Category Archives: Bees – What’s new

Dealing with varroa

Any beekeeper that has kept bees for a number of seasons will understand and know, there comes a time when your colony requires assistance in dealing with varroa, or the colony will die. This is a sad fact of modern beekeeping, but, if we are going to apply good animal husbandry concepts to our bee stock, there are times when it’s necessary to intervene and try keep our stock healthy.

To begin with, when modelling mite interventions (Treatments), I have chosen two of the common organic acid methods to introduce as tools for managing mites.

Formic Flash:- The formic flash treatment is one commonly used in our area, it’s a single day application of formic acid to the colony. The benefit of the formic acid treatment over others, it will apparently effect mites under cappings as well as phoretic mites. One can read endlessly about efficacy, and eventually you realize, the numbers quoted in different sources are all over the map. I have chosen to model the formic flash treatment with a very high efficacy level, not because I believe it is this high, but to show how even with high efficacy on a treatment, an out of control mite population will still kill the hive even after a mite treatment is applied. For the purposes of this model, the formic flash treatment kills 90% of the mites under cappings and those in a phoretic state. This is a highly effective mite kill. But a huge caveat, reading at Randy Oliver’s site at scientific beekeeping, he tried multiple rounds of formic flash to try improve mite kill. A second round of formic a week after the first resulted in a dead colony. Reference available here.

Oxalic Acid Vapour:- The Oxalic Acid Vapour treatment is less effective than the formic treatment in that it only affects phoretic mites. Easily applied on a small scale using a wand style vaporizer that takes about 5 minutes per colony for a full treatment, or using a blower style of vaporizer that takes about a minute per hive when doing larger numbers. The OAV treatment puts oxalic acid crystals in the hive which work for about 24 hours killing phoretic mites. Literature suggests this treatment is about 95% effective, in that when properly applied it will kill 95% of the mites. As it lasts over roughly 24 hours, for the purposes of modelling, we kill off 95% of phoretic mites on the day it is applied, and also get 95% of the mites emerging over the next 24 hours.

The OAV treatment only gets phoretic mites, and one strategy to help with this problem that I’ve read about online a number of times is folks are trying 3 treatments a week apart with the expectation this will get all of the mites thru a brood cycle. That would be true if the mite brood cycle turns over on a weekly basis, but, it doesn’t, it turns over on a 5 day period, the amount of time a mite remains phoretic. I added two more OAV options to the model, one of them applies 3 treatments at a 1 week interval, and another that applies 4 treatments at 5 day intervals. for those with a small number of hives, these may be viable options for mite control. If your colony count is such that you cant get thru them all in 5 days of work, then these become less viable options.

Modelling Varroa

So the bee population model is more or less complete, but it still is not representative of the real world. Out here in the real world, we have the varroa mite. To properly model the growth of varroa within a colony, we first need to understand the life cycle of this critter.

After reading endlessly in various literature on the subject, my conclusion is, the life cycle of the mite is fairly well understood, and is dramatically effected by what type of cell a given foundress mite enters. We need some numbers to realistically place timeframes on varroa development, a good reference is found here.

The phoretic period may last 4.5 to 11 days when brood is present in the hive or as long as five to six months during the winter when no brood is present in the hive. Consequently, female mites living when brood is present in the colony have an average life expectancy of 27 days, yet in the absence of brood, they may live for many months.

To get a handle on the reproductive success of those mites, another quote from the same article

Considering mortality in brood cells and improper mating, the average foundress mite produces about one offspring per worker cell she enters, and about two offspring per drone cell. Drones take longer to develop so more mites are produced in drone cells.

To try model these numbers is fairly strait forward. When a mite emerges we keep them in a phoretic state for 4 days. Starting on day 5, we assume that half of the mites available for going into cells will successfully find their way into a cell to try and reproduce. A fertile varroa mite going into a worker cell will produce one offspring, so two mites will emerge. That original foundress has been under the cap for 10 days and spent 5 days phoretic, so is now 15 days old, and after another 5 days of phoretic behaviour will enter another cell, so we have two fertile mites entering worker cells at this time. 10 days later we will have 4 mites emerge, but the original foundress is now fully aged and dies of age. The net result is, after two varroa brood cycles in worker brood, a single foundress mite has resulted in 3 mites in the colony.

