Culex (Culex) invidiosus 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 : 86-87

Culex (Culex) invidiosus Theobald

subspecies invidiosus Theobald, 1901d —original combination: Culex invidiosus . Distribution: Sub-Saharan Africa, countries north of approximately 10° S latitude—including Benin, Burkina Faso, Cameroon, Côte d’Ivoire, Democratic Republic of the Congo, Gabon, Gambia, Ghana, Kenya, Liberia, Mali, Nigeria, Republic of the Congo, São Tomé and Príncipe, Senegal, Sierra Leone, South Sudan, Sudan, Tanzania, Uganda ( Wilkerson et al. 2021).

subspecies vexillatus Edwards, 1941 —original combination: Culex (Culex) invidiosus var. vexillatus (subspecific status by Harbach & Howard 2007). Distribution: Cameroon, Democratic Republic of the Congo, Nigeria, Republic of the Congo, Uganda ( Wilkerson et al. 2021).

subspecies vicinalis de Meillon & Lavoipierre, 1944 —original combination: Culex (Culex) invidiosus ssp. vicinalis . Distribution: Democratic Republic of the Congo ( de Meillon & Lavoipierre 1944).

Like many species of Afrotropical Culex , Cx. invidiosus is very poorly known. It was last treated by Edwards (1941), who distinguished vexillatus as a variety based on five males and a female from Kampala, Uganda (Mattingly 1956) that closely resembles the typical form except for the shape of seta f of the subapical lobe of the male gonocoxite. Three years later, de Meillon & Lavoipierre (1944) described vicinalis as a subspecies of Cx. invidiosus based on a single male collected at Yangambi, a town located on the Congo River in the central region of present-day Democratic Republic of the Congo.

A review of the taxonomic history of Cx. invidiosus following its original description by Theobald (1901c) begins with Edwards (1911b), who indicated that it belonged to a group of species that are “very difficult to classify” because they lack “clearly marked distinctions.” Ironically, Edwards formally recognized Cx. euclastus Theobald, 1903b , Cx. chloroventer Theobald, 1909 and Cx. aquilus Graham, 1910 as synonyms of Cx. invidiosus , and those names have remained as synonyms of Cx. invidiosus to the present.

Wesché (1910) described the larva of Cx. invidiosus (as Cx. aquilus ) and included it in a key to the larvae of African Culicidae . Edwards (1912d) updated the key and illustrated the head and terminal abdominal segments of Cx. invidiosus . Although Edwards was “unable to separate the larvae of C. decens [now considered a valid species]… and C. invidiosus ”, and found that the characters given by Wesché were unreliable, he believed the two species were distinct because Cx. decens could be distinguished by the reddish thorax (brown in Cx. invidiosus ) and the banded abdominal segments of males. Despite treating them as separate species, he concluded that “It is therefore quite possible that the two are really only forms of one species; they generally occur together, but specimens bred from one batch of larvae exhibit little variation.”

Edwards (1914) acknowledged that species of Culex are most readily separated by features of the male genitalia, but indicted “As previously stated, I can detect no difference whatever between the hypopygia [genitalia] of this species [ Cx. invidiosus ] and of C. decens .” Despite this comment, Edwards treated Cx. invidiosus as a distinct species and surmized that it “is probably a purely West African species.” He illustrated the phallosomes and gonocoxites of Cx. invidiosus , Cx. antennatus (Becker, 1903) (as Cx. laurenti Newstead, 1907, in Newstead et al. 1907) and Cx. perfuscus sp. nov. to show the close similarity of the genitalia of seemingly unrelated species.

Macfie & Ingram (1920) conducted a detailed comparison of the pupae of Cx. decens and Cx. invidiosus , but were unable to find differences to distinguish them. In summary, they stated: “The question then arises, are C. decens and C. invidiosus separate species or are they varieties of a single mosquito. There are indeed certain differences in the adults, but the genitalia of the males are identical according to Edwards, the larvae cannot be separated [reiterated by Hopkins 1936, 1952], and the same remark applies to the pupae. Under these circumstances we think there can be little doubt that they should be regarded as varieties and not as distinct species; we propose to retain for the species the name C. decens .” Based on these findings, Edwards (1932a) listed invidiosus as a variety of Cx. decens , with the three synonyms noted above.

