Eriozona laxus (Osten Sacken, 1875):48

Adapted from Vockeroth (1969).

Large robust species with broadly oval, moderately convex abdomen with broad, divided, yellow or greenish-yellow fasciae.

Megasyrphus species have pilose eye, the pile below less dense and rather restricted; face yellow with dark brown to black medial vitta; scutum black, shining, at most very slightly yellowish laterally; scutellum yellow-brown; pleura blackish, shining, the posterior part of anepisternum and dorsal part of katepisternum distinctly pale poIlinose, sometimes slightly yellowish in ground colour; dorsal and ventral katepisternal pile patches narrowly separated posteriorly because of posterior broadening of both patches, otherwise broadly separated; metasternum with many long black pile; metacoxa with tuft of strong pile at posteromedian apical angle; vein R4+5 shallowly, broadly, symmetrically, but distinctly dipped into cell R4+5; wing membrane entirely microtrichose; abdomen broadly oval, usually distinctly convex dorsally, with strong margin from distal third of tergum 2 to end of tergum 5.

Megasyrphus laxus (Osten Sacken, 1875).

Osten Sacken, C.R. (1875) A list of the North American Syrphidae. Bulletin of the Buffalo Society of Natural Sciences 3, 38-71.

Megasyrphus was erected as a new genus by Dusek and Laska (1967). As indicated by these authors and Vockeroth (1969), Megasyrphus resembles Didea with similarities in body shape and abdominal pattern, while male genitalia characters are similar to Eriozona. Rotheray and Gilbert (1989) suggested a closer relationship to Didea and proposed to synonymize Megasyrphus under Didea. Vockeroth (1992) did not accept the synonymy due to adult morphological differences.

Thompson and Rotheray (1998) placed Megasyrphus as a subgenus of Eriozona in the Manual of Palaeractic Diptera in his identification based on adult morphology. Mengual et al. (2008) resolved Megasyrphus laxus and M. erraticus as siter group of the genus Didea, in congruence with larval characters. In the same analysis, Eriozona was resolved as the sister group of Dideoides, a placement not suggested earlier, and related with Dideopsis.

Synonyms:

Didea laxa Osten Sacken, 1875: 66.

Didea syrphoides Hull, 1925: 278.

Didea daphne Hull, 1925: 280.

Syrphus catalina Curran, 1930:14. (synonym following Vockeroth 1992, but valid species Megasyrphus catalina sensu Thompson 2010 in the Systema Dipterorum database)

Metasyrphus nigrocomus Hull, 1943: 48.

Adapted from Vockeroth (1992).

Species robust with broadly oval moderately convex and strongly margined abdomen with broad deeply emarginate or divided yellow or greenish yellow fascia on terga 3 and 4.

MALE.

Head: Eye with long dense pile above, less dense pile below. Frontal triangle of male black, densely yellow-gray pollinose on upper two-thirds; frons of female black with two large oblique joined or narrowly separated yellow-gray pollinose areas. Face yellow with dark brown to black median vitta.

Thorax: Scutum black, shining, at most very slightly yellowish laterally. Scutellum yellow-brown. Ventral scutellar fringe complete. Pleuron black, shining; posterior part of anepistemum and dorsal part of katepisternum distinctly pale pollinose, with slightly yellowish ground color in some specimens. Anterior anepisternum, meron, and metapleuron bare. Dorsal and ventral katepisternal pile patches narrowly separated posteriorly because of posterior broadening of both patches, otherwise broadly separated. Metasternum with many long black pili. Wing membrane entirely trichose; vein R4+5 with shallow broad symmetrical but distinct dip into cell r4+5. Hind coxa with tuft of strong pili at posteromedial apical angle.

Abdomen broadly oval, usually distinctly convex above, with strong margin from two-thirds length of tergum 2 to end of tergum 5. Tergum 2 with pair of large yellow maculae; terga 3 and 4 with broad deeply emarginate or divided yellow or greenish yellow fascia. Sterna yellow, 2-4 each with broad medially expanded subapical black fascia.

GenBank accession number for this species are: protein-coding COI gene (EF127302), rRNA 28S gene (EF127381).

The Nearctic species Megasyrphus laxus and the Palaearctic species Megasyrphus erraticus (Linnaeus), previously known as Megasyrphus annulipes (Zetterstedt), are extremely similar and perhaps should be considered conspecific. However, European specimens can be distinguished from those of M. laxus by slight differences in the shape of the yellow bands of terga 3 and 4; they are narrower, less strongly emarginate medially and at most very slightly narrowed laterally.Japanese specimens studied by Dr. Vockeroth and Dr. Thompson agree with European rather than with Nearctic specimens. This supports recognition of two species, although study of Siberian material is desirable (from Vockeroth 1992).

Body length: 10.2-15.6 mm (Vockeroth 1992).

Mengual et al. (2008) resolved Megasyrphus laxus and M. erraticus as sister group of the genus Didea in congruence with larval characters, using the mitochondrial COI gene and the ribosomal rRNA 28S gene.

Nearctic species known from Alaska to Newfoundland, south to California and Mexico (Thompson 2010).