Helochares (Helochares) pallens ( MacLeay, 1825 )

Minoshima, Yûsuke & Hayashi, Masakazu, 2011, Larval morphology of the Japanese species of the tribes Acidocerini, Hydrobiusini and Hydrophilini (Coleoptera: Hydrophilidae), Acta Entomologica Musei Nationalis Pragae (suppl.) 51, pp. 1-118 : 53-60

Helochares (Helochares) pallens ( MacLeay, 1825)

( Figs. 1E , 29–34 )

Material examined. JAPAN: HONSHÛ: Shimane-ken : 1 L2, 4 L3, Okinoshima , Sono-chô, Izumo-shi (artificial pond made for conservation purpose), 25.viii.2007, MH ; 38 L1, same locality, 13.v.2008 (egg cases carried by adults collected in the field, 15.v.2008 fixed), MH .

General morphology. Third instar. Colour. Head and sclerotised parts light yellowish brown; membranous parts milky white ( Fig. 1E ).

Head. Nasale projecting further than epistomal lobes ( Fig. 33A ). Epistomal lobes rounded, somewhat asymmetrical; right lobe projecting further than left lobe.

Antenna ( Fig. 33B ) short, somewhat slender. Scape slightly shorter than pedicel.

Mandibles ( Figs. 33 C–D): Inner teeth of left mandible with a small subapical tooth; inner face of mandible serrate basally.

2 Based on all instars of H. (Helochares) pallens and H. (Hydrobaticus) nipponicus , and the first instar of H. (Hydrobaticus) anchoralis .

Maxilla ( Figs. 33 E–F): Maxillary palpomere 1 about as long as palpomeres 3 and 4 each, palpomere 2 the shortest; palpomere 1 the widest.

Labium ( Figs. 33 G–H): Mentum bearing small, strong cuticular spines dorsally. Labial palpi about as long as mentum; palpomere 1 much shorter than palpomere 2.

Abdomen. Segment 1 with four dorsal sclerites on each side; two small sclerites on anteromedian part, posterior one larger than anterior one; remaining two sclerites very small, situated behind the former dorsal sclerites, each bearing one rather long seta and sometimes undetectable; segments 2 to 7 similar to segment 1 but with very indistinct dorsal sclerites.

Spiracular atrium ( Fig. 32B ): Segment 8 with large, oval dorsal plate; plate with four projections on median part of posterior edge, each median projections slightly bifid, with two setae; lateral portion of dorsal plate with three setae each, median one long, remaining two rather long; procercus with one rather short, stout seta and two rather long setae. Segment 9 trilobed; median lobe with one small, incompletely sclerotised projection on each side; two rather short and two moderately short setae on posterior edge of median lobe; each lateral lobe with two long setae on posterior edge.

Second instar. Similar to third instar larva, but more weakly sclerotised.

Head. Antenna: Scape shorter than pedicel ( Fig. 31B ).

First instar. Similar to second instar larva, but more weakly sclerotised.

Head. Epistomal lobes somewhat asymmetrical; inner part of lobes strongly curved, lateral part slightly rounded ( Fig. 29C ).

Antenna proportionally short, stout ( Fig. 30A ). Scape distinctly shorter than pedicel.

Maxilla: Maxillary palpomere 3 slightly shorter than palpomere 4 ( Figs. 30 D–E).

Labium: Labial palpi longer than mentum ( Figs. 30 F–G).

Thorax. Mesonotum with six long setae on each posterior dorsal sclerite. Metanotum with six long setae on each dorsal sclerite.

Primary chaetotaxy of head. Frontale altogether with 44 sensilla ( Figs. 29A, C ). FR 2 situated more anteriorly and mesally than FR 1. FR 5 short seta; FR 6 moderately long scalelike seta, close to FR 7; FR 7 moderately short. Nasale with a group of six stout, short setae and three pore-like sensilla (gFR1), the latter sensilla on lateral margin of median two large teeth. Each epistomal lobe with two short setae on inner part, and one short, scale-like seta on median part of outer margin (gFR2). FR 10 placed posteriorly to FR 9; pore-like sensillum ( FR 14) situated anteriorly to inner margin of antennal socket. Location of FR 11–13 slightly asymmetrical; FR 12 situated between FR 11 and FR 13 but laterally of line connecting them; FR 11 situated anteriorly to FR 12, close to lateral seta on nasale; sensilla on left lobe more closely aggregated than those on right lobe.

Parietale ( Figs. 29 A–B): PA 1–5 forming irregular row. PA 7 very long, trichoid seta; PA 12 rather long seta. PA 20 rather long seta. PA 17 close to PA 16, situated more posteriorly and more mesally than PA 16; PA 16 long, narrow scale-like seta. PA 26–28 situated ventrally at midlength and in lateral 0.36 of parietale; PA 27 between PA 26 and PA 28. Two pore-like sensilla ( PA 29–30) located ventrally on basal fifth of parietale.

Antenna ( Fig. 30A ): Antennomere 2 with one pore-like sensillum ( AN 6) situated dorsally close to distal margin of sclerite; five setae ( AN 7–11) on intersegmentary membrane between antennomeres 2 and 3; AN 7 rather short, rounded apically; AN 8 rather stout, shorter than AN 7; AN 9 minute; AN 7–9 on outer face of antenna next to sensorium SE 1; setae AN 10–11 on inner face of antenna; AN 10 long, narrow scale-like, AN 11 short, both setae situated close to each other.

