Aedes (Stegomyia) flavopictus (Yamada)

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 : 52-54

Aedes (Stegomyia) flavopictus (Yamada)

subspecies downsi Bohart & Ingram, 1946a —original combination: Aedes (Stegomyia) downsi (subspecific status by Tanaka et al. 1979). Distribution: Amami and Okinawa Islands, Japan ( Tanaka et al. 1979).

subspecies flavopictus Yamada, 1921 —original combination: Aedes flavopictus . Distribution: Guam, India, Japan, Russia, South Korea ( Wilkerson et al. 2021).

subspecies miyarai Tanaka, Mizusawa & Saugstad, 1979 —original combination: Aedes (Stegomyia) flavopictus miyarai . Distribution: Ishigaki and Iriomote Islands, Ryukyu Archipelago, Japan ( Tanaka et al. 1979).

Yamada (1921) described Ae. flavopictus from specimens collected in Shiba, which was a ward of Tokyo until 1947 when it was merged with two other wards to form present-day Minato Ward. The Shiba area is in the eastern and southern parts of Minato Ward, and Tokyo is located on Honshu Island, which lies within the Palaearctic portion of Japan and has a humid subtropical climate. In contrast, the type localities of subspecies downsi and miyarai are located on southern islands of the Ryukyu Archipelago, which lie within the Oriental Region. Unlike the northern islands of the archipelago, which have a climate similar to that of Honshu Island, the southern islands have a tropical rainforest climate. The type locality of downsi is on Okinawa Island, located approximately 1,140 km south of the main island of Honshu, and that of miyarai is on Ishigaki Island, which lies approximately 410 km south of Okinawa Island.

Subspecies downsi , originally described as a species by Bohart & Ingram (1946a), was reduced to a subspecies of flavopictus by Bohart (1953). Huang (1972) re-instated downsi to its original species rank, but it was returned to its previous subspecific rank by Tanaka et al. (1979) based on a much more detailed morphological analysis of adults, larvae and pupae. Huang (1979) retained downsi as a species, but she was apparently not aware of Tanaka et al. (1979). The following observations and rationale for the taxonomic acts of these investigators are extracted from their publications.

Bohart & Ingram (1946a):

[Ae. downsi ] is probably most closely related to flavopictus Yamada from northern Japan and Korea which according to Yamada’s figure of the male genitalia… has an irregular margin of the ninth tergite [tergum IX] and stout setae on the basal [mesal] lobe of the basistyle [gonocoxite]. This species differs from flavopictus , however, in having no spot at the end of the scutal suture, in the more angular and sharply serrate male ninth tergite and the stouter setae of the basal lobe of the male dististyle.

Bohart (1953):

From a comparison of this material [type series and reared adults of flavopictus ] with paratypes and other specimens of downsi … I am of the opinion that downsi represents a subspecies with the following tendencies: (1) restriction of the silver stripe on the front surface of the hind femur to the basal two-thirds or three-fifths of the femur, (2) expansion of the white markings of hind tarsal IV to cover five-sixths to nine-tenths of the segment [hindtarsomere 4], (3) reduction of the tergal pale stripes of the abdomen to weak or incomplete bands especially on III. The gills [anal papillae] are variable in length, often quite short, and always unequal. The fifth pentad hair [seta 5-VIII] almost always has more than 4 branches…. In the typical subspecies from various of the main islands of Japan the fifth pentad is 6 to 20 branched according to Sasa and Kano (1951) and 5 to 17 branched according to LaCasse and Yamaguti (1950).

Huang (1972):

The similarity between these two forms is so close that one would be inclined to regard downsi as a subspecies of flavopictus . However, it can be separated from flavopictus by the diagnostic characters mentioned in the key. In addition, the immature stages of downsi are markedly differentiated from flavopictus . The larva of downsi has the saddle incomplete, hair [seta] 14-P with 3–4 branches, hair 11-M and 11-T usually single (l–2); in flavopictus the saddle is complete, hair 14-P has 5–7 branches, hair 11-M is double and 11-T double or 3-branched. The pupa of downsi has hair 9-VI much stouter than 9-V, at least twice as long as 9-V, hair 9-VI usually single and barbed; in flavopictus hair 9-VI about same magnitude as 9-V, always single and simple. Based on the morphological difference in all stages of these two forms, I believe that downsi should be recognized as a distinct species.

Tanaka et al. (1979):

Huang (1972) elevated it again to a species. Her discussion of downsi appears accurate as far as specimens from Okinawa are concerned. However, more local and individual variations occur.

