Aedes (Bifidistylus) boneti Gil Collado

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 : 20-22

Aedes (Bifidistylus) boneti Gil Collado

subspecies boneti Gil Collado, 1936 —original combination: Aedes (Aedimorphus) boneti . Distribution: Known only from the type locality, Isla de Bioko ( Fernando Po), Equatorial Guinea ( Gil Collado 1936).

subspecies kumbae Chwatt, 1948 —original combination: Aedes (Aedimorphus) boneti s.sp. kumbae . Distribution: Republic of Cameroon ( Chwatt 1948).

The nominotypical subspecies was described from a single male from Rebola, Bioko Island, Equatorial Guinea. The island has an area of 2,017 km 2 and is 32 km from the coast of Cameroon (https://en.wikipedia.org/wiki/ Bioko; accessed 7 April 2022). Gil Collado credited F. W. Edwards for identifying the species as new, stating: “I must tender my thanks to J. W. Edwards [sic], who... examined the material... verifying my findings and alerting me to a new species of Aedimorphus , represented by a specimen it had been impossible for me to identify due to its somewhat deficient state of preservation [translated from the Spanish].” The male holotype is in the Museum, Madrid University School of Agriculture, Madrid, Spain. We used a published translation of the description from the Spanish along with the original article for this treatment. The description is detailed and accompanied by a drawing of a dorsal view of the head and appendages (antenna, maxillary palpus, proboscis) and a hindleg. The forelegs are not described, leaving the impression that they are missing. Damage to the specimen noted by the author included: “The scutellum has very wide whitish scales in its middle lobe, those from the sides [lateral lobes] having been removed... Anterior pronotum [antepronotum] has two groups of 5 to 6 bristles [setae]; the posterior [postpronotum], some 4, though in our specimen, they are somewhat destroyed…. Supra-alar scales are dark and numerous; those from the dorso-central area of our specimen have been torn off….” Our assumption is that characteristics of the cuticle (setae, scales, pollinosity, etc.) might be modified enough to render an accurate description problematical. Re-examination of the holotype is needed to be certain. Gil Collado also noted: “This species presents traits which closest approximate lamborni Edw. [the only other species now included in the subgenus Bifidistylus ], in whose group they must be included because of their tarsal rings; however, in spite of the fact that the specimen’s [as in translation] hypopygium [genitalia] was destroyed in preparation, the coxa [gonocoxite] does not seem as pronounced as in that species...”. Gil Collado then compared boneti with lamborni Edwards, 1923a. To our knowledge the holotype of boneti is the only known specimen of this species. However, given the intense study of Anopheles and malaria control on Bioko (e.g. Cook et al. 2018), it is not surprising that species of other genera might have been overlooked, with the exception of the relatively recent invasive Aedes albopictus ( Skuse, 1895) ( Toto et al. 2003) , and pest species of Culex (e.g. Fuseini et al. 2019). Gil Collado (1936) documented about 30 mosquito species on Bioko. All but Anopheles lloreti Gil Collado, 1936 are also found on mainland Africa. The type of An. lloreti is perhaps the only specimen of this species as well.

An attribute that to us stands out as unique is paired spots of erect black scales on the vertex of the head. “Head with a broad vertical zone of narrow, reclining, white scales, among which numerous dark standing scales appear; on each side there is a rounded blotch of dark scales, which in turn, has a lateral region of white, narrow, reclining scales, and in the same posterior angle of the eyes there is a small dark spot.” These spots are not noted in Ae. lamborni, but they are present in subspecies kumbae .

Subspecies kumbae was described from Kumba, British Cameroons [ Republic of Cameroon] by Chwatt (1948). The type localities of kumbae and the type form are 117 km apart (determined by David Pecor on 04/07/2022, https:// arcg.is/CqOTz1) and, as stated above, the island and mainland are separated by 32 km of ocean. The description and illustrations of kumbae are detailed and based on a series of specimens: 10 larvae, three pupal exuviae and two adult males with dissected genitalia mounted with the associated pupal exuviae. Of these, Townsend (1990) found two males and six larvae in the Natural History Museum, London. Chwatt (1948) apparently relied on the description of the male of boneti to compare subspecies kumbae with boneti since there is no indication that he examined the holotype of boneti . Hopkins (1952) included boneti in a key but reproduced the description and larval illustration of subspecies kumbae to represent boneti .

For purposes of comparison, therefore, we only have the descriptions of the adult male of each nominal form. The following are comments and characters that Chwatt (1948) used to justify giving kumbae subspecies status: “In Edwards’s (1941) key to the Ethiopian species of Aëdes the two male adults [the two specimens used to describe subspecies kumbae ] would run down to A. boneti Gil Collado , described in 1936 from a single damaged male captured on the Island of Fernando Po. The similarity between the two adults described above and the original description of A. boneti is considerable. Nevertheless, there are several notable differences―mainly the more extensive, rather differently shaped, dark scaling of the head, the pale (instead of golden) colour of the investiture of the mesonotum, the presence of prescutellar rows of scales, the scaling of the abdominal sternites [sterna], the presence of small pale apical spots on the dorsal surface of the femora, the presence of basal white spots on the costa, and the markings of the last hind tarsal segments.” We itemized the above characters and extracted text from the original descriptions of kumbae and boneti , i.e. from Gil Collado (1948) and Chwatt (1936), respectively, as follow .

