Revision of Lineostethus (Heteroptera: Pentatomidae: Discocephalini)

Lineostethus Ruckes, 1966 has four species, L. clypeatus (Stål, 1862), L. graziae Hildebrand & Becker, 1982, L. marginellus (Stål, 1872), and L. tenebricornis (Ruckes, 1957); mostly restricted to Central America, but with distribution records in the southern North America. Lineostethus is one of the discocephaline genera with discoid head. The last review of the genus, from the 1980’s, focused on the genital morphology and failed to provide updated descriptions or a key to species. We had access to material from different collections, including several specimens representing new species of Lineostethus, and males of L. marginellus which shows important variations in genital morphology. Here we update the generic description of Lineostethus and its known species and describe the new species Lineostethus acuminatus sp. nov. (holotype male in DZUP: Costa Rica, Guanacaste), Lineostethus auritus sp. nov. (holotype male in AMNH: Mexico, Oaxaca), Lineostethus otarus sp. nov. (holotype male in AMNH: Mexico, Michoacán) and Lineostethus sinuosus sp. nov. (holotype male in DZUP: Mexico, Yucatán). Additionally, we provide identification keys and distribution maps.


INTRODUCTION
Members of Discocephalinae are recognized primarily by the labium inserted usually on or posterior to an imaginary transverse line crossing the head on the anterior limit of eyes, and by the abdominal trichobothria usually placed lateral to the spiracles (Grazia et al. 2015, Rider et al. 2017).Two tribes restricted to the Americas, Discocephalini and Ochlerini, are classified in Discocephalinae (Rolston andMcDonald 1979, Rolston 1981).A generic key is available for the genera of Ochlerini (Rolston 1992) and another for the genera of broadheaded discocephalines (Rolston 1990), and though both are outdated, Lineostethus Ruckes, 1966 can be identified using the latter.
Discocephalini comprises 44 genera and 193 species (Grazia et al. 2015, Rosso andCampos 2017) of light-brown to brown hues, often mottled with black or shiny black, distributed mostly in the Neotropical region.Ruckes (1966) revised Platycarenus Fieber, 1861, raising the subgenus Discocephalessa Kirkaldy, 1909 to genus, and describing five new genera to include species removed from both Discocephalessa and Discocephala Laporte, 1832, along with new species.Lineostethus Ruckes, 1966 was proposed to include three species, Platycarenus (Discocephalessa) tenebricornis Ruckes, 1957, Platycarenus (Discocephalessa) clypeatus (Stål, 1862), its type species, and Platycarenus (Discocephalessa) marginellus (Stål, 1872).Ruckes (1966) considered P. (D.) marginellus a subspecies of P. (D.) clypeatus and provided a key to the species of Lineostethus.Along with a morphological study of the genitalia for the genus, Hildebrand and Becker (1982) considered P. (D.) marginellus a valid species, and described Lineostethus graziae Hildebrand & Becker, 1982.However, although the authors characterized the genitalia of both sexes for all species, the general body morphology was not described nor an updated key for the species was provided.
Looking through specimens of Discocephalini available from different collections, we found specimens matching the characteristics of Lineostethus that did not fit in any of the described species, as well as several males of L. marginellus showing important variations on the genital morphology.Here Lineostethus is revised with the redescription of the four known species, and the description of four new species from Central America.Identification keys for males and females are presented, and a distribution map is given.

