Mecocephala Dallas, 1851

de Barros, Lurdiana Dayse, Barão, Kim Ribeiro & Grazia, Jocelia, 2022, Taxonomic updates on the Mecocephala group (Hemiptera: Pentatomidae): redescription of Mecocephala Dallas and Paramecocephala Benvegnú, Journal of Natural History (J. Nat. Hist.) 55 (43 - 44), pp. 2691-2747 : 2694-2698

Mecocephala Dallas, 1851

Mecocephala Dallas, 1851: 180 ; Lethierry and Severin 1893: 132; Kirkaldy 1909: 71; Pirán 1970: 126; Benvegnú 1968: 88, 93–94; Schwertner et al. 2002: 169–184; Frey-da-Silva et al. 2002a: 209, 211; Frey-da-Silva et al. 2002b: 179–181; Ruschel et al. 2013: 553; Coscarón 2017: 227–228; Barão et al. 2017: 110; Barão et al. 2020: 780; Barros et al. 2020b: 321, 349, 351, 355.

Type species. Mecocephala acuminata Dallas, 1851 , by monotypy.

Diagnosis. Sub-triangular head, at least 1.4 times longer than wide; mandibular plates pointed apically and lateral margins before the eyes rectilinear; clypeal suture inserted anteriorly to an imaginary line crossing anterior margin of compound eyes; antenniferous tubercles not visible in dorsal view of head; extremely long labium, surpassing the middle of abdominal sternite 7. Valvifers 8 flat, mesial margins reflected.

Redescription. Body oval. Dorsal and ventral surface of body convex. Head longer than wide, triangular. Mandibular plates shorter than clypeus, pointed at apices; outer margins of mandibular plates rectilinear and lower than inner margins. Clypeus base narrower than its apex, apex obtuse; clypeus at a higher level than mandibular plates in lateral view; clypeal suture inserted anteriorly to an imaginary line crossing anterior margin of compound eyes ( Figure 1 ).

Anteocular processes present or not. Antenniferous tubercles not visible in dorsal view, each with an obtuse lateral process. Proportions of antennomeres: 1> 2 <3> 4 <5. Antennomere 1 not reaching apex of head; antennomere 2 apparent ( Figure 1 ); antennomere 3 showing interespecific varibility variable speciesin shape; antennomere 4 slightly flattened dorsally, grooved or not dorsally. Bucculae tapering towards base of the head, not reaching head base ( Figure 2 ).

Labium surpassing the middle of abdominal sternite 7. First labiomere contained between bucculae, labiomere 2 flattened laterally and smaller than 3 and 4 combined ( Figure 2 ). Labiomeres 3 and 4 flattened. Pronotum trapezoidal; each anterior angle of pronotum with an obtuse process, directed laterally, varying in length; anterolateral margins of pronotum straight, explanate and reflexed dorsally, with variable outline; humeral angles not produced; posterolateral margins of pronotum sinuous; posterior margin of pronotum rectilinear ( Figure 1 ). Mesosternum with a low carina, higher anteriorly, smooth. Metasternum with a shallow groove. Each ostiole of the thoracic ESES elliptical, opening posterolaterally; periostiolar depressions present; each ostiolar peritreme spout-like, long, reaching half of the distance to lateral margin of evaporatorium. Evaporatorium punctate, reaching more than half of the width of meso- and metapleuron. Anterolateral margins of evaporatorium on metapleura rounded. Evaporatorium on mesopleuron surpassing the limits of mesocoxal sutures, reaching its anterior and posterior lateral angles, and the outer margin ( Figure 3 ).

