Varroa Mites & Honeybee Viruses

In our last Snippet, “What is the Varroa Destructor Mite?” we talked about what a Varroa Mite is and how they operate. Now that you know that they live and reproduce under honeybee cell cappings, and will also feed on an adult honeybee’s hemolymph (bee blood), you’re ready to find out more about the kind of effect the presence of mites can have on a colony’s health, especially the developing brood.  

As if it isn’t bad enough that the Varroa mite will impact the lifespan directly of the honeybee they’re feeding on, they transmit viruses through the wounds they create by feeding on adult honeybees or pupae under cell cappings. These viruses go on to sicken and kill bees throughout the entire colony.  

If mite infestations are left untreated, the viruses they transmit can spread and can even kill entire colonies. In addition to transmitting viruses to the bees in a colony, the presence and feeding of mites can cause the honeybees’ immune systems to be suppressed. A suppressed immune system doesn’t work quite right and can leave bees further susceptible to varroa-related viruses and other illnesses.  

Transmission of Viruses

Varroa Destructor are transmitters of at least eight different honeybee viruses. Just like with viruses in humans, viruses can be transmitted from one bee to another.  

Many of the viruses that are often transmitted by Varroa mites were present long before the mites were prevalent, but they didn’t typically cause issues or symptoms. Since Varroa mites can actually activate some viruses in honeybees, their presence can cause symptoms that may not have been an issue without the mites to enhance transmission.  

The combination of the mites’ feeding habits and the viruses they help transmit are causing a huge issue among honeybee colonies. The presence of viruses or mites alone is a much smaller risk than when both are present in the hive at once, which is often one of the leading causes of colony death.  

Here are some of the common honeybee viruses that are transmitted by Varroa Destructor mites:

  • Deformed Wing Virus (DWV) – By far the most prevalent honeybee disease, DWV is now considered a worldwide epidemic. DWV’s symptoms are seen in honeybees that have deformed, and/or dysfunctional wings. Honeybee pupae often acquire DWV from Varroa mites while still in their cell and rarely survive the pupal stage. If they do, infected adults quickly die as they are not able to fly or perform tasks. Levels of deformed wing virus are lower in colonies without Varroa mites, so keeping mite levels low is the best way to maintain low levels of DWV. 
  • Sacbrood – Sacbrood is most often found to affect colonies during springtime, or in times of dearth. It’s also the first-known honeybee virus and is one of the most commonly seen honeybee viruses across the globe. This virus causes an interruption of the development cycle, where a honeybee turns into a pupa from the larval stage. A sac filled with fluid forms around the larva and if punctured can even infect other honeybees inside the hive. This virus has little impact on adult bees, but can be managed through proper nutrition and maintenance of the colony. It’s important to note that although Sacbrood is often associated with the presence of Varroa, it has not yet been confirmed to vector the virus, though mites can carry it.  
  • Acute Bee Paralysis Virus (ABPV) – ABPV wasn’t previously a serious problem within the honeybee colonies of the U.S., until the spread of Varroa mites, that is. ABPV can infect both brood and adult bees and may cause symptoms like darkened hair or hair loss, or bees that are trembling and unable to fly. At high infection levels, bees with ABPV can die very quickly, in just a day or so.  
  • Parasitic Mite Syndrome (PMS) – Parasitic mite syndrome is seen when a colony is in the most advanced stage of Varroa mite virus infestation. It has varied symptoms but is typically characterized by high levels of mites, diseased brood infected with multiple viruses, and adult honeybees with deformed wings caused by DWV. There are typically mites visible on adult bees and brood may be spotty or have cell cappings that are perforated or torn off.  

How to Handle Possible Viruses in Your Hive 

As always, prevention is the best method, but if you suspect that honeybees in your hive have been affected by one or more of the viruses above and were killed by varroa mites, it may be time to review your Integrated Pest Management (IPM) system and start a new varroa mite testing and treatment plan.  

Using IPM to monitor, control, and lower amounts of Varroa present within your honeybee colonies can also help to lower the number of transmitted viruses.  

Read through our PerfectBee Snippet “What is Integrated Pest Management?” to find out how you can use an IPM system to most effectively combat varroa mites in your hive.

Learn More

We’ve compiled some of our free resources below, with articles, guides, lessons, and blog posts specific to the dreaded Varroa Destructor Mite.

As is the case with most beekeeping tasks, there are special tools and pieces of equipment that can help with managing Varroa mites in your bee yard. Check out the PerfectBee Store to find all of your Varroa mite testing, management, and treatment needs.

Here are a few of our favorite options: 

  • Varroa EasyCheck – For measuring a mite count using the alcohol wash method. 
  • Sugar Roll Testing Kit – For assessing mite count using the sugar roll method. 
  • Oxalic Acid Kit – A kit that gives you all you need to complete an oxalic acid dribble 
  • Drone Frame – Adding a drone frame to your hive can help manage varroa mite levels, but only if timed perfectly right before the drones inside emerge and a ton of mites emerge with them! 
  • The Langstroth Screened Bottom Board and Varroa Monitoring Tray – Use the screened bottom board with tray to take a 24-mite count by counting how many phoretic mites fall off of bees within that time period 
  • A Field Guide to Honeybee Maladies – An excellent guide to many honeybee viruses, diseases, and pests. Includes information and photos of Varroa Mites and the issues they cause. 

Colony Member Resources

Colony members, check out these member-only Academy lessons to learn even more about Varroa Mites: 

And head over to the Colony Forum to view some interesting discussions specific to Varroa Mites: