For the Love of Bees and Beekeeping
The Messy Picture of Honey Bee IPM
by Keith Delaplane
Last month I spelled out an IPM regimen for Varroa control that I think does a good job summarizing the state of the science on this important topic. I also made it clear that in my opinion the state of this science is not very good. I can say this in good conscience because I’m an active contributor to this literature and acutely aware the limits of my own work. The truth is, it’s all too common nowadays for beekeepers to practice more or less exactly what I spelled out – and still experience catastrophic losses. Moreover, I reiterate the point I made last month that the fundamental premise of IPM – delaying chemical treatments until the pest reaches a critical population threshold – may be unrealistic if the pest causes serious damage at even small densities. I raised the specter of this for Varroa given the fact that Varroa is almost always confounded with one or more bee viruses, the most dangerous being Deformed Wing (DWV).
In other columns I have also laid out the conundrum that chemical-based pest control is a double-edged sword: the right miticide at the right time can cause immediate and dramatic mite control, but the miticides themselves cause sublethal damage to bees, interact dangerously with agri-chemicals and other Varroa miticides, and contribute to the toxic stew of background environmental contamination that’s earning agriculture a bad rap in the popular press. What’s the way out of this mess?
Lacking an immediate and brilliant answer, I default to what I think is the best move – getting real data on all the pieces of the puzzle so the discussion can proceed as much as possible from a factual basis. Fortunately, I am able to contribute new information on the state of IPM thanks to funding from the EPA and the USDA Managed Pollinator CAP – a four-year inter-institutional consortium, many members of which contributed a series of columns in this magazine from 2009-2012. I’d like to describe a project where my lab conducted a survey and boots-on-the-ground hive inspections in an effort to associate specific beekeeper practices with subsequent bee colony health.
Twenty beekeepers in the Southeast participated in an on-line survey that was designed to associate bee management and IPM practices with actual colony survival, queen replacement rates, and colony parasite and pathogen loads. Four of these participants were commercial beekeepers and the rest were hobbyists or small sideliners. Adult bee samples were collected from participants’ hives during Spring 2011, Fall 2011, Spring 2012, and Fall 2012. All samples were processed for Varroa mite levels, pesticide residues for 7 organic compounds in hive materials, and pathogen loads. Statistical associations among these variables was done with multivariate analysis, with some of the significant associations shown in the Figure. As with any correlation analysis, these associations do not necessarily show cause-and-effect relationships, but rather show simultaneous movements between two variables which can be either negative – such that one decreases while the other increases, or positive – such that the direction of movement is the same. In the figure I have used iconic graphs to illustrate these relationships – positive or negative. These lines are not the actual computed lines; they are simply showing the direction of movement for simplicity of discussion.
Here are the results in bullets:
● Varroa counts decreased as the likelihood increased that the beekeeper would use hygienic queens as an IPM Varroa control.
● Varroa counts decreased as the number of simultaneous IPM practices increased.
● Varroa counts decreased as the number of educational beekeeper meetings attended increased.
● Colony winter mortality increased as the hive concentration (ppb) of coumaphos increased.
● Varroa counts decreased as the hive concentration of coumaphos increased.
● Queen supersedure increased as the likelihood increased that the beekeeper would use powdered sugar dusting as an IPM Varroa control.
● The beekeeper’s likelihood of using thymol as a Varroa miticide decreased as the the hive concentration of coumaphos increased.
● The beekeeper’s likelihood of using screen floors as an IPM Varroa control decreased as the the hive concentration of coumaphos increased.
● The beekeeper’s likelihood of using survivor queens as an IPM Varroa control decreased as the the hive concentration of coumaphos increased.
These results support some of the premises and arguments in favor of IPM, namely the use of simultaneous IPM practices and use of genetically mite-resistant queens. I thought it was interesting that beekeepers who attend educational meetings are likely to have fewer mites in their hives. The results for coumaphos were typically paradoxical, with increasing chemical residues associated with both lower mite levels, as well as higher colony winter mortality. Unfortunately, powdered sugar dusting gains little traction from these data, showing a positive relationship with queen supersedure.
The chemical residue data give interesting insights into ...