Aedes (Stegomyia) gardnerii (Ludlow)

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 : 54-55

Aedes (Stegomyia) gardnerii (Ludlow)

subspecies gardnerii ( Ludlow, 1905) —original combination: Stegomyia gardnerii . Distribution: Bangladesh, Cambodia, Indonesia, Malaysia, Philippines, Singapore, Thailand, Vietnam ( Wilkerson et al. 2021).

subspecies imitator ( Leicester, 1908) —original combination: Stegomyia imitator (subspecific status by Mattingly 1965). Distribution: Bangladesh, Cambodia, India, Malaysia, Nepal, People’s Republic of China, Taiwan, Thailand, Vietnam ( Wilkerson et al. 2021).

Ludlow (1905) described the female and male of Stegomyia gardnerii from specimens captured on the Philippine Island of Mindoro (Bulacao), but she also examined specimens from Luzon Island (Angeles, Pampanga).A lectotype male was designated by Knight & Hull (1952), who described the adults in more detail, described the fourth-instar larva and illustrated the male genitalia. Leicester (1908) described Stegomyia imitator from two females captured in jungle near Kuala Lumpur, Malaysia. One of the females was selected as the lectotype by Mattingly (1965). Mattingly described and compared the adults (both sexes), pupa and fourth-instar larva of gardnerii sensu stricto and subspecies imitator , and illustrated the scutal scale-pattern and hindleg of both, the midfemur and entire pupa of imitator , the head and terminal abdominal segments of the larva of the type form, and the male genitalia of imitator . Huang (1977) provided more detailed descriptions of the male, female, pupa and larva, and illustrated the scutal and pleural scaling of both subspecies. For gardnerii sensu stricto, she also illustrated the maxillary palpus and genitalia of the female, the midfemur, male genitalia, entire pupa and entire larva. It is worth noting that in available identification keys ( Mattingly 1965; Huang 1977, 1979), the two subspecies are only distinguishable as adults based on the pattern of the scutal scaling. The scutum of the nominate form bears a pair of longitudinal, midlateral stripes of white scales that extend from the anterior margin to the antealar area. The stripes are absent in subspecies imitator , which bears a large patch of white scales on the anterior margin that may be divided medially into two anterolateral patches. The two forms are included but are not distinguished in keys for the male genitalia, pupae and larvae.

Huang (1977) seems to have contradicted herself, by saying on the one hand that “Although imitator (Leicester) can easily be distinguished from that of gardnerii (Ludlow) by the scutal markings”, and on the other that “this adult external morphological character (the scutal markings) seems to be geographically variable.” We believe she intended to say that due to variation in the scutal pattern of imitator , “I have here followed Mattingly (1965) in considering imitator as a sub-species of gardnerii .”

Wilkerson et al. (2021) mistakenly combined the country records for imitator with those of gardnerii . In the case of gardnerii , the records for Bangladesh, Cambodia, China, Malaysia, Singapore, Thailand and Vietnam apply to subspecies imitator , based on the records of Mattingly (1965), Matsuo et al. (1974, Taiwan), Huang (1977), Darsie & Pradhan (1990, Nepal), Lu et al. (1997, China), Jeffery et al. (2010, Singapore), Rattanarithikul et al. (2010, Thailand), Irish et al. (2016, Bangladesh), Bui & Darsie (2008, Vietnam) and Maquart et al. (2021, Cambodia). As indicated by Huang (1977), the nominate subspecies “is apparently confined to the Eastern part of Indomalayan area… presently known from the Philippines, Sabah [ Malaysia], Sulawesi and Alor Island.”

Two partial sequences of the cytochrome c oxidase subunit I (COI) gene are registered in GenBank for Ae. gardnerii:Accession MW 321943 (667 bp), Ae. gardnerii from Singapore ( Yeo et al. 2021) and accession MK654753 (661 bp), Ae. gardnerii imitator from Thailand (P. Somboon). A BLAST search revealed that the two sequences are identical. Obviously, the sequence from Singapore is derived from a specimen of subspecies imitator , which concurs with the recorded occurrence of this form in the island country (Jeffrey et al. 2010).

Although the male genitalia, larva and pupa of gardnerii sensu stricto and subspecies imitator may be indistinguishable, the fact they exhibit distinct and constant differences in the pattern of white scales on the scutum and have separate distributions is a clear indication that they are probably separate species. We believe this is likely to be proven when COI sequences become available for the nominate form. Therefore, it seems prudent to formally reinstate imitator to its original specific status: Aedes (Stegomyia) imitator ( Leicester, 1908) . Aedes imitator is currently listed as a species in the Encyclopedia of Life.

Four nominal species originally described as species of Stegomyia Theobald, 1901 (in Howard 1901) are regarded as synonyms of Ae. imitator : argenteomaculata Theobald, 1907 (Narcondam Island; synonymy by Huang 1977); christianus Dyar, 1921b ( China; synonymy by Mattingly 1965); minutissima Theobald, 1910 a ( India; synonymy by Huang 1977); and indosinensis Borel, 1928 (Indochina; synonymy by Huang 1977). These nominal species should remain in synonymy with Ae. imitator ; however, it is possible that argenteomaculata could be a distinct species because it is described from a remote island outside the continental range of Ae. imitator .