428 



POPULATIONS 



PHYSIOLOGICAL INTEGRATION 



Like the hormones and induction agents 

 of the organism, chemical agents seem to 

 integrate the social supra-organism. 



Particularly through the experiments 

 upon termites conducted by Light (1942- 

 43, 1944) and his associates, it is well 

 estabhshed that the presence of mature 

 males, females, or soldiers, respectively, in- 

 hibits the development of the same caste 

 from undifferentiated nymphs. Gregg 

 (1942) has also experimentally demon- 

 strated that soldier ants inhibit the develop- 

 ment of more soldiers (see also Flanders, 

 1945, 1946). The most adequate theory to 

 account for the facts is that each of these 

 castes gives off an exudate or "exohormone" 

 that passes to the developing individuals, or 

 possibly to the unlaid eggs in the Hymen- 

 optera, by licking or feeding or nutritive 

 physiology, thus inhibiting the development 

 of either reproductives or soldiers unless the 

 population increases beyond the minimum 

 threshold effects of a certain amount of the 

 inhibiting agent. Theoretically, the vi'orker 

 does not inhibit the development of other 

 workers, but inhibition by reproductives 

 and soldiers results in the development of 

 workers. This theoretical physiological 

 mechanism accounts for the periodic pro- 

 duction of mature reproductive individuals 

 in the colony. We may thus see a possible 

 analogue to the honnonal mechanism that 

 periodically controls the production of 

 mature gametes in the vertebrate organism. 



It might be expected, if these physio- 

 logical mechanisms determine caste pro- 

 duction in termites, that the proportion 

 of the castes would be automatically con- 

 trolled. Some evidence has been reported 

 by Miller (1942) that the numbers of 

 soldiers of Prorhinotermes simplex in ex- 

 perimental colonies reach an average pro- 

 portion (one soldier to 3.5 "workers," with 

 a standard deviation of 2.3 and a standard 

 error of 0.55) regardless of the number of 

 soldiers at the beginning of the experiment. 



In the honeybee, the worker and drone 

 larvae are fed brood food (royal jelly— a 

 nitrogenous secretion from pharyngeal 

 glands opening into the mouth) for the 

 first two or three days, and are fed bee 

 bread (a mixture of nectar and pollen) for 

 another three days, after which the cells 

 are capped. Queen larvae are fed en- 



tirely with royal jelly— normally for live 

 and one-half days. The trophogenic sub- 

 stances may carry activating or inhibiting 

 agents that direct caste development. 



BEHAVIOR INTEGRATION 



As might be expected in a population 

 system without protoplasmic contact be- 

 tween the individuals of the group, inte- 

 gration is established through behavior 

 mechanisms. The behavior is initiated 

 through sensory stimuli, particularly 

 through senses responsive to temperature, 

 humidity, and auditory, chemical, visual, 

 and tactile stimuU. 



The sensory apparatus involved in re- 

 actions to temperature and humidity in in- 

 sects are unknown, but there is no doubt 

 of the response. Bumblebee and honeybee 

 workers station themselves at the entrance 

 to their nests on hot days and circulate air 

 by vibrating their wings (see pages 215 and 

 363). 



Ant mounds of a few north temperature 

 species (i.e., Formica ulkei, F. rufa, and 

 F. truncocorum) may be constructed with 

 a long gradual slope toward the south and 

 a steeper slope toward the north, thus offer- 

 ing more surface for the absorption of the 

 sun radiation. Dreyer (1942) reports a 

 40 per cent greater area of the sunny slope 

 compared with that of the shady slope of 

 a mound of Formica ulkei in northern 

 Illinois (see p. 362). 



The meridian mound nests of a tropical 

 termite (Amitermes meridionalis) in north- 

 ern Australia are oriented with a long axis 

 of about 10 feet running north and south, 

 and a short axis of about 2 feet running east 

 and west, and a sharp edge on top (Figs. 

 150, 151). It is presumed that the shape 

 of the nest, with its broad faces toward the 

 rising and setting sun and its narrow edge 

 toward the vertical rays, gives a relatively 

 stabile internal nest temperature during the 

 daytime. 



Without experimentation, it is difficult to 

 separate the reactions to temperature from 

 those to humidity. Worker termites that 

 construct definitive mound nests (i.e., those 

 of the termitid, Amitermes foreli, in 

 Panama) always move to the moist end of 

 a humidity gradient. One may conclude 

 that the nest-building behavior of termites 

 produces a homeostatic humidity close to 

 100 per cent within the nest environment 



