A revision of the Megachile subgenus Litomegachile Mitchell with an illustrated key and description of a new species (Hymenoptera, Megachilidae, Megachilini)

Abstract The species of Megachile subgenus Litomegachile are revised with a review of the species morphology, biology, and plant associations. A new species, Megachile pankus, is described and illustrated. Megachile mendica snowi Mitchell is elevated to species. Megachile var. nupta Cresson and Megachile texana var. cleomis Cockerell are synonymized with Megachile brevis and Megachile texana, respectively. An illustrated key for Litomegachile is also provided.


Introduction
Litomegachile is a subgenus of Megachile Latreille, a large genus including leafcutting and resin bees. Leafcutting bees are solitary and get their name from their habit of using leaf pieces and other plant materials to form the lining of their nests (Michener 2007). Although sometimes difficult to separate from other Megachile, certain combinations of characters can be useful in identifying Litomegachile. For males, the combination of fore coxal spines present, mandible tridentate, forelegs slender, unmodified and a tomentum of white hair on the sixth metasomal tergum is diagnostic. In females the combination of mandible with face dull in apical half, four-toothed (sometimes with dorsal tooth subtruncate), with distinct cutting edge between 2 nd and 3 rd teeth, sixth sternum with apical margin not upturned, scopal hairs uniformly covering ventral surface, and metasomal sterna lacking apical fringes of white hair separates them from other Megachile.
The subgenus was first described by Mitchell (1935). He provided a key to five species: Megachile brevis Say, 1837, Megachile coquilletti Cockerell, 1915, Megachile gentilis Cresson, 1872, Megachile mendica Cresson, 1878, and Megachile texana Cresson, 1878, and six infraspecific taxa: Megachile mendica var. snowi Mitchell, 1927, Megachile brevis var. onobrychidis Cockerell, 1908, Megachile brevis var. nupta Cresson, 1872, Megachile brevis var. pseudobrevis Mitchell, 1936, Megachile texana var. cleomis Cockerell, 1900, andMegachile texana var. lippiae Cockerell, 1900. There is a questionable record from Peru, that Mitchell named Megachile buchwaldi Mitchell, but it was never described and no type was ever designated (Raw 2004), so it is a nomen nudum. Sheffield et al. (2011) published a key to the Megachile of Canada in which he raised Megachile onobrychidis, Megachile lippiae and Megachile pseudobrevis to species level. Specimens from Mexico identified as M. onobrychidis and other unidentified specimens were found to be a new species, M. pankus, described below (Figures 1-2). Ten species are recognized here. The life history and nesting biology of Litomegachile species is relatively well known (Michener 1953, Krombein 1967, Baker et al. 1985, Packer 1987. These bees are cavity nesters, usually choosing an existing cavity in wood, a plant stem, or the ground, where they construct a nest of several individual cells. The cells are arranged in a linear fashion, and are cylindrically shaped. Leaf or petal pieces are used to form a cup shape, and are often glued together by the female bee biting the edges to create adhesion (Krombein 1967). Kim (1992) found that cell size determines how much pollen is provisioned, which in turn determines the size of the resulting offspring. These bees follow the pattern shown in many other solitary bees which construct a linear nest. The females are larger than the males, and are placed in the rear of the nest behind the males, since they usually take longer to develop and emerge (Kim 1992). carina is a structure in males at the functional apex of the metasoma. It arises from the medial discal area of T6 and terminates in a notched or irregularly jagged edge ( Figure 6C-I). Below the carina of T6, is the true apical margin, with four teeth: two submedial and two lateral ( Figure 6A-B). The tomentum is a patch of white hair on T6 of males that is thick enough to hide the discal surface. Pubescence is defined as branched body hairs, such as those found on head, mesosoma, and discal surfaces of metasoma and apical fringes of hair of tergal segments. Setae are those unbranched, "eyelash-like" hairs found on the metasoma along the margins of tergal segments, and that make up the scopa on the sterna of females. Abbreviations used for measurements as illustrated in Fig. 3 are as follows: MCL=marginal cell length, SL= stigma length, WCL= forewing length in region with cells, HWL=hind wing length, LTV=length to vannal lobe, LTJ= length to jugal lobe, HW= head width, HL=head length, ASO= distance from antennal socket to anterior ocellus, AD= antennocular distance, ID= interantennal distance, CW=clypeus width, DTL=distitarsus length, TRL=tarsus length, BTL=basitarsus length, TSL=tibial spur length, TBL=tibia length, FL=femur length, TL=trochanter length, CL=coxa length.

