﻿Taxonomic revision of Romaleosyrphus Bigot (Diptera, Syrphidae), including descriptions of seven new species

﻿Abstract The genus Romaleosyrphus Bigot is reviewed, including the description of seven new species (R.argosi Moran, sp. nov., R.bigoti Moran, sp. nov., R.drysus Moran, sp. nov., R.nephelaeus Moran & Thompson, sp. nov., R.soletluna Moran & Thompson, sp. nov., R.vockerothi Moran & Thompson, sp. nov. and R.woodi Moran, sp. nov.). Romaleosyrphusarctophiloides (Giglio-Tos), comb. nov. is transferred to Romaleosyrphus. Romaleosyrphusstat. rev. is redefined to represent the monophyletic unit of species within Criorhinina which possess holoptic males, a proximal ventral half of vein C with setae, a broad intersection of vein R1 with vein C, the distal part of R4+5 beyond M1 longer than cross-vein h and appressed pile on the abdomen. Descriptions, habitus and genitalia photographs, distributions, and an illustrated key for all nine Romaleosyrphus are presented. DNA barcode data are provided for eight of the species with a cytochrome c oxidase subunit I gene tree presented and discussed.


Introduction
Romaleosyrphus Bigot, 1882 are large flies of the family Syrphidae (Eristalinae, Milesiini, Criorhinina) and are Batesian mimics of Bombus Latreille, 1802. Williston (1892) combined the genus with Crioprora Osten Sacken, 1878, where it remained until Thompson (1976) combined it with Criorhina Meigen, 1822. Romaleosyrphus is Neotropical in distribution, with one described species, R. villosus Bigot 1882, and appears to be restricted to high elevation cloud forests. Members of this genus possess the classic anteroventrally produced face predominant throughout the subtribe Criorhinina. Little is known of their natural history, with larvae never illustrated or described, but like their relatives, immatures likely live on decaying roots, in rot holes, sap-runs, or decaying wood in general (Speight 2020). Moran et al. (2021) resurrected Romaleosyrphus, as the single Neotropical species sampled was recovered sister to the genus Matsumyia Shiraki, 1930. Neotropical species concepts of Criorhina s. l. have never been reviewed. Considering this revived generic status, a detailed examination is necessary to explore species membership in the genus and to confirm that separation of Matsumyia from the older concept of Romaleosyrphus Bigot, 1882 is warranted.
In the present study we provide evidence to justify the split between Romaleosyrphus and Matsumyia, transfer Criorhina arctophiloides (Giglio-Tos, 1892) to Romaleosyrphus, describe seven new species of Romaleosyrphus, provide habitus and genitalia photographs and distributions for all the species, and provide the first identification key to the group.

Examined collections
A list of material examined is provided in Suppl. material 1. All specimens are labelled with a unique reference number, either with their unique collection number or in the format KM MXXXX. Label data from the studied individuals were transcribed by hand into the online CNC database and can be accessed at https://cnc.agr.gc.ca/. Specimens were borrowed from the following institutions: The primers, COI-Fx-A-R, B-F, B-R, and C-F are designed to sequence the standard animal DNA barcode region in three portions, labeled A, B, and C after the primers, increasing the chance of successfully sequencing heavily fragmented DNA. This enabled DNA barcoding of species for which only older material, typically considered unsuitable for DNA barcoding, was available.
Taxa in the tree are labeled in the following format BOLD Process ID | Taxon Name | Institution Sample ID. Table 1. Cytochrome c oxidase I mitochondrial gene primers used in this study.
Wing. Cell r 1 open; stigmatic cross vein present; cross-vein r-m at outer ¼ of cell dm; broad intersection of vein R 1 with vein C (Fig. 3); vein R 4+5 straight; distance between apices of veins R 1 and R 2+3 longer than distance between apices of veins R 2+3 and    Abdomen. Oval, slightly longer than broad, with dense appressed pile. Male genitalia. Surstyli symmetric; aedeagus segmented, with phallapodeme separated from basiphallus and distiphallus; phallapodeme rounded, not banana-shaped; well-developed ctenidion present in male genitalia.
