beekeeping equipment varroa mites

Mite management in large hives

I have been asked to explain why I believe large colonies make winter mite management easier. It’s important to note that I said easier and not easy. You still have to pay attention and you still have to do something.

It is interesting to me that people who prefer triple-deep hives frequently report successful mite management, and people who have not tried them claim that triples are mite factories. In my own case, I had been successfully overwintering 80 to 100 percent of my hives for many years until last year, when I switched from ApiLife Var to HopGuard. I “misinterpreted” the instructions, treated all my hives in the same insufficient way, and ended up losing most colonies to mites. I just happened to have a few triples in that group, and oddly enough, it was the triples that survived despite huge mite loads.

Okay, my story is merely anecdotal, but it piqued my curiosity. I began asking others about their experience with triples and heard many similar stories. I also did a lot of reading about the population dynamics of both mites and bees. So I will explain my theory but, alas, it is only a theory.

First, I agree that triples are mite factories but only because more bees produce more mites. For most of the year, mites/bee is no different in small colonies than in big ones. There is a maximum mite/bee ratio that can be reached before the colony just collapses—big or small.

The timing of mite treatments

Mite treatments have to be performed at the right time regardless of hive size. That time is when brood production is lowest, usually late summer or early fall depending on where you live. A small number of brood cells provide few places for the mites to breed, so most of them are riding around on the backs of bees. These adult mites are exposed to the mite treatment and are killed by it.

Some colonies have virtually no brood for a short period in late fall, so if you can time your treatments right, you can get about a 95% kill rate. Some mites will survive, of course, and others will ride into the hive on visiting bees, but for the moment at least you have very few mites.

Hygienic behavior plays a part

All bees have some hygienic behavior, and bees can and do rid themselves of some adult mites and even pull infected brood out of cells and dispose of them. If you have two colonies—one small and one large—and both have nearly zero brood for that brief period—the large colony will have many fewer mites/bee than the small one. This gives the large hive a distinct advantage. Although both hives will experience an increase in mites subsequent to the treatment, the large colony has more bees to deal with each individual mite as they go into winter.

Although a large colony has a larger brood nest than a small colony, large colonies tend to have a smaller proportion of brood to adult bees. This is probably due to the fact that the colony is so large—enough bees to keep warm, enough bees to defend the hive, enough bees for hive duties, and certainly enough mouths to feed—that there is no compelling reason to make it larger or even to keep it as large. If the number of brood cells per adult bee stays low for an extended period, the winter cluster is in a better position to keep mite numbers down using only standard amounts of hygienic behavior. No matter what the task, large colonies nearly always out-perform small ones.

Can mites drown in a gene pool?

Related to this is simple genetics. A large population has a bigger pool of genetic traits, so in a large colony there is a greater probability that there are some bees that can successfully deal with mites. Remember that although the bees in a colony have the same mother, they have a variety of fathers, so there can be quite a bit of genetic variation. More bees mean more genetic variation and a higher probability that some bees will have good hygienic behavior.

During the winter neither small nor large hives have drone brood, which means mite built-up over winter is slower than in spring and summer. The reduced rate of mite build up allows the larger colony to maintain its advantage over the smaller one until colony expansion and drone production begin in the spring.

The ratio is key

Once spring expansion begins, however, the large colony will produce mites like crazy—lots of brood and especially lots of drones. If left alone at this time, mites will begin to overwhelm the colony. But by this time, the large colony can be split, re-queened, treated, or whatever the beekeeper prefers. The point is, the colony m­ade it through the winter because of a high bee to mite ratio at the critical time.

In this scenario, it is always the ratios at specific times of year that are important, never the specific numbers. The ratio of mites to bees and the ratio of bees to brood during the fall and winter are what tip the balance in favor of the large colony surviving until spring.



  • Thanks for responding to my question!

    I’m a bit confused by your statements first that “for most of the year, mites/bee is no different” then later “if you have two colonies – one small and one large – and both have nearly zero brood for that brief period – the large colony will have many fewer mites/bee than the small one.” Somehow I’m not following your logic. If you start out with 20 mites/bee in both colonies and kill 95% with treatment, you still have 1 mite/bee, regardless of colony size. What am I missing?

    I’m also a bit skeptical of the genetics idea. If a queen mates with 12 drones, her offspring will have 12 different sets of genes. More bees means more of each of these 12 classes, but doesn’t really increase total genetic diversity.

