Tonight we were privileged to hear Jennifer Berry speak on IPM management of the varroa mite. It's always fun when Jennifer comes to speak both because she is so entertaining and is so full of good information.
First she talked about the Varroa mite and how it reproduces. As most of you probably know, the mite enters the cell just before the cell with the larvae is capped (on about the seventh day). Within the cell, the foundress mite lays her first egg, a male, and then follows with female eggs. She has 13 days in a worker cell to procreate effectively. She has 16 days in a drone cell, so the varroa mite prefers the drone cell.
Jennifer first discussed the ways varroa has been addressed chemically. Beekeepers used a chemical approach, first with apistan (fluvalinate) and later with coumaphos. With the Apistan, mites quickly developed a resistance to the chemical. With coumaphos there were many issues including bad queens who laid poor brood patterns and didn't live long. She had slides from studies showing that drones survived better in hives with no chemicals and that queens had better, more long lasting reproduction with no chemicals.
Thus, we use integrated pest management or IPM, as it is known in the bee world. There are four main IPM approaches: biological, cultural, genetic and chemical.
The biological approach has not worked with the varroa mite. The idea would be to develop a fungus that kills the mite but it has not been efficacious to follow this approach.
The second approach is the cultural one. This includes screened bottom boards, drone brood trapping, powdered sugar shakes, and brood cycle disruption.
- Bottom screens allow mites to fall or be groomed off of the bodies of the bees and when they fall through the screen, they can't get back up into the hive and onto the backs of a bee.
- In drone brood trapping, the drone brood is cut out of a frame or a whole frame is pulled and then the brood is either destroyed or frozen. Since the varroa prefers to breed in the longer developing drone cell, this rids the hive of a lot of varroa.
- Powdered sugar seems to be effective, especially when the sugar is sifted over the hive pre-spring brood build-up. This means that the most effective time to do powdered sugar shakes in Atlanta would be between January and March while it is still winter.
- Finally brood cycle disruption means doing something to stop the queen from laying. This could include doing a split so that half the hive would be queenless while they make their own queen. It could also include caging the queen for days - Jennifer has done it for seven days; Brother Adam did it for ten. These approaches stop the laying in the hive and since the varroa mite needs larvae on which to lay her eggs, it also disrupts the varroa cycle.
The final approach is chemical. Jennifer pointed out that she doesn't use Coumaphos or Fluvalinate. There are a few chemicals that are essential oils with a thymol base that she would consider using. Jennifer also talked about oxalic acid which is WOOD BLEACH. She asked would you want that in your hives with your bees? She also felt similarly about formic acid which is caustic, corrosive to equipment, dangerous for human's eyes, lungs, etc. and hard on bees and brood. She was not in any way positive about the use of these caustic substances.
Part of IPM includes understanding the economic threshold. IPM recognizes that there are pests in the hive and rather than focus on eliminating the pest, the IPM approach is about recognizing when the level of pest in the hive is above a manageable level to a point called the Economic Injury Level, where the hive will be harmed because of the presence of the pest.
Jennifer suggested that at this time of year in general a mite drop in 24 hours of 60 mites or 125 in a larger, more thriving colony, is at the economic threshold. If your colony measures at that drop level, then you need to do something such as one of the previously mentioned IPM approaches.
In the UGA bee lab, Jennifer is now doing research on the effectiveness of powdered sugar shakes, looking at the timing (doing them before the queen starts laying brood for spring) and the delivery method(top down or bottom up - blowing sugar into the hive from the bottom).
Julia and I left the meeting and decided to put a sticky board under one of the Blue Heron hives with the plan of looking at it on Sunday at our Metro Hive Inspection.