Xyelidae | |
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Megaxyela sp. from Oklahoma | |
Xyela, the type genus of Xyelidae, from British Entomology | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Arthropoda |
Class: | Insecta |
Order: | Hymenoptera |
Superfamily: | Xyeloidea Newman, 1834 |
Family: | Xyelidae Newman, 1834 |
Genera | |
See text |
The Xyelidae are a comparatively species-poor family of sawflies, comprising about 80 extant species in five genera worldwide, and is the only family in the superfamily Xyeloidea. [2] [3] The fossil record of the family is extensive, comprising more than 120 species [4] and including the oldest fossil Hymenoptera species dating back to the Triassic, between 245 and 208 million years ago. Xyelidae are to be regarded as living fossils since they represent one of the oldest lineages of insects and include still extant forms.
The extant species occur in the Northern Hemisphere, especially in boreal regions of the Holarctic, though there are a few Oriental species. Two genera and about 15 species occur in Europe. [5] [6] Considering additional fossil records from Australia, [7] South Africa [8] and Argentina, [9] the extant species display a relict distribution. The species in the subfamily Xyelinae are associated with conifers (esp. Pinus and Abies ), where the larvae feed on pollen or within buds. The larvae of the subfamily Macroxyelinae feed on the leaves of deciduous trees (various Juglandaceae and Ulmus ).
The family is characterized by the appendages of the head, which are remarkable in that the antennae and palpi are nearly leg-like in structure, with a long basal segment followed by a series of tiny segments, as in the tibia-tarsus.
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 [6] is the product from the ontogenetic fusion of several antennal articles, and it is unique among the extant Hymenoptera species. In Pleroneura , Xyelecia and most species of Xyela the maxillary palps are strongly enlarged and bear specialized setae on the distal articles. The wing venation is the most complete among Hymenoptera: Only in Xyelidae the radial sector Rs furcates into the veins Rs1 and Rs2, while in other Hymenoptera Rs1 is absent. The females bear a more or less long ovipositor, which in some species of Xyela may be as long as the body. Morphology of the ovipositor and the ovipositor sheath are important characters for identification to species level. The penis valves of the males are densely setulous, which is a rare character state among the basal lineages of Hymenoptera. Females and males mate with the bodies directing in opposite direction. In Xyelinae the genital capsule of the males are revolved for 180° after disclosure from the pupal skin (strophandry). Macroxyelinae are orthandrous after emergence. They mate in the same position as Xyelinae, but the male genital capsule is rotated yet in course of mating (facultative strophandry). [10]
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 [4] ) or they resemble bird droppings. [11] [12] 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.
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. [6] This stage represents the already developed (pharate) imago which is still enclosed by the pupal skin. At this stage, the wings are not expanded, and in females, the ovipositor and its sheath curve dorsally above the tip of the abdomen. The decticous pupae are capable of biting open the cocoon, digging to the surface of the ground, moving around on the surface, and drinking (figs 22-23 in [13] ). [14] This pupal form is an ancestral character of holometabolan insects. In other orders, it occurs in including Neuropterida, Mecoptera, Trichoptera and in the basal lineages of Lepidoptera. [15] [16] [17] The Hymenoptera excluding Xyelidae are characterized by immobile adecticous pupae.
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. [18] Larvae of Pleroneura feed inside young shoots of firs. Only the Japanese Pleroneura piceae is associated with spruce. [19] 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. [20] [21] [22] For Xyelecia nearctica an endophagous life style and an association with firs is supposed. [23]
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. [24] [25] 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, [14] but supposedly such records are often based on taxonomic problems to separate morphologically similar species of Xyela properly. [6] Through molecular access, true oligophagy could be demonstrated recently for Xyela bakeri (associated at least with Pinus contorta , Pinus ponderosa and Pinus sabiniana ) [26] and Xyela brunneiceps (associated with Pinus flexilis and Pinus strobiformis ). [27] 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. [22] [28]
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. [12] 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. [13] [25] [27] In Pleroneura, unlike practically all other Hymenoptera, the hard and conical ovipositor sheath is used in addition to the ovipositor proper to penetrate the resinous buds of firs. [13] 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. [29] [21] [12]
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. [30] [13] [25]
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). [14] [25] The enlarged maxillary palps of most Xyela (and supposedly also of Pleroneura and Xyelecia) serve for the extraction of pollen from the flowers. [14] [6]
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. [31] 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. [32] [33] [34] [22]
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. [35] 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.
The Electronic World Catalog of Symphyta [2] 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.
The European species can be identified with help of „The Western Palaearctic Xyelidae“ of Blank (2002), [13] all Eurasian species of Xyela with Blank et al. (2013). [25] The North American Macroxyelinae were revised by Smith & Schiff (1998), [20] the North American species of Xyela by Burdick (1961), [14] the North American species of Pleroneura by Smith et al. (1977), [28] the East Asian species of Megaxyela by Shinohara (1992), [21] the East Asian species of Pleroneura by Shinohara (1995), [19] and the species of Megaxyela of the World by Blank et al. (2017). [22]
The Electronic World Catalog of Symphyta [2] 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
Hymenoptera is a large order of insects, comprising the sawflies, wasps, bees, and ants. Over 150,000 living species of Hymenoptera have been described, in addition to over 2,000 extinct ones. Many of the species are parasitic. Females typically have a special ovipositor for inserting eggs into hosts or places that are otherwise inaccessible. This ovipositor is often modified into a stinger. The young develop through holometabolism — that is, they have a wormlike larval stage and an inactive pupal stage before they reach adulthood.
