Agabus bipustulatus ♂
|( Linnaeus , 1767)|
Agabus bipustulatus is a beetle fromthe swimming beetle family . The genus Agabus is represented in Europe by three sub-genera. Agabus bipustulatus belongs to the subgenus Gaurodytes , which is represented in Europe with twenty-nine species . Agabus bipustulatus is a common and widespread beetle. Recent work shows that the separation of the species Agabus bipustulatus and Agabus solieri is probably not justified.
Notes on the name
The species was first described by Carl von Linné in 1767 under the name Dytiscus bipustulatus . The description contains the sentence capite postice punctis duobus rubris ( Latin at the back of the head with two red dots). The obvious species names bipunctatus (with two dots) and bimaculatus (with two spots) were already assigned within the genus Dytiscus in its delimitation at that time, bimaculatus as early as 1764 by OF Müller , bimaculatus by Linné himself in the same edition under number 21. So wich Linné on the species name bipustulatus (Latin with two pustules ). The two red points can also be indistinct or missing. There are also related species that also have two red spots on the back of the head. The name of the subgenus Gaurodytes derives from altgr. γαύρος "gāūros" for "magnificent" and δύτης "dýtes" for "diver". The generic name Agabus is one of the names that do not refer to the properties of the animals mentioned, but merely represent a personal name used in ancient times. The species has also been described under several synonyms.
Properties of the beetle
The beetle has the flat, elongated oval shape that is typical of swimming beetles, the rear legs are row-shaped as swimming legs . The beetle reaches a length of eight to eleven millimeters. The males (Fig. 1) can be recognized by the thickened tarsi of the forelegs (Fig. 12 right), but they have no suction cups. The upper side of the females (Fig. 2) is matt with a delicate silky sheen, while the males are shiny. The black-brown beetle has red-brown antennae, buttons and front tarsi.
The front edge of the eyes is indented near the antennae (Fig. 5). The antennae are thread-shaped and eleven-limbed. At the rear edge of the head there are two nearer transverse areas where the color is lightened reddish (Fig. 4a). These are eponymous for the species. They are more or less covered by the pronotum when the beetle lifts its head. Often they are also very poorly developed or completely absent (Fig. 4b).
The pronotum is widest at the base and there as wide as the elytra in front. The lateral edge of the pronotum ends at the front corners and does not continue inwards (Fig. 6 when enlarged). The row of dots at the front edge of the pronotum is not broadly interrupted in the middle (Fig. 4a and b). The label is clearly visible.
The elytra, like the pronotum, show a reticulate structure with strongly stretched, predominantly longitudinal meshes (Fig. 4b). The surface is shagreened within the mesh. The rows of points on the wing covers are made up of medium-sized and elongated, isolated points. The submerged parts of the upper wing (epipleurs) suddenly taper sharply towards the rear and run out at the level of the second abdominal segment (Fig. 8, epipleurs on the right tinted red, numbers 1 and 2 are numbers of the abdominal segments).
The tarsi are all five-part. In the males, the three basal links of the anterior tarsi are thickened and tomentose-soled (Fig. 12b). The male's outer front claw is very elongated, roof-like and twisted laterally (Fig. 13), the inner front claw (in Fig. 12b and in Fig. 13 tinted green) has a distinct tooth at the base. In the female, the inner and outer claws of the anterior tarsi are the same (Fig. 12a). In both sexes the hind tarsi are slender, the second to fourth limbs at least twice as long as they are wide (Fig. 9). The outer and inner rear claws are of equal length (Fig. 10). The two end spines of the posterior splint are shorter than the first tarsal segment (Fig. 9). The rear thighs have a group of bristles on the outer corner of the rear edge (clearly visible from below, Fig. 11). The lateral lines of the rear hips are not almost extinguished towards the front, but rather merge clearly into the rear edge of the rear chest, widening outwards (Fig. 8, left rear hip, tinted yellow). The lateral runners of the rear breast (in Fig. 8 the rear breast tinted green) are not narrow, but broadly triangular.
