Black-tie dress code: two new species of the genus Toxomerus (Diptera, Syrphidae)

Abstract Toxomerus hauseri Mengual sp. n. and Toxomerus picudus Mengual sp. n. are described from Peru and Ecuador respectively. Toxomerus circumcintus (Enderlein, 1938) is treated as a valid species and not considered synonym of Toxomerus marginatus, and Toxomerus ovatus (Hull, 1942) is considered junior synonym of Toxomerus nitidus (Schiner, 1868). An identification key for the Toxomerus species with dark abdomens is given along with diagnoses for each studied species.


Introduction
The tribe Toxomerini (Diptera: Syrphidae) comprises the single genus Toxomerus Macquart, 1855. Toxomerini is endemic to the New World, from southern Canada to southern Argentina and Chile (Thompson and Thompson 2006). There are only 6 endemic Nearctic species and more than 130 Neotropical species of Toxomerus (Borges and Couri 2009;Thompson et al. 2010), although only 101 species are published and validly named (Thompson 2010). Toxomerus species are one of the most abundant flower flies in the New World and they are typically relatively small, usually about 6 mm. Nevertheless, there are some species larger than 9 mm (see Metz and Thomp-son 2001 for a review). Adults feed on pollen and nectar acting as flower pollinators (Thompson and Thompson 2006;Ssymank and Kearns 2009), but data about larval feeding habits of Toxomerus are limited. Most of the known species larvae are predacious feeding frequently on soft-bodied Hemiptera, but also on Acari, Thysanoptera and larvae of Lepidoptera (Rojo et al. 2003). However, there are two well-known pollen-feeder species, Toxomerus politus (Say, 1823) (Riley and Howard 1888;Marín A. 1969) and Toxomerus apegiensis (Harbach, 1974) (Reemer and Rotheray 2009). Enderlein (1938) established the tribe Toxomerini for Toxomerus and eight other genera but it was Vockeroth (1969) who recognized and re-classified this tribe as monogeneric. Toxomerini taxonomy is based mostly on the characteristic markings of the abdominal tergites and the male genitalia. Unfortunately, the abdominal pattern of some species may show a great variation and it may appear obscured or lost (Curran 1930;Hull 1943;Thompson 1981). Hull (1943) provided the last key for the genus but he did not include all the species. Metz and Thompson (2001) provided an excellent overview on the systematics of Toxomerus. More recently, Borges and Couri (2009) presented a key for the Brazilian species of Toxomerus with very helpful illustrations.
The monophyly of Toxomerus is supported by morphological characters (Vockeroth 1969(Vockeroth , 1992Thompson 1981) and molecular evidence ) but there is no subgeneric classification for Toxomerus (Hull 1943;Vockeroth 1969;Metz and Thompson 2001). Hull (1943) indicated in a scheme the possible relationships among Toxomerus species groups based on the abdominal pattern. In that diagram, Hull grouped together the species with uniformly black abdomen or abdomen reddish and gave two examples, T. anthrax (Schiner, 1868) and T. nitidus (Schiner, 1868).
The aim of this study is to describe two new, very distinct Toxomerus species with uniformly black abdomen and to provide an identification key and some diagnostic notes for Toxomerus species without a clear yellow/black abdominal pattern. I do not think that "black abdomen" species are a natural group but are a phenotypic cluster instead. However, the abdomen without medial yellow pattern combined with a more important morphological character, the presence/absence of a continuous lateral yellow vitta on scutum, may suggest a clade within Toxomerus with phylogenetic importance. Following this argument, Mengual et al. (2011, see also Mengual 2008 recovered a clade with "dark abdomen" species of Toxomerus with the lateral yellow scutal vitta interrupted or reduced, which included T. anthrax, T. dispar (Fabricius, 1794) and T. flaviplurus (Hall, 1927).
The two new species, T. hauseri sp. n. and T. picudus sp. n., are very distinct from the other included species. Both have a continuous lateral yellow vitta from postpronotum to scutellum; scutum without a pollinose pattern; eye with triangular emargination large, approximately the half of eye width in lateral view; face yellow with two sublateral black vittae; and abdomen strongly concave, shiny black with lateral margins yellow from tergum 2 to tegum 5. Moreover, T. picudus has a unique morphological character among Toxomerus species, a dorsal knob on occiput posterior to ocellar triangle.

