The subgenus Chalepochile in Argentina (Hymenoptera: Megachilidae: Megachile )

. The subgenus Chalepochile Gonzalez & Engel of Megachile Latreille was known only from males of two species. In this contribution the female of M. ardua Mitchell, type species of Chalepochile , is described, as well as a new species based on both sexes. The new species M. ( Chalepochile ) bilineata occurs in the provinces of Córdoba, La Rioja and Mendoza in Argentina. The phylogenetic relationships of the subgenus Chalepochile are discussed in the light of characters of the females.

The subgenus Megachile (Chalepochile) was proposed by Gonzalez & Engel to include two South American species known only from the male sex (Gonzalez et al., 2018). These species had been previously assigned to either the subgenus Ptilosaroides Mitchell (Schlindwein, 1998), Ptilosarus Mitchell (Raw, 2002(Raw, , 2007Silveira et al. 2002), or Rhyssomegachile Mitchell (Moure et al., 2007;Moure & Melo, 2022). All these subgenera, together with Neochelynia Schrottky and Zonomegachile Mitchell, form a group of closely related Neotropical subgenera (Gonzalez et al., 2018;Gonzalez et al., 2019). The morphological distinctiveness of Chalepochile among all these subgenera is hampered by the lack of knowledge of the female sex, because females bear important features used for characterizing subgenera. The subgenus Chalepochile has been recently synonymized under Rhyssomegachile (Moure & Melo, 2022).
The purpose of the present contribution is to describe for the first time the female of Megachile ardua Mitchell, type species of Chalepochile, and to describe a new species from central western Argentina, based on both sexes. All this new information is used to expand the phylogenetic analysis of Gonzalez et al., (2018), based on adult morphology, to test the validity and phylogenetic position of Chalepochile.
The specimens studied are deposited in the Museo Argentino de Ciencias Naturales, Buenos Aires, Argentina (MACN). The maximum diameter of the median ocellus (MOD) is used as a reference to express the length of the

The subgenus Chalepochile in Argentina (Hymenoptera: Megachilidae: Megachile)
pubescence and other structures. The metasomal terga (T) and sterna (S) are identified with Arabic numerals. PD stands for puncture diameter.
The phylogenetic analysis of Gonzalez et al., (2018) is expanded to include the female of M. ardua and the new species described below. Their data matrix is modified by the addition of the new taxa, but no new characters are added. Parsimony analysis was performed with the program TNT (Goloboff et al., 2003). Characters were treated as nonadditive and equally weighted. The algorithm Implicit Enumeration, which gives exact solutions, was used for the search of most parsimonious trees. In the descriptions below, some features are followed by a pair of numbers in parentheses separated by a comma. The first number corresponds to the number in the list of characters used by Gonzalez et al., (2018) while the second corresponds to the character state here attributed to the added taxa. Inapplicable character states are indicated by a question mark. The trees obtained with TNT were submitted to the program WinClada (Nixon, 2002) for delayed character optimization and printing.

Phylogenetic analysis
The phylogenetic analysis produced two equally parsimonious trees (tree length 145), the strict consensus of which is shown in figure 1. The topology of the two trees only differs in the position of the species within the subgenus Rhyssomegachile. The new species M. bilineata clusters with M. ardua and M. tacanensis, justifying its inclusion in the subgenus Chalepochile. All the characters that support Chalepochile are female characters (Fig. 1). The relationships of Chalepochile in the cladogram are similar to those obtained by Gonzalez et al. (2018), but the clade sister to this subgenus is better resolved.
The subgenus Chalepochile was proposed to include two closely related and very similar species: Megachile ardua Mitchell, and M. tacanensis Moure, the latter having been described as a subspecies of M. ardua (Moure, 1948). Since the original diagnosis of the subgenus was exclusively based on the male sex, it is appropriate to expand the diagnosis based on characteristics of the female.
Females of Chalepochile can be recognized by their mandibles with four teeth, the fourth being truncate, incised, and with cutting edges in the second and third interspaces (incomplete and complete cutting edge respectively) (Fig. 2); by the lack of a preoccipital carina; by the scutum with small, nearly coalescent punctures; by the presence of a scuto-scutellar band of pale hairs; by the metanotum slanting to rear; by the forewing darkened along the costal margin; by the ovoid metasoma; by the T6 with stiff, semierect hairs interspersed with the appressed pubescence; by the S6 evenly setose and without a bare apical lip; and by the metasomal sterna with lateral apical fasciae under the scopa. The inclusion of the new species M. bilineata and the female M. ardua in the phylogenetic analysis corroborates the relationships found by Gonzalez et al. (2018). The placement of Chalepochile as a synonym of Rhyssomegachile (Moure & Melo, 2022) is not supported. Chalepochile can be distinguished from Rhyssomegachile by the lack of a preoccipital carina, the metanotum slanting to rear, the presence of a scuto-scutellar band of short, plumose hairs, the male clypeus densely covered with hairs on its entire surface, and the presence of a longitudinal patch of short hairs on the inner surface of the male hind femur. Rhyssomegachile has a distinct preoccipital carina, at least behind the gena, the metanotum is vertical, there is no scuto-scutellar band, and no specialized patch of hairs on the male hind femur.

Distribution
Diagnosis. This species is distinguished by the unusual pattern of yellow apical bands on the metasoma. Both sexes have yellow bands on T1 and T4, contrasting with the dark pubescence of other terga; the male also has yellow pubescence basally on T4. The wings are dusky, not yellowish brown as in related species. The metanotum is covered with short pale plumose hairs, much as in species of the subgenus Neochelynia. Females are further distinguished by the capitate hairs of the scopa and the hind tibiae and basitarsi. The male lacks pale appressed pubescence on T6, unlike the related M. ardua and M. tacanensis.

Male.
Total length 8.0 mm; length of forewing 5.8 mm.
Etymology. The species name refers to the two tergal apical bands on the metasoma.