FEMALE. As male except for the following character states. Eyes widely separated; frons fully brown pruinose; face without pruinosity; metafemur only slightly swollen, never curved or with apicoventral ridge; metatibia never modified; always without tubercle on hind trochanter; wing always less microtrichose with species-specific characters as in species description.
Remarks. Generally, species of Romaleosyrphus show little variation in pile color patterns, at least given the limited material we worked with. However, there are a few exceptions. Romaleosyrphus soletluna Moran & Thompson, sp. nov. is drastically dimorphic in pile coloration with a mostly orange morph and mostly black morph. The single northern specimen of Romaleosyrphus arctophiloides from the Sierra Madre Occidental has fully black pilose legs. This contrasts with the population surrounding Mexico City, from which the type was collected, which have a streak of yellow pile at the base of the fore and mid femora. Finally, pile color on the proepimeron is variable inside multiple species with observed character states being fully yellow, fully black or a mix of the two. We suspect that additional material will likely show proepimeron pile color to be variable in all species.
Thorax. Matte black; postpronotum variable pilose: black or mixed black and yellow; scutum black pilose; scutellum yellow pilose, except black pilose anteromedially; postalar callus variable pilose: yellow, black or mixed black and yellow; proepimeron black pilose; posterior anepisternum yellow pilose; katepisternum yellow pilose posteriorly with broadly separated patches; metasternum variable pilose: black, yellow or mixed black and yellow; anepimeron with anterior portion yellow pilose; lower calypter with long black pile.
Legs. Coxae black; femora black except extreme apex of femora; remainder of legs reddish; hind trochanter rounded, not tuberculate as in Fig. 8A; fore and mid-coxae black pilose; hind coxa mixed black and yellow pilose; fore femur black pilose, except occasionally with small mix of yellow pile basally; mid femur fully black pilose or with stretch of yellow pile on posterior side; hind femur black pilose; tibiae and tarsi black pilose; hind tibia as in Fig. 9A.
Wing. Microtrichia absent from following areas: broad anterior margin of cell cua. Abdomen. Tergites shiny to subshiny black; tergite I with scattered, yellow pile medially, except with short black pile in lateral corners; tergite II with dense yellow pile; tergite III with dense pile which is yellow anteromedially, rufous from anterolateral corners to posteromedial margin and black in posterolateral corners; tergite IV variable, dominantly black pilose, but sometimes with rufous or yellow pile medially or posteriorly; grey pruinosity as follows: tergite I pruinose posteriorly, all of tergite II, tergite III except in posterolateral corners; sternites I-III yellow pilose and not pruinose; sternite IV variable: black or rufous pilose or some mix of the two; pile of postabdomen rufous or yellow.
Male genitalia. (Fig. 11A) Cercus yellowish brown, broader at apex, covered with long yellow pile; surstylus brown, ca. 2 × as long as broad, broadened basally with apical third tapering, directed ventrally and with an acute apex, ventral margin concave, undulated; pile on dorsal surface of surstylus, increasing in length posteriorly; minute spines on ventral surface and apical 3/4 th of lateral inner and outer surface.
FEMALE. As male, except for usual sexual dimorphism; microtrichia on wing absent in following areas: broad anterior margin of cell cua, medial area of cell bm, anterior margin in cell dm, small region anteriorly in cell m 4 near cross-vein m-cu.

Habitat. Trans-Mexican Volcanic Belt pine-oak forests ecoregion.
Remarks. Romaleosyrphus arctophiloides is the only known member of Romaleosyrphus in which the hind trochanter is not tuberculate in the male. Although males are not known for Romaleosyrphus argosi sp. nov., R. drysus sp. nov. and R. woodi sp. nov., males of their closest relative in the COI gene tree, R. nephelaeus sp. nov., possess a tuberculate hind trochanter. It is therefore expected that males of these three species also have a tuberculate hind trochanter.
