457 



NEW SPECIES OF AFRICAN SIMULIIDAE AND FURTHER STUDIES 



OF THE EARLY STAGES. 



By A. W. J. PoMEROY, M.B.E., F.E.S., 



Government Entomologist, Nigeria. 

 (Plates XIII & XIV.) 

 It has been stated by Malloch and other authors that the superficial differences 

 between the various species of Simulium in the adult stage are often so minute as 

 to be discernible only after a very careful study of the genus. Previous studies 

 had led the writer to believe that the characters of the pupal respiratory filaments 

 would prove to be of constant specific value, but further investigation has caused 

 this view to be modified with regard to the actual branching, though the structure 

 of the chitinous wall and the general appearance still seem to be constant specific 

 characters. 



Tn the case of one species described in this paper, 5. hirsutiim, and the varieties 

 S. hirsutum var. dubiiim and S. hirsutum var. adersi, though the branching of the 

 filaments varies very considerably, even in the same pair of filaments from the same 

 individual pupa, yet the chitinous structure of the filament wall appears to be the 

 same in all specimens. 



The difference in the position and actual number of the branches seems quite 

 understandable from a morphological point of view and may be explained on the 

 supposition that the filaments primarily arise from three main stems, which form 

 into a single stem at the base. The pupa of the var. dulmmi, though bearing the 

 same number of branches as the type that has been selected as the true hirsutum, 

 namely eight, differs in that the branching takes place, in the case of the second 

 and third main stems, at a very considerable distance from the base. 



These two forms were taken from the same locality and were in the greatest 

 number amongst the specimens obtained, though individuals were taken at the time 

 showing considerable variation in the distance of the branching point from the base. 

 With regard to the form adersi, this was obtained from a very different locality and 

 altitude, but it will be seen from the figure given (PI. xiv, fig. 6) that the first 

 main stem has developed a further branch, the second main stem divides again into 

 two more branches and in the case of the third main stem the branching appears 

 to have retracted until the three branches arise from nearly the same point. The 

 position of the branching of this form appears to vary very considerably in a series 

 of specimens, but no difference can be observed in the chitinous structure of the 

 outer wall. The male genitalia, wing venation, hind claws of the female, and the 

 general appearance and colour of the adults of all these three forms appear to 

 be the same. 



A similar case of variation in the pupal branching occurs in the species 5. alcocki, 

 S. alcocki var. violaceum and 5. alcocki var. coalitum, described in this paper. The 

 adults of these varieties appear to differ slightly in colour, but in no definite 

 structural character. 



The actual position of the branching of the filaments may depend a great deal 

 on the growth of the larva. Taylor* states that the rudimentary pupal filaments are 

 developed in the very young larvae at the same time as the imaginal rudiments ; 

 on this point the writer is fully agreed. 



* Taylor, T. H., Trans. Ent. Soc, London, 1902, pp. 701-716. 



