Mycetina rufipennis rufipennis Motschulsky, 1861

Zaitsev, A. A., 2022, Larval description of two species of Mycetina Mulsant, 1846 (Coleoptera: Endomychidae: Lycoperdininae) from Russian Far East, Russian Entomological Journal 31 (4), pp. 392-406 : 393-398

Mycetina rufipennis rufipennis Motschulsky, 1861

MATERIAL. 6 first-instar larvae, 8 second-instar larvae, 10 third-instar larvae (two reared to adult): Russia, Kunashir Island , Kurilsky Nature Reserve, near Saratovsky cordon, 44°15´550´´N 146°06´270´´E on trunk of Abies , covered in mold fungi, 4.IX.2009, leg. A. Zaitsev, adult determined by K. Makarov.

First-instar larva

Figs 3–23 , 32–37 . Maximum body length (from anterior margin of frontal sclerite to the apex of abdominal segment IX) 1.6 mm; head length (from the base of epicranial suture to the apex of labrum) 0.3 mm; head width 0.5 mm; maximum width of thorax 0.6 mm; maximum width of abdomen 0.6 mm. Head 0.8 as wide as prothorax; body elongate, cylindrical; widest across metathorax, then tapering posterad; urogomphi present ( Figs 3–5 ). Head greyish-yellow, antennae lighter, mandibles and maxillae brownish, stemmata transparent. Edge of head capsule at the base of mandibles strongly pigmented. Body light-gray, sclerites slightly stronger pigmented. Legs greyish-yellow, tibiotarsus a little lighter than others joints.

Head capsule as well as tergites and pleurites are covered mostly with frayed setae of various length; ventral surfaces membranous, covered with simple, mostly short setae.

Head ( Figs 6–15 , 32 ) hypognathous, triangular, about 0.6 as long as wide. Epicranial suture short; frontal sutures Ushaped, long, reaching the level of anterior stemma ( Figs 6, 8 ). Frontoclypeal suture and epistomal ridge distinct. Stemmata four on each side, not pigmented, partly surrounding antennal insertion: a pair located posteriorly, one anterior, and one ventral ( Fig. 5 ).

Clypeus transverse, with rounded lateral margins; bearing two simple mesosetae on each side ( Figs 6–7 ). Clypeolabral suture distinct. Labrum ( Fig. 9 ) about 0.5 as long as basal wide; its anterior margin serrate, with 15 pointed denticles; dorsally with five simple setae and single pore on each side: one micro- and one mesoseta on anterior margin, one meso- and one macroseta on lateral edge, one mesoseta closer to posterior margin and one pore located anteriorly to it. Moreover, unpaired medial pore present between posterior mesosetae. Entire surface of frontal sclerite with numerous small granules ( Fig. 32 ); each side with eight macrosetae: three simple setae located in the anterior part and five frayed setae posteriorly; single pore situated close to the anterior end of frontal suture ( Fig. 6 ). Parietal sclerites dorsally ( Figs 6, 8 ) covered with the same granulae; each sclerite with 14 frayed macrosetae and two simple microsetae located close to the postoccipital ridge; three pores present: one rather close to the antennal insertion, another near the anterior microseta and the third located near anterior stemma. Ventral surface of parietal sclerites smooth, each sclerite with single simple anterior mesoseta and single frayed macroseta located close to ventral stemma ( Figs 6–7 ). Hypostomal ridge with transverse curvation below cardo; hypostomal rods diverging posteriorly, rather short, far from reaching posterior margin of the head capsule. Paragular area smooth, with two simple microsetae near the postoccipital ridge ( Fig. 6 ).

Antenna ( Fig. 10 ) short, with three antennomeres, 0.2 as long as head capsule length, with broad insertion area. Antennomere I very short, almost entirely sclerotized, 0.25 as long as wide, ventrally with two pores. Antennomere II slightly sclerotized, rectangular, 5.2 as long as antennomere I and 1.3 as long as wide, its apical part with two dorsal and single ventral simple mesosetae as well as elongated conical sensorial appendage, which is almost twice as long as antennomere III. Antennomere III also slightly sclerotized, 0.4 as long as antennomere II and 1.2 as long as wide; with two dorsal and single ventral simple microsetae; its apical part with three elongated sensilla and single shorter one.

Epipharynx ( Fig. 9 ). Anterior part on each side with several microtrichia of various length, absent in central area, where two sensilla located; three mesosetae present laterally. Four sensilla located posteriorly, as well as numerous microtrichia and small tubercles.

Mandibles ( Fig. 11 ) symmetrical, broad, almost as long as basal width, with well developed membranous area. Apex unidentate, incisor area with 7–8 acute teeth; prostheca with several microtrichia; mola well-developed, with numerous acute teeth; accessory ventral process distinct. Outer edge of each mandible with two simple setae: basal macroseta and microseta located anteriorly to it; single pore located between them. Dorsally each mandible with two basal pores.

