Toxorhynchites (Toxorhynchites) brevipalpis 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 : 121-123

Toxorhynchites (Toxorhynchites) brevipalpis Theobald

subspecies abyssinicus Ribeiro, 1991 —original combination: Toxorhynchites (Toxorhynchites) brevipalpis abyssinicus .

Distribution: Ethiopia ( Ribeiro 1991).

subspecies brevipalpis Theobald, 1901a —original combination: Toxorhynchites brevipalpis . Distribution: Angola, Benin, Burkina Faso, Cameroon, Central African Republic, Côte d’Ivoire, Democratic Republic of the Congo, Ghana, Kenya, Liberia, Malawi, Mozambique, Nigeria, Senegal, South Africa, Tanzania, Uganda, Zambia, Zimbabwe ( Wilkerson et al. 2021).

subspecies conradti Gr ̧nberg, 1907—original combination: Toxorhynchites conradti (subspecific status by Hopkins 1936). Distribution: Burkina Faso, Cameroon, Côte d’Ivoire, Democratic Republic of the Congo, Equatorial Guinea, Gabon, Ghana, Gambia, Liberia, Mali, Nigeria, Republic of the Congo, Sierra Leone, South Sudan, Sudan, Uganda ( Wilkerson et al. 2021).

Theobald (1901a) described brevipalpis from two females collected in “Natal”, now known as KwaZulu-Natal, a coastal province of South Africa. Steffan & White (1981) noted that the two specimens were originally “in Walker’s collection”, but “Since only one of the ♀♀ mentioned by Theobald is now in the BM Collection [Natural History Museum, London], it is designated as the lectotype.” This is the specimen Edwards (1941) indicated was from Durban, which is considered to be the type locality even though the name of the city does not appear on the labels that accompany the specimen ( Steffan & White 1981). Edwards apparently gleaned the locality from other information associated with Walker’s collection.

Subspecies conradti was originally described as a distinct species by Gŗnberg (1907) based on a female and a male captured on different dates at the Johan-Albrecht-Ĥhe station on the crater rim of Lake Barombi near Kumba in the Southwest Region of Cameroon. The species was listed as a synonym of brevipalpis , without explanation, by Edwards (1912b, 1932a) and remained so until Hopkins (1936) described the larva of “ brevipalpis ” (as a species of Megarhinus ) and inadvertently referred to conradti as a variety: “The description and figures are of var. conradti Gr ̧nberg.” The figures that Hopkins ascribed to conradti were reproduced from Macfie & Ingram (1923), who described and illustrated the larva of “ Megarhinus (Toxorhynchites) brevipalpis ” from specimens collected at localities in present-day Ghana: Nsawam and Sekondi (the twin city of Sekondi-Takoradi). They prefaced their description as follows: “A figure showing the paddles and the last three abdominal segments of the pupa of this mosquito has been published, together with a few words of explanation, by Bacot (Yellow Fever Commission, West Africa, Reports, iii, p. 145); and a larva, presumed to be that of M. brevipalpis , has been briefly described by Edwards (Bull. Ent. Res. iii, p. 375). Neither of these authors, however, has given sufficient details to distinguish the species, and indeed it seems not unlikely that the characters mentioned by them are mainly generic. As we have in our possession specimens of both larvae and pupae of M. brevipalpis , we have taken the opportunity of examining them in detail.” The specimens were apparently identified to species, in the absence of associated adults, with the help of G. A. K. Marshall, Imperial Bureau of Entomology, and F. W. Edwards, British Museum. The Toxorhynchites of Africa were so very poorly known at the time that the identification of the specimens as conradti by Macfie & Ingram (1923) was probably presumptive, based on its known distribution in West Africa. Incidentally, we note that Hopkins (1936) is wrongly credited with the recognition of conradti as a subspecies in all subsequently published mosquito catalogs ( Stone et al. 1959; Knight & Stone 1977; Wilkerson et al. 2021) when in fact the author clearly referred to it as a variety of brevipalpis . It appears that conradti was first formally recognized as a subspecies by Edwards (1941).

Removal of the records listed for the presence of subspecies conradti in Benin and Senegal, which were not corroborated in the study of Ribeiro (1991), and discounting the separate contradictory records for the presence of conradti and the type form in the Central African Republic, Kenya and Nigeria, it would appear that the two forms are largely sympatric in the tropical rain forest region of central Africa, mainly in the Democratic Republic of the Congo. It must be borne in mind that all country records for both forms are based solely on differences in the amount of white scaling in the caudolateral tufts of abdominal tergum VI of females (nearly or completely white in the type form; all black or with a few anterior white setae in conradti ) and the presence or absence of basal white scaling on foretarsomere 2 of males and females (present in the type form; absent in conradti ). It must also be noted that Ribeiro (1991) found “intermediate forms” (sex not mentioned) in Angola, Burkina Faso, Nigeria and Uganda with black and white scale-tufts on abdominal tergum VI, which he considered to be brevipalpis x conradti hybrids. Because the two forms are otherwise distinct throughout their ranges, we believe the “intermediate forms” may be morphological variants of one or the other form or, perhaps more likely, a currently unrecognized species.

