Managing Varroa in Summer

Varroa mites have been in the USA for over 30 years. When Dr. Chris Cripps, one of the owners of Betterbee, was working as a bee inspector in Ohio during veterinary school, mite control seemed easy: Every fall after harvesting honey, simply put a couple of strips of Apistan in each hive. Mites were brand new, people were just starting to find them, and that was the best advice at the time for controlling mites. Fast forward 30 years and we find there are still people that are studying these mites and their deleterious effects on honey bees because there's still more for us to learn. Some people even get Ph.D.s in the subject (like Betterbee's Director of Research and Education, Dr. David Peck).  

One of many dreary research benches that Dr. Peck spent his 20s sitting behind, carefully studying varroa mite biology.

So, while these smarty-pantses studied mites in their ivory towers, we have to ask: What have they learned to help us beekeepers keep mites under control?

First, the key lesson is that things change, and while something might work for you this year, there may be better techniques or products that come out in the future. If you learned to use Apistan in 1992 and you are still using it successfully, you are in the minority of beekeepers. ("Varroa," Dr. Peck explains, "rapidly evolved resistance to the chemicals in Apistan, and after multiple years of using it some apiaries will be filled with Apistan-resistant mites. The treatment is only effective on non-resistant mite populations.") In beekeeping, never think you completely understand something and that you're free to move onto the next subject. Bees and mites will always find ways to keep you humble.

Mite wounds hurt but the viruses they transmit can kill

One of the big things we have learned is that while mites might inflict damaging wounds, the biggest mite-related problems come from the viruses that they harbor and spread between bees. Harmful bee viruses might feel like a new threat to our bees, but many of these virus species have been around for much longer than the varroa mites. The viruses didn't cause problems in our hives because there was no good way for them to spread between bees. If a virus was transmitted in food, a lot of virus particles had to be transferred to the next bee to make her sick. Usually, the bees poop out most of the virus, and only a few viruses could get through the intestines and into the hemolymph (blood) of the bee. Very few bees ate enough virus particles to become sick. With the mites on the scene, everything changed. The mites stab holes in the bees so they can eat parts of their internal organs. They act like dirty hypodermic needles, spreading viruses right into the inside of the bee. Many bee viruses can make the bee sick with a lot fewer individual virus particles if they are injected directly into the bees.  

Once we learned that mites spread viruses between the bees, we knew to start looking for the effects of viral disease on our bees. Back in the 1990s, the only virus we worried about was Sacbrood virus. Now, there are over 20 named viruses that have been found in bees and mites. The viral effects include things that are easy to see like deformed wings, or blackened queen cells, or greasy hairless bees, or paralyzed bees. The viruses might have other effects that are harder to see. How do we see that a bee has lost her memory or sense of direction and cannot find her way home? Or that she ages prematurely and skips out on some of the duties that bees are supposed to do as they mature in the hive?

Deformed wing virus bee.

As we study these viruses and how they affect bees, we are also learning more about the honey bee immune system. Vaccinations are in the news a lot now, so most people understand that vaccines cause an "antibody response," where the body learns to recognize and attack proteins on disease-causing microbes. Many people don't know that vaccines can have an effect on the "cellular" part of the immune system, where specialized immune cells find and then consume or destroy invading microbes. Bees do not make antibodies, so they rely on other forms of immunity like cellular immunity. These immune cells can sometimes reduce the amount of virus in a bee's body, but sometimes the virus will overwhelm the immune system and kill the bee. If you want healthy bees going into the winter (you do!) you've got to keep the virus levels low before the colony starts making long-lived winter bees. If you treat mites late in the year, you may kill a lot of mites with your treatment, but maybe not in time for the colony to reduce the virus levels inside the hive. You will probably need to treat one or more times during the summer to reliably control mites, and to keep the virus levels from increasing and increasing to out-of-control levels by the time winter bees are being produced.  

Summertime mite treatments have several issues that you need to consider:

• During the summer, bees are often collecting honey for human consumption. It is important to use products that do not have honey super withholding times (an amount of time after the treatment that you can't put honey supers on your hives) to avoid contaminating your honey crop. Formic Pro and HopGuard are two products that do not have honey super withholding times.  
• Formic Pro must be used at the proper temperatures. On the low end, it needs to be warm enough to make sure the formic acid can off-gas out of the gelatinous matrix that forms the Formic Pro pads. On the high end, it needs to be cool enough not to have the formic acid off-gas too fast. The label says the temperature needs to be 50 to 85 degrees F. You must be especially careful to avoid those high temperatures during the first 3 days of the treatment when most of the formic acid leaves the product, not during the entire 14-day treatment.  
• Many mites will be under the cappings of the brood where they feed on the pupating bees, reproduce, and hide from most contact miticides. HopGuard is a contact miticide while Formic Pro is a gas that can penetrate the cappings to kill mites where they hide. To kill mites under the brood caps, we recommend the full-strength Formic Pro treatment that involves simultaneously applying two pads to each colony.
• Hives that do not have the regular Langstroth hive configuration might not have enough ventilation to accommodate Formic Pro and to allow the appropriate amount of ventilation of the formic acid vapor. In our double nuc boxes, the entrance is very small because the hive is divided down the middle, so we have to use a treatment other than Formic Pro in these hives. Since these double nuc hives spend their summer and fall growing before we sell them in the spring, we do not harvest honey from them and we can treat them with Apivar, whose label prohibits its use in hives that are making honey destined for humans.

So, if you did not do the summer treatments, is all lost? No! You've hurt your hives' chances to survive the winter, but they are still far from zero. One good approach would be to put on an Apivar treatment as soon as you've harvested any honey you plan to take this year. The label for Apivar says to insert a strip for every 5 frames of bees, and then to leave it in for 42 to 56 days. A hive that has bees on all frames in two deep boxes would thus need 4 strips. (The product comes in packages of 10 or 50 strips.) Once opened and exposed to oxygen, the active ingredient starts to degrade, so you don't want to store Apivar for later use. Leave the strips in for 56 days to have maximum contact time between the treatment and the bees, and therefore the highest mite kill. 

At Betterbee we even give our bees a vaporized oxalic acid treatment in the winter, to keep mite populations low throughout the year.

We know a lot more about mite treatments than we did 30 years ago. One of the most important findings is that you need to keep the virus levels low throughout the year, and especially before the colonies are making winter bees.  This means you must apply treatments earlier in summer to keep mites under control while avoiding honey contamination with the treatments. To navigate this, carefully read the labels for each treatment so you can follow the directions sent by the manufacturer. And if you are late on your summer mite treatments this year? Don't give up - treat the bees as soon as possible to try to help them get rid of the mites, hope for the best this winter, and plan to stay on top of mite control even better next summer.