addition to the ovipositor proper to penetrate the resinous buds of firs. Megaxyela gigantea and most other species of Megaxyela has strikingly long hind legs which are used to fold a newly growing leaf to provide shelter for their eggs which are fixed with glutinous material between on the upper sides of the folded leaf. Many species of Xyelidae facultatively diapause for several years. In Xyela alpigena and Xyela obscura a diapause of at least two years is obligate. This strategy might have evolved to ensure well developed cones are available for oviposition: the host plants Pinus cembra and Pinus mugo produce cones very irregularly in the subalpine zone of the European Alps. Adults of Xyela are pollen feeders of a variety of plants, which bear flowers with easily accessible pollen (e.g., Betula, Cercocarpus, Ostrya, Pinus, Purshia, Quercus, Salix). The enlarged maxillary palps of most Xyela (and supposedly also of Pleroneura and Xyelecia) serve for the extraction of pollen from the flowers. Although they feed upon often economically important tree species, Xyelidae are usually of only small significance as pest organisms. Pleroneura piceae damages the growth of Sakhalin spruce, since the larvae destroy the young shoots. 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 represent the most basal lineage of Hymenoptera and very likely the sister taxon of all other extant Hymenoptera. This assertion is supported by phylogenetic analyses of both morphological characters and DNA sequences. 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 provides a complete account of the valid extant genera and species, their synonyms, the concerning references to original descriptions and distribution data on the level of countries and provinces. Xyelinae Pleroneura Konow, 1897: at least eight species in Eurasia 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