Click beetle

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Click beetle
Click beetle before departure

Click beetle before departure

Systematics
Class : Insects (Insecta)
Order : Beetle (Coleoptera)
Subordination : Polyphaga
Partial order : Elateriformia
Superfamily : Elateroidea
Family : Click beetle
Scientific name
Elateridae
Leach , 1815
A click beetle ( Agrypnus murinus ) "snaps"
Click beetle on the back. The “quick mechanism” with the hook is easy to see
Click beetle on a branch

The click beetles (Elateridae) are a family of beetles within the superfamily Elateroidea . Almost 10,000 species in more than 400 genera are known worldwide . The external appearance of the click beetle is very uniform. Characteristic is their eponymous ability to catapult themselves into the air with the help of a jumping device. A snapping noise can be heard when it jumps up, which is why this family of beetles are also called "click beetles" in English. The larvae live burrowing in the ground , the litter , or in dead wood , some as roommates (equilines) in termite nests. They feed saprophagous , phytophagous or predatory. Some species - for example the wireworms of the sniper beetle - feed on the roots of crops and are known to be agricultural pests.

features

Beetle

The beetles are 0.9 to 75 millimeters long. Their bodies are moderately to very elongated and 1.7 to 5.2 times longer than they are wide. As a rule, the sides of the body are parallel-edged, with the wings (elytra) somewhat widened at the base and truncated at their tips. The prothorax is clearly curved to the side in many species and has its narrowest point at the connection to the wing. The beetles are somewhat flattened to the back and sides moderately curved. They are either hairless or fluffy. As a rule, males and females do not differ in appearance, but in some species the females are larger, their bodies are more convex and have more curved sides. The puncturing can also be different.

The mouthparts are directed forward (prognath) to moderately downward. The frontal region on the head is very variable. The compound eyes are undivided and often large and protruding. In the females they are often smaller. They are hairless and finely faceted; the ommatidia are exoconic . The deflections of the feelers are moderately to far apart. Viewed from above, they are visible or hidden. In some species they are raised or are in bowl-shaped indentations. The antennae are usually 11-parted, but in some genera and tribe they have 12 parts. In most species they are thread-like or serrated, in some species they are pinnate, double-pinnate or lamellar, with the lamellae beginning at the third or fourth antennae. The scapus is usually much longer than the pedicellus . In the species with lamellar antennae, these are usually only developed in the males, whereas the females then have serrated or feathered antennae. The mandibles are crescent-shaped from short to wide to long and narrow. There is often a hair brush at its base.

The prothorax is about 0.4 to 1.35 times as long as it is wide and is usually widest at the back. The sides are more or less curved, but in some species they are also straight or only curved at the front. The front angles are rounded, truncated or directed slightly forward. At the rear they are more or less pointed and often strongly extended backwards (posterior) or laterally backwards (posterolateral). They are often also grooved, with the grooves sometimes reaching down to the disc of the pronotum or seldom continuing sublaterally. The rear edge of the pronotum is usually clearly curved or with a differently curved edge. The prosternal process is fully developed and has parallel lateral edges or is tapered at the tip. It usually extends well behind the hips ( coxes ) of the front legs. It is slightly curved or raised abruptly behind the hips and fits into an indentation on the mesoventrite . The indentation is moderately to very long and deep, occasionally also shallow. It carries an abutment into which the prosternal process engages in order to trigger the click mechanism. The scutellum is well developed, in some species it is abruptly raised. The deck wings are usually at least twice as long as together wide and two to six times longer than the pronotum. They usually have nine distinct rows of dots or stripes. Some species are irregularly dotted. The tips of the wings usually form a common rounding, but in some species they are each rounded, tapering to a point or have apical spines. There are also species in which the apex of the wing is shortened so that the apical tergites of the abdomen are visible, such as in the females of some species of the Cebrioninae . The hind wings are well developed in almost all species. Only in a few groups do the females have no or receding hind wings. They are usually 2.5 to 3.5 times as long as they are wide. The radial cell is usually well developed and elongated. All three pairs of legs have five tarsal links . They are usually simply built, with some species they have hairy areas on the underside or membranous lamellae on the penultimate or several tarsal links.