Legs not concolorous with ventral surface of body. Femora unarmed, femora longer than tibiae. Tibiae grooved dorsally. Tarsi 3-segmented. Scutellum longer than wide; apex rounded, surpassing the posterior margin of abdominal tergite 5. Basal angles of scutellum foveate, foveae smaller than the diameter of a compound eye. Corium longer than scutellum, surpassing apices of abdominal tergite 5; apex of radial vein calloused or with inconspicuous callosity, callus varying in size and colour; membrane with linear veins, varying in number. Membranal suture sinuous. Apex of hemelytra not surpassing apex of body. Connexivum exposed. Abdominal sternites with medial longitudinal groove reaching sternite 7. Posterolateral angles of sternites unarmed, straight. Callus mesial to each spiracle. Spiracles elliptical, black. Trichobothria lateral to an imaginary longitudinal line tangent to the spiracles. Genital cup of pygophore narrow, opened dorsoposteriorly, and occupying less than half the length of pygophore. Middle region of dorsal rim entire, and extension of dorsal rim obsolete. Layers of ventral rim not separated by a carina; area between layers depressed and striated in caudal view. Superior layer of ventral rim projected over genital cup, developed laterally to segment X, not covering parameres; lateral margins of superior layer of ventral rim entire in superior view; superior processes present or not. Inferior layer of ventral rim with processes, except in M. bonariensis . Segment X ogival (rectangular, with arcuate apex), carinate, with tumescent processes basally. Parameres present, crown reduced. Dorsal connectives of articulatory apparatus short, reaching the middle of phallotheca. Processus capitati longer, reaching phallotheca distal margin. Phallotheca piriform, long, and with three pairs of projections; dorsal processes of phallotheca wider basally, apically curved, and longer than the posterodorsal projections of phallotheca; conjunctiva with one pair of processes, and two or three pairs of lobes ( Figure 9 ). Process of vesica long. Ductus seminis distalis long or extremely long, in relation to conjunctiva, convolute. Valvifers 8 flat, partially covering valvifers 9, mesial margins emarginate and juxtaposed. Valvulae 8 not visible externally. Laterotergites 8 lacking spiracles. Valvifers 9 flat, except in M. bonariensis , level with segment X in lateral view, with sclerotised lateral arms attaining anterior margins of laterotergites 9. Laterotergites 9 surpassing the abdominal tergite 8, mesial margins divergent. Valvulae 9 with 1 + 1 medially sclerotised areas. Ring sclerites elliptical. Arcuate posterior portion of thickening of vaginal intima longer than the round anterior portion. Median wall of vesicular area enlarged subproximally. Proximal ductus receptaculi long or extremely long in relation to length of vesicular area. Anterior annular flange smaller than pars intermedialis and posterior annular flange wider than capsula seminalis . Pars intermedialis rectilinear. Capsula seminalis globose and shorter than pars intermedialis ( Figure 10 ).

Distribution. Brazil, Argentina and Uruguay ( Figure 29 ).

Key to Mecocephala species

1 Body size smaller than 13.00 mm; body colour light brown ................................................ 2 – Body size larger than 15.00 mm; body colour dark brown to dark reddish brown..... 3

2 Mandibular plates shorter than clypeus ( Figure 1c ), labium surpassing the anterior portion of abdominal sternite 7. Projections of superior layer of ventral rim with 1 + 1 acute processes, lateral margins of projections of superior layer of ventral rim entire, processes of inferior layer of ventral rim separated by more than the width of the segment X................................................................ ................................................................ M. curculionoides – Mandibular plates and clypeus sub-equal in length ( Figure 1e ), labium reaching the anterior portion of abdominal sternite 7. Projections of superior layer of ventral rim with 1 + 1 rounded processes, lateral margins of projections of superior layer of ventral rim notched ( Figure 7f ), processes of inferior layer of ventral rim separated by less than the width of segment X ( Figure 7f )...................... ...................... M. maldonadensis

3 Posterior margins of laterotergites 8 and 9 acutely projected ( Figure 8d )...... M. zikani – Posterior margins of laterotergites 8 and 9 not projected .................................................... 4

4 Outline of anterolateral margins of pronotum distinctly red, impunctate ( Figure 1b ). Inferior layer of ventral rim without processes ( Figure 5f–g )...................... M. bonariensis – Outline of anterolateral margins of pronotum concolourous with pronotum colour, punctate. Inferior layer of ventral rim with a pair of processes........................................... 5

5 Labium clearly surpassing the posterior portion of abdominal sternite 7 ( Figure 6b–c ). Apex of each radial vein with a large, orange to red callosity (at least twice as large as fovea) ( Figure 6a )......................................................... ......................................................... M. magna – Labium reaching the anterior portion of abdominal sternite 7 ( Figure 4b–c ). Apex of each radial vein with a small, pale yellow callosity (smaller than fovea) ( Figure 4a )..... ............................................................................................................................................... M. acuminata

Figures

Figure 1. Head and pronotum of Mecocephala in dorsal view. (a) Mecocephala acuminata; (b) Mecocephala bonariensis; (c) Mecocephala curculionoides; (d) Mecocephala magna; (e) Mecocephala maldonadensis; (f) Mecocephala zikani. Scale bars = 0.5 mm.

Figure 2. Head and prothorax of Mecocephala in lateral view. (a) Mecocephala acuminata; (b) Mecocephala bonariensis; (c) Mecocephala magna; (d) Mecocephala maldonadensis; (e) Mecocephala zikani. Scale bars = 0.5 mm.

Figure 3. Thoracic external scent efferent system (ESES) of metasternal glands of Mecocephala. (a–d) Mecocephala acuminata; (e–g) Mecocephala bonariensis; (h) Mecocephala magna. (a–h) mesopleuron and metapleuron in ventral view; (b–g) scanning electron microscopy images of characters of ESES of metasternal glands. Abbreviations: cx2 – mesocoxe; cx3 – metacoxae; ev – evaporatorium; ms – mesopleuron; mt – metapleuron; mts – metathoracic spiracle; o – ostiole; om – outer margin; pod – periostiolar depression. Scale bars: a, h = 0.5 mm; b, e = 500 µm; c–d, f–g = 200 µm.

