Coleoptera (LAWRENCE & NEWTON, 1995)

Fikáček, Martin, Skuhrovec, Jiří, Šípek, Petr & Fikáček, for abstracts see, 2010, Abstracts of the Immature Beetles Meeting 2009, Acta Entomologica Musei Nationalis Pragae 50 (1), pp. 321-340 : 328-329

( Coleoptera , Hydrophilidae , Horelophopsinae )

Yûsuke MINOSHIMA 1), Masakazu HAYASHI 2), Norio KOBAYASHI 3) & Hiroyuki YOSHITOMI 4)

1) Systematic Entomology, Graduate School of Agriculture, Hokkaido University, Sapporo, 060-8589 Japan; e-mail: [e-mail]

2) Hoshizaki Green Foundation, Okinoshima 1659-5, Sono-chô, Izumo, Shimane Pref., 691-0076 Japan

3) Hokkaido University Museum, Hokkaido University, Sapporo, 060-0810 Japan

4) Ehime University Museum, Ehime University, Bunkyo-chô 3, Matsuyama, 790-8577 Japan

Horelophopsinae is a subfamily of the family Hydrophilidae established for a single genus Horelophopsis Hansen, 1997 , which includes two rare species, H. avita Hansen, 1997 from New Guinea and H. hanseni Satô et Yoshitomi, 2004 from Japan. The Horelophopsinae was recognised as a basal group of the family Hydrophilidae (s. str.) (HANSEN 1997, ARCHAN- GELSKY et al. 2005). However, this subfamily was not included in most recently published phylogenetic studies. In particular, immature stages of Horelophopsinae have hitherto been completely unknown.

In the recent years, we have examined unknown hydrophilid larvae collected with the adults of H. hanseni from river estuaries of Amami-ôshima and Shikoku, Japan. It was a surprise that these larvae were very similar to larvae of the genus Agraphydrus Régimbart, 1903 ( Hydrophilinae , Hydrophilini , Acidocerina ), despite their expected assignment to the genus Horelophopsis . Adults of the genus Agraphydrus were collected upstream of the collecting sites of Horelophopsis hanseni and the reliable identification were therefore not possible just by association of larvae with adults. To confirm the identity of the unknown larvae, we sequenced ca. 570 bp-long portion of the mitochondrial COI gene of the unidentified larva and adults of Horelophopsis hanseni . In addition, we also compared the larval morphology of the unidentified larva with Agraphydrus larvae.

Firstly, we were able to identify the unknown larvae as H. hanseni based on COI gene analysis. Secondly, morphological comparison of Horelophopsis with Agraphydrus larvae suggests that these larvae are distinguishable by the following characters: 1) sensorial appendage of antennae; 2) inner tooth of the right mandible; 3) inner margin of the left mandible; 4) shape and setae of labium. However, other larval characters are very similar between Horelophopsis and Agraphydrus , and some characters are shared with other genera of the tribe Hydrophilini (e.g., body shape; asymmetrical anterior margin of head capsule; rather long sensorial appendage of antennomere 2; distinctly asymmetrical mandibles; inner margin of stipes with four slightly branched setae; incomplete sclerotised maxillary palpomere 1; abdomen with short setose “prolegs”).

It has been postulated that the subfamily Horelophopsinae is branched off at the base of the Hydrophilidae (s. str.) (HANSEN 1997, ARCHANGELSKY et al. 2005), and the subfamily was therefore recognised as the sister taxon of Hydrophilinae + Sphaeridiinae , which include almost all species of Hydrophilidae (s. str.). Our observations of the larval morphology suggest two plausible conclusions: 1) Horelophopsis is closely related to Agraphydrus and the phylogenetic position of the subfamily Horelophopsinae is dubious; 2) adult morphology of Horelophopsis , which seem to be unique within the Hydrophilidae , may be a result of its adaptation to the habitat.

ARCHANGELSKY M., BEUTEL R. G. & KOMAREK A. 2005: Hydrophiloidea. 10.1. Hydrophilidae . Pp. 157–183. In: BEUTEL R. G. & LESCHEN R. A. B. (eds.): Coleoptera, Volume 1: Morphology and Systematics (Archostemata, Adephaga, Myxophaga, Polyphaga partim). Handbook of Zoology, Vol.IV: Arthropoda: Insecta. Walter De Gruyter, Berlin, 567 pp.

HANSEN M. 1997: A new subfamily for a remarkable new genus and species of Hydrophilidae from New Guinea ( Coleoptera : Hydrophilidae ). Annales Zoologici (Warszawa) 47: 107–110.