By: Tina Sebestyen
Tina Sebestyen
As mentioned in my previous article, miticides, and even organic miticides, have detrimental effects on honey bees at all levels; workers, drones and their sperm count and viability, and queens and their reproductive capacity. This is why repeated treatments and prophylactic treatments (when you don’t even know if you need them) are such bad ideas. Don’t get me wrong, treat when necessary or be prepared to kill a colony if you are unwilling to treat. But, there are all kinds of things we beekeepers can do to help our girls keep mites under control. That is the topic for this month.
Life Cycle of Varroa destructor
Varroa mites live in our honey bee colonies and reproduce inside brood cells along with our baby bees. The foundress mite (the mother) enters a brood cell in response to pheromone signals of the larva as it prepares to be capped and pupate. She then hides under the larval bee in the royal jelly until the larva spins its cocoon. Then she sets to work. She lays her first egg 60 hours after capping occurs, this will be her son. Every 30 hours thereafter1, she lays another egg, girls from here on, that will hatch and mate with their brother. The baby mites are all white at first, and as they age, the girls turn light red. The male stays white and will never develop the exoskeleton that would harden and allow him to live outside the brood cell. The food for the mother and all of her babies comes from the pupating bee. The foundress marks the side of the cell in the ten o’clock position with frass, or mite poop, so that her babies can find the place on the bee where she has drilled a hole and injected digestive fluid into the bee’s fat body (kind of like a liver) so that they can eat and grow big and strong and ready to reproduce. Mites also inject viruses into bees, which means that the bee is not only compromised by having its fat body eaten, but it also needs to fight a disease, often this is Deformed Wing Virus.
Mites in drone brood. Varroa destructor loves to reproduce with drone brood. This makes it easy to cull them.
What the Fat Body of Honey Bees Does2,3
The fat bodies of honey bees store energy, just like our livers do for us humans. This energy will be used to fuel the bee’s metabolism, help regulate brood nest temperatures, and in Winter, get through times when it is too cold for the cluster to move to honey. Fat bodies help bees get through times of decreased nutrition so that they can continue to feed larval bees properly. They also store other nutrients, such as 24-methylene cholesterol which must be fed to larval bees in order for them to shed their skins and grow from one in-star to the next. A larval bee that does not receive this nutrient, either from in-coming pollen or fat body storage in the nurse bee, dies since it is imprisoned in a too-small skin.
Fat bodies help bees mount an immune response to viruses and bacteria (and remember, mites carry these diseases to the bees). They help adult bees synthesize lipids, otherwise known as beeswax and oil. One of the things bees do with wax and oil is to coat their exoskeletons with cuticular hydrocarbons to help regulate hydration and keep diseases from entering through the skin. Bees with a too-thick cuticle cannot dehydrate poop that they must hold during the Winter, they get too full of fluid, stop eating and die of starvation with food right there, but no room to hold it. Bees with a too-thin cuticle get dehydrated and die, or get a disease.
Bee must also detoxify pesticides, and that doesn’t just mean Round-up and 2-4 D. Plants themselves produce toxins to keep bugs from eating them. Bees bring these chemicals home in the pollen, and their fat bodies help them utilize this food without harm to themselves. Fat bodies fuel pupating bees while their cells re-organize in metamorphosis, and are crucial to storage and production of vitellogenin, a hormone critical to many things in the honey bee. All that is to say that it is very important for us to keep mite numbers low, rather than just knocking them down with poison periodically.
Medium frame with drone brood. When a medium frame is placed in a deep hive body, the bees will often draw drone comb below the bottom bar. This can easily be cut off, though cutting on this one should be done judiciously, since there are active queen cells in the middle of it. As a bonus, this frame could be used in the first super to draw bees up into a new hive body.
Integrated Pest Management Techniques
It has been said that the first step in IPM is monitoring for mites, and that surely is very important. As a seasonal timeline, however, the first step in IPM is drone brood removal.4 In the Spring, mites are as anxious to reproduce as honey bees are, and even more than the usual 75% of the mites in the colony will be under brood cappings. Mites prefer drone brood to reproduce with since the longer pupation time allows for more mature mites to emerge with the drone than could occur with female bees. So, removing the first batch of drone brood in early Spring will eliminate many of the mites within the colony. This can be done quite easily by purchasing the green plastic frame with bigger cells embossed on it. Other methods are adding a frame without foundation to the edge of the brood chamber or a medium frame into a deep hive body. Without foundation as a guide, the bees will often draw comb for drones or honey (which will work for drone brood). These frames of drone brood can be frozen for 24 hours and returned to the hive for cleaning, or simply cut out and fed to the compost pile (my chickens don’t like drone brood at all). The trick is doing this on time, without fail. If the drone brood is allowed to emerge, the mite population may increase dramatically. It takes 24 days for drones to emerge from their cells, not a month. Drone brood can be culled any time after it has been capped. I remove drone brood throughout the Summer. I don’t pull all of it, but the big clusters or full sheets that I find go in a nuc across the yard, which will usually make its own queen. I put a milder miticide in this nuc to knock the mites off of the emerging drones, so that I can still help with filling DCA’s, but am not producing my very own mite bomb.
