BIOSYNTHESIS OF IRIDOID MONOTERPENES IN INSECTS - DEFENSIVE SECRETIONS FROM LARVAE OF LEAF BEETLES (COLEOPTERA, CHRYSOMELIDAE)

Larvae of the leaf beetles Phaedon amoraciae, Phaedon cochleariae, Gas trophysa viridula, and Plagiodera versicolora biosynthesize the two ir idoids chrysomelidial 1 and/or plagiodial 3 from geraniol 7 by an oxid ative sequence related to that known from plants en route to the irida ne skeleton. Following omega-oxidation of geraniol 7 the resulting 8-h ydroxygeraniol 8 is oxidized further to 8-oxocitral 9. The mode of the cyclization of 8-oxocitral 9 to chrysomelidial 1 depends on the chrys omelid species. In larvae of Gastrophysa viridula chrysomelidial 1 ori ginates directly from the acyclic precursor 9 while in both Phaedon sp p. chrysomelidial 1 is produced via plagiodial 3 followed by isomeriza tion of the endocyclic double bond.