Platyceraphron muscidarum, Kieffer, 1906

Forshage, Mattias, Hanssen, Oddvar & Staverløkk, Arnstein, 2016, Platyceraphron Kieffer, 1906 (Hymenoptera, Megaspilidae) in the Nordic countries, Norwegian Journal of Entomology 63, pp. 125-129 : 126-128

Platyceraphron muscidarum in other Nordic countries

No specimens from Finland or Denmark are known. Curators of the Helsinki and København museum as well as active microhymenoptera collectors confirm this.

Biology of Platyceraphron

The old Swedish specimen is reared from oak ( Quercus robur ), emerging in february. No host is specified. Since the collector is a coleopterist, the wasp probably emerged from a whole piece of wood brought in for rearing beetles.

More substantial biological information exists for the type specimens of P. muscidarum and its synonym P. corticis Kieffer, 1906 . They were reared from Diptera puparia in Populus trees in Amiens, France ( Kieffer 1906). Since the trees were referred to by their French name “peuplier”, we cannot be certain what tree species it concerns. Aspen ( Populus tremula ) is most commonly referred to in French as “tremble”, so it is more likely to be a poplar species, perhaps the black poplar ( Populus nigra ) which is common in the area. Kieffer details how collector Léon Carpentier reared the types of P. muscidarum from four different kinds of fly puparia. Most specimens were from puparia identified as Lonchaea tarsata Fallén, 1820 , and L. laticornis Meigen, 1826 (both Lonchaeidae ), but these identifications should be taken as very tentative since L. tarsata is not known as a saproxylic species and L. laticornis represents a species complex (McGowan, pers. comm.). Other specimens were from puparia of “ Aricia , probablement A. laeta ”, which corresponds to Phaonia laeta (Fallén, 1823) ( Muscidae ), and an unidentified fly. Kieffer’s phrase “Muscide non déterminée” does not necessarily imply Muscidae , since he refers to the lonchaeids as “Muscides” too. Dessart (1971) studied the type material, selected lectotypes and synonymised the two species, which were differentiated by size and an inconsequential minor difference in the antenna. Identifications of the host puparia have not been confirmed. If the Phaonia record is correct, Platyceraphron is obviously capable of utilising as host different muscomorph flies in the subcorticeous environment.

Norwegian specimens as well as the recent Swedish one are all caught in traps, which unfortunately give little details about the biology of the species. The three trapping sites had a dominance of aspen, oak and pine, respectively, but aspen was present in the immediate vicinity of the two latter as well. Dead Populus with their deep subcambial layer is particularly favored by Lonchaea species but also oaks and pines provide suitable habitats, while several other lonchaeid genera are more generalised saprophages not connected with tree species ( Smith 1989, MacGowan & Rotheray 2008, MacGowan pers. comm.).

The scarcity of specimens indicate that it is indeed a rare species. But, with the four presently known localities widely separated over the Scandinavian peninsula, all with rich and very nice forest habitats with natural dynamics and notable biological diversity, but far from unique, we would assume that it can be found in other places in between as well.

The flatness is odd. In other wasps of the North European fauna, we see something similar in at least four other groups. Many Bethylidae are flat, parasitoids of Coleoptera and Lepidoptera larvae, both in saproxylic environments and human storage and other concealed places. The platygastrid wasps of the genus Platystasius are very flat, associated with Coleoptera eggs in both saproxylic and other concealed locations. While the genus Spalangia , constituting the subfamily Spalangiinae of Pteromalidae , parasitises Brachycera larvae in various concealed locations, not particularly saproxylic, and the scelionid Telenomus danubialis Szelényi, 1939 attacks flattened Lepidoptera eggs in grasses. Elsewhere, at least many Agaonidae and some Mymaridae are as flat. Spontaneously it is possible to make a tentative association between flatness and a subcorticeous lifestyle, which is definitely true in a large number of Coleoptera , but it is more difficult to find analogous cases in Hymenoptera , and indeed the known Hymenoptera parasitoids of subcorticeous and saproxylic Brachycera and Coleoptera are usually not flat.

Acknowledgments. Christer Hansson gave information about the UZML collections and hosted MF during a visit, Yvonnick Gerard found the Swedish specimen in the IRSNB, Juho Paukkonen, Lars Vilhelmsen, Lars Ove Hansen and David Notton checked the collections of MZH, ZMUC, NHMO and BMNH, respectively. István Mikó helped with background knowledge and access to literature. Veli Vikberg, Martti Koponen, Peter Neerup Buhl and Lars-Ove Wikars responded helpfully to enquiries. Ingvar Stenberg kindly letting us use a photo from Botnahaugen, and Forsvarets logistikkorganisasjon (FLO), Vedlikehold Horten, gave AS access to Mellomøya.An anonymous reviwer provided helpful comments.