ETHIOPIAN NASUTITERMITINAE 77 



dilated terminally or tapering. Pilosity of head capsule rather evenly fine, arising from small 

 sockets of regular size with a few larger scattered sockets among them. 



Soldier. Dimorphic in most species, with traces of subdivision of " major " and " minor " or 

 almost complete inter-gradation occurring in some colonies or local populations of some species. 

 Nose cylindrical to strongly conical. Vestigial mandibles usually without points. Head 

 capsule without any constriction behind antennae, and devoid of prominent setae except on 

 nose (major soldier only, minor soldier often has constricted head capsule). 



The longer cutting edges of the imago mandibles, and the right molar plate, 

 distinguish this genus from Nasntitermes. The only genus closely resembling 

 Trinervitermes in this respect is Baacaliotermes gen. nov., included in Trinervitermes 

 by Emerson (i960) but differing in having monomorphic soldiers and certain other 

 features. 



The genus is mainly grass and leaf feeding and occurs only in the savannah and 

 steppe vegetation types, (Keay et al., 1959). Wherever agricultural practices have 

 degraded the vegetation to grassland in the fringes of the forest zones, Trinervitermes 

 has been found, though it has not been recorded from similar areas deep in the forest. 

 Conversely, in equatorial western Uganda, the recent degradation of a forest barrier 

 to grassland has not yet led to the mingling of the West African species to the north 

 of it, with the East and Central African species to the south. 



There are four groups of species which are recognizable as differing in their geo- 

 graphical distribution. The " West African " group reaches northern Uganda and 

 the Sudan. The " East African " group includes species both widespread (7\ 

 rapulttm and T. dispar) and more restricted (7\ gratiosus and '/'. bettonianus). There 

 is a single " Central African " species, T. rhodesiensis, and one in South Africa, 

 T. trinervoides. The distributions of the East, Central, and South African species 

 overlap to a considerable extent, as can be seen from a comparison of maps 20, 

 25, 26, and 29. 



Trinervitermes is the most difficult genus in the Xasutitermitinae, and perhaps in 

 the order Isoptera. In both imagos and soldiers there is wide variation, and few 

 reliable taxonomic characters ; some are of value for one or two species, and value- 

 less for the rest. The majority of those used by earlier workers in the genus have 

 been abandoned as useless, and a number of new features are used for the first time. 

 Unlike the genus Nasiditermes, the species are represented by numerous specimens. 



An interesting result is that the localised operation of distinctive genes or gene 

 complexes has been observed in certain species, for example : the partial or com- 

 plete suppression of the outer corners of the imago pronotum, or the development of 

 unusually large ocelli. Both of these occurred in a number of colonies of T. dispar 

 from the same or nearby localities. 



In the case of the soldier caste, only the major soldiers are identifiable to species. 

 It would be possible to key the minor soldiers to groups of species, but these would 

 be too large to be of practical value ; even in the case of the major soldiers, the key- 

 is based on the characters of the majority, since there are specimens of several 

 species which cannot be reliably identified in the absence of their imago. On the 

 other hand, some species are more readily separated in the soldier caste than in the 

 imago. 