Cultural Control
These are things that affect the entire colony. One example is apiary location. Hives that are in full sun have mites and small hive beetles that are less able to reproduce because it is warmer and may even have temperature spikes as bees work harder to maintain a proper interior climate.5 Another cultural control that is not relative to mite monitoring since it should always be done is having mite-resistant queens. There are several mechanisms by which bees themselves work to control mite numbers; grooming one another and themselves, biting the legs off of mites (ankle-biters), removal of sick pupae (hygienic bees), removal of mite-infested bees (VSH), Pol-line queens, Russian queens and others. Mite resistant queens can be bought and should be monitored to ensure that later generations remain resistant (unlikely).
Physical or Mechanical Controls
The previously mentioned drone brood culling is a physical control. The second most important physical control is the brood break. That means that there needs to be a time in each colony when there is no capped brood. Life is dangerous for mites when they can’t hide under cell cappings. They can be damaged, bitten or fall off of bees. They are vulnerable when in their dispersal phase (what used to be called the phoretic phase). Timing of the brood break is important. Mites can out-reproduce bees if a queen is allowed to produce enough consecutive brood cycles. This leads us to the July re-queening mentioned in my July article. Caging of the queen, either in a standard cage or on a sheet of drone comb can work, as well. Adding a sheet of young drone larvae from another colony to an otherwise broodless colony is what is known as Dutch Drone Brood Trapping.7 All of the mites in dispersal will gravitate to the drone brood just before it is capped, and this can be culled.
Screened bottom boards were previously thought to reduce mite numbers since mites dislodged from bees would fall to the ground and be unable to climb back up into the hive. It has since been discovered that a screened bottom board with the slider (the mite drawer) removed, actually increases mite reproductive success.6 With the slider out, the hive will be a bit less humid, and mites reproduce better in lower humidity. Yes, the bees are working to maintain the humidity in a range suitable for honey bees. It just so happens that at the lower end of that range, mites do better than in the higher end of the range.
Also, the higher humidity that is present in a hive with a solid bottom (or screened bottom and slider) means that the bees work harder to maintain perfect brood temperatures. More humidity equals higher temps, and even temperature spikes, which also can kill mites or reduce reproductive success. Honey bees do quite well at the top end of both humidity and temperature ranges maintained within the hive, mites do well at the lower end. A screened bottom with a greased slider works great for capturing fallen mites.
A mechanical control that is important but not well-known as a mite control measure is removal of old brood comb. We all know that old comb harbors disease pathogens and pesticides, but as it turns out, old comb is invaded by reproducing mites four times more often than newer comb.8,9 As brood comb is successively used for brood-rearing, layers of cocoons and feces reduce the distance from the cell rim to the surface of the comb. Mites are then able to more easily detect the pheromones that the larval bees are using to signal readiness for capping.
It was thought for a time that since smaller bees emerge a bit sooner, mites would be less successful in reproducing in small-cell comb. This has since been disproven. In fact, mites can increase over-all numbers more quickly in small cell combs, since each comb contains more larval bees, and thus more places for mites to reproduce. One study found an average of 5.1% mite load in small cell colonies versus a 3.3% mite load in current standard-sized foundation colonies.10
Biological Control
An example of biological control is keeping a cat for catching mice. In honey bee colonies, this means finding a bug that eats or kills mites. One such bug has been found, the pseudoscorpion, but when introduced to colonies it mostly moved to the floor of the hive where it lived in the duff and ate already-dead mites. More work is being done on this, but it isn’t there yet. Work in developing microbes or fungi that attack mites is also failing to deliver so far.
Monitoring for Varroa
While the previously mentioned mite control strategies should be practiced all of the time regardless of mite loads, monitoring for mites is the only way to know when a chemical control should be used. Monitoring not only alerts us to dangerous levels of mites, it also helps us find genetic lines of bees that naturally keep mite numbers lower. The alcohol or detergent wash is considered the most accurate method by busy scientists. Many backyard beekeepers would prefer to use the powdered sugar method since it doesn’t kill bees and isn’t quite as big a risk to the queen if she should happen to be accidentally included in the half-cup of bees necessary. When powdered sugar is used properly, it can be equally effective, the term “properly” being of prime importance here. The way to learn to do an effective powdered sugar roll is to follow it with the alcohol or detergent wash. If more mites fall during the alcohol wash after a powdered sugar roll has been done, then the beekeeper needs to shake the bees in the sugar more vigorously, for longer, or both, until no more mites are washed off in the following alcohol wash.
