The bee research group in my country, bijen@wur, organized a symposium last month which I didn’t attend. One of the speakers there was bee researcher Dennis van Engelsdorp (weirdly dutch sounding last name, translates to “English village”). He presented statistical data from a beekeeper survey that suggested that annually replacing to much of the comb (50% or more) negatively influences colony health. Often the idea of replacing comb is to prevent buildup of pesticides and/or pathogens, but it also looks ugly blackish comb. But the data shows that beekeepers who replaced 50% or more of their comb compared to beekeepers who don’t replace any, lose more colonies over winter.
It is unclear what causes this, the survey was not comprehensive enough for any analysis like that but the data is clear. They suggest not to replace more than about 20% of your comb annually. I was aiming to replace about a third of the comb but according to this information I will have to amend that. Apparently reusing comb from old colonies is also not advised as it also caused more winter deaths. The only problem is the lack of additional information in the survey. For instance it is unclear what the origins where of the reused combs. Perhaps the old colony died of disease.
So much is unclear, it wasn’t a study but only a survey. What is clear is that you shouldn’t renew to much of your combs annually. See the accompanying video for yourself (there is also a link to the web page in its description):