OLFACTION AND LEARNING IN MOTHS AND WEEVILS LIVING ON ANGIOSPERM AND GYMNOSPERM HOSTS

摘要

The olfactory system of herbivorous insects is challenged by the large diversity of volatiles emitted by plants. The knowledge of how plants synthesize and regulate the production of compounds has increased during recent years, based on the identified genome of Arabidopsis thaliana1 and the advanced methods of isolation and characterizations of plant genes. Interesting evolutionary aspects of the enzymes involved in the various pathways of biosynthesis have appeared in studies of different plant species'. Focus has also been on responses of plants to abiotic and biotic factors causing variability of the released blends.3'4 Light, temperature, humidity, airborne or water mediated chemicals, as well as feeding by various herbivore larvae can induce the release of compounds, not only in increased amounts but also as a changed composition. In trying to determine how plant volatiles iniluence the behavior of insects, it is important to consider all emitted volatiles as potential odorants. Obviously, volatiles released by the host plants of insects should contain the most relevant odorants guiding the insects to a suitable source for feeding, mate finding, or egg-laying. Also, volatiles released by non-hosts may be important in giving clues about unsuitable plants. However, various species of plants produce hundreds of compounds of which many are common in both hosts and non-hosts.* Even plants of gymnosperms and angiosperms, have enzymes producing the same compounds, such as the different terpene synthases that are suggested to have undergone convergent evolution.2 6 Also, considerable differences exist between the emitted blends of these plants, reflecting the specificity of the various groups of enzymes, which gives the chemical signature of the species and individual plants. Monoterpenes dominate in gymnosperms, whereas sesquiterpenes are typical for angiosperms.