, and there are two main methods:
1/ alcohol wash
-get 300 bees (½ cup, level), preferably nurse bees as they have most contact with the brood where the mites will breed/emerge
-put in container or handy dandy mite check kit, add alcohol to cover (I use 70%)
-shake/swirl thoroughly for a minute or so. Let it sit, strain out the bees/alcohol, count the number of mites.
-benefits: most accurate sampling method
-downside: kills bees (but this is a tiny fraction of a healthy colony)
-Apiary Dave’s bee math: 300 bees = 0.005%-0.015% of population; 1 sample a month from April to Oct =2100 bees, which averages out to about 10 bees/day. And a healthy queen can lay between 1-2K eggs PER DAY. Some perspective there.
2/ sugar shake
-300 bee sample again
-add to jar with 2-3 tbsps powdered sugar
-shake
-mites supposed to be dislodged.
-shake out onto a white surface to help you spot mites
-return bees to hive
-benefit: doesn’t kill bees (though they probably don’t appreciate it!)
-cons: can be hard to do correctly, which leads to inaccurate mite count
For both these methods, you should identify your queen and place her/her frame somewhere safe so you don’t accidentally include her in your sample!
Also best to choose frames with both open and capped brood but use what you have.
In terms of your mite counts, a general guide:
General: 6-9 mites per 300 bees
Spring: 3:300
Late summer: 9:300
Zero mites? Doesn’t mean they aren’t there, just undetectable for time being. Keep testing.
21:100 bees/ 63:300; mite bomb. This hive is dead, it just hasn’t stopped kicking yet.
Please note: use of sticky boards for counting mites or just visually inspecting bees is NOT AN ACCURATE MEASUREMENT OF MITE LOAD. Don’t be that guy. Do a proper test.
Treatment
I’m going to talk about synthetic chemical control, and naturally occuring chemical control methods. What do I mean by this?
You might see certain treatments labeled as ‘chemical treatments’, in contrast to ‘natural treatments’. But what the eff does that mean? It’s clearly biased wording and it doesn’t tell you much. Everything can be broken down into chemicals. Yes, even ‘natural’ things. And natural DOES NOT EQUAL SAFE OR SAFER. A popular naturally occurring treatment for varroa is oxalic acid, a substance so dangerous that you need to wear a respirator mask when vaporising it. Does that sound safe?
So to be clear, I’m differentiating between synthetic (human created) chemical treatments and those derived from naturally occurring sources.
SYNTHETIC:
-Apivar (amitraz).
=miticide
=Strips you put into the hive between frames (2 to a deep). 6 week treatment.
=up to 99% effective
=must remove honey supers first
=no harmful residues left behind
=up to 2 year storage of unopened containers
=varroa developing resistance to miticides in general so very important not to overuse this treatment, or use it without testing first. This could diminish its efficacy in future.
NATURALLY OCCURRING:
-Formic Acid
=Mite Away Quick Strips (MAQs) popular brand
=natural acid found in honey and bees
=up to 95% kill rate
=2 strips per hive body
=bees do not like this; watch them run!
=wear mask; strong scent/fumes and not good for you to breathe
=chemical burns reported; wear gloves!!
=once you expose strips to air, must use them immediately
=reports of absconding, bee and brood death, and queen death
=safe to use with honey supers on
=temp sensitive; READ THE LABEL
=ineffective if temp below 50F/10C, and dangerous in high temps (increase die off of bees)
-Oxalic Acid
=mechanical kill method/immediate effect, doesn’t linger
=hive MUST be broodless
=vapor is very dangerous; wear a correctly rated respirator mask
=vapor considered more effective but equipment can be expensive and you need safety gear
=dribble method not as effective and seems to have larger margin of error
=most effective as Fall application
=can cage queen for 14 days to reach broodless state
=not approved during honey flow
=must remove honey supers
-Hop Guard
=organic acid derived from hops
=cannot penetrate capped cells
=applied via strips placed between frames
=leaves no residue in honey
=apply to broodless hive
=great article on this by Randy Oliver at scientificbeekeeping.com (will share on blog)
=my preliminary reading indicates this is not a very effective method of treatment.
-Thymol
=Apiguard
=slow-release
=works best in temps above 25C/77F
=approved for organic farming by Europea Union
=some brood loss, according to Randy Oliver
=remove honey supers (safe for honey but leaves strong taste; Listerine??)
=not for use below 60F/16C as it won’t evaporate
=or above 105F/41C as it will evaporate too quickly
=I might try this next year.
