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Oct. 17, 2022

Winter Storage, CO2, and Varroa with Dr. Brandon Hopkins (S5, E18)

Winter Storage, CO2, and Varroa with Dr. Brandon Hopkins (S5, E18)

Would you believe varroa mites, carbon dioxide and indoor wintering are working together to make keeping bees easier and more profitable? Well, believe it. Today, we talk with Dr. Brandon Hopkins from Washington State University. His research has...

Would you believe varroa mites, carbon dioxide and indoor wintering are working together to make keeping bees easier and more profitable? Well, believe it.

Today, we talk with Dr. Brandon Hopkins from Washington State University. His research has shown that if colonies are overwintered in an environmental chamber that can control the levels of the gasses the bees are exposed to, that by adjusting the level of carbon dioxide from a normal 0.04% to over 8.5%, mites in those colonies die. Really. And what’s more, the bees don’t, really!

Temperature was set at just about 40 degrees, the chamber was dark, and after 64 days, mite mortality was extremely high. High enough to prove that this could be a mite controlling tool to use in indoor wintering.

To show a difference, another chamber was set up with a 0.12% carbon dioxide concentration, and there was a significant difference in mite mortality was recorded between the two. High carbon dioxide equally high mortality, low concentration equals low mortality.

There is much more research underway. Stay tuned!

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


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S5, E18 – Winter Storage, CO2, and Varroa with Dr. Brandon Hopkins


Jeff Ott: Welcome to Beekeeping Today Podcast presented by Bee Culture. Beekeeping Today podcast is 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 honey bees. 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 pattie is right for your area and your honey bees. 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

Jeff: Thanks Sharine. Thank you Global Patties. Each week we get to talk about how much we appreciate our sponsor's support and we know you'd rather we get right to talking 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's been the magazine for American Beekeeping since 1873. Subscribe to Bee Culture today.

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Hey everybody, thanks again for listening today because we have a great guest joining us. Dr. Brandon Hopkins from Washington State University is here to talk to us about his research on the effects of carbon dioxide, CO2 on Varroa on honeybees in over wintered cold storage facilities. This is a fascinating discussion on research that has practical applications for beekeepers. That is up shortly.

First, some of you may remember this past spring, I joined Bee Informed Partnerships 2022, Sentinel Apiary Program. As part of this program, I sent in monthly samples from four of my bee yard colonies from May through October. I also collected pollen samples for pesticide analysis. Although in full disclosure, I missed a deadline for that analysis due to time management issues. Anyways, I also entered inspection and management data from the field on a very convenient app for my cell phone and iPad. For participating in this program, I received monthly analysis of the number of Varroa found on each hives sample, as well as the results of two nosema tests. All of this is tracked and reported back to me on a dashboard the BIP team created for each participant.

My data is also combined with other Sentinel Apiary Program participants, hobbies, sideline, and commercial beekeepers for national reporting on the health of honeybees. This reporting can be found on the BIP website. Check for a link in the show notes.

What did I learn from this exercise? I have to admit that being a BVD beekeeper, wait a minute, now get those tidy whitey visuals out of your head. Just don't go there. It's not pretty. What I mean is, as someone who learned beekeeping Before Varroa Destructor, it's reinforced on me, the absolutely an utter destructive nature of the Varroa mite on a colony. It has taught me that one must take regular mite samples. Yes, it's not fun killing 300 plus bees per colony a month in a sample. However, what you gain, what I gained is a true understanding of how the Varroa are impacting my colonies right under my nose.

You know from the outside, a colony will appear normal. If you pop open the top and peer inside, it will look normal. Look at the top of the frames, everything will appear normal. If you pull a frame, the bees will be working hard and all will appear normal. The bees will appear healthy until they don't and the colony dies. Usually, this is during the winter while surrounded by a full hive body of honey. It is depressing to open up colonies in the spring and find they died earlier in the winter. Odds are, if you left enough honey on them, they didn't die because of starvation or the cold or moisture or temperature swings or mice or anything else. They died because of Varroa mites. That of course is a broad generalization, so take it as that, but in this case, a corollary to Occam's razor is definitely in play.