As a result of the above diagnosis on 13 adult characters, the populations of Palaearctic Japan and Korea, Amami, Okinawa and Yaeyama are considered as a single species. The Palaearctic population is the nominate subspecies, flavopictus . The Amami and Okinawa populations are identical, conforming to subspecies downsi . The southernmost population (Yaeyama) of flavopictus , is identical with subspecies flavopictus in 2 characters, with subspecies downsi in 2 characters, intermediate in 4 characters, different from both in 5 characters, 3 of the lattermost not appearing clinal. This population is assigned to another subspecies, miyarai .

The larvae of f. flavopictus are characterized by stiff stellate body setae, but the variation is wide…. No definite hairy type was found in… downsi and miyarai , whose setae have in general fewer branches and are usually weak. … The larvae of f. downsi and f. miyarai are, contrary to the adult, fairly homogenous, there being only minor differences, e.g., the laterobasal fringe of spicules of the comb scales is usually very weak and basally restricted in f. downsi , usually a little stronger and extending up to near middle of the apical spine in f. miyarai ; the number of the pecten teeth [spines] is 4–12 (19; x = 6.7) in f. downsi , 7–19 (20; x = 11.6) in f. miyarai . Subspecies downsi and miyarai differ from flavopictus in the longer seta l-VII (the average length relative to the antenna being 1.63, 1.57 and 1.06 in downsi (19), miyarai (13) and flavopictus (30), respectively) and in that the ventral anal gill [papilla] is usually shorter than the dorsal one, while in 75% of flavopictus they were equal. …It is interesting that, in f. flavopictus , many setae, such as 14-P, 5-T, 2-I, III–VII, 5-III-V, 9-VI, 13-I, III–V, have double or quadruple the numbers of branches found in the equivalent setae of f. downsi and f. miyarai . The non-hairy type in f. downsi and f. miyarai may represent an ancestral form of this species.

In our opinion, the morphological data indicate that the three forms are distinct polythetic taxa that are diagnosed by unique combinations of characters. Polythetic species are common in many groups of mosquitoes, particularly large groups like Aedes and Culex .

Numerous sequences for the COI and ND5 mitochondrial genes are available in the GenBank depository, including the entire mitochondrial genome for specimens of flavopictus from South Korea (NC_050044). Among these are COI, ITS1 and ITS2 sequences for flavopictus from the Palaearctic region of Japan, downsi from the Amami and Okinawa Islands and miyarai from Ishigaki and Iriomote Islands in the southern region of the Ryukyu Archipelago. Phylogenetic analysis of the ITS1 and ITS2 sequences ( Toma et al. 2002) produced a cladogram comprised of three distinct lineages, corresponding to the three subspecies. Despite this, because the three forms have allopatric distributions and “reproductive isolation cannot be tested, except experimentally”, Toma et al. were only willing to acknowledge that “the molecular genetic information we have gathered supports the current classification of the complex based on morphological data.”

Drawing conclusions about the status of the subspecies of flavopictus has been a problem of uncertainty. However, we believe the available data provide an alternative interpretation: The geographic isolation is analogous with reproductive isolation, the morphological data are seen as an indication of polythetic species, and the ITS1 and ITS2 sequence data support the specific status of the three forms. In light of this, we believe that Bohart (1953), Tanaka et al. (1979) and Toma et al. (2002) were very circumspect in their decision to treat the three forms as subspecies. As in the case of subspecies of Culex hayashii , Toxorhynchites manicatus and Uranotaenia novobscura treated below, we believe it is appropriate to return downsi to its original specific status and to recognize miyarai as a separate species: Aedes (Stegomyia) downsi Bohart & Ingram, 1946a and Aedes (Stegomyia) miyarai Tanaka, Mizusawa & Saugstad, 1979 . Aedes downsi and Ae. miyarai are currently listed as species in the Encyclopedia of Life.

It is important to note that Miyagi & Toma (1976) showed that laboratory cross mating between flavopictus from Nagasaki, Kyushu Island (Palaearctic) and downsi from Okinawa Island produced hybrid offspring. However, this is meaningless as hybridization between the two forms is unlikely to occur in nature. Besides, the ability to hybridize does not invalidate the existence of separate species, which is amply supported by hybridization studies between members of species complexes, e.g. the Dirus Complex ( Walton et al. 2001) and Gambiae Complex ( Besansky et al. 1997; Thelwell et al. 2000) of the genus Anopheles .