Culex (Eumelanomyia) horridus 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 : 96-97

Culex (Eumelanomyia) horridus Edwards

subspecies horridus Edwards, 1922 —original combination: Culex horridus . Distribution: Angola, Benin, Burkina Faso, Cameroon, Central African Republic, Comoros, Côte d’Ivoire, Democratic Republic of the Congo, Ghana, Kenya, Liberia, Madagascar, Mali, Mozambique, Nigeria, Republic of the Congo, Republic of South Africa, South Sudan [but not Sudan ( Simsaa et al. 2021)], Tanzania, Togo, Uganda, Zambia, Zimbabwe ( Wilkerson et al. 2021).

subspecies rageaui ( Hamon & Rickenbach, 1955) —original combination: Neoculex horridus var. rageaui (subspecific status by Harbach & Howard 2007). Distribution: Cameroon ( Hamon & Rickenbach 1955). These authors considered specimens from Benin and Burkina Faso that they compared with subspecies rageaui to be specimens of the nominotypical form (see below); thus, those two countries were erroneously included in the distribution of rageaui in the catalogs of Knight & Stone (1977) and Wilkerson et al. (2021).

Edwards (1922) proposed horridus as a replacement name for Protomelanoconion fusca Theobald, 1909 , type locality Accra in present-day Ghana, which was preoccupied by Taeniorhynchus fuscus Theobald, 1905d , a synonym of Culex (Culiciomyia) fragilis Ludlow, 1903 . Unfortunately, Edwards (1922, 1941) only briefly described (with lack of detail) and did not illustrate the male genitalia of horridus . Hamon & Rickenbach (1955) examined two series of specimens, one consisting of three males, one from Benin and two from Burkina Faso, and the other consisting of six males from Cameroon. They provided two illustrations of the subapical lobe of the gonocoxite, one drawn from a male from Burkina Faso labelled as horridus and the other drawn from the holotype of rageaui from Cameroon. The two illustrations are similar except in the former there is only one seemingly flexible simple seta (d or e) in group d–f and the three rod-like setae a–c are closely aligned parallel to each other with c inserted slightly distal to a and b. Subspecies rageaui has two straight (stiff?) setae (d and e) in group d–f and seta c projects at a 90-degree angle from setae a and b, which is very unusual and could be due to distortion. Except for setae d and e, the characteristics (shapes) of the other setae (a–c and f–h) are otherwise the same. Jupp (1996) also illustrated the subapical lobe of horridus , but setae d–g are very different than those illustrated by Hamon & Rickenbach. Whereas group d–f of the males from Burkina Faso and Cameroon consists of one or two simple setae (d and e) and four blades (f) with rounded tips and three or four apical barbs, group d–f of the specimen illustrated by Jupp consists of setae d and e and a single seta f with a bifid tip (which Jupp indicated may be an artefact). Whereas seta g is distinctly asymmetrical and as long as or slightly longer than seta f in the specimens illustrated by Hamon & Rickenbach, it is symmetrical and shorter than seta f in the specimen illustrated by Jupp. Obviously the species illustrated by Jupp is not conspecific with the species examined by Hamon & Rickenbach.