Taxonomic revision
Differential diagnoses, synonymies, and distributions are given for all species included in the study. New species are described in full, with terminology following Thompson (1999). Synonymies in full, citations and other references are given in Appendix I. An asterisk (*) in the distribution statement means records from the literature or from Systema Dipterorum (Thompson 2010). The acronyms used for collections follow the standard of the Systema Dipterorum (Thompson 2010), and their equivalents are listed below:

AMNH
American Museum of Natural History, New York, USA.

ANSP
Academy of Natural Sciences, Philadelphia, USA.

BMNH
The In the description of type labels, the contents of each label is enclosed within quotation marks (" ") and the individual lines of data are separated by a forward slash ( / ). Complete data for the studied specimens are given in Appendix I. In the material examined section, the use of ellipses follows Standard English practice and merely indicates that the missing information is the same as that in the preceding record. Google Earth was used to find the type locality coordinates of T. picudus sp. n.
All measurements are in millimeters and were taken using a reticule in a Wild M5A microscope. Illustrations of male genitalia were drawn using a camera lucida mounted on an Olympus BX51 compound microscope. Manual drawings were redrawn as a vec-tor image using Adobe Illustrator (version CS3). Photographs were composed using the software CombineZP based on images of pinned specimens taken with a Canon EO-S40D mounted on a Microptics Camlift and the help of Adobe Lightroom (version 3.3).
In the identification key, I included four species whose typical form has yellow markings in the center of the abdomen, i.e. T. hieroglyphicus (Schiner, 1868), T. paragrammus (Schiner, 1868), T. incaicus Sack, 1941 and T. dispar. The reason of this inclusion is the occurrence of dark forms due to the high variability of the abdominal pattern. The species Toxomerus sp. 1 (CR-11), T. sp. 2 (75-5) and T. sp. 3 (CR-B) are new species to science discovered by F. C. Thompson (USNM, Smithsonian Institution). These codes by F. C. Thompson are placeholders for undescribed species, and are widely used among people working on Syrphidae. Here, I used them for taxa that will be formally described in the future by F. C. Thompson. These codes are not species names and are not valid descriptions according to the code.
Identification key for the Toxomerus species with dark abdomens  (Fig. 14). Pro-and mesotibiae bright yellow; wing slightly infuscated, brownish, entirely microtrichose; in males, medial black facial vitta surrounding antennal bases form-ing narrow dark area between antennal bases; in females, abdomen with black pollen pattern forming at least a black pollinose fascia on tergum 2 (Fig. 10)  Notopleuron black, at most with triangular small yellow macula anteriorly, with a submedial position, not on the most lateral margin (Fig. 15); supraalar area dark and post-alar callus dark brown; scutellum black basally and laterally, yellow only apically. Male genitalia: postanal process more triangular, broader at the base than long (Fig. 29)  Note: Some specimens of Toxomerus dispar may have notopleuron entirely yellow but they also have abdomen mainly yellow or with evident yellow markings (Figs 1, 2, 4). 17 Abdomen partially black on lateral margins: male usually with terga 1 and 2 black, and following terga dark reddish-brown; female usually entirely black (Figs 3, 5). Pro-and mesotibiae yellow. Postanal process of male genitalia long, more than half as long as surstylus (Fig. 8)

Toxomerus sp. 2 (75-5)
Differential diagnosis. Species with yellow face medially, brown to black laterally, white pollinose laterally; scutum bronze pollinose with lateral yellow vitta. Scutellum black with lateral and posterior margins yellow, sometimes yellow margins not well differentiated from central disc covered by bronze pollinosity, black and/or yellow pilose.
Wing entirely microtrichose. Male abdomen is shiny black with a central black pollinose macula on terga 2 to 5 and small yellow macula on each anterobasal half of terga 2-4; tergum 5 yellow on lateral margins. Female abdomen similar but medial black pollinose macula extended laterally forming a fascia on terga 2 to 5, and lateral yellow macula extending and broadening towards medial line.