Occam's razor, the simplest solution is almost always the best. A corollary is the simplest because it was almost always the reason, in this case, Varroa. If you do not manage year-round for Varroa, your bees will die. What's more, before your bees die, there's a strong likelihood they will take Varroa with them to your neighbor's hive. Varroa is a gift that just keeps giving.

Regardless of your approach to beekeeping, natural or chemical free, Langstroth or top hive, Warre or horizontal, have a solid management plan for Varroa and do a regular mite count. They will not go away on their own. You can join BIP Sentinel Apiary Program in 2023 yourself. Force yourself to look in the mirror and see just how effective your current management practices are against Varroa. You may surprise yourself.

Okay, up next is Kim and my chat with Dr. Brandon Hopkins. First, a quick word for my friends at Strong Microbials.

Strong Microbials: 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 on 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 to this show, sitting across the virtual Zoom table right now with us is Dr. Brandon Hopkins from the Washington State University, Bee Lab. Brandon, welcome to Beekeeping Today podcast.

Brandon Hopkins: Hey, I'm happy to be here. Thank you.

Kim: That's nice to finally get to meet you, Brandon, welcome aboard.

Brandon: Yes, happy to talk to you, Kim. Thank you.

Jeff: We invited you on to the show today because of your research on the effects of CO2 and Varroa mites and honeybees and storage, and I'm not sure if that goes on beyond just the storage aspect, but let's talk about that and go from there.

Brandon: Yes, I was excited to finally get that work published on the effects of CO2, on Varroa mortality, and still working on that, at least in the way of scaling it up to see if it could have an impact on a commercial scale.

Kim: One of the things, Brandon, that we've talked to in the past here, John Miller, who does indoor wintering, and we talked to Gloria DeGrandi-Hoffman down in Tucson on her work on indoor wintering. Neither of them brought CO2 into the discussion other than it needed to be below a certain level. I'll let you go through the CO2 levels that you had in there, but not being a physiologist, how much CO2 can I breathe and not have a problem? What's the percentage of CO2 because normally it's less than 1%, you're sitting outside and you're breathing less than 1% CO2, right?

Brandon: You're right. Correct. It's quite a bit less than 1% CO2. I think it's 0.05 or something like that, depending on your elevation and where you're at. There are certainly human safety considerations when dealing with high levels of CO2 in these tight spaces, like in these indoor storage buildings and other facilities as well. A lot of this really comes from controlled atmosphere storage that they do generally for apples and tree fruits like pears and things like that, where they have these large structures, very much like the indoor storage for bees and potatoes and onions, but they control the atmosphere to extend the shelf life of the tree fruit.

They'll lower the oxygen levels and increase the CO2 levels by quite a bit, higher than what's safe for humans to be breathing. Off the top of my head, I'm pretty sure it's somewhere around 2% you get into these OSHA warnings and limited amounts of time and then it's not much higher than that before you get into lethal levels for humans to be breathing.

Kim: Your research used two different kinds of containers that you put your bees in. I'm going to have you describe how they went, but the levels of CO2 you were using in there were way higher than that.

Brandon: Correct. What we were using, what we were targeting was around 8% CO2, so that's 80,000 parts per million. I think 10% is certainly lethal to humans. Like I said, even around a half a percent has a, you can only work a certain amount of time at levels around that, less than 2%. It's deadly to humans. It'll certainly cause you to pass out if you were in there for more than a few minutes.

Kim: Well, why don't you go ahead and describe the two different levels of CO2 that you use and how you set it up and maintain those levels and what other aspects of the environment that you manipulated?

Brandon: I should start by saying that this wasn't a new idea by us necessarily. We had gotten this idea from a couple different areas. One being that we had a commercial beekeeper here in Washington that we were working with and he happened to have been using and then purchased an older tree fruit storage facility. Some of the rooms in that facility were these, what they call CA rooms or controlled atmosphere storage rooms for tree fruit.