MATERIAL AND METHODS
Specimens were observed and measured under stereomicroscope.The following morphometric parameters were taken: length and width of the head, pronotum and scutellum; length of the antennal and labial segments; total length, from the apex of clypeus to the apex of segment VII of connexivum; and maximum abdominal width.Measurements (mean ± standard deviation, minimum, and maximum) are given in millimeters.Internal genitalic structures were studied after boiling in 10% KOH aqueous solution and staining in Congo red.Specimens and genital structures were photographed using a stereomicroscope Nikon AZ100M and pictures stacked with Nikon NIS-Elements AR Microscope Imaging Software.Line drawings were made with a vectorial image processor on the pictures taken and checked under stereomicroscope.For the phallus, the dorsal and ventral views have no significant variations in morphology between the species and so, these views are illustrated only for the type species of Lineostethus.
Site collection data were georeferenced using the Global Gazetteer Version 2.2 (Falling Rain Genomics Inc 2010) for those specimens without geographic coordinates informed in the respective labels, and the distribution map for the studied specimens was made with the software QGIS 2.10.1.
The specimens examined are deposited in the following collections: AMNH -American Museum of Natural History, New York, USA; CAS -California Academy of Sciences, San
Redescription.Body oval, general color ivory with brown punctures.Head discoid, flat, wider than long.Mandibular plates longer than clypeus, overlapping at apex; lateral margins of mandibular plates outlined in brown close to the eyes.Ocelli minute.Area between eyes and ocelli with 1+1 elliptical spots without punctures (Figs 1-8).Antennae 5-segmented.Head ventrally tumescent between eyes and along bucculae.Bucculae weakly developed.Labium reaching the abdominal segment III.
Pronotum trapezoidal, wider than long; cicatrices flat and outlined by punctures.Anterolateral margins straight.Scutellum longer than wide, reaching connexival segment VI; apex usually uniformly convex to angulate.Corium longer than scutellum, reaching connexival segment VII; unpunctured area lateral to the apex of each radial vein subequal to or smaller than the width of one eye.Marginal area of anterolateral margins of pronotum and coria delimited by a line of punctures.Membrane fumose, reaching or surpassing the apex of abdomen, with 6 to 9 veins.Prosternum furrowed; mesosternum with 1+1 tumescent lateral areas, xyphus carinated; metasternum lozenge, carinated medially.Mesopleural evaporatorium sinuous, extending laterad beyond half of mesopleura; lateral margin of mesopleura without evaporatorium, except its posterior angle.Metapleural evaporatorium extending laterad beyond half of metapleura and with lateral margin sinuous; both meso-and metapleural evaporatorium concolorous with the body.Peritreme spout-shaped, scalpel-like.Legs with brown spots; tibiae with dorsal furrow.
Connexivum narrowly to widely exposed; tergite VIII of females usually visible from above.Abdomen furrowed ventrally at least on base and with punctures concentrated on lateral thirds; spiracles brown.
Remarks.Lineostethus was named by Ruckes (1966) after the thin carina both in xyphus and metasternum.The genus is possibly related to the other Discocephalini with a discoid head (e.g., Acclivilamna Ruckes, 1966, Alveostethus Ruckes, 1966, Discocephala, Ischnopelta Stål, 1868, Platycarenus and Phoeacia Stål, 1862) grouped by Rolston (1990) for identification purposes as the 'broadheaded' discocephalines.Lineostethus can be differentiated from the remainder of broadheaded genera by the body shape, especially the head uniformly convex, with an inconspicuous anteocular process, the pronotum subtrapezoidal, with anterolateral margins slightly convex, and the scutellum reaching the abdominal segment VI with lateral margins narrowing evenly toward the concave apex.
Lineostethus have a homogeneous general morphology making it difficult to identify the species based on characteristics other than genitalic.In addition, we examined a large number of specimens from different localities and were unable to confirm the characters of general morphology treated by Ruckes (1966) as diagnostic for some species (e.g., antennae uniformly tenebrous in L. tenebricornis, and the distribution of punctures on anterolateral pronotal margins and on basal costal margins in L. clypeatus and L. marginellus).The male genitalia are clearly diagnostic for the genus, and species can be promptly separated by the morphology of pygophore, especially the foliaceous expansions of dorsal rim (Figs 9,19,27,37,45,54,62,70) and the projections of the superior layer of ventral rim (20)(21)(28)(29)(30)(31)(38)(39)(46)(47)(55)(56)(63)(64)(71)(72).However, differences between female genitalia are subtle making the determination of female specimens difficult.Exceptions are L. sinuosus Kochenborger & Garbelotto sp.nov., L. auritus Garbelotto & Kochenborger sp.nov.and L. otarus Garbelotto & Kochenborger sp.nov., which have sinuous posterior margin in gonocoxites VIII.Since non-genital characters are insufficient for distinguishing species of Lineostethus, the keys presented below, one for males and another one for females, use only genital characters.

