Aedes (Aedimorphus) vexans (Meigen), 2021

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 : 16-17

Aedes (Aedimorphus) vexans (Meigen)

subspecies arabiensis ( Patton, 1905) —original combination: Culex arabiensis (subspecific status by White 1975). Distribution: Gambia, Mauritania, Mauritius, Nigeria, Saudi Arabia, Somalia, South Africa, South Sudan, Sudan, Tanzania, Yemen ( Wilkerson et al. 2021).

subspecies nipponii ( Theobald, 1907) —original combination: Culicada nipponii (subspecific status by Bohart & Ingram 1946b). Distribution: Georgia, Japan, Mongolia, People’s Republic of China, Russia, South Korea ( Wilkerson et al. 2021).

subspecies nocturnus ( Theobald, 1903a) —original combination: Culex nocturnus (subspecific status by Bohart & Ingram 1946b). Distribution: Australia, Cook Islands (Polynesia), Fiji, Indonesia, Kiribati, Malaysia, Mariana Islands, Marshall Islands, New Caledonia, Palau, Papua New Guinea, Samoa, Solomon Islands, Timor, Tonga, Tuvalu, Vanuatu ( Wilkerson et al. 2021).

subspecies vexans ( Meigen, 1830) —original combination: Culex vexans . Distribution [sensu lato]: Afghanistan, Albania, Algeria, Armenia, Australia, Austria, Azerbaijan, Bangladesh, Belarus, Belgium, Belize, Bosnia and Herzegovina, Bulgaria, Cambodia, Canada, Corsica, Crimean Peninsula, Croatia, Czech Republic, Denmark, Estonia, Fiji, Finland, France, Former Yugoslav Republic of Macedonia, Gambia, Georgia, Germany, Greece, Guam, Guatemala, Honduras, Hong Kong, Hungary, India, Indonesia Iran, Iraq, Italy Japan, Jordan, Kazakhstan, Kiribati, Kosovo, Laos, Latvia, Liberia, Libya, Lithuania, Macedonia, Malaysia, Malta, Mariana Islands, Mauritania, Mexico, Micronesia, Moldova, Mongolia, Montenegro, Morocco, Myanmar, Nepal, Netherlands, New Caledonia, New Zealand, Norway, Pakistan, Papua New Guinea, People’s Republic of China, Philippines, Poland, Portugal, Romania, Russia, Samoa, Saudi Arabia, Serbia, Singapore, Slovakia, Slovenia, Solomon Islands, South Africa, South Korea, Spain, Sri Lanka, Sweden, Switzerland, Taiwan, Tajikistan, Thailand, Tonga, Turkey, Turkmenistan, Tuvalu, Ukraine, United Kingdom, United States, Uzbekistan, Vanuatu, Vietnam, Yemen ( Wilkerson et al. 2021).

Aedes vexans sensu lato, occurs worldwide except for South America. Since Ae. vexans sensu lato is a common, medically important species, it has attracted worldwide interest. In summary, we think that two of the nominal subspecies have characteristics that adequately separate them from typical vexans : subspecies nipponii ( Japan and the eastern Palaearctic) and subspecies arabiensis (northeastern Africa and Arabia [ South Africa?]). However, the third subspecies, nocturnus (Central Pacific and Australasia) has generated taxonomic inconsistency since there are no clear differences to distinguish it. There are regional keys to identify the four nominal subspecies from cooccurring species of Aedes , but there are no keys to separate the subspecies from each other. A partial exception is Reinert (1973), who compared a worldwide concept of vexans vexans with the allopatric vexans nipponii .

Nominotypical vexans

To compare the nominal forms, we first define nominotypical vexans using a recent description from Europe, the continent of the type locality, Berlin, Germany. The nominotypical subspecies was described from a single female. The type specimen is in the Muséum National d’Histoire Naturelle, Paris, France. There are descriptions for what has been called vexans from many parts of the world, but it is sensible to use a recent description from Europe ( Becker et al. 2020). The caveat is that the provenance of specimens and/or literature used for this description are not documented. It will nevertheless serve as a basis for comparison with characters of subspecies and descriptions of vexans from other parts of the world. The following is paraphrased from key characters (diagnoses) followed by more complete descriptions, a format often used by F. W. Theobald.

Adult female.Tarsomeres with pale rings only; proboscis distinctly longer than forefemur; scutellum with narrow, curved, yellowish or pale scales; pale basal bands of tarsomeres very narrow, usually not exceeding 0.25 length of tarsomeres; abdominal terga with basal white bands constricted medially, giving them a bilobed appearance.