We started looking at this because he was very concerned about the rising CO2 while the bees were in these tightly sealed controlled atmosphere facilities. He would open the doors every night in order to allow fresh air in. He came to us with those concerns and then looking in the literature, we found that work out of Rob Curry's lab in Canada had published a couple papers showing that Varroa mites that they had this increased mortality at higher levels of CO2 that the bees seemed to be able to tolerate.

Then known for a long time, I think it was even maybe Tom Seeley's work where they measured CO2 levels in the center of the cluster. When bees are in their natural state in the hive or in a hollowed out tree during winter months or cold periods when they're clustered tightly, the CO2 there in the center of the cluster can be as high as 6% CO2. We were fairly confident based on that the bees could handle that level without seeing any increased mortality.

At least that around 6% CO2 levels. Rob Curry's work had showed that they had higher levels of Varroa mortality as with CO2 concentrations as low as 2.5%. I think that that was close to 50% mortality after only 72 hours or 48 hours. I can't remember. It wasn't very long. We were highly encouraged that with the 60 to 90 days that bees were being held in these storage facilities and even the potential of using higher levels of CO2 that we could potentially kill a lot of mites on a lot of colonies. That's what inspired us to do this work.

Kim: You had them in containers, they were in if I recall an 8-frame deep nook.

Brandon: We do our work now in 20 foot cargo containers that were graciously paid for by beekeepers and the Almond Board of California and the Washington Tree Fruit Research Commission. That work was before we got to that scale, so that they were held in incubators, environmental chambers, if you will that are really the size of a really large refrigerator in your house.

We used eight frame colonies because that's what fit and it actually was so tight we had to cut the landing board off of the bottom board and so it fit almost exactly the depth of a eight frame deep and that allowed us to put eight colonies in there. There were single deep eight frame colonies in these environmental chambers that we could control the CO2 and temperature in.

Kim: What temperatures were you running them at?

Brandon: At four degrees Celsius or about 40 degrees Fahrenheit.

Kim: Both chambers are the same temperature?

Brandon: Correct. Yes.

Kim: You're eliminating that as a variable. That's good. You got the container the same, you got the temperature is the same. What you were manipulating was the percentage of CO2 in the chamber?

Brandon: One of the chambers we allowed to ventilate as much as possible and set the CO2 as low as we could. Even with that high level of ventilation and with that enclosed space and all those bees, the CO2 did rise, I think in average of point, I can't remember off the top of my head, maybe 0.2% or something like that. It's slightly higher than normal atmospheric CO2 levels, but you know much below the treatment group which was around 8% CO2.

Kim: Well, just out of curiosity on these controlled atmosphere buildings that I said, we've talked to John Miller and Gloria about, do you have a feel for what the CO2 level is even if those rooms are ventilated? As you said, bees produce a fair amount of CO2 when they're clustering and even though these buildings are ventilated, does the CO2 go up at all, some, a lot?

Brandon: That's a good question. It's really highly variable because there are so many different types of these buildings are built by different people or repurposed from different things. In some of these repurposed potato or onion sheds, especially older ones, there's probably a little more ventilation, they're not as well sealed. Some of the newer facilities are a little more tightly sealed. This is a constant concern for the beekeepers that use these.

Oftentimes, especially in the newer ones, they have CO2 sensors and they even have safety protocols built into the control systems that are set to run the ventilation fans and bring in fresh air if the CO2--Generally, I think beekeepers have been worried about it if it gets around 2% CO2, 1% to 2% CO2, the fans automatically kick on and bring in fresh air to keep the CO2 levels down. The answer is yes, it certainly will build up and I don't know that anyone knows how high that CO2 level will climb in their building because I don't think anyone's really willing to take that risk when you have your livelihood and your employees with anywhere from 5,000 to 40,000 colonies in the room that nobody's really trying to experiment too much.

