For this reason I am so fixated on the closed hive atmosphere even if it is hot outside. Michael Bush keeps his hives closed all year around and he has only high entrances. He does not treat against Varroa at all (not even sugar dusting).
Im thinking to close the hive today and keep it that way. Even if I close it there will be small gaps between the meshfloor and side walls. Michael Bush sais that bees keep a steady temperature inside a hive even if it is much warmer outside. My hive is placed between a few tall Birch trees which shade it ok I think.