Preventatives
1/ honey bee strains resistant to varroa; hygienic behaviour, etc; Russian bees; VSH Varroa Sensitive Hygiene Bees
2/ mid-summer split/brood breaks
-good management practice
-might not work for slow building first year colonies
-split; 50% mites
-cage the queen for a brood break; allowing all capped pupa to emerge
-treat hive during the brood break
-3 week break + treatment before releasing queen. She will take another week to start laying and a week after that until sealed brood, giving you a total period of 5 weeks to get rid of those pesky mites
-queenless half of the original colony goes through a natural brood break as they raise their own queen
-hopefully a queen mated in your area will have access to strong, local genetics
-OR you can requeen with a varroa resistant queen
-you get 2 strong colonies w/ no mites and vigorously laying queens
-well-fed, low/no viral loaded bees
-you don’t get much honey for them to overwinter with so keep an eye on them and feed aggressively if needed
3/ Drone brood trapping/drone comb
-mites prefer drone brood
-add drone comb
-during active season, healthy colony will allow 10-15% of frames to be drone comb; take advantage of this
-when most cells capped, remove and freeze
-feed to chickens!
-must time this well or you’re creating a mite bomb
-sometimes bees won’t draw the drone comb; drones are not the priority of a hive so stress can deter them from producing drones; anything from drought, too much rain, pesticides in area, pollen or honey dearth, etc.
IPM: Integrated Pest Management
-preventatives
-mechanical methods (trapping, etc)
-treatment
-begin with safest to potentially harmful pesticides
Treatment Free
What is this and is it even possible?
I need to do a lot more reading on this subject since many things I found were unclear. For one, many can’t even agree on what ‘treatment free’ means. Some will use things like brood comb but draw the line at miticides; others consider even feeding bees to be a form of treatment and basically encourage doing as little as possible to/with your colonies.
In the world of the varroa mite, how is this possible? I’m not convinced it is.
I found a great article on Thoughtscapism called ‘Treatment-Free Beekeepers give Varroa Mite Free Reign” (see link at top of the blog).
I like this article a lot because the author provides citations and links to his sources. European and US studies on beekeepers (hobby and commercial), treatment, and mite levels are referenced extensively.
Treatment-free beekeepers appear to believe that refraining from treating varroa will allow honey bees to steadily gain resistance. This isn’t entirely illogical. In fact, Thomas Seeley’s book (The Lives of Bees) that I referenced earlier addresses this issue. At the conclusion of his book, he recommends 14 things that we can do to cultivate healthy colonies, and the final recommendation is not to treat varroa.
HOWEVER, this is not the same as allowing varroa free reign to decimate your colonies and those around you. YOU DO NOT LIVE IN A VACUUM. Your mite bombs effect my hives and vice versa, AND we affect the wild colonies that live in our shared territories.
Seeley says it best so I am going to quote him:
“If you pursue treatment-free beekeeping without paying close attention to the mite levels in your colonies, then you will create a situation in your apiary in which natural selection is likely to favor Varroa mites, not Varroa-resistent bees. To help natural selection favor Varroa-resistent bees, you need to monitor the mite levels in your colonies and kill those whose mite populations are skyrocketing long before those colonies collapse from heavy infections of viruses spread by the mites.”
And this is a key point; simply refusing to treat hives and letting them die from varroa infestations DOES NOT MEAN YOU ARE BREEDING RESISTANT BEES. And if you keep going to the same stock to try again, you’re only helping the mites. And, if you’re doing all this and refusing to test, you’re part of the problem and you’re infecting colonies around you. You are ground zero for varroa mites in your community.
To quote Seeley again:
“If you don’t perform these preemptive killings, then even the most resistant colonies in and around your apiary can become overrun with mites and die, in which case there will be no natural selection for mite resistance among the colonies in your apiary. If you are unwilling to kill your colonies with dangerously high mite loads, then you will need to give them a thorough treatment with a miticide and replace their queens with queens of a mite-resistant stock.”
I really need to do a whole post on this book as Seeley addresses a number of issues that appear to allow wild colonies resistance to varroa.
What did I do this year?
Mite checks (using the alcohol wash method)!
Apivar was my chosen treatment. Originally, I had this confused with what one of my teachers uses (Mite Away Quick Strips). When I realised my mistake, I looked into it more and decided that it was a happy accident. Although not being able to use with honey supers on is a bother, it has a lower rate of queen death and absconding over time compared to formic acid treatments. Also, I have no intention of harvesting honey this year and studies show that this treatment doesn’t leave harmful residue in honey for the bees. So I left the honey on (most wasn’t capped anyway, making it impossible to safely store) and will mark the boxes/frames used so I know to use them exclusively for brood in future to avoid any risk of contamination to future honey harvests.
Researching this topic was fascinating! I learned new things, clarified existing concepts, and even changed my mind about some treatments. I hope you benefit from it too!
Feel free to reach out to me at homesteadhensandhoney@gmail.com; leave a comment here, or find me on Instagram at homesteadhensandhoney, and Twitter at HomesteadHens.
Until next time! Remember, hug your hens, and then wash your hands. :)