Sterols nutritional requirement

Finally, there are general nutritional requirements for essential amino acids, fatty acids, sterols, and vitamins by pests. The absence or deficiency of one or more of these may limit growth or development. 

In crustaceans cholesterol is a predominant sterol, but considerable amounts of desmosterol and small amounts of C28- and C29-sterols are also present. It is now established that [ C]acetate and [ C]mevalonate are not incorporated into sterols, indicating incapability for the de novo synthesis of sterols. A nutritional requirement for sterol has been demonstrated for the prawn Penaeus Japonicus [109]. After feeding prawns phytosterol, the sterol isolated was predominantly cholesterol [110]. Dealkylation of 24-methyl and 24-ethyl sterols to yield cholesterol has been demon-... 

Yeast cells grovhng aerobically synthesize sterols and incorporate them into membranes. However, under anaerobic conditions yeast cells do not survive unless they are provided "with an exogenous source of sterok. Explain the metabolic basis for this nutritional requirement. 

Insecta, could have arisen from annelids, which never acquired the ability to biosynthesize sterols. To date, no insect has been found to be capable of biosynthesizing the steroid nucleus (3). Thus, insects require a dietary source of sterol to support development and reproduction, and this dietary requirement for sterol is the only known difference in nutritional requirements between insects and... 

---