The Distribution of Senescence 



sectioning of 'that which dies of itself has yet to be assessed in 

 the literature. 



A considerable amount of work has been done upon the 

 physiological factors which influence longevity in worker bees. 

 Winter bees are known to be considerably longer-lived than the 

 summer brood even when they are kept under similar conditions 

 of temperature and activity. Maurizio (1946) found that caged 

 winter bees had a mean survival of 36 days from eclosion com- 

 pared with 24 days in caged summer bees. The life-span of 

 summer bees can be prolonged in two ways — by feeding pollen 

 to caged bees (Maurizio, 1946), or by removing all the sealed 

 brood regularly from the colony, so that the same bees continue 

 with brood-rearing throughout life — under these conditions 

 bees may live as long as 72 days (Moskovljevic, 1939; Maurizio, 

 1950). 



Two factors appear to influence the longevity of workers. One 

 of these is certainly activity. Ribbands (1950) found that anaes- 

 thesia with C0 2 had the effect of causing young bees to begin 

 foraging earlier than usual: in bees which forage early, expect- 

 ation of imaginal life is less (30T ±1*2 days), but expectation 

 of for aging- life is greater (15-0 ±1*2 days) than in late starters 

 (37-1 ± 0-6 and 10-8 ± 0-8 days). The second appears to be 

 dietary. 'Winter bees differ from summer bees in the greater 

 development of their pharyngeal glands and their fat-bodies. 

 This development results from autumn consumption of pollen, 

 in excess of the requirements for immediate brood-rearing. In 

 queen-right colonies in summer, prevention of brood-rearing 

 can produce similar consequences, and in pre-swarming colonies 

 temporary interruption of brood-rearing produces conditions 

 different only in degree.' In all these cases the increased expect- 

 ation of life is associated both with enhanced development of 

 the pharyngeal glands and fat-body, and with decreased activity 

 (Ribbands, 1953). It appears that worker bees have a life-span 

 which is partially expressible in 'flying-hours', and that this 

 life-span, and the total output of work per life, can be increased 

 by increasing pollen consumption (Maurizio, 1950), but summer 

 bees only increase their life-span in this way if they are deprived 

 of brood. There is also ground for believing that the activity of 

 worker bees is reduced by the possession of internal food 



101 



