Volatile monoterpenes in Porophyllum gracile and P. ruderale (Asteraceae): identification, localization and insecticidal synergism with alpha-terthienyl

摘要

Volatiles occurring in the Asteraceae Porophyllum gracile and P. ruderale were identified to assess their role in integrated chemical defences against insects. Headspace and steam distillation techniques yielded a total of 12 mono- and sesquiterpenes and fatty acid derivatives. The glandular secretory cavities present on leaves of P. ruderale were large enough to permit direct sampling and were found to be particularly rich in volatile monoterpenes (73.6% of the integrated FID trace). Using reduction of relative growth rate of 3rd-instar larvae of the pyralid Ostrinia nubilalis as an index of insecticidal activity, the volatiles released from the secretory cavities located on the leaves of P. ruderale had no significant effect alone, but they synergized the effects of alpha-terthienyl, a secondary compound also present in P. gracile and P. ruderale. This synergistic interaction was shown to be related to an enhanced accumulation of alpha-terthienyl in O. nubilalis larvae when they were exposed tothe volatiles emitted from the foliar secretory cavities of P. ruderale.