We suspect that a single specimen "CNC_Diptera142464" collected in the Sierra Madre Occidental may represent a distinct species from specimens collected in the Trans-Mexican Volcanic Belt pine-oak forests. Although no genital or discrete morphological differences could be found, the legs of this specimens are fully black pilose while those of all the others have a streak of yellow pile at the base of the fore and mid femora. Unfortunately, while a barcode was obtained for this specimen, no barcode sequences were obtained from specimens from specimens collected in the Trans-Mexican Volcanic Belt pine-oak forests. Thorax. Matte black; postpronotum white pilose; scutum white pilose along margins and black pilose medially; scutellum white pilose; postalar callus white pilose; proepimeron black pilose; posterior anepisternum white pilose; katepisternum white pilose posteriorly with broadly separated patches; metasternum mixed black and white pilose; anepimeron with anterior portion white pilose; lower calypter with long black pile.

Romaleosyrphus argosi
Legs. Coxae black; femora black except extreme apex of femora; remainder of legs reddish; fore and mid-coxae black pilose; hind coxa mixed black and white pilose; fore femur black pilose, except small mix of white pile basally; mid femur black pilose, but with stretch of white pile on posterior side; hind femur black pilose; tibiae and tarsi black pilose.
Wing. Microtrichia absent in following areas: cell c along margin of vein Sc running from 2/5 and ending at 4/5 of length of the cell, anterior 1/5 of cell r 1 , cell br except along spurious vein the part right below the start of cell r 2+3 , all of cell cua except extreme posterior, cell bm, cell cup along the margin of vein CuP in the anterior third of cell, cell m 4 from cross-vein m-cu to end of vein M 4 and in following regions of cell Abdomen. Tergites shiny to subshiny black; tergite I with scattered, white pile medially, except with short black pile in lateral corners; tergite II with dense white pile which runs diagonally from anterolateral corner until it reaches the posterior margin at a point which is ca. at 1/3 width of the tergite, remainder of tergite is black pilose; tergite III with black pile except mixed white pile anteromedially; tergite IV with black pile; tergites not distinctly pruinose; sternites I-III white pilose and not pruinose; sternite IV black pilose; pile of postabdomen black.
Habitat. Central American montane forests ecoregion. Etymology. Named argosi, from the Greek argos (white), to highlight the coloration of this species. It is a noun in apposition. Head. Face shape as in Fig. 10B; face gold pruinose; gena black pilose posteriorly; anterior tentorial pit variable pilose: yellow or black; frons broad, ca. as long as broad at antenna, 2/3 as broad at vertex as at antenna, black pilose and silver-gold pruinose; vertex triangular, longer than broad, black pilose and brown pruinose; postocular setae black; occipital setae variable: yellow or black; antenna reddish orange.
Legs. Coxae black; femora black except extreme apex of femora; remainder of legs reddish; hind trochanter tuberculate as in Fig. 8B; fore and mid-coxae black pilose; hind coxa mixed black and yellow pilose; fore femur black pilose, except small mix of yellow pile basally; mid femur black pilose, but with stretch of yellow pile on posterior side; hind femur black pilose; tibiae and tarsi black pilose; hind tibia as in Fig. 9B.
Wing. Microtrichia absent from following areas: broad anterior margin of cell cua. Abdomen. Tergites shiny to subshiny black; tergite I with scattered, yellow pile; tergite II with dense yellow pile; tergite III with black pile; tergite IV with black pile; grey pruinosity as follows: tergite I pruinose posteriorly, all of tergite II pruinose; sternites I-III yellow pilose and not pruinose; sternite IV black pilose; pile of postabdomen black.
Thorax. Matte black; postpronotum yellow pilose; scutum yellow pilose along margins and black pilose medially; scutellum yellow pilose; postalar callus yellow pilose; proepimeron yellow pilose; posterior anepisternum yellow pilose; katepisternum yellow pilose posteriorly with broadly separated patches; metasternum mixed black and yellow pilose; anepimeron with anterior portion yellow pilose; lower calypter with long black pile Legs. Coxae black; femora black except extreme apex of femora; remainder of legs reddish; fore and mid-coxae black pilose; hind coxa mixed black and yellow pilose; fore femur black pilose, except small mix of yellow pile basally; mid femur black pilose, but with stretch of yellow pile on posterior side; hind femur black pilose; tibiae and tarsi black pilose.
