Toxorhynchites (Afrorhynchus) viridibasis (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 : 116-117

Toxorhynchites (Afrorhynchus) viridibasis (Edwards)

subspecies viridibasis ( Edwards, 1935) —original combination: Megarhinus aeneus var. viridibasis (specific status by Edwards 1941). Distribution: Burkina Faso, Central African Republic, Côte d’Ivoire, Mali, Nigeria, South Sudan, Sudan, Uganda ( Wilkerson et al. 2021); also the Democratic Republic of the Congo (see below).

subspecies voltaicus Ribeiro, 2005 —original combination: Toxorhynchites (Afrorhynchus) viridibasis voltaicus . Distribution: Burkina Faso ( Ribeiro 2005).

Edwards (1935) described viridibasis (as a variety of Megarhinus aeneus Evans, 1926 ) from two adult females collected in Uganda, the type specimen from Kampala and the second female from Soroti. The description was very brief and did not include illustrations. In addition to a slightly more detailed description of the two females, Edwards (1941) provided a very brief description of a dubious adult male, stating: “Although the male is damaged I think it must belong to the same species as the females: it is clearly quite different from the male of erythrurus, but it is quite possible that both viridibasis and aeneus should be regarded as subspecies of lutescens ; the available material is too scanty for any conclusion to be formed of the point.”

Ribeiro (2005) based the description of subspecies voltaicus on a single adult male captured on 18.7.54 at Banankélédage (Banankeledaga), cercle (circle, area) Bobo-Dioulasso, Haute-Volta (now Burkina Faso)— Banankeledaga is a village located near the city of Bobo-Dioulasso, the capital of Houet Province. Ribeiro did not mention how he identified the specimen as being conspecific with the female of the nominate form, but he distinguished the two subspecies in a key for the identification of males of species of the subgenus Afrorhynchus Ribeiro, 1992 . Oddly, the two subspecies keyed out in different couplets, with the nominate subspecies keying out in a couplet with Tx. ruwenzori ( van Someren, 1948) and subspecies voltaicus keying out in a couple in which the alternate character state leads to two consecutive couplets that identify Tx. capelai Ribeiro, 1992b , Tx. lutescens ( Theobald, 1901a) and Tx. zairensis Ribeiro, 2005 . Scaling on the mesokatepisternum was used to distinguish subspecies viridibasis from subspecies voltaicus and the other three species: In the nominate subspecies, “Golden scales on mesokatepisternum restricted to the lower portion of the sclerite [sternum]”; in subspecies voltaicus, “A patch of golden scales present on the upper portion of the mesokatepisternum, at base of prealar knob”. According to Edwards (1941), the female of the nominate form has “much of the pre-alar area (except the knob) clothed with white scales.” It is uncertain whether the prealar area of the male also has white scaling as Edwards only mentioned that the male “resembles ♀ in colouring of body and legs (thorax much denuded).”

In the diagnosis of voltaicus, Ribeiro mentioned that the male also differed from the male of the type form in having “a purple third tergum” and the coloration of the maxillary palpus, which is “extensively golden” in the nominate form and “mainly purplish golden with violet reflections” in voltaicus. He noted that “No significant differences were found between the male genitalia of Tx. v. voltaicus and those of the male Tx. v. viridibasis from Coquilhatville, Congo ” [Coquilhatville is the former name of present-day Mbandaka, a city on the Congo River in the Democratic Republic of the Congo]. For clarity, Edwards (1941) stated that the maxillary palpus of the questionable male of the nominate form that he examined was “as in lutescens ”, which he described as having the “shaft and penultimate segment golden beneath, only tip of latter dark, and with some golden scales above, terminal segment all dark”.

In the original description of viridibasis, Edwards (1935) characterized the female as having the “First three abdominal segments almost entirely green-scaled, contrasting with the remainder, which are purple.” In 1941, he more precisely described the abdominal terga: “Abdomen with first three tergites [terga I–III] clothed with metallic green scales, a slight admixture of purple scales on the third, rest purple.” Although this pertains to females, it suggests that the third tergum may not always be entirely green-scaled and could prove to be predominately or entirely purple on inspection of a much larger number of specimens; perhaps more so in males.

The larva and pupa of Tx. viridibasis were described by Lewis (1945, southern Sudan) and Wolfs (1947, Democratic Republic of the Congo), and minor details of the larva were provided by Hamon (1954, Burkina Faso). In each case, larvae were reared to adults, which were used to identify the species. Wolfs apparently described the larva from exuviae associated with two individually reared males.

It is noteworthy that the holotype male of voltaicus designated by Ribeiro (2005) was collected and identified as Tx. viridibasis by J. Hamon, who recorded the following: “we obtained an ex larva [from a larval rearing] specimen which allows us to add the following indications to the descriptions of Lewis and Wolfs: head seta B [seta 6-C] has 5 branches; the subventral bristle of the siphon [seta 1-S] is bifid on one side and simple [single] on the other [translated from the French].” For comparison, Wolfs (1947) indicted that setae 6-C and 1-S are both 4-branched in larvae from the Democratic Republic of the Congo, whereas Lewis (1945) indicated that specimens from Sudan have seta 6-C with 2 or 3 branches “near the tip” and seta 1-S single, but “may have 1 or 2 branches near its tip.” It was not obvious until now that the holotype male of voltaicus is one of the two males which Hamon (1954) reared from larvae collected in an area that “forms approximately a circle with a radius of 50 kilometers and is entirely included in the administrative subdivision of Bobo Dioulasso [translated from the French].” Therefore, one of the larval exuviae examined by Hamon (1954) is the larval exuviae of the holotype of voltaicus.

Based on the scant morphological data listed above, it would seem that subspecies voltaicus differs from the nominate form principally in features of the adults—abdominal tergum III entirely with purple scales (entirely green or with a few intermixed purple scales in the type form), upper mesokatepisternal scale-patch comprised of golden scales (these scales white in the type form), maxillary palpus of the male mainly clothed in purplish golden scales with violet reflections (mainly clothed in golden scales in the type form). Because the interpretation of color is subjective and dependent on lighting, and may be variable within a species, we consider such differences to be of questionable value in recognizing species-group taxa. With regard to the larva, the paucity of information shows that the larva of voltaicus shares the single or bifid seta 1-S with the type form in Sudan, and both differ from the form in the Democratic Republic of the Congo in which this seta is 4-branched. There seems to be a greater difference in the branching of seta 6-C, which has two or three apical branches in Sudanese larvae and is four- and five-branched in larvae from the Democratic Republic of the Congo and the type locality of subspecies voltaicus, respectively. It is impossible to know whether these differences are attributable to variation across the range of a single species or an indication of a potential species complex. In the absence of firm evidence, we feel it is prudent at this time to formally consider voltaicus as nothing more than a local morphological variant of the nominotypical form: voltaicus Ribeiro, 2005, junior subjective synonym of Toxorhynchites (Afrorhynchus) viridibasis ( Edwards, 1935) . Consequently, voltaicus should be removed from the species of Toxorhynchites listed in the Encyclopedia of Life.