Psammoecus simoni Grouvelle, 1892

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 : 94-98

Psammoecus simoni Grouvelle, 1892

[Japanese name: Hababiro-semaru-hiratamushi] ( Figs 1 C, D, 4–7)

Identification. The examined larvae were obtained by rearing adults of P. simoni . Identifications of these larvae were confirmed by comparing 658 bp fragments of mitochondrial DNA gene sequences (COI) among the larvae and adults of this species and other Psammoecus species in order to exclude the possibility of contamination of eggs of other taxa from dead leaves provided as substrate. Genetic differences among species were 15.17–17.25%, and the larvae were grouped with P. simoni , which confirmed the identification ( Table 1 ). Recently, other studies performed identification of larvae by such a molecular-based method (e.g. Hayashi & Sota 2010).

1st instar larva. Head capsule width: 0.22–0.26 mm (n=92).

Body ( Figs 1 C, 4A). Translucent, apices and molae of mandibles and region containing gut darkened.

Standard error (%) Thorax and abdomen ( Fig. 4 A). Shape easily deformed according to posture. Prothorax subquadrate, maximum width around anterior margin; meso- and metathorax rounded; 1st to 7th abdominal segments transversely oblong, 7th segment widest posteriorly, 8th trapezoidal, maximum width near posterior margin, 9th absent, 10th elongate. Pubescence composed of some medium length and short setae, a pair of long fine lateral setae on 3rd to 8th segments, positioned in each maximum width of segment. Legs elongate; trochanter quadrate, with a several short setae near anterior margin; femur with several medium length to long setae and some short sparse setae; tibiotarsus moderately thin, a few medium length and many short setae densely; claw more than 0.5 times as long as tibiotarsus, with two short setae.

Specimens examined. Slide preparations of two specimens.

2nd instar larva. Head capsule width: 0.29–0.32 mm (n=36).

General morphology ( Fig. 4 B). Very similar to 1st instar larvae. Length of a pair of long fine lateral setae of abdominal segments relative to body length shorter than that on 1st instar larvae.

Head ( Figs 4 B, 5A–F). Transversely oblong. Frontal arms U-shaped ( Fig. 5 A). Antennae relatively stout and rounded; 1st antennomere stout and short; 2nd antennomere more than twice longer than 1st, maximum width at anterior 1/3, anterior portion narrowed gradually, sensorium around apex of inner margin moderately long and thick; 3rd antennomere comparatively thick, less than twice longer than 1st, with relatively short seta on apex ( Fig. 5 B). Mandibles triangular, with three teeth on the apex of right mandible, with four closely spaced teeth on the apex of left mandible; a triangular prostheca on inner margin of anterior 1/4, maximum width in apical half; molae with many small strong cuticular spines, base of inner margin of left mandible protruded roundly with several fine cuticular spines ( Fig. 5 C, D). Maxilla longitudinally oblong, dorsally with many but relatively sparse, small spines near base of stipes, with four long teeth near apex ventrally, inner margin of mala with relatively long setae in a longitudinal row; maxillary palpus with three palpomeres, 1st palpomere short, 2nd less than twice longer than 1st, 3rd about three times longer than 2nd with a few very small spines on apex ( Fig. 5 E).

Specimens examined. Slide preparations of two specimens.

3rd instar larva. Head capsule width: 0.36–0.42 mm (n=42).

General morphology ( Fig. 6 A). Length of a pair of long fine lateral setae of abdominal segments relative to body length shorter than that of 2nd instar larvae.

Specimens examined. Slide preparations of two specimens.

4th instar larva. Head capsule width: 0.45–0.52 mm (n=28).

General morphology ( Fig. 6 B). Thorax and abdomen comparatively more sclerotized than previous instar larvae.

Specimens examined. Slide preparations of two specimens.

Last instar larva. Head capsule width: 0.56–0.63 mm (n=12).

General morphology ( Fig. 6 C). Very similar to 4th instar larvae.

