Lineostethus Ruckes, 1966

Garbelotto, Thereza de Almeida, Kochenborger, Ana Paula Leite & Campos, Luiz Alexandre, 2018, Revision of Lineostethus (Heteroptera: Pentatomidae: Discocephalini), Zoologia (e 21232) 35, pp. 1-24 : 2-4

Lineostethus Ruckes, 1966

Lineostethus Ruckes, 1966: 22–26 , figs 2, 9, 12, 17–18; Hildebrand and Becker (1982: 773–784); Rolston (1990: 30).

Type species. Discocephala clypeata Stål, 1862 – by original designation.

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.

Male genitalia. Pygophore globose. Dorsal rim with 1+1 subtriangular to subrectangular foliaceous expansions projected on each side of segment X; cutting of dorsal rim U-shaped or subquadrangular around the segment X ( Figs 9, 19, 27, 37, 45, 54, 62, 70: fdr, dr). Basal impression of the foliaceous expansions subrectilinear to sinuous ( Figs 9, 19, 27, 37, 45, 54, 62, 70: bi). Posterolateral angles of pygophore reduced, obtuse or acute, usually not covered by the foliaceous expansions ( Figs 9, 19–20, 27, 37, 45, 54, 62–63, 70: pa). Segment X elliptical, twice longer than wide and surpassing ventral rim margin. Margin of superior layer of ventral rim sinuous to concave, median excavation reduced and U-shaped to drop-shaped ( Figs 10, 20, 28, 38, 46, 55, 63, 71: vr). Margin of the inferior layer of ventral rim with one or two lines of short bristles below the projections of the superior layer of ventral rim, bristles associated or not with punctures ( Figs 10–11, 20–21, 28–29, 38–39, 46–47, 55–56, 63– 64, 71–72: b). Superior layer of ventral rim projected ventrally, forming 1+1 projections varying in contour, length, width, and shape of apex, these projections forming an acute to obtuse angle with the posterolateral angles ( Figs 10–11, 20–21, 28–31, 38–39, 46–47, 55–56, 63–64, 71–72: psl, pa). Parameres placed laterally to segment X, at least reaching the expansions of the dorsal rim; base of parameres circular and head subtriangular to sublozenge ( Figs 12–13, 22–23, 32–33, 40–41, 48–49, 57–58, 65–66, 73–74). Phallotheca longer than wide, narrowing toward vesica; ventral surface of phallotheca subrectilinear to concave, with a ventro-apical projection ( Figs 14–16, 24, 34, 42, 50, 59, 67, 75: ph, ap). Vesica cap-shaped, apex concave to acute, apical margin following or not the ductus seminis distalis ( Figs 14–16, 24, 34, 42, 50, 59, 67, 75: v, av, ds).

Female genitalia. Posterior margin of urosternite VII uniformly concave, or sinuous with median third subrectilinear ( Figs 17, 25, 35, 43, 51–52, 60, 68, 76: VII). Gonocoxites VIII subrectangular to subtriangular; posterior margin subrectilinear to convex; sutural angles not juxtaposed ( Figs 17, 25, 35, 43, 51–52, 60, 68, 76: gcVIII). Laterotergites VIII subtriangular; posterior margin subrectilinear to concave; spiracles visible ( Figs 17, 25, 35, 43, 51–52, 60, 68, 76: la8, s). Gonocoxites IX subtrapezoidal. Laterotergites IX digitiform to subtriangular. Segment X rectangular, surpassing half of laterotergites IX; posterior margin concave to subrectilinear. Thickening of gonapophyses IX paired, varying in shape ( Figs 18, 26, 36, 44, 53, 61, 69, 77: tgIX). Ring sclerites present and circular. Thickening of vaginal intima circular to subquadrangular ( Figs 18, 26, 36, 44, 53, 61, 69, 77: vi). Ductus receptaculi with median duct of vesicular area enlarged distally; anterior annular crest parallel or turned to distal ductus receptaculi; pars intermedialis completely sclerotized or just on basal and apical thirds; posterior annular crest perpendicular to or directed toward capsula seminalis; capsula seminalis globose, without processes.

Distribution ( Fig. 78). USA: Arizona, Texas. Mexico: Nuevo León, Tamaulipas, San Luis Potosi, Veracruz, Jalisco, Hidalgo, Michoacán, Morelos, Puebla, Oaxaca, Tabasco, Chiapas, Campeche, Yucatán, Quintana Roo. Belize (new record). Guatemala: Alta Verapaz, Baja Verapaz, Sacatepequez. Honduras: Cortes, Santa Barbara, Comayagua, El Paraiso. Costa Rica: Guanacaste. Panama: Los Santos.

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.

The genitalic morphology in Lineostethus is also diagnostic, both the female genital plates and the male pygophore. The female well exposed gonocoxites IX and segment X ( Figs 17, 25, 35, 43, 51–52, 60, 68, 76), and the male foliaceous expansions of the dorsal rim and the ventral projections of the superior layer of ventral rim of pygophore ( Figs 9–11, 19–21, 27–31, 37–39, 45–47, 54–56, 62–64, 70–72: fdr, psl) are features seen only in Lineostethus within the Discocephalini. The males of Acclivilamna also have paired expansions of the dorsal rim, but extremely sclerotized, not foliaceous, and short in length if compared to Lineostethus . Undeveloped posterolateral angles of pygophore are also seen in Acclivilamna and in some undescribed species of Ischnopelta ; though in Ischnopelta the dorsal and ventral rims have neither projections nor expansions.

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 ( Figs 10–11, 20–21, 28–31, 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.

Lineostethus is the Discocephalinae genus with the northernmost distribution and the only so far recorded in the Nearctic Region. Though this Nearctic occurrence was previously known ( Ruckes 1957, Hildebrand and Becker 1982), the discocephalines have been regarded as occurring exclusively in the Neotropical region [restricted to the Neotropics sensu Grazia et al. (2015), endemic to the Neotropics sensu Rider et al. (2017)]. Following classic as well recent biogeographic regionalization systems ( Morrone 2014, 2015) the Mexican Transition Zone and the Nearctic region should also be considered as part of the distribution of the subfamily.