Introduction
Alcohol washes are an accurate and fast way to determine the Varroa mite infestation rate on a subset of the adult bees within a colony. Test results allow you to compare the infestation rate with published thresholds and make decisions about whether, or not, treatment is warranted.
It’s a good idea to monitor regularly throughout the entire bee-working year to make sure mite levels remain below economic thresholds and to plan ahead for treatment opportunities. It’s also a smart idea to do a post-treatment alcohol wash approximately 10-14 days afterward to verify that the treatment was effective.
Because the actionable levels of infestation (e.g. when treatment is needed to protect the colony from harm) are quite low - only 2 or 3%, a particular subset of the bees in the colony is chosen to act as surrogates for all the adults in the hives. The bees with the highest infestation rate are the young nurse bees occupied tending the brood. Phoretic-state Varroa mites congregate on the bees working near the open brood so that they can easily enter a mature larva’s cell before it is capped.
To maintain the accuracy of the test, it’s important to choose the sampled bees correctly and consistently, both as to the location they are taken from, and the number of bees in the test sample. The methods described below will help you do that.
Doing alcohol washes regularly will improve your skill in collecting the sample and performing the test accurately. It may seem a bit awkward at first, but with experience it will become faster and easier and a routine part of your hive management skills.
An alcohol wash uses isopropyl (rubbing) alcohol or non-foaming, winter windshield wiper fluid to separate the mites from the sample of bees. Using a Varroa EasyCheck sampler is an accurate method to determine mite levels. Compared to a sugar roll, an alcohol wash is faster because you do not have to return the tested bees to the hive. The disadvantage is that the sample of 300 bees is sacrificed during the test..
Many beekeepers are hesitant to kill the tested bees. Keep in mind that although 300 bees seems like a large number, a queen typically produces between 1,000 and 1,500 eggs per day and the loss of 300 bees has no harmful consequence. We use the Varroa EasyCheck to check our bees for mites.
What you need to do the test:
- Varroa EasyCheck sampling device
- Half-cup measuring scoop
- Isopropyl (rubbing) alcohol or non-foaming, winter windshield washer fluid
- Large plastic tub -- a big cat litter box is a good choice
- Timer
- Fine mesh strainer
- Quart-sized plastic container to use during straining
- Larger, lidded container to collect used sampling fluid if you are doing more than a few tests.
How to use the Varroa EasyCheck
One important note to start out: Because this test kills all the bees that are tested, it’s important to be able to find your queen and make sure she isn’t among the bees being tested. If you cannot be certain that you will be able to spot your queen, select a frame away from the brood nest and use that one for the test.
Before you start Fill the Varroa EasyCheck device with isopropyl (rubbing) alcohol or windshield washing fluid. Add enough fluid so that it’s above the bottom of the inner perforated cylinder.
Find and, if possible, isolate the queen. You can temporarily place the queen and the frames she’s in a nuc box.
The bees with the most amount of mites on their bodies are likely to be the nurse bees caring for the open brood. Those are the bees you want to test. Select a frame that is at the outer edge of, or just outside, the brood area. Look the frame over carefully to make sure the queen is not on it.
Set the plastic tub on the ground near the stack. Hold the selected frame firmly and give it a sharp downward shake directly over the tub. This will dislodge the bees and drop them, unharmed, into the box. The nurse bees, unlike the foragers and drones, will stay in the box for a short period. As soon as the bees are off the frame, put it back into hive to keep the brood warm and safe.
Get the bees into the sampling container. This is a critical step in achieving test accuracy. A precise, and consistent, sample size (the number of bees actually tested) is the key to getting reliable results so take some care with this step.
First, consolidate the bees in the plastic tub by giving one corner a sharp thump on the ground. This will drop all the bees down into that corner of the box.
Use a half-cup measuring scoop to gather the bees to be tested up from those in the corner of the box. Remove the lid of the Varroa EasyCheck and dump the bees into the inner basket. Put the lid back on.
An alternative way to select the bees to be sampled: After finding and isolating the queen, select a frame from the brood nest. Use the empty basket to collect the bees by sliding it gently down the frame which will cause bees to fall down into it. Continue until the level of bees in the basket comes up to the upper line on the cup which is equivalent to a 300 bee sample. Then place the cup into the outer container and put the lid on.
Doing the test:
- Shake once to wet the bees and then open the container and add fluid up to the upper line on the outer container.
- Shake the container gently for 60 seconds.
- Hold the container up to the light and count the mites.
- Divide the mite count by 3 to get a percentage (e.g. 15 mites per 300 bees = 5 per 100, or 5%).
After you’ve counted the mites, lift the basket out and discard the bees. Pour the sampling fluid through the strainer to remove the mites and debris. The sampling fluid can usually be reused a few times before it needs to replaced.
Watch this short YouTube video on how to perform the test using the Varroa EasyCheck
Evaluating the results: Although some beekeepers will allow a 3% infestation rate (nine mites revealed after the test), here at Betterbee we consider the treatment threshold to be 2% (no more than six mites per 300 bees.) Over time, you will develop your own thresholds based on the success of your hives, but 2% is a good starting point.
