Drosophila pachea

It is worthy of note that low stereospecificity in utilizing 24-stereoisomers of 24-methylcholesterol was demonstrated with Manduca sexta. However, it was reported that in Dermestes maculatus there was a preference for (24/ )-alkylsterols (acetate) over 24S isomers, and Drosophila melanogaster utilizes both (247 )- and (24S)-methylcholesta-5,7-dien-3/8-ol, while Drosophila pachea preferentially utilizes the 245 isomers and Drosophila mojavensis prefers the 247 isomers as reported by Kircher and Rosenstein [163], Our studies revealed that 24-stereoisomers of 24-methyl- and 24-ethylcholesterols and their 22-dehydro analogues can sustain the growth of the silkworm B. mori and are all converted into cholesterol to a similar extent [164],... 

Drosophila pachea is limited to the senita cactus (Lopho-cereus schottii) by a biochemical dependency on sterols found in that cactus. Unlike most insects that can utilize such compounds as P-sitosterol (4) to synthesize ecdysones, flies of this Drosophila species must have the compound schot-tenol (37) in which a particular double-bond position is found (Fig. 23.18) (Harbome, 1982 Herout, 1970 Kircher, 1982). This cactus contains 3-15% dry weight of complex isoquinoline alkaloids that are toxic to both adults and larvae of Drosophila nigrospiracula, D. mojavensis, and D. mela-nogaster. 

Schottenol Sa-stigma-7-ene-3p-ol, a widely distributed phytosterol (see Sterols), M, 414.72, m.p. 151 °C, isolated, e.g. from the cactus Lophocereus schottU. S. is an essential dietary constituent for the insect Drosophila pachea, which lives on this plant. 

Phytosterols in the various cactus species exist as glycosides or saponins. Yeasts found in the rotting cactus plants hydrolyze these saponins and make the phytosterol agly-cones available to the insects (Spencer, 1987). Both 24/ -and 24S-methyl groups occur in phytosterols. Individuals of Drosophila melanogaster utilize both 24/ - and 24S-meth-ylcholest-5,7-dien-3p-ol (37), whereas those of D. pachea prefer the 24S-isomers and those of >. mojavensis prefer the 24/ -isomers (Rees, 1983). 

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