The larva of Agabus bipustulatus was described in 1901 by the Dane Frederik Meinert . The larva shows the elongated shape typical of the swimming beetle larvae with a round, flat (lens-shaped) head, the chest section with three pairs of long legs and the abdomen made up of eight segments, the last segment bearing a pair of two-part cerci . There are three different larval stages, with the first larval stage deviating more from the two older larval stages than these from each other. The following information applies to the third larval stage. The larva becomes thirteen millimeters long in the last stage. It is brown, the rear edge of the body segments dark brown. There are several bright spots on the head and rows of four narrow, lightened spots on the back plates. The larva is almost bald, with some short hairs behind.
On each side of the head, six individual eyes form an eye field. The individual eyes are arranged in two vertical rows with three ocells each. Four individual eyes are visible from above, two from below. The temporal region lies behind the eye field and in front of the neck. Three or four short spines arise laterally near the neck, standing in a longitudinal row and forming a kind of crest (aculei temporales). The four-part antennae are bare and have no appendages. The first and second antennae are equally long, each twice as long as the fourth and only a little longer than the third. The front end of the head is formed by a region, the top of which is the clypeus and the bottom of which is the folded upper lip. At the front edge of this region there are two rows of very short, flat hairs protruding forward, which are also called lamellas or row-shaped hairs (in Fig. L3, only one row can be seen on the edge of the upper lip). The two upper jaws (blue in Fig. L1 on the right) are relatively short and curved inwards. As with all swimming beetles, they have a deep furrow on the inside through which the liquid or liquefied food can drain or be sucked off to the mouth opening (outer part of the canalis cibarius). The oral cavity is closed. Two canals (inner part of the canalis cibaris) run from it laterally forward and open on the underside of the frontal cusps (anguli frontales, Fig. L3 a). When eating, the upper jaws are so wide open that the basal opening of the food canal comes to rest on these mouths. The stipes of the lower jaw (green in Fig. L1 on the right and an enlarged section of Fig. L2 a) has an extension to the front (Fig. L2 b), from which a cone-shaped extension rises inwards, which Maenert calls mala exterior (Fig. L2 c ). Underneath are two hook-shaped curved extensions on the inside. The root of the jaw probe sits to the left of the extension of the stipe (outside). This is slender and tripartite, its first and third link are the same length, the second link a little longer. The lower lip (Fig. L1 a) is two and a half times as wide as it is long. The lip probes that arise at the front corners of the lower lip consist of two slender links, the end link is less than half as long as the base link.
The larvae of the species are also characterized by the length ratios of the last abdominal segments and the two-part cerci. In Agabus bipustulatus , the eighth abdominal segment is slightly less than twice as long as the seventh (13: 7), the base member of the cerci is slightly longer than the eighth abdominal segment, and the end member of the cerci is almost completely regressed and not very clearly separated. The cerci are almost bare. Four short hairs arise at the base of the end link, which protrude many times over the end link. There are three more, longer hairs on either side near the base of the cerci.
The six-limbed legs (hip, thigh ring, thighs, splint, tarsus, claws) are hairy in a characteristic way. The hair on the front leg of Agabus bipustulatus is shown in Fig. L4, the hair on the hind leg in Fig. L5 (thighs tinted yellow, splint tinted pink). The enlarged sections show the hair on the hind leg on the inner edge of the thigh (Fig. L6) and on the inner edge of the splint (Fig. L7).
Young larvae, second larval stage and old larvae differ most noticeably in the length proportions of the body parts and the color. For example, in the old larva the outstretched hind legs hardly reach the 7th abdominal segment, while in the 2nd stage they reach the 8th segment and in the young larva they clearly protrude beyond the end of the abdomen. The head is almost black only in the young larvae. But less conspicuous features are also developed differently in the various larval stages, for example only the young larvae have egg teeth and no spines in the temporal region, the second larval stage has more such spines in the temporal region than the old larvae. The second part of the cerci is still clearly developed in the 2nd stage.
