Dryocosmus Giraud, 1859

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 : 31-32

Dryocosmus Giraud, 1859

Figs 207–213, 214–220, 221–228

Type species: Dryocosmus cerriphilus Giraud, 1859 . Original designation by monotypy ( Giraud 1859).

Diagnosis. See Diagnosis to Chilaspis and the generic key.

Redescription. Body length 1.4 – 2.6 mm, yellow to dark brown; metasoma usually darker; with very few short setae. Head slightly broader than high in anterior view, nearly 2.0 times as broad as long from above; smooth, alutaceous to delicately coriaceous, without setae, with or without striae radiating from clypeus. Gena not (sexual generation) or broadened (asexual female) behind eye. POL slightly shorter or equal to OOL. Malar sulcus absent, malar space very short. Transfacial distance slightly longer than height of eye. Clypeus projecting over mandibles. Sexual female antenna with 12 – 13, asexual female with 11 – 12, male antenna with 13 flagellomeres, F 1 in male excavated and clearly expanded apically. Mesosoma convex and nearly as high as long in lateral view, with very few white setae. Mesoscutum smooth or alutaceous. Notaulus complete, deeply impressed; median mesoscutal line absent or in a form of very short triangle, anterior parallel and parapsidal lines absent. Mesocutellum smooth, or uniformly coriaceous; scutellar foveae absent or present (e.g. D. caspiensis Melika, Sadeghi, Atkinson, Stone & Barimani ), usually anterior transverse impression present, indistinctly delimited posteriorly from mesoscutellar disk, sometimes a narrow, weak central carina extending to mesoscutum, dividing anterior impressed area into two. Mesopleuron and speculum uniformly alutaceous or smooth. Lateral propodeal carinae strongly curved outwards medially; central propodeal area with or without median longitudinal carina, usually with some irregular wrinkles. Tarsal claws simple, without basal lobe. Forewing margin with cilia; sometimes fuscous around veins; radial cell 3.5 – 4.0 times as long as broad, opened. Metasoma compressed laterally, as long as high and higher than mesosoma (in D. kuriphilus Yasumatsu metasoma is more cylindrical); all tergites without setae and punctures (except D. kuriphilus , metasoma of which in uniform dense micropunctures, except 2nd metasomal tergite); prominent part of ventral spine of hypopygium short, with short and sparse setae, never forming apical tuft.

Around 25 species of Dryocosmus are known world-wide, including 16 in the Nearctic Region ( Burks 1979). However, some nearctic species have been placed in Dryocosmus erroneously ( Dailey 1969; Dailey & Sprenger 1973). It has been clearly shown, for example, that the nearctic species D. favus Beutenmüller , is phylogenetically distinct from palaearctic Dryocosmus and is more closely allied to Andricus ( Ács et al. 2007) . The remaining nearctic Dryocosmus either represent a morphologically convergent lineage otherwise distant from palaearctic Dryocosmus , or a related lineage separated from palaearctic relatives by a host oak shift.

Most Dryocosmus species have alternating sexual and asexual generations. The seven Western Palaearctic species induce galls exclusively on Cerris section oaks, while all but two of the nearctic species induce their galls on red oaks (section Lobatae). The exceptions are the nearctic species Dryocosmus castanopsidis (Beutenmueller) and Dryocosmus rileypokei Morita & Buffington , which gall chinquapins, Chrysolepis Hjelmq. ( Beutenmueller 1917; Buffington & Morita 2009), and the only known Eastern Palaearctic species, D. kuriphilus , which galls chestnuts, Castanea L. (details in Aebi et al. 2006; Abe et al. 2007). Details of the lifecycles, gall morphology, biology, geographic distribution, and detailed morphological descriptions of the species are given elsewhere ( Dalla Torre & Kieffer 1910; Melika et al. 2000; Pujade-Villar et al. 2003; Azizkhani et al. 2006; Melika 2006a; Tavakoli et al. 2008; Buffington & Morita 2009).