Aedes (Aedimorphus) hirsutus (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 : 13-14

Aedes (Aedimorphus) hirsutus (Theobald)

subspecies adenensis Edwards, 1941 —original combination: Aedes (Aedimorphus) hirsutus var. adenensis (as ssp. in Pao & Knight 1970, explicitly elevated to ssp. by White 1975). Distribution: Yemen ( Edwards 1941).

subspecies hirsutus ( Theobald, 1901a) —original combination: Culex hirsutum [sic]. Distribution: Benin, Burkina Faso, Côte d’Ivoire, Ethiopia, Kenya, Madagascar, Mali, Mauritania, Namibia, Nigeria, Senegal, South Africa, South Sudan, Sudan, Togo, Zambia, Zimbabwe ( Wilkerson et al. 2021).

The nominotypical subspecies was described from a female and a male from Salisbury, Mashonaland [Harare, Zimbabwe]. The detailed description has a separate color illustration. Theobald’s (1901a) diagnosis follows here (after Theobald 1901a [plates]): fig. 80, pl. XX): “Thorax dark chestnut-brown, with dull creamy scales forming a broad median line and four creamy spots. Abdomen dark umber-brown, with basal yellowish-white bands and with two large dull yellow apical spots on the fifth and sixth segments; venter mottled with black, yellow and white scaled patches. Legs with broad basal white bands, femora, tibiae and metatarsi [tarsomere 1] hirsute, bases of the femora pale, remainder black, with a few pale scales.” Also, “palpi short, dark brown, with numerous pale scales at the apex”. Subsequent authors ( Edwards 1911b, 1912 b, 1941; Jupp 1996) noted that there is a white costal fringe on the distal part of the wing, which was not mentioned or illustrated by Theobald (1901a).

Theobald (1903a) described a similar taxon, Culex transvaalensis , but he did not note a similarity with hirsutus . In the collection of the Natural History Museum, London, Townsend (1990) found three syntype females from South Africa [Transvaal], Pretoria, and a male labelled “type”, which he stated had no type status since only the female was described. Without comment Edwards (1911b) reduced transvaalensis to a synonym of hirsutum . Theobald (1913a) distinguished the two species in a key: “Abdomen basally banded” for transvaalensis and “Abdomen with two apical spots on 5th and 6th segments as well as bands” for hirsutum . He also stated: “Edwards considers this [ hirsutum ] the same as Culex transvaalensis, Theobald. The two marked apical spots on both fifth and sixth abdominal segments in Culex hirsutum never occur in Culex transvaalensis and the thorax is differently ornamented. The type has either been altered or this young writer has been unable to appreciate the distinctive characters.” He further added: “As pointed out under C. hirsutum, Theobald, Edwards is in complete error in vaguely assuming this [ transvaalensis ] is the same as that marked species.” The discussion was apparently put to rest by Edwards (1915), who stated: “Theobald... has criticised my statement that his Culex hirsutum and C. transvaalensis are one and the same species. I have re-examined the specimens, and find no reason to modify my previous opinion, except in one in particular. The male and female types of C. hirsutum belong to different species.... The female type must be taken as the type of the species, the male… being really O. nigeriensis (Theo.) [currently a synonym of Ae. (Aed.) fowleri (de Charmoy, 1908)].”

Other described life stages of the nominate form hirsutus , a widespread African species, include the adult male ( Edwards 1911b), pupa ( Ingram & Macfie 1919), male genitalia ( Edwards 1941), larva ( Hopkins 1952), larval mandible and maxilla ( Pao & Knight 1970) and the adult female and male genitalia ( Jupp 1996).

Edwards (1941) described subspecies adenensis as a variety of hirsutus from two sites in the West Aden Protectorate [southwestern Yemen], as revealed by Mattingly (1956): Jebel Jihaf , 7100 ft., ix.1937, 2 females, and Dhala, 4800 ft., 14.ix.1937, 1 male and 7 females. “Since the critical factor, if any, is likely to be altitude I have marked one of the ♀ from Jebel Jihaf as the hololectotype and the ♂ from Dhala as allolectotype.” David Pecor (pers. comm.) investigated the localities and noted that the West Aden Protectorate was renamed as part of the independent nation of Yemen, and the locality names were perhaps misspelled when translated from Arabic. Instead they are probably Jabal Jihaf [Jabal is “mountain” in Arabic] (GeoNames ID 74169, coordinates 13.7607 44.67656, altitude 2,402 m) and Dhale, (GeoNames ID 80384, coordinates 13.69572, 44.73137, altitude 1,517 m). The two sites are approximately 9 km apart. Edwards’s (1941) description of adenensis follows: “Structurally identical with the typical form, and also resembling it in the white-scaled distal part of costa, but differs in colouring of abdomen; the pale basal bands of the tergites [terga] are yellowish rather than white and all the tergites have apical median patches of yellowish scales, usually occupying an extensive area; in some extremely pale specimens the abdominal scales are almost all yellowish, with only a few black ones across the middle of each tergite.”

Mattingly & Knight (1956) stated that the male genitalia [of adenensis ] “are indistinguishable from those of the type form.” In their keys they noted: “Wing [of adenensis ] with relatively few pale scales which are mainly confined to the basal half”. They then compared the larva of adenensis to Ae. (Aed.) natronius Edwards, 1932b: “Antenna more strongly spiculate; pecten teeth of more normal type; head seta 6 normally single, rarely double, much longer and usually stouter than 5”. The illustration in the original description showing the presence of white scaling on the costa of the wing contradicts Mattingly & Knight (1956), who reported the presence of a few pale scales, those confined to the proximal half of the costa. The head of the larva of hirsutus illustrated by Hopkins (1952), who did not mention adenensis , shows seta 5-C multi-branched and 6-C single, with the latter about twice the length of the former. Unfortunately, Mattingly & Knight (1956) did not note whether 6-C was branched or not.

The inconsistent description of white scales being present or absent apically on the costa in both hirsutus and adenensis can only be solved by re-examination of the types and study of variation in these taxa. The only character that separates these two, for now, is the pattern of scaling on the abdomen of adenensis , which has median, apical patches of yellowish scales that are absent in hirsutus . No description of variation in hirsutus across its range in Africa includes median apical abdominal pale scales that would suggest adenensis represents a morphological variant of the type form. However, the type form has not been well studied morphologically. The type locality of adenensis , near the eastern border of the distribution of hirsutus , is at a fairly high altitude compared to most mosquito species and appears to us to possibly reside in an extremely dry environment, though indications of green in valleys can be seen from satellite photos. Until further study can be undertaken, we believe adenensis is sufficiently different from hirsutus to be afforded species status: Aedes (Aedimorphus) adenensis Edwards, 1941 . Aedes adenensis is currently listed as a species in the Encyclopedia of life.