Culex (Culiciomyia) nebulosus Theobald

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 : 94-95

Culex (Culiciomyia) nebulosus Theobald

subspecies nebulosus Theobald, 1901d —original combination: Culex nebulosus . Distribution: Benin, Burkina Faso, Cameroon, Central African Republic, Comoros, Côte d’Ivoire, Democratic Republic of the Congo, Ethiopia, Gabon, Ghana, Kenya, Liberia, Madagascar, Mali, Niger, Nigeria, Republic of the Congo, Republic of South Africa, Saudi Arabia, Senegal, Sierra Leone, Tanzania, Togo, Uganda, Yemen, Zambia ( Wilkerson et al. 2021, listed in error from Malaysia).

subspecies pseudocinereus Theobald, 1901c —original combination: Culex pseudocinereus ( Stone et al. 1959 and Knight & Stone 1977 erroneously attributed subspecific status to Edwards 1941, who actually treated the taxon as a variety; however, as explained by Harbach 2018, pseudocinereus is deemed to have subspecific rank). Distribution: Botswana, Democratic Republic of the Congo, Lesotho, Malawi, Namibia, Nigeria, Republic of South Africa, Tanzania, Zimbabwe ( Wilkerson et al. 2021).

Culiciomyia is a very difficult group taxonomically. Females are generally difficult to distinguish, some are indistinguishable, and the identification of species depends mainly on anatomical features of males and fourth-instar larvae. Nineteen species of the subgenus are currently recognized in the Afrotropical Region ( Cornel et al. 2020). The adults of both sexes and larvae are known for 12 of the species, albeit inadequately or incompletely described, only males are known for six species and one species is only known from the larval stage. As for most species of the subgenus, the adults and larva of Cx. nebulosus sensu stricto and subspecies pseudocinereus are known but have not been studied and described in detail. Their identification relies on subtle differences in the extent of scaling on areas of the thorax of adults, the development of the maxillary palpal comb scales of males and the form of the pecten spines and spiracular apodeme of larvae. Note. The palpal comb ( Cornel et al. 2020) is a ventral row of long outstanding hair-like scales ( Belkin 1962) on the distal half of palpomere 3 ( Edwards 1941).

Cornel et al. (2020) quoted Edwards (1941) for the development of the palpal comb scales of the typical form, but their photographic illustration differs slightly from Edwards’s line drawing. The palpal comb depicted by Edwards consists of a proximal set of 6 long spear-like scales separated by a small gap from a distal set comprised of 7 smaller, distally broader and apically hooked scales. In contrast, the proximal comb set illustrated by Cornel et al. consists of 7 scales of two sizes, a proximal group of 4 distinctly longer scales similar to those illustrated by Edwards and a distal group of 3 shorter, broader, apically pointed scales; a gap separates the proximal set from the distal set, which consists of 8 or 9 scales about the same length as the distal scales of the proximal set but developed as illustrated by Edwards. Variation in the composition of the palpal comb of the type form is further illustrated by Jupp (1996): The proximal comb set consists of 7 scales separated by a gap from the distal set comprised of 8 scales, the scales of both sets are as illustrated by Edwards. In summary, the palpal comb of the type form consists of a proximal set of 6 or 7 lanceolate scales separated by a gap from a distal set of 7–9 distally broadened, apically hooked scales. The palpal comb of subspecies pseudocinereus has never been illustrated; however, Edwards (1941) noted that “Scales in distal part of palpal comb slightly different in shape from typical nebulosus , being bluntly pointed but without strongly hooked tips.” During the course of this study, we had an opportunity to examine the holotype male of pseudocinereus and noted that the comb scales gradually grade from large scales proximally to smaller scales distally with little change in shape and no apparent gap or clear delimitation of proximal and distal sets. In addition to differences in the palpal comb scales, Edwards also noted that pseudocinereus “Closely resembles typical nebulosus but differs in both sexes in having much more numerous flat white scales on the mesepimeron; propleura [proepisternum] with a large patch of scales; lower mesepimeral bristle [seta] often accompanied by from one to three short hairs [small setae] (between it and the scales).” Edwards did not find any differences in the male genitalia of the two forms, but this is likely to be due to inattention to delicate structural detail.

Bram (1967) stated that species of Culiciomyia are most reliably distinguished in the larval stage; for this reason, it is surprising that Hopkins (1952) did not treat the larva of pseudocinereus , the omission of which may have lead Mattingly & Lips (1953) to consider that larvae of nebulosus and pseudocinereus were indistinguishable. As is the case with most species of Afrotropical Culex , the larva of nebulosus is superficially and inadequately described. For this reason, it was only possible for Peters (1955) to compare larvae of pseudocinereus with the description of the type form provided by Hopkins (1952). In doing so, Peters was only able to determine that the larva of pseudocinereus differs from the type form in the development of the pecten spines and the spiracular apodeme (“stirrup-shaped piece”). The pecten spines of the former have a broad base and a single denticle as opposed to a narrower base and usually at least two denticles in the type form. More striking is the development of the spiracular apodeme, which is much broader with the arms of the U-shaped distal end more widely separated and the narrower arm longer and differently shaped than in pseudocinereus . As shown for two species of the subgenus Culex in Central America ( Strickman 1990), the form of the spiracular apodeme is indicative of different species.

Collection records indicate that nebulosus sensu stricto probably occurs throughout sub-Saharan Africa. Discounting records of subspecies pseudocinereus in Nigeria and the Democratic Republic of the Congo, it appears that this form is prevalent in southeastern and southern countries of the continent where it is probably sympatric with the type form. This is supported by the occurrence of the adults of both forms in Elizabethville, Belgian Congo ( Peters 1955), now known as Lubumbashi in the Democratic Republic of the Congo, which is located in the southeast of the country adjacent to the border with Zambia.

Based on the forgoing analysis of morphological and distributional information, it seems highly likely that nebulosus and pseudocinereus are separate species; hence, the latter form is herewith formally returned to its original specific status: Culex (Culiciomyia) pseudocinereus Theobald, 1901c . Culex pseudocinereus is currently listed as a species in the Encyclopedia of Life.

Culex nebulosus has a single synonym, Cx. nigrochaetae Theobald, 1901c (♀ only of type series; type locality: Lagos, Nigeria) and Cx. pseudocinereus has three synonyms, Cx. freetownensis Theobald, 1901c (type locality: Freetown, Sierra Leone), Cx. invenustus Theobald, 1901d (type locality: Degama, Rivers State, Nigeria) and Pectinopalpus fuscus Theobald, 1909 (type locality: Obuasi, Ashanti Region, Ghana). These four nominal forms are based on superficial descriptions of adults: The type specimens of the first three are females and the type of fuscus is a male. Until reared specimens from the type localities of these nominal species are available for critical comparative study, they must remain synonyms of their senior synonyms.