Varroa mites (Varroa destructor) are small, reddish-brown tick like pests which feed on the hemolymph (“blood”) of the honey bees. The European honey bee (Apis mellifera) is not the original host to varroa mites. The mite is native to Southeast Asia where it is a parasite to the Eastern Honeybee (Apis cerana). The Eastern Honeybee has developed grooming habits and can survive with the mites. The European Honeybee however, has not developed such habits and a colony will often decline and die as a result of a mite infestation.

It is believed the mites “jumped” from the Eastern to the European Honeybee in the 1960’s and did so in the former USSR. The Russian bees having been exposed the longest to the mites and have developed an increased resistance, more so than most other strains of the European Honeybee. The varroa mite arrived in the U.S. in the mid to late 80’s, where it has devastated beekeeping operations, both large and small. Since then, our understanding and knowledge of the mites and the interactions with our honeybees has expanded tremendously.

The reproduction of the mite is directly tied to bee reproduction. Just before the cell of a maturing bee is capped (sealed) a female mite enters the cell. Once the cell is capped, she waits about 60 hours before she begins to lay eggs and then she will lay one egg every 30 hours. The first egg will be a male mite and subsequent eggs will be female. The maturing mites will feed on the pupating bee. The feeding of the mites on the bee opens wounds which are sites for possible infection. In addition, the mite will infect the bee with viruses, much the way a mosquito can transmit malaria. The mites mate in the cell and only sexual mature female mites will exit the cell when the adult bee emerges.

Worker bees are capped for about 12 days and drones are capped for about 14 days, as a result more mites will be able to reproduce in drone cells than workers. A single mite reproducing in a worker cell, on average will result in 1.8 mites emerging with the bee, but 2.8 mites will emerge with a drone. Not only do the mites reproduce more successfully in drone cells, but they also gravitate to them and enter them more frequently than worker cells.

There are two widely used methods to assess the mite levels in your hive. The first is a sticky board. This is a board which slides under a screened bottom board. When the mites fall from the hive they stick to the board and can then be counted. Our IPM bottom boards come with a sheet printed with a grid to aid in the monitoring and counting of the mites. This sheet can be sprayed with Pam or cooking oil to serve as a sticking agent. Insert the sheet for 3 days and then remove it to count the mites. Once you have a total, divide it by 3 to get the average mite drop in a 24 hour period.

The second method is a sugar shake. Place a few table spoons of powdered sugar in a mason jar. Next, scoop up about ½ cup of bees (about 300) and dump them in the jar. Replace the lid with #8 hardware cloth and screw it onto the jar using the band. Now gently “slosh” the bees around in the sugar to ensure they are fully coated. The sugar dislodges the mites which can then be shaken through the screen to be counted.

Below is a very general guide to determine if the colony should be treated. However, the prevailing thought is if you have a window of opportunity to treat your colony you should treat.

Integrated Pest Management (IPM) methods work with the behavior and biology of the target pest to aid in its control. There are several IPM methods a beekeeper can utilize to help control the mite population in a hive. A few of the more commonly used are screened bottom boards. As the mites attempt to transfer from one bee to another, some fall. A screened bottom board allows the mite to fall out the bottom of the hive. These also help ventilate the hive in both summer and winter.

Perhaps the most successful IPM method in reducing the population of mites is drone trapping, also referred to as Varroa trapping. As mentioned above the mites gravitate to the drone cells. By providing drone foundation, either plastic or wax, the colony will concentrate the drone rearing to that frame. After the cells are capped, it can be removed (about 21 days after the frame was installed) and along with it all the mites trapped under the cell caps. Freezing the frame for 48 hours will kill the mites. The frames can be reused and the bees will even clean it out for you, just make sure the frame is thawed before reinstalling it.

IPM methods often are not a sufficient form of control and pesticides need to be used. We, and many in the scientific community, strongly encourage the use of “soft chemicals”. These are naturally occurring products and many naturally existing in honey. The two most common are Api Life VAR and MiteAway II. Api Life VAR is thymol, which is using is mouthwash, and other essential oils. Evaporative wafers are placed on the hive and the thymol vapor kills the varroa. MiteAway II uses food grade formic acid, which naturally occurs in honey. For other methods of control see our medication table.