Wing. Microtrichia absent in following areas: cell c along margin of vein Sc running from 2/5 and ending at 4/5 of length of the cell, cell br except along margins of cell and along spurious vein and the part right below the start of vein r 2+3 , all of cell cua except extreme posterior, ventral half of cell bm, cell m 4 from cross-vein m-cu to end of vein M 4 and cell dm in ventral 1/3 of cell and along broad margin following vein M 2.
Abdomen. Tergites shiny to subshiny black; tergite I with scattered, yellow pile medially, except with short black pile in lateral corners; tergite II with dense yellow pile on anterior 2/3 and black pile on anterior third; tergite III with black pile; tergite IV with black pile; tergites not distinctly pruinose; sternites I-III yellow pilose and not pruinose; sternite IV black pilose; pile of postabdomen black.

Distribution. Honduras.
Habitat. Central American montane forests ecoregion. Etymology. Named drysus, derived from the Greek drys for oak, in reference to the high elevation oak forests this species lives in. It is a noun in apposition.   Fig. 10C; face gold pruinose; gena yellow pilose posteriorly; anterior tentorial pit variable pilose: yellow or black; frons broad, ca. as long as broad at antenna, 2/3 as broad at vertex as at antenna, black pilose and silver-gold pruinose; vertex triangular, longer than broad, black pilose and brown pruinose; postocular setae black; occipital setae yellow; antenna reddish orange.
Thorax. Matte black; postpronotum mixed black and yellow pilose; scutum yellow pilose along margins and black pilose medially; scutellum completely yellow pilose; postalar callus yellow pilose; proepimeron yellow pilose; posterior anepisternum yellow pilose; katepisternum yellow pilose posteriorly with broadly separated patches; metasternum variable pilose: black, yellow, or mixed black and yellow; anepimeron with anterior portion yellow pilose; lower calypter with long black pile.
Legs. Coxae black; femora black except extreme apex of femora; remainder of legs reddish; hind trochanter tuberculate as in Fig. 8B; fore and mid-coxa black pilose; hind coxa mixed black and yellow pilose; fore femur black pilose, except small mix of yellow pile basally; mid femur black pilose, but with stretch of yellow pile on posterior side; hind femur black pilose; tibiae and tarsi black pilose; hind tibia as in Fig. 9C.
Wing. Microtrichia absent from following areas: broad anterior margin of cell cua. Abdomen. Tergites shiny to subshiny black; tergite I with scattered, yellow pile medially, except with short black pile in lateral corners; tergite II black pilose, except yellow pilose in anterolateral corners; tergite III black pilose, except lateral margins mixed black and yellow; tergite IV yellow pilose; tergites not pruinose; sternites I-III yellow pilose and not pruinose; sternite IV black; pile of postabdomen mixed black and yellow pilose.
Male genitalia. (Fig. 11C) Cercus yellowish brown, broader at apex, covered with long yellow pile; surstylus brown, ca. as long as hypandrium, broadened basally with apical half tapering and directed ventrally with a rounded apex, ventral margin concave, undulated; pile on dorsal surface of surstylus, increasing in length posteriorly; minute spines on ventral surface and apical 3/4 of lateral inner and outer surface.
Head. Face shape as in Fig. 10D; face gold pruinose; gena black pilose posteriorly; anterior tentorial pit black pilose; frons broad, ca. as long as broad at antenna, 2/3 as broad at vertex as at antenna, black pilose and gold pruinose; vertex triangular, longer than broad, black pilose and brown pruinose; postocular setae black; occipital setae black; antenna reddish orange.
Thorax. Matte black; postpronotum mixed black and yellow pilose; scutum black pilose, except sometimes scattered yellow pile along lateral margins; scutellum black pilose, except with scattered yellow pile along posterior margin; postalar callus black pilose or mixed black and yellow pilose; proepimeron yellow pilose; posterior anepisternum yellow pilose; katepisternum yellow pilose posteriorly with broadly separated patches; metasternum mixed black and yellow pilose; anepimeron with anterior portion yellow pilose; lower calypter with long black pile.
