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Sept. 19, 2022

HBHC Varroa Management Guide Updates with Dr. Dewey Caron (S5, E14)

On today’s episode we are joined by professor, author and noted speaker Dr. Dewey Caron. Dewey is an active member of the Honey Bee Health Coalition where he helps with the creation and maintenance of the Coalition’s Hive Management program. Today...

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On today’s episode we are joined by professor, author and noted speaker Dr. Dewey Caron. Dewey is an active member of the Honey Bee Health Coalition where he helps with the creation and maintenance of the Coalition’s Hive Management program. Today he joins us to talk about the just updated, Varroa Management Guide.

Varroa management is a very serious problem for beekeepers around the world. Sadly, varroa was just found in Australia this year with devastating consequences as hundreds, if not thousands of colonies, have been destroyed in an attempt to eradicate the mite before it establishes a foothold on the last, varroa-free continent.

The HBHC has published several useful tools for beekeepers to help them manage varroa to a level where the negative effects of varroa, such as the varroa associated viruses and diseases can be limited. This is includes varroa management videos, the Varroa Management Decision Tool, Commercial Beekeeper Case Studies, the Varroa Resistance and Testing Team and today’s topic the Varroa Management Guide.

The Management Guide explains the tested, practical, and effective methods to manage the mites in your colonies. Dewey talks with us about the updates, varroa and also talks about the latest edition of his book, “Honey Bee Biology and Beekeeping.”

We hope you enjoy the episode. Leave comments and questions in the Comments Section of the episode's website.

Thank you for listening!

Links and websites mentioned in this podcast: 

Honey Bee Obscura


This episode is brought to you by Global PattiesGlobal PattiesGlobal offers a variety of standard and custom patties. Visit them today at and let them know you appreciate them sponsoring this episode! 

We welcome Betterbee as sponsor of today's episode. Betterbee’s mission is to support every beekeeper with excellent customerBetterBeeservice, continued education and quality equipment. From their colorful and informative catalog to their support of beekeeper educational activities, including this podcast series, Betterbee truly is Beekeepers Serving Beekeepers. See for yourself at

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Podcast music: Be Strong by Young Presidents; Epilogue by Musicalman; Walking in Paris by Studio Le Bus; A Fresh New Start by Pete Morse; Original guitar background instrumental by Jeff Ott

Beekeeping Today Podcast is an audio production of Growing Planet Media, LLC

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S5, E14 – HBHC Varroa Management Guide Updates with Dr. Dewey Caron


Jeff Ott:Welcome to Beekeeping Today Podcast presented by Bee Culture. Beekeeping Today podcastis your source for beekeeping news information and entertainment. I'm Jeff Ott.

Kim Flottum:I'm Kim Flottum.

Global Patties:Hey Jeff and Kim. Today's sponsor is Global Patties. They're a family-operated business that manufactures protein supplement patties for honeybees. It's a good time to think about honeybee nutrition. Feeding your hives protein supplement patties will ensure that they produce strong and healthy colonies by increasing brood production and overall honey flow. Now is a great time to consider what type of patty is right for your area and your honeybees. Global offers a variety of standard patties as well as custom patties to meet your needs.

No matter where you are, Global is ready to serve you out of their manufacturing plants in Airdrie, Alberta, and in Butte, Montana, or from distribution depots across the continent. Visit them today at

Kim:Thanks Sherry and thank you Global Patties. You know each week we get to talk about how much we appreciate our sponsor support, and we know you'd rather we get right to talk about beekeeping. However, our great sponsors are critical to help making all of this happen. From the transcripts, the hosting fees, the software, the hardware, the microphones, the subscriptions, the recorders. They enable each episode. With that, thanks to Bee Culture magazine for continuing their presenting sponsorship of this podcast. Bee Culture has been a magazine for American beekeeping since 1873. Subscribe to Bee Culture today.

Jeff:Hey everybody, thanks for joining us. We're really happy you're here. Before we get started, just a quick reminder to subscribe or follow Beekeeping Today podcast and give us a five-star rating. It really does help. Also, we are now adding complete transcripts of each episode on the website after the show notes, check them out. You can also leave questions and comments online. Under each show you can leave a comment, ask a question, reply to a question - ours or a listeners. Click on leave a comment at the top of the episode's show notes to join the discussion. Have you listened to an episode and thought that person sounds really interesting? I'd like to know more about him.

