Toxomerus marginatus (Say)
Toxomerus marginatus (Say, 1823).
Say, T. (1823) Descriptions of dipterous insects of the United States. Journal of the Academy of Natural Sciences of Philadelphia 3, 9-32 [1823.04.??], 33-64 [1823.05.??], 73-104.
Toxomerus Macquart, 1855 belongs to Syrphinae (Syrphidae) and it is the only genus included in Tribe Toxomerini, with approximately 150 species described in the world. It occurs mainly in the Neotropical Region with 143 species, followed by the Neartic Region with 16 species (9 endemic) (Borges and Couri 2009).
The genus Toxomerus is characterized by : eye with distinct triangular emargination on posterior margin; gena narrow; arista bare; postpronotum bare; meron bare; anatergum bare; katatergum bare; posterior spiracle with short pile on margin; metasternum bare; metaepisternum pilose; metaepimeron bare; male genitalia well sclerotized, very short to long postanal process arising from fused surstylar apodemes and projecting caudad between bases of surstyli (Borges and Couri 2009).
Toxomerus marginatus is a small species (less than 9 mm in lenght), scutum with lateral yellow vitta continuos from postpronotum to scutellum; thorax with yellow macula above procoxa; scutellum yellow, black pilose; anepimeron black; and abdomen with pale medial areas with submedial black vittate maculae.
Head: Face produced forward ventrally, with facial tubercle, yellow, yellow pilose; gena black, yellow pilose; frontal triangle yellow, yellow pilose; vertical triangle black, black pilose; antenna yellow, arista brown; eye bare, dichoptic, eyes separated by aristal width; occiput black, silvery-golden pollinose, withish-yellow pilose.
Thorax: Scutum black with yellow vita on lateral margin from postpronotum to scutellum, bronze pollinose with dorsomedial white pollinose vitta, yellow pilose; postpronotum yellow, bare; scutellum yellow with dorsomedial brown macula, black pilose, subscutellar fringe sparse with yellow pile. Pleuron mostly black, except proepimeron yellow, posterior anepisternum yellow on posterior half, and katepisternum black with dorsal yellow macula; metasternum bare; calypter yellow; plumula yellow; halter yellow; spiracular fringes yellow. Wing: Wing membrane slightly bronish, stigma dark yellow; mostly microtrichose, bare basally on 2nd costal cell and cells R1, R, BM and CuP. Alula broad, microtrichose. Legs: Entirely yellow except procoxa black, meso- and metatarsi brown, black and yellow pilose.
Abdomen: Parallel-sided. Dorsum: 1st and 2nd terga yellow pilose, the rest black pilose; 1st tergum black except lateral and anterior margin yellow continuous with the lateral margin of the other terga; 2nd tergum black except lateral margins yellow, with medial broad yellow fascia; 3rd and 4th terga with lateral and submedial black vittae connected posteriorly with a black fascia interrupted in the medial point of the tergum, with submedial maculate vittae (sometimes the black fascia connecting vittae is not present); 5th tergum with a medial black macula on anterior margin and 2 sublateral black vitta.
GenBank accession number for this species are: protein-coding COI gene (HM062546; AY261705; EU409160), rRNA 28S gene (HM062624; AY261752; EU409214),18S gene (EU431555; EU409277), 12S gene (HM062596; AF154745), 16S gene (AF154821; AF154820), phosphogluconate dehydrogenase gene (HM062762), CAD gene (HM062742), triose phophate isomerase gene (HM062690), white-like gene (HM062701), elongation factor 1a gene (HM062672), alanyl-tRNA synthetase gene (HM062649), and cytochrome b gene (HM062568).
Ecology and Distribution
Widespread species ranging from Canada south to Central America. It was introduced in Hawaii.
Larva (from Fluke 1929).
4 to 4.5 mm long, 1 mm wide. Body light greenish yellow. The only dark areas are where the viscera show through. Integument transparent, very slightly papillose. Segmental spines very short and light in color; no integumental vestiture. The posterior respiratory organ situated O:n a papillose base which is as high as the appendage is long. The chitinous ring is not very strong and surrounds the entire organ with gentle indentation curves both dorsal and ventral. In the evolutionary development of this species, spiracles II and III have migrated so that II now occupies the position of III. This also means that the inner or mesal ends of the spiracle were once the outer or distal ends.
Puparium (from Fluke 1929).
Length 5.2 mm., width 1.5 mm., widest at the front one-third; evenly rounded anteriorly, tapering gradually to rear. Ventral line almost straight. Two prominent irregular, curved dark lines along the sides, the more dorsal one running from near the front end to within 1 mm. of the rear. Lower line a little more than half as long as the pupa.
Evolution and Systematics
Nomenclature and Synonymy
Mesograpta circumdata Bigot, 1884: 107.
Mesogramma comma Giglio-Tos, 1892: 4.
Scaeva marginata Say, 1823: 92.
Syrphus limbiventris Thomson, 1869: 495.
Toxomerus is the single genus of the tribe Toxomerini. Recently, Mengual et al. (2008) included several species of Toxomerus in their phylogenetic analysis and Toxomerini was resolved as a monophyletic group within the clade of the genus Ocyptamus.