Legs. Coxae black; femora black except extreme apex of femora; remainder of legs reddish; hind trochanter tuberculate as in Fig. 8B; fore and mid-coxae black pilose; hind coxa mixed black and yellow pilose; fore femur black pilose, except small mix of yellow pile basally; mid femur black pilose, but with stretch of yellow pile on posterior side; hind femur black pilose; tibiae and tarsi black pilose; hind tibia as in Fig. 9D.
Wing. Microtrichia absent in following areas: broad anterior margin of cell cua, cell br except along spurious vein and the part right below the start of cell r 2+3 ; Abdomen. Tergites shiny to subshiny black; tergite I with scattered, yellow pile; tergite II with dense black pile medially and yellow pile on lateral sides; tergite III with black pile except mixed yellow pile anteromedially and yellow pile in anterolateral corners; tergite IV with black pile; tergites not distinctly pruinose; sternites I-III yellow pilose and not pruinose; sternite IV black pilose; pile of postabdomen black.
Male genitalia. (Fig. 11B) Cercus yellowish brown, broader at apex, covered with long yellow pile. Surstylus brown, ca. 2 × as long as broad, broadened basally with apical half tapering, directed downward and with an acute apex, ventral margin concave, undulated; pile on dorsal surface of surstylus, increasing in length posteriorly; minute spines on ventral surface and apical 3/4 of lateral inner and outer surfaces.
Description rufous morph. MALE. Same as black morph except as follows.
Abdomen. Tergite II with dense rufous pile medially and yellow pile on lateral sides; tergite III with rufous pile except mixed yellow pile anteromedially and yellow pile in anterolateral corners; tergite IV with rufous pile; sternites I-IV rufous pilose; pile of postabdomen rufous.
FEMALE. As male, except for usual sexual dimorphism; microtrichia on wing absent in following areas: middle third of cell r 1 , cell r 2+3 along margin of vein R 2+3 on the anterior third of cell, cell br except along spurious vein and the part right below the start of cell r 2+3 , all of cell cua except extreme posterior, ventral 2/3 of cell bm, cell cup along the margin of vein CuP in the posterior half, cell m 4 from cross-vein m-cu to end of vein M 2 and cell dm except for a thin line of microtrichia extending from cross-vein bm-m into middle of cell and the margins of cross-vein dm-m.
Distribution. Costa Rica and Panama.
Habitat. Talamancan montane forests (one specimen was collected in lowland rainforest).

Remarks.
Color morphs are considered to be intraspecific variation. No morphological differences were found outside of pile coloration in male genitalia or external characters. Additionally, these morphs are not associated with distinct COI haplotypes. It is difficult to argue in favor of interspecific variation without the addition of contradictory genetic evidence or fieldwork showing these morphs do not interbreed.
Etymology. Named soletluna, a combination of the Latin words sol, for sun, and luna, for the moon. It is a reference to the duality of the color morphs in this species. It is a noun in apposition.  Williston, 1891: 73. -Aldrich (1905): 401. -Coquillett (1910: 528.
Legs. Coxae black; femora black except extreme apex of femora; remainder of legs reddish; hind trochanter tuberculate as in Fig. 8B; fore and mid-coxae black pilose; hind coxa mixed black and yellow pilose; fore femur black pilose, except small mix of yellow pile basally; mid femur black pilose, but with stretch of yellow pile on posterior side; hind femur black pilose; tibiae and tarsi black pilose; hind tibia as in Fig. 9E.
Wing. Microtrichia absent from following areas: broad anterior margin of cell cua; Abdomen. Tergites shiny to subshiny black; tergite I with scattered, yellow pile; tergite II with dense yellow pile on anterior half and rufous pile on posterior half; tergite III with dense rufous pile on anterior third and black pile on posterior 2/3; tergite IV with black pile; grey pruinosity as follows: tergite I pruinose posteriorly, all of tergite II, tergite III anteriorly; sternites I-III yellow pilose and not pruinose; sternite IV black pilose; pile of postabdomen black.
