Addit..re the heat..it gets pretty hot here and bees tend to work the cooler ends of the day. Heat/dry might affect what is flowering and how much nectar it contains but it shouldn't affect ability to forage too much. Stronger the hive, the greater foraging range and strength and they are more able to find anything that is out there. Like Scott said, there is that population hump a hive needs to get over before it can devote bees to do the foraging work. You can go round in circles..not bringing in much, queen stops laying because of this, population drops, leads to less foraging and not bringing in much...But there could be many reasons for the hive to get this way..eg poor queen, post swarm, disease etc. Are they italians? They cope with heat pretty well here.