INTERRELATIONS OF INSECTS 269 



however, and the departed queen is soon, if not already, replaced by a 

 new one. 



Determination of Caste. The difference between queen and 

 worker depends solely upon nutrition, both forms being derived from 

 precisely the same kind of egg. To produce a queen, a large cell ot 

 special form is constructed, and its occupant, instead of being weaned, is 

 fed almost entirely upon the highly nutritious secretion which worker 

 grubs receive only at first and in limited quantity. This nitrogenous 

 food, the product of cephalic glands, develops the reproductive system 

 in proportion to the amount received. Drone larvae get much of it ? 

 though not so much as queens, while an occasional excess of this " royal 

 jelly" is believed to account for the abnormal appearance of fertile 

 workers. 



Parthenogenesis, or reproduction without fertilization, is known to 

 occur in the bee, as well as in various other insects. The always un- 

 fertilized eggs of workers produce invariably drones, as do also unfertil- 

 ized eggs of the queen, but it does not follow that males never come from 

 fertilized eggs, as Dzierzon believed. Dickel and others hold that all 

 the eggs laid by a fertilized queen have been fertilized. Dickel stated 

 that the sex is determined by the nutrition of the larva, but it seems 

 more probable that the sex is determined before the egg is laid. 



BUMBLE BEES 



Familiar as the bumble bees are, their habits have been little studied 

 in this country. The queen hibernates and in spring starts a colony, utiliz- 

 ing frequently for this purpose the deserted nest of a field mouse or some- 

 times the burrow of a mole or gopher. The queen lays her eggs in a 

 small mass of pollen mixed with nectar (Putnam). The larvae eat out 

 cavities in the mass of food and when full grown spin silken cocoons, 

 from which the imago cuts its way out; the empty cocoon being sub- 

 sequently used as a receptacle for honey. At first only workers are 

 produced and they at once relieve the queen of the duties of collecting 

 nectar and pollen, caring for the young, etc. The workers are of dif- 

 ferent sizes, the smaller ones being nurses or builders and the larger ones 

 foragers the kind commonly seen out of doors. In the latter part of 

 summer both males and females are produced, but when severe frost 

 arrives, the old queen, the workers and the males succumb, leaving only 

 the young queens to survive the winter. 



