Varroa Mites: Monitoring and Treatments
Monitoring and Treatment of Varroa Mites
Don’t be concerned if your hive has Varroa Mites, virtually all hives do. Some colonies tolerate mites better than others. Your main goal as a beekeeper is to monitor your mites and understand that a few mites might not be a problem but a heavy load of mites in your hive create a situation for a high probability of colony loss.
There are many ways to monitor mites but the simplest is to use a screened bottom board with a removable tray. Cover the tray with a coating of oil such as mineral oil or regular cooking oil. Leave it in place for 24 hours and then count the mites and use the chart below to estimate your infestation level. A more accurate way is to leave it in place for 48 hours and then divide you count by 2 to get an average for a 24 hour count.
Counts should be done and numbers recorded at least once per month. You are looking for trends; usually mite populations build in late summer and fall. Thresholds of 1% in the spring or over 3% in the fall should signal concern and treatments are recommended.
Varroa Percent Infestation for a Natural Mite Drop:
24 hour mite drop Percent Infestation
0 - 2 0 - 1%
3 - 15 1% - 2%
16 - 32 3% - 4%
33 - 43 5% - 6%
These numbers are estimates and can vary from hive to hive and from day to day, but if you monitor a lot, you can see trends, and these become more valuable.
Also keep in mind that these numbers are for larger colonies of 40,000 to 50,000 bees, so smaller colonies showing fewer drops may have higher infestations. For example, if a hive only had 20,000 bees you would need to double the listed infestation rates.
Varroa Mites Life Cycle
Varroa mites live attached to bees and reproduce in comb cells. During build up in the spring and summer, 85% of the Varroa in the hive reside in the capped cells and are reproducing along with the bee larva. In the fall, Varroa reside more on the bees and comb because there is limited or no brood for them to reproduce within the cell. This is important to understand when determining the method you use to control them.
They reproduce better with drone brood because it takes 3 days longer for the drone brood to emerge giving the Varroa more time to develop in the cell. The mite enters the cell just before it is capped and lays about 4 to 8 off spring but only produced about 1.2 mites per cell.
Varroa mites are 9 times more likely to infest a drone brood when available than a worker brood. The chart below shows that drone cells will produce more mites than worker cells because they are capped for 3 days longer and that gives the varroa mite more time to develop. Varroa lay 6 or 7 offspring in the capped cell, but in worker cells they can only develop one or two of these. Given a few more days to develop in a drone cell they can significantly increase that to 4 to 6 viable varroa that will emerge for the cell.
Current Management Solutions for Varroa Mites
Non-Treatment IPM Approach
Do nothing: depend upon the natural selection process. This works for a year or so until the mite populations build to an unmanageable level and most likely the hive will collapse over winter.
Introduce superior mite resistance genetics. Progress in this area is getting better and is important for finding a sustainable solution. Some genetics are better than others but non-have provided a solution yet.
Screen Bottom Boards (SBB). Open screen to allow the mites to drop through the hive. Studies show this might reduce mite population about 15% but not enough to keep the bees alive. Good part of and IPM program but not a solution. Better use is for monitoring mites
Dust with powdered sugar. Controls mites on the bees not in the brood. Should be done 3 weeks in a row. Moderate success.
Mist with oil. (not proven to be effective)
Canola oil on a paper towel (not proven to be effective)
Trap and remove drone brood. A very labor intensive but can be a viable part of an IPM program.
Move to small cell foundation (not proven to be effective)
Move to Natural cell sizes (not proven to be effective)
Breaking the brood cycle. Helps but not a solution
Soft Chemical Treatments:
Apiguard (Thymol 25%) essential oil. Strengths: Considered a natural treatment; Use in warm temps. Can be used from 60 to 105 degrees F. Weaknesses: 50 to 70% control; Must remove honey supers
API- Life Var (Thymol 74%, Eucalyptus Oil 16%, L-Mentol 3.7%. Strengths: Considered natural treatments. Easy application for a small beekeeper. No resistance issues. Weaknesses: 3 treatments 7 to 10 days apart.30 day treatment.; Thymol persistence odor; Temperature range, 59 to 69 degree average; not above 90 degrees. Honey supers must be removed.
Mite-Away Quick Strips (MAQS) (formic acid) NOD Apiary. Strengths: Fast application of 7 days; Formic acid is not considered a hard chemical. Honey suppers may remain during application. No known resistance issues. Weaknesses: First 3 days must not exceed 95 degrees F. Hard on bees.
Formic Pro (formic acid) NOD Apiary. Strengths: Slower release than MAQS; Formic acid is not considered a hard chemical. Honey supers may remain during application. No known resistance issues. Weaknesses: First day of application should not be above 85 degrees F; first 3 days must not exceed 92 degrees F. 14 to 21 day treatment; Hard on bees.
HopGuard hop plant extract (from/by Mann Lake) Strengths: Easy application; Natural product; they say all food grade; Good queen and bee tolerance. Weaknesses: Not good when heavy brood is present; May take multiple applications.
Oxalic Acid: Applied by trickling, fumigating. Strengths: 90% control when colonies are broodless. Negative features: Not good when heavy brood is present. 60% control Negative effects on brood and bees when multiple applications at short intervals.
Apistan (tau - fluvalinate) by Wellmark International. Strengths: The standard for 20 years. Simple application. Not weather dependent. Effective on not resistant mites. Must be above 50 degrees. Weaknesses: Big resistance problems. Considered a hard chemistry Honey supers must be removed. Treatment lasts 42 to 56 days. Accumulates in the beeswax.
Check-Mite (Coumaphos) by Bayer Strengths: Effective on non resistant mites. Works also on Small Hive Beetle. Weaknesses: Resistance issues. Considered a hard chemistry. Treatment lasts 45 days. Requires 2 trips to the hive. Honey supers can not be applied for 2 weeks after the treatment.
Apivar® (Amitraz) Apivar® (active ingredient: 3.33% amitraz) is a sustained-release plastic strip designed for use in honey bee hives. Strengths: Effective on non resistant mites .Works for up to 6 weeks. Weaknesses: Resistance issues. Considered a hard chemistry. Treatment lasts 6 weeks. Honey supers cannot be applied for 2 weeks after the treatment.