Key to the species of Litomegachile
Females 1 Mandible angulate between teeth 3 and 4 ( Figure 4B)  Punctures on surface of T6 near the edges of tomentum crowded, edges form between depressions ( Figure 6C); T2 with apical fringe of white hair ( Figure  6J)  Punctures on surface of T6 not crowded, shiny surface apparent between depressions ( Figure 6D). T2 with no apical fringe of hair or fringe only present laterally ( Figure 6K)   T6 with a white tomentum that obscures the discal surface ( Figure 6G) .....7 -T6 without tomentum, or if tomentum present, sparse, tergal surface visible beneath white hairs ( Figure 6H) Figure 5A). The comparable species have more black setae and no white appressed pubescence on T6. The male has brown tarsi that distinguish it from M. coquilletti ( Figure 4E), and a tomentum on T6 which distinguishes it from M. onobrychidis. Female. Body length 9-12 mm. Mandible 4-toothed, with no angulation between teeth 3 and 4 ( Figure 4A). Head with white pubescence, vertex with black pubescence. Mesosoma with white pubescence, scutum with black pubescence. T2-3 with deep transverse basal grooves, T4 with shallow groove. T1 with white pubescence, T2 with white pubescence basally and black pubescence apically, T3-5 with black pubescence. T6 convex basally and concave apically in profile, and concave laterally in dorsal view; with black erect setae basally and black appressed pubescence, with some white appressed pubescence apically. S1-5 with ivory setae; S6 with ivory setae and few black setae apically ( Figure 5A).
Male. Body length 7-9 mm. Mandible 3-toothed. Ocellocular distance equal to ocelloccipital distance ( Figure 4D). Head with white pubescence. All mesosomal pubescence white or ivory (may appear yellow in early season specimens). T1-5 with white discal pubescence. T5 with complete apical fringe of white hair that covers marginal zone. T6 with tomentum ( Figure 6G); transverse carina variable in shape, but usually with indistinct medial notch and asymmetrical jagged projections; true apical margin with submedial teeth closer to lateral teeth than each other ( Figure 6B). Genitalia and hidden sterna shown in Figures 7A1-A4.
Variability. The transverse carina of the male can vary significantly in this species, with some specimens barely showing any medial emargination, but most with jagged projections, where others have a medial notch. Females can have a few black scopal setae on S6 or all ivory colored scopae. Ecology. Michener (1953) published a detailed biology of Megachile brevis including a description of nest making, provisioning and development. Megachile brevis flies during the warmest parts of the year, with two to four generations per year, depending on locality and resources. It disperses widely from its natal site. Michener found that flower sources used by this species are diverse, but female bees tend to have a preference for blue, purple and white flowers, and a general faithfulness to a single type of pollen per collecting trip. Megachile brevis nested in a variety of situations, always nesting in preexisting hollows, including stems, burrows of other insects, dense foliage or spaces between rocks (Michener 1953). He also observed that M. brevis hunted for nesting sites by flying a few inches above the ground, and tended to nest near the soil surface. Larvae go through at least 4 instars (Baker 1985). Megachile brevis nests are parasitized by a variety of species, including the megachilids Coelioxys sayi Robertson and Coelioxys octodentata Say, a clerid beetle (Phyllobeanus sp.), and wasps, including Aprostocetus coelioxydis Burks (Eulophidae), Leucospis affinis affinis Say (Leucospidae) and Melittobia chalybii Ashmead (Eulophidae) (Baker 1985).  Comments. Megachile brevis is the type species of the subgenus Litomegachile. It ranges across North America, north to southern Saskatchewan, Canada, and south into Mexico. There is also a record from as far south as northern Costa Rica (not shown on map) (Ascher and Pickering 2011) ( Figure 8). Diagnosis. Female M. coquilletti can be distinguished by the combination of a mandible with an even concavity in between teeth 3 and 4, and a slightly concave T6. It resembles M. gentilis, which has an angulation between teeth 3 and 4 of the mandible, and M. brevis, which has a much more concave T6 and much less black scopal setae on S6. Male M. coquilletti are easily distinguished from other Litomegachile by the foreleg with bicolored tarsomeres; the first 4 apical tarsomeres are yellow, contrasting with the darker basitarsus ( Figure 4F). The males of all other species in the subgenus have uniformly brown foretarsi ( Figure 4E). Female. Body length 11-12 mm. Mandible 4-toothed, with no angulation between teeth 3 and 4 ( Figure 4A). T2-3 with deep transverse basal grooves, T4 with shallow groove. T1-5 with apical fringes of white hair that covers marginal zone; T1-2 with thin fringes of white hair, with white discal pubescence, T3-5 with black discal pubescence. T6 slightly concave in profile and laterally in dorsal view; with black appressed pubescence and black erect setae basally. S1-5 with ivory setae; S6 with some ivory setae basally, mostly black setae ( Figure 5B).