Eggs and doll
Freshly laid eggs are slender, pale yellow, 1.4 millimeters long and less than half as wide. Older eggs are brownish, larger, and more rounded. The doll reaches a length of eight to nine millimeters and a width of five millimeters. It is white-yellow and shows no special features compared to other swimming beetle pupae. Fig. P shows an Agabus doll from a publication from 1865, a link to a photo of a doll of the genus can be found in the individual records.
The adult animals can be found all year round, at least in Central Europe. The eggs are laid in the water. The larvae develop in the water and, like the finished beetles, live predatory. They mainly feed on sick, weakened animals, mainly mosquito larvae. Together with other swimming beetles, they represent an important member of the aquatic health police. The species occurs in almost all types of water, it belongs to the generalist group with regard to the choice of habitat. Above the tree line, they can be found in shallow lakes with stony to muddy subsoil. In the mountain region you can find the beetle in small rivulets, springs and pools with or without vegetation. A wide variety of bodies of water are populated in the lowlands, from temporary bodies of water such as puddles or water-filled fairways to brackish water zones and peat bogs, cattle troughs and garden ponds. In contrast to other water beetles, Agabus bipustulatus can remain in the moist surrounding soil for months when the water bodies dry out and only retreats into permanent water bodies when it is completely dry. In a comparative study, the probability of the occurrence of the species in biotopes with a wet phase of three to four months was found to be greater than in waters with a longer or shorter wet phase. Newly created biotopes are populated very quickly. However, standing water or sluggishly flowing sections in flowing water with abundant vegetation and a sediment of decomposing plants are preferred. This is also where reproduction takes place. The beetles show well developed flight muscles and are good fliers who are attracted to light.
The main time of reproduction in Central Europe is in late autumn, but copulations can be observed until spring. Despite the specialized front tarsi of the male, the male has difficulty holding the female. The female escapes easily if she can hold onto aquatic plants. The male tries to push the female into the open water. The male strives for the posture adopted when breathing on the surface of the water, as the adhesion to the surface of the water gives him a certain stability. If the male can reach this position while holding the female, the female usually soon gives up resistance. The male tries to set himself and the fixed female in a rocking motion by alternately bending and stretching the last abdominal rings. This seems to stimulate the female. The rocking motion is occasionally interrupted by a violent tremor in the horizontal direction, which is triggered by the male's rapid beating of the tip of the abdomen. Following this tremor, the male's saber-like penis emerges and tries to reach the female genital opening. The transfer of the sperm in a spermatophore seems to succeed only if the female approaches the male in the original sense of the word by stretching out the tip of the abdomen and thus clears the way to the vagina.
Egg laying and embryonic development
Newly mated females can be recognized by the fact that the tip of the three millimeter long spermatophores introduced by the male is still visible at the tip of the abdomen in the form of a one millimeter long, transparent gelatinous strip. After the light yellow sperm mass has migrated from the spermatophore in the direction of the semen container of the female, the female rejects the remains of the spermatophore and thus also the externally visible part a few hours after separation from the male. The egg-laying also takes place from autumn to spring, but is interrupted at low temperatures. In aquariums without plants, the eggs are released freely into the water or, less often, loosely glued to the walls and floor. In nature, eggs are found attached to living or dead plant material from a wide variety of plant species. Shoot tips are preferred, whereby the eggs, without damaging the tissue, are pushed deep between the youngest leaves of the vegetation cone and are glued there with a mass that hardens quickly. The eggs, which are initially 1.4 millimeters long, enlarge considerably and become less slender. The chorion bursts and the yolk skin becomes the egg shell. The eggs are 1.75 millimeters long and 0.95 millimeters thick. Embryonic development takes six to seven weeks at six to seven degrees Celsius. The pigmentation of the individual eyes is to be observed first, then the tanning of the upper jaw.