Mandible ( Figs. 30 B–C): MN 2 between MN 1 and MN 3, close to MN 1; MN 4 on lateral face. MN 5 pore-like.

Maxilla ( Figs. 30 D–E): One pore-like sensillum ( MX 12) and one very long seta ( MX 13) situated dorsally on outer face of palpomere 1, close to distal margin of sclerite; MX 13 situated more ventrally than MX 12; one long seta ( MX 14) situated ventrally on median part of distal margin. MX 23 on distal part of outer face of sclerite; MX 20 behind MX 23; MX 21 situated ventrally on anterolateral part; MX 22 behind MX 21. MX 24 long seta.

Labium ( Figs. 30 F–G): LA 1 very long.

Secondary chaetotaxy of head. Second instar. Frontale ( Fig. 34A ): One short secondary seta between FR 1 and FR 5, close to frontal line.

Parietale ( Fig. 34A ): One seta located close to frontal line, medially of line connecting PA 6 and PA 7. Two short secondary setae situated posteriorly to lateral part of antennal socket, one slightly posteriorly to PA 9, one slightly laterally of PA 8. One pore-like secondary sensillum and one rather short secondary seta close to outer margin of antennal socket, between PA 9 and PA 19; the seta situated more mesally than pore-like sensillum. One rather short secondary seta behind PA 21; one rather short secondary seta situated close to PA 14, laterally of line connecting PA 13 and PA 14; one rather short secondary seta between PA 15 and PA 16; one rather short secondary seta situated slightly anteriorly to PA 17; one short secondary seta close to PA 18.

Mandible ( Figs. 31 C–D): Three pore-like secondary sensilla on medioposterior part of outer face of mandible; three rather short secondary setae located basally on outer part of mandible.

Maxilla ( Figs. 31 E–F): Outer face of stipes with three trichoid secondary seta; one very long seta on apical part; remaining setae rather long, situated on anterior third and two-thirds respectively; inner part of stipes with one rather long secondary seta situated ventrally on anterior portion of sclerite.

Labium ( Figs. 31 G–H): Dorsal surface of mentum with three rather short, stout secondary setae on lateral face, one on apical part, two on median part; one pair of rather short, moderately stout setae situated dorsally on median part of anterior margin of mentum.

Third instar. Parietale ( Figs. 34 B–D): One to two rather long to rather short secondary setae close to frontal line, medially of line connecting PA 6 and PA 7. One pore-like secondary sensillum and one or two rather short secondary setae close to outer margin of antennal socket, between PA 9 and PA 19; pore-like sensillum close to PA 19, setae close to PA 9. One short secondary seta between PA 22 and PA 26, but sometimes absent; one or two short secondary setae close to PA 18 but sometimes absent.

Habitat. Standing water. Larvae were found in water ( HAYASHI 2009a).

Identification. First instar larvae were reared from the identified female which carried an egg case underneath the abdomen. Second and third instar larvae were collected in the field and compared with the morphology of the reared first instar larvae; as their morphology matched the first instar larvae in all characters except those known to vary between instars, we identify them as clearly belonging to H. pallens .

Figures

Fig. 1. Habitus of the third instar larvae of Acidocerini and Hydrobiusini. A – Agraphydrus narusei (Satô, 1960), dorsal and lateral view; B – Enochrus (Holcophilydrus) simulans (Sharp, 1873), dorsal view; C – E. (H.) umbratus Sharp, 1884, dorsal view; D – E. (Methydrus) japonicus (Sharp, 1873), dorsal view; E – Helochares (Helochares) pallens (MacLeay, 1825), dorsal view; F – H.(Hydrobaticus) nipponicus Hebauer, 1995, dorsal view; G – Hydrobius pauper Sharp, 1884, dorsal and ventral view.

Fig. 29. Head capsule of Helochares (Helochares) pallens (MacLeay, 1825), first instar.A – dorsal view; B – ventral view; C – detail of anterior margin of head capsule, dorsal view.

Fig. 30. Head appendages of Helochares (Helochares) pallens (MacLeay, 1825), first instar. A – antenna, dorsal view; B–C – mandibles, dorsal view; D – maxilla, dorsal view; E – maxilla, ventral view; F – labium, dorsal view; G – labium, ventral view.

Fig.31. Helochares (Helochares) pallens (MacLeay, 1825), second instar.A – clypeolabrum, dorsal view; B – antenna, dorsal view; C–D – mandibles, dorsal view; E – maxilla, dorsal view; F – maxilla, ventral view, G – labium, dorsal view; H – labium, ventral view.

Fig. 32. Helochares (Helochares) pallens (MacLeay, 1825), third instar. A – head, dorsal view; B – spiracular atrium, dorsal view.

Fig. 33. Helochares (Helochares) pallens (MacLeay, 1825), third instar.A – clypeolabrum, dorsal view; B – antenna, dorsal view; C–D – mandibles, dorsal view; E – maxilla, dorsal view; F – maxilla, ventral view; G – labium, dorsal view; H – labium, ventral view.

Fig. 34. Helochares (Helochares) pallens (MacLeay, 1825), chaetotaxy of head capsule, dorsal view. A – median part of head capsule, second instar. B–D – third instar larva: B – median part of head capsule; C – intraspecific variation of secondary sensilla between PA6 and PA7; D – intraspecific variation of secondary sensilla on outer part of antennal socket. Secondary sensilla are marked by a black rhombus.