118
J.F. Cavaletto and W.S. Gardner
cholesterol) is also an important membrane component, and it is fairly abundant in
the worms. Combined PL and ST represent 70% of tubificid total lipid (Table 6.1).
The acetone mobile polar lipids (AMPL) are polar lipid compounds that are
mobile in 100% acetone; this lipid group includes chlorophyll. AMPL may represent a portion of the worm's gut contents. Lipid reserves (TAG) are not a large
component of tubificid lipids (Table 6.1). It is possible that because oligochaetes
feed below the sediment surface, they have a more constant but probably a lowquality food resource (i.e., detritus and bacteria) compared with organisms that
feed closer to the sediment surface. This relatively constant food supply may
allow oligochaetes to maintain its growth, respiration, and reproduction with only
a minimum of lipid reserves (Gardner et aI., 1985a).
6.2.2.3. Insecta
The aquatic midge larvae, members of the family Chironomidae, are ubiquitous in
lentic and lotic environments. They are most common in shallow «8 m) environments where food is relatively abundant. Chironomid larvae feed on surficial
sediment, and many species build feeding tubes where they draw in food particles
by self-produced currents. Chironomids are selective feeders, and it has been
demonstrated that food items in their gut are at a higher concentration than food
items in the surrounding sediments (Johnson et aI., 1989). Although they feed on
detrital particles and bacteria, algae (especially diatoms) can be an important part
of their diet (Pinder, 1992; Johnson et aI., 1989). In fact, chironomid larvae that
were fed detrital particles alone did not survive or grow as well as larvae that were
fed both detritus and diatoms (Pinder, 1992). Chironomids inhabiting the nearshore areas of Lake Michigan likely rely on diatoms as an essential part of their
diet. Following the spring diatom bloom, chironomid larvae from Lake Michigan
show an increase in total lipid levels by midsummer (Fig. 6.4). Storage lipids
(TAG) occur at intermediate levels in chironomids as compared with other Great
Lakes benthic invertebrates (Table 6.1). These quantities of lipid classes are
comparable with levels found in chironomids from a Scottish river where TAG
was 54% and PL was 31 % of total lipids (Bell et aI., 1994).
Chironomids are holometabolous insects, and their metamorphosis from larvae
to adult is a high energy activity. A study of biochemical components (protein,
carbohydrates, and lipids) of chironomid larvae revealed that the instar prior to
prepupal reorganization had a more rapid increase in carbohydrates and lipids
than the earlier instars. When prepupal tissue organization did begin, carbohydrates and lipids were the components that were used most rapidly (Beattie,
1978).
Accumulation of lipid reserves was also necessary for proper metamorphosis
and reproduction to occur in the caddis fly Clisoronia magnifica. Caddis fly larvae
that were fed a high-quality diet (high carbohydrate) accumulated more lipid,
spent less time in the larval form, took longer to pupate, and lived longer as adults
than individuals on a low-quality diet (Cargill et aI., 1985). Like the chironomid
larvae, the majority (i.e., 80%) of lipid reserves that accumulated in the caddis fly
larvae occurred during the last instar.
J.F. Cavaletto and W.S. Gardner
cholesterol) is also an important membrane component, and it is fairly abundant in
the worms. Combined PL and ST represent 70% of tubificid total lipid (Table 6.1).
The acetone mobile polar lipids (AMPL) are polar lipid compounds that are
mobile in 100% acetone; this lipid group includes chlorophyll. AMPL may represent a portion of the worm's gut contents. Lipid reserves (TAG) are not a large
component of tubificid lipids (Table 6.1). It is possible that because oligochaetes
feed below the sediment surface, they have a more constant but probably a lowquality food resource (i.e., detritus and bacteria) compared with organisms that
feed closer to the sediment surface. This relatively constant food supply may
allow oligochaetes to maintain its growth, respiration, and reproduction with only
a minimum of lipid reserves (Gardner et aI., 1985a).
6.2.2.3. Insecta
The aquatic midge larvae, members of the family Chironomidae, are ubiquitous in
lentic and lotic environments. They are most common in shallow «8 m) environments where food is relatively abundant. Chironomid larvae feed on surficial
sediment, and many species build feeding tubes where they draw in food particles
by self-produced currents. Chironomids are selective feeders, and it has been
demonstrated that food items in their gut are at a higher concentration than food
items in the surrounding sediments (Johnson et aI., 1989). Although they feed on
detrital particles and bacteria, algae (especially diatoms) can be an important part
of their diet (Pinder, 1992; Johnson et aI., 1989). In fact, chironomid larvae that
were fed detrital particles alone did not survive or grow as well as larvae that were
fed both detritus and diatoms (Pinder, 1992). Chironomids inhabiting the nearshore areas of Lake Michigan likely rely on diatoms as an essential part of their
diet. Following the spring diatom bloom, chironomid larvae from Lake Michigan
show an increase in total lipid levels by midsummer (Fig. 6.4). Storage lipids
(TAG) occur at intermediate levels in chironomids as compared with other Great
Lakes benthic invertebrates (Table 6.1). These quantities of lipid classes are
comparable with levels found in chironomids from a Scottish river where TAG
was 54% and PL was 31 % of total lipids (Bell et aI., 1994).
Chironomids are holometabolous insects, and their metamorphosis from larvae
to adult is a high energy activity. A study of biochemical components (protein,
carbohydrates, and lipids) of chironomid larvae revealed that the instar prior to
prepupal reorganization had a more rapid increase in carbohydrates and lipids
than the earlier instars. When prepupal tissue organization did begin, carbohydrates and lipids were the components that were used most rapidly (Beattie,
1978).
Accumulation of lipid reserves was also necessary for proper metamorphosis
and reproduction to occur in the caddis fly Clisoronia magnifica. Caddis fly larvae
that were fed a high-quality diet (high carbohydrate) accumulated more lipid,
spent less time in the larval form, took longer to pupate, and lived longer as adults
than individuals on a low-quality diet (Cargill et aI., 1985). Like the chironomid
larvae, the majority (i.e., 80%) of lipid reserves that accumulated in the caddis fly
larvae occurred during the last instar.