Male genitalia. (Fig. 11F) Cercus yellowish brown, broader at apex, covered with long yellow pile; surstylus brown, ca. 3 × as long as broad, broadened basally with apical third tapering, directed ventrally and with a rounded apex, ventral margin concave, undulated; pile on dorsal surface of surstylus, increasing in length posteriorly; minute spines on ventral surface and apical 3/4 of lateral inner and outer surfaces.
FEMALE. As male, except for usual sexual dimorphism. Microtrichia on wing absent in following areas: broad anterior margin of cell cua, medial area of cell bm, anteriorly in cell dm.
Distribution. El Salvador, Honduras, and Mexico.

Romaleosyrphus vockerothi
Differential diagnosis. Scutellum completely yellow pilose. Tergites II and III extensively rufous to yellow pilose. Tergite IV dominantly black pilose. Hind trochanter tuberculate in male. Male hind tibia as in Fig. 9E. Male genitalia as in Fig. 11D.
Description. MALE. Body length: 13.8-14.5 mm. Wing length: 9.8-10.5 mm. Head. Face shape as in Fig. 10F; face silver or gold pruinose; gena black pilose posteriorly; anterior tentorial pit black pilose; frons broad, ca. as long as broad at antenna, 2/3 as broad at vertex as at antenna, black pilose and silver-gold pruinose; vertex triangular, longer than broad, black pilose and brown pruinose; postocular setae black; occipital setae variable: yellow or black; antenna reddish orange.
Thorax. Matte black; postpronotum variable pilose: black or mixed black and yellow; scutum either yellow pilose along margins with black pile medially, or completely black pilose; scutellum completely yellow pilose; postalar callus variable pilose: yellow, black, or mixed black and yellow; proepimeron black pilose; posterior anepisternum yellow pilose; katepisternum yellow pilose posteriorly with broadly separated patches; metasternum variable pilose: black, yellow or mixed black and yellow; anepimeron with anterior portion yellow pilose; lower calypter with long black pile.
Legs. Coxae black; femora black except extreme apex of femora; remainder of legs reddish; hind trochanter tuberculate as in Fig. 8B; fore and mid-coxae black pilose; hind coxa mixed black and yellow pilose; fore femur black pilose, except small mix of yellow pile basally; mid femur black pilose, but with stretch of yellow pile on posterior side; hind femur black pilose; tibiae and tarsi black pilose; hind tibia as in Fig. 9E.
Wing. Wing completely microtrichose. Abdomen. Tergites shiny to subshiny black; tergite I with scattered, yellow pile medially, except with short black pile in lateral corners; tergite II with dense yellow pile; tergite III with dense pile which is yellow anteromedially and rufous on the remainder; tergite IV with dense black pile, although sometimes red pilose medially; tergites I-III pruinose; sternites I-III yellow pilose and not pruinose; sternite IV variable: black or rufous pilose or some mix of the two; pile of postabdomen black or rufous.
Male genitalia. (Fig. 11D) Cercus yellowish brown, broader at apex, covered with long yellow pile; surstylus brown, distinctly longer than hypandrium, broadened basally with apical third tapering and not distinctly curved with a rounded apex, ventral margin concave, undulated; pile on dorsal surface of surstylus, increasing in length posteriorly; minute spines on ventral surface and apical 3/4 th of lateral inner and outer surface.

Distribution. Mexico.
Habitat. Sierra Madre Occidental pine-oak forests. Etymology. Named after J. R. Vockeroth in honor of his lifetime of work on Syrphidae and who was the first to recognize characters distinguishing this species from the sympatric Romaleosyrphus arctophiloides many years ago. Thorax. Matte black; postpronotum mixed black and yellow pilose; scutum black pilose, except yellow pilose along lateral margins; scutellum yellow pilose, except black pilose anteromedially; postalar callus yellow pilose; proepimeron black pilose; posterior anepisternum yellow pilose; katepisternum yellow pilose posteriorly with broadly separated patches; metasternum mixed black and yellow pilose; anepimeron with anterior portion yellow pilose; lower calypter with long black pile.