Maxilla ( Figs 12–14 ) with triangular cardo, which is “divided” by the internal sclerotization into proxicardo with smooth surface, and disticardo bearing single mesoseta; maxillary articulating area membranous. Stipes ventrally smooth, with two mesosetae. Dorsal side of stipes mostly membranous. Mala gradually narrowed anteriorly; its apex rounded. Ventral surface of mala ( Fig. 13 ) with single basal microseta and one subapical mesoseta on inner margin; apical area with several heavy sclerotized unci. Dorsally ( Fig. 14 ) mala with two microsetae near inner margin; apical area covered in numerous elongated spines, which makes certain difficulties in distinguishing of setae.

Maxillary palps three-jointed, palpifer with two ventral mesosetae ( Fig. 12 ). Palpomere I 0.5 as long as wide; ventrally with single apical pore, dorsally with several small asperities. Palpomere II 1.1 as long as palpomere I and 0.7 as long as wide; with single lateral mesoseta; ventrally with single apical pore. Palpomere III almost twice as long as palpomere II and 2.1 as long as wide; with microseta on inner margin; ventrally with single subapical pore, dorsally with medial digitiform sensillum. Apex of palpomere III with a group of six short conical sensilla.

Labium ( Figs 12, 15 ). Ligula broad, rounded apically; anterior margin with numerous small microtrichia, ventrally with single mesoseta and pore on each side. Prementum ventrally on each side with one micro- and one macroseta. Labial palps with single palpomere, which is 1.6 as long as basal wide; ventrally with basal microseta on outer margin and two pores: one subapical and other near inner margin; also single microseta present on inner margin; apex with a group of five short conical sensilla. Mentum distinct, trapezoidal, membranous, each side with single macro- and microseta. Submentum with single anterior macroseta on each side. Hypopharynx ( Fig.15 ) with numerous microtrichia; hypopharyngeal sclerotisation consists of well-defined sclerome, bracon and a pair of parallel rods.

Thorax ( Figs 3–5 , 16–18, 33 ). Cervicosternum membranous, with three microsetae on each side ( Fig. 4 ). Thorax about 0.4 as long as total body length, widest across metathorax. Prothorax is 0.4 as long as wide, 1.4 as long as mesothorax and 1.5 as long as metathorax.

Prothorax with a pair of large pronotal sclerites, covered in numerous small tubercles ( Fig. 30 ) except invaginated areas of muscles attachment, and well developed, lobe-like laterotergites; ecdysial line not distinct. Each pronotal plate ( Fig. 16) with eight frayed setae (three macro- and five mesosetae) as well as five pores; moreover two microsetae located on membranous area anterior to each sclerite. Membranous area surrounding pronotal plates with numerous small microasperities. Each laterotergite bearing five frayed macrosetae ( Fig. 16).

Meso- and metathorax with each notal plate divided in two sclerites: larger dorsal tergite and smaller dorsolateral tergite ( Fig. 16). Each tergite covered in numerous small tubercles and bearing three frayed setae (one macro- and two mesosetae) and single pore; two simple microsetae located anterior on membranous area. Each dorsolateral tergite with two frayed macrosetae and single pore. Membranous area with the same microasperities as on prothorax. Meso- and metathoracic laterotergites similar to those on prothorax, however there are two simple microsetae located on membranous area anterior to each lobe ( Fig. 16).

Mesothoracic spiracle annular, with two nearby structures of uncertain function ( Fig. 17), being possibly clusters of sensilla, mentioned for Epipocinae [ McHugh, Pakaluk, 1997] or gland openings; they are temporary named as “spiracular disks”. Metathoracic spiracle rudimentary, barely visible.

Prothoracic episternum with four simple microsetae; epimeron with single simple microseta ( Fig. 5 ). Prosternite faintly sclerotized with single simple medial microseta on each side ( Fig. 4 ).

Meso- and metathoracic episternum differs from that on prothorax by having only two simple microsetae; epimeron also with single simple microseta ( Fig. 18). Meso- and metasternite with three simple microsetae on each side ( Fig. 4 ).

Thoracic endoskeleton is of the same structure as was described earlier for M. marginalis [ Tomaszewska, Zaitsev, 2012].

Legs ( Figs 18–19) five-jointed, rather long and slender, slightly increasing in size posteriorly; all three pairs similar in structure and chaetotaxy, covered in simple setae of various length; length ratio of its joints to coxa is 0.5: 0.9: 1: 0.3. Coxa covered in asperities arranged in short transverse rows; with 16 setae: five dorsal (three macro- and two microsetae), three ventral (two macro- and one microseta), three anterior microsetae and five posterior microsetae. Trochanter with five setae: two anterior (one meso- and one microseta), one posterior microseta and two ventral (one macro- and one mesoseta); seven pores present: five anterior and two posterior. Femur partly covered in short asperities, with seven setae: one dorsal microseta, one ventral macroseta, three anterior and two posterior mesosetae; one anterior pore present. Tibiotarsus elongat- ed, with 27 setae: six anterior microsetae, six posterior (four micro- and two mesosetae), eight ventral mesosetae and seven dorsal microsetae; two dorsal pores present. Apical part of tibiotarsus with several ventral spines. Pretarsus with single elongated claw bearing single microseta.

