Anopheles (Cellia) sergentii (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 : 73-75

Anopheles (Cellia) sergentii (Theobald)

subspecies macmahoni Evans, 1936 —original combination: Anopheles (Myzomyia) macmahoni (subspecific status by Mattingly & Knight 1956). Distribution: Algeria, Burkina Faso, Côte d’Ivoire, Djibouti, Eritrea, Ethiopia, Ghana, Guinea, Kenya, Mali, Republic of South Africa, Senegal, Somalia, South Sudan, Sudan ( Wilkerson et al. 2021).

subspecies sergentii ( Theobald, 1907) —original combination: Pyretophorus sergentii . Distribution: Albania, Algeria, Bulgaria, Burkina Faso, Cameroon, Chad, Côte d’Ivoire, Djibouti, Egypt, Eritrea, Greece, Iran, Iraq, Israel, Italy, Jordan, Libya, Kenya, Morocco, Pakistan, Portugal, Saudi Arabia, Senegal, Spain, South Sudan, Sudan, Tunisia, Turkmenistan ( Wilkerson et al. 2021).

The female of the nominotypical form was described by Theobald (1907) based on two adult females from an unspecified locality in Algeria (see below). He described them as a gray to brown species with three palpal bands, one of them the entire palpomere 5; with the abdomen brown without scales; legs brown, unbanded, and “Wings dark scaled; costal border with five large dark spots, four spreading evenly on to first long vein [R]; a few pale spots on wing field, notably at the cross-veins and bases of the fork-cells [ R 2 and M 1].” All primary wing veins except 1A end at a pale fringe spot. There was no explicit mention of the nature of the dark and pale areas on vein R 4 +5 but “most of the veins” were described as “uniformly dark scaled”. Subsequently , Christophers (1933) described all life stages from specimens collected in presesnt-day Pakistan.

Subspecies macmahoni was described as a species by Evans (1936) based on two larval cotypes and a male and a female with associated larval and pupal exuviae from Isiolo, Kenya. She noted: “The larvae of this species can be identified easily by the characters of the tergal plates…”, which are unusually broad. In the adult female, the maxillary palpus has three narrow pale bands, the tarsi lack definite pale rings and the wings are predominantly dark with the third vein (R 4+5) mainly or entirely dark-scaled. Based on additional specimens from the same locality, Evans stated that the hindtibia has a “rather distinct white spot at the base, as well as the usual apical spot.” Two years later, in her treatise on Afrotropical anophelines, Evans (1938) more precisely described variation observed for vein R 4+5: “Third vein ranging from entirely dark to about ⅔ pale, usually about ¼–½ pale; pale area when present usually situated distally as in A. funestus , but in 3 cases it was median in the vein.” Subspecies sergentii was not mentioned in Evans (1936) or Evans (1938).

De Meillon (1947) followed the descriptions of Evans (1936, 1938) and additionally noted the presence of five parabasal setae on the gonocoxite of the male, the innermost borne on a prominent eminence, and vein R 4+5 all dark and the pale area, when present, at the center or with a long basal dark spot and a small apical one. Subspecies sergentii was also not mentioned in this publication.

Mattingly & Knight (1956) in “Mosquitoes of Arabia” examined larvae of subspecies macmahoni from the Western Aden Protectorate ( Yemen) “and consider them to be those of An. sergenti [sic] of which An. macmahoni is, in our view, a subspecies probably mainly confined to the African portion of the Somali-Arid District. The latter is therefore eliminated from our list.” Differences they noted in the cibarial armature of females, also noted by others, were deemed to be too variable to be indicative of separate species. However, two principal differentiating characters were noted. Vein R 4+ 5 in macmahoni “is normally extensively pale scaled in the middle and only exceptionally dark.” Subspecies sergentii , in contrast, “is constantly dark except at base and extreme tip”. The other feature used to separate the two nominal taxa was the large size of the main tergal plates present in larvae of macmahoni .

Senevet et al. (1959) conducted a comprehensive study of the larval tergal plates of sergentii and macmahoni in Algeria. Whereas Theobald (1907) merely indicated that the type specimens of sergentii were collected in Algeria by Dr E. Sergent, Senevet et al. revealed that the specimens were found by Edmond Sergent in “El Outaya (région de Biskra, partie N. du Sahara algérien).” Based on this revelation, we hereby restrict the type locality of Anopheles sergentii Theobald, 1907 to El Outaya (35.040868, 5.56491), Biskra Province, Algeria. Senevet et al. noted that one of them had collected sergentii on the south side of the Aurès Mountains at the northern limit of the Sahara. For comparison, they obtained specimens from Tassili N’Ajjers, a national park in the Sahara located north of Djanet in southeastern Algeria. El Outaya and Djanet are about 1,000 km apart. The authors summarized their findings as follow: “we are dealing with two types: the group ́small plates» corresponds to the variety ́typicus » [ sergentii ]; the ́large plates» group corresponds to the subspecies macmahoni . The first of these groups does not in fact differ much from the form considered as typical by most authors [translated from the French].”