The abdomen usually has five ventrites , only with the Cebrionini and Aplastini there are species that have six or seven. The first four are mostly fused. Functional spiracles are located on the eighth abdominal segment and on the third to seventh abdominal segment in the pleural membranes. The ninth tergite is truncated to deeply indented or almost completely separated into two parts. The tenth tergite is usually well developed and exposed. Only rarely is it partially fused with the ninth or completely membranous.

larva

The larvae are 10 to 60 millimeters long. The body is elongated in almost all species and has more or less parallel edges. It is flattened to more or less cylindrical in cross section. In the Tetralobini and Thylacosterninae the body is broader and maggot-shaped. The top and bottom of the body are similarly dark or lightly pigmented. In lightly pigmented species, the head capsule and the ninth tergum are darkly pigmented, the dorsal side of the body is also darker than the ventral or the dorsal surface is dark and lightly patterned. The cuticle is usually smooth, in some species tubercles, oblique grooves or areas with special setae are formed. The body is usually hairy or only fluffy. In the case of the Tetralobini, thick growth with long hair occurs. The head is usually directed forwards or slightly downwards, in the Cebrionini and Aplastini it is angled sharply downwards. It is more or less flattened, but in the Cebrionini and Aplastini it is spherical. Pointed eyes ( stemmata ) are often missing, in some groups only a single pointy eye is formed. The labrum is completely fused with the front edge of the frontoclypeal plate and in many species is strongly nasal in the middle. The tripartite antennae are moderately long. The mandibles are symmetrical. They are usually either narrow and sickle-shaped, broad at the base and narrow at the top, or stocky and wedge-shaped. They have one to three teeth. The maxillary palps are four-limbed, the labial palps two-limbed.

With the exception of the Cebrionini and Aplastini, the prothorax is no longer than the meso- and metathorax combined. The ventral side of the prothorax usually has a large, roughly triangular plate, which in some species is divided in the middle and which is rarely adjoined by a small additional sclerite in front. The other two thoracic segments often have no distinct plates on the ventral side. The legs are usually well developed and either slender or stocky. They have fine setae or short, strong thorns. Including the claw-shaped pretarsus, they are usually five-limbed and have two setae on the pretarsus. In the Thylacosterninae they are regressed, four-limbed and have no setae on the claws.

The terga of the abdomen are simple in many species and are finely hairy. Without the abdominal appendages, the ninth abdominal segment is usually shorter or only slightly longer than the eighth segment, does not form a movable plate and always extends to the ventral side, so that the tenth segment is oriented ventrally or posteroventrally. With the Cebrionini and Aplastini, however, the ninth segment is much longer. The ninth tergum is very variable and often carries double-forked urogomphi in pairs . The ninth sternum is always partially or completely free, only in the Cebrionini and Aplastini it is covered. It is simple or sometimes U-shaped with horns or teeth on the sides of the tips. It is not enclosed by the eighth sternum. The tenth segment often forms a short pygopod with a cylindrical cross-section , which is flanked in many Agrypninae by teeth or hooks arranged in pairs. In the Cardiophorinae, pairs of moderately long pygopods are formed.

Click beetle larvae are usually well identifiable up to the level of the genus, but the species can usually only be determined by breeding through to the adult beetle.

Doll

The doll is cream-colored or whitish-cream colored. The body is smooth or has short or long hairs or setae. Seen from above, the head is more or less covered by the pronotum. When viewed from below, the small eyes are partially covered by the antennae. The mouthparts are clearly visible from there. The antennae are parallel on the ventral side of the sides of the prothorax. The large pronotum is variable. In some species a pair of protrusions and setae are usually formed on the leading edge and / or near the center or at the tips of the trailing edge. The legs are free and visible from the stomach side. The rear pair of legs is almost completely covered by the wing sheaths, only the distal segments of the tarsi are visible and protrude beyond the third or fourth ventricle. The abdomen has nine visible tergites and seven or eight visible sternites. In some species, the ninth tergite has paired appendages that are reminiscent of the urogomphi of the larvae or has variable ornamentation. The trachea of ​​the first to the seventh segment are located in the pleural membranes and can be seen in some species from above.

