A remarkable new species group of green seed beetles from genus Amblycerus Thunberg (Coleoptera, Chrysomelidae, Bruchinae), with description of a new Brazilian species

Abstract Representatives of the subfamily Bruchinae (Coleoptera: Chrysomelidae) are usually small and inconspicuous, with only a few species drawing the attention. Here we deal with several unusually colored species of Amblycerus Thunberg, 1815, one of the two most diverse bruchine genera in the Western hemisphere. We define the virens group that consists of five species whose bodies are covered with a green vestiture, including one new for science, Amblycerus medialis Ribeiro-Costa, Vieira & Manfio, sp. n. (Type locality: Brazil: Pará, Rondônia). This study also provides redescriptions, diagnoses, comparative notes, illustrations, geographic distribution records and a key to the species in this group.


Introduction
Bruchinae Latreille, commonly known as seed beetles, is one of the 13 subfamilies of Chrysomelidae (Bouchard et al. 2011). This subfamily encompasses more than 1700 species (Ribeiro-Costa and Almeida 2012) that are distributed worldwide. In the Western hemisphere, two genera, Amblycerus Thunberg, 1815 (Amblycerini: Amblycerina) and Acanthoscelides Schilsky, 1905 (Bruchini: Acanthoscelidina), stand out as the most hyperdiverse genera (Kingsolver 1990, Ribeiro-Costa 1999, the first with 340 species (Kingsolver 1990) and the second with more than 100 species (Romero et al. 1996, Ribeiro-Costa 2000. For Acanthoscelides, several molecular analyses indicate that the genus is likely paraphyletic (Kergoat and Silvain 2004, Kergoat et al. 2005, 2008, which is not surprising considering the lack of clear diagnostic characters for the genus (Borowiec 1987, Kergoat andSilvain 2004). On the contrary, a morphological cladistic analysis of Amblycerus sampled in the United States and Mexico (Romero et al. 2002) suggests that the genus Amblycerus is possibly monophyletic.
Members of Amblycerus are well defined and easily recognized by their subovate body, shallowly emarginate eyes, hind tibia without prominent lateral carinae, and the presence of two apical spurs on hind tibia (Romero et al. 1996, Kingsolver 2004. Though most species for which host plants are known usually develop on Fabaceae (Romero et al. 1996(Romero et al. , 2002, several Amblycerus species are quite remarkable because they are associated with other plant families (Romero et al. 1996(Romero et al. , 2002. In total, at least 13 distinct plant families have been thus recorded for the genus Amblycerus, a pattern that contrasts with most bruchine genera that are only associated with one or a few host plant families (Borowiec 1987). Another interesting feature of Amblycerus is the unusual coloration pattern of a few species. In general seed-beetles have a black, yellow or reddish non-metallic body (Borowiec 1987). Their vestiture is more or less dense, and is usually not made of conspicuous colors. Among Amblycerus, several species clearly depart from this pattern as they exhibit a conspicuous green vestiture. The first species with such an unusual coloration pattern, Amblycerus virens (Jekel, 1855), was described in 1855 from French Guiana. Following a revisional work initiated almost 20 years ago as a part of a thesis on Brazilian Amblycerus species (Ribeiro-Costa 1995), three other species were later described in 1998: A. virescens Ribeiro-Costa, 1998A. viridans Ribeiro-Costa, 1998and A. viridis Ribeiro-Costa, 1998. At that time, phenetic analyses were used to place these four species in a distinct species group (Ribeiro-Costa 1995), but a clear formalization of the corresponding species group (virens group) is lacking to date. As these species with a green vestiture do not occur in the United States and Mexico they were also not included in the morphological cladistic analysis of Romero et al. (2002).
To advance in the taxonomy and systematics of the virens group we propose a revision of the entire species group, including a redescription of A. virens and a description of a new Amblycerus species that also harbors this unusual green vestiture. We also provide an identification key, geographic distribution data and a diagnosis for the group based on comparisons of morphological characters used at group level in previous taxonomic and cladistic studies (Romero et al. 1996(Romero et al. , 2002. All these species possibly form a natural group, but comprehensive phylogenetic studies (with a dense sampling of Amblycerus species) are definitely required to precise this hypothesis.

