498 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 64 



damage to ^vood, and care for the other castes (fig. 1) . Wliere work- 

 ers are not present, nymphs or pseudoworkers take over their duties. 



The inhibition theory of caste differentiation first developed by 

 Drs. A. L. Pickens and G. B. Castle of the University of California 

 in the early 1930's has recently been substantiated by the Swiss en- 

 tomologist Dr. Martin Liischer (1952) in his studies of hormones. 

 Their theory is that males, females, soldiers, and workers secrete ecto- 

 hormones which inhibit the nymphal development of individuals of 

 the same sex or caste as that of the form secreting the hormone. In 

 small colonies where reproductive forms are fully functioning, the 

 development of any additional sexual forms is inhibited by the secre- 

 tions of the parent reproductive forms of the king and queen. 



This substance is supposed to be distributed throughout the colony 

 by the grooming habit of the individuals. Or each caste, if present 

 in the colony in sufficient numbers, tends to delay or inhibit the de- 

 velopment of the individuals of the same caste by a hormone 

 regulation. 



Dr. Liischer found that this inhibitory effect can operate only when 

 workers can touch the functional reproductives. He theorized that 

 it is the saliva, feces, or exudates of the reproductives that possibly 

 contain an ectohormone that is the inhibiting agent. The surplus 

 supplementary reproductives are eaten by the workers. If contact 

 is cut off, the inhibiting influence that prevents the production of 

 supplementary reproductives does not operate. 



At the Fourth International Congress for the Study of Social In- 

 sects, held at the 600-year old University of Pavia, in Italy, I presented 

 a paper (Snyder, 1963) dealing with the fate of the supplementary 

 reproductives in small colonies of eastern species of Reticulitermes 

 in the United States. In the spring, large numbers of supplementary 

 reproductives are present in colonies before the annual colonizing 

 flight or "swarm" of the winged adult. These disappear just before 

 or at the time of the flight of the winged. Are they killed by the 

 workers as being unnecessary in the parent colony where reproduc- 

 tives are already present? Or, impelled by the same stimuli as the 

 winged, do they migrate — with or without workers — by subterranean 

 galleries to form new colonies ? 



In the discussion which followed the presentation of the above, 

 it appeared that there exist substantial differences between the habits 

 of species of Reticulitermes in Italy and the habits of those species 

 commonly found in eastern United States. In Italy, Reticulitermes 

 colonies are headed only by supplementary reproductives, whereas in 

 the United States colonies are commonly founded by winged or ma- 

 cropterous adults. In France, both reproductive forms found 

 colonies. 