Well, now you can. Each episode links to a guest profile. Each profile has a guest photo, bio, contact information including Instagram and Twitter details if they have them. Check it out. Finally, share the podcast with your beekeeping friends, email them links or mention them at your next beekeeper meeting. Hey, everybody. Thanks again for joining us. We have a really good and a really important episode for you today. Before we get going, I need to correct a misstatement from last week's opening where I was recommending an episode on 2 Million Blossoms podcast.

Talking about Amitraz I referred to the product Apistan. Apistan is the trade name of the honeybee formulation of the miticide fluvalinate. I should have referred to Apivar which is the product containing Amitraz. I apologize for any confusion I may have caused. I still highly recommend you check out that 2 Million Blossoms episode with Adrian Fisher. What is the number one problem you face with your colonies? Bad queens, neighbors, out yard locations, wind, maybe pesticides, lack of forage. Man the list of possibilities is long, isn't it and they are all problems at one time or another. I suggest your number one problem in your colonies right now are Varroa mites.

There are many people and organizations who've been working on this problem for the past 30 years. We've had several of them on our podcast. The question is who is synthesizing all of the data and making it readable, usable by you and me? One organization is a nonprofit group of beekeepers, growers, researchers, government agencies, agribusinesses, conservation groups, manufacturers, and consumer brands dedicated to improving the honeybee health. Who is this? They are the Honeybee Health Coalition. If you've been listening to the podcast, you know we've had guests on from the coalition over the past five years.

Today, we welcome Dr. Dewey Caron back to the podcast to talk about the latest and ace release of the coalition's Varroa management guide. The guide really should be your management Bible for dealing with Varroa. You could go out and research it all yourself. Do all the trial and error experiments on your bees to see what works or you could read this guide instead. The coalition reviewed the research data, took it out of the labs in the field studies then summarize it down to which tools for which different management approach actually works. In fact, how do you know when to use which tool?

It's like knowing when you should use a framing hammer and when you should use a tack hammer To drive this analogy into the ground I'll continue. Perhaps you don't want to use a big hammer. In our case synthetic chemicals to treat Varroa. Maybe you still want to use a hammer but maybe a smaller one such as an organic chemical. Do you know when to use which? Is it the same in the spring as it is in the fall? The Honeybee Health Coalition has put this into a usable guide for you, for free. Check out their Varroa management decision tool and feel confident you are not experimenting with your bees. You're treating them using tested tools at the right time of the year.

All of that is coming up in our talk with Dewey about the honeybee Health Coalition's updated Varroa management guide. First, a quick word from our friends at Strong Microbials.

StrongMicrobials:Hey beekeepers. Many times during the year, honeybees encounter scarcity of floral sources. As good beekeepers, we feed our bees artificial diets of protein and carbohydrates to keep them going during those stressful times. What is missing though, are key components. The good microbes necessary for a bee to digest the food and convert it into metabolic energy. Only super DFM Honeybee by Strong Microbials can provide the necessary microbes to optimally convert the artificial diet into energy necessary for improving longevity, reproduction, immunity, and much more. Super DFM Honeybee is an all-natural probiotic supplement for your honeybees.

Find it at or at Fine Bee supply stores everywhere.

Jeff:While you're at the Strong Microbial site, make sure you click on and subscribe to The Hive. The regular newsletter full of interesting beekeeping facts and product updates. Hey everybody, welcome back. Sitting across the virtual Zoom table right now is one of our most frequent guests. We love him here at Beekeeping Today podcast, Dr. Dewey Caron. Dewey, welcome back. I think this is about your fifth time on the podcast.

Dewey:Yes, I think it is. Yes. Thank you. Good afternoon, wherever you are. Hello.

Kim:It's good to see you again Dewey. I just got to recommend just before we get started here. I have been using your new book, the book you and Larry Connor did Honeybee Biology, and Beekeeping it's the third edition. It's the best one yet. If you haven't read it, folks get a copy. It's worth every penny and you will be a better beekeeper.

Dewey:Thanks, Kim. The third edition was a real labor of love. We revised everything. We went through every page and of course, it's completely updated. Added a couple of new chapters and it continues to be very popular before it's a teaching tax for universities and colleges. Also for a lot a number of the clubs that are teaching a beekeeping course, and as a personal reference. People tell me they like it because they can find things and keep going back to it. Thank you appreciate it. Yes, thank you.

Jeff:Is it a book you keep by the bedside and read every day?

Dewey:Some keep it there by the bedside. We've added like 100 pages so it's a perfect doorstop to [laughter] to know as well.

