246 Discussion 



before sundown, for example, most foraging bees will start to come 

 back to the hive, even on a hot summer day, so it is not a matter of 

 temperature. 



Holt: What is the mode of life of tropical bees? 



Maurizio: I think that in the tropics there are no winter bees, 

 because they can fly all the year. They have pollen and nectar, 

 they seem to have brood the whole year and there are no long-lived 

 bees in the colony. But a proper study of bees in the tropics has 

 yet to be made. 



Hinton: That would be primarily an adjustment to food supplies 

 and not necessarily to temperature. 



Maurizio: It is complex. In the tropics there may be no over- 

 wintering, but during the two or three months of the dry season 

 there may be long-lived bees in the colony. 



Rocksiein: There is probably more than one factor, such as light 

 or temperature, that would produce the end-result of conserving the 

 colony. In Minnesota, bees begin brood-rearing in January when 

 temperatures are sometimes at —30° f. These animals are being 

 continually decimated during the winter months because some of 

 them have emerged in August, some in September and some in 

 October, and we are going to end up with a very small nucleus from 

 the last-laid eggs by the end of winter. There appears then to be a 

 social pressure upon the hive which stimulates brood-rearing late in 

 the winter. Somehow, the queen is aware of this, even in the dead of 

 winter. As far as light is concerned, the shortest day is in mid- 

 January in Minnesota, but the queen begins to lay eggs again at that 

 time. 



Hinton: What is the temperature in the cluster in winter in 

 Minnesota? 



Rockstein: The centre of the cluster is always maintained at a 

 temperature of about 33° c. This has been established by thermo- 

 couple measurements. The bees on the outside of the cluster change 

 places with bees from the inside; otherwise those on the outside 

 would fall torpid from cold. These outside bees must feed, generate 

 heat, enter and allow the inner bees to move out. If the cluster gets 

 too far away from the food stores, the whole cluster will die, with the 

 queen the last one to go. 



Hinton: Thus social insects can be said to be homoio thermic. 



Rockstein: I would rather say that the colony as a whole can 

 be said to be homoiothermic. 



