I think Finsky means that when bees get severly overheated they get a fever and die????
Protein start to denaturate about 43 C or more. When bees fly their muscles generate more heat. I do not know what kind of upper temperature bees body stands. I have not seen that figure.http://jeb.biologists.org/cgi/content/abstract/35/4/930
Here is interesting research about swarm bee temperature. Temperature of good heated muscles are almost 41C. http://www.nbb.cornell.edu/neurobio/department/Faculty/seeley/PDFs/Warming_of_swarms_(96).pdf
For rapid flight bee needs 35-40 C temperature in muscles, at least 33-35C.
Last spring I followed my bees in what temperature they were able to gather pollen? When sun was shining and weather was 16C, they only gathered piece of pollen. In temperature 18C they made full size pollen balls.
At late winter when temperature is +5C, sun is shining sharply and bee stand on snow, it is able to rise on wings and return to hive.
I have read that water pools are essential for Australian feral bees. Without water they cannot regulate their hive temperature.
We have cool weather but if bees have strong honey flow hive will be heatened and big group stop working. It is difficult to get them work again.
From my water pool I could see when bees need water and when not. If honey flow is heavy they do not take water from pool.
We have warm weather when it is over 20C. It is quite seldom over 25C.