Male. Body length 9-12 mm. Mandible 3-toothed. Ocellocular distance less than ocelloccipital distance ( Figure 4C). Foretarsus pale yellow, contrasting with   darker basitarsus ( Figure 4F). Head and mesosoma with white pubescence. T5 with apical fringe of white hair that covers marginal zone, interrupted medially. T6 with tomentum ( Figure 6F); with transverse carina variable in shape, but usually with distinct medial notch and projections; true apical margin with submedial teeth closer to lateral teeth than each other ( Figure 6B). Genitalia and hidden sterna shown in Figures 7B1-B4.
Variability. Male tergal discal pubescence is variable in color. Some female specimens in fresh condition show a slight angulation between mandibular teeth 3 and 4. These may still be differentiated from M. gentilis by the lack of black setae on S5.
Male. Body length 9-11 mm. Mandible 3-toothed. Ocellocular distance less than ocelloccipital distance ( Figure 4C). Head with white pubescence; vertex with black pubescence. Mesosoma with white pubescence, scutum with black pubescence. T2 with thin apical fringe of white hair ( Figure 6J). T5 without complete apical fringe of white hair that covers marginal zone, may have some hair laterally. T6 with tomentum; punctures crowded, nearly contiguous ( Figure 6C); transverse carina with distinct medial notch; true apical margin with submedial teeth closer to each other than lateral teeth, or distances equal ( Figure 6A). Genitalia and hidden sterna shown in Figures 7C1-C4.
Variability. As with other Litomegachile species, individuals that appear early in the flight season may have pubescence that appears yellow instead of white.
Male. Body length 11-13 mm. Mandible 3-toothed. Ocellocular distance less than ocelloccipital distance ( Figure 4C). All pubescence white (may appear yellow in early season specimens). T5 with complete apical fringe of white hair that covers marginal zone. T6 with tomentum; transverse carina with deep distinct medial notch and fingerlike projections ( Figure 6I); true apical margin with submedial teeth closer to lateral teeth than each other ( Figure 6B). Genitalia and hidden sterna shown in Figure 7D1-D4.
Variability. Male tergal discal pubescence is variable in color. Body hair may appear yellow in early season individuals. Females can have black setae that occur laterally on T4. Comments. Megachile lippiae was originally described as a subspecies of M. texana (Mitchell, 1935). It was raised to species level by Sheffield et al. (2011). Megachile lippiae is primarily a western North American species, though records exist from eastern localities (Figure 11  dorsal view. The appressed pubescence on T6 is brownish in color. The scopa is yellowish, distinguishing it from other Litomegachile females which have a pale ivory colored scopa. An exception is M. pankus, which also has a yellow scopa, but it can be separated by its concave T6 in contrast with the straight T6 of M. mendica. The male M. mendica can be distinguished from M. gentilis by the distance between punctures on T6. Megachile mendica punctures occur roughly 0.25-0.5 the width of a puncture apart so that you can see the shiny discal surface in between ( Figure 6D) Male M. mendica also lack the apical fringe of white hair on T2. Males of other species of Litomegachile have a complete apical fringe of white hair on T2.
