SIMULIIDAE OF AFRICA 81 



phoretic partner, particularly the shift of the posterior larval circlet to an almost 

 completely ventral (instead of terminal) position and the reduction of the cocoon and 

 associated multiplication of securing hooks ; on the other hand it is difficult to see 

 the significance of some of the structural modifications that occur in the larvae, for 

 instance the extreme reduction of the antennae in S.(P.) lumbwanum de Meillon, the 

 aberrant head fans in S.{P.) copleyi Gibbins, or the unique form of hypostomium in 

 S.(P.) berneri Freeman, although they are presumably related in some way to the 

 demands of a larval life spent attached to motile mayflies. 



The adults of Phoretomyia are moderately large (wing-length about 2-9-3-3 mm.) 

 and are particularly striking and handsome among African Simulium because of the 

 thick and even covering of rich yellow to deep golden scales on the first two abdominal 

 segments (discounting the basal scale) that contrast very conspicuously with the 

 remainder of the abdomen which is black (either with bronze-black scales and sparse 

 black hairs, or with bronze-black scales intermixed with clumps of pale yellow to 

 golden scales). In most species the fore tarsi are enlarged and flattened with a short 

 dorsal hair crest (e.g. Simulium copleyi Gibbins, Text-fig. 81) and the fore basitarsus 

 in these forms is usually only about 4-5 times as long as its greatest width ; this 

 strongly dilated fore tarsus distinguishes most Phoretomyia from almost all other 

 Ethiopian Simulium except the species of subgenus Edwardsellum such as S.(E.) 

 damnosum Theobald (Text-fig. 82), in which the fore tarsus is similarly enlarged, but 

 the resemblance between Phoretomyia and Edwardsellum in this character is certainly 

 convergent. 



The characters of the immature stages, being largely aberrant as compared to 

 those of typical Simulium and apparently adaptive characters rapidly evolved for 

 phoretic life, cannot safely be used for attempting to determine the phyletic affinities 

 of the subgenus Phoretomyia ; only adult characters can be considered for this 

 purpose. Of these the haired base to the radius, the lack of definite scutal pattern, 

 the toothed claws of the female, the smoothly rounded gonapophyses of the female 

 terminalia, the retention of a more or less definite seventh sternite in the female 

 abdomen, the small simple male styles, the presence of only one long main para- 

 meral hook and of a haired lamellate ventral plate in the male hypopygium all 

 indicate general affinity with the more primitive (or at least most generalized) sub- 

 genera of Simulium such as Eusimulium, Pomeroyellum and Meilloniellum, and 

 particularly with Meilloniellum. 



The Ethiopian species living in association with mayflies were, in fact, assigned by 

 Rubzov (1962 : 1497) to his genus Meilloniellum, erected by him for all the species 

 previously placed in the hirsutum-gvonp of Simulium by Freeman & de Meillon 

 (1953), and it is to hirsutum Pomeroy and its allies (here treated as the subgenus 

 Meilloniellum in a more restricted sense than that of Rubzov) that the phoretic forms 

 on mayflies appear most nearly related : this is suggested especially by the form of 

 the male ventral plate, which is closely similar in Meilloniellum and Phoretomyia, and 

 for instance almost identical in S.(M.) hirsutum Pomeroy and S.(P.) lumbwanum de 

 Meillon. On balance of characters, excluding the difference of ecological habit and 

 associated larval and pupal modifications, a better classification into subgenera 