Toxomerus sp. 3 (CR-B)
Differential diagnosis. Species with yellow face in male, females with a medial broad black vitta continuing along frons and ending at vertex. Scutum black, bronze pollinose wit a medial whitish pollinose vitta and two submedial brown vittae; scutum black laterally except postpronotum yellow, at least on posterior half. Scutellum black, sometimes with apical margin yellow, pale pilose. Wing partly bare, costal cell bare only very basally, cell BM bare on basal half and anterior margin, cell CuP bare basally, cells R and R1 bare before bifurcation RS. Abdomen black, in some specimens becoming reddish at terga 4 and 5, with lateral margins yellow, although this character is not present in all the studied specimens. Species very similar to Toxomerus dispar, but T. sp. 3 has pro-and mesotibiae yellow usually with medial dark ring of variable length, the postanal process of the male genitalia is short, much less than half as long as surstylus, and female has metaepisternum entirely black.
Length (5): body, 6.3-7.1 (6.7) mm; wing, 5.0-5.9 (5.5) mm. Differential diagnosis. Male and female with medial black facial vitta, but in males does not continue laterad or dorsad antennal bases. Scutum black laterally except post-pronotum yellow and notopleuron sometimes with a small yellow vitta sublaterally, not on the most lateral margin. Wing extensivey microtrichose with small bare area on both sides of vein M on the basal portion of cell bm, and costal cell bare very basally or along vein SC (posterior margin). Abdomen black, terga 3-5 sometimes dark brown to yellowish-orange, with or without yellow lateral margins; shiny, without pollinose markings.
T. anthrax is similar to T. circumcinctus but the last has the notopleuron entirely yellow and postalar callus yellowish and the scutellum black with a well-defined broad yellow margin. Male genitalia are different.
Remarks. The illustration of Mesogramma portia in Hull (1943: 31, Fig. 17) has two submedial short yellow vittae on terga 3, 4 and 5, forming a U-shaped macula on tergum 5. These submedial yellow vittae are at both sides of the medial black pollinose vitta. This illustration refers to a paler form of T. basalis.
Differential diagnosis. Species with yellow face and a medial broad black vitta, which ends ventrad to antennal bases. Scutum black, yellow pilose, with postpronotum and notopleuron entirely yellow; supra-alar area looks black, although it might have a thin yellow vitta connecting to the yellow postalar callus. Scutellum black with lateral and apical margins yellow. Pleuron black except katepisternum with a dorsal broad yellow macula and posterior anepisternum yellow on posterior third. Halter and calypter yellow. Femora dark brown with yellow apical tips, pro-and mesotibia yellow, metatibia brown with basal and apical extremes yellow, and tarsi brown. Abdomen dark brown, becoming yellowish brown on terga 4 and 5, with continuous yellow lateral margins from tergum 1 to tergum 5. Toxomerus circumcinctus is similar to T. anthrax but the last has the notopleuron black and postalar callus dark brown, and the scutellum black with apical margin yellow (Fig. 15). Male genitalia are different (see Figs 28,29).
Length. body, 6.0 mm; wing, 5.1 mm. Distribution. Species only known from the holotype, collected in Peru. Material examined. ♂ holotype. Remarks. After the original publication (Enderlein 1938), this species has been only cited in two works. Fluke (1956) listed T. circumcinctus in his Neotropical catalogue as Mesograpta circumcinctum, and Thompson et al. (1976) -5), and this is the main reason to have such a high number of synonyms. Species very similar to Toxomerus sp. 3, but T. dispar has pro-and mesotibiae yellow, postanal process of male genitalia long, more than half as long as surstylus and female has metaepisternum partly or entirely yellow. The present key only works for dark forms of this species.
Length (5) Differential diagnosis. Male with yellow face with a medial broad dark vitta surrounding antennal bases forming narrow dark area between antennal bases and dorsad to antennal bases, black ventrolaterally, yellow pilose, white pollinose laterally. Female face and frons yellow with medial black vitta joining medial black frons vitta until the vertex, surrounding laterally the antennal bases. Scutum black, greenish-brown pollinose with dorsomedial broad bluish pollinose vitta and two submedial bronze pollinose vittae, entirely yellow pilose; postpronotum yellowish-brown, slightly lighter than scutum, notopleuron black; supra-alar area and postalar callus yellowish; scutellum black with broad yellow vitta on lateral and apical margins, pale pilose. Pleuron mostly black, except posterior anepisternum black on posterior third, pale pilose; katepisternum with dorsal yellow macula reduced. Wing membrane light brown, entirely microtrichose. Male abdomen shiny black, pale pilose, with tergum 8 as long or longer than tergum 5; male genitalia with long postanal process (Borges and Couri 2009: 21, Fig. 47). Female abdomen a bit more oval, shiny black with a black pollinose pattern (Fig. 10) Length (5): body, 7.2-7.7 (7.4) mm; wing, 6.6-6.9 (6.8) mm. Distribution. Guatemala, Costa Rica, Brazil, Panama, Trinidad*. Material examined. 