CHEMICAL CONSTITUENTS AND TOXICITY OF ESSENTIAL OILS OF ORIENTAL ARBORVITAE, Platycladus orientalis (L.) FRANCO, AGAINST THREE STORED-PRODUCT BEETLES

Plant secondary metabolites play an important role in plant-insect interactions and therefore such compounds may have insecticidal or biological activity against insects. Fumigant toxicity of essential oils of leaves and fruits from oriental arborvitae (Platycladus orientalis [L.] Franco) (Cupressaceae) was investigated against adults of cowpea weevil (Callosobruchus maculatus Fab.), rice weevil (Sitophilus oryzae L.), and red flour beetle (Tribolium castaneum Herbst). Fresh leaves and fruits were subjected to hydrodistillation using a Clevenger-type apparatus and the chemical composition of the volatile oils was studied by gas chromatography-mass spectrometry (GC-MS). Twenty-six compounds (92.9%) and 23 constituents (97.8%) were identified in the leaf and the fruit oils, respectively. The major components of both leaves and fruits oils were alpha-pinene (35.2%, 50.7%), alpha-cedrol (14.6%, 6.9%) and Delta-3-carene (6.3%, 13.8%), respectively. Both oils in the same concentration were tested for their fumigant toxicity on each species. Results showed that leaf oils were more toxic than fruit oils against three species of insects. Callosobruchus maculatus was more susceptible than S. oryzae and T. castaneum. LC50 values of the leaf and the fruit oils at 24 h were estimated 6.06 and 9.24 mu L L-1 air for C. maculatus, 18.22 and 21.56 mu L L-1 air for S. oryzae, and 32.07 and 36.58 mu L L-1 air for T. castaneum, respectively. These results suggested that P. orientalis oils may have potential as a control agent against C. maculatus, S. oryzae, and T. castaneum.