Landcare Research - Manaaki Whenua

Landcare-Research -Manaaki Whenua

FNZ 2 - Osoriinae (Insecta: Coleoptera: Staphylinidae) - Historical Review

McColl, HP 1982. Osoriinae (Insecta: Coleoptera: Staphylinidae). Fauna of New Zealand 2, 96 pages.
( ISSN 0111-5383 (print), ; no. 02. ISBN 0-477-06688-7 (print), ). Published 23 Dec 1982

Historical Review

The Osoriinae are immediately recognisable by their lack of paratergites on the abdomen, which gives them a distinctively cylindrical form, and by their prominent procoxae having a transverse sulcus on the anterior face. It was the absence of paratergites which led Blackwelder (1942) to elevate the tribe Osoriini of subfamily Oxytelinae to subfamily status. He placed three tribes - Osoriini, Leptochirini, and Lispinini - in Osoriinae, distinguishing Osoriini by the prominent procoxae with the transverse anterior sulcus. Moore (1964) used these characters to define Osoriinae, and does not regard the Lispinini, which he elevates to subfamily status, as being closely allied to Osoriinae.

Holotrochus Erichson, 1840, the genus to which all species described from New Zealand had been assigned, was included in the Osoriini by Blackwelder (1943). When erecting Holotrochus, Erichson distinguished it from Osorius by the absence of spines on the protibiae and by the rounded apex of the mentum. Lacordaire (1854) added the near-parallel borders of the prothorax to this definition. Blackwelder (1943) redefined the genus, retaining Duponchel's (1841) choice of Holotrochus volvulus Erichson, 1840 from Puerto Rico as the type-species. Other West Indian species were included. Blackwelder regarded the elevated prosternal process and the impunctate metasternum as important generic characters, and described secondary sexual characters of the seventh and eighth abdominal sternites of male H. volvulus.

Fagel (1955) revised the genus, keeping H. volvulus as the type-species but disagreeing with Blackwelder on the relevance of several characters. He included Palearctic, Ethiopian, Oriental, and Neotropical species. His diagnostic characters for Holotrochus included the presence of sutural striae, lack of modification of the mandibles, which have a flat upper surface, and the absence of secondary sexual characters in the male. He further confused matters by assigning three New Zealand species described by Fauvel (1900) - anophthalmus, helmsi, and vagepunctus - to a new genus, Typhlhotrochus, on the basis of absence of sutural striae and, in the male, presence of a small carina on the right mandible and secondary sexual characters on the last sternite. These three species do not conform to Fagel's diagnosis of Typhlhotrochus. All have sutural striae, and in both sexes of helmsi and vagepunctus the right mandible has a small but obvious carina. H. anophthalmus is known only from Fauvel's two male specimens, which possess a similar mandibular carina. Male helmsi and vagepunctus show only very slight modification of sternites 7 and 8, and in anophthalmus these are unmodified. In Typhlhotrochus the eye is supposedly composed of 5 or 6 facets. The eye of anophthalmus is greatly reduced, consisting of 1 small facet (overlooked by Fauvel). The eye of helmsi comprises 6 to 9 facets, and that of vagepunctus about 10, Thus, inclusion of these New Zealand species in Typhlhotrochus is not warranted. (It is interesting to note that Fagel omitted H. microphthalmus Fauvel, 1900 from Typhlhotrochus, since the four Fauvel species were described together, and appear to have been kept together in the Fauvel collection.)

The New Zealand species of Osoriinae have characters that do not conform to Erichson's, Fagel's, or Blackwelder's concept of Holotrochus. The sutural striae, carinate mandibles of both sexes, and in the male the frequent occurrence of secondary sexual characters do not fit Fagel's descriptions, and the small prosternal process, pubescence, punctate metasternum, and tibial spines deviate from Erichson's and Blackwelder's diagnoses. Thus, they are species in search of a genus, and I here propose two new genera for New Zealand's Osoriinae; Nototrochus and Paratrochus. I am aware that erection of genera only on a geographical basis can be unsound, but until Holotrochus and its close relatives are redefined using constant characters, preferably of phylogenetic relevance, I feel that new genera for the New Zealand Osoriinae are justified.

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