Downsiomyia nivea (Ludlow, 1903) (in Theobald, 1903) , original combination: Stegomyia nivea.
Subfamily Culicinae, tribe Aedini. Downsiomyia includes 30 species. Genus abbreviation – Do.
The adults of Downsiomyia species are easily recognized by the presence of broad decumbent scales on the vertex and erect scales on the occiput of the head[/no-oglossary], the presence of patches of pale scales covering the scutal fossae and by the absence of acrostichal and dorsocentral setae and postspiracular scales. Patches of pale scales also occur on the scutal fossae of members of the Gubernatoris Group of 'Ochlerotatus (Finlaya)' sensu auctorum, and a similar condition occurs in some species of Stegomyia, but those species differ in having pale scaling on the supraalar area, which is dark-scaled in Downsiomyia. The [no-lexicon]simple aedeagus with small apical teeth of Downsiomyia males is somewhat similar to the aedeagus of some species of Ochlerotatus, but otherwise differ in numerous other features. Larvae of Downsiomyia resemble those of Ayurakitia in having setae 4,5,6-C multiple branched and inserted slightly anterior or posterior to seta 7-C, but differ in having seta 12-I and fewer comb scales arranged in a single row.
Like other genus-group taxa of tribe Aedini, the life stages of Downsiomyia are diagnosed and distinguished by combinations of characters, as follow. ADULTS – Vertex of head with only broad decumbent scales, erect scales confined to occiput; eyes contiguous; antennal pedicel with scales and setae on mesal surface; maxillary palpus and proboscis dark-scaled; acrostichal and dorsocentral setae absent; scutal fossa with pale falcate scales; supraalar area dark-scaled; all lobes of scutellum with broad scales; paratergite, postspiracular area, subspiracular area and metameron without scales; wing entirely dark-scaled; hindleg, except proximal part of femur, dark-scaled; fore- and midungues of males unequal, each with 1 tooth. FEMALE GENITALIA – Tergum VIII and sternum VIII with numerous broad scales; tergum IX comprised of 2 narrow lobes each with few apical setae; insula lip-like with few long setae in lateral patches; upper vaginal sclerite small; cercus short and broad, with 5–7 stout distolateral setae; one large (Nivea Group) or one large and 2 smaller (Albonivea Group) spermathecal capsules. MALE GENITALIA – Gonocoxite with ventromesal cluster of several to numerous broad fusiform scales (except Do.mikrokopion) and a narrow thumb-like setose lobe borne dorsomesally at base; gonostylus short with long gonostylar claw at apex; claspette columnar with long longitudinally striated claspette filament at apex; aedeagus simple, scoop-like with 1 or usually 2 or more small apical teeth on each side. LARVAE – Antenna spiculate; seta 1-A multi-branched; seta 1-C single, attenuate distally; setae 4–7-C well developed, multi-branched; seta 12-I present; seta 7-I large and single, seta 7-II short and multi-branched; seta 6-II shorter than seta 6-III; setae 2- and 4-VIII both single; spines of siphonal pecten evenly spaced; seta 1-S branched, inserted distal to pecten; saddle incomplete; seta 1-X inserted on saddle. PUPAE – Seta 1-CT long, stout and normally single; seta 2- and 3-CT short and slender; seta 5-CT distinctly longer than seta 4-CT, often long and single; seta 11-CT long, stout and single; seta 3-I long and stout, longer than seta 6-I; seta 6-VII short, with few branches, inserted posterior to seta 9-VII; seta 9-VII long, stout and normally double or triple; seta 9-VIII long, stout, multi-branched, inserted on margin of segment; paddle without hair-like marginal spicules, midrib well developed. See Aedini.
Downsiomyia appears to be most closely related to genera Danielsia, Finlaya and Haemagogus based on the cladistic analysis of extensive morphological data by Reinert et al. (2009) that generated relationships of these genera expressed parenthetically as (Finlaya + Danielsia) + (Downsiomyia + Haemagogus). The genealogical affinities of Downsiomyia require further study as the character support for its sister relationship with Haemagogus was not very strong. It is interesting, however, that Downsiomyia appeard to be more closely related to Haemagogus than to either Danielsia or Finlaya, which include species that were previously classified with the species of Downsiomyia in the traditional polyphyletic concept of Aedes (Finlaya). Downsiomyia formed a single branch in the large unreloved polytomy recovered in the study of Wilkerson et al. (2015). In contrast with the finding of Reinert et al. (2009), Downsiomyia was recovered as sister to a clade comprised of Danielsia + Luius in the maximum likelihood phylogeny of Soghigian et al. (2017) based on seven molecular markers.
Downsiomyia are forest mosquitoes. The immature stages normally inhabit water in tree holes but they are found occasionally in stump holes, bamboo stumps, bamboo internodes, bamboo cups and split bamboo on the ground (Macdonald & Traub, 1960; Rattanarithikul et al., 2010). Two species, Do. niveoides and Do. novonivea, have been found in an artificial container and a rock hole, respectively (Rattanarithikul et al., 2010). Adult females of some species, e.g. Do. albolateralis, Do. harinasutai, Do. niveoides and Do. vana, are known to bite humans at ground level and in forest canopy during the daylight, early morning and evening hours (Macdonald, 1957; Wharton, 1962; Macdonald et al., 1965).
Downsiomyia nivea and Do. harinasutai are vectors of Wuchereria bancrofti in the Philippines (Rozeboom & Cabrera, 1964) and Thailand (Gould et al., 1982). Zagaria & Savioli (2002) also listed these two species as vectors of filarial parasites. Shriram et al. (2005) found females identified as Do. nivea (as Ochlerotatus niveus) in the Andaman and Nicobar Islands of India to be naturally infected with microfilariae of W. bancrofti, but the identification of the species is questionable (Huang & Rueda, 1998). Rudnick et al. (1986) reported that species of Downsiomyia (as members of the Niveus Subgroup of Aedes subgenus Finlaya) were sylvatic vectors of dengue fever virus in Malaysia.
Species of Downsiomyia occur in the Oriental Region and adjoining areas of the Australasian and Palaearctic Regions.
Reinert et al., 2004, 2006, 2008, 2009 (generic status, morphology, phylogeny); Reinert & Harbach, 2006 (taxonomy); Reinert, 2008 (female genitalia); Rattanarithikul et al., 2010 (Thailand, keys, bionomics); Wilkerson et al., 2015 (as subgenus of Aedes, phylogeny); Soghigian et al., 2017 (as subgenus of Aedes, phylogenetic relationships).