“...the more extensive, rather differently shaped, dark scaling of the head...”.

— kumbae : “Occiput with two, dark, dorsolateral, conspicuous, oval or comma-shaped spots, formed by dark-brown upright forked scales. The remainder of the upright scales pale. Prominent dark-brown bare vertical area along the median suture [coronal suture].” [large dark spots illustrated]

— boneti : “Head with a broad vertica1 zone of narrow, reclining, white scales, among which numerous dark standing scales appear; on each side there is a rounded blotch of dark scales, which in turn, has a lateral region of white, narrow, reclining scales, and in the same posterior angle of the eyes there is a small dark spot.” [dorsolateral and lateral dark spots evident in the illustration]

We do not interpret these two descriptions to be substantially different, in addition the illustrations of the heads are quite similar, especially the two large dark spots of erect scales.

“...the pale (instead of golden) colour of the investiture of the mesonotum [scutum]...”.

— kumbae : “Mesonotum covered with a mixture of narrow, curved, dark-brown and pale scales...”.

— boneti : “Mesonotum, except for its anterior edge, has sparse gold scales mixed with wider black scales.”

Pale scales versus sparse gold scales could be explained by differences in lighting used for the observations.

“...the presence of prescutellar rows of scales... ”.

— kumbae : “...dark-brown and pale scales, the latter broader on the anterior and anterolateral borders [of the scutum] and broad and flat around the prescutellar bare area.”

— boneti : “In the middle region, in front of the scutellum, there are some white scales.”

Neither description mentions rows of scales in front of the scutellum or provides a clear distinction between the two.

“...the scaling of the abdominal sternites [sterna]...”.

— kumbae : “Sternites covered almost entirely with broad flat pale scales.”

— boneti: Not noted.

No applicable difference.

“...the presence of small pale apical spots on the dorsal surface of the femora...”.

— kumbae : “Fore femora dark, with a paler basal ventral surface and a few white scales at the distal end of the dorsal surface; middle femora similar, with a rather more extensive pale ventral area; hind femora dark on the dorsal side, except for a white distal spot, mainly pale on the ventral side...”.

— boneti: Forefemur not noted. “Legs II [midlegs]: femora with their anterior and dorsal surfaces dark, and the posterior surface completely pale at the base, this coloration narrowing progressively toward the apex, where there is only a single white ventral line…”. “Legs III [hindlegs] with predominantly white femora, and a narrow black dorsal strip, while the anterior face is peppered with abundant dark scales.”

The apical pale femoral spot in kumbae is described only for the hindfemur. The illustration of the hindleg of boneti does not show an apical spot. We think this remains ambiguous pending comparison of the holotypes of the two nominal forms.

“...the presence of basal white spots on the Costa ... ”.

— kumbae : “Wings with scales dark and a small basal patch of pale scales on the lower and anterior surface of the costa.”

— boneti : “The wing scales are dark, and even blackish over C and R 1.”

A few pale scales at the base of the costa can be variable.

“...and the markings of the last hind tarsal segments [which markings not stated].”

— kumbae : “hind tarsi... first segment [tarsomere 1] dark, with an apical white band, second with one basal and one apical white band, the latter about twice the length of the former, third with one apical and one basal narrow band. The fourth tarsus [tarsomere 4] shows some variation: in one specimen it has a dark median band, while in the other the dark scales form only a narrow longitudinal line on the apical half of the lower surface. In both specimens the fifth tarsus [tarsomere 5] is white but has a similar dark line on the lower surface.”

— boneti : “The metatarsi [hindtarsomeres 1] are black, with bristles of the same color, and a white spot at their apices which is a little longer than their width. The 2nd article [tarsomere 2] has a narrow pale basal zone, and another at its apex which is two and a half times its thickness; the 3rd with an apical ring the same as the 2nd and one at the base which is a little greater than its diameter. The 4th is white with a middle dark zone of one fourth its total length, and the 5th, completely white.” [roughly matches the illustration of the hindleg]

No defining differences are given.

Chwatt (1948) wrote: “This Aedimorphus is described here under the provisional name of A. boneti s.sp. kumbae . Should the still unknown larva of A. boneti prove to be different from the one described above, A. boneti s.sp. kumbae will have to be treated as a new species, A. (Aedimorphus) kumbae .” Our interpretation is that when kumbae was described, no significant characters were given to distinguish the two nominal taxa, and we therefore treat kumbae is a synonym of boneti until proven otherwise: kumbae Chwatt, 1948 , junior subjective synonym of Aedes (Bifidistylus) boneti Gil Collado, 1936 . Should the larvae be found, the larva of kumbae possesses some potentially unique characteristics for diagnosis, such as an array of variously shaped spines on the siphon and a dense patch of comb scales. The nominal subspecies kumbae , which is listed as a species in the Encyclopedia of Life, must be removed from the list of valid species of Aedes .