Recently I went around to the various Runamuk apiaries to perform my annual mite-tests, and while the 12 colonies under my care have struggled to produce surplus honey, I am happy to say that compared to last year when mite problems ran rampant throughout the state–and even my own hives–this year mites have posed less of a problem.
While I strive to utilize more natural methods of beekeeping, with our transition to foundationless combs, au-naturale hives, and our continued dedication to un-heated, raw honey, I still firmly believe that control of mite-populations in honeybee hives is imperative.
What are Varroa mites?
Varroa mites (Varroa destructor) are the biggest problem facing beekeepers world wide today. Originally the parasites of Asian honeybees, Varroa were initially discovered in Wisconsin in 1987. Today they are present in every state in America, with the exception of Hawaii, and have wiped out nearly all of the feral honeybee populations. Studies have proven that without treatment, hives will eventually weaken and die within 1-3 years.
The mites are visible to the naked eye at 1.5mm, and can be found on the surface of both adult and immature bees. They are shiny, reddish-brown, shield-shaped, and can be seen clinging to bees or crawling around on hive parts. Varroa spead quickly throughout an apiary because they reproduce in the sealed cells of the brood comb, and a whopping 80% of the mite population may be hidden there, with only a minimal 20% visible upon the mature population of the honeybee colony.
Why you should monitor mite populations in your beehives
By puncturing the body of the bee and sucking the fluids, the Varroa feed on the bees, and increase the severity of diseases introduced to the hive’s inhabitants. Diseases and viruses associated with high mite levels include European Foulbrood, American Foulbrood, the Deformed Wing Virus, and Israeli Acute Paralysis Virus.
Often a hive may appear healthy and strong at the start of the season, and signs of infestation can go unnoticed until it is too late, since the tiny mites can easily be overlooked. However, by late summer or fall, colonies afflicted with high mite loads will rapidly dwindle and die once the mites have emerged from the brood cells with their host-bee. What’s more, the situation can be accelerated by the lack of a nectar flow (which may be the result of a regional drought, or by constant rain and cold weather).
Monitoring the mite populations in your hives can help you decide when to treat colonies to reduce mite populations.
How to detect current mite loads
There are several methods for assessing population levels of mites within your apiary. Ideally tests should be done periodically throughout the season, the first in the spring, again mid-summer, and finally at the end of the season as you put the hives to bed for the winter. You should also test anytime you suspect a serious problem, such as when you see signs of Deformed Wing Virus, mutated or ill-formed bees, or bees that cannot fly and merely crawl around the exterior of the hive. Observation is key in the fight against Varroa.
Methods for mite detection:
- Un-capping brood – Use a capping scratcher to open about 100 or so cells (drone cells especially, are the favorite breeding grounds of the Varroa mite). A 10% infestation is enough to start damaging the colony and you should take action to reduce the mite loads within the hive.
- Ether roll – known as the “quick and dirty” method of Varroa detection, the Ether roll relies on taking a sample of bees (a cup’s worth will yield approximately 300 bees) in a pint-sized mason jar. Spray carburetor starting fluid into the jar, which kills the bees instantly; screw a lid onto the jar, shake vigorously for about 30-seconds, then dump the bees out and count the number of mites sticking to the sides of the glass. If you see 15 mites or more, it is recommended that you treat the hive.
- Alcohol wash – again involves taking a sample of bees in a pint-sized mason jar. You can use straight alcohol (the same kind you have in your medicine cabinet–not the kind in your liquor closet!), which kills the bees instantly, or first use about an inch of alcohol to kill the bees, then add detergent such as windshield wiper fluid to rinse the mites off the bees. Commercial beekeepers with hundreds and thousands of hives often use the detergent wash, since it is more cost effective for them. Simply cover the bees in the jar with the alcohol or detergent, swirl them around for about thirty seconds, then fit a #8 mesh screen onto the jar and pour the liquid and the mites into a bowl or dish (I find a white container works best, so that you can easily see the mites to count them).
- Powdered sugar roll – another test reliant on a sample, though this one allows for release of the bees afterwards–that being said however, it is not nearly as accurate and reliable as the ether roll or the alcohol wash methods. Collect your sample in a jar, put a #8 mesh lid onto the jar to contain the bees, and put 2 tablespoons powdered sugar down into the jar. Slowly and gently, so as not to damage the bees too much, roll the jar to coat the bees. The sugar is supposed to make the mites slip off the bees. Open the jar again to release the bees, then dump the sugar and mites into your white bowl or pan to count the mites. You can add water to dissolve the sugar and make it easier to see the mites.