    Thinking about it a bit more, I wonder if it isn’t mostly about size. Let’s say a colony needs 5000 bees through the winter in order to survive, thrive, and build up well in spring. If doubles go into winter with 10,000 bees and triples go into winter with 15,000 bees, and both hives suffer 60% mite-related mortality, the small hive will be left with 4000 while the triple has 6000 – a definite advantage.

    • Mark,

      The percentages stay the same until you approach zero. Theoretically, if there were no brood you could kill all mites. So, for illustration, let’s say we killed all mites in two hives, one with 20,000 bees and one with 40,000. When the first mite arrives it is 1/20,000 vs 1/40,000 or twice the ability to find it and kill it. If the small hive fails to kill it, but the large one succeeds, and then a second mite arrives it will now be 2/20,000 vs 1/40,000, a good advantage for the big hive. Or if the small hive killed the first mite and the large one failed (less likely by half), it would now be 1/20,000 vs 2/40,000 (or equal). That is why as the brood approaches zero during mite treatment, a large hive gains the advantage.

      About genetics. Yes, the genetic diversity remains the same but there are more of each type. Say just one drone father in each hive had excellent hygienic behavior and all drone fathers were represented equally. In the small hive 1/12 or 1,667 bees are good mite killers. In the large hive 1/12 or 3,333 are good mite killers. So you have doubled the number of bees that are really after the mites. Couple this with the paragraph above (fewer mites as you climb up from zero) and you have a more effective mite program.

      I think all the factors have to be taken together. It’s not just one difference between small and large colonies, but a whole series of them.

  • I went to a talk on varroa by one of our UK National Bee Inspectors this summer; he told us that in his opinion feral colonies could last longer without varroa treatment than a managed colony. This is because feral Apis mellifera colonies are more similar in composition and behaviour to the mite’s native host, the Asian honeybee Apis cerana, which lives in small colonies which swarm frequently. Apis mellifera feral colonies are smaller and swarm more often, meaning there is less brood for the mites to reproduce in and regular breaks in the brood cycle after each swarm.

    As you say, a good idea to split large colonies in the spring, as otherwise a large colony can become overwhelmed by the mites. Our inspector told us that he sees many beekeepers who lose their biggest and best colonies to varroa – it’s the number one killer of bees here in the UK.

  • I expect that the best approach varies depending on one’s climate, too. The big problem I have is that, regardless of whether I treated for mites or not, my hives ended up going great guns for three years, but with high mortality the second winter and then being wiped out by mites early in the third winter. Apparently it doesn’t get/stay warm enough around here (northern Michigan, next to Lake Superior) for a lot of mite treatments to work, and so they mostly didn’t.

    My current practice was recommended to me by a fellow a bit south of here. The idea is that, immediately after the mid-July honey harvest, all of the hives get divided into walk-away splits to raise new queens. *All* of them get broken up; there are none left to produce a big enough mite surge to start the domino effect that wiped me out in the past. The need to raise new queens makes a hard break in the brood cycle, and essentially resets the mite load. Then in September I go through, and make sure they all have enough stores to get through the winter (by a combination of feeding and combining).

    In addition to knocking back the mites, this also results in about tripling the number of hives, so that in the spring I have extra hives that I can either keep as build up, or sell as nucs. It worked well last winter (no losses, and when I check for mites with powdered-sugar dusting I find much fewer than I used to find before. But this winter is the kicker – in my old cycle, this corresponds to the year that they all die. I’ll let you know how it comes out in the spring.

    • Tim,

      Savage beasts, they are. I will be interested in hearing how you do this winter. I think splitting is one of the best control measures, but it seems that often our best efforts go south. It’s been 25 years since mites appeared in the US and it seems we haven’t made much progress. As you point out, what works at one place and time doesn’t necessarily work at another place or another time. So frustrating.

  • I have to agree with the mid summer splits as being the best way to keep an apiary going from year to year. But I am still left thinking that most problems with colony longevity is that those nasty treatments are what are limiting queen longevity and not allowing colonies to develop their own resistence to all apiary issues, including varroa. I still believe that nature must be allowed to evolve bees to deal with the current state of our environment, and not man and our unnatural way of dealing with changes.

