Psammoecus scitus Yoshida & Hirowatari, 2014

Yoshida, Takahiro & Hirowatari, Toshiya, 2015, Larval and pupal morphology of three species of the genus Psammoecus Latreille (Coleoptera: Silvanidae: Brontinae) in Japan with reference to the number of larval instars, Zootaxa 3937 (1), pp. 90-102 : 92-94

Psammoecus scitus Yoshida & Hirowatari, 2014

[Japanese name: Yotsumon-semaru-hiratamushi] ( Figs 1 A, B, 2 and 3)

Identification. The examined larvae were collected with adults of P. scitus and there were no other adults of Psammoecus species. The identification was confirmed by rearing some of these larvae to adult stage. Last instar larva. Head capsule width: 0.59–0.67 mm (n=8).

Body ( Figs 1 A, 2A). Elongate. Head reddish-brown basally, frontal arm white, antennae blackish, bases and apices of 2nd and 3rd antennomeres white, 1st somewhat lightened. Thorax and abdomen blackish-brown, darker toward posterior apex, lightened around lateral, anterior and posterior margins of each segment, 10th abdominal segment reddish-brown, lighter toward apex.

Head ( Figs 2 A, 3A–E). Transversely oblong. Frontal arms U-shaped ( Fig. 3 A). Antennae elongate; 1st antennomere stout; 2nd antennomere less than three times longer than 1st, maximum width near apex, sensorium around apex of inner margin comparatively long and thick; 3rd antennomere less than three times longer than 1st, very short fine seta on apex ( Fig. 3 B). Mandibles triangular, with three closely spaced teeth on the apex of right mandible, with four closely spaced teeth on the apex of left mandible; a long triangular prostheca on inner margin of anterior 1/5, maximum width in basal half; molae on bases of inner margins with many small strong cuticular spines, base of inner margin of left mandible protruded with several fine cuticular spines ( Fig. 3 C, D). Maxilla longitudinally oblong, stipes dorsally with many moderately dense small spines on middle, with four long teeth near apex on ventral, inner margin of mala with relatively thick and long setae in a longitudinal row, anterior three setae thick; maxillary palpus with three palpomeres, 1st palpomere short, 2nd about 2.5 times longer than 1st, 3rd about 1.5 times longer than 2nd with several very small spines on apex ( Fig. 3 E). Six stemmata on each side ( Fig. 3 A).

Thorax and abdomen ( Figs 2 A, 3G). Shape easily deformed according to posture. Prothorax subquadrate; meso-, metathorax and 1st to 4th and 8th abdominal segments relatively wide, 5th to 7th subquadrate, 9th absent, 10th elongate, posterior angles of 8th protruding a little. A pair of long fine lateral setae and some medium length setae on lateral segments, it on 1st comparatively short. Legs elongate; trochanter quadrate, with a few medium length setae; femur with a long seta and a few short to medium length setae very sparsely; tibiotarsus thin, some medium length and many short moderately dense setae; claw a little more than 0.5 times as long as tibiotarsus, with two short setae ( Fig. 3 F).

Specimens examined. 8 exs. (including one slide-mounted).

Pupa. Body length: 2.30–2.58 mm (n=6).

Body ( Fig. 2 B, C). Moderately flattened. Surface white (immature) to yellowish-brown, antennae, anterior and lateral portions of pronotum, wing pads and lateral portions of abdomen somewhat darkened ( Fig. 1 B).

Thorax ( Fig. 2 B, C). Prothorax transversely oval, dorsal surface enlarged, a pair of oblong pits on anterior portion gradually shallower toward posterior portion, lateral portions with furrows, shallow furrow along the posterior margin, a small tooth on each anterolateral margin, lateral margins with three large teeth, posterior angles protruding a little. Mesothorax transversely oblong, with furrow along anterior margin, shallow longitudinal furrow at the middle extending to 6th tergite, posterior portions near bases of each wing pad depressed, with several longitudinal furrows on each basal wing pad. Metathorax comparatively longitudinally large, surface uneven, furrow on middle anterior portion comparatively deep.

Abdomen ( Fig. 2 B, C). First to 6th abdominal segments transversely oblong, 7th triangular, 8th segment transverse, 9th small; posterior angles of 3rd to 6th segments protruding a little, with several short teeth; anterior angles of 4th to 7th segments ventrally with sockets for teeth of immediately anterior segments (teeth of 3rd and 6th in Fig. 2 B fitting into sockets of segments immediately posterior). Large protuberance on each lateral portion of 2nd to 7th and 9th segments; protuberance I on positioned posteriorly and triangular, II positioned mid-laterally, enlarged in apical half, apex pointed posterolaterally, III positioned anteriorly, II, IV and V similar in shape, positioned between anterior angles and mid-laterally, mostly enlarged, bases narrowed, apices pointed posterolaterally, VI positioned at anterior angles, mostly enlarged, apices pointed almost laterally, VII on bases of lateral portions, similar to shape of II and III. Eighth tergite with longitudinal ridge in the middle; middle of posterior margin and right posterolateral margin pointed. Ninth segment completely divided into tergite and sternite, sternite bilobed.

Specimens examined. 6 exs. (including one slide-mounted).

Biology. The larvae of this species were collected from dead leaves of Japanese pampas grass Miscanthus sinensis Andersson with their adults.

In the laboratory, we observed that the pupae fixed their body by attaching the apex of abdomen to dead leaves in the petri dish. The posterior three abdominal segments were covered with the exuvium of last instar larva. In particular, the posterior two abdominal segments were tightly enveloped with the exuvium of 10th abdominal segment ( Fig. 1 B). Surface of immature pupa was mostly white.

Figures

FIGURE 1. Photographic images of immature stages of Psammoecus spp. A and B, Psammoecus scitus Yoshida & Hirowatari; C and D, P. simoni Grouvelle. A and D, Last instar larva; B, pupa; C, first instar larva. Scale: 1.0 mm.

FIGURE 2. Habitus of immature stages of Psammoecus scitus Yoshida & Hirowatari. A, Last instar larva; B and C, pupa in dorsal (B) and ventral (C), with midlegs missing. Scales: 1.0 mm; a for A; b for B and C.

FIGURE 3. Psammoecus scitus Yoshida & Hirowatari, last instar. A, Head, dorsal view; B, right antenna, dorsal view; C, right mandible, ventral view; D, left mandible, ventral view; E, right maxilla, dorsal view; F, left foreleg, dorsal view; G, 8 th and 10 th abdominal segments, dorsal view. Abbreviations: cl—claw; fa—frontal arm; fe—femur; ma—mala; mo—molae; mp—maxillary palpus; pr—prostheca; se—sensorium; sp—stipes; st—stemmata; ti—tibiotarsus; tr—trochanter; 1 a— 1 st antennomere; 2 a— 2 nd antennomere; 3 a— 3 rd antennomere; 8 as— 8 th abdominal segment; 10 as— 10 th abdominal segment. Scales: 0.1 mm; a for A, F and G; b for B; c for C – E.