Tibiae dark-scaled dorsally, pale-scaled ventrally; narrow basal bands present on foretarsomeres 2 and 3, midtarsomeres 1–4 and on all hindtarsomeres. Proboscis and maxillary palpus dark-scaled, palpus with some apical white scales; head covered with narrow curved pale and dark decumbent scales and numerous dark brown erect forked scales which extend anteriorly to interocular space. Scutal integument dark brown, covered with narrow curved dark scales and narrow pale scales forming indistinct patches on anterior submedian, prescutellar and dorsocentral areas; acrostichal and dorsocentral setae well developed; postspiracular area with large patch of narrow curved or moderately broad pale scales; upper and lower mesokatepisternal scale-patches present. Wing veins covered with moderately broad dark scales and isolated pale scales at bases of costa and subcosta. Abdominal terga with basal white bands, distally dark-scaled; basal bands on terga III–VI distinctly narrowed medially, giving a bilobed appearance; sternum VIII with distinct apical V-shaped notch.

Adult male. Maxillary palpus about as long as proboscis; gonostylus attached at apex of gonocoxite, simple, not divided; gonostylus distinctly expanded apically; claspette elongate, well separated from base of gonocoxite; gonostylus gradually expanded toward apex; gonostylar claw articulated subapically, straight. Tergum IX strongly bilobed with 6–11 setae on each lobe. Gonocoxite long and moderately broad with scattered scales on lateral and ventral surfaces; basal and apical lobes absent; gonostylus widens toward apex; gonostylar claw straight, inserted on a small subapical tubercle; claspette moderately broad basally, apex slightly expanded and rounded, with crown of numerous spine-like setae, some curved apically; claspette filament absent; paraproct with pointed apex; aedeagus strongly sclerotized with lateral plates connected at base.

Larva. Integument not covered with obvious spicules. Antenna less than half length of head, with numerous scattered spicules; seta 1-A 5–10 branched, inserted proximal to middle of antenna. Labral brush with median setae apically serrate (in contrast to unmodified setae in Ae. rossicus and Ae. cinereus ). Setae 5–7-C arranged in a triangular pattern, 5-C posterior to 6,7-C; 5-C 1–4-branched, 6-C 1- or 2-branched, 7-C 7–9 branched. Comb with 7–13 scales arranged in 1 or 2 irregular rows; scales with long median spicules and small spicules at base. Siphon index 2.3–3.0; pecten with 13–18 spines, apical 2 or 3 spines larger and unevenly spaced; basal spines with 1–3 lateral denticles; seta 1-S inserted beyond middle of siphon, with 3–8 short branches, length about half width of siphon at setal insertion. Saddle large but incomplete; seta 1-X with 1 or 2 branches; seta 4-X with 3 or 4 precratal setae; anal papillae distinctly longer than saddle.

The notion that vexans is a single species across Europe and North America was recently questioned in two studies. Krtinić et al. (2013) used allozyme data to analyze two European populations ( Serbia and Germany) and one North American population (California, USA). They found unambiguous differences between European and North American vexans . “We observed that populations of Am. [as genus Aedimorphus ] vexans from the Palearctic ( Germany and Serbia) and from the Nearctic ( USA) formed two genetically distinct populations that had no genetic exchange.” In other words, they are genetically separate species. Also, they cited Becker et al. (2020), who wrote that unlike invasive species such as Aedes albopictus , which oviposits above the water line, vexans lays eggs onto moist soil, which argues against it being an invasive species in North America. Since a single North American population was sampled, these results require verification. Lilja et al. (2018), using the mitochondrial COI gene and two nuclear genes found two sympatric genetically isolated vexans clades in Sweden and elsewhere in northern Europe. Considering COI data only, including sequences in GenBank from other parts of the world, they found four distinct groupings: “Group 1 vexans variant,” Ae. vexans nipponii, Ae. vexans North America and Ae. vexans Europe. Given a lack of morphological vouchers for study and weak branch support in some cases, Lilja et al. (2018) did not attempt to interpret the taxonomic meaning of their findings, recommending further work. These two studies generate many uncertainties, but they suggest that North American vexans could be a different species and that an unrecognized cryptic species occurs in Europe.

Synonyms of Aedes (Aedimorphus) vexans ( Meigen, 1830) ( Wilkerson et al. 2021) : Culex parvus Macquart, 1834 (type locality: Bordeaux [Gironde], France); Culex articulatus Rondani, 1872 (type locality: Italy); Culex malariae Grassi, 1898 (type locality: Italy); Culex sylvestris Theobald, 1901a (type locality: various, all in Canada) [montcalmi Blanchard, 1905 is incorrectly listed as a replacement name for sylvestris in Wilkerson et al. 2021, see Townsend (1990) for more information]; Culicada minuta Theobald, 1907 (type locality: India); Aedes eurochrus Howard, Dyar & Knab, 1917 (type locality: Popcum, British Columbia, Canada).