August 2014 – It’s Time to Sample for Varroa Mites

Hopefully, most beekeepers in Mississippi have almost finished extracting their major honey crop from the spring and mid-summer.  Afterwards is the perfect time to sample your bees to determine your varroa mite loads.  I suggest that you estimate the number of mites on your adult bee population by washing the mites from a sample of 300-500 bees that are taken from the broodnest of each colony.  Many of you prefer the sugar shake method for sampling the mites, but the humidity during this time of year causes the powdered sugar to cake.  The caked sugar is not very good at dislodging the mites because this depends on having a fine powdery texture that interferes with the ability of the mites to grab and hold bees.  Therefore, use of the sugar method in the late summer can give a gross underestimate of the real mite load in your colony.

Varroa_young

I will not give all of the details for sampling using the alcohol wash here, but consult the file entitled “Managing Varroa Mites” under our “Resources” heading.  I strongly encourage everyone to sample their bees to make decisions about whether they need to treat them with chemicals to reduce harmful levels of the mites.  The concept hinges on two principles:

First, one can never completely eliminate varroa mites from colonies, and the bees can tolerate mite levels below a certain threshold.  A good threshold for late summer in Mississippi is a 5% mite load on bees.  This means that when the mite population in a colony exceeds 5 varroa mites per hundred bees that your colony will very soon reach a mite population that harms the bees.  If you treat when the mite population just exceeds or meets the threshold, you can save the bees from damage or economic loss in productivity.

Second, the use of a threshold to make treatment decisions is a better approach to managing varroa mites than to regimentally treat all of your colonies on a set calendar schedule.  Regimental treatment with any drug can quickly lead to the development of mite populations that are resistant to that chemical.  Additionally, using chemicals at a regular interval can lead to the use of drugs when they are not even needed.  For example, mite population growth can vary year to year.  In some years, growth will be slower than others, and the mite populations may not even reach the threshold level.  If a chemical is used blindly, the beekeeper tends to waste time and money.  Finally, the use of chemicals can lead to secondary problems in hives.  Many treatment chemicals can contaminate wax, and these contaminants may have long term health effects on bees.  Please see “Managing Varroa Mites” under the “Resources” heading for complete details.

We have begun sampling our colonies here at the Mississippi State University apiaries.  In looking at the data for the first 25 colonies, we have two colonies with mite populations that are near the 5% threshold (3.8 and 4.2%).   The remaining colonies are low with mite populations at 0 – 2%.  We will continue sampling all of our remaining colonies (n=75) over the next week or so.  If these numbers hold for the remainder of our hives, we will not likely need to treat any of the colonies.

Jeff Harris