Quote Originally Posted by prakel View Post
How effective is the annual renewal of a third of a colony's brood combs with regards to maintaining/improving colony health?

My thoughts are that it's akin to washing one (alternate) hand each day.... but I welcome scientific evidence to the contrary.
I am not sure about that one either and I don't habitually replace comb.
I do fumigate boxes of spare comb over winter with 80% acetic acid along with apideas and other equipment but the comb is always going to be the biggest disease risk.
last couple of years I have been removing some comb and letting the bees draw some fresh stuff of their own on frames reinforced by fishing line.

In the US, the commercial beekeepers irradiate old comb to kill pathogens.

Here is a fera document on comb replacement