The Xyelidae are a species-poor family of sawflies with about 80 extant species worldwide, of which about 15 in Europe. The family has been demonstrated since the Triassic, and thus with an age of about 200 million years ago one of the oldest living insects families.
Xyelidae are small Hymenoptera, the European species are about 3-5 mm long, living in East Asia and North America Macroxyela and Megaxyela are 10-15 mm in length significantly greater. As with most insects, the head bears two compound eyes, three ocelli and chewing mouthparts. The four wings are membranous. At the front edge of the forewing is usually a large pterostigma. The legs are made of normal walking legs. On the rail ( tibia ) of the front leg is seated at the front end a redesigned spur, which serves as a cleaning tool for the antennas. As is typical of all sawflies, the abdomen is sitting without constriction ( wasp waist ) wide at the thorax, on the top two so-called " Cenchri " (bonding pad) are in rest position to hold the wings.
The body of the animals is sometimes solid black, but often colored contrast with white, yellow or orange drawing. Very striking and unmistakable is the construction of the sensor Xyelidae. Said third member (ie, the first member of the antenna whip ) taken together in comparison to the members of the following longer and wider, and sometimes longer than the other members. In the third term follow at least five, in case of European species always nine or more narrow and short limbs scourge. The extended third antennal segment is formed by fusion of several original members scourge. Such " Synantennomer " occurs within the recent Hymenoptera except for the Xyelidae only with the Blasticotomidae. In Pleroneura, Xyelecia and most Xyela - species Maxillarpalpen are greatly enlarged and wear on the distal limbs specialized bristles that serve the food assistance. The prothorax is narrow and the posterior margin straight. On the wings of the Flügelgeäder falls on having one for Hymenoptera unusually high number of cross- veins and cells. The wings are glabrous ( Xyela ) or hairy (eg Pleroneura ). The coloration of wing membrane and veins varies. The Xyelidae branches of the radial sector Rs, a vein in the front half of the wing, in the veins Rs1 and Rs2, while other Hymenoptera missing Rs1. At the middle and hind legs sit in the middle and before the end of three spurs. In females at abdome falls on a more or less long ovipositor ( ovipositor ), which is straight, or slightly bent stretched backward. It can reach body length in some species. Its shape and length are critical for the determination of many kinds.
The larvae possess, as with many sawflies in the body shape is very similar to caterpillars ( " erucoider " larval type). Living in plant species are colored in white, wild species whitish- green or yellow. Larvae of Megaxyela are strikingly black dots (Plate 21 Fig 3 ) or resemble bird droppings The roundish head with strongly sclerotized head capsule bears on either side a larval eye ( Stemma or Ocularium ), which is obtained from Minierern only as a relic, and very short, five-membered antennas. He has strong, serrated mandibles. Labial and Maxillarpalpen are tripartite. At the lip of the open Labialdrüsen with which the larva silk-like threads can spin that are used to build the cocoons. The reservoir of the gland is very large and extends almost throughout the body until the abdomen. The mouthparts are directed downwards ( orthognathic ). On thorax sit three short, tripartite pairs of legs. On abdomen sit at all segments simple legs. The larvae of all other Hymenoptera and most caterpillars do not have the pair of legs on the first segment. In free-living Xyelidae ( Macroxyela, Megaxyela ) the Abdominalbeine are clear and bipartite. For eating in plant species ( Pleroneura, Xyela ) they are formed only as inconspicuous lateral beads.
Xyelidae have a so-called Pupa dectica in the sensor, legs and mandibles are free and movable. In fact, it is already developed, yet surrounded by doll skin ( " pharate " ) Imago. The wings are not spread out at this stage and the ovipositor of the female is still hunched over the abdomen. The Pupa dectica opens the cocoon, digs to the surface and is walking around in the situation there, take 4 Plate 21 Fig and in liquid.
The Pupa dectica belongs to the basic plan of Holometabola and also comes with many other sub-groups of these, such as the Netzflüglerartigen ( Neuropterida ), beak flies ( Mecoptera ), caddisflies ( Trichoptera ) and in basal families butterfly (Lepidoptera ) ago. The Hymenoptera excluding Xyelidae have adectica an immobile pupa.
Way of life
All Xyelidae are herbivores ( phytophagous ) on trees. Larvae of the comparatively rich in species, widespread in Europe genus Xyela live in the adolescent male inflorescences of pine species and feeds on the immature pollen grains. The North American Xyela gallicaulis causes of fresh shoots of pine gall, where it eats. Larvae of the spread in Europe Pleroneura - species eat the young shoots of fir (Abies ). Only the Japanese Pleroneura piceae comes before spruce (Picea ). The larvae of Macroxyelinae feed freely on the leaves of deciduous trees. The two North American Macroxyela species feed on elms that the spread in East Asia and North America Megaxyela species on various plants such as walnut walnuts ( Juglans ), hickory ( Carya ) and wing nuts ( Pterocarya ). For the larvae of Xyelecia nearctica an internal life and binding to Tannen is suspected.
For many Xyelidae species only a single larval food plant is known. Monophagie is probably only Xyela species, whereas in the other genera lack of data Monophagie probably often is deceiving. The pollen -eating larvae as Xyela species oviposition must be coordinated very closely with the relatively short development time of male pine flowers. This probably prevented the transition to other host species. For some North American species Xyela a bond has been reported in several pine species ( Oligophagie ), but may be taxonomic problems in the separation of very similar Xyela types based.