Newly hatched larvae measure three millimeters without cerci. The animals darken within a few hours, the head capsule turns black-brown. The gap in the mouth, which is initially still open, is closed by folding the upper lip downwards and backwards. The young larvae can swim short distances freely with paddling movements, but usually move crawling on the aquatic plants. First the front leg moves, then the middle leg on the opposite side and finally the hind leg on the starting side. Once the three legs have found support, the same process takes place in mirror image on the other half of the body. The abdomen does not touch the surface. The long claws allow good anchoring on the base. The larvae prefer to stay in the dense water grass of the bank zones. Here they often stay motionless for hours near the surface of the water. Hunting larvae crawl around like lizards. If they come across someone they can flinch and flee. If, on the other hand, they feel equal to the other, they vigorously hit the mandibles into the opponent, even in physically larger conspecifics. After a bad bite, the larva retreats quickly, only to carefully approach the prey again after a while. At 12 ° C, it takes about half an hour for a fellow of the same age to process. Young larvae can be found outdoors from December to April, but at higher temperatures, molting to larvae of the second instar can already take place after eleven days. This grows from an initial 5.5 millimeters to eight millimeters. It is no longer buoyant and moves more sluggishly, while crawling the end of the body rubs against the ground. Fly larvae are the main prey, occasionally tadpoles and young larvae of the same species. The next molt occurs at around 18 ° C after seven days, at temperatures around 12 ° C to 15 ° C after 10 days. The adult larva is similar in color to the second larval stage. It grows from just under eleven millimeters to fourteen to seventeen millimeters, the increase in size in relation to the second stage is almost sixty percent. The need for atmospheric air is significantly greater, the movements even more clumsy. This also changes the potential prey animals. After the meal you can sometimes see cleaning movements in which the front legs are pulled over the head several times from back to front. The duration of the third larval stage depends on the temperature and the food available. Most adult larvae overwinter. They are already numerous in January, but are present until April, and in colder climates probably even in May. Complete freezing is fatal, even if it only lasts twelve hours and the larva is not cooled to freezing temperature in the process. However, the larva survives partial freezing, even if only a small part of the animal remains ice-free.
Pupation, construction of the doll's cradle
The sufficiently aged larva stops feeding and begins to wander around restlessly. At night she tries to get ashore. There it moves more skillfully than in water and can also overcome significant obstacles. Then the larva digs itself in to pupate and builds a hollow sphere from earth with a clear width of eight to twelve millimeters and a wall thickness of three millimeters. This housing is sunk up to half or two thirds into the surrounding soil, at most lightly woven with it and mostly surrounded by an air wall. Older, dried out housings are easy to remove from the ground. To produce it, the larva curves the abdomen upwards and forwards on a suitable surface until the tip of the body touches the head. Then it secretes a droplet of liquid from the anus, which drains over the head and finally wets the entire back evenly. This keeps the insect moist for a long time. Now the larva pushes its head into the ground, breaks loose small chunks of earth and piles them up in front of itself. It rotates in a circle, with small pauses, until it is surrounded by a ring wall. Soon, however, the walls will no longer be pulled up at the same time, but rather continued to be built on one side. Here the wall is first made vertically ascending, then overhanging, dome-shaped and finally descending again on the opposite side, in which the broken crumbs are glued on. The soil is now preferably dug under the descending wall and glued over it, so that a gap remains free between the wall growing downwards and the soil standing on the side. This is continued so that the resulting cave takes on a spherical shape and the excavated material is used to shrink and close the cave opening. After one to several weeks of rest, the moulting takes place to the pupa. The duration of the pupal stage depends mainly on the temperature and also on the humidity. At 18 ° C, the imago hatches after about two weeks. At higher temperatures this time is hardly shortened, at lower temperatures it increases considerably, at an average of 11 ° C it is about six weeks. The young beetles remain in the pupa cradle after they have hardened; with exceptions they only appear in autumn.
