Akira Terahara

Effects of sterols on feeding and nutrition of the silkworm, Bombyx mori L.

Abstract The feeding responses of the silkworm, Bombyx mori L., as tested on agar-diets showed that β-sitosterol, isolated from mulberry leaves and identified by gas-chromatographic analysis, stimulates feeding. A commercial sample of β-sitosterol was entirely inactive but showed a stimulating activity after recrystallization from an organic solvent. Gas-phase chromatography of recrystallized commercial β-sitosterol showed three peaks, namely, β-sitosterol, stigmasterol, and probably campesterol. Pure stigmasterol also stimulated feeding. Campesterol of either 90 or 93 per cent purity, the only impurity of which was β-sitosterol, showed a positive stimulation. Soybean sterol, rape-seed sterol, and pulp (waste liquor) sterol, all of them mixtures of sterols, also stimulated feeding. On the other hand, cholesterol lacked stimulatory activity, as had been shown previously. Nutritional studies with these sterols were also carried out by the use of semi-defined diets. The results confirmed previous results that the silkworm requires dietary sterol for normal growth and development. In these nutritional tests the various sterols, except cholesterol, had almost equally high value, irrespective of their stimulatory action on the feeding. Even cholesterol improved the efficiency of diets. It therefore appears that dietary sterols are primarily nutritional but also play a minor part as phagostimulants. It is also evident that β-sitosterol does not explain the unique relation of the silkworm to mulberry leaves. Further, a triterpenoid, C30H50O, was isolated from mulberry leaves and shown to elicit feeding.