Things change when there is drone brood available, literature suggests the varroa much prefer to hop into a drone cell over a worker cell. When a varroa mite enters the drone cell, she remains under the cap for 14 days, and will produce two viable daughters. After a phoretic period, all 3 of these mites will enter drone cells, and all 3 produce 2 more viable daughters, for a total of 9 mites emerging on the second round. At this time the original foundress mite dies of age, but leaves behind 8 viable mites as daughters and grand daughters.

As this math shows, there are two very distinctly different details when comparing the varroa life cycle to the honeybee life cycle. The bee population is based on a single queen laying eggs, and will grow in a linear fashion limited by the rate of egg laying of the queen when not limited by temperatures for brood incubation. The varro life cycle is shorter, and not limited by a single queen laying eggs, it grows exponentially rather than linearly because all fertile varroa mites are producing offspring.

To model varroa growth, we know the mites prefer a drone cell so it would be easy to just place all of the fertile varroa into drone cells when they are available, but, this is not realistic. There are 10 worker cells open on capping day for every drone cell that is open, not all of the varroa will find a drone cell. To account for this, we have prefererred drones when it’s time for varroa to enter cells, but assume only half of them find a drone cell, the other half entering cells will end up in a worker cell. This is the basis on which the varroa growth has been incorporated into the colony growth model.

Introducing varroa into the colony growth model does introduce another new concept, that of the ‘sick bee’. We know that bee virus are vectored by the varroa mite, and a colony with extremely high varroa levels will show lots of sick bees in the form of deformed wing virus and other inflictions. To account for this, a new type of bee has been incorporated into the population model, the ‘sick bee’. Any bee emerging from a cell that was populated with a varroa mite during the brood development is not placed in the normal bee population to graduate from nurse to wax maker and on up to forager. Instead, they are placed into the ‘sick bee’ population, ie, deformed wing etc. I cant find any suitable references in the literature to suggest how long a sick bee will live, but, we chose a rather arbitrary ‘it make sense to me’ way of handling the sick bees. If the bee is inflicted with deformed wing, it can still manage to crawl around on the frames, clean cells, etc. Where trouble begins for that bee is when the time comes to orient and graduate to foraging, instead of flying out of the hive, it ends up crawling out because it cant fly. Once a sick bee crawls out of the hive, it’s gone, so we have arbitrarily set the numbers so that sick bees crawl out and die at an age of 25 days, shortly after they should have graduated from being a house bee to a foraging bee.

The final tweak to the handling of varroa and sick bees came from a comment I saw in an online video by Jamie Ellis from the University of Florida. His comment was, when varroa population gets large, some cells will end up with two or more varroa feeding on the pupae in that cells. With two or more varroa feeding on a pupae, that bee will be dead or very close to it when it emerges. This final detail explains one symptom we often see when a hive crashes due to varroa load, we see numerous bees that were in the process of emerging and never completely got out of the cell when doing the post mortem. After adding this little bit into the math for handling varroa populations as they explode, the graphs mimic almost perfectly what we see from hives crashing due to varroa loads.

Expanding on the colony growth model

The first run at modeling bee colony population growth through a season was meant to validate some of the math and get a rough idea of how it would all work. Once the framework was in place the job becomes one of accounting for more details. The single biggest detail missing from the original math set was incorporating drones into the colony growth.

Much of the reading I’ve done both online and in books, many folks tend to view drones in a colony as a waste of resources, they produce no honey and do no work in the colony. All they do is eat, and fly out. This view may be correct for folks that have an outlook of ‘honey produced this season’ and they buy in all the queens they need over time. But if we raise our own stock and have an outlook that looks beyond the results of this year, the drone population we raise in this season is a very important component of our results the following season. Those drones will mate with the queens we raise this season, so they are providing half of the genetic input to our bee population next year. So while some folks view drones as a drag on the colony, my own person view is, our drone crop this year is responsible for a good honey crop next year. Another place where drones actually help the colony is during the spring buildup. While the drones are out flying during the day, overnight they are in the cluster, and that cluster is incubating the early brood rounds when nights are cold. The drone population can and does help incubating brood overnight.

