Plateumaris obsoleta Jacobson, 1894

Geiser, Elisabeth, 2023, Revision of the Palaearctic species of the genus Plateumaris C. G. Thomson, 1859 (Coleoptera, Chrysomelidae, Donaciinae), ZooKeys 1177, pp. 167-233 : 167

? Plateumaris obsoleta Jacobson, 1894

Figs 14 , 15 , 16

Type locality.

Russia, Far East, Primorsky Krai, Bay of Posyet.

Type material.

Holotype: Russia • 1 ♀; Far East; Primorsky Krai; Bay of Posyet; ZIN. Only the holotype exists. It was examined from photographs only (Figs 14 , 15 ).

Remarks.

At first, I intended to synonymise P. obsoleta with P. sericea based on studies of the type material and description, but doubts remained that it is more likely that P. obsoleta is a synonym with P. shirahatai . I am sure that P. obsoleta , described based on one female specimen and never recorded again in more than 100 years, is a synonym. However, I cannot prove if it belongs to P. sericea or to P. shirahatai because it is impossible to distinguish these two species by external morphological characters. These two species differ only by subtle morphological differences in the apical part of the endophallus (Fig. 12 ).

Plateumaris obsoleta was described by Jacobson (1894) (see Geiser and Geiser 2023) based on a single specimen collected in Russia, Far East: Posyet in Primorsky Krai. No other specimen of P. obsoleta has been recorded in the last 130 years; it only appears regularly in identification keys. Jacobson found it most similar to P. discolor and P. sericea . All characters he described are also typical characters of P. sericea . Whereas many specimens of P. sericea have a sharp and prominent tooth at the metafemur, in some specimens this tooth can be blunt or is lacking completely. According to Jacobson (1894) this holotype is a male specimen. However, Bieńkowski (2014) wrote in his key: only one single female specimen is known. He also published four drawings of some details of this specimen. In fact, the holotype is stored in ZIN, from which I obtained some detailed photographs (Figs 14 , 15 , 16 ).

The controversy about the sex of this specimen can now be solved: the apical part of the ovipositor protrudes, which Jacobson misinterpreted as a part of the aedeagus. Although Askevold (1991) had not seen the holotype, but he suspected that the specimen described by Jacobson was female. According to the original description, "Pygidium apice rotundatum" is a description of a female specimen because no known males of species of Plateumaris have a rounded pygidium. All the characters described by Jacobson and the characters which could be examined on the photographs of the holotype fit easily within the variation range of P. sericea . However, P. shirahatai also occurs in southern Primorsky Kraj ( Hayashi and Tominaga 2005). Photographs (Figs 14C , 15A ) show that many features of P. obsoleta are consistent with those of Plateumaris shirahatai identified in Primorsky (Fig. 13D, E ) including metallic legs and an indistinct median line on the pronotum. In addition, the antennae of P. shirahatai are variable in colouration, with some individuals having the same colouration as the type of P. obsoleta . This strongly supports the possibility that P. shirahatai is a synonym of P. obsoleta . On the other hand, P. obsoleta has a small metafemoral tooth, but it is suspected that the shape of this tooth may be malformed. This is a recurrent problem with species described on single specimen (pers. comm. M. Hayashi, 04 Apr 2023). Therefore, it seems more likely that P. obsoleta is synonym with P. shirahatai than with P. sericea , that was also suspected by Askevold (1991), Hayashi and Tominaga (2005), and Warchałowski (2010). The pronotum of the type specimen of P. obsoleta (Fig. 15A ) looks similar to the pronotum of P. shirahatai (Fig. 13A, D ). All in all, the decision of the synonymisation cannot be made now.

Perhaps it will be possible in the near future to solve this problem without destroying this single specimen with more elaborate methods than historical DNA analysis. The solutions used to extract the DNA may be destroy the connecting membranes between the chitinous parts. Nowadays, nobody can guarantee that this specimen would NOT be damaged! Additionally, it is very questionable whether the results will be clear enough. Usually, the DNA in old, stored insects is fragmented and cannot be sufficiently reconstructed to make the decision to which species the specimens belong. Plateumaris sericea and P. shirahatai are closely related, which was proofed by DNA analysis ( Hayashi and Sota 2014). There are only few sections of the DNA where the differences are shown. It is unlikely that exact these few sections could be tracked down by the current methods. Therefore, according to the current state of knowledge, I cite it as a "probable new synonymy". If it once can be prooved that P. shirahatai and P. obsoleta are synonyms, the name P. obsoleta has priority because it was described in 1894 and P. shirahatai in 1971.

Figures

Figure 12. Schematic sketch of the endophallus. Median ejaculatory guide blackened A Plateumaris sericea (and specimens identified as P. discolor) with apex of median ejaculatory guide rounded. The endophalli of specimens from Poland, Italy and Japan all look the same as in this sketch B Plateumaris shirahatai with apex of median ejaculatory guide notched (drawings by G. Geiser based on photographs from Askevold 1991 and Hayashi 2020).

Figure 13. Plateumaris shirahatai A habitus (photograph by K. Matsumoto) B cap of tegmen, shape slightly variable C median lobe (B, C from Hayashi 2020) D, E habitus from dorsal and ventral F endophallus (D-F photographs by M Hayashi). Scale bars: one unit - 1 mm (A); 0.5 mm (B-E).

Figure 14. Plateumaris obsoleta holotype A habitus B lateral view C right antennae with red base of the antennomeres (photographs by A. Moseyko).

Figure 15. Plateumaris obsoleta holotype A pronotum B ovipositor protruding from abdomen (photographs by A. Moseyko).

Figure 16. Plateumaris obsoleta: All labels tagged to the holotype (photographs by A. Moseyko).