- Heinz Joy, Karl Wilhelm Harde, Gustav Adolf Lohse: The beetles of Central Europe . tape 3 . Adephaga 2 - Staphylinoidea 1. Goecke & Evers, Krefeld 1971, ISBN 3-87263-015-6 , p. 63 .
- Systematics and distribution of Agabus bipustulatus in Fauna Europaea.
- Marcus K. Drotz, Anssi Saura, Anders N. Nielssen: The species delimitation problem applied to the Agabus bipustulatus complex (Coleoptera, Dytiscidae) in north Scandinavia . In: Biological Journal of the Linnean Society . tape 73 , no. 1 , 2001, ISSN 0024-4066 , p. 11-22 , doi : 10.1111 / j.1095-8312.2001.tb01343.x ( researchgate.net [PDF]).
- Konrad Dettner: Chemotaxonomy of water beetles based on their pygidial gland constituents. In: Biochemical Systematics and Ecology. Volume 7, No. 2, 1979, pp. 129-140
- Carolus Linnaeus: Systema Naturae…. Volume 1, Part 2, 12th Edition, Stockholm 1767, p. 667, No. 17 ( biodiversitylibrary.org ).
- Otto Frederik Müller: Fauna Insectorum Fridrichsdalina…. Copenhagen and Leipzig (Hafnia Lipsia) 1764, p. 44:20 No. 194 ( gdz.sub.uni-goettingen.de ).
- Sigmund Schenkling: Explanation of the scientific beetle names (kind).
- Sigmund Schenkling: Explanation of the scientific beetle names (genus).
- Frederik Meinert: Vandkalvelarverne (Larvae Dytiscidarum). Copenhagen 1901 in Det kongelige Danske Videnskabernes Selskabs Skrifter Series 6, No. 9, Naturvidenskabelig og mathematisk Afdeling p. 372 Larva Agabus bipustulatus drawings of the larva .
- Photo of the larva .
- Henri PI Bertrand: Larves et Nymphes of Coléoptères aquatiques du Globe. Imprimerie Paillard, Paris 1972.
- Hans Blunck: Small contributions to the knowledge of the sexual life and the metamorphosis of the Dytisciden 3rd part Agabus bipustulatus. In: Entomological leaves. Vol. 17, 1921, pp. 184-194 ( biodiversitylibrary.org ).
- Photo doll .
- Adolf Horion : Käferkunde for nature lovers. Vittorio Klostermann, Frankfurt am Main 1949 pp. 32, 33.
- A. Nilson, M. Holmen: The aquatic adephaga of Fennoscandia and Denmark II Dytiscidae. In: Fauna Entomologica Scandinavia. 1995.
- Donald A. Yee (Ed.): Ecology, Systematics and Natural History of Predaceous Diving Beetles (Coleoptera, Dytiscidae). Springer, Dordrecht 2014, ISBN 978-94-017-9108-3 , ISBN 978-94-017-9109-0 (eBook) doi: 10.1007 / 978-94-017-9109-0 p. 323 in the Google book search .
- Dorothy J. Jackson: Observations on the Capacity for Flight of Water Beetles . In: Proceedings of the Royal Entomological Society of London Series A, General Entomology . tape 27 , no. 7–9 , 2009, ISSN 0375-0418 , p. 57-70 , doi : 10.1111 / j.1365-3032.1952.tb00155.x .
- Hans Blunck: Small contributions to the knowledge of the sex life and the metamorphosis of the Dytisciden 1st part. In: Zoologischer Anzeiger. Volume 41, 1913, p. 541 ( biodiversitylibrary.org Mating of Agabus undulatus , according to Blunck identical to the mating behavior of Agabus bipustulatus ).