Robert Madsen worked at UM for many summers.  He built hives with thermocouples over every 1 inch of space.  The brood nest combs varied less than 0.5 degree C from top to bottom, left to right, and diagonally.  Overall, no significant change in temperature occurred until the boundary area of the cluster was reached.  He produced animated videos of this - as the day warmed and night cooled, the cluster and it's self-generated heat expanded and contracted.  It was very distinct and easily seen in the animations.   The biggest temperature change was btw the side-wall of each box and the first frame, which could be as high as 50 degree C on a sunny day.  Btw the 1st and 2nd frame from the side, in a hive full of bees, on a sunny day,the temperature generally dropped dramatically to be closer to that of the  brood nest.
I agree with other posters - the cocoons are unlikely to have much, if any effect on temp in the brood nest - it's the bees themselves, with fine adjustments made by individual heater bees to individual cells.
The speculated added benefit of propolis in cocoons has to be weighed against the chance of long-dormant, but still viable, AFB spores btw the layers of cocoons.  Obviously, the propolis doesn't kill all of the spores of AFB.  IF it did, we wouldn't see eruptions of AFB when bees tear down and rebuild old brood comb.



             ***********************************************
The BEE-L mailing list is powered by L-Soft's renowned
LISTSERV(R) list management software.  For more information, go to:
http://www.lsoft.com/LISTSERV-powered.html