Key for males of
Diagnosis.Males of L. clypeatus differ from the other species by the shorter and more rounded foliaceous expansions of the dorsal rim of pygophore, and by the projections of the superior layer of ventral rim short and tapering to its apex psl).The female genital plates are very similar to L. marginellus but can be differentiated by the slightly shorter gonocoxites VIII.The helicoidal distal portion of ductus receptaculi, the fusiform thickening of gonapophysis IX, and the elliptical thickening of vaginal intima also help to differentiate L. clypeatus from the other species.
Hemelytral membrane slightly surpassing the apex of abdomen, with 6-7 veins.Ventrally, punctures sparse and concentrated laterally.Femora with sparse brown circular spots on apical half.
Remarks.From the data retrieved of specimens' labels, cotton (Gossypium hirsutum L., Malvaceae) is a possible host plant.
Diagnosis.The specimens of L. tenebricornis may have brown antennae, also observed in L. auritus sp.nov.and L. otarus sp.nov.The males of L. tenebricornis are recognized by the subquadrangular foliaceous expansions of the dorsal rim of pygophore, covering dorsally the posterolateral angles (Figs 19-21: fdr, pa); the projections of the superior layer of ventral rim elongate and rounded at apex (the last feature similar to L. graziae) (Figs 21,39: psl); the presence of two lines of short bristles below the projections of the superior layer of ventral rim (Figs 20-21: b); and the apical margin of vesica along with the ductus seminis distalis (Fig. 24: av, ds).In the females, diagnostic features are the posterior margin of urosternite VII subrectilinear on its median third along with subrectangular gonocoxites VIII (Fig. 25: VII, gcVIII); and the thickening of gonapophysis IX subrectangular with a median constriction, combined with a subtriangular thickening of vaginal intima (Fig. 25: tgIX, vi).The median third of the posterior margin of urosternite VII and the subtriangular thickening of vaginal intima are also found in L. otarus sp.nov.However, L. tenebricornis has shallower genital plates than L. otarus sp.nov.(Figs 25,68), and the thickenings of gonapophysis IX have different shapes (Figs 26,69: tgIX,vi).
Redescription.Antennal segments usually brown, sometimes ivory with longitudinal brown line on segments I-II; segment III usually longer than II.Anterolateral margins of pronotum and proximal portion of lateral margin of corium punctured.Unpunctured area laterad to the apex of radial vein of coria smaller than the width of one eye.Hemelytral membrane at least reaching the apex of abdomen, with 8 veins.Ventrally, punctures uniformly distributed.Femora with brown circular spots on the entire length or concentrated on distal half.

Lineostethus graziae
Redescription.Antennal segments I-IV with longitudinal brown lines.Anterolateral margins of pronotum and proximal portion of lateral margin of corium without punctures.Unpunctured area laterad to the apex of radial vein of coria smaller than the width of one eye.Hemelytral membrane surpassing the apex do abdomen, with 7 veins.Anterior and posterior margins of connexival segments with one or two lines of black punctures (Fig. 4).Ventrally, punctures sparse and concentrated laterally or gradually dispersed toward the midline.Femora with sparse brown circular spots on distal half.

Lineostethus acuminatus
Description.Antennae ivory; segments II-III with longitudinal brown lines.Anterolateral margins of pronotum and proximal portion of lateral margin of corium punctured in some specimens.Scutellum may present a spot of brown punctures on disc and on post-frenal lobe.Unpunctured area laterad to the apex of radial vein of coria smaller than the width of one eye.Hemelytral membrane reaching the apex of abdomen, with 6-7 veins.Ventrally, punctures sparse and laterally concentrated.Femora with sparse brown circular spots on distal half.
Etymology.The epithet refers to the shape of the apex of each projection of the superior layer of ventral rim of pygophore; Latin adjective masculine, acuminatus (-a, -um) = pointed, sharpened.Diagnosis.Lineostethus otarus sp.nov.and L. auritus sp.nov.share similar features in both male and female genitalia: the long foliaceous expansions of the dorsal rim of pygophore; two lines of bristles on the ventral wall, one of them not associated with punctures; and broad gonocoxites VIII.Lineostethus otarus sp.nov. is distinguished by the wider foliaceous expansions of the dorsal rim, hiding the posterolateral angles of pygophore; the sinuous proximal portion of the lateral margin of the expansions; and the projections of the superior layer of ventral rim more elongated.Females of L. otarus sp.nov.are distinguished by the posterior margin of urosternite VII subrectilinear over laterotergites IX, and the sinuous posterior margin of gonocoxites VIII.
Description.General color of the specimens with some variation, in melanic specimens margins of connexival segments with lines of black punctures more evident.Antennae ivory; segments II-III with longitudinal brown lines dorsally and ventrally; segments IV-V usually darker than the previous.Anterolateral margins of pronotum and proximal portion of lateral margin of corium punctured.Anterior margin of scutellum with two to four brown spots, and one ivory spot medially; post-frenal lobe with 1+1 lateral brown maculae.Unpunctured area laterad to the apex of radial vein of coria inconspicuous to equivalent to the width of one eye.Hemelytral membrane at least reaching apex of abdomen, with 6 veins.Ventrally, punctures uniformly distributed, absent on sterna.Femora with sparse brown circular spots on distal half.
Male genitalia.Foliaceous expansions of dorsal rim subrectangular, elongated, longer than wide, narrowing towards the apex; proximal portion of the lateral margin of expansions sinuous; apex rounded, surpassing the posterior limit of ventral rim by half of the expansion length, and visible dorsally when fixed at the specimen (Fig. 62 Distribution (Fig. 78).México: Michoacán, Puebla (Fig. 78).
Etymology.The epithet refers to the shape of the foliaceous expansions of dorsal rim of pygophore; adjective otarus (-a, -um), latinized from Greek otaros = large-eared.Description.Antennae usually brown, with lateral lines ivory, sometimes antennae variegated.Anterolateral margins of pronotum and proximal portion of lateral margin of corium punctured.Anterior margin of scutellum with two to four brown spots, and at least one ivory spot medially; post-frenal lobe sometimes with lateral brown maculae.Connexival segments with lines of black punctures on anterior and posterior margin of each segment.Unpunctured area laterad to the apex of radial vein of coria at least equivalent to half of eye width.Hemelytral membrane slightly surpassing the apex of abdomen, with 9 veins.Ventrally, punctures concentrated on lateral margins of abdomen.Femora with sparse brown circular spots on distal half.

