630
16 Sterols and Steroids
Sitosterol
Fucosterol
Fucosterol- 24,28 -epoxide
yJy-yJy--h-~
Campesterol
24 - Methylene - cholesterol
Desmosterol
Cholesterol
--~_/
Stigmasterol
b)
5,7,24 - Cholestatrien -3~ -01
7 - Dehydro-cholesterol
HO
5,7,22,24 - Cholestatetraen -3~-01
---~--~
Sitosterol
Stigmastanol
Cholestanol
Lathosterol
C)
,15
Stigmasterol
_J
t
~
d)
l
II
~--~
Ergosterol
24 - Methylene - cholesta5,7,24(28) -trien -3~-01
+
Fig.16.4a-d. The metabolism of phytosterols in insects
[99, 112]. a The pathways found in Bombyx mori, Manduca
sexta and many other insects. b The corn beetle Tribolium
confusum has a different pathway of stigmasterol metabolism that leads via 5,7,24-cholestatrien-3~-ol to 7-delyzed during embryo development and are thus
probably a storage form [112].
For a long time ClS, C19 and C2l steroid hormones were considered to be exclusive to the vertebrates. It was therefore a surprise when, in 1966,
Cholesterol
I
~
22 - Dihydro - ergosterol
hydrocholesterol. c The Mexican bean beetle Epilachna
varivestis produces mainly saturated sterols such as
stigmastanol and cholestanol. d The leaf-cutting ant Atta
cephalotes is unable to 24-dealkylate the ergosterol in its
diet
Schildknecht found large amounts of the corticosteroid cortexon in the secretion from the prothorax defence glands of the great water beetle
Dytiscus marginalis. Since then the defence secretions of other water beetles (Dytiscidae) have