    There are several extremely successful apiaries around this country that don’t use any chemicals or antibiotics and don’t see the catastrophic collapses that many of us experience. Each region has it own specific needs for kept bees, and kept bees are very different from feral bees. I do many removals around my area and the most healthy and long-lived colonies seem to be in trees. My guess is that a tree has a moderated internal temperature due to respiration, which most painted hive bodies and buildings don’t normally have. Also, not allowing any frames inside hive bodies to remain idle can make a big difference when dealing with SHB. We can fight our ever-changing environment with disappointment, or allow nature to evolve and embrace the changes with enjoyment and less work and heartache. Best of life to all!!!

    • Bill,

      Although I too believe natural evolution would be the best answer, bees have been on earth for more than 120,000,000 years. Most of the major problems for bees (globalization, chemical pesticides, introduced diseases and parasites, monocrop agriculture, climate change) have occurred since about 1945—67 years ago. Those years represent 0.0001% of bees’ existence on earth, at most. There is no way that natural bee evolution, which is a glacially slow process occurring over millions of years, can keep up with the rate of change we humans are causing.

      Add to that, we know from analyzing their genome that bees do not have the genetic structure to evolve as fast as other insects like cockroaches, mosquitoes, and flies which can evolve relatively quickly. Many creatures that the bee is competing with evolve much more rapidly, which puts the bee at a disadvantage. Varroa mites for example evolved resistance to in-hive chemicals in no time—but those chemicals still damage or kill the honey bee. No contest.

      The bee may indeed evolve to survive our new environment, but we may need to wait a few a million years to see it happen.

  • I guess “evolve” is too strong a word for this discussion…perhaps I should have used “adapt” instead to avoid the confusion. We do know that there are several strains of domesticated bees that indeed have “adapted” to varroa destructor and been living amoung them for millenniums, one being the strain we call russian. I believe, from all that I have read and the information I have received from speaking to many old timer bee folks, is that human intervention has always caused more serious side effects. One such side effect now known is antibiotics magnify the toxic effects of most pesticides used to control varroa in a hive, making the bees much more sensitive to pesticide exposure than non-treated colonies. This has an accumulative effect on colonies, thus shortening their lifespans. It is my belief that more folks loose their colonies only to find fault with varroa population, not knowing that the persistent use of all the treatments, chemicals and antibiotics, are the main culprits in their colony mortality.

    Our apiary does see a few colony mortalities, and that does not bother me as life and death are two sides to a living coin. Humans have create a very complicated world in which we try and subvert nature and inadvertently transport pests around the world. I believe that it is in the best interest of bees to start to simplify the ways in which we keep bees and strive to eliminate the unnatural ways we try and keep colonies alive by selecting and raising colonies that can adapt to our ever changing local environments and the pests that bees are in contact with, but then again we must all do what we think is right for our own apiary.

    Best of life to all!!!

    • All good points, especially the synergistic effects between various chemicals. Sometimes the toxic effects are multiplied hundreds or even thousands of times.

  • Rusty, how long must the brood cycle be interrupted to clear adult mites out of the colony?? I ask as while I agree making splits is a great way to interrupt the mite reproductive cycle, you still have the “original” queen (the one presiding over the hive before splitting)…how can you manage that original queen and her attendants such that they are largely free of adult, reproductive mites BEFORE they begin capping brood again? The splits will have a long brood interruption while they raise, a new, fertile queen to laying age. But the original queen…should you take away all capped brood from her hive and for how long??

    Many thanks,

    • Janet,

      Brood takes about 21 days to go from egg to adult. Therefore, once you interrupt egg-laying, you must wait 21 days for all the brood to hatch as adults. However, you won’t be able to clear mites out of the colony completely. Many will be riding around on adult bees until they get the opportunity to climb into a brood cell and new ones will come in from outside the hive. We manage mite populations, we don’t eliminate them.

      If you want your original queen to stop laying eggs, put her in a queen cage. Use the type that fits right in the hive and allows the house bees to care for her through the screen. When you are ready, just open the plug and re-release her into the colony.

  • In your post you mention that “Some colonies have virtually no brood for a short period before fall build up” I know I wrote before but I’m more confused that ever. I went out yesterday to combine hives (which your post about fall angst addressed) and found that NEITHER of my two hives had any evidence of reproduction, despite both being loaded with bees. I combined anyway, feeling that I had nothing to lose. When you say virtually no brood, do you mean No Brood? My own notes suggest I didn’t see any eggs ( didn’t mention larvae, so either no larvae or bad note-taking) on Sept 7 and then no eggs or larvae on Oct 6. When would fall build up happen and why? I can’t understand how both hives would just stop reproducing, despite being apparently healthy in all other regards. And have I just ruined them anyway by exposing every frame at this cold time of year?

