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COLEOPTERA, Dytiscidae (DeGeer
1774) --
<Images> & <Juveniles> Please refer also to the following
link for details on this group: Dytiscidae = Link 1 Description &
Statistics
Larvae and adults are predaceous; all species are aquatic and
excellent swimmers. They feed
primarily on aquaticinsects, but sometimes also on tadpoles and young fish.
Most species live on the immature stages of other aquatic insects,
mainly Ephemerida, Hemiptera and Odonata.
Larvae and adults have generally the same food source, though the
latter, being more agile, receive a greater choice. Although generally considered beneficial for biological control
of mosquitoes, they have never been used for biological control. An early detailed review of Dytiscidae was
given by Balduf (1935). During feeding, the beetles bit away portions of the prey and
swallow them a little at a time, while the larvae utilize only liquid food, a
habit that is made possible by the presence of a narrow canal or channel
extending from near the tip to the base on the inner margin of each
mandible. Like many Coleoptera, most
dytiscid larvae inject a digestive secretion into the prey's body, which to a
considerable extent liquifies the solid tissues. Adult Dytiscidae are not limited to an aquatic life, for some
species are able to use their legs for running and most are able to fly
extensively. However, their bodies
have been modified for aquatic life, as is shown by a closer union of the
body parts, a pronounced streamlining of the body, the flattening of legs,
and the development of fringes of heavy hairs on the inner margins of the
tarsi. Clausen (1940) noted that in
incompleteness of this adaptation to aquatic life was revealed by the
pupation habit. After feeding is
completed, the mature larvae heave the water to form their pupation cells in
mud or soil, under stones and other objects, or among trash. A distinct spherical, oval or pyriform
cell is formed, which in larger species may be 5 cm. or more in diameter. The different species show differences in their manner of
locomotion. Some species in several
genera move about solely by crawling over the bottom or over rocks and
vegetation. Other species swim only
occasionally, but many are very active swimmers and come to the surface to
capture prey. The bodies of these are
light which enables them to come to the surface easily. The legs of some species are equipped with
fringes of hairs that facilitate swimming. Eggs of some dytiscids are laid in masses in mud or debris at the
water's edge, singly on the surface of floating leaves, or in individual
incisions in submerged plant tissue.
The latter behavior is typical in most species. Some damage may at times be inflicted to
ornamental aquatic vegetation through excessive oviposition, which results in
wilting and death of leaves and stems (Clausen 1940/1962). There is usually only one generation annually, although adults
may live for several years. The life
cycle depends on temperature of the surrounding water, and egg incubation may
be prolonged from one week or less to several months. Most species overwinter as adults in
water, becoming active and ovipositing early in springtime. Other hibernate as larvae, and adults
appear in midsummer. Clausen (1940) referred to the interesting feature of larval
dytiscids in their ability to regenerate lost body parts. Legs and antennae seem to be only partly
replaced at the following molts but are fully regenerated in the pupa. Such replacement is much more complete when
the parts are lost by 1st instar larvae than when they are lost by older
instars. Dytiscidae is a large
widespread family with more than
4,000 species. Key characters of
these predaceous diving beetles include an elongated filiform antennae,
11-segmented, generally bare and longer than the maxillary palps. The hind coxae are much enlarged,
contiguous and fixed to the metathorax.
Their size varies, the head is broad and closely joined to the
prothorax. The tibiae and tarsi of
the hind legs are bordered with hairs that are designed for swimming = = = = = = = = = = = = = = = References: Please refer to <biology.ref.htm>, [Additional references
may be found at: MELVYL
Library] Bailey, P., Boon, P. & Morris, K. 2002. Australian Biodiversity Salt Sensitivity Database. Land &
Water Australia. Chessman B. 2003. SIGNAL 2 - A Scoring
System for Macroinvertebrate 'Water Bugs' in Australian Rivers,
Monitoring River Heath Initiative Technical Report no 31, Commonwealth of
Australia, Canberra DeFoliart, G.
R. 2002. Chapter 26 - Eastern Asia: China, Japan,
and other countries. In: The Human Use of Insects as a Food Resource: A
Bibliographic Account in Progress. Gooderham, J. & Tsyrlin, E. 2002. The Waterbug Book: a guide to the freshwater macroinvertebrates
of temperate Australia. CSIRO Publishing. Jach, M.
A. 2003. Fried water beetles Cantonese style. American Entomologist
49(1): 34-37. Kefford, B.J., Papas, P.J., Nugegoda, D. 2003. Relative salinity tolerance of macroinvertebrates from the
Barwon River, Victoria, Australia. Marine and Freshwater Research, 54:
755-765. Larson, D. J.,
Y. Alarie & R. E. Roughley. 2000.
Predaceous Diving Beetles (Coleoptera: Dytiscidae) of the Nearctic
Region, with emphasis on the fauna of Canada and Alaska. NRC Research Press,
Ottawa. Lawrence, J.F. & Britton, E.B. 1991. Coleoptera Beetles. Pp. 543-683, in Insects of Australia: A
textbook for students and research workers. CSIRO. 2nd Edition. Lawrence, J.F., Weir, T.A. & Pyke, J.E.
2002. Australian Faunal Directory: Checklist for
Coleoptera: Adephaga: Dytiscidae. Australian Biological Resources Survey,
Department of the Environment and Heritage. Miller, K. 2003. The phylogeny of diving beetles
Coleoptera: Dytiscidae and the evolution of sexual conflict. Biological
Journal of the Linnean Society, 79: 359-388. Minnesota Pollution Control Agency. 2004. Wetlands: Monitoring Aquatic Invertebrates. Omer-Cooper, J. 1965. So. Afr. Animal
Life 11: 59-214. Pederzani, F. 1995. Keys to the identification of the genera and subgenera of adult
Dytiscidae sensu lato of the world Coleoptera Dytiscidae. Atti della Accademia Roveretana degli Agiati, Serie
7 B, 4: 5-83. Ramos-Elorduy,
J. & Pino M. 1990. Caloric content of some edible insects of Mexico. Revista de la Sociedad Quimica de Mexico 342: 56-68.
Smith, R. L. W. et al. 1967. Ann. Ent. Soc. Amer. 60: 908-10. Tindale, N.B. 1966 Insects as food for the
Australian Aborigines. Australian Natural History, 156, p. 179-183. Water and Rivers Commission. 1996. Macroinvertebrates & Water Quality. Water Facts 2. Watts, C.H.S. 1978. A revision of the Australian Dytiscidae Coleoptera. Australian
Journal of Zoology, Supplementary Series no 57: 1-166. Watts, C.H.S. 2002. Checklists & Guides to
the Identification, to Genus, of Adult & Larval Australian Water Beetles
of the Families Dytiscidae, Noteridae, Hygrobiidae, Haliplidae, Gyrinidae,
Hydraenidae and the Superfamily Hydrophiloidea Insecta: Coleoptera.
Identification and Ecology Guide no 43. Cooperative Research Centre for
Freshwater Ecology. Zimmerman, J.
R. 1970.
Mem. Amer. Ent. Soc. 26: 1-275 |