2♂ paratypes, 50♂ 37♀. Remarks. Toxomerus flaviplurus can have yellow markings in the abdomen, with yellow fasciate vittae on terga 2 to 4 and submedial yellow vittae on terga 3 to 5 (see Borges and Couri 2009: 17, Fig. 28). The species key works for the dark form of this species. Some dark specimens of T. flaviplurus can have an almost continuous lateral yellow vitta on the scutum. For this reason, T. flaviplurus appears in two different couplets in the key. Reemer (2010) synonymised flaviplurus under T. costalis (Wiedemann) based on the overall similarity of these species after studying photographs of the paratypes of T. flaviplurus and the holotype of T. costalis. Reemer (2010: 185, Figs 94, 95) included photographs of new costalis material from Surinam and male and female look similar to pale forms of flaviplurus. The holotype of T. costalis has glued an abdomen of a Eupeodes species; the head is also glued but it is the original. After the study of the paratypes of flaviplurus and the holotype of costalis, I found only a minor difference that is within the variability range of this species: the holotype of costalis has the scutellum with a broad yellow vitta on lateral and apical margins. Based on my limited material of T. costalis and the fact that the holotype lacks the abdomen, I have no morphological characters to disagree with Reemer, but I have molecular evidences to not accept this synonym at this moment. Mengual et al. (2011, but see Mengual 2008 inferred the phylogenetic relationships among the genera Toxomerus and Ocyptamus Macquart, 1834 and their results placed a specimen of T. costalis from Surinam (identified by M. Reemer) distantly related to a specimen of T. flaviplurus from Venezuela. The study of more material and a broader sample of specimens for DNA studies are required to better understand these taxa. Differential diagnosis. The female holotype has yellow face with a medial broad black vitta continuing until the vertex, surrounding antennal bases. Scutum black with three broad blue-steel pollinose vittae divided by two submedial brown-bronze pollinose vittae. Pro-and mesofemora entirely yellow, katepisternal yellow macula reduced, as broad as anepisternal yellow vitta, as wide as or narrower than mesofemur. Wing partly bare basally. Abdomen entirely black with terga 2 to 5 with a medial black pollinose vitta and two submedial triangular macula of black pollen. Toxomerus funestus is a very distinct species with a unique abdominal and scutal patterns, and pro-and mesolegs yellows except coxae, trochanters and femora basally brown.
Differential diagnosis. Species with yellow face with two sublateral black vittae, and eye with triangular emargination large, approximately the half of eye width in lateral view. Profemur yellow; cell BM bare on basal third and on anterior and posterior margins. Scutum shiny black with lateral yellow vitta and abdomen shiny black, convex, with lateral margins entirely yellow. Very similar to T. picudus sp. n. but differs by having costal cell microtrichose on apical third, metafemur entirely black with at most the apical edge yellow, and occiput rounded posteriorly on dorsal section, without any protuberance.
Length: body, 6.6 mm; wing, 5.9 mm. Distribution. Species only known from the holotype, collected in Peru. Differential diagnosis. Species with yellow face in male, sometimes with a brownish macula on tubercle. Scutum black, bronze pollinose medially and a medial bluish pollinose vitta, with a continuous lateral yellow vitta from postpronotum to scutellum, narrowed on notopleuron and supra-alar area. Scutellum black with yellow lateral and apical margins. Wing partially bare basally, costal cell bare on basal half or a bit more. Abdomen with medial yellow markings on terga 3 to 5; tergum 1 with yellow lateral margins, tergum 2 black with a yellow macula on anterolateral half extending narrowly towards the center of the tergum, and with a roundish black pollinose macula in the center; tergum 3 and 4 black with anterolateral yellow maculae and two submedial curved yellow vittae that divides a central black pollinose area; tergum 5 black with anterolateral yellow maculae and two submedial short yellow vittae.

