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COLEOPTERA, Hydrophilidae -- <Images> & <Juveniles> Description & Statistics
There is a much greater variety in
behavior among members of this family than in the wholly aquatic
Coleoptera. Most species are aquatic,
but a number of the subfamily Sphaeridiinae are terrestrial in all stages,
living in moist soil or associated with animal wastes (Legner et al. 1980, 1981). Adults are commonly known as "water
scavenger beetles." Balduf
(cited by Clausen, 1940) provided an extensive early account of hydrophylid
behavior. Aquatic
hydrophilids are most often found in ponds, especially those having extensive
vegetative growth, although they also may be found along streams. Adult beetles are principally scavengers,
consuming decaying animal matter and also living on dead plant tissue. Many species feed mostly on algae and
other lower forms of plant life.
Although most larvae are predaceous, there are some exceptions. Predaceous forms feed on various worms,
snails, insect larvae and pupae, Entomostraca, small fish, crayfish and
tadpoles. They may actually swallow
bits of solid matter, but seem to prefer body fluids of their prey. Several species of the genus Dactylosternum are predators of crop
pests. Dactylosternum dytiscoides
F., D. hydrophiloides M'Leay and D.
cycloides Knisch. attack larvae of
the sugarcane beetle borer, Rhabdocnemis
obscura Boids., in the
Philippines. These species were
imported to Hawaii during 1925-1926 for biological control. D.
abdominale and D. dysticoides were
imported to Jamaica for biological control of banana borer, Cosmopolites sordida Germ. Oviposition behavior is
distinctive because of the silken case within which the eggs of many species
are contained. Several more primitive
subfamilies lay their eggs singly, with little or no covering. In a few genera, the cases are attached to
the body of the parent by silken strands, while in others they are enclosed
in a folded leaf, placed on foliage underneath the water, or float free on
the surface (Clausen 1940/62). The
larvae of many aquatic species are unable to swim, but rather move about by
crawling along the bottom or on vegetation, and may be found only partially
submerged. Larvae of most species
construct their pupal cases out of the water, near the water line in mud,
under various objects, or on plants above ground. Enochrus is reported
to form its case from floating strands of Spirogyra. Hydrophilidae have more than 500
species. They are cosmopolitan. Although primarily aquatic beetles, many
species have terrestrial habits. Diagnostic
characters of these are the long and slender maxillary palpi, as long or
longer than the antennae. Antennae
have 6-10 segments with the apical segments shaped into a distinct club. All the tarsi have the same number of
segments; the prosternal sutures are distinct; the gular sutures are double
and the hind coxal craters do not divide the first ventral abdominal segment. The larvae of Hydrophilidae are
voracious predators on a variety of insects and other aquatic animals; while
the adults are scavengers on decaying plant and animal matter (Legner et al.
1980). Several species have been
introduced for biological control with no reported success. There are 1-2 generations annually, and overwintering
is as adults (Clausen 1940/62). = = = = = = = = = = = = = = = References: Please refer to <biology.ref.htm>, [Additional references
may be found at: MELVYL
Library] Balduf, W. V. 1935. The Bionomics of Entomophagous
Coleoptera. J. S. Swift Co., NY. 220 p. Bland, R. G. & H. E. Jaques. 1978. How to Know the Insects,
3rd ed. Dubuque, Iowa: Page 193,Wm. C. Brown Co. 409 p. Borror, D. J & R. E. White. 1970. A Field Guide to the
Insects. Boston: Houghton Mifflin Co. Pages 156-157 Borror, D. J., C. A. Triplehorn, & N. F. Johnson. 1989. An
Introduction to the Study of Insects, 6th ed. Page 417 Philadelphia: Saunders
College Publishing. 875 p. Daly, H. V., J. T. Doyen, & A. H. Purcell III. 1998.
Introduction to Insect Biology and Diversity, 2nd ed. Page 464 Oxford
University Press. 680 p. Legner, E. F., D. J. Greathead & I. Moore. 1980.
Population density fluctuations of predatory and scavenger arthropods
in accumulating bovine excrement of three age classes in equatorial East
Africa. Bull. Soc. Vect. Ecol.
5: 23-44. Legner, E. F., D. J. Greathead & I. Moore. 1981.
Equatorial East African predatory and scavenger arthropods in bovine
excrement. Environ. Entomol.
10(5): 620-625. Legner, E. F., D. J. Greathead & I. Moore. 1981b.
Equatorial East African predatory and scavenger arthropods in bovine
excrement. Environ. Entomol. 10(5): 620-625. Regimbart, M. 1902.
Ann. Ent. Soc. France. p. 158-232. White, R. E.. 1983. A Field Guide to Beetles of
North America. Boston: Pages 104-108 Houghton Mifflin Co. 368 p. |