Acheron Lefebvre 1842

Genus Acheron Lefèbvre, 1842

Acheron Lefèbvre, 1842: 6. Type species: Ascalaphus longus Walker, 1853: 435. Designated by McLachlan, 1873a: 265.

Diagnosis. The presence of distinct lateral spines on the basal antennal segments in the male and the larger forewing length (c. 45 mm) are diagnostic characters for distinguishing this genus from all known genera in the tribe Ascalaphini except Glyptobasis McLachlan, 1873 in Pakistan. It can be distinguished from Glyptobasis by lack of distinct triangular projection on the anal area of forewing (Fig. 2), which is well-developed in Glyptobasis (Fig. 8). Apart from other differences, considerable variation in wing coloration has been noticed in this genus.

Note. McLachlan (1873a) speculated about the stages of maturity in four species described by Walker (1853) belonging to the genus Ascalaphus, i.e., A. anticus and A. longus from Bengal, A. loquax from Brazil [misprint for Bengal], and A. trux without label data. These species were described based on the variability of color patterns. Later, McLachlan attempted to correlate the color patterns to the maturity of individuals within the species, i.e., the older the specimens, the darker the coloration. Thus, he treated A. anticus, A. loquax and A. trux as the junior synonyms of A. longus and transferred them to Acheron. Since the coloration in owlflies is known to change after preservation (Michel & Mansell 2018), the two subspecies, viz. A. trux trux (Walker) and A. trux loquax (Walker) proposed by Ghosh (1988) based on variations in wing markings, have been considered as synonyms (van der Weele 1909).

Tauber et al. (2019) reported that the type depository of Acheron longus comprised three female specimens at Oxford University Museum of Natural History (OUMNH), United Kingdom; two of them have label data as Silhet, Bangladesh (previously known as East Bengal). Instead of following McLachlan’s work (1873a), van der Weele (1909) synonymized A. anticus, A. loquax and A. longus under A. trux. Following van der Weele (1909), later taxonomists used A. trux as a valid species name (Fraser 1922; Ghosh & Sen 1977; Ghosh 1988, 2000; Michel 2005; Wang et al. 2018), a practice that was recently corrected by Tauber et al. (2019) in accordance to ICZN Article 24, since the first reviser “was justified in establishing precedence among the simultaneously published names”. Thus, A. longus, which is the name the authors selected as the senior synonym, has priority over the other three names. The distributional range of this monotypic genus is widespread in the Oriental region.