Etymology. This species is named after Martin
Toxomerus hieroglyphicus is close in the key to the two new species, T. picudus and T. hauseri, but they are very different as already noted in the key.
Length (4): body, 5.6-6.2 (5.9) mm; wing, 5.0-5.7 (5.2) mm. Distribution. Venezuela, Ecuador, Colombia*. Material examined. ♂ lectotype, ♂ paralectotype, 3♂. Remarks. Toxomerus hieroglyphicus has usually yellow markings in the center of the abdomen. Thus, it should not be included in the present key. However, the study of a dark specimen prompted me to tentatively include this species in case darker specimens might appear with completely black abdomen with lateral yellow maculae. yellow, black pilose. Legs entirely yellow except metatarsi dark brown. Wing mostly microtrichose, bare only on anterior margin of cells R, BM and CuP and cell R1 basally. Abdomen black with lateral margins yellow, tergum 1 with anterior margin yellow, and terga 6 to 9 yellow; terga 2 to 5 with a central dark pollinose macula; and terga 3 to 5 with two submedial, small, round yellow maculae. Length (2): body, 6.0-6.2 (6.1) mm; wing, 5.7-5.8 (5.7) mm. Distribution. Peru, Bolivia*. Material examined. 1♂ 1♀ paralectotypes. Remarks. Toxomerus incaicus has usually medial yellow maculae on terga 3 to 5. Again, this species should not appear in the present key. However, I included this species in case darker specimens might appear with completely black abdomen with lateral yellow margins. Differential diagnosis. Species with yellow face and a medial black facial vitta in both sexes, geba black. Scutum black, green-bronze pollinose with a medial bluish-white pollinose vitta, sometimes with two submedial whitish vittae. Postpronotum yellow and notopleuron partly yellow, usually with triangular yellow macula anteriorly narrowing towards transverse suture. Wing partly bare basally, with costal cell entirely microtrichose and brown, darker than the rest of the wing except stigma. Male abdomen usually bicolor, with terga 1 and 2 black (tergum 1 with yellow anterior corners) and terga 3 to 5 reddish-orange; postanal process of the male gentialia long. Female abdomen usually shiny black with black lateral margins; tergum 2 with submedial black pollinose fascia and terga 3 and 4 with four black pollinose vittate maculae (Fig. 9). Species close to T. dispar and T. sp. 3 but males of nitidus have black facial vitta and notopleuron partly yellow.
Remarks. Males of Toxomerus nitidus always have a bicolored abdomen and females may have yellowish markings as noted by Hull (1943) (see Fig. 9), although most of the studied specimens had shiny black abdomens with a black pollinose pattern.
Toxomerus nitidus has been cited few times after its original description but only in catalogues (see Appendix I). I had the possibility to study two syntypes of T. nitidus and compared them with males of T. ovatus at USNM. Male genitalia were identical and females of ovatus did key out as nitidus. Thus, I realized that T. nitidus was only known from male specimens. Therefore, T. ovatus is here considered to be a junior synonym of T. nitidus.
Remarks. Toxomerus paragrammus is another species that most of the times will not run through the key because the presence of yellow maculae on the abdomen. I included this species because I think some dark specimens might have black abdomen with yellow lateral margins. Description. FEMALE. Head: Face with distinct low facial tubercle, more pointed forward than rounded, yellow with two submedial black vittae that reach oral margin, brownish lateroventrally, scarcely yellow pilose; gena brown to black; lunule yellow, yellow also between antennal bases; frons yellow laterally with broad medial black vitta that surrounds antennal bases and continues with the two submedial facial vittae, yellow-golden pilose; vertical triangle shiny black, black pilose; antennae on small produced tubercle, antenna orangish, basoflagellomere dark brown dorsally; arista brown, bare (Fig. 21); eye bare, lateral triangular eye emargination large, approximately the half of eye width in lateral view; occiput with dorsal knob posterior to ocellar triangle, black, grey pollinose, yellow pilose on ventral 2/3 and black pilose on dorsal 1/3 (Fig. 23).

