Mite counting

Sugar roll vs alcohol wash: How to accurately monitor your bees for varroa destructor mites

There are two widely accepted methods for inspecting hives for the presence and number of varroa destructor mites. These are the alcohol wash method and the sugar roll method. Note that a simple visual inspection is not recommended for varroa mites, because the mites are very small (slightly smaller than fleas), they tend to attach to bees on their bellies, not on their backs, and the vast majority of varroa mites in a hive are hidden within the capped brood cells. Monthly inspection for varroa mites is recommended.

The alcohol wash method is considered the most accurate, but it does require the sacrifice of about 300 bees. The tradeoff, however, is that these 300 bees may save thousands of other from dying of mite infestation. The sugar roll method may be less accurate, but the sample bees usually survive, if perhaps a bit dizzy and confused after the process. It is sometimes difficult to discern mites from hive debris, but with experience you will see them more easily. When counting mites, remember that 3 mites from a 300 bee sample = 1%. Treatment thresholds range from 1% to 3%, while some beekeepers start organic treatments anytime they find more than one mite in their sample.

Pro tip: Since varroa mites are known to show a preference for drone brood, you may want to test a frame with drone brood present in order to get an optimal mite count.

Sugar roll method

You will need:

• Wide mouth mason jar with a lid ring equipped with #8 hardware cloth

• 2 tablespoons powdered sugar

• 1/2 cup measuring cup

• White dishpan (or a white top feeder tray can work for this)

• Spray bottle with water

Method:

First, isolate the queen to ensure her safety. Then remove a brood frame and tap or shake it over a tray or dishpan (or an empty top feeder tray if you have one) and scoop 1/2 cup of bees into a wide mouth mason jar. This will gather a sample of about 300 nurse bees. Apply a screened lid to the mason jar and pour about 2 Tbspn powdered sugar (confectioner's sugar) onto your bee sample. Gently roll the jar until the sample bees are well coated with sugar, then leave it for about 2 minutes in a shaded area, to give the mites time to separate from the bees. Invert the jar and shake vigorously over a white tray or paper plate (the same dishpan or top feeder tray you used to collect the sample can work for this, if it is white), to collect all the sugar and mites on a white surface. Mist with water until the sugar melts and become transparent, and carefully check for mites. Remove lid and return surviving bees to the top bars of the brood chamber.

Alcohol wash method

You will need:

• Alcohol wash test kit

• Rubbing alcohol and water (according to kit instructions)

• 1/2 cup measuring cup

• Tray, such as a dishpan, paint tray, paper plate, or empty top feeder tray

Method:

Prepare the test kit according to its instructions by filling the jar with diluted rubbing alcohol to the fill line. Next, isolate the queen to ensure her safety. Then remove a brood frame and tap or shake it over a tray to collect a sample of nurse bees. Scoop 1/2 cup or about 300 bees and place them in the sample basket included in the test kit. Place the basket into the jar, tightly close the lid, and shake for one full minute. Allow a minute for the fluid to clarify and for mites and debris to settle, then hold the jar up to the light or toward the sun and count mites in the bottom of the jar.

Mite drop method

Another method for detecting the presence of varroa destructor mites, though it is far less accurate for counting them, is the sticky board or mite drop method. This method uses a screened bottom board under the brood chamber with a sticky board placed underneath. The sticky board fits into the grooves in the sides of the screened bottom board, and as the bees pick mites off during regular hygiene, they will drop them through the screen where they will stick to the board. One of the greatest weaknesses of this method is that it does not take hive population into account, so comparing mite loads can be difficult, even in the same hive over time as the bee population waxes and wanes seasonally.

Method:

Using a white tray (often a board of corrugated plastic, like garage sale sign material), thoroughly wash the tray clean and be sure it is dry. Using a clean cloth, apply a thin film of vegetable oil to the upper surface of the tray (or use cooking spray and just spray on a light, even coating), and slide it into the grooves under your screened bottom board. Note the time. Remove the tray 24 hours later, and count the mites on it. Repeat at regular intervals (such as every two weeks or every 30 days), and note each count in your hive log. Remember treatment thresholds will be very different using this method. Ontario Tech recommends treating if more than 9 mites are detected in the spring or more than 12 mites are detected in the fall, in a 24-hour mite drop.

When to treat

Treatment thresholds vary, both between monitoring methods and among individual beekeepers. The following thresholds for treatment are recommended by the Honey Bee Health Coalition:

DWM 6/10/21