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The Classroom

The Classroom – April 2022

- April 1, 2022 - Jamie Ellis - (excerpt)

The Classroom - ABJ - Jamie Ellis
OAV vs. Apivar in winter

 There is a difference of opinion on whether or not to use Apivar in late December/early January or use an oxalic acid vapor (OAV) treatment. Some do OAV and not Apivar; however, old-schoolers seem to prefer the strips. Some think it is too risky putting strips into a cluster for fear of

1) unnecessarily killing bees and

2) possibly rolling/killing your queen midwinter. What are your thoughts?

Ray Johnson
New Jersey, January



I am a big fan of rotating treatments throughout the year. That way, Varroa is less likely to develop resistance to the treatments we have available to use for its control. With that in mind, my strategy to control Varroa relies heavily on using treatments that demonstrate high efficacy against Varroa when considering two major criteria: (1) What time of year is it when the Varroa population needs treating, and (2) what is the colony condition at that time? Let me elaborate.

The time of year is incredibly important for each treatment. For example, I can use Apivar throughout the year. It is always available as a tool for treatment against Varroa, pending the label conditions are met (as an example, the treatment is applied when colonies are not producing harvestable honey). In contrast, I cannot always use formic acid and thymol-based treatments throughout the year. This is because the outside temperature often exceeds the temperature range listed on the product labels. Put simply, it is often too hot in Florida to use these products. Thus, I need to save them for use when the labeled temperature conditions are met. In practical terms, I can use Apivar much of the year but I can only use formic acid or thymol products from late fall to early spring. Consequently, I try not to use Apivar during winter when other products are efficacious.

What about “colony condition”? Colonies undergo a number of phases throughout their yearly lifecycle. In spring, they are growing fast and rear a lot of brood. In summer, the population of adult bees and brood has stabilized. In fall, the population of both begins to decrease. In winter, the population of bees slowly decreases while there is nearly no brood at all.

What does all of this have to do with the treatment I choose? Well, oxalic acid treatments are not that efficacious when colonies have brood, especially a lot of brood. This is because a large percentage of the mites go into brood cells to reproduce. An OAV treatment at this time will miss many of the mites in the hive, effectively rendering the treatment moot. That said, OAV is a great treatment in late fall/winter because all of the mites are on adult bees, given there is little-to-no brood. In times like this, you need to use a treatment that demonstrates efficacy over time due to how the treatment is administered (such as in a strip).

Putting all of this together, I make my treatment decisions based on efficacy, labeled use, colony condition, and time of year. When possible, I rotate treatments as much as I can. Even still, I strongly recommend sampling the Varroa population before treatment and after treatment, just to make sure your treatment works. This treatment strategy should be built on the back of non-chemical control options (resistant queen stock as an example) and administered under the umbrella of Integrated Pest Management.

The members of the Honey Bee Health Coalition have published a lot of information about this topic on the coalition’s website: They even developed a decision support tool to help you know which treatment to use and when to use it, all based on colony condition, time of year, labeled use, and product efficacy. Please check out the decision support tool. You will not be disappointed!

Ok, I recognize I have been rambling and have not answered your questions directly. I would probably use OAV if the labeled conditions are met. As noted, I would do this in an attempt to save the Apivar treatment for a time of year/colony condition for which it is the best option. Incidentally, I plugged your exact situation into the Honey Bee Health Coalition’s decision support tool and it told me that OA was one of my two best options (the other being Hopguard II). Apivar was not listed, not because it is a bad option, but because it would be better to use OA during the season it has its highest efficacy. Apivar strips would probably be easier to apply, but I think OAV remains the better option, purely from a chemical rotation perspective.

Back from the dead

 As a backdrop, I treated for Varroa right up into early December and began feeding in October or November, depending on the colony and weather conditions. I feel Varroa were under control following treatments. All of my colonies appeared healthy and active right up to the 23°F weather we had in early-to-mid January. With intermittent warm afternoon temperatures just prior to that, we had a strong flush of pollen deliveries. I felt like my colonies weathered early winter and were ready to tough out January and February cold snaps.

On January 23, I stopped at one isolated colony at the edge of clear-cut. This is a colony started from a package I bought last spring. Bees were not flying in the sunny afternoon, even with the temperature above 50°. I suspected the colony either froze or starved. Hesitant to open the hive, I found a very small, motionless cluster, many worker bees with heads down in the cells and no honey adjacent to the cluster. There was nectar in the super above the brood box.

I took the colony to the house. There were two seams of bees on 2-3 frames in a small cluster. I took it apart, videoed and inspected the bees. No activity whatsoever. I took one frame into the house to give a closer inspection of the bees and comb. All bees appeared dead, even my marked queen. I did see capped and uncapped brood showing the queen had been laying fairly recently. As the bees warmed to the inside temperature, I noticed they started to move after only 10 minutes! Even the queen appeared to be recovering. I began my first bee triage! I leaned over them and breathed on them and they responded to the warm air with more motion. I went outside and looked at the other frames sitting in the sunlight, and they too showed movement!