Jeff: Just to be clear on your experiments, you were introducing CO2 to the rooms, to the containers as opposed to letting it build up naturally through the respiration of the honeybees?

Brandon: We did, it's a little of both. We did, because these are environmental scientific chambers, we did have CO2 tanks attached to them and it had a control module and a valve and so we set it at 8% so it would allow CO2 to come in and then until it reached 8% and then it would vent if it got too high. It controlled it at 8%. It was a little hard to know, it was using CO2 from the tank and so the short answer is, we don't know what it would've built up to on its own in there and it certainly drew CO2 from the tank to maintain that 8%.

Jeff: Did you also control the humidity levels?

Brandon: We did. We tried to keep that the same, but just because bees are living organisms or for some reason there was some slight difference in the humidity between the two chambers. That's something that we did hopefully discussed well in the discussion is that because we didn't or were not able to control the humidity tightly, it's something that can't be ruled out really as a potential factor in the mortality that we saw of the Varroa mites. It's actually something that was proposed in Rob Curry's paper as a potential mechanism for the Varroa mortality at high CO2 levels.

Kim: You just said the magic word, Varroa mites. In a perfect world there were the same number of mites for hundred bees and all of those colonies that went into both tanks. I can also imagine that being nearly impossible to get exact. How were you able to equalize the number of mites in both treatments?

Brandon: That's good. What we do is we cheat a little bit is that we just go in and we take from a large pool of colonies, we take those mite samples, the alcohol washes, and we just determine the Varroa population level in all the colonies that are potential colonies before the study begins. Then we rank those based on their mite levels, right? We, in this case had the two treatment groups that are in these containers. Like you said, it's variable across all the colonies we sample. You have the highest one, let's say is 10 mites per 100 bees. The second one, the next highest is nine mites per 100 bees and eight mites per 100 bees, et cetera.

Then we just rank them You just say the highest one goes in chamber one and the next one goes in chamber two, and then you alternate. In the end what you get is two groups that on average have the same levels of Varroa mites. That's how we make sure that the two treatment groups together have the same levels of Varroa mites.

Kim: How about sealed brood?

Brandon: Yes, we manipulated that a little bit by, well, the environment and the timing of this work helps with that a lot, because we waited as long as we could before putting them into this. Here that's the beginning of November, something like that, there's very little sealed brood in those colonies. I think on average they had a quarter of a frame of sealed brood on average by the time they went into the study.

Kim: Okay. You didn't have many mites hiding when you put them in the box, they were all hanging on a bee somewhere outside.

Brandon: Yes. That's a bit of an assumption we have to make or didn't do because the only way to do that would be to open all the uncapped brood or to alcohol wash the whole colony at the end.

Kim: You've got two containers, same number of bees, same number of mites, atmospheres are identical except for the level of CO2. How long did you have them in these containers?

Brandon: We ran them in the containers, I think 62 days is what it happened to be. We were targeting that about a 60-day timeframe. That's what some of these commercial guys here in Washington were storing for. They were starting in mid-November and then coming out for almond pollination in mid-January.

Kim: One of the other things that I was wondering about, of course at the end of the experiment you opened the door and did any die because of colonies die?

Brandon: Yes. We had plenty of bees die and we were also, they weren't sealed the entire time. Another thing that we did during the course of the study that also required to have the external CO2 levels is that we were interested in the might mortality, not just at the beginning and end, but during the course of the experiment.

Once a week we would open the containers as quickly as we could and we would swap sticky boards. Those are those cards with, we'd put Vaseline on ours with a screen on it and all of the material falling down out of the cluster sticks to that board and that's including the mites. What we were monitoring on a weekly basis during this experiment was the mite fall between the two colonies. That's why it was really helpful to have the external CO2 so that as soon as we closed the door, the system would allow CO2 to go into the container and get that level back up as quickly as possible.

Jeff: Let's take this quick opportunity to make a quick break and hear from our sponsor Betterbee.

