New intermediates in the conversion of stigmasterol to cholestanol in the Mexican bean beetle

Three intermediates involved in the conversion of stigmasterol to cholestanol in the Mexican bean beetle,Epilachna varivestis, were isolated and identified from an insect for the first time. The three new insect sterols, 22‐stigmastenol, 22,24‐cholestadienol and 24‐cholestenol, were shown to be metabolites of [3H]stigmasterol and accumulated in insect tissues when larvae were fed lima bean leaves coated with azasteroid inhibitors. The side chain metabolism of the ubiquitous phytosterol stigmasterol in the Mexican bean beetle is similar to that in other species that produce cholesterol from C28 and C29 phytosterols; however, the Mexican bean beetle initially reduces the Δ5‐bond and produces mainly cholestanol and lesser amounts of lathosterol as dealkylation products.