Ongoing Hive Management: Defending against Varroa

Solving the Varroa problem would make a world of difference to the health of honey bees

By Dick Rogers, M.Sc., Principal Scientist/Entomologist/Manger, Bayer Bee Care Center

The Western honey bee, Apis mellifera, is a highly valued insect, as honey bee colonies not only produce honey but also other useful products, including wax, propolis, pollen and venom. However, the most important role of this species is the pollination of agricultural crops which require insect pollination.

Bee in a Flower
Figure 1. Honey bee on apple blossom. Honey bees are essential for crop pollination because they are managed pollinators that can be relatively easily increased in numbers and can be moved to where crops need pollination services.

Since these insects are so essential to our food supply and in our environment, ongoing surveys of their health are conducted by various organizations. Honey bee colony loss surveys conducted by the Bee Informed Partnership (BIP), Apiary Inspectors of America (AIA) and the U.S. Department of Agriculture (USDA) since 2006 have documented beekeeper-reported losses at over 30 percent at the beginning of the survey years; there has, however, been a downward trend to the current level of losses: 21 percent.

Beekeeper Self Reported Overwintering Loss
Figure 2. As beekeepers improve monitoring and management of Varroa, and other factors affecting honey bee health, colony survival will improve. Data from BIP shows a significant improvement in winter survival of colonies since 2006 when surveys were started. There is still room for improvement, but we are on the right path.

Both crop protection and bee protection products have been blamed for colony losses and for threatening our food supply due to a lack of pollination. In fact, the best way to ensure the availability of nutritious and reasonably-priced fruits, nuts, vegetables and seeds is by using Integrated Pest Management tools and strategies, including warranted use of pesticides, to protect both our crops and honey bee colonies from the many pests that can potentially devastate them.

One such pest is the parasitic mite, Varroa destructor, the number one enemy of Western honey bee colonies.

Bee with Varroa Mite
Figure 3. A female Varroa mite on the back of a newly emerged worker honey bee. The bee is also suffering from deformed wing virus (DWV), which causes the wings to be crumpled and useless for flight. Bees affected by the deformed wing condition will not survive.

Varroa, first seen in Indonesia in 1904, has been spreading around the world since the 1950s and was first detected in the U.S. in 1987, only two years after another parasitic mite, Acarapis woodi, arrived.

Varroa Mite Map
Figure 4. Map showing the timeline for the spread of Varroa globally. Source:

As Varroa spread throughout the U.S. and Canada, it caused devastating honey bee colony losses. If it weren’t for the rapid development and availability of two treatment products, including one from Bayer, the commercial bee industry would have suffered even more losses back in the early 1990s. Since then, there have been other new pests introduced, including the small hive beetle (Aethina tumida), a honey bee gut parasite (Nosema ceranae) and at least several bee viruses. Also, the challenges of effectively managing the increasing number of colonies and the reductions in efficacy of treatments, again threaten the survival of the commercial bee industry.

Varroa Mite Chart | Bayer Bee Health
Figure 5. Number of Honey Producing Honey Bee Colonies in US, 2006 to 2016 (only operations with five or more colonies counted). Source: USDA NASS (

Beekeepers with Hive Boxes
Figure 6. Commercial apiary established as a holding yard prior to moving hives to almonds for pollination service. Honey bees are not at risk of going extinct anytime soon; however, commercial apiculture can only continue if bee health challenges can be successfully and cost-effectively managed.

That being said, after many years of investigating the complex set of factors affecting bee health, it is now clear that improvements in the monitoring and treatment of Varroa would go a long way to reducing honey bee colony losses, both during the active season and over winter.

There is no risk of honey bees going extinct anytime soon as some reports suggest; however, continuing the downward trend of losses will require enhanced dedication by beekeepers to monitor and effectively manage Varroa. Testing the efficacy of Varroa control products is essential to determine if the mite is becoming resistant to the products, and to help develop an effective resistance management plan. This assessment requires collecting Varroa-infested bees and exposing them to various treatments in a test chamber. The number of Varroa that drop off the bees can then be compared to the total number of Varroa in the sample of bees, and efficacy can then be calculated.

Testing Honey Bees
Figure 7. Loading a test chamber with honey bees to determine the efficacy of the varroacide being tested. This process also results in a count of the number of Varroa per 100 bees, which is a measure that can be compared to treatment threshold values and can help forecast colony survival.

Although I am very confident and hopeful that honey bee colony health and survival can be improved, I am also certain that it will require making further improvements in the 3Ms – Monitoring, Management and Mite control. It is essential that we manage Varroa, but we must not overlook or neglect the many other factors that affect bee health. Accepting the challenge and adopting the tools and techniques of better management will move apiculture into an era of sustainability and a new normal of improved practice.