Occurrence

The four largest subfamilies of the click beetles, the Agrypninae , Cardiophorinae , Denticollinae and Elaterinae , are widespread. The tribe Pyrophorini of the Agrypninae occurs mainly in the Neotropic and with two genera in Oceania . The Agrypnini tribe, on the other hand, is known from all biogeographical regions of the world, but has its main distribution in the Afrotropic and Oriental . The less species-rich subfamily Negastriinae is just as widespread, but particularly species-rich and common in the northern hemisphere. The subfamilies Thylacosterninae , Physodactylinae and Oxynopterini are pantropically distributed. A number of subfamilies, for example the Eudicronychinae , Hemiopinae , Morostominae and Subprotelaterinae occur only in the eastern hemisphere, whereas the Campyloxeninae and Semiotini occur only in the Neotropic. Within the subfamily Lissominae , the tribe Lissomini is pantropical, the Oestodini occur in North America and the Protelaterini in New Zealand and Chile. The subfamily Cebrioninae is very widespread, but has its main distribution center in the drier areas of North, Central and South America, southern Europe, North and South Africa, Asia Minor and Central Asia. The Pityobiini are known with one genus each from North America, Chile and New Zealand and with several genera from Australia.

Way of life

Characteristic of the family is their clicking up, which is usually performed when the animals are lying on their backs. The jump is triggered by a sudden movement of an extension on the prosternum into a mesoventral indentation. The energy required for this is provided by a pair of large muscles in the thorax . The muscle tension is generated by the fact that the extension on the prosternum locks into an abutment at the opening of the mesoventral indentation. If the beetle applies enough force, the extension slips behind the abutment into the indentation. This extremely fast movement raises the animals' center of gravity fast enough that they are thrown into the air. The beetles also use this behavior to push themselves back onto the belly side, but it can be triggered in any position and is primarily used to escape from predators. In general, however, the beetles initially react with dead spots when disturbed . Species that are capable of bioluminescence also begin to glow after a long period of disturbance and are very active.

The adults can be observed regularly in the vegetation, but also at night by light sources. They feed on plant sap as a phytophagus . In captivity, they can also be fed sugar solution. To date, the knowledge about the life cycle and the pre-imaginal stages is very sketchy. The economically important species are an exception to this. As a rule, the development of the beetles takes one to two years, but under unfavorable conditions it can take five to eight years. For example, Fulgeochlizus bruchi has demonstrated complete development from egg to imago lasting six years . In Melanactes densus it is even 12 years for a single larva. Pupation takes place in an oval chamber in rotted wood or in the earth that the larva creates at the end of a corridor. The larvae of the Tetralobini tribe build thin, brittle, oval cocoons from a black-brown secretion. The pupa usually lasts two to three weeks, after which the adults live on average one to two months. In the temperate latitudes, the adults hibernate in the doll's cradle and only hatch in spring.

Larvae

There are three types of larvae. The first type, which comprises the Pyrophorinae as defined by Hyslop of 1917 and which thus includes the Agrypninae, denticollinae, Pityobiinae, Negastriinae and some other groups have a different extents sclerotized cuticle, a dorsoventral flattened body, arranged in pairs Urogomphi ( i.e. a ninth tergum forked at the tip ) and sickle-shaped mandibles. They actively dig either in hard earth or under bark and in dead wood. They can move very effectively within the corridors created with the help of their thorny legs and urogomphi as well as the anal hooks.

The second type larvae include the Elaterinae. They are known as wireworms . Your body has a cylindrical or approximately cylindrical cross-section and a more or less evenly and heavily sclerotized cuticle. The ninth tergum is simple and has no urogomphi, the mandibles are just as sickle-shaped. Due to their physique and the lack of suitable body appendages, the larvae of this group can only use existing passages and cavities. They live in loose soil, but also under bark or in rotting dead wood that is already more or less rotten and loose.

The Cardiophorinae are among the larvae of the third type. They have a soft cuticle, a body that is cylindrical in cross section and that is divided into pseudo-segments. They also have no urogomphi and double-lobed mandibles. They are often found in loose soil, where they actively dig, using their unusually shaped mandibles to break up bits of earth.

