Trout brook beetle
| Trout brook beetle | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name of the family | ||||||||||||
| Amphizoidae | ||||||||||||
| LeConte , 1853 | ||||||||||||
| Scientific name of the genus | ||||||||||||
| Amphizoa | ||||||||||||
| LeConte , 1853 |
The trout brook beetles ( Amphizoa ) are the only genus in the beetle family Amphizoidae . Only five species are currently known, but new species yet to be discovered are suspected, especially in western and southwestern China.
features
Beetle
The beetles have a body length of 11 to 16 millimeters. They look similar to ground beetles of the genus Metrius or some black beetles , but differ from them by the indentations for the hips ( coxes ) of the middle legs, which are of a complex type and the completely immobile and strongly overgrown hips of the rear legs, as in others Water beetles. Their body is oval in shape and slightly curved on the sides and back. The angle at the transition between the pronotum and the wings is very noticeable. The dark to deep black body surface is matt and has a characteristic microstructure. The head is almost square and about a third shorter than the pronotum. The oval compound eyes are relatively small and protrude slightly. The front plate ( clypeus ) is about three times as wide as it is long. The short, eleven-segment feelers are thread- shaped . They do not reach the posterior margin of the prothorax . The antennae are hairless, the antennae are only extremely short, spiky sensory hairs. The scapus is wider than the pedicellus and flagellomeres and has a spherical base, the pedicellus is shorter than the subsequent segments. The third through eleventh antennae are about two times longer than they are wide. The mandibles are short and wide and almost rectangular. They are heavily obscured by the labrum and labium , but can be seen from the side.
The basal prothorax is slimmer than the cover wings. It has slightly rounded teeth on the sides. The indentations for the hips of the front legs are open on the outside, the procoxae are spherical. The mesoventrite is short and has a hexagonal indentation. The hips of the middle legs are clearly separated from each other and lie in indentations of the complex type, and are thus laterally bounded by the mesepimeron and metanepisternum. The broad wings are indistinctly grooved lengthways. On the ventral side of their tips there is a series of short, wide spines, the function of which is currently unknown. The hips of the hind legs are broad and touch the wings laterally. The membranous pair of wings (alae) is well developed. The splints ( tibia ) of the front legs lack a cleaning device, the splints of the middle and rear legs have loosely arranged tufts of short, fine webbed hair. The spurs of the rails are short. All three pairs of legs have five tarsal links .
On the abdomen, the sternites of the second to seventh segments are visible, with the second sternite only being seen from the side. The seventh sternite has a roughly triangular shape. The defensive glands have no connection to the anus, their openings lie laterally in front of the tergite of the eighth abdominal segment.
Larvae
The body of the larvae is flattened dorsoventrally and fairly wide, with the widest point being around half of the body and the abdomen narrowing towards the rear. In relation to the body length, the larvae are the widest in the first instar. In the third stage, the larvae reach a length of 12 to 17 millimeters and a width of 3.5 to 4.7 millimeters. They are colored brown to black on the back in adaptation to the inhabited substrate, the underside of the body is largely unpigmented. All tergites are sclerotized and separated by a central suture. The mouthparts are directed forward, the head is flattened and narrower than the prothorax. There are six point eyes ( ocelli ) in two rows. The labrum has grown together with the frontal plate. The four-part antennae are very short and only slightly longer than the head is wide. The fourth link is extremely small. The antennae have no sense organs. The pointed, curved mandibles are rather slender. The prothorax is no longer than the meso- and metathorax combined. The hips are more than twice the diameter of the hip bases. The legs of medium length and about the same length for all three pairs of legs are six-limbed. They have two posable claws. The stigmata on the thorax are not functional. The abdomen has eight fully developed segments. The sternas on the first to seventh segment are weakly sclerotized, the eighth segment is trapezoidal. On the ninth, receding segment, there are single-limbed but large, conical urogomphi . The spiracles on the first to the seventh abdominal segment are on the ventral side and are also not functional. The tracheal openings on the eighth abdominal segment are large and lie between the bases of the urogomphi.
Occurrence
The distribution of Amphizoa insolens , Amphizoa lecontei and Amphizoa striata extends from the Pacific coast and the Rocky Mountains of Alaska to southern California and east to Arizona, Colorado and Montana. Amphizoa sinica and Amphizoa davidi have been found from eastern China and North Korea. There are speculations that the distribution of the beetles extended from the Cretaceous to the Eocene, from northeast Asia to northwest North America.