The drones live on a different life cycle as compared to the worker bees, and it is very important to model this different cycle correctly. A drone egg is laid, then emerges as a larvae 3 and a half days later, just like the worker bee. The drone cell is capped on day 10, so it sits open for a day longer than a worker, then emerges on day 24. This is a critical difference as the drone cell is capped for 14 days vs the 11 days for which a worker is capped. After the drones emerge, they spend a week or two hardening and maturing in the colony before they start making regular afternoon flights to the drone congregation area. This is another important detail, because it tells us about our ability to successfully mate a new queen. You cannot successfully mate a new queen till a couple weeks after you see the first drones on frames in the colony.

So, when do the bees start raising drones ? Just about everything I’ve read on the subject suggests that the bees will start raising drones later than when they start raising workers during the early spring buildup. But this is not what we see in our hives here in Campbell River. Our bees typically start the first round of brood in the mid February timeframe, and that’s about the time we will start to consider spring feed in the form of patties. We dont normally go deep into the hives lifting frames to inspect until mid to late March. On the late March first inspection, we often see some drones walking on the frames, not a lot, but there are some. If we do the math on drone development time, seeing drones on the frames in mid March suggests they were laid as eggs in mid to late February. I am convinced the first drone eggs are indeed placed in cells as soon as the first round of replacement bees is started.

How many drones do the bees raise ? Again, reading literature provides a wide range of numbers, really depends on ‘which book did you read’ to get a handle on that number. I’ve seen numbers as low as 5 percent, and as high as 20 percent. Our own experience in looking at colonies where we place a drone frame, bees tend to fill one side completely, and the second side partially, which works out to approximately 10 percent of the brood is drone cells.

Another detail that we need to account for is drone eviction. It’s well known, as we get into the later part of the season, worker bees evict the drones from the colony. With no basis other than ‘it makes sense’, we need to consider another important date then when modelling hive populations. If the bees are evicting the living drones on a given date, when did the queen stop laying eggs in drone cells ? It takes 24 days for a drone to develop from egg to emerging bee, so it does make sense to assume that no more eggs are placed in drone cells when we are 24 days before the date at which the bees will evict drones.

After going over all of the numbers I’ve seen over time, and trying to make a realistic mathematical model for colony development, I chose to model drones by having the queen place 10% of the eggs into drone cells while she is laying eggs, and stops laying in drone cells 24 days prior to the date when the bees evict the drones. The way eviction is modelled, on days after the start of the eviction process, half of the remaining drone population gets evicted from the colony, resulting in a drone population that declines rapidly once eviction starts.

Hive models

So Ian is showing the work in progress hive model on Youtube now.

Find it here:- Hive model

We have seen in numerous presentations the population dynamics chart originally produced by Randy Oliver with respect to bee population growth and dynamics in a healthy bee colony. It was a bit inspiring, but, we wanted something that would allow us to modify the start conditions and see how different start conditions would change the dynamics.

Honeybee duties are based on the age of the bee, there is a pretty good description found on Wikipedia.

The way the calculations work is strait forward. The starting population is distributed by age based on the start condition. A package is an even spread of bees of all ages. A wintered unit starts out with all winter bees, and a nuc starts with a population of all house bees, along with the number of brood frames selected, with the brood spread evenly over all ages.

When the simulation runs, the date is advanced one day at a time, and all the bees / brood are aged by a day, then tally up how many in each age group to plot population of that group. During the process realistic restrictions are incorporated, ie the queen doesn’t lay more eggs than the current population can support for feeding and incubating brood.

Some assumptions are made during the simulation. It is assumed the bees will have all the necessary protein and carbohydrates available for feeding the brood, if not available naturally then they should be beekeeper provided. It is also assumed there is always enough comb available for eggs to be laid at the best rate the queen is capable of. During the buildup, it’s also assumed that a queen doesn’t go from 0 to thousands of eggs overnight, it takes time for the rate of eggs laid to ramp up. An arbitrary number was chosen, on any given day queen will be capable of at least a couple hundred eggs, and the rate of eggs being laid can increase by 25% day over day, so when the simulation first starts, there is a ramp on the rate of eggs going into cells.