The two nominal taxa belong to the demeilloni section of Gillies & de Meillon (1968) (= Demeilloni Group in Wilkerson et al. 2021). Gillies & de Meillon placed adult females of subspecies macmahoni in their key in Section XI, with the following characters: “Mosquitoes with 1 pale spot on upper branch of 5th vein [M 3+4], no pale interruption on 3rd dark area [preapical dark spot] of 1st vein [R 1]; costa with at least 1 pale spot on basal half; palps [maxillary palpi] with less than 4 bands, pale at apex; legs not speckled, hind tarsus 4 and 5 [hindtarsomeres 4 and 5] not entirely pale; abdomen without laterally projecting tufts of scales.” We point out that both nominal taxa have dark tarsomeres, maxillary palpus with three pale bands, two narrow ones, plus the entire palpomere 5, basal area of vein R 1 entirely pale-scaled, all veins except 1A ending in a pale fringe spot. Gillies & de Meillon placed fourth-instar larvae of both subspecies in their key in Section VI: “Larvae with wide abdominal plates [tergal plates], equalling on segment 5 three quarters or more the distance between bases of palmate hairs [setae]; saddle hair [seta 1-X] with less than 5 branches; no coarse spicules on sides of thorax and abdomen; outer clypeal hairs [seta 3-C] with less than 8 branches; inner clypeal hairs [seta 2-C] wide apart and not strongly branched.” Both nominal taxa have one of the long mesopleural “hairs” [seta 9- or 10-M] plumose and the inner shoulder “hair” [seta 1-P] with 15–20 branches inserted on a well-developed tubercle. In subspecies sergentii , the width of the main tergal plate on segment V is at most four-fifths the distance between the palmate setae, whereas in subspecies macmahoni the main tergal plate on segment V is equal to greater than four-fifths the distance between the palmate setae.

Gillies & de Meillon (1968) summarized their view of the two taxa as follows. Anopheles sergentii sergentii : “A widespread and important vector of malaria, extending into southern Arabia. As pointed out by Mattingly and Knight (1956) it differs from subsp. macmahoni only in the larval stage. From this it is separable by the width of the main tergal plates, which are at most ⅘ the distance between the palmate hairs [setae].” “LARVAL HABITAT: According to Senevet and Andarelli (1956), sergentii occurs in oases and irrigated areas in many types of water, shaded and unshaded, with and without vegetation.” “ADULT BIOLOGY: Attacks man readily, often entering houses to do so. Often found resting indoors by day, but also makes extensive use of outdoor shelters which are sometimes remote from dwellings. It was formerly, at least, an important vector of malaria...”. Gillies & de Meillon illustrated the distribution of the two subspecies in map form (fig. 53), on which they drew a non-overlapping line of demarcation. They further commented that “We ourselves would note in passing that, despite the close similarity between sergentii and macmahoni , the behaviour of the adults of the two is very different, suggesting that there are more profound biological differences between them than their morphology would suggest.”

The nature of the dark and pale spots on vein R 4+5 (“third vein”) has often been used to separate Anopheles species. In the case of sergentii and macmahoni , a great deal of variation has been noted or illustrated for R 4+ 5 in subspecies macmahoni . This could be an indicator of cryptic species or normal variation. Subspecies sergentii , according to Theobald (1907), Christophers (1933), Mattingly & Knight (1956) and Senevet & Andarelli (1956), has vein R 4+5 all dark or only with a median pale spot and/or small pale spots at the base and apex. In comparison, the scaling of vein R 4+ 5 in subspecies macmahoni has been characterized differently by several authors: “Third vein ranging from entirely dark to about ⅔ pale, usually about ¼–½ pale; pale area when present usually situated distally as in A. funestus , but in 3 cases it was median in the vein” ( Evans 1938); “all dark, pale area if present may be at the center” or pale with a long dark basal spot and a small apical dark spot ( de Meillon 1947); “it appears that it is normally extensively pale scaled in the middle and only exceptionally dark [all dark?]” ( Mattingly & Knight 1956); and Gillies & de Meillon (1968) illustrated the wing showing R 4+5 with a long (⅓ of total length) pale area subapically and perhaps small pale spots at the base and apex, and stated that “3rd vein variable, sometimes broadly pale as figured, in others entirely dark except at base and apex as in subsp. sergenti [sic].”

A problem with recognizing subspecies as legitimate ranks, at least for mosquitoes, is illustrated by Irish et al. (2020), who only recognized the nominotypical subspecies and therefore listed the occurrence of only sergentii in countries of sub-Sharan Africa, and Coetzee (2020) who did not include subspecies macmahoni in keys to the adult females of Anopheles in the Afrotropical Region. This prevents macmahoni from being known and confuses records and recognition of both putative subspecies.

The two nominal taxa, sergentii and macmahoni , were not recognized as related taxonomically ( Evans 1936, 1938; de Meillon 1947) until Mattingly & Knight (1956) considered macmahoni to be a subspecies of sergentii . Subspecies macmahoni is probably mainly confined to the “African portion of the Somali-Arid District” ( Mattingly & Knight 1956) and zoophilic, while subspecies sergentii is a north African-Mediterranean anthropophilic malaria vector ( Gillies & de Meillon 1968) . There exists abundant morphological variation but the only reliable way to separate the two forms is by the relatively large size of the larval tergal plates that characterize macmahoni ( Gillies & de Meillon 1968) . In a recent review of the mosquitoes of Algeria, Merabti et al. (2021) stated that “Subspecies macmahoni is an Afrotropical form that occurs in many of the countries where the typical form is also found, which suggests that Evans (1936) may have correctly recognized it as a distinct species.” Mattingly & Knight (1956) eliminated subspecies macmahoni from their list for mosquitoes in Arabia while distinguishing it morphologically and bionomically from sergentii . These observations conform to our criteria for species status, i.e. allopatry (and sympatry) with morphological and bionomical distinctions. We therefore reinstate macmahoni to species status: Anopheles (Cellia) macmahoni Evans, 1936 . Anopheles macmahoni is currently listed as a species in the Encyclopedia of Life.

Anopheles macmahoni has a single synonym, An. macmahoni var. barkhuusi Giaquinto-Mira, 1950 (type locality: Valley of Becilo, Ethiopia), synonymy by Stone et al. 1959. It is possible that barkhuusi may be a distinct species, but until proven otherwise, it is retained as a synonym of An. macmahoni .