Material and methods
The material examined was loaned from museums/collections listed below (acronyms of museums/collections and curators' names are also provided). Most characters were observed from dry pinned insects. Male genitalia were studied following Manfio et al. (2013), except for A. virens for which we followed Ribeiro-Costa (1998). Colored images of the external morphology were captured with a LEI-CA DFC 500 digital camera attached to a LEICA MZ16 stereomicroscope, and subsequently processed using Auto-Montage Pro (Syncroscopy) image processing software of the "TAXon line-Rede Paranaense de Coleções Biológicas" at the Departamento de Zoologia, Universidade Federal do Paraná (UFPR). The terminology adopted was that of Ribeiro-Costa and Silva (2003) except for some thoracic and abdominal sclerites for which we followed Lawrence et al. (2010). Measurements were obtained using AXIOVISION version 4.8.2.0 over images captured with a SONY CYBER-SHOT DSC W350 digital camera coupled in the stereoscopic microscope CARL ZEISS DIS-COVERY version 8. Measurements of body parts (body length and width, ocular index and sinus, postocular lobe, antennomeres length and width) were carried out on one randomly chosen specimen of each species following traits highlighted in Ribeiro-Costa (1998: 631, Figs 1, 2, 3, 5 and 8). The following abbreviations were used: BL, body length (from anterior margin of pronotum to elytra apex) and BW, body width (the largest width on the subapical region of the elytra).

Results and discussion
The virens species group consists of five species: Amblycerus virens (Jekel, 1855), A. virescens Ribeiro-Costa, 1998, A. viridans Ribeiro-Costa, 1998, A. viridis Ribeiro-Costa, 1998 and A. medialis Ribeiro-Costa, Vieira & Manfio, sp. n. It can be distinguished from other Amblycerus species groups by combinations of characters that are listed below in the diagnosis. Comparative notes. Within the virens group, A. virens, A. virescens, A. viridans and A. viridis, share more morphological similarities to each other than with A. medialis Ribeiro-Costa, Vieira & Manfio, sp. n. The most obvious difference between them is the fact that for A. virens, A. virescens, A. viridans and A. viridis, the pubescence on pronotum and elytra is not variegated and does not present stripes.

Group virens
In comparison with other Amblycerus species, it is worthy to note that A. medialis presents two long, serrate blades in the internal sac of male genitalia. Interestingly, these serrate blades (character 24(1), pg. 7, Romero et al. (2002)) are also found in two species (A. barcenae and A. pictus) of the marmoratus clade (Romero et al. 2002). The broader blades of A. viridis, A. virescens and A. viridans are more similar with those of many other Brazilian species studied by Ribeiro-Costa (1995). Amblycerus viridis, A. viridans and A. virens also share the presence of two plates with small tubercles on the dorsal surface of the internal sac of male genitalia (character 25(1), pg. 7, Romero et al. (2002)) with the clade anosignatus (composed of A. anosignatus, A. chiapas and A. guerrerensis). The issue of determining whether these morphological similarities are homoplastic or not is complex, and will clearly benefit from results of future phylogenetic analyses of molecular datasets.
Sexual dimorphism. Sexual dimorphism was not observed even in the shape of the apex of the last abdominal ventrite. Pronotum and elytra with mid strip of vestiture (Fig. 7), antennae serrate from 4 to 10 antennomere (Fig. 8 Median lobe of male genitalia with blade sclerites about one half of wishbone sclerite length, with denticles restricted to subapical region (Fig. 5) (Figs 1-4). Body mostly black, mouth parts and antennomeres 1 and 2 brown to yellowish, apical spurs of hind tibiae reddish brown, pygidium and abdomen rufous with golden shine.
Mesothorax and metathorax. Scutellum as long as wide; round or unidentate at apex (Fig. 1). Elytron with striae 1 and 10 moderately impressed; 2, 3, 8 and 9 weakly impressed until the third apical region of elytron then only isolated punctures representing striae; 4-7 striae formed only by isolated punctures; 4 and 5 anastomosed before the fusion of 6+7. Interstriae with moderately coarse and sparse punctures. Metaventrite moderately protuberant (Fig. 2) with moderately coarse and sparse punctures; median sulcus one-half as long as metaventrite. Metepisternum with moderately coarse and sparse punctures; metepisternal sulcus forming straight angle, with transverse axis straight and not reaching lateral margin of metepisternum. Mid coxae lower than anterior coxae, in lateral view (Fig. 2). Hind femur about 2.5 times longer than wide. Hind coxae with moderately coarse and sparse punctures. Hind tibia lateral spur about 1.5 times the length of median spur; 1-tarsomere about 1.5 the length of the lateral spur and 2.5 times the median spur. Abdomen (Fig. 4). Ventrites with moderately coarse and dense punctures; last ventrite as long as 4-ventrite. Pygidium one-third covered by the elytra; apical margin rounded, with moderately coarse and dense punctures.
Male genitalia. Median lobe (Fig. 5) about 4.15 times its widest at apical region; ventral valve with lateral margins straight; dorsal valve with lateral margins concave and acuminate apex. Internal sac (Fig. 5) in the apical region without anterior sclerites; a pair of tuberculate median sclerites; a pair of ovoid and denticulate posterior sclerites. Median region with a pair of sinuous blade sclerites, sinuous at base and denticulate at apex; a long wishbone sclerite, about two times longer than the blade sclerites, curved and denticulate at apex and with stems moderately separated. Basal region of sac without sclerites; apical and median regions with several spines. Tegmen (Fig. 6) slightly emarginated between lateral lobes expanded.  (Figs 1-2); scale bars = 0.5 mm (Figs  3-4, 6); scale bar = 0.2 mm (Fig. 5) Notes. Jekel (1855) described the material quoted by Dejean (1837) but in his description, he did not specify how many specimens were studied. Therefore the exemplar received from BMNH, from the locality quoted in the original description, is a type specimen and regarded as a syntype.