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Kim: I think you mentioned earlier Brandon worked done by others had shown that the CO2 level in a normal colony, outside in the regular world was certainly higher than the CO2 level in the atmosphere around US all of the time. Something like three to 6% or something in the middle of a cluster, I don't know, were you able to monitor that CO2 level in that cluster during this or would that not have been important?

Brandon: It would've been important. We just didn't have the capabilities at the time to measure the CO2 in the cluster. All those CO2 readings are of the atmosphere around the hive. My guess would be that the hives and the control with the low levels of CO2 would've had similar internal CO2 levels between 3% to 6% and that's at the very center. Then you have to imagine that those numbers drop as you radiate out from the center but I think with the treatment group at the 8% CO2, our assumption would be that it would be 8% all the way through. That's what the external CO2 levels would be and it's hard to imagine how that center cluster would regulate it any less than that.

Kim: When they're surrounded by 8%, you're going to replace it with 8%. That makes perfect sense. Exactly.

Brandon: Well, we don't know and I think one of the shortcomings in not having measured it was if that center cluster would've been higher than 8%.

Kim: Next time.

Brandon: Right. Yes.

Kim: One of the things that you just mentioned, you were counting mite fall captured on sticky boards and you would check those once a week during the whole time of the experiment. Did you see any difference between the two of them, the mite falls the first week, second week, third week, were they different and were there lots of them the first two weeks and then it just trailed off? Or was it the same every week?

Brandon: Yes, it was that mortality was fairly steady, but you could see it, those curves start to separate fairly early but maintain sort, well you could imagine as the same slope. The higher levels of CO2 had a steeper slope. The population of mites was, well the population of dead mites was higher than the other one. They were dying faster, but then the control, but it was over time that was fairly steady.

That's a great question because, and actually you mentioned talking to John Miller about this and one of the things he was interested in was that same question like, does a greater percentage of the mites die in the last two weeks of that storage? Basically could you just dose them in the last few weeks of the storage period and kill a bunch of mites before they come out? But unfortunately that's not what we saw. We saw it was a steady die off really from the first week to the last week. It just was at a higher rate for the high levels of CO2.

Jeff: I'm not sure if you answered this before, I think Kim was leading up to it, but does this affect only the phoretic mites or does it affect the mites that are under any cappings?

Brandon: Yes, that's something we don't know. Fortunately, the system is fairly simple in these storage buildings in that there's almost guaranteed to be a point when there really is no capped brood in the storage facilities. A lot of people assume most of the colonies coming out have no capped brood at all. It's more likely probably to affect the phoretic mites anyways but that micro environment inside the capped brood is probably-- There is air exchange between the inside of that capped brood and outside. It's likely that the CO2 levels inside the capped brood are also at 8% or whatever the cluster is experiencing.

Jeff: We've talked around this, but I'm not sure if I actually heard a direct answer. Is there a specific amount of time that the colony needs to be at that CO2 level to achieve a great effect of kill off of the Varroa mites? What's the ideal length of time at exposure to the high levels of CO2?

Brandon: Yes, there's not an ideal time, because that mortality curve was steady over time, it would mean the longer that they're in there, the more mites die and the shorter the time, the fewer the mites die. There's not a critical moment where you kill more mites than another. It just, the more time they're in there, the more mites die.

Jeff: My get-rich-scheme of CO2 bubbles to sell, wrap around a hive and dose it with CO2 and then walk away. That's probably not going to sell much?

Brandon: Yes, probably dashed I guess. Sorry about that.


Jeff: All right.

Kim: You try again, Jeff.

Brandon: Yes, for sure. Yes, keep thinking.

Jeff: Indiegogo, I'll have to cancel that one.

Kim: Got a question. How long were they in these containers?

Brandon: They were in the containers for 62 days.

Kim: Two months. Beekeepers put them in about the 1st of November?