The trout brook beetles have been found from cold mountain streams, such as Amphizoa insolens and Amphizoa lecontei from around 2000 meters above sea level, or such as Amphizoa striata from lower, relatively warm, slow-flowing waters, but occasionally also on lake shores. One of the species common in China is common in mountain conifer forests and lives in seepage water and pools adjacent to rocky slopes.
Way of life
The beetle's eggs are 2.1 millimeters long and one millimeter wide. They are placed in damp earth or under water, for example on sunken dead wood. The older larvae live in the water and leave it to pupate in the sand or mud some distance away from the water. Newly hatched adults are often covered in mud. Both the larvae and the adult beetles are poorly adapted to their aquatic habitats and have a semi-aquatic way of life. In the water, the beetles cling to driftwood, exposed roots or stones, but they also stay in the vicinity of the water. Their swimming abilities are no better than those of ground beetles (Carabidae). If you detach them from the substrate, they move sluggishly and can very often drift away with the current. When malfunctioning, the adults excrete a yellowish liquid from their pygidial glands, which smells bad due to the dimethyl disulfide it contains . The larvae are sociable. They remain motionless when disturbed and usually sink to the bottom of the water, ball their bodies together or float on the surface of the water.
Both the larvae and the adults come to the water surface from time to time to renew their air supply. As with the other beetles living in water, the larvae breathe through large tracheal openings at the end of their abdomen after they have pierced the surface of the water with their urogomphi. The adult beetles have an air bubble on the wing tip and can stay under water much longer than the larvae. During the day, both the larvae and the adults are very sluggish, but they are quite active at night. Both have a predatory diet and are apparently specialized in the larvae of stone flies (Plecoptera). The adult beetles also climb along the shore when hunting. Other insects such as dragonfly larvae or mayflies are rarely eaten. The larvae are cannibalistic and occasionally eat drowned insects. Since they distribute their digestive juices on the prey for extraintestinal digestion , they have to go above the surface of the water. The trout brook beetles form two generations per year, with the larvae in the first larval stage and the adults overwintering. The development time of the larvae strongly depends on the water temperature and the sea level of the habitat. In Amphizoa sinica molting takes place for the second larval stage in April after about 10 days development, the second molt place after two months in May / June instead, pupation after two months in June / July.
Systematics
The trout brook beetles share features with the ground beetles, such as the construction of their legs, and features with the swimming beetles (Dytiscidae), such as the two large sensory lobes on the epipharynx . It was initially assumed that the trout brook beetles represent a sister group to the group (Dytiscidae + Noteridae ) + {[(Parahygrobiidae + Coptoclavidae) + Hygrobiidae ] + Gyrinidae }. It is now assumed that the trout brook beetles share common ancestors with the Hygrobiidae and the Dytiscidae and belong to the superfamily Dytiscoidea , which is also supported by recent molecular genetic and morphological studies. The trout brook beetles are therefore a sister group of the group Hygrobiidae + Aspidytidae + Dytiscidae. The trout brook beetles share with the Aspidytidae the shape of the tip of the prosternal process, the indentations of the middle hips and the ground beetle-like legs.
The autapomorphies of the larvae are the almost completely reduced fourth antennae and the lack of sensory organs, the denser bristles, the broadly flattened terga on the thorax and abdomen and the single-segment, conical, pointed urogomphi. The autapomorphies of the adults are the one-segment galea, the absence of the submento-mental suture and a very small furca on the methatorax.
Five species of trout brook beetles are currently known:
supporting documents
Individual evidence
- ↑ a b c d e f g h i j k l Rolf G. Beutel, Richard AB Leschen: Handbuch der Zoologie - Coleoptera, Beetles, Volume 1: Morphology and Systematics (Archostemata, Adephaga, Myxophaga, Polyphaga partim) . 1st edition. de Gruyter , 2005, ISBN 3-11-017130-9 , p. 81 ff . (English).
literature
- Rolf G. Beutel, Richard AB Leschen: Handbuch der Zoologie - Coleoptera, Beetles, Volume 1: Morphology and Systematics (Archostemata, Adephaga, Myxophaga, Polyphaga partim) . 1st edition. de Gruyter , 2005, ISBN 3-11-017130-9 (English).
