Simulium (Eusimulium) tenerificum Crosskey, 1988

Crosskey, R. W. & BÁez, M., 2004, A synopsis of present knowledge of the Simuliidae (Diptera) of the Canary Islands, including keys to the larval and pupal stages, Journal of Natural History 38 (16), pp. 2085-2117 : 2101-2103

Simulium (Eusimulium) tenerificum Crosskey

Material from breeding sites

Gomera: Site G 2—1”(z), 2 pupae (6 June 1990) ( RWC). La Palma: Site LP 1— 2 larvae (17 April 1981) ( RWC) [recorded as aureum sibling ‘L’ in Leonhardt (1985)]. Tenerife: Site T 1— 18 pupae, 71 larvae (12 April 1991) ( BM / ANN / MB) and 3 larvae (8 November 1991) ( BM / ANN / MB). Site T 9— 17 pupae [genitalia of two

pharate „ on slides], 26 larvae [larvae misreported in Crosskey (1988b) as ‘ guimari ’] (8 April 1983) ( RWC), 1 pupa, 82 larvae (14 April 1991) ( BM / ANN / MB) and 3 pupae, 34 larvae (1 November 1991) ( BM / ANN / MB). Site T 14—2„(z) [including holotype], 3”(z), 36 pupae [genitalia of pharate „ on slide], 181 larvae [larvae misreported in Crosskey (1988b) as ‘ guimari ’] (9 April 1983) ( RWC); 1„(z), 26 pupae, 89 larvae (13 June 1990) ( RWC), 13 larvae (11 April 1991), 35 larvae (2 November 1991) ( BM / ANN / MB) and 118 larvae (14 April 2001) ( MB). Site T 23—31

pupae, 86 larvae (17 April 1991) ( BM / ANN / MB) . Site T 24— 9 pupae, 10 larvae (15 April 1991) ( BM / ANN / MB) .

Remarks

Description of this species (Crosskey, 1988b) was based on morphological differences from the closely related S. velutinum . The holotype (a reared male with its associated exuviae) is from the Barranco del Rio (Tenerife) and was part of the same sample collected ( RWC) there on 9 April 1983 from which larvae were used for chromosomal investigation. Other specimens were obtained simultaneously from the Barranco del Infierno stream near Adeje in Tenerife and the species later (1990) collected in Gomera. The species has never been found in Gran Canaria despite the extensive simuliid sampling in that island and we believe it to be absent. Emphasis was placed in the original description on the virtual absence of the larval postgenal cleft, but this ostensible distinction from velutinum is false now that it is known (Crosskey, 1995) that descriptions of the larval stage of tenerificum and guimari were reversed by mistake. The larvae that virtually lack the postgenal cleft are those of S. guimari (cf. comparative photographs of the venter of the head capsule in the two species in figures 41 and 42).

Following the invalidation of the supposed larval postgenal cleft character the morphological differences between Simulium tenerificum and S. velutinum become less tangible and raise the question whether the former should be considered a separate species. The similarity in the male genitalia is strong, the two nominal species having similarly small subtriangular ventral plates (cf. figures 3 and 25 in Crosskey, 1988b); the tip of the gonostyle, however, is more produced beyond the insertion of the apical spinule in tenerificum than in velutinum , in some specimens being quite pointed. The spermathecae of the two species are similar, inasmuch as they both (unusually for the aureum group) lack the dark nipple-like development of the spermatheca at the duct base—a character which is present in S. guimari . A few small differences are evident in the pupae (see characters in the identification key given earlier) but there seem to be none of note in the larva. The cytological situation recently revealed with the aureum group in North Africa further complicates the question of whether tenerificum and velutinum might be conspecific. Adler (personal communication) has recently seen larvae from Morocco with polytene chromosomes either conforming to sibling ‘I’ ( velutinum ), almost exactly conforming to sibling ‘L’ ( tenerificum ) or showing intermediate characteristics. The need for further research, both cytological and morphological, is evident but until more conclusive evidence is available we continue to treat S. tenerificum as a valid species; our colleague P. H. Adler (personal communication) concurs with this view.

Simulium tenerificum is endemic Canarian chromosomal aureum sibling ‘L’ defined and placed in a cytophylogeny for the Simulium aureum group by Leonhardt (1985); it was wrongly referred to by Crosskey (1988b), because of misassociation of the larva with other stages, as sibling ‘M’ (~ guimari , q. v. below ). Siblings ‘L’ and ‘M’ were both characterized on the basis of larvae present in the same samples and collected (by RWC on 9 April 1983) from the natural ravine streams in the barrancos Rio and Infierno; sympatry of tenerificum and guimari , evident from morphological characters differentiating these nominal species, was chromosomally confirmed. Leonhardt (1985) recorded that her sibling ‘L’ is a very close relative of the aureum group sibling ‘I’, that is to say S. velutinum , differing from that sibling only by one fixed inversion, IIS-17. Figure 43 shows the polytene chromosome complement with this inversion marked. Leonhardt’s findings are confirmed by P. H. Adler (personal communication), his examination of the chromosomes of 10 larvae (five males, five females) from the Barranco del Rio type locality (collected by MB on 14 April 2001) having shown them to match her description band for band. (One larva, however, had in sections 75–76 of chromosome arm IIS a tiny autosomal polymorphism expressed heterozygously as a knot.)

The two pupae and the pupal exuviae of the reared adult from Gomera locality G2 listed above require comment. The gill filaments at the base are rather more widely spread (figures 23, 24) than usual in tenerificum but more significant is the fact that the head plate and thoracic dorsum have fairly abundant microtubercles (as in velutinum ) instead of the polished and shining microtubercle-free cephalothorax found in all tenerificum pupae seen from Tenerife. The cocoons, however, of the pupae from Gomera are of tenerificum shape, having a short but definite median lip and a scooped outline to the anterior margin when seen in profile, exactly as the cocoon shape seen in pupae from Tenerife and illustrated in figures 31 and 32. This combination of cocoon with the tenerificum shape but the microtubercle condition of velutinum suggests possible hybridization having occurred in Gomera. Interestingly, no specimens of any life stage that are unambiguously velutinum have been found at any time in Tenerife.

Figures

FIG 43. Larval polytene chromosome complement of Simulium (Eusimulium) tenerificum (~aureum cytological sibling ‘L’), with marked position of diagnostic fixed inversion. Data: Barranco del Rio (Tenerife), 14 April 2001 (M. Báez).