Brandon: Yes. This work was done a few years ago. At that time, the beekeepers we were working with in Washington were targeting going into storage around before Thanksgiving. They hoped to have all their bees put away before that Thanksgiving holiday but now, and you might have covered this with Gloria especially has worked on this and so have the Millers is that they're going in sooner and sooner and beekeepers are more and more interested in getting in early. There's a lot of guys that are trying to get indoors by October 1st.

Jeff: There's also been discussion of putting the bees into storage right after Almonds, and inducing a break and introduces an opportunity to dose them with CO2 at that time as well.

Brandon: That's work that I've done quite a bit of, and have run some experiments on that. The idea of doing that for the brood break purposes either after Almonds or at some other time when there's a period of three weeks when the bees aren't either making honey or actively getting paid for pollination is a great strategy for those that can do it and pull it off. It's working for a number of guys that have figured out a way to use it, but I don't know that the CO2 thing is going to be helpful like I said, because three weeks is such a short window. I mean maybe you kill 20% of the mites or something like that, but that's nothing compared to what we're after.

As beekeepers we're wanting to get 90% or better, ideally 99% or something. The purpose really that brood break and then a single application when they come out, is going to be that 95% to 98% effective. I just wouldn't see the value in the low percentage of mites that would die from the high CO2 considering the infrastructure needs to have a room that's tight enough to allow that high CO2.

Kim: You just said leaving them in the container and then a single application and then moving them out, it sounds like beekeepers are taking them out of storage and then treating them with something for the residual mites that are in there?

Brandon: Yes. Then you can use some of these applications that some people call it as a flash treatment. These short lived ones that are very effective, but that would require multiple applications if you used it while there was capped brood, and so if you can get rid of all that capped brood, you get a highly consistent, highly effective treatment with just a single application.

Kim: Sort of the frosting on the cake, of course it comes down to cost. Do you have a feel for a building that's as big as a football field holding thousands of colonies, cost for colony or on any of this stuff, is there a ballpark figure you can say that's $20 a colony or $10 a colony whatever it is?

Brandon: Yes, I don't know what the building costs are up front, and it's tough, because we do get these questions a lot, but it's so highly dependent on where you're building the structure and utility costs and things like that, but we can go based on what beekeepers are paying for indoor storage as an estimate for what it probably costs to do it. I think it's anywhere and it's probably gone up now, with inflation I guess everything's gone up, but anywhere from $8 to $12 to $15 per hive to store a colony for those three months in the wintertime.

Jeff: Is CO2 expensive?

Brandon: Yes. The stuff we used was fairly expensive, because we used some medical-grade CO2 that we had at the university available there, but I don't think it's prohibitively expensive. Like I said, in these controlled atmosphere apple storage facilities, they use a lot of gases like this. I think they also use a lot of nitrogen to displace the oxygen levels which is also something that could be tried, but yes I don't think CO2 is super expensive. I mean they're trying to get the CO2 out of the atmosphere, because of this global warming--


Maybe this would be a way to encourage, they can pull CO2 out the atmosphere to put into [crosstalk]

Kim: There you go. [laughs] Well even at $15 a colony, let's take it one step further, Ballpark losses over winter colonies in these buildings it's not the 40% or 50% that commercial beekeepers or others are seeing, it's much lower, but you got to figure for what it is about?

Brandon: For what it is to, all the losses you mean?

Kim: The losses of colonies that have spent the winter indoors.

Brandon: From the numbers I hear people tell me, it's usually somewhere between 7% to 14% or something like that, I would say the Ballpark, but I will say for people out there listening, I don't want everyone to think that that's-- That's a number that you'd get coming out, but that's only if you do all this work up front. The difference, it's a total shift in management style. For beekeepers that have got their losses down to say 7% or something like that when they go through this indoor storage, what that number doesn't express is their losses before they go into the building.

If you want those kind of losses coming out of the building, it means that you take a lot of those losses before you go in the building. It just means you have to do a lot of that work up front. You don't spread that work out from October to January in holding yards in California, you'd cull heavily in the fall and you feed heavily, you get your mite treatments done in August and September, and then you only put hives that are clean of Varrroa mites and strong and heavy into the building.