Feeding of the larvae

The larvae are usually capable of extraintestinal digestion, so they liquefy their food outside of the digestive tract and absorb the resulting fluids. The ventral mouthparts are fused and form a maxillolabial complex, which is densely covered with short hair on the upper side, i.e. on the inner side. These hairs form a kind of filter that separates the liquids to be absorbed from solid particles. In the case of the Ctenicera aeripennis group, for example, it was observed that the larvae choke out a brown liquid that contains amylases . In order to eat, the larvae chew potato tissue, choke out their digestive fluid and absorb the fluid created by the enzymes. The digestive juices of Pyrearinus termitilluminans contain trypsin and various carbohydrases such as amylases, cellulases , trehalases and glucosidases .

Bioluminescence

About 200 species of the Pyrophorini tribe within the neotropical and oceanic Agrypninae and two species of the neotropical Thylacosterninae ( Balgus schnusei ) and Campyloxeninae ( Campyloxenus pyrothorax ) are capable of bioluminescence . The adults of Balgus schnusei emit a green glow from two bulges on the prothorax. The larvae of the species are unknown. The adults of the pyrophorini have a pair of oval vesicles that lie at the base of the posterior angles of the prothorax. They are colored yellow with no activity. Another area that lights up is on the abdominal side of the first abdominal segment. This only lights up during the flight, whereby the other two areas also light up at the same time. In the case of the Hifo genus , only this one area is developed. The areas on the prothorax emit a yellow glow, while the areas on the abdomen glow orange, yellow or red. In all of them, however, the light can be seen continuously. The glow is probably used to advertise sexual partners, but the behavior has not yet been researched. As with many other bioluminescent creatures, the animals glow through luciferin in connection with oxygen , luciferases and adenosine triphosphate .

Bioluminescence has also been documented from the eggs of some species, such as Pyrearinus termitilluminans , which glow faintly but continuously. The larvae of the pyrophorins glow in the green spectrum, especially on the pronotum. In some species, pairs, laterally arranged round or oblique dorsoventral areas light up on each abdominal segment. The glow in the larvae is interpreted as a defense measure against predators, but has not yet been researched in sufficient detail. The larvae of Pyrearinus termitilluminans are known to hunt flying insects - especially termites and ants attracted by them - with their head and the bright green prothorax, which they create from the opening of their tunnel system, which they create in ternite nests.

Economical meaning

A number of wireworms, especially from the genera Agriotes , Athous , Cardiophorus , Ctenicera , Conoderus and Melanotus, are economically relevant pests on cereal and forage plants.

Taxonomy and systematics

The click beetle family was considered a group in the earliest classifications of beetles. For the vast majority of genera, their position as a monophyletic taxon as a whole is certain, but the exact delimitation of the group from the closest related families has not been conclusively clarified. Despite various approaches, the relationships within the family have not been fully explored. Leschen, Beutel & Lawrence (2010) list the 17 subfamilies recognized by them only alphabetically. After an investigation of rDNA and mtDNA of the weakly sclerotized groups of the Elateroidea by Kundrata & Bocak (2011) it was shown that the subfamily Cebrioninae as tribe Cebrionini and Aplastini to the Elaterinae and the Oxynopterini, Pityobiini and Semiotini instead of in subfamily rank, in the rank of tribe to the Denticollinae . Accordingly, the click beetle family includes the following subfamilies:

Types (selection)

supporting documents

  1. ↑ a b c d e f g h i j k l m n o p q r s t u v w Richard AB Leschen, Rolf G. Beutel, John F. Lawrence: Handbuch der Zoologie - Coleoptera, Beetles, Volume 2: Morphology and Systematics (Elateroidea, Bostrichiformia, Cucujiformia partim) . de Gruyter, 2010, ISBN 978-3-11-019075-5 , p. 75 ff . (English).
  2. ↑ a b Robin Kundrata, Ladislav Bocak: The phylogeny and limits of Elateridae (Insecta, Coleoptera): is there a common tendency of click beetles to soft-bodiedness and neoteny? In: Zoologica Scripta. 40, No. 4, April 2011, pp. 364-378 doi : 10.1111 / j.1463-6409.2011.00476.x .

literature

  • Richard AB Leschen, Rolf G. Beutel, John F. Lawrence: Handbuch der Zoologie - Coleoptera, Beetles, Volume 2: Morphology and Systematics (Elateroidea, Bostrichiformia, Cucujiformia partim) . de Gruyter, 2010, ISBN 978-3-11-019075-5 (English).

Web links

Commons : Click Beetles (Elateridae)  - Collection of images, videos, and audio files