Romaleosyrphus woodi
Legs. Coxae black; femora black except extreme apex of femora; remainder of legs reddish; fore and mid-coxae black pilose; hind coxa mixed black and yellow pilose; fore femur black pilose, except small mix of yellow pile basally; mid femur black pilose, but with stretch of yellow pile on posterior side; hind femur black pilose; tibiae and tarsi black pilose.
Wing. Microtrichia absent in following areas: cell c along margin of vein Sc running from 2/5 of length and ending at 4/5 of length of the cell, anterior 1/5 of cell r 1 , r 2+3 along margin of vein R 4+5 starting from 2/5 of length and ending at cross-vein r-m, cell br except along spurious vein and the part right below the start of cell r 2+3 , all of cell cua except extreme posterior, cell bm, cell cup along the margin of vein CuP in the anterior third of cell, cell m 4 from cross-vein m-cu to end of vein M 4 and cell dm in ventral 1/3 of cell and along broad margin following vein M 2 .
Abdomen. Tergites shiny to subshiny black; tergite I with scattered, yellow pile medially, except with short black pile in lateral corners; tergite II with dense yellow pile which runs diagonally from anterolateral corner until it reaches the posterior margin at a point which is ca. at 1/3 of the width of the tergite, remainder of tergite is black pilose; tergite III with black pile except mixed yellow pile anteromedially; tergite IV with black pile; tergites not distinctly pruinose; sternites I-III yellow pilose and not pruinose; sternite IV black pilose; pile of postabdomen black.

Distribution. Mexico.
Habitat. Central American pine-oak forests ecoregion. Remarks. The specimen failed to barcode. Most similar in appearance to Romaleosyrphus drysus sp. nov. but R. woodi sp. nov. differs in having a scutellum which is only partly yellow pilose, instead having black pile anteromedially. Additionally, cell r 2+3 is bare along the margin of vein R 4+5 starting from 2/5 the length of cell and ending at cross-vein r-m.
Etymology. Named after dipterologist Monty Wood to honor his passion for flies and whose collecting trips throughout Central and South America provided many critical Syrphidae for this as well as other future studies.

Species concepts and DNA barcoding
DNA barcode data (5' end of the COI) were collected for eight of nine morphospecies to provide a database to assist with future identifications of all life stages. Complete barcodes were obtained for all species except R. woodi sp. nov. Additional sequences for Romaleosyrphus were obtained from the BOLD database.
The rufous and black morphs of R. soletluna sp. nov. are not differentiated by COI haplotype showing that coloration should be considered intraspecific variation. The barcode differs by an average pairwise (p) distance of 3.04% from its nearest neighbor Romaleosyrphus bigoti sp. nov. It has a maximum intraspecific variation of 0.93% and an average of 0.56%.
Romaleosyrphus arctophiloides is related to the R. villosus complex of species (R. villosus, R. vockerothi sp. nov., R. bigoti sp. nov.) with the barcode 2.34% different from the nearest neighbor Romaleosyrphus villosus. This is the only known species of Romaleosyrphus in which males lack a tubercle on the hind trochanter.
Separation of R. bigoti sp. nov. and R. vockerothi sp. nov. species from R. villosus is supported by DNA barcoding. The barcoded types are 1.52% and 1.55% different from their closest neighbor, respectively. This distance is nearly twice as high as the maximum intraspecific variation seen in R. soletluna sp. nov. (0.93%) and Romaleosyrphus nephelaeus sp. nov.(0.97%). Morphological differences are found in the shape of the male genitalia as well as the shape of the male hind tibia.
The nearest neighbor of R. argosi sp. nov. is Romaleosyrphus drysus sp. nov. with the COI barcodes diverging by 3.05%. The nearest neighbor of Romaleosyrphus drysus sp. nov. is Romaleosyrphus nephelaeus sp. nov. with the COI barcodes diverging by an average of 2.85%. These distinct barcodes along with the unique pile coloration patterns of Romaleosyrphus argosi sp. nov. and Romaleosyrphus drysus sp. nov. support the recognition of these specimens as new species.