You can't really compare say someone who goes down to Florida or California into holding yards for the winter the way a lot of people did and still do, and those losses can't compare directly to a guy that goes into storage and comes out at 7%, because you'd have to ask that guy, what percentage of hives did he cull in September and October?

Kim: Well, one of the 10 rules of beekeeping is take your losses in the fall.

Brandon: Yes. That's one nice thing about this indoor storage is that it forces you to do that. I do think there's a lot of these little advantages that as a researcher I never would've thought of or come up with, but these guys who are doing it and doing it well have found is that there's a big advantage, because then you know what your numbers are going to be for your available colonies for setting in Almonds. You're not guessing or crossing your fingers, "Are my losses going to be 20%, are they going to be 30%, are they going to be 40%?" You take those losses up front and you put good bees in the building, and then you know really precisely how many colonies you're going to have for February.

Kim: I think John's comment he made to us was junk in, junk out, and it sounds like that's exactly right.

Brandon: That's right. It's not a hospital for sure, the bees don't get better in there.

Kim: Knowing that going in it's going to save people a lot of money and a lot of time beforehand before they spend a lot of money doing this, so the results were what, losses high and low CO2?

Brandon: That's right. Yes, yes. The mortality for Varrroa mites at that high level CO2 were about 75%, so about 75% of the mites that went in at the beginning died during that 60 day storage period, and that's the high level CO2. For the control or for that really low level of CO2, the mortality I think it was about 45% of the mites died during the storage period.

Kim: I see. 75 versus 45, yes, that's a difference.

Brandon: Yes, it's a difference for sure, yes.

Kim: Bees can live with that I think. What's next on your plate with this?

Brandon: What's next is there's a few things. One is that, is doing it at a more realistic scale. We generally run two deep boxes here, and that's how most people over winter and go into storages, because of that constraint for space, we had to condense them into single eight frame deeps and we weren't able to control humidity very well, but basically the next steps are, and we have a trial this year trying to do pretty much the same thing, but on a more commercial scale. With these 20-foot refrigerated cargo containers, we'll have about 60 colonies in each one, so we'll have 60 in a container with high levels of CO2, 60 in a container with low levels.

Then we always run a set of bees now just sitting outdoors right outside the containers, and again, looking at this Varroa mortality, but additionally, not that I don't want to get people or take away hope for this thing, but since that study, and thinking about this in a more holistic approach, really those mites should be cleaned up anyways by then. I wouldn't want people holding out hope that this is going to be a replacement for your Varrroa control in the fall, because you really need the Varrroa cleaned up by August or by September, so those bees can produce healthy winter bees that are not being fed on by Varrroa mites and getting all these viruses.

You can't just not treat in the fall with the hopes that the CO2 is going to kill the mites. I do think if it has that added benefit and it cleans up the mites that somehow escape the Varroa treatment in the fall, then it's a positive, but the long story short is that I do think that there might be other benefits to this increased level of CO2. We had a more recent publication that was showing that bees that go through this indoor storage have higher levels of protein and they're hypopharyngeal gland and they have higher levels of lipids and so it maintains the bees in more of this nurse bee type state.

They are more like winter bees. They're healthier coming out than bees sitting outdoors. It looks like some of that may be caused by slightly higher levels of CO2. There may be other benefits besides the Varroa control that allowing the CO2 to build up in the buildings has for colonies and it may be in these physiological states.

Kim: Well you brought up one of the other 10 rules of modern beekeeping is take care of the bees, so take care of the bees that go into winter. That's exactly what you've done here. You've shown that it's going to help come spring. What have we missed on all of this, Brandon?