Sawflies are wasp-like insects that are in the suborder Symphyta within the order Hymenoptera, alongside ants, bees, and wasps. The common name comes from the saw-like appearance of the ovipositor, which the females use to cut into the plants where they lay their eggs. The name is associated especially with the Tenthredinoidea, by far the largest superfamily in the suborder, with about 7,000 known species; in the entire suborder, there are 8,000 described species in more than 800 genera. Symphyta is paraphyletic, consisting of several basal groups within the order Hymenoptera, each one rooted inside the previous group, ending with the Apocrita which are not sawflies.
Horntail or wood wasp are any of the 150 non-social species of the hymenopteran family Siricidae, a type of wood-eating sawfly. The common name "horntail" derives from the stout, spine-like structure at the end of the adult's abdomen, which is used to pierce the host's bark to allow the eggs to be inserted into the wood. A typical adult horntail is brown, blue, or black with yellow or red parts, and may often reach up to 4 cm (1.6 in) long. The pigeon horntail can grow up to 5 cm (2.0 in) long, among the longest of all Hymenoptera.
Alexandr Pavlovich Rasnitsyn is a Russian entomologist, expert in palaeoentomology, and Honored Scientist of the Russian Federation (2001). His scientific interests are centered on the palaeontology, phylogeny, and taxonomy of hymenopteran insects and insects in general. He has also studied broader biological problems such as evolutionary theory, the principles of phylogenetics, taxonomy, nomenclature, and palaeoecology. He has published over 300 articles and books in several languages. In August 2008 he was awarded the Distinguished Research Medal of the International Society of Hymenopterists.
Xiphydriidae are a family of wood wasps that includes around 150 species. They are located all over the world including North and South America, Australia, Europe, and others. Xiphydriidae larvae are wood borers in dead trees or branches of a range of trees. They are characterized as having long and skinny necks with dome-shaped heads. The oldest fossils of the group are from the mid Cretaceous.
The Orussidae or the parasitic wood wasps represent a small family of sawflies ("Symphyta"). Currently, about 93 extant and four fossil species are known. They take a key position in phylogenetic analyses of Hymenoptera, because they form the sister taxon of the megadiverse apocritan wasps, and the common ancestor of Orussidae + Apocrita evolved parasitism for the first time in course of the evolution of the Hymenoptera. They are also the only sawflies with carnivorous larvae.
Anaxyelidae is a family of incense cedar wood wasps in the order Hymenoptera. It contains only one living genus, Syntexis, which has only a single species, native to Western North America. Fossils of the family extend back to the Middle Jurassic, belonging to over a dozen extinct genera, with a particularly high diversity during the Early Cretaceous. Syntexis lay eggs in the sapwood of conifers, preferring recently burnt wood.
The Pamphilioidea are a small superfamily within the Symphyta, containing some 250 living species restricted to the temperate regions of Eurasia and North America. These hymenopterans share the distinctive feature of a very large, almost prognathous head, which is widest ventrally.
The Megalodontesidae are a small family of sawflies, containing a single living genus, Megalodontes, with some 40 species restricted to the temperate regions of Eurasia. Larvae of Megalodontesidae feed on herbaceous plants. They are distinguished from the closely related Pamphiliidae by their serrate or pectinate antennae.
Pamphiliidae is a small family within Symphyta, containing some 200 species from the temperate regions of North America and Eurasia. The larvae feed on plants, using silk to build webs or tents, or to roll leaves into tubes in which they feed, thus earning them the common names leaf-rolling sawflies or web-spinning sawflies. Some species are gregarious and the larvae live in large groups. Fossils of Pamphiliidae have been dated to the Jurassic period.
Cimbicidae, the Clubhorn Sawfly, is a family of sawflies in the order Hymenoptera. There are more than 20 genera and 200 described species in Cimbicidae. Larvae are solitary herbivores.
Tenthredinidae is the largest family of sawflies, with well over 7,500 species worldwide, divided into 430 genera. Larvae are herbivores and typically feed on the foliage of trees and shrubs, with occasional exceptions that are leaf miners, stem borers, or gall makers. The larvae of externally feeding species resemble small caterpillars. As with all hymenopterans, common sawflies undergo complete metamorphosis.
Acantholyda is a genus of sawflies.
Nematinae is a subfamily of sawflies belonging to the family Tenthredinidae. It contains over 1250 described species in ~40 genera. Members of this subfamily feed on a wide range of plants and employ a wide range of feeding habits, both internally and externally, on their host plants.
Allantinae is a subfamily of sawflies in the family Tenthredinidae, and the largest subfamily of that family, with about 110 genera. The subfamily is considered to consist of five to six tribes, and are medium to large sawflies.
Cephidae is a family of stem sawflies in the order Hymenoptera. There are about 27 genera and more than 160 described species in Cephidae.
Cimbex quadrimaculatus is a species of sawflies in the family Cimbicidae.
Monostegia is a genus of sawfly. The authority is based on the description by Achille Costa and Oronzio Costa, although earlier work grants this to Fabricius 1798., though the most common species, M. abdominalis, bears the authority of Fabricius.
Xyela is a genus of sawflies, belonging to the family Xyelidae.
Megaxyela is a genus of sawflies in the family Xyelidae. There are about 13 described species in Megaxyela, found in the eastern Nearctic and in the southeastern part of East Asia. Two fossil species have been discovered, in Colorado and Shandong, China.