Varroa & Treatment Options

Fig. 1
Fig. 2

Note: In the past varroa was known by the species name Varroa jacobsoni. Unless, specified otherwise in this document, the physical descriptions of varroa refer to the adult female stage of the varroa mite.

Varroa mites, Varroa destructor, are the most serious threat to honeybees. Every winter, Varroa mites and their associated viruses kill hundreds of thousands of colonies around the world. Several studies conducted in North America and Europe have found that high mite levels in summer and/or autumn predict colony death over winter. Varroa are relatively large external parasites that feed on the body fluids of adult and developing honeybees. While feeding on bees, varroa cause physical damage, weaken bees and transmit a variety of pathogens, particularly viruses. 

In almost all cases, varroa infestations of honeybee colonies will result in the death of the entire colony.

It is crucial that beekeepers manage the health of their honeybee colonies by suppressing the population of varroa in all of them throughout the beekeeping season. This usually requires chemical treatments. Beekeepers must monitor the severity of varroa infestations to ensure the levels of infestation are kept below damaging thresholds.

Developing an IPM

Integrative Pest Management (IPM) is a proactive approach that allows beekeepers to manage their mites before they reach damaging levels. Keeping attention and being aware of colonies’ mite levels throughout the year and using a variety of management options to keep levels low. This delays the need for treatments and reduces the amount of miticides introduced into the hive. It is helpful to develop a schedule to incorporate regular monitoring and to have intervention tools and treatments on hand to apply as soon as they are needed.

Mite infestation rate can accelerate in the late fall. 

It is important to be able to quantify the level of varroa infestation in a colony.
There are various methods of sampling for varroa in honey bee colonies, some more efficient than others:

  1. Alcohol wash
  2. Ether roll
  3. Sticky boards
  4. Sugar roll
  5. Uncapping Drone brood


The most efficient method and the one we use here at our apiary is the
Alcohol Wash method.

Unreliable Techniques for monitoring Mites
Visual Observation
Uncapping Drone Brood
Sticky Board
Ether Roll

 

Detection and Diagnosis
Varroa are typically concentrated in the brood nest of the honey bee colony and present in the brood cells. In severe infestations varroa mites may be observed on the surface of worker bees (figure 1).
Varroa mites are darkish red, oval in shape, 1.0 to 1.5 mm long x 1.5 to 1.9 mm wide with eight small legs at the front the body. Since varroa mites are about the size of and shape of a sesame seed they can be seen with the naked eye (figure 1). High levels of infestation will weaken a colony. Many worker bees, seen crawling in or outside the entrance of the colony, will exhibit symptoms of viruses, such as deformed wings (DWV). Once you start seeing signs of DWV in your bees, the damage to the colony at this stage is severe (figure 2).

Parasitic mite syndrome is the advanced stage of a Varroa mite infestation. At this point in time, colonies have very high mite levels, well above the treatment threshold. And they’re also accompanied by high levels of viruses that are transmitted by the mite.

There are various methods for collecting bees for samples
Two of the methods (alcohol wash and ether roll) for detecting and quantifying varroa from honey bee colonies require the beekeeper to obtain a sample of live bees so that the varroa mites can be collected directly from the bodies of the bees. In this way the beekeeper can estimate the level of infestation for the entire colony.

Collect a sample of bees from the brood chamber. This is where the highest number of varroa mites will be present.
Since the bees in the sample will be killed, beekeepers must be particularly careful not to include the colony’s queen in the sample. 

Beekeepers may locate and then cage the queen first.
For a representative sample of the colony, collect bees from at least three different frames.
There are two different ways of collecting bees from the colony
You can shake the bees directly off of the frame into a pan where the bees can then be scooped into a container or collect bees directly from the frame by gently running the container over the surface of the frame, with the frame tilted downwards at 30° so that the bees fall into the container.

There are many tools available for purchase to do alcohol wash but you can also get creative and make your own.

Treatment Thresholds

The following are treatment guidelines. These suggested levels vary depending on colony strength, apiary location and management. The best way to determine the proper timing for treatment solutions is to monitor regularly and compare results.

Treat when varroa levels are greater than or equal to those shown in table 2.

 
Monitoring MethodNumber of Varroa Mites in MayNumber of Varroa Mites in August
Ether Roll1 mite / 100 bees2 mites / 100 bees
Alcohol Wash2 mites / 100 bees3 mites / 100 bees
Sticky Board9 mites / 24 hr drop12 mites / 24 hr drop

When to Sample

Beekeepers should sample at least twice a year, in early spring and in late summer or every time before treating. This will give an idea of the varroa population immediately before the treatment period. Beekeepers may also consider taking a sample in mid-summer, particularly if the colonies appear weak and stressed. Even though a beekeeper may have administered a treatment, colonies can become re-infested from outside sources of mites (surrounding colonies). Beekeepers may also consider taking samples before and after a treatment is applied to determine if the treatment was effective at lowering the population of mites in the colony.

It can be difficult to determine how many colonies to sample within an operation. Ideally, beekeepers should sample all their colonies in all yards. However, not all beekeepers have the time and resources to do this. Several colonies from each yard should be sampled and all beeyards should be sampled. Individual beeyards and honeybee colonies will have variation in their varroa levels just as individual colonies differ in the population of worker bees. Beekeepers should monitor at least 10% of their colonies on a monthly basis from April–October in the Northeast US. As an example, if you have 30 hives in your apiary, you should sample at least 3 colonies.

Monitoring should take place once a month from April to October in the Northeast US.

 

 

In  order to treat a colony against Varroa, it’s important to remember that there are two stages in the life cycle of the Varroa mite: The reproductive stage and the phoretic stage.

Reproductive stage:
During the reproductive stage, the mite is inside the honey bee brood cell, reproducing and feeding on honey bee pupae.

Phoretic stage:
During the phoretic stage, the mite is found on the outside of the bees’ body, feeding on the bee. Mites can be found on the thorax or abdomen of bees, and even tucked between body segments and under wings.

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Varroa Treatment Options


Chemicals can be broken down into three classes: 
synthetic chemicals, essential oils, and organic acids. Each chemical has specific requirements that must be fulfilled in order to use the product safely.