Xyelidae

Imago (Adult) Xyelidae are small Hymenoptera. Most species are 3 to 5 mm long, but species of Macroxyela and Megaxyela of East Asia and North America are larger, measuring 10 to 15 mm. The imagines display a number of ancestral characters of Hymenoptera, which may be absent in more derived lineages of Hymenoptera. Those include the absence of a wasp waist (thorax and abdomen abut without constriction), presence of cenchri on the metathorax to fix the wings at rest, presence of an antennal grooming apparatus on tibia and first tarsomere of the fore leg, and presence of a molar tooth on the mandible. Most intriguing is the morphology of the antenna which bears a long and thick third article followed by a number of shorter and more slender antennomeres. This so-called synantennomere 3 Larva Like in many other sawflies, the larvae of Xyelidae are superficially similar to caterpillars of Lepidoptera ("eruciform" type of larvae). Larvae of species feeding inside plants are whitish, those of free-feeding species whitish green or yellow. Larvae of Megaxyela bear a conspicuous pattern of black spots (see plate 21 figure 3 in) or they resemble bird droppings. The roundish head capsule bears a larval eye (stemma) on each side, which is reduced in mining species, and short antennae comprising five articles. The thorax bears short legs comprising three articles. Unlike the larvae of all other Hymenoptera and Lepidoptera which lack prolegs on at least the first abdominal segment, larvae of Xyelidae have prolegs on all abdominal segments. In free feeding Xyelidae (Macroxyela, Megaxyela) the abdominal prolegs are conspicuous and consist of two articles, while in the mining species (Pleroneura, Xyela) they are reduced to inconspicuous transverse bulges. Pupa Unique among the Hymenoptera, the pupa of Xyelidae are of the decticous and exarate types, in which the antennae, legs and mandibles are free and mobile. This pupal form is an ancestral character of holometabolan insects. In other orders, it occurs in including Neuropterida, Mecoptera, Trichoptera and in some lineages of Lepidoptera. The Hymenoptera excluding Xyelidae are characterized by immobile adecticous pupae. == Ecology ==

The larvae of all Xyelidae are phytophagous and associated with trees. Larvae of the comparatively species-rich Xyela live inside the growing staminate cones of pines and feed on the sporophylls and the pollen. The North American Xyela gallicaulis is exceptional in causing galls on fresh shoots of some pine species, inside which the larva feeds. Larvae of Pleroneura feed inside young shoots of firs. Only the Japanese Pleroneura piceae is associated with spruce. Larvae of Megaxyela major (and supposedly also of Megaxyela langstoni) feed on leaves of pecan and are regarded as a pest of pecan plantations in the Southeastern USA. == Systematics and taxonomy ==

