Plectrone tristis (Westwood, 1842)

Vendl, Tomáš, VONDRÁýEK, Dominik, Kubá, VítČzslav & Šípek, Petr, 2014, Immature stages of Taenioderini (Coleoptera: Scarabaeidae: Cetoniinae): a report of hidden morphological diversity, Acta Entomologica Musei Nationalis Pragae 54 (2), pp. 571-604 : 594-597

Plectrone tristis (Westwood, 1842)

( Figs 2G ; 3G ; 4G ; 5G ; 7D–F,Q ; 8M–O,T ; 9K,S ; 10G ; 11G )

Material examined. 5 third instar larvae reared from adults obtained in February 2013 from the beetle breeder O. Jahn (Sušice, Czech Republic), collecting data and locality are not available.

Description of third instar larva. Body ( Fig. 2G ). Length 56.0–68.0 mm (n = 3, larvae not fully grown), dorsoventral interval of abdominal segments slightly larger than in thoracic segments (thus abdominal segments appear to be slightly thicker, abdominal segments VII and VIII are the thickest). Body, especially on ventral side, covered with numerous stiff, brown setae. Setae on both dorsal and ventral part of thorax and abdomen subequal in size and shape.

Head capsule ( Fig. 3G ). Maximum width 5.6–7.1 mm, surface of cranium with indistinct microsculpture, yellowish or reddish brown, parts of epicranium with numerous darker irregular spots. Frontal sutures bisinuated. Epicranial insertions of antennal muscles very distinct, dorsally emarginated with sickle-like line. Cranial chaetotaxy summarized in Table 2. Anterior and exterior frontal setae absent or composed of one or two minute setae.

Antennae ( Figs 3G ; 9K ). Relative length of antennomeres I–IV (an I–IV): an I Ŀ an IV> an II> an III), ultimate antennomere with 15–20 dorsal and 17–23 ventral sensory spots.

Epipharynx ( Fig. 4G ). Haptomerum: Zygum convex, with arcuate row of 15–17 stout, pointed setae and medial row of another ¿ve to eight stout setae. Sensilla of zygum in single row distad to the row of stout setae. Acroparia: Lateral lobes of epipharynx with four to ¿ve long setae, medial lobe with eight setae. Acanthoparia with four to ¿ve large tubercles each with single seta; the size of the tubercles, as well as the length of setae, increasing towards the apex of epipharynx.

Chaetoparia: Asymmetric, right side with single regular row of long stiff setae and ¿ve to six irregular rows, left side with single regular and three to four irregular rows of setae. Right side of chaetoparia with approximately 55–70, left with 40–50 setae, respectively. Pedium large. Dexiotorma somewhat crooked, long, narrowed toward medial end, right pternotorma absent. Laeotorma present, left pternotorma prolonged. Haptolachus: Sense cone large, broad at the base, conical, almost pointed at the tip. Plate-like sclerite large, occupying almost the entire area between sense cone and the regular rows on both sides of chaetoparia. Sensilla of haptolachus organized in two groups of two sensilla.

Mandibles ( Figs 7D–F ; 8M–O ). Stridulatory area absent, ventral surface of entire mandible smooth, rarely with few irregular ridges. Scrobis with three to four lateral setae. Longitudinal furrow present, extending towards apex of mandibles, with two prominent lateroapical setae and one or two posterior setae (occasionally absent).

Maxilla ( Fig. 5G ). Dorsal surface of cardo and labacoparia with four to eight stiff and 16–24 slender setae, respectively. Ventral surface of cardo and labacoparia with three to four and six to nine stiff setae, respectively, labacoparia with another 8–15 slender setae. Dorsal surface of stipes with approximately 13–20 slender hair-like setae and one to four anterolateral stout setae. Maxillary stridulatory apparatus on stipes with eight to nine, blunt, conical stridulatory teeth, blunt tubercle absent or of the same shape as the previous teeth. Ventral surface of stipes with single proximal and one to three distal setae (long and stout, arranged in transverse row). Galear portion of mala in dorsal aspect beside large falcate uncus with three to ¿ve large stiff and four to eight medium-sized hair-like setae respectively. Lacinial part of mala with around twenty mostly extremely long and stiff setae. Lacinial uncus beside large pointed claw with minute second pointed tip, and two conical, stout setae. Vental surface of mala with two longitudinal rows of setae; the exterior row with three to ¿ve mostly long and stiff setae, the interior row with three short and stout setae.

Hypopharyngeal sclerome ( Fig. 5G ). Around twenty tegumentary expansions (phoba-like processes) present on the left lateral lobe of hypopharynx, tegumentary expansions on right medial portion of scleroma present in all studied individuals.

Ligula ( Fig. 5G ). Dorsal surface laterally and anteriorly with two groups of around 11–15 hair-like setae (each group consists of longitudinal and oblique row) and central group of setae and sensilla. The central group is composed of two paramedial rows of two stout, conical setae, and transverse, basomedial row of ¿ve to seven conical setae.

