Aedes (Aedimorphus) tricholabis Edwards

Harbach, Ralph E. & Wilkerson, Richard C., 2023, The insupportable validity of mosquito subspecies (Diptera: Culicidae) and their exclusion from culicid classification, Zootaxa 5303 (1), pp. 1-184 : 14-15

Aedes (Aedimorphus) tricholabis Edwards

subspecies bwamba van Someren, 1950 —original combination: Aedes (Aedimorphus) tricholabis ssp. bwamba . Distribution: Benin, Kenya, Nigeria, Uganda ( Wilkerson et al. 2021).

subspecies tricholabis Edwards, 1941 —original combination: Aedes (Aedimorphus) tricholabis . Distribution: Benin, Burkina Faso, Central African Republic, Côte d’Ivoire, Kenya, Mali, Nigeria ( Wilkerson et al. 2021) .

This taxon is an example of the scant taxonomic work carried out on mosquitoes in Africa on all but the most important vectors of human and animal pathogens. Aedes tricholabis was described from the adult female, male and male genitalia, but not the larval or pupal stages. Subspecies bwamba was described, in addition to the larva and pupa, from the adult male and female, which were distinguished from tricholabis based on a single, but we think significant, character. Because the larval and pupal stages of tricholabis are not known, descriptions of the immature stages of bwamba have served to represent tricholabis (see below). The dearth of specimens needed to carry out direct comparisons of all life stages is surprising given that tricholabis sensu lato has been found to harbor Dengue, Sindbis and other viruses (e.g. Ochieng et al. 2013; Munyao et al. 2020; Musa et al. 2020). In a sample of published studies, we found that most authors cited Edwards (1941) as the authority for identifications, and therefore subspecies bwamba , not yet described in 1941, was subsequently ignored in post-1950 studies.

Aedes tricholabis was described from two males and five females collected in Gede (or Gedi), located north of Mombasa, Kenya. Townsend (1990) found two females and the lectotype male (designated by Mattingly 1956) in the collection of the Natural History Museum, London. Edwards distinguished tricholabis in a key using the following characters: Scutellum with narrow scales only; decumbent scales of vertex all narrow; femora and tibiae not striped; hindtarsus entirely dark; head in female with a distinct patch of dark decumbent scales on vertex (this patch absent in males); abdominal terga usually with complete basal pale bands; postspiracular scales all broad and flat; hindfemur pale beneath almost to apex; hindungues (as hindtarsal claws) simple. The description also states that all scutellar scales are narrow and yellowish, and, in addition to pale basal bands on all terga, there are also dark apical bands on the sterna. The adult male, as noted above, does not have a patch of dark decumbent scales on the vertex, which led Edwards to question if the males and females were the same species, because there were no associated larval and pupal exuviae to prove otherwise. To our knowledge, this query has not been answered. The most remarkable distinguishing feature of tricholabis (and subspecies bwamba ), however, is a gonostylus, which on the ventral surface (“outer edge”) is “provided with a row of long soft hairs [setae], most of which are branched, the one nearest the base having most branches.” The egg, larva and pupa have not been described and only the male genitalia have been illustrated.

Subspecies bwamba was described from the male holotype, six male paratypes, and five larval and nine pupal exuviae from Bwamba Province, Toro District, in western Uganda. Townsend (1990) found the holotype and four paratypes in the collection of the Natural History Museum, London. Van Someren (1950) provided detailed descriptions of the adult male, male genitalia, and larval and pupal stages. Only the male genitalia and pupa were illustrated. Van Someren stated: “The male terminalia of this species do not differ from the figure of A. (A.) tricholabis ...”. The description of the male of bwamba does not appear to us to differ from tricholabis , including the lack of a patch of dark decumbent scales on the vertex. However, the scutellum is “clothed with broad creamy white scales on all lobes.” This is in contrast to the scutellar scales being all narrow and yellowish in tricholabis . The larval stage of subspecies bwamba is apparently quite distinctive, as relayed in a personal communication to van Someren: “Dr. Haddow (personal communication) states that the larvae are very pale and transparent in life, with the eye spots very large and black. Usually the swimming is done with the mouth brushes, but when they are disturbed, body swimming movements occur. They are markedly restless, often looping the loop under water and have a habit of browsing. …The larval skins are very fragile, with all the setae pale and transparent and easily detached.” The larval stage of tricholabis is not known, precluding a comparison with subspecies bwamba .

Hopkins (1952) used van Someren’s description of the larva of subspecies bwamba to represent the type form and Pao & Knight (1970) described the larval mandible and maxilla of subspecies bwamba to represent tricholabis sensu lato. No explanation was given of how the taxonomic determination was made. Similarly, Cordellier & Geoffroy (1976) represented tricholabis sensu lato as both a species and as a species with a subspecies, without explanation.

The distributions of these nominal taxa, therefore, have not been documented, other than for the type localities and for surveys that used Edwards (1941) as an identification resource. Service (1960), however, added to the description of the larva of subspecies bwamba from Lokoja, Nigeria (7° 47′ 48″ N, 6° 44′ 25″ E). This site is far from the type locality of bwamba in Uganda and gives possible insight into the broad distribution of at least subspecies bwamba . Service (1960) also “fully endorsed” Haddow’s statement that “the larvae in life are pale and transparent with large dark contrasting eyes.”

We do not note consensus regarding the identity and distributions of the nominotypical form or subspecies bwamba . The only clear and significant distinction is that tricholabis adults have all scutellar scales narrow and yellowish whereas adults of bwamba have all scutellar scales broad and creamy white. We consider this a significant difference that stands out in a confused understanding of these taxa, which we think justifies elevation of bwamba to species status: Aedes (Aedimorphus) bwamba van Someren, 1950 . Aedes bwamba is currently listed as a species in the Encyclopedia of Life.