Xyelidae are very likely the sister taxon of all other extant Hymenoptera. The great age of the family is supported by numerous fossil records. All Hymenoptera recorded from the Triassic are classified as Xyelidae, while representatives of other hymenopterous families have been found no earlier than the Jurassic. During the Mesozoic and the Tertiary, the Xyelidae obviously were much more species-rich and more widely distributed than today. Thus, the comparatively few extant species can be regarded a relict group. Extant taxa The Electronic World Catalog of Symphyta and five in North America • Xyela Brébisson, 1819 (synonyms: Pinicola Dalman, 1818 [preoccupied by the genus-group name of birds Pinicola Vieillot, 1808], Xyelatana Benson, 1938 • Xyela (Xyela) Brébisson, 1819: 29 species in Eurasia and 20 in North America, but many additional species have not yet been described. • Macroxyelinae • Macroxyela W.F. Kirby, 1882: Macroxyela aenea (Norton, 1872) and Macroxyela ferruginea (Say, 1824) in eastern and central North America • Megaxyela Ashmead, 1898: six species in eastern Eurasia, seven species in North America. and Xyelecia nearctica in Western North America The European species can be identified with help of "The Western Palaearctic Xyelidae" of Blank (2002), The North American Macroxyelinae were revised by Smith & Schiff (1998), the North American species of Xyela by Burdick (1961), the North American species of Pleroneura by Smith et al. (1977), the East Asian species of Megaxyela by Shinohara (1992), the East Asian species of Pleroneura by Shinohara (1995), and the species of Megaxyela of the World by Blank et al. (2017). Extinct taxa The Electronic World Catalog of Symphyta provides a complete account of the valid fossil genera and species, their synonyms and the concerning references to original descriptions. Genus without classification into a subfamily of Xyelidae • †Potrerilloxyela Lara, Rasnitsyn & Zavattieri, 2014, 1 fossil species †Archexyelinae • †Archexyela Riek, 1955, 2 fossil species • †Asioxyela Rasnitsyn, 1964, 4 fossil species • †Dinoxyela Rasnitsyn, 1969, 1 fossil species • †Euryxyela Rasnitsyn, 1964, 1 fossil species • †Ferganoxyela Rasnitsyn, 1969, 2 fossil species • †Leioxyela Rasnitsyn, 1969, 5 fossil species • †Lithoxyela Rasnitsyn, 1969, 1 fossil species • †Madygenius Rasnitsyn, 1969, 2 fossil species • †Moltenia Schlüter, 2000, 1 fossil species • †Oryctoxyela Rasnitsyn, 1969, 2 fossil species • †Triassoxyela Rasnitsyn, 1964, 3 fossil species • †Xaxexis Pagliano & Scaramozzino, 1990 [= Euryxyela Hong, 1984], 1 fossil species • †Xiphoxyela Rasnitsyn, 1969, 2 fossil species • †Xyelinus Rasnitsyn, 1964, 2 fossil species Macroxyelinae • Genera without classification into a tribe of Macroxyelinae • †Bolboxyela Rasnitsyn, 1990, 1 fossil species • †Brachyoxyela Gao, Zhao & Ren, 2011, 2 fossil species • †Angaridyelini • †Angaridyela Rasnitsyn, 1966, 8 fossil species • †Baissoxyela Rasnitsyn, 1969, 1 fossil species • †Ceratoxyela J. Zhang & X. Zhang, 2000, 1 fossil species • †Lethoxyela J. Zhang & X. Zhang, 2000, 2 fossil species • †Liaoxyela J. Zhang & X. Zhang, 2000, 1 fossil species • †Nigrimonticola Rasnitsyn, 1966, 1 fossil species • †Ophthalmoxyela Rasnitsyn, 1966, 1 fossil species • †Ceroxyelini • †Ceroxyela Rasnitsyn, 1966, 1 fossil species • †Isoxyela J. Zhang & X. Zhang, 2000, 1 fossil species • †Sinoxyela J. Zhang & X. Zhang, 2000, 1 fossil species • †Gigantoxyelini • †Abrotoxyela Gao, Ren & Shih, 2009, 2 fossil species • †Chaetoxyela Rasnitsyn, 1966, 1 fossil species • †Chionoxyela Rasnitsyn, 1993, 1 fossil species • †Gigantoxyela Rasnitsyn, 1966, 1 fossil species • †Heteroxyela J. Zhang & X. Zhang, 2000, 1 fossil species • †Platyxyela Wang, Shih & Ren, 2012, 1 fossil species • †Shartexyela Rasnitsyn, 2008, 1 fossil species • Macroxyelini • †Anthoxyela Rasnitsyn, 1977, 4 fossil species • Megaxyela Ashmead, 1898, 2 fossil species in addition to extant species • Xyeleciini • †Microxyelecia Rasnitsyn, 1969, 1 fossil species • †Uroxyela Rasnitsyn, 1966, 1 fossil species • Xyelecia Ross, 1932, 1 fossil species in addition to extant species • †Xyelites Rasnitsyn, 1966, 2 fossil species †Madygellinae • †Chubakka Kopylov, 2014, 1 fossil species • †Madygella Rasnitsyn, 1969, 5 fossil species • †Samarkandykia Kopylov, 2014, 2 fossil species Xyelinae • †Liadoxyelini • †Aequixyela Wang, Rasnitsyn & Ren, 2014, 1 fossil species • †Anomoxyela Rasnitsyn, 1966, 1 fossil species • †Cathayxyela Wang, Rasnitsyn & Ren, 2014, 1 fossil species • †Kirghizoxyela Rasnitsyn, 1966, 1 fossil species • †Liadoxyela Martynov, 1937, 3 fossil species • †Lydoxyela Rasnitsyn, 1966, 1 fossil species • †Orthoxyela Rasnitsyn, 1983, 1 fossil species • Xyelini • †Enneoxyela Rasnitsyn, 1966, 4 fossil species • †Eoxyela Rasnitsyn, 1965, 5 fossil species • †Spathoxyela Rasnitsyn, 1969, 2 fossil species • Xyela Dalman, 1819, 7 fossil species in addition to extant species, including Xyela (Pinicolites) Meunier, 1920 • †Xyelisca Rasnitsyn, 1969, 1 fossil species • †Yanoxyela Ren, Lu, Guo & Ji, 1995, 1 fossil species ==References==