Culex (Culex) toroensis Edwards & Gibbins

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 : 91

Culex (Culex) toroensis Edwards & Gibbins

subspecies macrophyllus Edwards & Gibbins, 1939 —original combination: Culex vansomereni spp. macrophyllus (subspecific status by Edwards, 1941 concomitant with the elevation of toroensis to specific status). Distribution: Cameroon, Uganda ( Knight & Stone 1977).

subspecies toroensis Edwards & Gibbins, 1939 —original combination: Culex vansomereni toroensis (specific status by Edwards 1941). Distribution: Burundi, Cameroon, Democratic Republic of the Congo, Ethiopia, Kenya, Malawi, Republic of South Africa, Rwanda, South Sudan, Sudan, Uganda ( Wilkerson et al. 2021).

The typical form and subspecies macrophyllus were originally described as subspecies of Cx. vansomereni Edwards, 1926a . Edwards (1941) elevated toroensis to specific status based on “well-marked larval distinctions from C. vansomereni , together with the constant difference in pleural scaling”; consequently, macrophyllus became a subspecies of Cx. toroensis . Edwards & Gibbins (1939) and Edwards (1941) distinguished the subspecies based solely on features of the male genitalia. In the typical form, foliform seta g of the subapical lobe is about as long as seta f and more or less pointed, the lateral plate of the phallosome has about five denticles and the gonostylus is long and markedly narrowed distally. In comparison, seta g is much larger than seta f in subspecies macrophyllus , the lateral plate has a slightly different shape with about three denticles and the gonostylus is distinctly shorter and not narrowed distally. The larva of the typical form is known from specimens reared to adults ( Edwards 1941; Service 1959). The larva of subspecies macrophyllus is not definitely known, but larvae associated with adults collected at the type locality ( Edwards & Gibbins 1939) “bore a close resemblance” to the larva of Cx. andersoni Edwards, 1914 , which is very distinct from the larva of subspecies toroensis . The larva of the typical form has not been studied in detail—only features of the head and terminal abdominal structures have been described, with special emphasis on the anterior (dorsal) and posterior (ventral) clusters of spines near the apex of the siphon. As noted by Service (1959), specimens of toroensis from Kenya and Sudan examined in the “British Museum” did not exhibit the arrangement of 18 anterior siphonal spines illustrated by Hopkins (1952), and specimens from elsewhere had 0–9 anterior spines. It should be mentioned, however, that a male from Kisomoro, Uganda, the type locality of toroensis , was reared from a “larva similar to that figured by Hopkins [1936] … as sp. indet.” ( Edwards & Gibbins 1939), and was illustrated by Hopkins (1952) as the larva of Cx. toroensis . Both Hopkins and Service noted the variable presence of 0–3 posterior spines. In agreement with Service (1959) and Jupp (1996), the variable number of apical siphonal spines makes it impossible to reliably identify the species, e.g. to distinguish larvae from those of Cx. vansomereni . On the other hand, we feel that such variation may be an indication of a complex of closely related species.

Oddly, Edwards & Gibbins (1939) described macrophyllus (p. 31) prior to describing toroensis (p. 32); hence, macrophyllus could have been taken as the nominotypical species with toroensis as a subspecies of Cx. macrophyllus . Mattingly (1956) revealed that macrophyllus was described from six males, five with dissected genitalia, and four females collected at “Lugezi Camp between Mt. Mgahinga [Mt Gahinga] and Mt. Sabinio [Mt Sabyinyo]” located at the extreme southwestern fringe of Uganda along the border with Rwanda [actually, Mt Sabyinyo, an extinct volcano, is situated at the intersection of present-day Democratic Republic of the Congo, Rwanda and Uganda, and Mt Gahinga, a dormant/extinct volcano, is on the border between Rwanda and Uganda]. Lugezi Camp was apparently located on the Uganda side of the current border with Rwanda. The two mountains were located in the former Kigezi District, which included flanking areas of the two currently neighboring countries. The former Kigezi District now includes the Kabale, Kanungu, Kisoro and Rukungiri Districts and the two mountains are situated at the margins of the Kisoro District. Edwards (1941) indicated that macrophyllus was found at the “Saddle between Mts. Mgadinga and Sabinio, 8000 ft. [2,438 m]”, but according to Edwards & Gibbins (1939) Lugezi Camp was located at the side of “Mt. Sabinio” at an elevation of “ 7–8000 ft. [2,135 –2,438 m]”. Mattingly (1956) observed that toroensis was described from five males, two incomplete and three with dissected genitalia, and one female from Kisomoro, Uganda and nine males and nine females from Kararama Camp in the Namwamba Valley, and designated a male with dissected genitalia from Kisomoro as the name-bearing lectotype. Kisomoro (elevation 1,492 m), situated in the Bunyangabu District in the Western Region of Uganda, is located approximately 240 km north of the type locality of macrophyllus . It is interesting that the following statement made by Edwards & Gibbins (1939) regarding toroensis was apparently overlooked by later workers: “These specimens [from Kararama Camp, Namwamba Valley] have the male hypopygium [genitalia] almost exactly as in the typical form [ vansomereni ], and do not show the enlarged leaf and other slight peculiarities seen in specimens from Kigezi [i.e. Lugezi Camp].” The Namwamba Valley is located approximately 37 km southwest of Kisomoro, indicating that toroensis is probably widely distributed in the mountainous regions of western Uganda. In view of the differences in structures of the male genitalia of the two forms, especially the very different gonostylus, the extensive variation observed in the anterior siphonal spines of larvae identified as toroensis suggesting that it may be a species complex, the likelihood that the larva of macrophyllus is similar to the larva of Cx. andersoni , and the probability that toroensis and macrophyllus are likely to occur in sympatry, we feel confident that the latter form is a separate species and hereby formally accord it specific status: Culex (Culex) macrophyllus Edwards & Gibbins, 1939 . Culex macrophyllus is currently listed as a species in the Encyclopedia of Life.