Jeff:Well, no, no. I was just joking. It's a great reference and highly recommend if someone's starting their bee book collection and or need to add one that is very valuable.

Kim:It's one of two books I turned to when I got a question about anything bees and beekeeping. It's Honeybee Biology and then the recent ABC. You put those two together and there's probably pretty much everything beekeeping in the world in there.

Dewey:Did you have a copy there, Kim to show the people our new cover for the Honeybee Biology?

Kim:We'll put a cover on the web page, Dewey.

Dewey:I enjoyed it by the way contributed to the ABC as well. That was a bit of a long drawn out this time because of publishing issues, whatever. That is substantial. Again, it's easy to find things in ABC.

Kim:Everything's laid out alphabetically. Even I can find things in it. [laughs]

Dewey:Well, another new project that I've been working on is we have updated Honeybee Health Coalition tools for Varroa management. We're now in our eighth edition which is incredible. Like with the revision of Honeybee Biology, we did everything. We went right back and looked at every word, every paragraph that we had in our eighth edition. Many people have downloaded an earlier edition or clubs have downloaded and put it on their site. Very strongly recommend that people read, download it to their computer, or if clubs have done so to re-download it onto their club website. The eighth edition, Tools for Varroa Management from Honeybee Health Coalition.

Kim:I went so far, Jeff is to print it out. It's 37 pages long. It's not going to drain your paper or your ink and then you've got a copy in your toolbox that you can grab when you go to the bee yard.

Jeff:I want to talk about the Honeybee Health Coalition but I do wanted to go back. This reference guide, this Varroa management guide is so valuable, that I think it's one of the references every beekeeper needs to refer to it and understand exactly what the industry is saying about the Varroa.

Dewey:It's been extensively vetted with the committee that we have. We expanded the committee this year, they are listed there, so if you want to refer to it. I was responsible for the initial writing of it. As they say, we've gone to several revisions, this is now 8.3 version and we did, we looked at Eversen, we checked with the various manufacturers of the chemical compound to be sure we had approved language. Because there's not only the label for some of these chemicals but there's also a how to do it. They have their own brochures. It is really a one-stop of where this information that we need to know is.

It emphasizes the sampling as a method of knowing not just that you have mites but how many mites do you have, which gives us an element of risk. We're indicating that now, we keep bracketing down our recommendations in terms of how many mites is too many. Now we're saying 1 to 2% is the level that we should try to achieve when we're doing a sampling of the adult bees. If it exceeds that, then you're into that element of risk, and the higher it becomes greater than the 2%, the greater the risk.

Kim:Dewey, there's a lot of mud that I want to cover that you're doing this really well, but let me back up a half a step for people who aren't really familiar with the Honeybee Health Coalition, how did you get started quickly, and then who's on it, and what are the projects are you working on?

Dewey:The Honeybee Health Coalition is a gathering of folks from all aspects of what we call, our industry. Certainly, there are beekeepers at some of the regional groups and national groups, a couple of local groups that are members. There's the industry that provides the pesticides, industry that supply the supplies for beekeepers, but then a lot more than that. It is also the industry that benefits from bees, the apple growers, the sunflower growers et cetera. They're on that and users. It is a group now that has grown to about 50 individuals. We present our information by consensus, it is all science-based, it's not just conjecture or what people might be doing in terms of practices.

We are organized as task forces. There's a task force around forage and nutrition. A task force around pest management. I'm on the beehive management task force, and that's the one that has developed these tools for Varroa management. We also have a quick guide so that if you answer our five quick questions in terms of your philosophy and where you're bees are, you can then find the appropriate pages to go to with the tools for Varroa management. With our tools, we also did a recording of a dozen different videos so that, for example, if you've never used the Apivar, we have a short video, three to four minutes each of explaining how and demonstrating how you might use the Apivar strips as a Varroa management tool.

Kim:You're not only telling me, you're showing me. Wow. For a learning device that's exactly what you want. Your group, you meet regularly, or is this all virtual, or to see? How do you get your heads together?

Dewey:The pandemic has created some of those issues. We had been meeting two times a year, and during the pandemic skipped a couple of those meetings. We last met with the workshop in Michigan and our meetings are designed both to get us together, to talk about these various issues, collectively, and then separating as our task force, to come under the separate task force. When we identify our priority, for example, one of our last priorities was to identify that commercials do their Varroa management a little bit differently. How could we approach getting information to commercial beekeepers, those that have thousands of colonies?

