Metabolism of dietary Δ8‐sterols and 9β, 19‐cyclopropyl sterols by Locusta migratoria

Abstract

AbstractAdult female locusts were reared on wheat seedlings (experimental wheat) containing more than 97% of 9,10‐cyclopropyl sterols and Δ8‐sterols and less than 2% of Δ5‐sterols. These insects showed a dramatic decrease in their cholesterol, cholestanol and Δ7‐cholestanol content compared with control insects. These changes were more dramatic for steryl esters than for free sterols. Similar results were observed in eggs laid by the insects fed on experimental wheat. The decrease in Δ5‐, Δ0‐ and Δ7‐sterols in insects reared on experimental wheat was compensated by a marked accumulation of Δ8‐sterols and 9β, 19‐cyclopropyl sterols in the free sterol fraction and especially in the steryl ester fractions. The ecdysteroid content of eggs laid by experimental female insects was reduced by up to 80% compared with controls. These and other results suggest that the dietary 9β, 19‐cyclopropyl sterols and Δ8‐sterols cannot be used by Locusta in place of Δ5‐sterols for ecdysteroid biosynthesis. To give support to this hypothesis, the experimental wheat was supplemented with various sterols before being presented to the insects immediately after the first egg laying. When cholesterol, sitosterol, or cholestanol were used as supplements, there was a complete recovery of the ecdysteroid titer in the eggs, a disappearance of 9β, 19‐cyclopropyl sterols, and a restoration of the cholesterol content in both the animals and the eggs. Stigmasterol, stigmastanol, and ergosterol were much less efficient in reversing the effects of the experimental wheat. As expected, 9β, 19‐cyclopropyl sterols were totally ineffective. These results are discussed in the light of our information on the role played by sterols in insect development and on the structural features required by the sterols to fulfill their role.