Toxomerus picudus
Thorax: Scutum shiny, bronze pollinose very anteriorly, with a continuous lateral yellow vitta, yellow pilose; postpronotum yellow, bare; notopleuron yellow with a black vitta on the lateral side narrowing the lateral yellow scutal vitta; supra-alar area and postalar callus yellow; scutellum black with well-defined lateral yellow vitta, slightly narrowed apically, black pilose, subscutellar fringe absent (Figs 16, 17). Pleuron mostly black, except posterior anepisternum yellow on posterior third and katepisternum with dorsal broad yellow macula; metasternum bare; calypter yellow; plumula yellow; halter bright yellow; posterior spiracular fringes yellow. Wing: Wing membrane hyaline, stigma brown; extensively microtrichose, except costal cell bare, cell R1 bare beyond RS furcation until the middle of the stigma, cell R bare basal to furcation of RS, cell BM bare on basal fourth and on anterior margin, cell CuP bare on anterior margin. Alula microtrichose. Legs: Proleg yellow except coxa black, yellow pilose; mesoleg yellow except coxa black, mesofemur black on apical half with apical tip yellow, mesotarsi orangish; metaleg black except femur yellow on basal third and on apical tip, tibia yellow on basal tip and on apical 1/6-1/5 (Figs 16, 17).
Differential diagnosis. Species with yellow face with two sublateral black vittae, and eye with triangular emargination large, approximately the half of eye width in lateral view. Profemur yellow; cell BM bare on basal third and on anterior and posterior margins. Scutum shiny black with lateral yellow vitta and abdomen shiny black, convex, with lateral margins entirely yellow. Very similar to T. hauseri sp. n. but differs by having costal cell entirely bare, at most few microtrichia apically, metafemur black apically, yellow on basal third, and occiput with dorsal knob posterior to ocellar triangle pointing posteriorly. Moreover, the submedial black facial vittae reach oral margin in T. picudus but not in T. hauseri.

Distribution. Ecuador.
Etymology. The specific epithet is derived from the Spanish picudo that means having a knob, protuberance. It refers to the dorsal occipital knob that this species has. Species epithet is treated as adjective.