We came up with case studies of six different commercial individuals that discussed how they do Varroa, and how they are coping with this issue of the increasing developing resistance to the Amitraz. Amitraz is our only synthetic right now that we have available. We have the oils and we have acids as well, but this is the only synthetic we have. We're seeing that the bees are beginning to develop resistance to it. That's been the go-to, that's our gold standard, the one that's been effective. We developed the case studies, did the interviews with individuals, then develop that, subdividing that, also do some visuals with them.

We had some visitors do some commercial beekeeping operations here in Oregon, then Michigan, and then the midwest.

Kim:I think all of this information, at least most of this information is available on your webpage. Is that correct?

Dewey:That's correct. Honeybee Health Coalition. If you want to go specifically to the Varroa then /Varroa but simply then Varroa. You'll put that on the site, I'm sure.

Kim:Yes. That'll be there. Let's go back to, you started around, I'm looking at the management book here and you do some talking about Varroa mite biology, basically, seasonal development, and that seasonal development thing is critical when it comes to treating. People need to understand what's going on inside the hive. There isn't one treatment fits all and fits every time because things are different in the spring, summer, and fall. Expand on that just a little bit. If I take a look at this and I'm looking at the fall treatment schedule, and it's next, spring, what could go wrong?

Dewey:Yes. Well stated, Kim. It's certainly no one size fits all, and seasons are very different. In addition, we're trying to talk to beekeepers from various Southern Florida and up until Northern Canada. That is another of those variances. What we devised as a way to speak to all was to look at where your colony was in a seasonal development. We have a dormant period. Bees are not really dormant but they are at least inside their hive clustering. That's a very short time in Florida but obviously a much longer time in Canada. What we might do with our Varroa and treatments at that time is very different than for example during the active season.

We have a developing colony, we would call that spring, but spring is much earlier in Florida, obviously than in Minnesota. Then a peak population where often most of our beekeepers will have super sun and that in part dictates what you can use and what you should be using and should be avoiding in terms of your use. With colonies piled with super some of the management, options are not as easy to do. Finally then the decreasing population. that's not simply just bees losing bees, but it's also the bees growing the bees for the next season.

We talk about the fall of the year as the beekeeper's new year or beginning of the year, what we do in terms of our colony care in the fall is to try to help the bees so they'd have sufficient population of sufficient age, and with sufficient fat bodies to survive the winter. Obviously, this is a much tougher job for our beekeepers in our nothern states and then Canada than it is for our beekeepers in California, Texas, and Florida. It is still an issue because there is a period of time when many colonies go broodless or very limited amount of brood. Yes. There's no one treatment that's going to work in all instances or all seasons.

Kim:What's the best way to sample my bees? Where am I going to get the best answer?

Dewey:The sample number is what we're pegging than your element or risk, you want to try to get an effective sample. We do recommend that you sample bees from the brood area or upfront the frame that is adjacent to the brood area. We recommend a sample of 300 adults. Some people, some times a year, or for example when there's less of a population, 200 will do, but 300 is a little bit more reliable sample. We recommend that you then wash the mites from the bees using either alcohol. 95% is a little bit better than the 70% but both will work, or a non-sudsing soap that will, again, do the same thing.

We recommend swirling that, not shaking, protect them with the soap, you don't want to get all those bubbles going, swirling that. We got to get a release of the mites, at the time of our collecting sample, that are in the segments, particularly the lower body segments of the abdomen of the worker bees, the mites that are actually actively feeding on the fat body of the bees. We want to get them separated. We have a sampling device so that the bees are held in a basket above the liquid so that as we swirl it, the mites are released from the adult bodies and swirl out from that 300 adult bees and then accumulate in the liquid at the bottom.

Many people like or prefer to use powdered sugar to do the same thing. It's not quite as easy to use and there is a chance that you will not get as clean a sample. In other words, a good sampling number. Now more recently, Véto-Pharma has released a very popular collecting device that they've also modified so that you can use CO2 in terms of your material to get the mites to release from the bodies of the adult bees. That's our general recommendation. We recommend sampling ahead of time so you know the number. Some individuals say, "Well, I know the number is going to be too high, so I'm going to go ahead and treat," and that's perfectly okay, but if there is any treatment, we want to know, did it work? Has it been effective? The sampling post-treatment is also quite critical. Perhaps even more than that pre-treatment particularly looking at the fall of the year, the declining population period.

