File: <dytis1.ima.htm> [For educational purposes only] Terminology Glossary <Principal Natural
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Immature Stages of Dytiscidae
Larvae and adults of Dytiscidae are predaceous, all species are
aquatic and good swimmers. They feed
on aquatic animals, mostly insects, but sometimes also tadpoles or fish. However, 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 bite 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 liquefies 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. References:
Please refer to <biology.ref.htm>,
[Additional
references may be found at: MELVYL Library ] |