Head ( Figs 6 A, 7A–F). Transversely oblong. Frontal arms U-shaped ( Fig. 7 A). Antennae elongate; 1st antennomere stout; 2nd antennomere more than twice longer than 1st, maximum width at anterior 1/3, sensorium around apex of inner margin short; 3rd antennomere less than twice longer than 1st, a long seta on apex ( Fig. 7 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 triangular prostheca on inner margin of anterior 1/4, maximum width around basal 1/4; molae with many small strong cuticular spines, base of inner margin of left mandible comparatively widely protruded with several fine cuticular spines ( Fig. 7 C, D). Maxilla longitudinally oblong, stipes dorsally with many dense small spines on middle, with four long teeth near apex ventrally, inner margin of mala with relatively long setae in a longitudinal row; maxillary palpus with three palpomeres, 1st palpomere short, 2nd about twice longer than 1st, 3rd more than twice longer than 2nd with several very small spines on apex ( Fig. 7 E). Six stemmata on each side ( Fig. 7 A).

Thorax and abdomen ( Figs 6 A, 7G). Shape easily deformed according to posture. Prothorax subquadrate, maximum width around anterior margin; meso- and metathorax subquadrate, maximum width around half; 1st to 7th abdominal segments transversely oblong, 7th segment widest posteriorly, posterior angles pointed, 9th absent, 10th elongate. A pair of long fine lateral setae and some medium length and short setae on thorax and 3rd to 8th segments, a pair of long setae positioned in each maximum width of segment, no long setae on 1st and 2nd segments, some short setae around posterior margins of 10th. Legs elongate; trochanter quadrate, with a few short to medium length setae; femur with a few long seta and some short to medium length sparse setae; tibiotarsus thin, some short to medium length setae sparsely; claw a little more than 0.5 times as long as tibiotarsus, with two short setae.

Specimens examined. Slide preparations of two specimens.

Biology. It was inferred through DNA methods that the adults had laid their eggs on dead leaves during rearing. Thus all developmental stages (eggs, larvae, pupae and adults) of the Psammoecus species seem to inhabit the same environment.

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 4. Habitus of larval stages of Psammoecus simoni Grouvelle. A, First instar; B, second instar. Scales: 1.0 mm; a for A; b for B.

FIGURE 5. Psammoecus simoni Grouvelle, 2 nd 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, labium, ventral view; G, left foreleg, dorsal view; H, 8 th and 10 th abdominal segments, dorsal view. Scales: 0.1 mm; a for A, G and H; b for B; c for C – F.

FIGURE 6. Habitus of larval stages of Psammoecus simoni Grouvelle. A, Third instar; B, fourth instar; C, fifth instar. Scales: 1.0 mm; a for A; b for B and C.

FIGURE 7. Psammoecus simoni Grouvelle, 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, labium, ventral view; G, left foreleg, dorsal view; H, 8 th and 10 th abdominal segments, dorsal view. Scales: 0.1 mm; a for A, G and H; b for B; c for C – F.

Tables

TABLE 1. Pairwise genetic distances (K 2 P distance) among five Psammoecus species. Standard errors are shown above the diagonal and were obtained by a bootstrap procedure (1000 replicates).

P. simoni	P. scitus (Okinawa Is.)	P. scitus (Ishigaki Is.)	P. fasciatus	P. bipunctatus ( KJ967300 )	Larva
P. simoni -	1.84	1.84	1.72	1.63	0.29
P. scitus (Okinawa Is.) 16.46	-	0.20	1.74	1.73	1.88
P. scitus (Ishigaki Is.) 16.66	0.31	-	1.72	1.71	1.88
P. fasciatus 15.19	17.06	16.86	-	1.59	1.77
P. bipunctatus ( KJ967300 ) 15.37	16.13	15.74	15.17	-	1.63
Larva 0.61	17.05	17.25	15.77	15.37	-
Nucleotide sequence distance (%)