Powdered sugared bees. When done properly, a powdered sugar roll knocks off bees for counting. Four of five bees will die, but the rest will be fine. If half of them die, or take a long time to recover, you are shaking too hard. Check yourself by following with alcohol until you learn to get it right.
The timing of monitoring and real control of mites is important. The fat Winter bees will start to emerge in late August to mid-September, depending on your microclimate. Mite levels should be very low when these eggs are laid, so that the bees that need to survive Winter, help heat the colony and feed Spring brood have intact fat bodies and are disease-free. We can’t have mites damaging our fat Winter bees while they are pupating.
The astute beekeeper may be asking why we can’t use powdered sugar as a mite control agent, since it obviously knocks mites off of honey bees. Good question! This can be done, but it is very labor intensive. Since powdered sugar desiccates larval bees, all of the adult bees need to be removed from the colony and shaken with powdered sugar in a hive body that has a solid bottom and screened top. Just dropping powdered sugar between the frames does not work.11
The HoneyBeeHealthCoaliton.org website is great place to find up-to-date information about acceptable mite percentages and both organic and non-organic treatments. Even repeated chemical treatments are not very effective if no IPM is practiced, and those treatments are harmful to honey bees, since we are trying to use poison to kill a tiny bug on a slightly larger one. Be pro-active with IPM and be a better beekeeper with healthy, long-lived bees.
Tina keeps bees in three kinds of hives, and loves to speak to bee clubs about honey bees. For a list of topics, visit her web page at https://beequest.buzz, or contact her with bee stories or questions at bee.seeking@gmail.com.
- John Zawislak, illustrator, Honey Bee Biology and Beekeeping by Dewey M. Caron and Lawrence John Connor, 3rd Edition, 2022, pg, 382
- Otis, G. W. The Winter of 2021-22: What happened to Ontario bees? https://www.ontariobee.com/sites/ontariobee.com/files/Winter%20of%202021-What%20happened_0.pdf
- Ramsey, Samuel D., et al. “Varroa destructor feeds primarily on honey bee fat body tissue and not hemolymph.” Proceedings of the National Academy of Sciences 116.5 (2019): 1792-1801.
- Holly A. Wantuch, David R. Tarpy, Removal of Drone Brood From Apis mellifera (Hymenoptera: Apidae) Colonies to Control Varroa destructor (Acari: Varroidae) and Retain Adult Drones, Journal of Economic Entomology, Volume 102, Issue 6, 1 December 2009, Pages 2033–2040, https://doi.org/10.1603/029.102.0603
- Le Conte, G. Arnold, Ph. Desenfant, Influence of Brood Temperature and Hygrometry Variations on the Development of the Honey Bee Ectoparasite Varroa jacobsoni (Mesostigmata: Varroidae), Environmental Entomology, Volume 19, Issue 6, 1 December 1990, Pages 1780–1785, https://doi.org/10.1093/ee/19.6.1780
- Jean Pierre Chapleau Experimentation of an Anti-Varroa Screened Bottom Board in the Context of Developing an Integrated Pest Management Strategy for Varroa Infested Honey bees in the Province of Quebec 2002 https://www.delta-business.com/CalgaryBeekeepers/Bee-Club-Library-2/AV-BOTTOM_BOARD1.pdf
- Adrian Quiney, The Cavity Compromise. A sustainable system: how to integrate mite control, swarm control, honey production, and the overwintering of nucleus colonies in a northern climate using biotechnical controls and leveraging the bees’ own abilities. 2023
- Willem J. Boot, Ronald G. Driessen, Johan N. M. Calis, Joop Beetsma, Further observations on the correlation between attractiveness of honey bee brood cells to Varroa jacobsoni and the distance from larva to cell rim September 1995 https://doi.org/10.1111/j.1570-7458.1995.tb01966.x
- Giancarlo A. Piccirillo, and David De Jong Old honey bee brood combs are more infested by the mite Varroa destructor than are new brood combs Apidologie 35 (4) 359-364 (2004) https://doi.org/10.1051/apido:2004022
- Berry, J.A., Owens, W.B. & Delaplane, K.S. Small-cell comb foundation does not impede Varroa mite population growth in honey bee colonies. Apidologie 41, 40–44 (2010). https://doi.org/10.1051/apido/2009049
- Aliano, Nicholas P. and Ellis, Marion D., A strategy for using powdered sugar to reduce varroa populations in honey bee colonies (2005). Journal of Apicultural Research 44(2): 54–57 (2005) Faculty Publications: Department of Entomology. https://digitalcommons.unl.edu/entomologyfacpub/175
