Plagiotrochus Mayr, 1881

Melika, George, Pujade-Villar, Juli, Abe, Yoshihisa, Tang, Chang-Ti, Nicholls, James, Wachi, Nakatada, Ide, Tatsuya, Yang, Man-Miao, Pénzes, Zsolt, Csóka, György & Stone, Graham N., 2010, 2470, Zootaxa 2470, pp. 1-79 : 35-36

Plagiotrochus Mayr, 1881

Figs 234–239.

Type species: Cynips quercusilicis Fabricius, 1798 . Designated by Ashmead (1903).

Fioriella Kieffer , with only one known species, F. marianii Kieffer , was synonymized to Plagiotrochus ( Melika et al. 2001) .

Diagnosis. The gena in the asexual female is broadened behind the eye; the clypeus with radiating striae, does not project as a distinct lamella between mandibles, the malar sulcus is absent ( Fig. 234); the mesopleuron is shiny, with transversely delicately striate central part ( Fig. 239); the propodeum forms an obtuse angle with the mesoscutellum ( Fig. 239); lateral propodeal carinae are strongly curved outwards, with a more or less impressed, distinct median carina; the metasoma is compressed laterally; the ventral spine of the hypopygium is slender, short, with short sparse white setae not forming an apical tuft ( Fig. 238). Plagiotrochus somewhat resembles Chilaspis , however the latter differs from the former by a smooth mesoscutum and mesopleuron. See also the generic key. There is one species, P. cardiguensis (Tavares) which has an incomplete transscutal articulation, and thus somehow resembles the Neuroterus – Cerroneuroterus group. However, all other morphological characters and molecular phylogenetic reconstruction place this species in a monophyletic Plagiotrochus clade with high support ( Stone et al. 2009; Fig.1). Detail description of the genus and keys to the identification of Western Palaearctic species of Plagiotrochus are given in Nieves Aldrey (2001).

Biology. Alternation of generations is known. The asexual generation usually induces stem galls, the cells of which are hidden under the bark of twigs, while the sexual generation usually induces catkin galls. Some species induce leaf galls. The genus Plagiotrochus includes 15 Western Palaearctic species ( Bellido et al. 2000; Pujade-Villar & Ros-Farré 1998; Pujade-Villar et al. 2000; Melika et al. 2001, 2006a; Nieves Aldrey 2001), of which one, Plagiotrochus csokai Melika & Pujade-Villar , was recently described from Jordan ( Melika et al. 2009). There are three Eastern Palaearctic species, P. semicarpifoliae (Cameron) from the NW Himalayas, known to induce acorn galls on Q. semicarpifoliae Smith ( Bellido et al. 2000) , and P. smetanai Melika & Pujade-Villar and P follioti Pujade-Villar & Melika from Nepal ( Melika et al. 2009).

Distribution. Majority of species are known from the Mediterranean region (Southern Europe, North Africa, Turkey, the Middle East) ( Bellido et al. 2000; Pujade-Villar et al. 2000; Nieves Aldrey 2001). One species, P. marianii (Kieffer) , was recorded from Slovakia and Hungary ( Ambrus 1974; Melika et al. 2001; Melika 2006a), three species are known from the Himalayan area and one Western Palaearctic species, Plagiotrochus amenti Kieffer (= P. suberi Weld ), has accidentally been introduced to the USA (California) ( Weld 1926) and Argentina ( Díaz 1973). The lifecycle of P. amenti has recently been closed experimentally by pairing of a sexual generation ( P. amenti ) with an asexual generation previously described as P. suberi Weld ( Garbin et al. 2008) . Introduced populations of this species in North America are purely parthenogenetic ( Bailey & Stange 1966; Zuparko 1996; Garbin et al. 2008), and as a result these two forms have been regarded as separate species pending proof of their relationship ( Pujade-Villar & Ros-Farré 1998). Other authors (Pujade- Villar 1998; Pujade-Villar & Díaz 2001) have argued that even if P.amenti is confirmed to be the sexual form of P. suberi , there could be two effective biological species – an ancestral species with cyclical parthenogenesis, and a derived species with wholly parthenogenetic reproduction. Resolution of this debate requires population genetic and phylogenetic analysis ( Pujade-Villar & Díaz 2001). Geographic parthenogenesis, for example, is present in the Andricus mukaigawae complex ( Abe 1986, 2007). The situation is also complicated by the records of P. abdominalis (regarded as a synonym of P. suberi ) on Q. robur L. in Argentina, although this host oak association is probably incorrect ( Pujade-Villar & Díaz 2001).

Comments. Earlier phylogenetic analysis has shown that Plagiotrochus belongs to a plesiomorphic lineage of Cynipini ( Pujade-Villar & Arnedo 1997; Liljeblad & Ronquist 1998; Nylander 2004). The basal position of Plagiotrochus is supported by some morphological peculiarities of adults, and is also compatible with the apparent structural simplicity of the galls they induce. Plesiomorphic traits of P. semicarpifoliae (Cameron) , known from the Himalayan area, suggest a Southeast Asian origin for Plagiotrochus , and all the species known from the Mediterranean region probably are derived forms and represent a secondary radiation ( Bellido et al. 2000; Bellido & Pujade-Villar 2001; Ács et al. 2007; Melika et al. 2009). Recent analysis also supports Plagiotrochus as the sister group of Chilaspis ( Stone et al. 2009) . The Black oaks of the section Cerris, mentioned in the Introduction, are further divided into two groups: a semi-deciduous Cerris group and an evergreen Ilex group (Manos et al. 2001; Manos & Stanford 2001). Host shifts between Cerris and Ilex groups within the Black oaks are also inferred to have been extremely rare. Phylogenetic reconstructions for all datasets suggest a single switch from the Cerris group to the Ilex group by the common ancestor of the genus Plagiotrochus , followed by a single switch back to the Cerris group by P. amenti and P. marianii ( Stone et al. 2009) . Monophyly of Plagiotrochus and its positioning on the tree strongly supports the hypothesis of an Asian origin of Cynipini ( Stone et al. 2009) .