Thorax ( Figs 2G ; 7Q ; 8T ; 9S ). Prothoracic sclerite with approximately eight to twelve setae on the anteroventral margin and another one or two setae in the posterio-dorsal area. Each sublobe of prothorax dorsal with one or two rows of setae (short to long). Thoracic spiracle ( Fig. 7Q ) 1.1 × 0.8 mm (height × width), bullar opening narrow, not broader than the maximum perimeter of respiratory plate. Respiratory plate with approximately 50 holes across diameter. Pretarsus ( Fig. 8T ) conical with minute pointed tip and two apical setae.

Abdomen ( Figs 2G ; 10G ; 11G ). Each dorsal sublobe of abdominal segments I–VIII with one to three rows of setae. The anterior one or two row(s) irregular, with short setae. Posterior row regular with medium-long and long setae. Setae of abdominal segments IX–X, as well as the setae of the entire ventral body covered slightly stiffer than those on dorsal part. Spiracles on abdominal segments I–III elongate, similar to thoracic spiracle, abdominal spiracles on segments IV–VIII almost circular.

Raster ( Figs 10G ; 11G ). Rows of pali absent, tegilla fused, central part with medium-long hamate setae, other parts with stiff and long hair-like setae. Ventral anal lip with three rows of short apically recurved setae.

Figures

Fig. 2. Third instar larvae of Taenioderini.A–H – habitus.A – Chalcothea neglecta. B – Coilodera diardi. C –C. penicillata. D – Euselates cineraceus. E – E. laoticus. F – Meroloba suturalis. G – Plectrone tristis.H – Taeniodera sp. Figures not to scale.

Fig. 3. Third instar larvae of Taenioderini. A–H – cranium. A – Chalcothea neglecta. B – Coilodera diardi. C –C. penicillata. D – Euselates cineraceus. E – E. laoticus. F – Meroloba suturalis. G – Plectrone tristis. H – Taeniodera sp. Scale bars: Figs 3A–H = 1mm.

Fig. 4. Third instar larvae of Taenioderini. A–H – epipharynx. A – Chalcothea neglecta. B – Coilodera diardi. C – C. penicillata. D – Euselates cineraceus. E – E. laoticus. F – Meroloba suturalis. G – Plectrone tristis. H – Taeniodera sp. Scale bars = 1 mm.

Fig. 5. Third instar larvae of Taenioderini. A–H – maxillo-labial complex.A – Chalcothea neglecta. B – Coilodera diardi. C – C. penicillata. D – Euselates cineraceus. E – E. laoticus. F – Meroloba suturalis. G – Plectrone tristis. H – Taeniodera sp. Scale bars = 1 mm.

Fig. 7. Third instar larvae of Taenioderini. A–I – left mandible (dorsal, medial and ventral aspect), J–O – right mandible (ventral, medial and dorsal aspect), P–R – thoracic spiracle, S–T – pretarsus.A–C,P – Meroloba suturalis. D–E,Q – Plectrone tristis. G–I,R – Taeniodera sp. J–L,S – Chalcothea neglecta. M–O,T – Coilodera diardi. Scale bars: Figs A–O,S = 1 mm; Figs P–R = 0.7 mm; Fig. T = 0.1 mm.

Fig. 8. Third instar larvae of Taenioderini.A–O – right mandible (ventral, medial and dorsal aspect), P–T – pretarsus. A–C,P – Coilodera penicillata. D–F,Q – Euselates cineraceus. G–I,R – E. laoticus. J–L,S – Meroloba suturalis. M–O,T – Plectrone tristis. Scale bars: Figs A–P,T = 1 mm; Figs Q–S = 0.5 mm.

Fig. 9. Third instar larvae of Taenioderini.A–C – right mandible (ventral, medial and dorsal aspect), D – pretarsus, E–L– antenna (dorsal and ventral aspect), M–T – metathoracic leg: A–D – Taeniodera sp. E,M – Chalcothea neglecta. F,N – Coilodera diardi. G,O – C. penicillata. H,P – Euselates cineraceus. I,Q – E. laoticus. J,R – Meroloba suturalis. K,S – Plectrone tristis. L, T – Taeniodera sp. Scale bars = 1 mm.

Fig. 10. Third instar larvae of Taenioderini. A–H – ultimate abdominal segment, ventral aspect. A – Chalcothea ne- glecta. B – Coilodera diardi. C – C. penicillata. D – Eusela- tes cineraceus. E – E. laoticus. F – Meroloba suturalis. G – Plectrone tristis. H – Taenio- dera sp. Scale bars = 1 mm.

Fig. 11. Third instar larvae of Taenioderini. A–H – ultima- te abdominal segment, lateral aspect: A – Chalcothea neglecta. B – Coilodera diardi. C – C. peni- cillata. D – Euselates cineraceus. E – E. laoticus. F – Meroloba suturalis. G – Plectrone tristis. H – Taeniodera sp. Scale bars = 1 mm.