Lineostethus auritus
Male genitalia.Foliaceous expansions of dorsal rim subrectangular, elongated, longer than wide; lateral margins of expansions slightly concave; apex truncate, slightly wider than the median width, surpassing the posterior limit of ventral rim by half of the expansion length; not hiding the posterolateral angles (Fig. 70 Distribution (Fig. 78).Mexico: Oaxaca.
Etymology.The epithet refers to the shape of the foliaceous expansions of dorsal rim of pygophore; Latin adjective, auritus (-a, -um) = eared.

ACKNOWLEDGMENTS
We are thankful to all the curators of the listed collections, who provided access to specimens, types or not, especially to: Mike Narahara and Vicent F. Lee (CAS) and Peter T. Oboyski (EMEC) who provided photos of L. graziae, and Gunvi Lindberg (NHRS) who provided photos of L. clypeatus and L. marginellus.To Christiane Weirauch for providing access to specimens of several species, including some new species.
: fdr); and the projections of the superior layer of ventral rim acute at apex and forming an acute to right angle with the posterolateral angles.In this species the enlargement of the median portion of the projections of the superior layer of the ventral rim is variable, and consequently their apex length and shape also vary a little.The foliaceous expansions of the dorsal rim are subrectangular as in L. acuminatus sp.nov.but the species differ by the projections of ventral rim and by the phallus.The females are like L. clypeatus in the general shape of the genital plates, however in L. marginellus the gonocoxites VIII are longer(Figs  17, 35: gcVIII).Also, the sinuous thickening of gonapophysis IX, the subrectangular thickening of the vaginal intima, and the enlarged and straight ductus receptaculi distal are diagnostic and differ L. marginellus from L. clypetus(Figs 36: tgIX, vi, ddr).Redescription.Antennal segments II-III with longitudinal brown line.Anterolateral pronotal margins and proximal portion of lateral margin of corium punctured in some specimens.Scutellum sometimes with a spot of brown punctures on disc and on post-frenal lobe.Unpunctured area laterad to the apex of radial vein of coria subequal to the width of one eye or inconspicuous.Hemelytral membrane slightly surpassing the apex of abdomen, with 6-7 veins.Ventrally, punctures sparse and concentrated laterally.Femora with sparse brown circular spots on apical half.Male genitalia.Foliaceous expansions of dorsal rim subrectangular; apex of expansions not surpassing the posterior limit of ventral rim; posterolateral angles visible dorsally (Fig.27: fdr, pa).Basal impression of the foliaceous expansions subrectilinear, cutting of dorsal rim U-shaped (Fig.27: bi, dr).Posterolateral angles with rounded apex, sometimes with setae on the posterior margin (Fig. 27: pa).Margin of the superior layer of ventral rim sinuous, median excavation narrow and drop-shaped (Fig. 28: vr).Margin of the inferior layer of ventral rim with one arc of short bristles (Fig. 28: b).Projections of the superior layer of ventral rim forming an acute to right angle with the posterolateral angles; projections covered by setae on the posterior margin, base and median portions enlarged, apex acute (Figs 29-31: psl, pa); posterior surface of the projections usually depressed.Parameres parallel to segment X, usually projected over the cutting of the dorsal rim; head lozenge (Figs 29, 32-33: par, dr, X).Ventral surface of phallotheca subrectilinear (Fig. 34: ph, ap).Vesica apical margin sinuous, extending to mid of ductus seminis distalis (Fig. 34: v, av, ds).Distal portion of ductus seminis distalis half the length of vesica; uniformly wide (Fig. 34: ds).Female genitalia.Posterior margin of urosternite VII concave (Fig. 35: VII).Gonocoxites VIII subtriangular; posterior margin
indicated the Essig Museum of Entomology in the University of California Berkeley (EMEC) as deposit collection for the female holotype of L. graziae, but it is in the California Academy of Sciences under the type number 15923 and was examined by T.A.G.Lineostethus sinuosus Kochenborger & Garbelotto, sp.nov.http://zoobank.org/3786A48C-3F2B-4137-B1EC-EEBC72E9EC99Figs 5, 45-53, 78
