[Bonus] Short: Varroa Treatments - Non-Chemical Means

[Bonus] Short - Varroa Treatment Options: Non-Chemical Means

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Jeff: Welcome to Beekeeping Today Podcast shorts—your quick dive into the latest buzz in beekeeping.

Becky: In 20 minutes or less, we'll bring you one important story, keeping you informed and up to date.

Jeff: No fluff, no fillers, just the news you need.

Becky: Brought to you by Betterbee, your partners in better beekeeping.

Jeff: Hey, everyone, welcome to this Beekeeping Today Podcast short on varroa treatments. This is a multi-part series covering the different treatment, or actually the management options available to combat this honeybee pest. Hey, to shorten our series, we'll cover one specific treatment option. For the series, we've invited Dr. David Peck from Betterbee to join us. In this short, we'll be discussing non-chemical treatment options. Hey, Becky. Hey, David. How are you guys doing today?

Dr. David Peck: Hey, thanks for having me back once more.

Becky: Yes, this is such a pleasure. I have a lot of good feedback from many beekeepers of all different sizes, David, that you're really helping them through this, so you're doing good work.

David: Good. I'm glad we've been able to put this together. I think it's a really helpful resource for folks. I think today's going to be a fun one because we're planning here to talk about non-chemical varroa control. I think that there's a lot of people who get into their heads that if you want to fight varroa, you have to use chemicals, and if you don't want to fight varroa with chemicals, then you just don't do anything at all. You just hope the varroa might still cause any trouble, and that doesn't work.

In this, we're going to talk, I think, a little bit about some of the things that work and some of the things that people try that they wish would work, but they don't work that well. I think that'll be a useful conversation just to round out all of the different topics we've already covered about the various different miticides that folks can use.

Jeff: In the prior episodes, we have talked about all the chemicals, both organic and non-organic, non-chemical treatment options that're out there, and they are useful. What describes just a non-chemical treatment option? What are our options? [laughs]

David: I think the one I'd probably start with is one that absolutely works as a part of your varroa management, which is drone brood removal. I think this is a really slick move because it is essentially us hacking into the programming of the varroa mites. We know that they like to reproduce on drone brood. They can smell the difference between drone brood and worker brood.

If you put in a frame of drone comb, and if your queen fills it up with eggs about the same time, then you're going to have a whole bunch of drones that are getting capped at about the same time, and those nasty little varroa mites crawling around in the hive looking for somewhere to reproduce, are going to preferentially seek out and crawl into those drone cells. If you then go through and you pull out the drone frame and feed it to your chickens or pop it into a freezer, then you've got this opportunity to sacrifice a few drones, well, we won't really miss them anyway, and also kill a fair number of mites.

As long as the colony is in a mood to raise drones, it can be a really good strategy to at least knock your mite numbers down. You might not get all of them, but certainly in the spring, I know a lot of beekeepers who use drone brood removal as part of their overall mite management, and it works pretty well. I don't know if either of you have experience doing it in your own bees.

Becky: Accidentally, whenever I, for a short period of time, put a medium frame in a deep box, meaning to switch it out, and then the bees go ahead and they put a lot of drone comb on that medium, and then I say, "Wow, this is really good timing." I pull it out and just scrape the frame.

David: Yes, just wait for it to get capped, cut it all off, and toss it elsewhere, toss to the wax to be rendered or something like that.

Becky: David and Jeff, what do you think about that? You can put the specialized frames in so that the bees draw out the actual drone cells, and you've got a full frame, or you could let them see if they're going to build that comb on the bottom of smaller frames.

David: Certainly, putting a small frame in a big box is a cheap and easy way to do it. The only real disadvantage that I see there is that because you have to destroy the comb to get all of those drones out of there, you are necessarily imposing that extra cost to your bees, where they have to rebuild all that wax if you want to do another cycle of it. If you freeze a drone frame and then leave it in the freezer for 48 hours, bring it out, let it thaw, and then put it back into the hive, they'll rip out all the drones and dead mites, and then they can immediately reuse those cells.

There's an economy to using those specialized frames, but yes, absolutely, there's nothing wrong with someone who just throws a medium in a deep box, lets them build a patch of drone brood, and then cuts that out as part of trying to vacuum up some of those excess mites inside the hive.

Jeff: If you're going to use a drone brood frame—and they're typically green, right?—where in the brood box do you place it? Is it an outside frame or towards the center?

David: Ideally, you're going to put it in the place where the colony is going to build its own drones naturally. Bees will build drones wherever there's drone comb, and they'll build drone comb until they feel like they have enough, and if you cut open a bee tree and look at what percentage of the comb is drone versus worker-size cells, sometimes it's up to 30% drones. They'll have a few drones here, a few drones there, a lobe of drone comb here, a lobe of drone comb there.