While the type of R. woodi sp. nov. failed to produce a barcode, morphological evidence was found in favor of its recognition as a distinct species. The species is most similar in appearance to Romaleosyrphus drysus sp. nov. but differs in having a scutellum which is only partly yellow pilose, instead having black pile anteromedially. Additionally, cell r 2+3 is bare along the margin of R 4+5 starting from 2/5 the length of cell and ending at cross-vein r-m. Moran et al. (2021) resurrected Romaleosyrphus placing 'Romaleosyrphus sp. MZH Y247', now known as Romaleosyrphus soletluna sp. nov., sister to the genus Matsumyia.

Discussion
In concordance with the neighbor-joining analysis, as well as the multi-gene analysis of Moran et. al (2021), morphological evidence supports the monophyletic origin of these Neotropical species, their relationship with Matsumyia and also their separation. The two genera share several characters and are distinguished from members of Criorhina and Sphecomyia by: holoptic males, a proximal ventral half of vein C with setae, a broad intersection of vein R 1 with vein C, and appressed hair on the abdomen. Additionally, Romaleosyrphus is further distinguished from Matsumyia by a distal R 4+5 longer than cross-vein h. All species of Matsumyia examined, as part of an upcoming revision of the genus, however, had a distal R 4+5 shorter than cross-vein h. Romaleosyrphus stat. rev. is therefore redefined to represent the monophyletic unit of species within Criorhinina which possess these five character states.
Hampered by the rarity of Romaleosyrphus and the age of most specimens, more than one sequence was obtained for only two species and neither showed a high degree of intraspecific variation (Fig. 12). DNA barcodes reveal R. soletluna sp. nov. is dimorphic in pile coloration and these morphs are not associated with distinct COI haplotypes. The genetic distance between Romaleosyrphus species is lower than between species of most other Criorhinina genera. For example, Matsumyia species show a much higher degree of species differentiation both for DNA barcodes and external morphological characters. It is possible that Romaleosyrphus diversified more recently. This may explain their less divergent intrageneric morphology and it would be worth investigat-ing whether speciation coincided with the arrival of Bombus in Central America. Fresh material and more markers are needed to test these questions.
The discovery of the larvae of Romaleosyrphus would add critical biological knowledge about this genus and their microhabitats. Most likely, immatures live on decaying roots akin to the larvae of Matsumyia berberina (Fabricius, 1805), the most closely related species for which larvae is known, as also do larvae of some Criorhina species (Speight, 2020). Alternatively, larvae may be associated with rot-holes, sap-runs, or decaying wood in general as in other Criorhina species (Speight, 2020).
Moving forward, the authors suspect additional Romaleosyrphus species have yet to be discovered considering their apparent rarity and that their high elevation cloud forest habitat is highly conducive to speciation (Bruijnzeel, 2010). Currently, the center of diversity of the genus appears to be either the Central American montane forest ecoregion or the Central American pine-oak forest ecoregion, with three species each. One species each is known from the Sierra Madre Occidental pine-oak forest, the Talamancan montane forests and the Trans-Mexican Volcanic Belt pine-oak forests.
No species have been recorded from several similar ecoregions: Oaxacan, Chiapas, Chimalapas, and the Veracruz montane forests, along with the Sierra Madre de Oaxaca, Sierra Madre Oriental, Sierra Madre del Sur, and the Sierra de la Laguna pine-oak forests. It is also uncertain if the genus extends into the montane pine-oak forest ecoregions of South America. Additional collecting efforts focused on these ecoregions are necessary to discover the extent of Romaleosyrphus biodiversity.

Conclusion
Based upon molecular and morphological evidence we redefine Romaleosyrphus stat. rev. as the monophyletic unit of species within Criorhinina which possesses holoptic males, a proximal ventral half of vein C with setae, a broad intersection of vein R 1 with vein C, a distal R 4+5 longer than cross-vein h, and appressed pile on the abdomen. This requires the transfer of Romaleosyrphus villosus (Bigot, 1882a) comb. nov. and Romaleosyrphus arctophiloides (Giglio-Tos, 1892) comb. nov. to Romaleosyrphus.