Kim:Well, that makes perfect sense, that sampling, treating, and then sampling again to measure the effectiveness of the treatment. I'm probably guilty of that more often than I should be, is not getting back and doing that second sample. My assumption is that what I did worked. That's probably not a good way to proceed, is it?

Dewey:Hopefully it did work, but again, there can be a number of reasons why it did not work or did not work to the degree that you'd hope to do so. One of the examples is, some people will use oxalic acid, either vaporization or the dribble when there's a fair amount of brood in colonies. That does wash adult bees of their mites, but if there's a fair amount of brood, the majority of the mites at that period a time are inside worker cells or drone cells, if there's some, reproducing, and so we don't get a very good estimate. Many people have those modified bottom boards and have been using sticky boards with that.

Actually, a fairly decent post-treatment estimation of how well your treatment work is to put the sticky board in, and then, after your treatment, look at the number of mites. If that number is still too high, that says that I didn't get all of them or I didn't get enough of them or maybe something went wrong with the treatment and I better do it again or try a different treatment.

Kim:Explaining for the sticky board is, I put it in before I treat, then I treat, and then I wait a period of time and I put it in again?

Dewey:Yes. It's at least two. Some people will also sometimes put it in when they're doing a treatment. If it's oxalic acid, for example, the treatment works for the first couple of days, so it would have to be in that time. Some of the treatments have a delayed response if you've used formic acid as your treatment, for example. Immediately at the end of the treatment period, you put the sticky board in. You will still get bees that are dying from the treatment itself. You'll look on your sticky board and say, "Gee, there are a lot of mites," but there should be because that's what the pharma would do.

With a couple of treatments, it's a little bit better to make a bit of a delay of a week before you then do your post-treatment analysis.

Kim:How do you interpret those numbers? I've got a five-story colony and I put a sticky board in or I got a two-story colon and I put a sticky board in? What kind of numbers should I be looking at before treatment, maybe during, but certainly after treatment? What's the number that sets off the alarm?

Dewey:We have really no good science or consensus that will give you a good number to count, and so it's a three-way decision. If you look at a sticky board and you don't see much in a way of mites, you really got to look before you see any mites, that's good. Wait and do a sampling in another couple of weeks. If you see mites and it's more than one every couple hours falling onto that sticky board, in other words, more than a dozen for a 24-hour period, that means maybe your mite number is high, particularly if you got that big colony. If you look at the sticky board and you see mites, geez, oh my God, there's a lot of mites, that means it didn't work. You should see that during your treatment itself.

If you see it before the treatment, then you need to not delay in terms of trying to do a treatment.

Kim:Just a minute ago you mentioned drones. I know there are people who use integrated pest management and don't like to use chemicals, so they're using other techniques. If putting poison in a beehive is something that doesn't sit well with you, what can I do to monitor mites, A, and to, B, help control them without using chemical?

Dewey:If you are of this mind, a number of our beekeepers are, A, for monitoring. The monitoring with powdered sugar is less harmful to the bees. You really need to shake them and dehydrate them. Unfortunately, when you then get them all powdered up and you put those bees back in, many of them won't survive, won't survive very long. You will kill less as you do your sampling. CO2, the same thing if you have the right amount. If you overdose the CO2, you'll kill a lot of them, but they'll then recover. That'd be an alternative to using the alcohol or the nonsudsing soap. Now, B, treatment. In our tools for Varroa management, we do discuss integrated pest management at length.

That means that you're not using the same chemical time after time after time, but it also means that you're trying to use other methods, a technique management, as a way to help control mites. Particularly during the spring buildup, our major emphasis is to flatten the growth curve so that, one, there's not as many mites in a colony and, two, when they reach their peak population, they've not been as successful in reproduction. Some of this starts with the stock. Bees that have greater hygienic behavior, are more adept at finding the mites, finding the mites reproducing in the cap cells, and opening the cells, and then interrupting mite reproduction.

Now adult female mites only have a limited number of eggs that they're able to produce, and so a limited number of reproduction period. If you interrupt any one of those, you have perhaps shortened her ability to reproduce herself by as much as 25%. An average mite will reproduce up to four times, on average. In other words, go into four cap cells and try to reproduce a daughter. When they go onto the drone cells, however, they're much more successful. Another technique is to manage drones. This is how bee populations that don't have mite problems-- The original host for the mite is an Asian bee, another species, and they manage the mites because they control when they rear drones.