More often than not, people find the most success when they put the drone frames towards the edges of the brood nest, not on the very outside boxes, that's often just going to be filled with honey, but towards the edges where it's a little bit cooler, where bees in nature are more likely to raise their drones if you give them their druthers.

Becky: I would also say and suggest that if you're going to use this method, a calendar event that actually supports your timing of the event, it's the difference between you raising mites and calling mites.

David: It's really the matter of life and death for your bees. When I was doing research and I had to make mites kill colonies so I could study how that would happen, the easiest and best way to do it was simply to fill a colony with drone comb and then never take any of it out because they raised all those drones and they raised all those mites and the mite population grew exponentially, and the colonies all collapsed.

If you can't trust yourself to be absolutely rock solid ironclad with that calendar, it goes in on this day, it comes out on that day, then you shouldn't be messing with drone brood removal because it's giving the mites everything they've ever dreamed of if you don't pull it out before those cells start to have the drones emerging from them.

Jeff: One of the new options that people are talking about now is the use of heat or heating the colony.

David: Yes, it's a new option, and it's also an old option because people keep inventing heating tools to kill varroa mites, and they keep not quite working.

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David: It's the short version of it. It's a really good idea in principle. We know that varroa mites, and this is true of a lot of parasites, that the parasite is more sensitive to temperature changes than the host is, because a bee has to fly outside the hive, be inside the hive in cold weather, in hot weather. Varroa mite is in a climate-controlled beehive year-round, and so they are more sensitive to heat.

The idea is that if I can heat up a hive, I can heat up the varroa mites and kill them or hurt them, and I won't hurt the bees because they can cope with it. The issue is bees spend an awful lot of their time and energy climate-controlling their hive. They don't want it to be the wrong temperature. They don't want their brood to be the wrong temperature. They harvest all of that honey so that they can keep themselves warm when it gets too cold. They pull in gallons and gallons of water so that they can evaporate it and keep themselves cool when it's too hot.

By trying to go in and artificially heat the colony so we can kill the mites, we're essentially fighting against these bees, and bees are pretty darn good at controlling their own temperature. There's some methods that involve using the sun to heat up part of the hive. There's some methods that involve basically using a little electric space heater to heat them up. There are some methods that involve actually putting a little resistance coil, a little wire coil, into your foundation so you heat up the core of the comb and you kill the mites that are down in it, but you don't hurt the brood because it's not quite hot enough that the brood suffer even though they're in close contact with the wire.

They're all really smart, clever ideas. I just haven't seen one that really controls varroa consistently.

Jeff: Yes, and at scale.

David: Oh, yes. To lug a space heater and a fan from hive to hive to hive and have to heat them up for 20 minutes at a time is not something most beekeepers are interested in doing, especially if they've got 20 or 200 or 2,000 colonies.

Jeff: One of the big options that we first had was the IPM board or the screen bottom board, that's almost the default bottom board these days. A lot of folks use the screen bottom boards, and there was a period of time where they were being sold so you could monitor how many mites were falling under the hive, but they also were meant to cause those mites to fall down and then get eaten by ants down on the grass or something like that.

Unfortunately, for the most part, by the time a mite is falling down onto the bottom of the hive, she's probably not going to be reproducing too much more in that hive. She's pretty well at the end of her lifespan. The mites that you lose aren't really the mites that are causing that much trouble for you. There was a big meta-analysis that was done a few years ago, basically taking a bunch of scientific research and then looking at the average results of all of them.

What they found was that using screened bottom boards, very, very, very, very, very, very, very, very, very slightly reduced the total number of mites in the hive, but it didn't solve anybody's problem. It's a good monitoring tool, but I don't push screen bottom boards for mite control. Yes, it's true that a live mite might get unlucky and stumble and fall down onto the bottom board, and yes, if it's a solid bottom board, she'd be able to crawl back up and get onto a bee. Sure, you're going to get some advantage, but it's not really enough to move the needle very far.

I guess, on the same vein, I would also bring up powdered sugar dusting because there's some folks who are reading about how they can monitor for mites, and they read about the sugar shake. They read that I can take powdered sugar, confectioner's sugar, put it onto a sample of bees, shake them around, and then that's going to dislodge the mites that are on those bees. They think, "Hey, wait a second, I can afford a fair amount of sugar."

They go to the grocery store, they buy a 5-pound bag of powdered sugar, and they dump that all over their hive in between every frame, and they cover up the bees. You wind up with a whole bunch of powdered white bees, and they do start to groom themselves. As they groom, they will dislodge some Varroa mites. It's not totally crazy, but you have to put an awful lot of sugar into a hive just to dislodge a pretty small number of the mites.

