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 Macroxyelinae are free feeders of deciduous tree species. The two North American species of Macroxyela feed on elms, the East Asian and North American species of Megaxyela on Juglandaceae like walnuts, hickory and wingnuts. For Xyelecia nearctica an endophagous life style and an association with firs is supposed. Many species of Xyelidae are host specific, with only a single larval host plant known. Monophagy is the prevailing life style in most species of Xyela. For this genus, the date of oviposition is closely correlated with the development of the staminate cones of the host pines, which might prevent a host shift in many cases. For some North American species of Xyela the association with each several species of pines (oligophagy) has been reported in literature, but supposedly such records are often based on taxonomic problems to separate morphologically similar species of Xyela properly. Through molecular access, true oligophagy could be demonstrated recently for Xyela bakeri (associated at least with Pinus contorta, Pinus ponderosa and Pinus sabiniana) and Xyela brunneiceps (associated with Pinus flexilis and Pinus strobiformis). Lack of reliable, reproducible host data could cause inaccurate reports of monophagy or oligophagy in many taxa of Xyelidae, but at least some of the species included in Megaxyela and Pleroneura are truly oligophagous. After completing feeding, Xyelidae larvae dig into the ground and form an earthen cell, where they usually spin a cocoon and develop into a pupa. Absence of a cocoon has been observed in Megaxyela togashii from Japan. The imago emerges in the following spring to mate. Subsequently, the female deposits eggs with the ovipositor. In most species of Xyela, the tip of valvula 3 of the ovipositor sheath is equipped with specialized sensory structures called sensilla trichodea and sensilla campaniformia, which are involved in the oviposition process. In Pleroneura, unlike practically all other Hymenoptera, the hard and conical ovipositor sheath is used in