Our Africanized bee populations in the southern US do the same thing. They manage mites by managing when they produce drones. They don't produce drones through the whole year like our European bee colonies will do. We can manage drones if we're not raising drones for mating. We can manage drones by drone brood removal. There're a number of good techniques to do this. You can purchase a drone foundation frame and insert that next to the brood area or my favorite way is in my standard-size boxes, I put a medium-depth brood frame, and so there's too much space below the bottom bar. There's that three to four inches. During spring buildup, the bees will more than likely fill in that space.

They don't like the space themselves. We'll fill in that space with a sheet extending from the bottom bar that's drone cells. Drone brood removal has us wait until the drone cells are capped and then we remove those drone cells from the colony at the cap stage.

Jeff:Hey, Dewey. Hold that thought. I have a question for you, but we need to hear from one of our sponsors.


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Jeff:Kim, I'm just thinking about Dewey's medium frame in a deep in the springtime and all that drone brood. Is that what you harvest and then you put in a frying pan and eat?

Kim:You can, actually drone brood isn't bad. Actually, you got to catch them a little bit earlier than sealed, or at least I like them a little bit as they start getting tough and they start forming cuticle and whatever, but I'll tell you who really likes that drone brood is my chickens, I'll just take that chunk of wax if I'm using a short frame, I'll take the whole frame and I'll throw it in the chicken coop. I got to build a thing that the frame can stand upright in.

There's a dozen chickens on both sides of that frame fighting over the drone brood so they benefit and I have a good time watching, so--

Dewey:I can't think of anything worse than someone saying, I got a piece of lettuce or broccoli in my teeth and someone pointing out, "Hey, you got a Varroa in your teeth." So sorry.

Jeff:Just in addition to chickens, if you don't have chickens, if you hang up that comb, by the way, there are a number of birds that also will eat insects, and boy they'll come and really have a feast on it.

Dewey:That's a great idea. That is a really good idea.

Kim:What other techniques of integrated pest management can I employ if I don't want to put poison in my beehive?

Jeff:Let me go back to the screen bottom board real quick. It raises a question because currently in the last several years there's been the thought of returning to a more natural approach to a bee environment that beehive and a log hive is often used as an example and a concern about the screen bottom board providing too much air and too much ventilation to the bees. Is there any way to satisfy the desire to be a more natural environment for the bees and this IPM approach?

Dewey:Very definitely. I do surveys out here in the Pacific Northwest of our beekeepers in the Oregon, Washington, Idaho. One of the questions I have is screen board use and fully 75% of the individuals indicate they are using a screen bottom board replacing the solid, but then also during a winter period, do you close or at least partially close off that screen bottom board? Then I key that to results in terms of survivability. I do it by losses, but the other part of that number is survival, and indeed those that do close or partially close the screen bottom board during the winter do join an increased percentage of survivability of the other counties.

One of our issues, in the bee tree, there's a very small entrance, the bees have narrowed the entrance by propolis and so there's a very small entrance of new fresh air into the colony. If we think of that screen bottom board, that's all that air entering the colony, not just at our entrance, at our entry board, but also from the bottom. Yes, it does improve survivability, at least here for our bees that we survive in the survey in a Pacific northwest by closing or partially closing that open screen during the winter period. Kim, you were asking about some other treatments. Our initial season as the bees are building up is we want to try to work at that flattening that curve.

Bee stock, citing colonies, how close to colonies are, and ensuring that bees have a distinctive address, in other words, different painted colors or something above the entry board, that is something that they can recognize and each of them being very different. Then doing dividing of colonies too strong not only to control swarming but in addition to helping then you can do some different types of mite treatments. As the numbers build up, we're often looking at some chemical intervention. For example, in the beginning, to help flatten the curve, we find that the essential oils, the thymol-based products, Apiguard, and ApiLife Var are pretty effective at helping reduce the number of mites that are successful in their reproduction.

During the time that we have supers on and for some of us, for very early flows, for example, that's pretty darn early in the season. You're trying to get low locus bloom and flow in the east, you're trying to get big leaf maple flow out here in the Pacific Northwest. You've got to get those supers on even in March and any of the years to be able to catch that bloom. That limits the types of other chemical interventions that we might be able to use and then gives the mites an advantage to be able to build up. About all we can use during that time is formic and unfortunately if we use formic, we often will have collateral damage of killing queens or stopping the queen from laying eggs.