Male. Body length 8-10 mm. Mandible 3-toothed. Ocellocular distance less than ocelloccipital distance ( Figure 4C) Head with white pubescence, vertex with black pubescence. Mesosoma with white pubescence, scutum with black pubescence. T1-2 pubescence white; T3-5 white pubescence basally, black pubescence apically. T2 without thin apical fringe of white hair ( Figure 6K). T5 without complete white hair fringe that covers marginal zone; may have some hair laterally. T6 punctures separated; shiny discal surface visible between; with tomentum; transverse carina with a distinct medial notch ( Figure 6D); true apical margin with median teeth closer to each other than to lateral teeth, or distances equal ( Figure 6A Ecology. Megachile mendica seems to be flexible in its choice of nesting sites across different habitats. When it nests in trap nests, it prefers a cavity diameter of around 8 mm, which is also preferred by Megachile brevis (Baker et al. 1985). In Texas, M. mendica was found to nest in sandy soil, and like M. texana, it will also excavate burrows in the soil (Williams et al. 1986). Krombein (1967) reared M. mendica from wooden block traps placed on limbs of pine oak and hickory. Generation number and times differed based on the locality (Krombein 1967). Medler (1965) reared M. mendica at 21 degrees Celsius and found that they went from egg to mature larva in one week, spun a cocoon in one day, and took about 3 weeks for pupal development and adult emergence. An M. mendica larva was illustrated and described by Baker et al. (1985). In addition to Coelioxys sp. and Leucospis affinis affinis (Leucospidae), M. mendica nests are known to be parasitized by the flies Anthrax irroratus irroratus (Bombyliidae) and Megaselia sp. (Phoridae) (Baker et al. 1985). Comments. Megachile mendica is distributed across North America south to Zacatecas, Mexico, though it was considered more of an eastern species by Mitchell (1934) (Figure 12).
Diagnosis. The male M. onobrychidis is best distinguished from other species in this subgenus by the lack of a white tomentum on T6. The female M. onobrychidis resembles M. brevis, but with entirely black setae on S6 and apically on S5, and no pale appressed pubescence on T6.
Male. Body length 7-9 mm. Mandible 3-toothed. Ocellocular distance equal to ocelloccipital distance ( Figure 4D). T1-2 with white discal pubescence; T4-6 with white discal pubescence basally, black pubescence apically. Head and mesosoma with white pubescence (may appear yellow in early season specimens). T5 with complete fringe of white hair that covers marginal zone. T6 without tomentum, hairs sparse and discal surface clearly visible beneath ( Figure 6H); transverse carina variable in shape, usually with indistinct medial notch and asymmetrical jagged projections; true apical margin with submedial teeth closer to lateral teeth than each other ( Figure 6B). Genitalia and hidden sterna resemble those of M. brevis ( Figures 7A1-A4).
Variability. Male M. onobrychidis are separated from M. brevis in part by the lack of a tomentum on T6. Some specimens have no tomentum while others have sparse tomentum type hairs, but as long as these hairs are sparse enough so that the tergal surface is still visible, they are M. onobrychidis. Comments. Mitchell (1935) listed this species as a subspecies of M. brevis. It was elevated to species level by Sheffield et al. (2011). It is a western North American species extending south to Sinaloa, Mexico. (Figure 13). Diagnosis. Megachile pankus is unique among Litomegachile species because the female has a mandible with an angulation between teeth 3 and 4, and T6 is basally convex and apically concave. No other species in the subgenus has this combination of characters. The female M. onobrychidis has similar metasomal features, but has more black setae on S6, while M. pankus has only a few black setae on T6. It can also be further distinguished from M. onobrychidis and M. brevis by the angulation between teeth 3 and 4 of the mandible. T6 is convex basally and concave apically in profile, and concave laterally in dorsal view, which distinguishes it from M. mendica or M. gentilis.

Megachile pseudobrevis
Male. Body length 7-9 mm. Mandible 3-toothed. Ocellocular distance equal to ocelloccipital distance ( Figure 4D). T5 with complete apical fringe of white hair covering marginal zone. T6 with tomentum; transverse carina variable in shape, usually with indistinct medial notch and asymmetrical jagged projections; true apical margin with submedial teeth closer to lateral teeth than each other ( Figure 6B). Genitalia and hidden sterna resemble those of M. brevis (Figures 7A1-A4).
Ecology. Packer (1987) observed Megachile pseudobrevis nesting in tufts of grass, creating nests of single cells. Megachile pseudobrevis preferred the commonest flowering plant Bidens pilosa (Asteraceae) at the site as a source for cutting nesting material, but also used petals from Eustoma exaltatum (Gentianaceae). Nests were parasitized by the meloid beetle Nemognatha punctulata LeConte (Packer 1987).

Diagnosis.