Winter bees are a special case, and there is really no good numbers available in literature for modelling the winter honeybees. But we can make some intelligent guesses. Looking at the division of labour by age, bees are nursing brood from ages 3 thru 11 days for a total of 8 days. Larvae is open from day 3 thru 8 for a total of 6 days, so the ratio of nurse bees to open larvae is 4/3 in a hive with a steady state population at maximum potential. During the fall slowdown there is a period where the ratio of nurses to open larvae gets much larger, so we have a surplus of nurse bees that have the body fats of the freshly emerged bees, but are not expending them nursing new larvae. These are the bees we allocate to the ‘winter bees’ population. Conversly in the spring, when winter bees are pressed into nursing duty, that starts the aging clock for them to age out on the normal bee age cycle. During spring buildup, the way this is modelled, when there is a shortage of nurse bees for the open larvae, bees are taken from the winter bees category and placed into the nurse bee role at age of 4 day, and then allowed to age out in the normal progression.

Ofc, we all know, there is bee die-off thru the winter, not all of the winter bees survive thru till the spring. Again, to simulate this I have found no strong references in the literature for death rates, so we go back to our own experience and look at what we’ve seen in colonies in our back lot. My best guesstimate for that is, winter bees die off at approximately 10% per month.

On the ‘To-Do’ list. The next addition will be modelling growth of the drone population along with the worker bees. When that’s done, plan is to home in on the biology of varroa mites, and introduce a varroa mite population that runs in conjunction with the bee population model.

The Honey House

When we bought this property in 2013, we set out a fairly extensive list of improvements to add over time. One of the larger items, and the last item on that list, was building a place to process honey and store bee equipment, we want to free up the garage for use as a garage.

Over the last two weeks, the project has been underway, and is now complete. The structure is 12×20 with a 4×12 section on one end carved out by an interior partition to be used as a warm room during the honey extraction process. The work area is 12×15 and will have the extractor permanently mounted, along with the bottling table and storage for all the relevant equipment. The building is finished, and over the next couple of weeks we will tackle the job of moving all the bee equipment from the garage into the honey house.


It was raining on Saturday, so we did spend most of the day on ‘inside work’, one of those tasks was to insulate the warm room (closet) in the honey house. The building is 2×4 framing, so we put fiberglass insulation between the studs, then stapled reflectex over that to contain the fiberglass and add another R3 of insulation value to the room as a whole. Based on how well the room heated up with two of us working in there after the fiberglass was in, and we were busy putting on the reflectex, it wont take much heat to keep it at a temperature suitable for storing honey boxes waiting on extraction.


The whole build was sized around a ‘serious sideline’ bee endeavor. The warm room can hold 50 medium supers stacked 5 high, which means no lifting of heavy supers up over shoulder height. With the Mann Lake 9/18 extractor, 50 supers is 25 loads in the extractor, so roughly 5 to 6 hours of extracting. A honey pull from 25 hives with 2 supers on each turns into a weekend project, extract on Saturday and we can bottle on Sunday, with an expected yield of between 1000 and 1500 pounds of honey in bottles after weekend of processing. We usually have two of us working when extracting honey, but the setup in this facility will be laid out so it can be a one person job, uncapping the next load of frames while a load spins in the extractor. No more storing honey in 5 gallon buckets till we can get around to setting up for bottling, it’ll always be ready.

For winter storage, the warm closet has enough room to squeeze in 150 supers stacked floor to ceiling. This will be sufficient for us for the next few years.

The interior of the main work room is set up with the washtub, extractor permanently mounted, the bottling table set up under the window, and shelving for equipment storage on the other walls.



Hive scales and snow

So it’s been an interesting season with regards to using a hive scale to monitor the bees this year. We haven’t learned much about the bees, but, we have learned a lot about snowloads. As it turns out, a scale hive is a fantastic way to understand the snowloads on your buildings. When we had the huge dump of snow in February, I was concerned about snowloads and trying to figure out if we needed to shovel some roofs. After some thought, I realized, the scale under the hive can answer that question quite handily. The telescoping cover is about 2.25 square feet, and it the scale showed a weight increase of just over 90lb thru that blizzard, so just under 40lb per square foot of snowload. This was well under the loads required by building code, so I relaxed with respect to shovelling the roof.

