THE CUTICULAR STRUCTURES LINING THE ALIMENTARY CANAL OF TERMITES AND THEIR PHYLOGENETIC SIGNIFICANCE

A detailed study of the cuticular structures of the oesophagus, crop, proventriculus, stomodaeal valve, first proctodaeal segment, enteric valve, paunch, colon, rectal valve and rectum of the lower termite genera belonging to the families Mastotermitidae, Kalotermitidae, Termopsidae, Hodotermitidae and Rhinotermitidae has been made.\ud \ud The cuticular structures lining the alimentary canal of termites provide a highly reliable character in identifying termite genera and higher taxa and in establishing their phylo genetic relationships. In some cases it is possible to identify even species. No single character has hitherto proved as useful as the cuticular ornamentation of the alimentary canal in the generic recognition of termites. The imago worker mandibles used by Ahmad (1950) for study of termite Phylogeny do not show such a wide array of size, shape, type and arrangement as do the cuticular structures of the alimentary canal. While it is possible to identify many genera on the basis of imago-worker mandibles, in some cases, however, only generic grouping can be done using this character (Ahmad, 1950). On the other hand all the genera included in the present study are recognizable on the basis of the cuticular structures lining the alimentary canal.\ud \ud The comparative study of the cuticular structures present in the oesophagus, crop, proventriculus, first proctodaeal segment, enteric valve and rectal valve shows that the ornamentation in each part of the alimentary canal has its own level of importance in termite taxonomy. The armature of the oesophagus, crop, proventriculus and rectal valve is of value in the recognition of families although in some cases it can also help in the identificat ion of lower taxa.\ud \ud The armature of the first proctodaeal segment and enteric valve is much important than the ornamentation of any other portion of the alimentary canal for study of taxonomy and phylogeny of termites. It provides a set of characters demarkating each genus and, in some cases, species also. On the basis of which a key to the families and genera is produced.\ud \ud The cuticular structures lining the alimentary canal of termites, particularly in the region of the first proctodaeal segment and enteric value, has been found to be very helpful in unstanding termite phylogeny (Grasse and Noirot, 1954; Ahmad,1976. 1963,Sands,1972; Ahmad and Akhter, 1981). Their conservative nature is further revealed by the present study.\ud \ud The phylogenetic relationships of lower termites established as a result of the present study generally lend support to most of the studies made by earlier workers. In some cases, however, new relationships are indicated.\ud \ud The position of the family Mastotermitidae in the Isoptera as determined by earlier workers is supported by the present study also. The phylogenetic scheme of the family Kalotermitidae worked out on the basis of the cuticular ornamentation of the alimentary canal, however, shows several important differences from the phylogenetic study of Krishna (1961).\ud \ud The findings of the present study are more in agreement with Grasse (1949) in regard to the status of the genera Hodotermes, Microhodotermes, Anacanthetermes, Archotermopsis, Zootermopsis, Porotermes and Stolotermes. Based on the cuticular ornamentation of the alimentary canal, these genera fall in two distinct groups, one represented by Archotermopsis, Zootermopsis, Stolotermes and Porotermes and the other by Hodotermes, Microhodotermes and Anacantho termes. According to the present study also, the two groups should have the status of families, Termopsidae and Hodotermitidae, as suggested by Grasse (1949).\ud \ud The origin of Rhinotermitidae from a stock which had imago worker mandibles conforming to Archotermopsis-Stolotermes type as suggested by Ahmad (1950), Emerson (1968, 1971) and Emerson and Krishna (1975) is also supported by the present study. According to the characteristics of the cuticular ornamentation of the alimentary canal also, the rhinotermitid genera can be put into two groups, representing the two main branches of the phylogenetic tree as suggested by Ahmad (1950), First group includes the genera of the Rhinotermitinae and the second the genera belonging to other subfamilies of Rhinotermitidae.\ud \ud The assignment of the genus Prorhinotermes to its proper place is still prob1ematic. The earlier worker (Ahmad 1950, Emerson 1971), Emerson and Krishna 1975 also reported that Prorhinotermes shared characters of the both groups but on the basis of then existing knowledge, they preferred to treat it as a member of the subfamily Rhinotermitinae. The present study, however, indicates its greater affinity with the second group, I am therefore putting it on the second main branch and assign to a new subfamily, Prorhinotermitinae. The present comparative study of the cuticular ornamentation lining the alimentary canal of termites shows that some of the characters have regressed while some have more advanced during the course of evolution