Factors Influencing the Lifespan of Bees 233 



pharyngeal glands. The newly emerged bee has undeveloped 

 hyaline pharyngeal glands of irregularly angular shape; its 

 fat body consists of a very delicate transparent cell layer with- 

 out inclusions. In the approximately ten-day-old summer bee 

 performing nursery duties, the pharyngeal glands are rounded, 

 milky-white to yellow, with well-filled lobes completely 

 covering the secretory ducts. In its third week of life, when 

 the bee assumes different duties, the pharyngeal glands 

 slowly degenerate but the wax glands attain full develop- 

 ment. In the four-week-old summer flying-bee the pharyngeal 

 and wax glands have already degenerated, and under normal 

 conditions the fat body of the summer bee remains un- 

 developed throughout its life. This form of presentation is 

 somewhat schematic, because we know from studies carried 

 out by Lindauer (1953), Ribbands (1952), Sakagami (1953), 

 and others that the division of labour within the colony varies 

 greatly; thus it is possible that the length of any of the above- 

 mentioned duties can be prolonged, shortened or even omitted, 

 and the degree of development of the pharyngeal and wax 

 glands shows parallel fluctuations. 



The life of the bee emerging in autumn follows quite a dif- 

 ferent course. The bee makes its appearance in the colony 

 at a time when the brood is greatly reduced, the stores pre- 

 pared and the bees ready for overwintering. The young bee 

 feeds for several weeks on pollen without having to perform 

 nursery duties (maximal pollen consumption is between 

 September and October — Lotmar, 1939). Thus the pharyngeal 

 glands and the fat body attain full development and remain 

 in this state until spring, when the autumn bee takes up the 

 nursing of the newly emerging brood. The pharyngeal glands 

 of the winter bee therefore remain in the nursing state for six 

 to seven months, and the fat body consists of several densely 

 folded layers, the cells of which are milky- white, rounded, and 

 packed full with inclusions. At the same time the bee's 

 expectation of life increases, and it becomes a long-lived 

 winter bee, remaining in the colony six to eight months 