It’s Feb 26, records from prior years show we should be well into the spring bloom cycle. Well, maybe not this time, this morning there is another dump of snow sitting on the ground. It’s only about 10cm this time, but it’s a much heavier and wetter snow. The scale shows that there is roughly 11lb of snow sitting on top of the scale hive this morning.

I’m done with this now, I’ve had enough of winter, spring can come any time, we would be quite happy to be rid of this white stuff and see blooms starting, and I’m sure our bees feel the same way about it.

Hive sensors, some cause and effect

We had problems with the original broodminder unit set into the hive on the scale last fall, the issue was batteries going dead in a couple of days. The weather turned cold and I stopped trying to deal with that problem, we had reached the time of year where we dont want to open hives anymore, bees have the propolis seals in place for winter and I dont want to break those seals at that time of the year.

Earlier this week we had some nice weather, and on Monday we got out to do the first spring look at the bees. We popped the lids off of all of them, put on the first round of spring supplements, and while we had the lid off of the scale hive, I replaced the temperature and humidity sensor. So far, the replacement seems to be working much better, battery levels are reporting consistently in range of 87%. By Thursday the snow had melted enough I could get the lawn tractor into the back lot, so we took the chance to do a round of oxalic acid vapor to try knock down the mite population before the spring brood starts in earnest.

When we fed the bees, the pollen supplement went directly over the cluster and the temperature sensor right beside the supplement. I watched the graphs for a couple days, and the data looks good this time around, consistent measurements. The Broodminder is set to take a reading hourly, and it is providing temperature updates every 58 minutes like clockwork. The data proved to be very interesting, with definite patterns. The sensor went in on Monday, and thu till Friday we can see that the internal hive temperature is slightly above outside temps, and goes up and down with the ambient temp. On Friday this changed. Through the day on Friday the internal temperature went from around 15c strait up to 30c, which is approaching brood incubation temperatures, and it did not take the big drop overnight like we see on previous nights.


We normally see brood starting in early February, this winter has been much colder than years gone past, with hives buried in snow last week. But the internal temperature is fairly definitive this morning, the bees have started to incubate brood. The 2017 bee season has begun in Campbell River.

The question to ponder this morning. We put supplement on the bees on Monday, they have started to incubate brood by Friday. Is this a cause and effect relationship, or, is it just the normal time of year for them to start brooding ?

As an aside, the hive weight graphs are a bit skewed right now, but we did learn something interesting in the process. Last week the snow just dumped on us, it just kept on falling. At the peak, scale showed there was almost 80lb of snow sitting on top of a beehive. On the bright side, nature’s snowplow (rain) made it go away as fast as it came. There is a dramatic weight loss on the hive scale on Monday morning, that came about as we swept the remaining snow off the covers when lifting lids to check the bees. It was a nice warm day, the bees were flying, and we saw endless yellow spots on the snow as the bees got out to relieve themselves. That was a sure sign the bee season is about to begin, and the sudden increase in brood nest temperature is a confirmation, bee season has started.

More hive sensors

We’ve had a hive on a scale now for 3 seasons, and have learned a LOT from that data. I have many times pondered putting more sensors into and on the hive, just to see what else there is to learn. The only reason it hasn’t been done, I just dont have the time and patience to sit down and wire up a bunch of things onto an arduino in a way that will stand up to the rigors of living in a beehive. The folks at have solved part of that problem for me, they produce a set of gadgets meant to be used in and under hives, and altho on the surface it may look a bit expensive, in reality, when I tally up my raw cost for purchasing the bits needed to make one, then the time and effort required to get it going, my final choice is just order it and get collecting data instead of pondering how to get more sensors into the hive.

I ordered two of the temperature and humidity gadgets, one to put in the scale hive, and one to use intially in the office for getting all of our software running, then later it can go in another hive. While I was at it, I ordered one of the scales. The scale will be sitting in a temperature exposed, but rain protected spot for a few weeks where I can log some data over time and figure out temperature compensation for this one, then stick it under another hive.