We have to be very careful on that application. We can return to chemicals after the supers come off. This is when doing a pre-treatment sample is most advantageous. If you do a pre-treatment sample once the supers are off. This would be at peak numbers or maybe beginning of the decrease of colonies, what we'd call a fall and the numbers have high and that would be saying that they're above this 2% you want to get the numbers down quickly so the bees have a chance to rear those fall bees. About the best treatment at that time is formic acid.

The formic Pro is designed to cause less of that collateral damage and you can according to the label, use a half treatment so that you don't have to put a full treatment on particularly the smaller colonies, but on all your colonies. That will bring the numbers down pretty quickly then try to help the bees rear those fall bees that are going to get through winter. At that point, the synthetic, the Apivar, the strips will work pretty good. They have to go in for about six week period of time. Now, if your numbers persist being high in the fall, in other words decreasing population, at that point, some people will use oxalic acid, either vaporization or we'll use it as a dribble or use formic Pro for the second period of time that is permitted then hopefully your numbers are down.

Over the winter period, once the brood has decreased, naturally has decreased in colonies, some colonies never go broodless but is very limited, then the-- A very useful tool at that point is oxalic acid, either as vaporization or as a dribble. Now if you wait until the bees are very tightly clustered, so it's a very cold day in the later fall below 50 degrees, the bees are going to be in a cluster inside of their colony. In other words, they're going to form into that cluster. The outer part of that cluster is bees that are like an umbrella and so if you put the dribble on that it just runs right off the bodies of that cluster of bees.

That's why vaporization is a preferred method for oxalic acid but it's harmful for us as well. You've got to have acid-approved respirator yourself, gloves, long sleeves, long pants. Also, we do recommend eyewear when you use vaporization, and certainly don't get in a situation where you're breathing in the vapors that develop once you cook your crystals into the gas form.

Kim:That sounds complicated. I know a lot of people that use it and they like it because it does what you just said it does, but tough to do or tougher than the other ones.

Dewey:The analogy I give, all of these are tools that we can use and so if you wanted to put a nail and a piece of wood, you could use a screwdriver, you could use pliers, but a hammer does an awful lot better job of putting the nail in the wood and so too are tools for Varroa. The drone brood removal works in the spring when the bees want to raise drones, it doesn't work in the fall because they're not in that same behavior of raising drones in the fall.

You feed them, yes, heavily feed them, you can make them raise drones into the fall, but they're not normally wanting to do that. Too with our tools and oxalic is a perfect example. Oxalic acid is a very good tool for washing the mites off adult bee bodies, but it's no good for those mites that are reproducing. If you've got brood, a lot of brood in a colony, it is only getting a fairly small portion of the Varroa mites in your colony so it's a good tool when there is a little amount or less amount of brood. It's not a good tool there at peak population or when your colony is growing so strongly in the spring.

Kim:Well that makes perfect sense.

Jeff:For our listeners who are still struggling with an approach or management style to deal with Varroa, is the Honeybee Health Coalition's Varroa treatment decision tool. That's a fantastic tool, I've directed multiple beekeepers to help them decide what type of approach they want with their treatment modality and the time of year and the population dynamics of their colonies is which tool to use at that particular time. It's really good at giving you options. It's a great resource.

Dewey:Honeybee Health Coalition has if you go to, just to the coalition and look at varroa, we have both the management tool, the quick decision tool, and best management practice as well. We also have these case studies in terms of the commercial beekeepers and how commercial beekeepers are approaching their Varroa management, which is different is the commercial beekeepers-- That's their livelihood. They cannot allow the mites to get ahead of their colonies. One of the things we emphasize in our tools for Varroa management is you need to manage them with an integrated approach through the season.

It is very difficult once the number of mites get elevated in a colony to bring that number back down. You want to keep it from getting up to a level where it's going to cause all of this harm.

Kim:Dewey, all of this is on your webpage and a lot more that we talked about. I certainly encourage people to go to the webpage, to look at the videos, to download the management. What's the message we've missed that you want to share? What's the one thing most important I think?

Dewey:That last point I think I made is that we've got to manage the mites, we can't let them get ahead of us. There is no one tool, no one technique that does it best. We need to think in terms of integration, manage that curve so that never grows very large and so our colonies have a chance to stay healthy. Stressed colonies will have a greater difficulty trying to manage their Varroa mite. It's not just Varroa mites that are our issue here. It's some other things as well, decreasing forage, decreasing ability to find good, safe spots for location of colonies so that they have enough forage to get those resources that they need.