Distribution. Brazil (Mato Grosso).
Comparative notes. Amblycerus viridans differs from all other species in the group by the structure of the internal sac of male genitalia, which includes a pair of sclerites formed by dense denticles (Ribeiro-Costa 1998: 634, Fig. 14: EPL) (character absent in A. virescens, A. viridis, A. virens and A. medialis). This species is similar to A. viridis because they both have a wishbone sclerite that is shorter than the blades; in addition both species also share the presence of a pair of slender denticulate sclerites on median region (Ribeiro-Costa 1998: 634, Fig. 14: EPC). Additional information on external morphological similarities is also presented in the section dedicated to A. virescens.

Distribution. Brazil (Mato Grosso).
Comparative notes. Amblycerus viridis differs from the other species in the group by its shorter hind femur, which is 2.32 times longer than its width (in others species the ratio is superior to 2.5 times). Additional information on external and internal similarities is also presented in the sections dedicated to A. virens and A. viridans. Integument color (Figs 7-10). Body black except mouth parts brownish; apical spurs of hind tibiae brownish to black.

Amblycerus medialis
Vestiture (Figs 7-10). Pronotum with a predominantly green vestiture but also with yellowish setae on the anterior margin, lateral areas and median line; elytra with a predominantly green vestiture but also with yellowish setae on 1 interstria; thorax and abdomen covered with pale yellowish setae. Head (Fig. 9) covered with fine and dense punctures. Frons without frontal carina. Eyes moderately faceted, strongly prominent laterally. Ocular index: 2.23; ocular sinus: 0.78; postocular lobe 0.34 the eye length. Antennae not reaching anterior margin of hind coxa (Fig. 8); serrated from 4 to 10 antennomeres; from 3 to 11 antennomeres 1.94 longer than wider; 11 antennomere with truncate apex (Fig. 8). Frontoclypeal suture indistinct. Clypeus covered with fine and dense punctures except on a narrow band on apical portion. Labrum with few fine punctures on basal margin. Prothorax (Fig. 7). Pronotum semicircular; covered with fine and dense punctures, moderately coarse punctures intermixed all over pronotum. Lateral carina complete, almost reaching the anterior margin of pronotum. Cervical sulcus absent. Prosternal process longer than anterior coxae, gently arched between coxae and slightly constricted between coxae.
Mesothorax and Metathorax. Scutellum longer than wide with tridentate apex. Elytron with striae moderately impressed, not fused apically. Interstriae with moderately coarse and dense punctures (Fig. 7). Metaventrite slightly protuberant with moderately coarse and sparse punctures; median sulcus one-half as long as metaventrite. Metepisternum without punctures; metepisternal sulcus forming straight angle, with transverse axis straight and reaching lateral margin of metepisternum. Mid coxae lower than anterior coxae, in lateral view (Fig. 8). Surface of hind coxae without punctures. Hind femur 3 times longer than wide. Hind tibia lateral spur about 1.5 times the length of median spur, and 1-tarsomere about 1.5 the length of lateral spur and 2.5 times the median spur. Abdomen (Fig. 10). Ventrites finely punctulate, the last about 2 times wider than the 4-ventrite; pygidium one-half covered by the elytra, with apical margin rounded, with fine punctures.
Distribution. Brazil (Pará and Rondônia). Comparative notes. Amblycerus medialis can be easily separated from others species in the group by the presence of yellow pubescent stripes on the pronotum and elytra (Fig. 7) (others species are exclusively with a green vestiture); antennomeres about 2 times as long as wide (Figs 7-8) (others wider than long).
Additional information on external and internal similarities is also presented in the sections dedicated to A. virens and A. viridans.
Etymology. The specific name refers to the median line on dorsum.