In the week since I got the Broodminder gadgets, I whipped up a small program that can run on a raspberry pi to read the bluetooth le advertisements produced by the gadget. With that program up and running, we added a bit more so the data will get stored into a database over the network as the new readings arrive, and we can plot the live graphs for hive temperature the same way we do for hive weights. This is all in place now, and we have almost a full day of measurements. On the scale hive page you will notice a new graph has been added, hive temperature vs outside temperature.

My starting point was to put the Broodminder-TH on top of the frames in the top box of the hive currently on the scale. The hive configuration for winter is a double deep with the top box full of winter feed for the bees, cluster is currently in the bottom box, a fairly large cluster. What was very interesting to note, the day I put it in was a nice warm day, around 14C in the bee yard, bees flying everywhere. When I lifted the lid, lots of bees on top of the frames in that box, temperature was around 30C, what I expect for a probe just above a brood nest. Two days later, after we had a very cold overnight (frost on the car window in the morning), I went out and pulled the data from the broodminder, and to my horror, the broodminder was reading 14C for temperature. Did they die off that quickly ? And this turned into a big ‘aha’ moment for me, very similar to some of the ‘aha’ moments we’ve taken from the scale data.

This colony is in a double deep, with the cluster in the bottom box, and above the cluster is a full box of stored honey. The frames of honey above the cluster are one great big heat sink, so any heat rising off the cluster is being absorbed by the frames of honey before it reaches the temp sensor at the top of the hive. The interesting tidbit I take from this, over the years I’ve heard the debate, do bees heat the whole box, or just the cluster. Some folks say ‘just the cluster’, others point to snow melt on a lid and are adamant they heat the whole box because warm air rises. Well the light bulb turned on when I saw this, and now I better understand the dynamics of heat flow in the hive. Warm air will rise off the cluster, but, any frames of honey will act as a big heat sink as that air rises to the top of the box, and, by the time it reaches the top, it’ll be a lot cooler than when it rose off the cluster.

It will be interesting to watch this as winter progresses, and get a better understanding of what’s happening inside the colony thru the winter. The biggest detail I expect to learn, we will see the temperature at this probe just under the inner cover start to rise dramatically after the bees have moved up into the top box, and start the first round of brood in the winter. I have LONG suspected that our bees raise the first brood a lot earlier than we have been told over the years. Having this probe giving us temperature and humidity measurements from inside the box will answer my questions in this area quite definitively.

New toys

This has been the week of new toys around the farm. The week started with arrival of the shiny new JB700 oxalic acid blower, which should make the job of hitting the mites with Oxalic Acid Vapors a LOT faster. Using the older pan style vaporizer, it takes roughly 4 minutes per colony to do a round of oxalic treatments. After placing the pan into the hive entrance and blocking it, the unit has to be powered for a minute and a half to get up to temperature, then left in place for another minute to finish vaporizing. Add another minute and a half to take it out, reload, and prepare the next colony, works out to 4 minutes per hive.

With the new JB700, things change a bit, no, a lot. A single load of Oxalic in this vaporizer will do 4 hives, and it’ll do them in under 2 minutes. You fill the pan in the vaporizer with the OA, turn it on, and about 30 seconds later the acid starts to sublimate. Turn on the fan and stick the nozzle into the entrance of the first hive. When you see the vapor coming out of the cracks at the top, move on to the next one.


Wow. I took this shot 2 minutes after I vaporized the hives with the new JB700. If I had any doubt about enough OA in the colonies from a blast out of this thing, I dont anymore.


On my first outing, I did all of our colones (currently 18 of them) in 20 minutes, but half of that time was spent testing the new toy and getting to understand how it works. I ran one load of OA thru from start to finish with it just sitting on top of a hive to get a feel for how much vapor comes out of this gadget. This video shows the result. Do watch to the end when I walk around and take show the cloud of OA vapour drifting across the bee yard.
JB700 in action

If that wasn’t enough new toys for the week, this weekend another one showed up on Sunday afternoon.


I think this will certainly change how we do a lot of things around here. The small flat deck will be more useful than a regular pick up box and is very convenient for hauling bee hives around.

Varroa in the Comox Valley

Varroa has been an ongoing issue for us over the years, but, in most years we have managed successfully, more by accident than by design. 2015 was the exception, and late in the season that year we had a number of hives experience the classic ‘varroa crash’ during August. This inspired me to learn a lot more about this pest in hopes of better managing it in the future.

