Toxorhynchites (Toxorhynchites) christophi (Portschinsky)

subspecies aurifluus (Edwards, 1921a) —original combination: Megarhinus aurifluus (subspecific status by Danilov 1987).

Distribution: Taiwan (Wilkerson et al. 2021, not Indonesia, see below).

subspecies christophi (Portschinsky, 1884) —original combination: Megarhina [sic] christophi. Distribution: Japan, Russia, South Korea (Wilkerson et al. 2021), China (Danilov 1987; Lu et al. 1997).

Portschinsky (1884) described Toxorhynchites christophi (as Megarhina christophi) from an unspecified number of adult females from “Amur”, the present-day Amur Oblast, located in the south of the Russian Far East region on the border with Heilongjiang Province of China. Subspecies aurifluus was originally described as a species of Megarhinus based on four males and a single female collected at several localities on the island of Formosa, present-day Taiwan (Edwards 1921a). The adults (both sexes), larva and pupa are known for both forms and have been described and partially or fully illustrated and treated as separate species by various researchers: Tx. aurifluus — Lien (1965), Lu et al. (1997); Tx. christophi — Tanaka et al. (1979), Lu et al. (1997).

Tanaka et al. (1979) provided the following assessment, which serves as a prelude to an understanding of the taxonomic status of the two nominal species.

Toxorhynchites christophi appears to be very closely allied to aurifluus (Edwards) from Taiwan. The male genitalia are apparently identical. The aedeagus has no sclerotized tergomedian band in specimens studied (2 Korean christophi and 2 aurifluus); Lien (1965) does not show any band on the aedeagus of aurifluus; it appears the same in Siberian christophi.* [Footnote: “* Danilov 1977, personal communication.”]

Korean specimens of christophi are identical with aurifluus (3 males and 4 females from Taiwan were examined) in the presence of a yellowish brown median area on the mid- and hindtibiae, but different from it in the existence of a pale median band on the proboscis, the golden color of the scutal marginal metallic scales (bluish green in aurifluus), the more developed white scaling of the tarsi, the lack of the sublateral patches on female abdominal tergum IV (occasionally a few white scales present) (aurifluus has sublateral patches sub-equal to those of III in size), and in that the lateral tufted bristles [setae] on female abdominal tergum VI are all dark (anterior 0.33–0.40 of lateral bristles are yellow in aurifluus). In the larvae, only minor differences are detected (Table 40).

The metallic coloration in insects in general is quite variable, it easily changes within a species between green, blue, purple, coppery golden, etc. Such variability must be considered. White scaling of the tarsi was found to be more developed in the northern populations of towadensis [Tx. towadensis (Matsumara, 1916)] than in the southern ones. Differences in the tarsal white scaling between Korean christophi and Formosan aurifluus appear to be a similar case. All the differences in the larvae are in the branching of minor setae, and their significance may not be very great. Thus, important characters will be: (1) the pale median band of the proboscis, (2) the yellowish brown median area of the mid- and hindtibiae, (3) the sublateral patches of female abdominal tergum IV and (4) the lateral tufted bristles of female abdominal tergum VI. Korean christophi differs from aurifluus in (l), (3) and (4). They are, however, consistent in other essential characters, the tergomedian band of the aedeagus, the lateral tufted bristles of abdominal terga VII–VIII, and larval seta 11-II. On the basis of present knowledge, they appear allopatric. Thus, there might be 2 possible interpretations, they are either 2 distinct species, or local forms (subspecies) of a single species. For a final decision of their taxonomic statuses, much more material must be studied.

Danilov (1987) examined more material of Tx. christophi and reportedly observed longitudinal clinal variation in the average lengths of several larval setae, which he interpreted as “grounds to consider Tx. aurifluus not an independent species, but a subspecies of Tx. christophi — Tx. ch. aurifluus Eds. (comb. n.), common only on Taiwan, where the type locality is located, i.e., no longer in the Palearctic, like Tx. ch. christophi, but in the north of the Oriental Zoogeographic Region [translated from the Russian].”

Ten years later, Lu et al. (1997) published a monumental treatise on the mosquito fauna of China in which both aurifluus and christophi are treated as species. The authors recorded Tx. christophi from Jilin Province in northeastern China, bordering North Korea and Russia, and stated that Tx. aurifluus is found in Taiwan, Hubei and Hainan. Hubei is a landlocked province in east-central China approximately 700 km northwest of the Taiwan Strait and Hainan is an island province located off the southernmost point of mainland China. Assuming that specimens from Hubei and Hainan Provinces were correctly identified, aurifluus is distributed south of approximately latitude 42° N and christophi north of approximately latitude 44° N. There are no records of the two forms between these latitudes. We note that aurifluus was most recently treated as a species by Lin et al. (2016).

Based on available records, the distribution of christophi includes the Primorye and Khabarovsk regions of far eastern Russia, northeastern China and the Korean Peninsula, whereas aurifluus occurs in eastern China from Hubei Province to Taiwan and southward to Hainan Island. As noted by Danilov (1987), the distribution of christophi lies in the Palaearctic Region and that of aurifluus is in the Oriental Region. Based on the morphological differences recorded by Tanaka et al. (1979) and Lu et al. (1997), and the apparent allopatric distributions of the two forms, we agree with Lien (1965), Lu et al. (1997) and Lin et al. (2016) that aurifluus should be recognized as a separate species: Toxorhynchites (Toxorhynchites) aurifluus (Edwards, 1921a). Toxorhynchites aurifluus is currently listed as a species in the Encyclopedia of Life.

Wilkerson et al. (2021) list two synonyms for Tx. aurifluus: Megarhinus aurifluus variety formosaensis Ogasawara, 1939 and Toxorhynchites changbaiensis Su & Wang, 1981. The former, synonymized by Lien (1962), is correct, i.e. formosaensis is undoubtedly conspecific with aurifluus. The latter, however, credited to Danilov (1987), is incorrect. Toxorhynchites changbaiensis was described from specimens collected in the Huang-Song-Pu forest area of Jilin Province in northeastern China. As explicitly noted by Danilov (1987), and correctly listed by Lu et al. (1997), changbaiensis is a synonym of Tx. christophi, not Tx. aurifluus.

A note needs to be added here to address the record of aurifluus in Indonesia, which was first addressed by Danilov (1987), who suggested “it is possible that another subspecies of Tx. christophi, which has not yet been described, occurs there, since, for example, the pupa from Sumatra described as Tx. aurifluus [by] (Brug, 1932) differs in the shape of the paddles from the pupae of Tx. ch. aurifluus from Taiwan [translated from the Russian].” The records of aurifluus in Indonesia listed in the catalogs of Stone et al. (1959), Knight & Stone (1977) and Wilkerson et al. (2021) should be disregarded because they are certainly based on misidentifications. The record by Brug (1932) is based on the identification of an adult (sex not indicated) reared from a pupa collected from a pitcher plant in Sumatra, a habitat that is highly unlikely to be utilized by larvae of aurifluus, which thrive in bamboo stumps, tree holes and artificial containers (Lien 1965); the record of aurifluus in Sulawesi (as Celebes) by Brug (1939) is based on an undisclosed number of females, but the identification was regarded as uncertain because aurifluus was originally described from a male and the female was unknown at the time. As revealed by Lane (1992), the new species from Sulawesi which he described as Tx. auranticauda was confused in previous literature with aurifluus from Taiwan. Consequently, Indonesia should be deleted from the distribution of Tx. aurifluus.