Unique Sterol in the Ecology and Nutrition of Drosophila pachea

Abstract

Drosophila pachea, which breeds only in the stems of senita cactus (Lophocereus schottii) throughout the Sonoran Desert, requires the cactus as a dietary supplement when reared on laboratory media. Δ⁷-Stigmasten-3β-ol, isolated from the cactus or synthesized, can replace the cactus in the diet of flies reared nonaseptically or axenically. Δ⁷-Cholesten-3β-ol and Δ^{5, 7}-cholestadien-3β-ol could be substituted for the cactus sterol; Δ^{5, 7}-stigmastadien-3β-ol produced infertile females. Cholesterol, 4α-methyl-Δ⁷-cholesten-3β3-ol, β-sitosterol, stigmasterol, ergosterol, and Δ⁷-ergosten- 3β-ol did not support larval growth.