    • Andrea,

      First, that was poor wording on my part. I changed it to read, “Some colonies have virtually no brood for a short period in late fall.” This nearly broodless period can occur anywhere from late October until the winter solstice in late December. By definition, “virtually” means “in effect but not in fact.” What it describes is essentially no brood. There could be zero cells, or ten cells, or even 100 cells, but it is still basically none—it has the same effect as none.

      Late in the year, the brood building begins again. When all this happens—which month or week or day—has a lot to do with your latitude and local climate. In some places it will be earlier and in some places later. Beekeepers take advantage of these broodless periods to treat for mites, because many mite treatment have no effect on mites inside the brood cells, so by treating when there are no brood cells, you can kill more mites.

      Bees “just stop reproducing” to lower the number of individuals going into winter. A colony that is too big will run through its stores too quickly, so yes, they stop reproducing, and in some places it occurs earlier than in other places. Once the colony is down to size, brood rearing my increase somewhat (fall buildup) but just enough to offset continued losses. A big build-up won’t occur until after the winter solstice.

      You probably didn’t harm your bees by opening the hive for a few minutes because it is the brood that would be most affected, and you just said you had no brood.

      Did you see a queen in either hive? That would be an important clue as to what is going on and, of course, you don’t want to combine the queens along with the rest of the colony.

  • I lost two colonies last spring, quite unexpectedly, from mites and mite damage. They looked great coming out of winter but were crashing as the first big waves of brood (attempted) to hatch out. That was the end of trying to rely exclusively on IPM strategies for mite control (screened bottom boards, essential oils, grease patties, brood breaks, mineral oil)…maybe that is enough for some but I concluded I have neither the expertise, time or equipment to make it work for me. This year I did formic acid treatments in spring and fall, and will do an oxalic acid vapour treatment in early December.

  • Two questions. 1) It has been a few years since the above was written. I believe I have been seeing a trend to treat much earlier than the fall when brood in minimal. I am in mid-MD. I take my honey supers off by mid-July. Soon thereafter the treatments begin (for me, Apivar.) Surely I begin treating by Aug. 1 in order to minimize the negative impact of mite-vectored viruses on the winter bees that will soon start to be produced. Rather than waiting until the fall to treat when there is minimal brood, is it not best to treat in late summer and then treat again in fall if need be? 2) Have you written about how to split a triple? I want to minimize the number of colonies I have and would rather not have one triple turning into three colonies 🙂 Is there a way to keep splits to a minimum?

    • Dave,

      I haven’t really changed my treatment schedule from the time I posted this, but I did move it up by two weeks. So whereas I used to complete treatments by August 31, I now complete treatments by August 15. I usually treat again just after the winter solstice.

      I don’t think that splitting a triple is much different than splitting a double—just split into a single and a double. If you get too many colonies, you can always recombine later.

  • Thanks for this reply. Yes, I am afraid of getting too many colonies! Have to draw the line somewhere.

  • Greetings from interior Alaska. I recently had a queenless period in my hive. My colony produced a replacement and she laid about 1/2 of one side of a deep frame of eggs. I decided this was a good time to halt brood production for a couple weeks so I caged my queen with only that 1/2 frame of eggs last weekend. In inspection now there are at least 3 frames both sides filled with brood in all stages in a good pattern. The queen was still in her cage. Any thoughts on what might be going on? Could I have a second fertile queen?

  • Hi Rusty,

    I noticed in another blog that you are moving toward smaller colonies, to 1 deep. How has this went? I thought it was for easier management and for a smaller hive to mimic more the natural hive. I was curious how that went, perhaps it would be spring before we see how the winter went. I would be interested. I always tried to have larger colonies to help get them thru winter. May have been my empirical data that really was skewed by other factors.

    Thank You,

    • Keith,

      I went to small colonies after reading much of the work of Thomas Seeley, who has explained in depth why natural-sized colonies seem to do better against diseases and parasites like mites. There are minuses, such as lower honey yield per hive. Then again, a dead colony doesn’t produce much honey at all. I think this is my third winter with smaller colonies, and I doubt I would ever go back to large ones.

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