Thesis (Ph.D.)--Chulalongkorn University, 2009

Plants emit volatile organic compounds (VOCs) that play important roles in their interactions with other organisms in the ecosystem and have a major impact on atmospheric chemistry. In order to obtain information on the relationships between VOCs and insects in tropical forests, the forest area of Doi Phu Ka National Park, Nan Province of Thailand was selected as a study site due to its high plant and insect diversities. A simple air trap was constructed to study the composition of VOCs in the understory air of the forest by using Super Q adsorbent packed in a plastic syringe and connected to a portable air pump. The air traps, together with insect traps, were both placed at selected 15 sites for simultaneous study of the VOC components and their effects on insects. The results revealed that seven VOCs identified as monoterpenes; α-thujene, camphene, 3-carene, p-cymene, limonene, (1,8)-cineole and camphor and other VOCs from the understory air. The results on the correlation between the VOC composition and the effect on insect showed that the insect types of Hymenoptera and Homoptera were attracted by camphene and limonene, respectively. Whereas, the insects types of Hymenoptera and Coleoptera were repelled by benzaldehyde and 1-octen-3-ol, respectively. On the other hand, the monoterpenes that are p-Cymene and (1,8)-cineole repelled not only the insects of Coleoptera but also the insects of Homoptera. In addition, the insects of Diptera were repelled by limonene. These results of interactions may be lead to the understanding of the chemical ecology of the tropical forests and may be applied to the area of agricultural management.