Most of the mites are protected inside the brood, so even if you did knock every single mite off of your bees by dusting them with powdered sugar, now you've still got all of the mites that are currently reproducing, who are totally unaffected. You'd have to re-dust, re-apply over and over again. I think Randy Oliver actually did a pretty neat little experiment on this, where he took one colony, and he dusted them aggressively, and then he took all the bees that had survived, and he alcohol-washed the entire colony. He killed them all, and he counted how many mites were left. What he found was, yes, a fair number of mites got knocked off, but a whole lot of mites were still there.

If you're looking for a treatment for your bees, we've already talked about a lot of treatments that are a lot more effective than dusting with powdered sugar. Sure, it does knock a couple of mites off here and there, but I think your question is, how much do you want to disturb your bees, and how much time do you want to spend out working a hive doing something that just isn't nearly as effective as these other strategies?

Becky: Powdered sugar has starch in it, and we don't know what the bees are ingesting. That's a whole nother study.

David: If I dump 5 pounds of powdered sugar into my bees, and then I harvest the honey that they're currently storing, what percentage of that honey is just dissolved powdered sugar? Can I really know for sure that I'm not basically sitting there adulterating the honey that I harvest? It's not a game that most beekeepers are interested in playing.

Jeff: One of the most popular non-chemical treatment options are brood interruption. There's multiple ways to produce a brood interruption with the queen. Let's talk about that for our remaining time.

David: Sure. Brood interruption, again, it's based on this principle, the idea that if the mites are trying to reproduce, running around looking for a cell to dive into to start laying eggs, and there just aren't any cells that have brood of the right age for them to reproduce on, that it seems like those mites are a little more likely to get caught unawares, grabbed by a bee, groomed and knocked down, or maybe they die of old age before they get a chance to lay eggs.

We know that interrupting brood rearing in a colony can help with varroa. It will both reduce the number of varroa in the hive, and obviously, no more can get in or can be reproduced because there's no brood to reproduce on. There are some folks who do it very simply. I was just talking to a beekeeper a couple days ago who was telling me that they know beekeepers who regularly just pinch all of their queens in their hives in the spring. The bees will make a whole bunch of honey during that honey flow while they're requeening, and by the time they've requeened, they've had a nice brood break, and they have lower varroa counts.

You can do that. You can just kill all your queens and wish the bees luck, and that will introduce a brood break. Most beekeepers aren't interested in that strategy, so there are other methods that have evolved. One of them is splitting the colonies. Making splits, any kind of split, is going to interrupt brood rearing one way or another. One side of that split gets a queen, the other side either has to make a new queen cell, or they need to get a new caged queen introduced to them. That's going to give them at least some time for a little brood break.

There are beekeepers who will do deliberate splits, where they'll basically pull all of the capped brood out of a hive, and that becomes one side of the split. That one has brought a whole bunch of varroa mites in with it, and they need to be managed one way. The other one has no capped brood, and they're the one that is potentially going to be easiest to control the mites in because there's just nowhere for the mites to hide them. Even easier is you make that split, and then you go in, and you hit them with a miticide because some of the miticides that can't penetrate the brood caps are still really effective when there's no capped brood.

You engineer the circumstances for that chemical tool to be way more effective than it had been previously. Splitting and also swarming, allowing a colony to swarm. Obviously, it's not good for honey production, but it's a form of splitting that will also buy you a little bit of respite from varroa reproduction. There is that gap in the brood cycle, which means that there's some mites that just aren't going to get to reproduce.

All of those are pinching all of your queens, or splitting all your colonies, or letting all of your colonies swarm. Those are some pretty easy methods to use. You don't need to understand that much to at least get a moderate benefit, but the most exciting brood interruptions seem to be based on deliberately going in and actually caging your queens. For that, there's, again, two different ways that you can do it.

If I'm caging my queens for mite control, one option is to cage my queen so that she has nowhere to lay. I put her in a little three-hole queen cage or a little plastic queen cage of one design or another, but there's nowhere for her to lay any eggs. I leave her in there for a while, might be one week, two weeks, three weeks, and then I let her out again. As long as she starts laying eggs again, I've created this great big brood break, and I've interrupted varroa reproduction. Maybe I'll also hit them with a treatment when there's no brood, and I can really, really knock my mite numbers down.

The problem is she may not start laying eggs again. If I cage a queen for three or four weeks, and then I put her back into a hive, there's no telling whether or not she's going to lay eggs and get right back into the swing of things or if she and her workers are going to be so out of joint that they'll supersede her, or she might just never be able to kick the machinery back into gear again.

The other way that you can cage your queens for mite control is that you cage them with a cage that goes around a frame, around some comb, so the queen has the opportunity to lay eggs inside of it. The advantage there is that my queen, while she's all caged up, still has some comb. She's still laying eggs, so she's not shutting down all of her machinery. There's still brood pheromones. The bees are a little happier with her, but we've limited that brood nest to just inside the cage.