Abdomen ( Figs 3–5 , 20–23, 34–37 ). About 0.5 as long as total body length, widest across abdominal segment I, then narrowing posteriorly. Each abdominal segment ( AS) I–VIII with undivided dorsal tergite, covered in small tubercules ( Fig. 34 ), as well as paired minute dorsolateral tergites and

Larval description of two species of Mycetina 397 well-developed convex laterotergites ( Figs 3 , 20). Tergites of AS I–VIII with three frayed setae (one macro- and two mesosetae) and single pore, as well as two simple anterior microsetae on each side ( Fig. 20). Each dorsolateral tergite of AS I-VII with single frayed mesoseta; each laterotergite of AS I–VII with three frayed setae (two macro- and one mesoseta) and single pore ( Fig. 20); laterotergite of AS VIII with additional mesoseta as a result of fusing with corresponding dorsolateral tergite ( Fig. 5 ). Membranous area surrounding sclerites with numerous small simple asperities.

18 17 16 20 21 22 19 23

Each hypopleurite of AS I–VIII with two frayed macrosetae ( Fig. 20). Abdominal sternites I–VIII faintly sclerotised, covered in numerous microasperities ( Fig. 35 ); on each side with one anterior microseta as well as two medial and two lateral setae, most of which increasing in size on subsequent segments ( Figs 4 , 21). Abdominal spiracles annular, significantly lesser than on thorax, with single spiracular disk located nearby each spiracle ( Fig. 36 ).

AS IX with tergite, laterotergites and hypopleurites fused, forming two large convex lobes with weak emargination between them, covered in numerous microasperities ( Fig. 22). Each lobe dorsally with single simple anterior microseta, four frayed posterior setae (two meso- and two macrosetae) and single pore; also true urogomphi [see Zaitsev, 2022] present as small, but distinct, heavy sclerotized medial projections, each with single simple seta ( Figs 22, 37 ). Ventrally ( Fig. 23) each lobe with three setae (one simple macroseta and two frayed setae: one meso- and one macroseta). Sternite IX ( Fig. 23) on each side with four simple setae: one anterior microseta and three posterior mesosetae. Pygopod (abdominal segment X) about 0.7 as long as abdominal segment IX, membranous except well-sclerotized protuberances from which setae arise; dorsally each side with four simple mesosetae, ventrally with 2 simple microsetae ( Fig. 23).

Figures

Figs 3–5. M. rufipennis rufipennis, first-instar larva, habitus: 3 — dorsal; 4 — ventral; 5 — lateral. Рис. 3–5. M. rufipennis rufipennis, личинка первого воЗраста, габитус: 3 — сверху; 4 — сниЗу; 5 — сбоку.

Figs 6–15. M. rufipennis rufipennis, first-instar larva: 6–8 — head; 9 — labrum and epipharynx; 10 — antenna; 11 — left mandible; 12 — labio-maxillar complex; 13–14 — mala; 15 — hypopharynx. 6, 9 — left — dorsal view, right — ventral view; 7 — lateral view; 8 — posterior view; 11, 14 — dorsal view; 10, 12–13, 15 — ventral view. Рис. 6–15. M. rufipennis rufipennis, личинка первого воЗраста: 6–8 — голова; 9 — верхнЯЯ губа и Эпифаринкс; 10 — антенна; 11 — леваЯ мандибула; 12 — лабио-максиллЯрный комплекс; 13–14 — мала; 15 — гипофаринкс. 6, 9 — слева — сверху, справа — сниЗу; 7 — сбоку; 8 — сЗади; 11, 14 — сверху; 10, 12–13, 15 — сниЗу.

Figs 32–39. M. rufipennis rufipennis, first (32–37) and second (38–39) instar larva, microsculpture (32–35, 37–39): 32 — frontal sclerite; 33, 38 — pronotum; 34, 39 — abdominal tergite II; 35 — abdominal sternite II; 36 — abdominal spiracle; 37 — urogomphus. Not to scale. Рис. 32–39. M. rufipennis rufipennis, личинка первого (32–37) и второго (38–39) воЗраста, микроскульптура (32–35, 37–39): 32 — фронтальный склерит; 33, 38 — пронотум; 34, 39 — II брюшной тергит; 35 — II брюшной стернит; 36 — брюшное дыхальце; 37 — урогомфа. Не в масштабе.

Figs 29–31. M. rufipennis rufipennis, third-instar larva, habitus: 29 — dorsal; 30 — ventral; 31 — lateral. Рис. 29–31. M. rufipennis rufipennis, личинка третьего воЗраста, габитус: 29 — сверху; 30 — сниЗу; 31 — сбоку.