Edwards (1941) is the last reviser of the subgenus Culex in the Afrotropical Region. He reiterated his earlier observation ( Edwards 1912d) that the adults of Cx. invidiosus differ from those of Cx. decens in having brown instead of reddish mesonotal (scutal) scales and abdominal terga without pale bands, and added that the male genitalia of Cx. invidiosus differ from those of Cx. decens in having seta f longer and distally expanded on one side and seta h with a kink at mid-length. He concluded that “Since it has now been found that small differences exist in the male terminalia [genitalia], supporting the more obvious differences in colouring, it may be more correct to treat C. invidiosus as a distinct species rather than as a variety of C. decens .” He then described vexillatus as a variety with male genitalia that “Closely resemble those of C. invidiosus in all respects except as regards the shape of appendage f of the coxite lobe [gonocoxite subapical lobe]; this is greatly expanded at the tip, like a small flag; seta h sinuous as in typical invidiosus .” In addition to the character of seta f, comparison of Edwards’s illustrations of the partial phallosomes of invidiosus and vexillatus reveals a difference not noticed by Edwards, i.e. the dorsal arms of the lateral plates are larger, distally tapered and project beyond the largest tooth of the lateral arm in the type form whereas in vexillatus the dorsal arms are smaller, slightly enlarged distally and do not reach beyond the largest tooth of the lateral arm.

Culex invidiosus vicinalis was described by de Meillon & Lavoipierre (1944) as “agreeing with invidiosus Theo. in all respects the only differences to be found in the male terminalia [genitalia]”, i.e. seta f of the subapical lobe is not enlarged apically, seta h is not sinuous and a unique double row of rather sharply bent setae is borne adjacent to the subapical lobe on the lateral surface of the gonocoxite. The authors pointed out that a similar double row of setae is present in an unnamed variety of Cx. ornatothoracis Theobald, 1909 (see Edwards 1941: fig. 118g), but because vicinalis bears an overall closer resemblance to Cx. invidiosus, de Meillon & Lavoipierre regarded it “as a subspecies of that species rather than of ornatothoracis .”

Based on many years of taxonomic work (REH) on species of the genus Culex , especially species of the subgenus Culex , it is apparent that seemingly minor differences in features of the male genitalia are indicative of separate species. In the case of vexillatus and the typical form, differences now apparent in the development of the dorsal arms of the phallosome, supporting the previously noted differences in the form of setae f and h of the subapical lobe, it is more appropriate to treat vexillatus as a distinct species: Culex (Culex) vexillatus Edwards, 1941 . The situation with vicinalis is very different. Based on the diagnostic presence of a unique double row of setae on the gonocoxite, coupled with the distinctive development of setae f and h, it is surprising that vicinalis was not originally recognized as a distinct species; thus, it is hereby afforded specific status: Culex (Culex) vicinalis de Meillon & Lavoipierre, 1944 . Both Cx. vexillatus and Cx. vicinalis are listed as species in the Encyclopedia of Life. The larva of Cx. invidiosus is partially known ( Wesché 1910; Edwards 1912d); the larvae of Cx. vexillatus and Cx. vicinalis are unknown. Once the larvae of all three species are known and have been studied and compared in detail, it is likely that morphological differences will be found that support their recognition as separate species. Molecular data are also expected to support their specific status.

Three nominal species are recognized as junior synonyms of Cx. invidiosus : Cx. euclastus Theobald, 1903b (type locality: Gambia), Cx. chloroventer Theobald, 1909 (type locality: Accra, Ashanti Region, Ghana) and Cx. aquilus Graham, 1910 (type locality: Lagos, Nigeria). The type locality of Cx. invidiosus is the island town of Bonny in Rivers State in southern Nigeria.As there is no evidence that one or more of the three nominal forms might be conspecific with either Cx. vexillatus (type locality: Kampala, Uganda) or Cx. vicinalis (type locality: Yangambi, Tshopo Province, Democratic Republic of the Congo), they must remain as junior synonyms of Cx. invidiosus .