Environmental Engineering Reference
In-Depth Information
FIGURE 9.9
Some representative aquatic insect larvae: (A) the mayfly
Baetis,
1 cm; (B) the
caddis larva
Polycentropus,
1.5 cm; (C) the aquatic beetle
Stenelmis,
0.5 cm; (D) a beetle
larva,
Dineutus,
1 cm; (E) the midge larva,
Chironomus,
0.5 cm; (F) a semiaquatic springtail,
1 mm; (G) a megalopteran,
Sialis,
2 cm; (H) an odonate damselfly larva,
Calopteryx,
1 cm;
(I) a stonefly,
Isoperla,
0.7 cm; (J) an adult hemipteran backswimmer,
Notonecta,
1 cm (A-C,
E, F, reproduced with permission from Thorp and Covich, 1991b; D, G-J, reproduced with
permission from Hilsenhoff, 1991).
thos of some lakes. Mayfly larvae are distinguished from other aquatic in-
sects by long filaments on their posterior end (generally three) and the pres-
ence of conspicuous gills on the first seven abdominal segments (Fig. 9.9A).
Another unique feature of mayflies is the subimago stage. It follows the lar-
val stage and precedes the adult stage. The subimago stage is the only
winged preadult stage known in insects. Most mayfly larvae crawl on the
substratum, but some are rapid swimmers. Mayflies are diverse in well-
oxygenated, unpolluted streams and are used as indicators of good ecosys-
tem health. Adult mayflies do not feed and live for only a few days while
they attempt to reproduce.
The Odonata (dragonflies and damselflies) are voracious predators as
aquatic larvae and terrestrial adults. About one-third of the larvae are lotic
and two-thirds are lentic (Hilsenhoff, 1991). The larvae can be distin-
guished by the long hinged labium that has been modified to eject rapidly
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