Of course, we still have issues in some locations with the internal gut parasite, Nosema, and the spring buildup we have the issue with the bacterial disease of European foulbrood. It's a multifaceted approach using our best management practices so that we can help the bees. We'd love to keep them the way they keep themselves, in tree hollows naturally, but it's not the way we're going to manage bees. We've got to join their battle. We just can't put them in a box, leave them and say good luck bees, because it's just they're not going to have a great deal of luck particularly with Varroa.

Jeff:Again, it's been an out of having you on the show. Look forward to having you back and further this discussion. There's so many different avenues we could go down, especially on treating Varroa but everything else that you've touched on, so look forward to having you back.

Dewey:Thank you, Jeff. Thank you, Kim. Appreciate the opportunity to join everyone. Hope you have a good overwintering period. Many of you will view this now during the fall and over the wintering period, might your bees come out strong and healthy, and that what we didn't capture this year with a surplus honey we get next year.

Kim:Good. Thanks, Dewey.

Jeff:Thank you, Dewey. I'm glad we had Dewey on this whole Varroa topic. I don't think we can talk about it enough. I know it's been said too many times, but maybe not enough. If you have honeybees, you're managing two critters, The honeybee, and the Varroa.

Kim:That goes without saying. I think this new management book goes a long way in giving beekeepers not only more tools but better ways to use the tools that we've already got. I want to back up one-half step and say something about the Honeybee Health Coalition itself. The fact that this group of people coming from every angle that you can come at in agriculture and sitting down at a table and talking to each other without throwing things is a pretty amazing feat. I hope this industry appreciates what that group is doing and what they're accomplishing to help all of us.

Jeff:I have directed so many beekeepers to the Honeybee Health Coalition website. The information that's available there and the tools available to beekeepers are far superior than anything else that you'll find. I'll pick on YouTube then you'll find on YouTube. It's vetted, it's real information and you can trust what you read. We only talked about the Varroa management, but they do everything else and there's so much out there. I'm looking forward to the next version of everything that Dewey and Honeybee Health Coalition puts out.

Kim:They do a good job and we're lucky to have them.

Jeff:That about wraps it up for this episode. Before we go, I want to encourage our listeners to rate us five stars on Apple Podcast. Wherever you download and stream the show, your vote helps other beekeepers find us quicker. Even better, write a review and let other beekeepers looking for a new podcast know what you like. You can get there directly from our website by clicking on reviews along the top of any webpage. As always, we thank Bee Culture, the magazine for American beekeeping for their continued support of Beekeeping Today podcast. We want to thank our regular episode sponsor Global Patties. Check them Thanks to Strong Microbials for their support of this podcast.

Check out their probiotic line We want to thank Better Bee for their longtime support. Check out all their great beekeeping Thanks to Northern Bee Books for their support of Bee Books Old New with Kim Flottum. Check out all of their Finally, and most importantly, we want to thank you the Beekeeping Today podcast listener for joining us on this show. Feel free to leave us comments and questions that leave a comment section under each episode on the website. We'd love to hear from you. Thanks a lot, everybody.

[00:46:14] [END OF AUDIO]


Dr. Dewey CaronProfile Photo

Dr. Dewey Caron

Author, Professor Emeritus

Dr Dewey M. Caron is Emeritus Professor of Entomology & Wildlife Ecology, Univ of Delaware, & Affiliate Professor, Dept Horticulture, Oregon State University. He had professional appointments at Cornell (1968-70), Univ of Maryland (1970-81) and U Delaware 1981-2009, serving as entomology chair at the last 2. A sabbatical year was spent at the USDA Tucson lab 1977-78 and he had 2 Fulbright awards for projects in Panama and Bolivia with Africanized bees.

Following retirement from Univ of Delaware in 2009 he moved to Portland, OR to be closer to grandkids.

Dewey was very active with EAS serving many positions including President and Chairman of the Board and Master beekeeper program developer and advisor. Since being in the west, he has served as organizer of a WAS annual meeting and President of WAS in Salem OR in 2010, and is currently member-at-large to the WAS Board. Dewey represents WAS on Honey Bee Health Coalition.

In retirement he remains active in bee education, writing for newsletters, giving Bee Short Courses, assisting in several Master beekeeper programs and giving presentations to local, state and regional bee clubs. He is author of Honey Bee Biology & Beekeeping, major textbook used in University and bee association bee courses and has a new bee book The Complete Bee Handbook published by Rockridge Press in 2020. Each April he does Pacific Northwest bee survey of losses and management and a pollination economics survey of PNW beekeepers.