Figure 4. Mecocephala acuminata Dallas, 1851. (a–c) Habitus in dorsal, ventral and lateral view; (d–g) pygophore in dorsal, posterior, ventral and lateral view; (h) genital plates in posteroventral view. Abbreviations: alvr – area between layers of ventral rim; dr – dorsal rim; ilvr – inferior layer of ventral rim of pygophore; la8 – laterotergites 8; la9 – laterotergites 9; pilvr – process of inferior layer of ventral rim; pslvr – process of superior layer of ventral rim; slvr – superior layer of ventral rim of pygophore; vf8 – valvifers 8; vf9 – valvifers 9; vr – ventral rim; x – segment X. Scale bars: a–c = 2.0 mm; d–h = 1.0 mm. (Parameres and segment X not shown).

Figure 5. Mecocephala bonariensis Schwertner, Grazia and Fernandes, 2002. (a–c) Habitus of holotype in dorsal, ventral and lateral view; (d–g) pygophore in dorsal, posterior, ventral and lateral view; (h) genital plates in posteroventral view. Abbreviations: alvr – area between layers of ventra riml; dr – dorsal rim; ilvr – inferior layer of ventral rim of pygophore; pilvr – process of inferior layer of ventral rim; pslvr – process of superior layer of ventral rim; slvr – superior layer of ventral rim of pygophore; vr – ventral rim. Scale bars: a–c = 2.0 mm; d–h = 1.0 mm. (Parameres and segment X not shown).

Figure 6. Mecocephala magna Schwertner, Grazia and Fernandes, 2002. (a–c) Habitus of holotype in dorsal, ventral and lateral view; (d) pygophore in dorsal view; (e–f) pygophore in posterior view; (g) pygophore in ventral view; (h) genital plates in posteroventral view. Abbreviations: dr – dorsal rim; ilvr – inferior layer of ventral rim of pygophore; slvr – superior layer of ventral rim of pygophore; vr – ventral rim. Scale bars: a–c = 2.0 mm; d–h = 1.0 mm. (Parameres and segment X not shown).

Figure 7. Mecocephala maldonadensis Schwertner, Grazia and Fernandes, 2002. Holotype. (a–c) Habitus in dorsal, ventral and lateral view; (d) head in lateral view, detail of dorsal groove of antennomeres; (e–g) pygophore in dorsal, posterior and ventral view. Abbreviations: alvr – area between layers of ventral rim; dg – dorsal groove of antennomeres; dr – dorsal rim; ilvr – inferior layer of ventral rim of pygophore; pilvr – process of inferior layer of ventral rim; slvr – superior layer of ventral rim of pygophore; vr – ventral rim. Scale bars: a–c = 2.0 mm; d = 0.5 mm; e–g = 1.0 mm.

Figure 8. Mecocephala zikani Schwertner, Grazia and Fernandes,2002. Holotype. (a–c) Habitus in dorsal, ventral and lateral view; (d) genital plates in posteroventral view. Scale bars: a–c = 2.0 mm; d = 0.5 mm.

Figure 9. Phallus of Mecocephala species in dorsal (left column), lateral (center column) and ventral (right column) views. (a–c) Mecocephala acuminata; (d–f) Mecocephala bonariensis; (g–i) Mecocephala magna. Abbreviations: aa – articulatory apparatus; cj – conjunctiva; dc – dorsal connective; dpph – dorsal process of phallotheca; mlcj – median lobe of conjunctiva; pcj – process of conjunctiva; pdpph – posterodorsal projection of phallotheca; ph – phallotheca; plpph – posterolateral projection of phallotheca; pve – process of vesica; vbpph – ventrobasal projection of phallotheca; vlcj – ventral lobe of conjunctiva. Scale bars = 1.0 mm.

Figure 10. Female receptaculum seminis and aussenwand of Mecocephala species. (a, d) Mecocephala acuminata; (b, e) Mecocephala bonariensis; (c, f) Mecocephala magna. Abbreviations: aaf – anterior annular flanges; cs – capsula seminalis; ddr – distal ductus receptaculi; paf – posterior annular flange; pdr – proximal ductus receptaculi; pi – pars intermedialis; rs – ring sclerites; tvi – thickening of vaginal intima; va – vesicular area. Scale bars = 1.0 mm.

Figure 29. Map showing the geographical distribution of Mecocephala and Paramecocephala species. Yellow star = new record of P. subsolana.