In years gone past, I always tended to think of varroa populations in terms of bee brood cycles, and in my mind I roughly considered varroa to double over the 3 week interval which is a worker brood cycle. Reading and learning about this pest showed me that was a very serious mistake in understanding this pest. After reading many papers, and lot of online information, I digested it all into my own ‘simple’ form which is essentially a distilled version of everything I have read about this pest. During the bee brood season, the varroa life cycle runs two distinctly different phases, as the math below will show. Using averages which come from lots of different sources, the short form of the active life cycle boils down to a few basic numbers. A fertile varroa mite has an average life expectancy of 27 days during the summer season when bees are brooding. Like the bees, they live much longer when the colony is broodless and they are in ‘winter survival’ mode, but we will ignore that phase for this discussion, and focus on varroa populations during our active work bee season.

The female varroa mite will enter a cell shortly before it is capped, and does her reproductive magic under the capping with the developing bee brood. For a worker cell, the capped phase is 11 days, and during that time the female will produce one male offspring, and averages say something like 1.5 females. We all know that 1.5 offspring is not possible, so it really means some of them manage 1, and some of them manage to produce 2. For the sake of keeping our math simple, and estimating conservatively, we will just consider the case of 1 offspring produced. So in the typical cell, when the bee emerges, we will have 2 viable mites emerge from a worker cell, then spend approximately 4.5 days as phoretic mites before they once again enter a cell to reproduce. These numbers tell us, the reproduction cycle of the varroa mite runs at 15 days. Now follow thru what happens on the next round. Both of these fertile mites will once again reproduce and create one new fertile female each, to emerge with the developing worker bee. At the end of this cycle, we have 4 mites emerging, but, the original foundress mite is now reaching the end of her lifespan, and dies. So the net result is this, with one fertile mite at the start of the cycle, we go thru two full reproductive mite cycles which takes 30 days in total, and we end up with 3 viable mites in the colony. With only worker brood present, we expect the mite population to triple every 30 days.

The math changes when we have drone brood present, the mites will prefer the drone brood to reproduce if it’s present. So now follow the same cycle, but this time for drone brood. After spending the 4 days in phoretic phase of life, the female enters a drone cell which will be capped for 14 days. Literature suggests that the average offspring in drone brood with 14 days under capping will be something like 2.5, but again, we know you cant produce half a mite, so we will just look at the round numbers, assume she is producing 2 viable offspring. They emerge when the drone emerges 14 days later, and proceed to spend 4 days in the phoretic phase before entering cells to reproduce. On the second cycle we now have 3 viable mites entering cells, and all of them will produce 2 offspring, for a total of 9 mites emerging at the end of the cycle. One of those mites is the original foundress who has now reached end of life and dies, if she hasn’t already died in the cell. 14 days under the capping and 4 days phoretic gives us an 18 day reproduction cycle, and with one mite at the beginning of the cycle, after two cycles (36 days) we have 8 viable mites in the colony. An increase by a factor of 8 over 36 days is equivalent to doubling over 12 days.

Armed with this understanding of the mite reproduction cycle, lets look carefully at one bee season in the Comox Valley, or more specifically on our little farm here south of Campbell River. Our records show that we see hazelnut pollen typically around Feb 10, and checking on our bees shows that they are indeed starting a round of brood at that time, and have been every year we have been here, so, Feb 10 is the start of our season. Now lets follow the math for one colony that enters the season with one, and only one, viable mite ready to enter a brood cell on Feb 10.

In the early season, we have only worker brood, so the mite population will triple over a 30 day period. One mite on Feb 10 will result in 3 viable mites 30 days later, March 12. Another two mite breeding cycles takes us to April 10, and we now have 9 mites in the colony, but things are changing. On April 10 we will have drone brood available for the mites to breed in, so, instead of tripling over 30 days, we now reach the time of the season where mites can double every 12 days on average. By April 22 our 9 mites becomes 18, then May 4 we are up to 36. May 16 the number is 72, and reaches 144 by May 28. By 9th of June that number is up to 288, then 576 by June 21, the mid summer solstice. Assume we do a count of our mites at this time via a sugar roll or wash, bee population will be up near 50,000 bees, and there are just over 500 mites in the colony, our wash numbers say 1%, and everybody is happy, we are well below the ‘economic threshold’ for mites. or are we ??????