Brandon: Right there at the end was the main thing I wanted to cover, which was that, the indoor storage and the potential for CO2 to kill Varroa mites doesn't really replace the hard work that has to happen up front in August and September before we even get to the point where bees are in the building. I think everyone understands the feeling of wanting to kill mites at every chance that we can get. I think we need to know a little bit more about what happens to the bees themselves physiologically at these high levels of CO2.

The other thing that study was lacking was the number of replicates because it was only eight hives. We did have hives that died during that period of storage in those containers so we can't really rule out yet that there is some level of detriment caused by the high level of CO2. We know that bees survive in general but I would hate to recommend for somebody build a special building and then we find out a year from now that the high level of CO2 is actually not good for the bees. We still have a lot to learn before I think anyone really puts that into practice, especially at the levels that we're doing.

Jeff: Did you keep the atmosphere in those containers circulating so there weren't like pockets of heavier CO2 where the hives at the bottom left corner of the container was dosed with a higher level?

Brandon: Yes, that's a good point. There are are fans in there and so these are these environmental chambers and there's three or four fans. They're not giant fans because it's like a refrigerator but those fans run continuously in there. It is a tight space in there, it's not as say like well spaced or well ventilated as these commercial facilities. That's another reason why we immediately wanted to get away from that system for experimenting on this indoor storage and get these containers that are much more like a realistic situation where the spacing and ventilation is much more like a commercial facility.

Jeff: That's exciting research for sure.

Brandon: I think yes. We really like it.

Kim: Well Brandon, we're running out of time. It's been great having you here today. You've filled in a lot of holes on some of the things we've talked about here earlier and we're getting closer to the whole story. This has been great, I look forward to talking to you. We look forward to talking to you again when your next series of tests is over and you've taken this to the next step.

Brandon: Yes, I'd be happy to chat about it again and I appreciate talking with both of you.

Jeff: I'll have to come over to that side of the state and sit down with you.

Brandon: Yes, I would love that. You're welcome anytime.

Jeff: That'd be great. Well thanks a lot for joining us Brandon.

Brandon: Yes, thanks Jeff. Thanks Kim.

Jeff: That was really fun talking to Brandon and listening and hearing about the new research you're doing on the CO2 against the Varroa. I mean anything we can do to knock down the Varroa is good in my book.

Kim: Well I think what I like best about this was that I mentioned the golden rules of beekeeping and he touched on two of them and he's just making those two even more important. One is take care of the bees or take care of the bees that go into winter. That's one of them and the other one is take your losses in the fall, because that's what beekeepers are having to do even more so now that they're putting them in because as John said in his talk, "Garbage in, garbage out," so you want to put in the best bees you can. No matter where you're spending winter, you want to put the best bees into winter that you can, whether it's in a building or sitting in your backyard. I was really pleased to hear that because it just makes common sense.

Jeff: The other thing we touched on and then it's coming around full circle, is the concept of either the colony has a natural level of CO2 in the cluster. I started thinking about the "new concept" of the sealed hive that we've been talking about in the last couple years and even makes that point even a little bit more important because if you had a sealed hive without the fresh air coming in all the time, either at the top or bottom, maybe the CO2 levels internally would build up enough to help be part of an effective IPM.

Kim: That's a good point. Normal error is less than a 0.5% CO2 and they were running high CO2 at just over 70% and even the low CO2 was just over 40%, which is way higher than what you and I are breathing right now. A sealed colony, there may be even more advantage to that than we were thinking.

Jeff: Exciting research to come, I'm sure. Stay tuned. Well, 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.

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[00:47:00] [END OF AUDIO]

Dr. Brandon HopkinsProfile Photo

Dr. Brandon Hopkins

Assistant Research Professor

Dr. Hopkins got his BAE and MS at Eastern Washington University. He went on to get his PhD at Washington State University in Dr Sheppards lab. That is where he found his passion for bee research. Largely fueled by the amazing people of the beekeeping community and the fascinating biology of the species.

His work was originally focused on cryopreservation and reproduction, but has branched out into various aspects of commercial colony management. Current work includes Indoor Storage, varroa management, pollination and nutrition.