Hamon & Rickenbach stated that the genitalia of their two series of specimens are identical, and noted that they differed from Edwards’s description of horridus as follows: “the three rods (rods or blades) [setae a–c] are pointed at their apex, and at least two are curved into a hook; the four strong setae (blunt tipped setae) [seta f] are in fact narrow blades, rounded at their apex, and each bearing 3 to 4 subapical barbs; they are accompanied by one or two setae [d and e] thinner and shorter than themselves; the leaf [seta g], apparently unstriated, is very asymmetrical in shape and is accompanied by a strong seta [h] as long or longer than it…” (translated from the French). However, whereas the scutal scales are dark brown in the specimens of horridus from Benin and Burkina Faso, as described by Edwards for the typical form, the scutum of rageaui is “uniformly covered with yellowish-white scales” (translated from the French), whence the characteristic that distinguishes subspecies rageaui from the description of the type form provided by Edwards. The nature of the differences, especially the major difference in the color of the scutal scaling, prompted one of us (REH) to examine the syntype males of Protomelanoconion fusca Theobald, 1909 (for which Edwards replaced with the name horridus ) in the Natural History Museum (NHM), London. This resulted in an unexpected discovery. The subapical lobe shown in the two drawings of Hamon & Rickenbach (1955) is very different than the subapical lobe of the syntypes, and also different than the drawing of Jupp (1996). Out of curiosity, drawings of subapical lobes in Edwards (1941) were scanned to see if any of the other species he treated was similar to the syntypes of fusca (= horridus ). Edwards classified most species currently in the subgenera Eumelanomyia and Maillotia as species of the subgenus Neoculex . Astonishingly, the illustration of the subapical lobe he provided for Cx. salisburiensis Theobald, 1901c , a species of the subgenus Maillotia , agrees with that of fusca , particularly the shape of setae d–f and the distinctive foliform seta g with an elongate stem. Consequently, it seemed necessary to look at other treatments of salisburiensis , which resulted in another unexpected discovery. Knight (1953), in his paper on the mosquitoes of Yemen, consulted Peter Mattingly at the British Museum (Natural History) (now the NHM), concerning differences between the male genitalia of specimens they identified as salisburiensis and the genitalia of the species illustrated by Edwards (1941). Mattingly responded with the following.

I am afraid almost all of the differences you noted are due to errors in Edwards’ description. The only difference of any significance is that, while the Nairobi males have terminalia [genitalia] identical with the Yemen form, those from further south lack the longest of three accessory bristles [seta f] on the subapical lobe and one of the two small setae on the dististyle [gonostylus]. It is clear therefore that we have a northern and a southern form but it is impossible to say which is the type form since I have no males from Salisbury [Harare, Zimbabwe]…. It may be possible eventually to distinguish two subspecies. The southern forms are certainly much darker than yours, especially with respect to the scutal scaling but the Nairobi specimens are intermediate and, I should think, would probably intergrade in Eritrea. Also the two specimens from Chilanga [ Zambia] suggest that there is considerable seasonal variation since one, collected in January, is very dark, while the other collected in November, is as pale as the Nairobi form. Edwards’ figure for the length of the female palps [maxillary palpi] seems to have been based on a single aberrant or shrunken specimen; and the tergal bands are variable, even in the same locality. The other differences are just errors in description.

It appears that the figure of the subapical lobe that Edwards’s attributed to Cx. salisburiensis is that of Cx. horridus (i.e. P. fusca ). His descriptions of the genitalia of both species are brief, but the description given for Cx. horridus and the illustration attributed to Cx. salisburiensis clearly correspond with the syntypes of P. fusca . Therefore, there is little doubt that the species illustrated by Hamon & Rickenbach, and also Jupp, are not Cx. horridus and are separate species. The only problem that remains is the question about the color of the scutal scaling. Hamon & Rickenbach cite Edwards’s description of Cx. horridus , which says the scutal scales are dark. The scutal scales of the syntypes of P. fusca definitely are not dark, but are golden and those on the anterior margin are white. Examination of specimens in the NHM from several East African countries all have golden scutal scales with white scales on the anterior margin. This would suggest an error in the description, or perhaps Edwards’s interpretation of dark scutal scaling due the optics and light sources that were available at the time. However, as the genitalia of the males with dark and yellowish white scutal scales are the same, it would seem possible that this is due to seasonal or geographical variation within a single species, or they may be two different closely related species. In any case, the subspecific form described by Hamon & Rickenbach must be considered to be a distinct species, Culex (Eumelanomyia) rageaui Hamon & Rickenbach, 1955 , and the question of whether or not the form with dark scutal scaling is the same or a different species must await further study. Culex rageaui is currently listed as a species in the Encyclopedia of Life.