In the same paper, Ribeiro (1991) described subspecies abyssinicus based on a single male collected in the former Keffa (or Kaffa) Province of Ethiopia, which is now a Zone in the South West Region of the country. Ribeiro distinguished abyssinicus from brevipalpis sensu stricto by the absence of white scales on foretarsomere 2 (also entirely dark-scaled in conradti ), from conradti by the white-scaled tufts of abdominal tergum VI (as in the type form) and from both brevipalpis sensu stricto and conradti by the presence of fewer (8 and 10) setae on the ninth tergal lobes of the male genitalia (15–20 setae on each lobe in the other forms).

Hopkins (1936), after revealing he used the illustrations of the larva of conradti published by Macfie & Ingram (1923) to represent the larva of brevipalpis , stated that “The larva of the typical form has not been distinguished, but is known to be very similar and probably indistinguishable.” He did not indicate the source of this knowledge. Hopkins (1952) repeated verbatim his 1936 treatment of brevipalpis , except for the sentences from the last paragraph quoted above, which he changed to read “The descriptions and figures are of ssp. conradti Gr ̧nberg, but the larva of the typical form is not distinguishable (E. C. C. van Someren, 1946b).” This is a delusive statement because van Someren (1946b) actually stated that the larva of the type form is “Indistinguishable from that of M. brevipalpis subsp. conradti as described by Macfie and Ingram (1922 [ 1923]) and Hopkins (1936).” Obviously this chain of presuppositions obscures the fact that the larva of brevipalpis sensu stricto is essentially unknown and has not been the subject of detailed comparative morphological study.

If it is not obvious from the analyses of the previous three species of Toxorhynchites , it should be noted that species of Toxorhynchites are generally very poorly known taxonomically, extremely similar in all life stages and troublesome to identify. Most species have been distinguished based on pale scaling of the tarsi, which is often different in males and females of the same species, and the color of scales on areas of the thorax and abdomen, which may be variable or dependent on lighting and interpretation. Additionally, as pointed out by Steffan & Evenhuis (1985), “Species that are easily distinguishable in one stage may be entirely indistinguishable, or separable by only a single character, in another stage. …Because of the subtleties involved in distinguishing among the different species of Toxorhynchites in various stages, accurate identification necessitates well-preserved and prepared specimens of both sexes in each stage. Adults with associated pupal and larval skins [exuviae]… provide the most useful taxonomic information.” Unfortunately, individually reared adults with associated larval and pupal exuviae are lacking for Tx. brevipalpis and its currently recognized subspecies. Nevertheless, we believe that the available morphological and distributional information is sufficient to formally recognize the three nominal forms as separate species: The nominotypical species and Toxorhynchites (Toxorhynchites) conradti Grünberg, 1907 , which have largely allopatric distributions that overlap in central Africa, without demonstrable evidence of introgression, and Toxorhynchites (Toxorhynchites) abyssinicus Ribeiro, 1991 , which is diagnosed by a unique combination of characters and appears to be isolated from populations of Tx. conradti . Toxorhynchites conradti and Tx. abyssinicus are both currently listed as species in the Encyclopedia of Life.

Toxorhynchites brevipalpis has a single synonym, Tx. marshallii Theobald, 1903a , described from an adult male from Salisbury, Mashonaland, a region in northern Zimbabwe which today is divided into four provinces. The type locality of marshallii is within the allopatric range of Tx. brevipalpis , and should be retained as a synonym of that species. Toxorhynchites conradti has two synonyms, Tx. schultzei Enderlein, 1931 (type locality: “Franẑsisch Äquatorial-Afrika, Mongumba am Ubangi-Fluβ”—Mongoumba is a town on the Ugangi River in the Central African Republic), and Tx. tessmanni Enderlein, 1931 (type locality: “ Spanisch-Guinea. Uam-Gebiet: Alen Benito”—Alen Benito [?Benito River; Alen is a mountain], Uam area [ Rio Muni mainland], Equatorial Africa). These two nominal forms are each based on a single adult female. Their type localities are located in the allopatric range of conradti , and they should be retained as synonyms of that species.