179
Thus, in the present chapter, a moderate
discussion of the various terminologies regarding
the biota of wetlands and lakes has been done.
9.6
Insects of Inland Waters
Insects constitute a very important component of
the metazoan life of lakes, wetlands and other
inland aquatic habitats. Many insects are benthic,
living on or burrowing into sediments or occupying the vegetation growing upon them in various
ways. Many of them swim habitually between
places which they occupy for feeding, reproduction or other activities and may be regarded as
nektobenthic . However, very few insects are
planktonic, e.g. the larvae of the fl ies of the
Chaoborinae. They are meroplanktonic, in general.
A single species of Anisops is nektoplanktonic.
They are considered as somewhat social in the
fi shless Wisdom Lake in Long Island, Papua New
Guinea. Among the hemipterans, approximately
half the aquatic species live on the water surface
as epipleuston.
Detailed works had been done on the aquatic
insects of Pterygota (MacKerras 1970 ; Merritt
and Communis 1984 ). It may be noted here that
none of the members of Apterygota are aquatic.
The insects of the group Collembola are often
epipleustic. The group Diptera is considered as
by far the most diverse order of insects in freshwater. They are, in fact, one of the most diversifi ed of any major taxon of FW organisms.
9.6.1 Aquatic Life and Life History
In general, there are two main types of aquatic
insects, namely,
(a) Group I: This group includes those insects
whose adult stages are passed in water. This
group also includes the active immature
stages of almost all species, which are passed
in water.
(b) Group II: This group includes those insects
in which the adult stages emerge as a terrestrial or aerial being after a nymphal or larval
life in water. It may be noted here that many
insects, numbering approx. 500,000 species
live in some sort of terrestrial habitat in both
immature and adult stages. Both adult and
active immature stages of approx. 9,000
species seem to be in or on water.
Further, the aquatic life of the endopterygote
water beetles is interrupted by a pupal stage,
which, in almost every case, is formally terrestrial. The pupa generally lies in a dry cavity in a
cocoon constructed in the soil of the bank of the
stream, river, pond, wetland or lake, in which the
larva had lived and to which the adult ordinarily
will return. This is, however, not the case with
exopterygote water bugs.
It may be pointed out here that, in temperate
regions, insects of the fi rst group ordinarily pass
the winter as aquatic adults, while those in the
second group do so in some immature stage
(Macan 1965 ). However, there are exceptions to
this generalisation. It tends to be true wherever
the climate is markedly seasonal.
9.6.2 Food of Aquatic Insects
There is obviously wide variation in the food of
aquatic insects. In general, it is fi nally derived
from four kinds of food chains, namely, (a) those
based on phytoplankton (PP); (b) those based
on rooted or other kinds of benthic vegetation;
(c) those based on vegetation growing on land,
the products of which fall, are blown or are
washed into the water; and (d) arthropod fallout,
which is the major source for the surface insects
and perhaps also for aquatic larvae, e.g. Coleoptera and Odonata. Further, faecal products of
some fi shes may also be a contributor to insect
diet. This may be a major input in alpine and subalpine lakes.
Most of the production of the fi rst kind of
chain can potentially consist of propagules or of
material which is directly eaten, so that no material, perhaps, needed to be left ideally to form
detritus rather than immediately contributing to
new organisms of the same or of different kind as
the producers. However, what happens in planktonic communities in the free water of the
illuminated parts of lakes and large rivers, no less
9.6 Insects of Inland Waters
Thus, in the present chapter, a moderate
discussion of the various terminologies regarding
the biota of wetlands and lakes has been done.
9.6
Insects of Inland Waters
Insects constitute a very important component of
the metazoan life of lakes, wetlands and other
inland aquatic habitats. Many insects are benthic,
living on or burrowing into sediments or occupying the vegetation growing upon them in various
ways. Many of them swim habitually between
places which they occupy for feeding, reproduction or other activities and may be regarded as
nektobenthic . However, very few insects are
planktonic, e.g. the larvae of the fl ies of the
Chaoborinae. They are meroplanktonic, in general.
A single species of Anisops is nektoplanktonic.
They are considered as somewhat social in the
fi shless Wisdom Lake in Long Island, Papua New
Guinea. Among the hemipterans, approximately
half the aquatic species live on the water surface
as epipleuston.
Detailed works had been done on the aquatic
insects of Pterygota (MacKerras 1970 ; Merritt
and Communis 1984 ). It may be noted here that
none of the members of Apterygota are aquatic.
The insects of the group Collembola are often
epipleustic. The group Diptera is considered as
by far the most diverse order of insects in freshwater. They are, in fact, one of the most diversifi ed of any major taxon of FW organisms.
9.6.1 Aquatic Life and Life History
In general, there are two main types of aquatic
insects, namely,
(a) Group I: This group includes those insects
whose adult stages are passed in water. This
group also includes the active immature
stages of almost all species, which are passed
in water.
(b) Group II: This group includes those insects
in which the adult stages emerge as a terrestrial or aerial being after a nymphal or larval
life in water. It may be noted here that many
insects, numbering approx. 500,000 species
live in some sort of terrestrial habitat in both
immature and adult stages. Both adult and
active immature stages of approx. 9,000
species seem to be in or on water.
Further, the aquatic life of the endopterygote
water beetles is interrupted by a pupal stage,
which, in almost every case, is formally terrestrial. The pupa generally lies in a dry cavity in a
cocoon constructed in the soil of the bank of the
stream, river, pond, wetland or lake, in which the
larva had lived and to which the adult ordinarily
will return. This is, however, not the case with
exopterygote water bugs.
It may be pointed out here that, in temperate
regions, insects of the fi rst group ordinarily pass
the winter as aquatic adults, while those in the
second group do so in some immature stage
(Macan 1965 ). However, there are exceptions to
this generalisation. It tends to be true wherever
the climate is markedly seasonal.
9.6.2 Food of Aquatic Insects
There is obviously wide variation in the food of
aquatic insects. In general, it is fi nally derived
from four kinds of food chains, namely, (a) those
based on phytoplankton (PP); (b) those based
on rooted or other kinds of benthic vegetation;
(c) those based on vegetation growing on land,
the products of which fall, are blown or are
washed into the water; and (d) arthropod fallout,
which is the major source for the surface insects
and perhaps also for aquatic larvae, e.g. Coleoptera and Odonata. Further, faecal products of
some fi shes may also be a contributor to insect
diet. This may be a major input in alpine and subalpine lakes.
Most of the production of the fi rst kind of
chain can potentially consist of propagules or of
material which is directly eaten, so that no material, perhaps, needed to be left ideally to form
detritus rather than immediately contributing to
new organisms of the same or of different kind as
the producers. However, what happens in planktonic communities in the free water of the
illuminated parts of lakes and large rivers, no less
9.6 Insects of Inland Waters