- Sticky board test – this is a very good method for detection that is not invasive, and does not harm the bees. Infact, you don’t even need to open the hive to do the assessment. It involves 2 trips to the apiary, and first you will need to make the sticky board, which is simply a sturdy piece of cardboard (I like to use a cereal box), coated with vaseline (or–if, like me, you don’t wish to use petroleum products in your hives–mix beeswax with olive oil to make a non-petroleum jelly). With your screened bottom board simply pull the tray out, lay the cardboard on, and slide it back in. Leave it in place for 24-48 hours, then retrieve it and count the mites that fell during that time period. It is recommended that you treat if you see 50+ mites on the sticky board.
Acceptable thresholds of mite populations
What level of infestation is acceptable, and at what point should you take action to treat the colony for mites? I wish there were an easy answer to that question, but unfortunately there is not. The level of infestation that is tolerated is going to vary from one beekeeper to the next depending on individual philosophies, region, and even number of hives and interest/dedication to the cause.
Some beekeepers are more reluctant to use a miticide, and some abstain altogether.
My own personal threshold is 8 mites in a jar sample. Beyond that I feel the need to take action at least to knock the mite population down until a full treatment can be issued, either during the nectar derth at the end of July, or at the end of the season in September.
To determine what level you are comfortable with, be sure to do your homework–check out the resources listed at the bottom of this post for more information.
Methods for control
Currently there is a division in treatment methods for controlling mite populations within the beehive.
Synthetics – The harsher synthetic chemicals, include Apistan, Checkmite, and Apivar. Both Apistan and Checkmite have been in use for so long that the Varroa have built up a resistance to them, and they are generally ineffective. None of these treatments should be used while honey supers are in place, and Apivar must even be removed 2 weeks prior to the start of a nectar flow, so as to prevent contamination of the honey.
Organics – Often referred to as “soft” pesticides are made up of ingredients found in nature, concentrated and formulated for use in beehives. These treatments include ApiLife Var, whose active ingredients are thymol (thyme), eucalyptol, menthol, and camphor; also Apiguard–a thymol gel, Mite-Away Quick Strips, made with formic acid that is found naturally, and Hopguard, a newer pesticide derived from hops and formulated on cardboard strips.
Even these softer treatments should not be used in hives while honey is being produced, with the exception of Hopguard. Personally I still avoid using it while supers are in place, as Hopguard has a very pungent odor that I fear would permeate my honey, so as a rule I do not treat hives while honey supers are in place–but that’s just me.
Other methods for control of the Varroa mite include using a screened bottom board, which allows for mites to fall through the screen and out of the hive, or a sticky board that traps mites so they cannot climb back up into the hive. Making hive splits, and nucs, in the spring also helps to divide and reduce the mite population.
Because mite populations grow very fast, and because you can’t apply miticides while supers are on the hive, timing your pesticide applications is crucial. As a beekeeper, you need to learn when nectar flows occur in your area. Watch your hives for signs of a derth in nectar, and for increased nectar flow. Track these events in your beekeeping journal or log, so that you can refer back to it from one year to the next. Also, talk with other beekeepers in your area to learn about others’ observations–this is where participating in your local beekeeper’s group is beneficial.
Nectar flows will vary from year to year, so be mindful and ever observant.
Also–our Maine state apiarist, Tony Jadczak strongly recommends beekeepers perform a follow-up varroa sampling after they’ve treated their hives, so that they know what level the mite-population is at post-treatment.
That about sums it up!
When talking about mite sampling, it sounds harsh, I know, to use any method that kills our precious bees. But it is an indicator of the severity of the problem facing the honeybee that beekeepers would even consider such an action as the ether roll or the alcohol wash. Beekeepers need to know the level of Varroa infestation plaguing their colonies if they hope to maintain healthy hives long-term, and these sampling tests offer accurate representations of the population levels of the parasitic mites inside the hive.
Have you tested your hives for mites this year? What method do you use and what threshold have you set? Feel free to share so that others may learn!
References & Resources
Parasitic Mites of Honeybees – from the Purdue University, Dept. of Entomology.
Fighting Varroa; Reconnaissance mite sampling methods and thresholds – from Scientific Beekeeping.
Varroa Treatment Comparison – from the Maine State Beekeepers’ Association, The Bee Line.