Is the feeding phase completed, the larva leaves fall to the ground and digs a small Erdhöhlung in which they einspinnt in a cocoon. Here it molts into a pupa. The imago emerges from until the spring of the following year in order to mate. Then the females lay with her ovipositor the eggs into the plant tissue of their host species from. In many species, the pupae can hatch several years lie ( diapause ) and only in the second or third year. When living in the Alps on Swiss stone pine and mountain pine Xyela alpigena and X. obscura at least two years diapause is obligate, as these pine species of the subalpine zone bloom only irregularly.
The adults are, if known at all, unspecialized pollen eaters on a variety of plant species. The enlarged Maxillarpalpen of Xyela (and probably also of Pleroneura and Xyelecia ) are used for extraction of pollen from the flowers. Mating takes place on the ground where the animals away from one another, coupled with the Kopulationsorganen each other are. In the subfamily Xyelinae the copulatory organs of males are therefore rotated by 180 ° in the abdomen ( " Strophandrie "). The Macroxyelinae mating occurs in the same position, however, the male copulatory organs turn here only at Begattungsvorgang itself ( " optional Strophandrie ").
Although the species occur on economically important tree species, they are usually meaningless as pests. The larvae of Pleroneura piceae harm the growth of the Sakhalin spruce (Picea glehnii ) by the larvae destroy the young shoots.
Systematics and Taxonomy
The Xyelidae are morphologically most primitive group of the Hymenoptera and almost certainly the sister group of all other living Hymenoptera. This position results from numerous morphological features and also from molecular phylogenetic trees based on the comparison of homologous DNA sequences. The great antiquity of the family is supported by fossils. All found in the Triassic fossils of Hymenoptera are associated with this family, representatives of other families are the earliest detectable in the Jura. In Mesozoic and Tertiary in the family was significantly richer in species and more widespread than it is today, the few extant, living representatives can be seen as a relic group.
Within the Xyelidae the Xyelinae and Macroxyelinae be distinguished. In the meantime, it was assumed that the Xyelidae may be paraphyletic and form either the Xyelinae or Macroxyelinae alone the sister group of the remaining Hymenoptera. But this is true today as unlikely. The living ( extant ) species can thus be classified into the following system:
- Subfamily Xyelinae Xyelecia Ross, 1932: two species, X. japonica Togashi, 1972 in Japan and X. nearctica in western North America
- Pleroneura Konow, 1897: At least seven species in Eurasia and North America in five
- Xyela Brébisson, 1819 (synonyms: Pinicola Dalman, 1818 [ preoccupied by the bird genus Pinicola Vieillot, 1808 ], Xyelatana Benson, 1938) Subgenus Pinicolites Meunier, 1920: X. lata DR Smith, in 1990 in western North America
- Subgenus Xyela Brébisson, 1819: At least 28 species in Eurasia and at least 20 in North America
- Macroxyela W. F. Kirby, 1882 M. Aenea (Norton, 1872) and M. ferruginea (Say, 1824) in the eastern and central North America
- Megaxyela Ashmead, 1898: three species in eastern Eurasia, five species in North America
The European species can be determined with "The Western Palaearctic Xyelidae " by Blank (2002), the entire Eurasian species with Blank et al. ( 2013). The North American Macroxyelinae been revised by Smith & Ship (1998), the North American Xyela types of Burdick (1961 ), the East Asian Megaxyela types of Shinohara (1992 ), the East Asian Pleroneura types of Shinohara (1995), and the North American Pleroneura species described by Smith et al. (1977).
The recent Xyelidae come exclusively in the northern hemisphere, where the moderate ( temperate ) latitudes are clearly preferred. Representatives of Megaxyela and Xyela are up in the northern ( boreal ) zone and used in the subtropics. From the tropics no species are known. Macroxyela is found only in North America, while the remaining genera have a Holarctic distribution. In the case of Megaxyela and Xyelecia it is limited to East Asia and North America, while Xyela and Pleroneura are more widespread in Eurasia.
In Germany Xyela curva and Xyela julii are widespread and common. Pleroneura coniferarum, Pleroneura dahlii and Xyela longula are very rare. Significantly more species occur in the Alps and the Mediterranean, because more native pine species occur on the individual Xyela species are specialized: Xyela alpigena on Pinus cembra, Xyela curva, Xyela graeca and Xyela menelaus on Pinus nigra, Xyela obscura on Pinus mugo. Xyela curva originally reached its northern limit of distribution in the Vienna Basin. With planted in gardens, parks and forest of black pine, it expanded its distribution from secondary to central Europe and into the British Isles.
The earliest finds of Xyelidae dated to the middle Triassic. In the famous fossil site of Madygen in Kyrgyzstan with 220 to 230 million year old 25 species have already been found. In Jurassic and Cretaceous, the family is species-rich and widespread with more than 36 genera in four subfamilies worldwide. In the Tertiary already are comparatively less finds. Richest deposit here is the fossil deposit Rott near Bonn from the Oligocene with 11 species. Puzzling is the lack of family in Baltic amber that has arisen after the presumption by a pine species. In some fossils from the Mesozoic and Tertiary of fossilized gut contents from pollen was detected. Thus, a diet with pollen already developed from this period.