I assembled a 5-frame nuc and put the frames of bees and brood into it, adding a super with frames of nectar from the original colony. Much to my wife’s concern, I kept the sealed nuc in the house, isolated in a bathroom overnight. The next day, I moved the colony to an outyard miles away from home. When I unplugged the entrance, they happily walked onto the landing board and started orienting to their new home. The next time it is sunny and above 45°, I will go see if they are flying. The recovery of the bees and particularly the queen, all on video, seemed nothing short of miraculous, or was it?

So here are my questions. 1) Have you ever seen bees go into such a state of apparent near death and recover like that? 2) Is it possible that, rather than bees going headfirst into cells to eat and die, that maybe they are actually trying to keep warm and survive nestled in the cells?


Ken Leach,
South Carolina, January


I was chuckling my head off while I read your question. As I was reading, I knew exactly what was about to happen. It was déjà vu! Let me tell you my version of this story and then I will tell you what is happening.

I was very active in science fair when I was in high school. For my project, I administered a synthetic bee hormone to colonies and observed treated bee behaviors in observation hives. My parents did not allow me to manage the observation hives in the house. Instead, I had to keep my observation hives in an un-insulated shelter that my grandparents had on their farm. This building got very cold during winter so I had to insulate the observation hives to keep them from freezing. I checked them daily as part of my experimental design. One day, I was dismayed to find that one of the colonies had died. I assumed they had frozen to death (which I also felt I was going to do in that old place). I grabbed the observation hive, took it home, and placed it in the utility room, utterly destroyed that I had let a honey bee colony die.

The next morning, I heard my mother scream my name from across the house. I ran to the utility room to see what had happened. Her reason for screaming was obvious when I opened the door. The bees had reanimated and were flying around in the room. Not only were the bees alive, but I did not plug the hive entrance given I thought the bees were dead. I learned something very important that day. Bees can get to the point of freezing, but then “come back from the dead.”

Of course, they were not really coming back from the dead. Only one person has ever done that successfully. Instead, the bees were never dead in the first place. As you know, bees begin to cluster when the external temperature drops below 60°F. Clustering involves forming a tight layer of bees between frames, coupled with bees going headfirst into cells in the frames. This allows them to make a more cohesive cluster. When clustering, they use honey stores available in the hive as an energy source to generate the heat needed to survive. The bees cluster even more tightly when it is very cold. This is the point at which small colonies can die. They simply do not have the mass needed to keep the colony warm.

In my case, the single-frame observation hive was in considerable danger of freezing to death (your colony probably was too). Had I left it in the uninsulated house for 2-3 more days, the bees likely would have frozen. Bees can get so cold that they cannot break cluster to get to the honey they need to heat the colony. When this happens, they are doomed unless something occurs that allows them to break the cluster and get to the food. This can come by way of a natural warm spell, or by someone like me/you assuming they were dead and bringing them into our warm house. ☺ When the latter occurs, the bees warm up and give us quite a surprise.

To answer your questions: (1) Yes. I have seen this before. (2) Bees do go headfirst into empty cells as part of the clustering process. Now, you have a great story to tell the rest of your life.

Q  Requeening a defensive hive

 The February issue with the two questions about smoke was of interest to me. Last fall, I inherited two Apimaye hives that had not been cared for the last year or two. When I checked in early November, one hive was a deadout with wax moths flourishing. The second had two 10-frame deeps full of aggressive bees and capped honey. As I lifted a frame or two, dozens of bees hit my veil and suit. Smoke did not seem to calm them. I did notice a dozen or so small hive beetles and decided to come back with oil traps on a cooler day. A month later, and a 45°F day, did not slow them down.

My intent is to requeen this hot hive in the spring. What is the best procedure to inspect the hive to find the queen and how receptive will these bees be to a new queen? Should I divide the colony by separating the hive bodies? Can I take out several frames and place them in another hive body? Can frames without brood be placed in other hives?

I know the queen will start laying eggs in larger numbers in February and March around here, consequently producing more aggressive bees. Queens are not usually available until April. I would like to save the hive so any suggestions other than glove up and smoke them would be appreciated.

 Pat Wakeman
Kansas, January


Pat, you took away my best two options right at the end. I was going to say glove up and smoke those colonies. Nevertheless, I do have some pointers to share.

First, I have worked a zillion defensive colonies in my life. I lived in South Africa for three years. There, I encountered plenty of hot hives. Even still, the most defensive hives I have ever encountered have been here in the U.S., with the bees being of European honey bee descent. I share this to note that many folks worry that they have Africanized honey bees when they