Nebrioporus stearinus ( Kolenati, 1845 )

Toledo, Mario, 2009, Revision in part of the genus Nebrioporus Régimbart, 1906, with emphasis on the N. laeviventris-group (Coleoptera: Dytiscidae), Zootaxa 2040, pp. 1-111 : 72-73

Nebrioporus stearinus ( Kolenati, 1845)

Fig. 34

Since the description of Hydroporus variegatus Aubé, 1838 a , Hydroporus stearinus Kolenati, 1845 , Deronectes suavis Sharp, 1882 and Deronectes turca Seidlitz, 1887 , there was a long period of confusion due, principally, to the misguided use of some taxa names. In general, since the early XXth century, it has been the general practice to consider the specific epithets variegatus and suavis as formal synonyms for a species with large punctures thinly scattered over the abdomen and a more westerly distribution, while turca would be the single valid specific epithet for a second species with a more eastern distribution, very similar to the former but with smaller and thicker punctures on the abdomen. The specific epithet stearinus , finally, was considered as the valid name for yet a third species, occurring in Azerbaijan (type-locality) and Crete. This usage was still formally followed by e.g. Nilsson (2001; 2003).

The examination of types determined that, contrary to the above interpretation, Hydroporus variegatus Aubé , H. stearinus Kolenati and Deronectes turca Seidlitz are synonyms, whereas Deronectes suavis Sharp can be considered separate taxon. The wrong synonymy of H. variegatus and D. suavis is certainly due to a misinterpretation. In fact, in the description of Deronectes suavis, Sharp (1882: 430) quote: "abdomen magis fortiter punctato" (much more strongly punctured than the body), distinguishing, therefore, this from H. variegatus Aubé with "abdomen paulo magis fortiter punctato" (a little more strongly punctured). Seidlitz (1887: 55) possibly misunderstood H. variegatus to be the form with larger punctures on sternites (with D. suavis , therefore, as its junior subjective synonym) and describes the form with smaller and closer abdominal puncturation with the name D. turca . Sharp’s (1882) description of H. variegatus is cited by Seidlitz (1887) as " variegatus Sharp nec Aubé". Following authors ( Sahlberg 1913; Zimmermann 1920; 1933) used Seidlitz’s (1887) concept of H. variegatus . J. Balfour-Browne (1944a), possibly following this interpretation, rejected the name H. variegatus Aubé because of secondary homonym with Dytiscus variegatus ( Geoffroy 1785) [= Hydroporus palustris (Linnaeus) ], and gave to D. suavis Sharp the status of senior-synonym.

After Kolenati’s (1845) description of Hydroporus stearinus this taxon name was used by Zaitzev (1906),

who provided a diagnosis of the species on the basis of the type and another specimen from Armenia. Later ,

Zimmermann (1933) misidentified with this name a population of Nebrioporus living in Crete; this data was included by Zaitzev (1953) and the resulting distribution reflected in Nilsson (2003). In the present paper, this population from Crete is recognised as a new species ( N. amicorum sp.n.: see above). To finally solve this state of confusion, the points below are clarified:

i) Hydroporus variegatus Aubé, 1836 had been a secondary homonym of Dytiscus variegatus Geoffroy, 1785 during the years 1836 to 1882, before Sharp’s (1882) description of the genus-name Deronectes . When J. Balfour-Browne published his paper in 1944 (see above), the two names were already placed in different genera and, therefore, no longer considered congeneric. Nevertheless, following Article 59.3 of the ICZN, this replacement should be considered valid, the substitute name Deronectes suavis considered in use and, in consequence, Hydroporus variegatus "permanently invalid", although the relevant taxa are no longer considered congeneric; this is also in spite of the fact that Balfour-Browne's (1944) replacement was erroneous and the two taxa are not synonyms.

ii) Available synonyms of H. variegatus Aubé, 1836 are Hydroporus stearinus Kolenati, 1845 and Deronectes turca Seidlitz, 1887 . The former has priority and the latter becomes its junior subjective synonym.

iii) Finally, the study of sufficient material, originating from a geographical range encompassing practically the whole known distribution of both N. suavis and N. stearinus (sensu actualis), confirms that the two taxa are morphologically very similar, being distinguished only for the fine difference of punctuation on sternites; this agrees with Guignot (1958a: 67). In the literature additional characters have been noted (e.g. angles of pronotum, development of subapical spines of elytra, etc.) for their separation; however, these are of no practical use, as they are considered here as within the normal variability of both taxa. Despite of it, there seem to be consistent differences in the punctuation of the sternites between the specimens from two distinct areas (more oriental for N. stearinus and more occidental for N. suavis ), which overlap in few localities of the Anatolian Peninsula (Provinces of Adana, Içel, Erzurum). Some specimens examined from these Turkish localities share a punctuation intermediate between the two forms, whilst the remaining material has the typical punctuation of N. stearinus or N. suavis . In spite of the now resolved nomenclatural difficulties, the status of N. stearinus and N. suavis remains unclear. It is certain that there are localities in Anatolia where the two taxa co-habit and there are limited indications of intermediate forms. It is easily conceivable that N. stearinus and N. suavis are two subspecies, with almost identical morphologies but two sharply separated distributions with minimal overlap. At this stage, further research on the genetic and population structure could be expected to resolve this problem.

Nebrioporus stearinus stearinus and N. stearinus suavis can be separated only with the examination of sternite punctuation, according to the following key:

1. Sternites I–III with punctuation formed by large and dense punctures; space between punctures, especially on sternites I-II, smaller than their diameter ( Fig. 47) ...................................................................... N. stearinus stearinus

- Sternites I–III with punctuation formed by even larger punctures, more disperse; space between punctures similar, or slightly larger, than their diameter ( Fig. 48) .................................................................................. N. stearinus suavis