sutural angles are exclusive to L. sinuosus sp.nov.The shape of the thickening of the gonapophyses VIII is also exclusive inside the genus, and along with the helicoid distal ductus receptaculi is diagnostic to the species.Description.Antennae ivory; segments II-III with longitudinal brown lines.Anterolateral margins of pronotum and proximal portion of lateral margin of corium punctured in some specimens.Unpunctured area laterad to the apex of radial vein of coria smaller to subequal to the width of one eye.Hemelytral membrane at least reaching the apex of abdomen, with 6 veins.Ventrally, punctures sparse and laterally concentrated.Femora with brown circular spots on distal half.Male genitalia.Foliaceous expansions of dorsal rim subrectangular; apex of expansions at least reaching the posterior limit of ventral rim; posterolateral angles visible dorsally (Fig. 45: fdr, pa).Basal impression of the foliaceous expansions subrectilinear; cutting of dorsal rim U-shaped (Fig. 45: bi, dr).Posterolateral angles rounded, apex obtuse, sometimes with setae on posterior margin (Figs 45-46: pa).Segment X visible on the cutting of dorsal rim (Fig. 45: dr, X).Margin of the superior layer of ventral rim sinuous, median excavation U-shaped (Fig. 46: vr).Margin of the inferior layer of ventral rim with one arc of short bristles (Figs 46-47: b).Projections of the superior layer of ventral rim spatulate at apex, forming a right angle with the posterolateral angles; dorsal margin convex and ventral margin sinuous, median third enlarged in relation to the lateral thirds; setae on the posterior margin of the projections (Fig. 47: psl).Parameres sinuous, parallel to segment X, apex reaching the mesial margin of the foliaceous expansions of the dorsal rim; head lozenge (Figs 47-49: par, X, dr).Ventral surface of phallotheca subrectilinear (Fig. 50: ph, ap).Vesica obtuse and more sclerotized at apex; apical margin concave, extending to basal 1/3 of ductus seminis distalis (Fig. 50: v, av, ds).Distal portion of the ductus seminis distalis about 2/3 of vesica length, narrowing posteriorly (Fig. 50: ds).Female genitalia.Posterior margin of urosternite VII concave (Figs 51-52: VII).Gonocoxites VIII subtriangular; sutural margins diverging towards apex, sutural angles posteriorly projected; posterior margin sinuous, varying in intensity (Figs 51-52: gcVIII) with the sinuosity of the posterior margins, sometimes with lateral angles partially hiding the spiracles of the laterotergites VIII, and sutural angles projected over the base of the laterotergites IX, or not.Posterior margin of laterotergites VIII convex; limit between laterotergites VIII and tergite VIII indistinguishable (Figs 51-52: la8).Posterior margin of gonocoxites IX subrectilinear (Fig. 51: gcIX) to convex (Fig. 52: gcIX).Gonapophyses VIII visible and smooth (Figs 51-52: gpVIII).Laterotergites IX digitiform, with a median depression; varying in shape from lateral margins convex with apex rounded to lateral margins subrectilinear with apex acute (Figs 51-52: la9).Posterior margin of segment X subrectilinear (Figs 51-52: X).Thickening of gonapophyses IX sinuous, surpassing the lateral margin of the thickening of vaginal intima (Fig. 53: gpIX, tgIX).Thickening of vaginal intima subtriangular, flat (Fig. 53: vi).Distal portion of ductus receptaculi helicoid (Fig. 53: ddr); anterior annular crest turned to ductus receptaculi; pars intermedialis subequal in length to capsula seminalis; posterior annular crest turned to pars intermedialis (Fig. 53: pi, cs).

Figure 78 .
Figure 78.Distributional map for studied specimens of the species of Lineostethus.Countries with species records are in green.
Diagnosis.Males of L. auritus sp.nov.are distinguished by the long and narrow foliaceous expansions of dorsal rim truncate at apex, leaving the posterolateral angles of pygophore visible dorsally.The females have broad gonocoxites VIII with the posterior margin uniformly convex; the shape of the thickening of the gonapophyses IX and of the thickening of vaginal intima are also diagnostic.