Continue now thru mite breeding cycles and watch the numbers. With 576 in the colony on June 21, that becomes 1152 mites by the July 1 weekend, we are now at 2% infestation on July 3. By July 15, that number doubles again, and we now have 2304 mites in the colony, and the number climbs to above 4500 by July 27, and north of 9000 by August 8 for an 18% mite load. At this point, things will start to deteriorate rapidly for a number of reasons. First off, we have a mite on 1 out of 5 bees, but since mites prefer to stick with the nurse bees in the brood nest area, it’s more like one on every second bee in the brood nest, so we will be getting very unhealthy brood at this point, most of which will have mites in the cells, and to really compound this problem, it’s a time of year when the bees are contracting the brood nest and starting to think about raising winter bees.

All I can say to this after working thru the numbers is WOW, now I understand why the ‘typical mite crash’ happens thru the month of August, mites left unchecked at that point are growing in numbers exponentially over 12 day periods. But armed with knowledge, now we can start to think about how to better address this problem. One thing I learned from two decades in aviation, accidents dont just happen, they usually come about from a chain of small things that add up to one big thing, and the key to aviation safety is break that chain early in the process. This is why we developed systems of checklists, so we dont end up in the situation where one small item forgotten early in the process cascades to the big event farther down the chain. We can take the same attitude to our bees and mites, and just look at the chain of events of population doubling over various periods.

If I home in on the timeframes where drone brood is present in the hive, what really stands out is this. One mite we eliminate today, is 8 mites we wont have in 36 days, which becomes 64 we wont have in 72 days, ie 10 weeks down the road. Expand this by one more cycle of 36 days, and it’s 512 mites we will not have 108 days (15 weeks) down the road. So now if I do some calendar math, we see hives crashing from mites in the early August timeframe. Every mite we remove from a colony on May 1 is potentially 500 mites we will not see on August 15.

Doing the math on mite life cycles was an enlightening experience for me, it fully explained some of the things I’ve seen in the field, and more importantly, shows me the importance of mite control early in the season. If I do a sugar roll to count mites in May and find one, and only one mite on 300 bees, the typical thought train is that load is light enough to ignore. On average roughly 20% of the mites are going to be phoretic at any time, the rest are hiding under cappings with brood, so my population at that time is indeed 5 mites per 300 bees, about 1.5% which is a number we have always been told to be under the ‘economic threshold’ for mites. But left totally unchecked, that population is more than enough to grow exponentially thru the season and kill the colony by August. A sugar roll or wash count of 2 mites on May 1 left unchecked results in a dead hive in August.

The other really important detail I took from this exercise is looking at the phoretic phase, and the phase of mites in the cells under cappings. If we do an intervention that only gets phoretic mites today, after measuring a population of 1% with drones brood in the hive, then come back 12 days later and check again, the colony will look like we didn’t do anything, and measure roughly 2% infestation. An intervention that only gets phoretic mites will NOT show up in counts until _at least_ 18 days later, when the mite brood that would have been from those mites would start to emerge. In the meantime, all of those mites that were hiding under cappings will continue to emerge over that period. Reality is, if I do an intervention on July 1 of a type that only affects phoretic mites, by July 5 I would expect to see a 25% increase in the population when I check due to all the mites that emerged in the 5 days between intervention and testing. If I do a single intervention on July 1 that effectively eliminates phoretic mites, I dont expect to see a decline in numbers before July 20, and in the intervening 3 weeks, the numbers will continue to skyrocket upwards, so much so that by July 20 the effect will hardly be noticeable anyways. If all the mites were specific and jumping into cells exactly 4 days after emerging, we would see the noticeable difference around July 20, but, the 4.5 days phoretic is only and average, so by 20 days down the road the decrease will disappear in the averages.

There is lots of food for thought to ponder in all of this, but, this exercise of doing some simple math on the mite reproduction schedule has been enlightening for me, and has me seriously re-thinking mite strategies. My biggest takeaway from it all is, low counts early in the season are a leading indicator for hives crashing in August, not an indicator telling me ‘good enough’.