The downside is I've still got a place where mites can go. If I am not careful about it, I can cage up my queen, have her lay a bunch of eggs, have all of those young brood inside that frame get riddled with mites. Then, when they start to emerge again, I've increased the number of mites in the hive. That queen caging with the frame cages also requires removing the frames of capped brood before the mites are able to come out and mature.

It winds up being a two-part method. Number one, I cage my queen, and I keep her laying. Then number two, I'm going in a set schedule, maybe once every two weeks, and I'm pulling out the frames that have capped brood, and popping them in a freezer or melting off the comb, scraping everything off, sacrificing the brood, but also killing those mites. That has the advantage over the queen in a three-hole cage that she does keep laying, but it has the disadvantage that now I've got to do more calendar work. I've got to make sure that I'm pulling out the frames at just the right time.

Jeff: Have there been any studies that show that caging a queen can harm her or length of time that it becomes harmful?

David: I've done some work with caged queens myself, where we've caged queens, just queens that were here for sale, and kept them in cages for longer than we were comfortable selling them to a customer, and then putting them into hives and monitoring exactly how many days it took them to start laying again. What we found was that some of those really, really old queens, I think we've set the experiment up with 12 of them. I think four of them were killed. They weren't accepted, and I think part of it was because they didn't smell like a functional queen, and the bees weren't interested in accepting them.

Of the ones that were accepted, about four, maybe a third of them, I think, started laying eggs quickly within a day or two, and they pretty well got off to the races and were perfectly normal queens. The other ones, it took them sometimes up to a week to start laying eggs again properly. If I've caged my queen for two weeks, three weeks, now I've got another week before she lays eggs, there's a real genuine cost to the colony.

If I've got a month where no eggs are being laid, yes, the colony might survive it, but they're certainly not going to be thriving. They're not going to be primed for a great big honey flow in the next couple of weeks because they're going to be trying to desperately recover from this weird lack of brood that they've been suffering through.

Becky: We talked to Dave McComb about this, and he's able to complete the honey harvest. Then, when they go into their summer dearths, that's when he's caging them. Then I think he does a oxalic treatment, and then once those bees start going again, they're raising-- honestly, they're winter bees starting in August, but they're doing it without that mite pressure.

David: Yes, that's an excellent model, to be able to go in and basically time your queen caging so that it lines up with your dearth, so that when the bee colony's instincts might be saying, "Grow, grow, grow," you the beekeeper says, "No, no, no. I know what state you're in. We're not in Italy anymore. We're not in Carniola anymore." It's going to be time for a little bit of a pause on colony growth."

Yes, there are beekeepers who will very judiciously do this, but a lot like the drone brood removal, what that means is you're limited in when you can do it, because tamping down brood rearing is a good strategy right before a dearth. It's a bad strategy right before a honey flow, and trying to do drone brood removal in the fall when your bees are getting ready to kill all their drones and don't want to raise any more is not going to be a good mite control strategy.

Jeff: During the winter, when bees are coming out of storage, you hear about the increased CO2 in the storage units. Is that showing effectiveness to varroa control?

David: The CO2, again, it's like heat. It's something that the mites are a little more sensitive to than the bees are. Is putting a bunch of CO2 into a colony going to kill all of your mites? No. Are there examples where we can find CO2 that anesthetizes the mites, makes them knocked out so the bees can then grab them and bite their legs off? Sure.

There are even some mite sampling techniques that are based on that idea, putting a little dose of CO2 into a jar and then knocking all the mites off because of it. I think there's always going to be more tricks that we as beekeepers work out that let us say, "Hey, these mites really like drone brood. Let's pull the drone brood. Hey, these mites really don't like it when we cover the bees in powdered sugar." I think there's going to be more opportunities for us to be clever, but for now, the cleverness only goes so far, and a lot of it tends to be pretty seasonal, which means that what seems to work the best is combining some of these non-chemical control methods with using some of those chemicals.

If you want to reduce the number of chemical miticides you use, more power to you, but I think that if you do it, you want to make it count. If I'm only going to do one oxalic acid dribble this season, I want to make sure that I've got no capped brood in that hive so that I'm really, really hitting those mites hard. I might be doing some drone brood removal earlier in the season to compensate for that spring buildup of varroa.

By combining these different tools and methods together, I think it winds up making people much more capable mite managers, and it also requires being a little more thoughtful about what you're doing. You have to understand what you're doing. You can't just read the recipe that says, "Go in on this date and treat with this, and go in on that date and remove that drone comb." You really have to know what's going on to keep those mites under control.

Jeff: Thank you, David, for talking about the non-chemical management controls for varroa, and we'll look forward to talking to you again.

David: It's always a pleasure to join you guys. Thanks, Becky. Thanks, Jeff.

Becky: Thanks, David.

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