594
15 Lipids
protection against predators and parasites. The
wax material in all these species consists of C30 or
C32 oxo-acids and C34 or C36 oxo-alcohols with
central keto groups (Fig.15.16b) [164]. Oxoalcohols with 26-28 C atoms and oxo-groups in
positions 11 or 12 have also been found in pupae
of the moth Manduca sexta; these are mostly
esterified with acetoacetic acid, acetic acid or 3hydroxybutyric acid; the corresponding oxoaldehydes are also found [28].
The endogenous synthesis of cuticular hydrocarbons and wax esters has been demonstrated in
many insect species by tracer experiments with
14C-acetate. However, little is known about the
mechanisms of biosynthesis or the enzymes
involved [21, 22, 154]. As in many insects, acetate
is also rapidly incorporated into hydrocarbons in
the millipede Graphidostreptus tumuliporus. Corresponding experiments with the spider Aphonepelma sp. and the scorpions Centruroides sculpturatus and Paruroctonus mesaensis, however, gave
Fig.15.17a-e. Wax esters from the
honeycomb wax of the honeybee
[133]. (The components are: S, fatty
acid; A, alcohol; HS, (w-1)-hydroxy
fatty acid; D, 1,( OJ-I )-diol.)
a Monoester wax of the form S-A;
b hydroxy monoester wax of the
form S-D or HS-A; c acidic monoester of the form S-HS; d diester
wax of the form S-HS-A or S-D-S;
e triester wax of the form S-HS-HS-A
or S-HS-D-S
negative results. In these cases, it is not known
whether the hydrocarbons are of exogenous origin or simply have very low turnover rates. The
formation of extremely-long-chain hydrocarbons
apparently occurs by the elongation and ensuing
decarboxylation of fatty acids and not, as in bacteria, by head-to-head condensation and reduction. Thus, these insect hydrocarbons usually
have an odd number of C atoms. The decarboxylation of long-chain fatty acids to alkanes has
been shown directly in cockroaches and termites
by tracer experiments. However, whereas
extremely-long-chain fatty alcohols and hydrocarbons are detected in insects, the corresponding
fatty acids are not found; this suggests that reduction or decarboxylation occurs immediately after
elongation [267]. The main site of hydrocarbon
biosynthesis is the oenocytes derived from integument cells, although the integument cells themselves also have the capacity to synthesize longchain fatty acids and hydrocarbons. The surface
Table 15.13. Percentage composition of the cuticular lipids and comb wax of the honeybee Apis mell~fera and of the comb
wax of the stingless bees Trigona atomaria and T. australis [18, 21, 173]
Cuticula
Comb
Apis
Apis
T. atom.
T. austr.
Hydrocarbons
58
13-17
71
90
Monoester
23
31-35
26
6
Diester
9
10-14
Triester
2
3
Strongly polar lipids a
9
34
3
4
a Free fatty acids and fatty alcohols, and inApis also diols, hydroxymonoesters, hydroxypolyesters and acid monoesters
15 Lipids
protection against predators and parasites. The
wax material in all these species consists of C30 or
C32 oxo-acids and C34 or C36 oxo-alcohols with
central keto groups (Fig.15.16b) [164]. Oxoalcohols with 26-28 C atoms and oxo-groups in
positions 11 or 12 have also been found in pupae
of the moth Manduca sexta; these are mostly
esterified with acetoacetic acid, acetic acid or 3hydroxybutyric acid; the corresponding oxoaldehydes are also found [28].
The endogenous synthesis of cuticular hydrocarbons and wax esters has been demonstrated in
many insect species by tracer experiments with
14C-acetate. However, little is known about the
mechanisms of biosynthesis or the enzymes
involved [21, 22, 154]. As in many insects, acetate
is also rapidly incorporated into hydrocarbons in
the millipede Graphidostreptus tumuliporus. Corresponding experiments with the spider Aphonepelma sp. and the scorpions Centruroides sculpturatus and Paruroctonus mesaensis, however, gave
Fig.15.17a-e. Wax esters from the
honeycomb wax of the honeybee
[133]. (The components are: S, fatty
acid; A, alcohol; HS, (w-1)-hydroxy
fatty acid; D, 1,( OJ-I )-diol.)
a Monoester wax of the form S-A;
b hydroxy monoester wax of the
form S-D or HS-A; c acidic monoester of the form S-HS; d diester
wax of the form S-HS-A or S-D-S;
e triester wax of the form S-HS-HS-A
or S-HS-D-S
negative results. In these cases, it is not known
whether the hydrocarbons are of exogenous origin or simply have very low turnover rates. The
formation of extremely-long-chain hydrocarbons
apparently occurs by the elongation and ensuing
decarboxylation of fatty acids and not, as in bacteria, by head-to-head condensation and reduction. Thus, these insect hydrocarbons usually
have an odd number of C atoms. The decarboxylation of long-chain fatty acids to alkanes has
been shown directly in cockroaches and termites
by tracer experiments. However, whereas
extremely-long-chain fatty alcohols and hydrocarbons are detected in insects, the corresponding
fatty acids are not found; this suggests that reduction or decarboxylation occurs immediately after
elongation [267]. The main site of hydrocarbon
biosynthesis is the oenocytes derived from integument cells, although the integument cells themselves also have the capacity to synthesize longchain fatty acids and hydrocarbons. The surface
Table 15.13. Percentage composition of the cuticular lipids and comb wax of the honeybee Apis mell~fera and of the comb
wax of the stingless bees Trigona atomaria and T. australis [18, 21, 173]
Cuticula
Comb
Apis
Apis
T. atom.
T. austr.
Hydrocarbons
58
13-17
71
90
Monoester
23
31-35
26
6
Diester
9
10-14
Triester
2
3
Strongly polar lipids a
9
34
3
4
a Free fatty acids and fatty alcohols, and inApis also diols, hydroxymonoesters, hydroxypolyesters and acid monoesters