Megachile snowi is distinguished from M. mendica in males by the presence of a complete apical fringe of white hair on T5. Megachile mendica has little or no apical fringe of white hair on T5. Female Megachile snowi have white appressed pubescence on T6, and the few black scopal setae of S6 are only found apically. Megachile mendica has brown pubescence on T6, and S6 has more black setae.
Male. Body length 8-10 mm. Mandible 3-toothed. Ocellocular distance less than ocelloccipital distance ( Figure 4C). Mesosoma with white pubescence. T1-3 with white discal pubescence; T4-5 with white pubescence basally, black apically. T2 with thin apical fringe of white hair. T5 with complete apical fringe of white hair covering marginal zone. T6 with tomentum ( Figure 6E); transverse carina with a distinct medial notch; true apical margin with submedial teeth closer to each other than to lateral teeth, or distances equal ( Figure 6A). Genitalia and hidden sterna shown in Figures  Comments. This species was originally described as a subspecies of M. mendica (Mitchell, 1935). It is raised to species level herein, based on reliable morphological characters distinguishing it from M. mendica, and an overlapping range with the latter (Figures 12, 16). Mitchell (1935)   These carina projections tend to be shorter in M. texana, whereas the carina of M. lippiae often has long "fingerlike" projections. M. texana, Female. Body length 11-14 mm. Mandible 4-toothed, with no angulation between teeth 3 and 4 ( Figure 4A). T2-4 with deep transverse basal grooves. T1-5 with apical fringes of white hair covering marginal zone. T1 with black discal pubescence medially, white pubescence laterally. T2-5 with black discal pubescence and setae (Figure 5K). T6 with pale appressed pubescence and erect black setae basally. T6 deeply and evenly concave in profile and laterally in dorsal view. S1-4 with ivory setae; S5 with ivory setae basally, black setae apically; S6 with black setae ( Figure 5I).
Male. Body length 10-12 mm. Mandible 3-toothed. Ocellocular distance less than ocelloccipital distance ( Figure 4C). Head with white pubescence, vertex with black pubescence. Mesosoma with white pubescence, scutum with black pubescence. T5 with complete apical fringe of white hair covering marginal zone. T6 with tomentum; transverse carina with distinct deep medial notch and short jagged projections; true apical margin with submedial teeth closer to lateral teeth than each other ( Figure  6B). Genitalia and hidden sterna shown in Figures 7G1-G4.
Variability. Male tergal discal pubescence variable in color. Pubescence of male mesonotum and head can vary, making it occasionally challenging to differentiate this species from M. lippiae. Primarily, if there is any black pubescence on the mesonotum, Ecology. Megachile texana utilizes existing nesting sites in the ground and under rocks (Krombein 1970). Observations by Eickwort et al. (1981) showed that these bees also excavate their own nests. The cocoons completely fill their cells and are covered with an outer layer of reddish brown threads and an inner layer of brown threads (Eickwort et al. 1981). Comments. Megachile cleomis is one of the synonyms of M. texana. It was originally described by Cockerell in 1900, based on two cotypes from a locality in New Mexico, a male and a female. The male was later found to be a male M. snowi. The female is herein designated as the lectotype for M. cleomis, which remains in synonymy with M. texana. This situation illustrates the importance of correctly assigning holotypes. Megachile texana is a widespread species which is found across North America (Figure 17).

Conclusions and future directions
There is more work to be done with Litomegachile. There are issues regarding types that need to be resolved. Locating types is made easier through the databasing of collections, and there is still more to be done. Repositories for M. palmarum, M. pruinosa, and M. vernonensis are unknown. Neotypes were not designated for M. brevis, which appears to be missing a holotype, presumed destroyed. The neotype was not designated because of the possibility that it could be in a collection and sim-ply unaccounted for. A lectotype was designated by Cresson in 1916 for Megachile mendica but it was not located and so was not examined. Distribution maps and locality data can be greatly refined and expanded. The maps provided here only represent a portion of available collection data. As material from more collections are reliably identified and databased, records that are accurate and available to researchers will greatly improve this field of study. Knowledge of the nesting behavior, ecology, and plant associations of this group remains incomplete. Again, acquisition of additional data will aid compilation of host plant records and more detailed analysis of plant relationships. Additional collecting trips and review and identification of specimens in collections may reveal more diversity. Megachile pankus was uncovered in current collections. The male of M. pankus is unknown, and it is likely that there are more species to be discovered in tropical southern ranges of this group. A phylogeny using molecular and morphological data would further clarify the relationships between the species of this group.