6 Diversity of Insect Pheromones and the Mechanism of Olfactory Perception (in Japanese)
Among many kinds of insect semiochemicals, lepidopterous sex pheromones have been studied at the most depth and identified from females of more than 500 species in the world. Taxonomically related species secrete a common component, since they are derived from the same ancestor. However, scientists continue to be surprised at the diversity of the chemical structures of the pheromone components and their elaborate blending to produce species-specific communication systems, which play an important role in the reproductive isolation of sympatric insects. The olfactory perception of a pheromone is efficiently accomplished by sensilla trichodea on the male antenna. When the antenna is stimulated by the pheromone component, it shows an electrophysiological response recorded as an electroantennogram (EAG). The EAG is available for a detector of the capillary GC to exclusively analyze the pheromone components with high sensitivity. The lipophilic pheromones are combined with a pheromone binding protein (PBP) and transported to receptors on the dendrites of sensory neurons, which are covered with sensillum lymph. Although no receptors of insect pheromones have been characterized, PBPs, including three disulfide linkages in their 15 KDa molecular structure, have been identified from insects of 27 species, mainly in Lepidoptera, making a new protein family differentiated from the lipocalins of mammals.
Key words: sex pheromones, Lepidoptera, reproductive isolation, pheromone binding protein, electroantennogram.
7 Lepidopteran Sex Pheromones. In "The chemistry of pheromones and other semiochemicals"
As a consequence of the diversity of Lepidoptera, including 150,000 described species, interesting species-specific sex pheromone systems are exhibited in this insect group. The quite varied pheromones, which have been identified from nearly 530 species from around the world, are classified into groups of Type I (75 %), Type II (15 %) and miscellaneous (10 %), according to their chemical structures. While new sex pheromones from about 60 lepidopteran species have been reported in the last five years utilizing GC-EAD, GC-MS, LC, and NMR, our information about the pheromones is still rudimentary, and these kinds of semiochemicals remain an exciting research target for natural product chemistry. In addition to the overview of their chemical structures, this chapter deals with current methods for their identification. Furthermore, an actual application of the synthetic pheromones for pest control is briefly introduced.
8 Analyses of lepidopteran sex pheromones by mass spectrometry
Lepidoptera, including about 150,000 species in the world, comprise the second largest insect group, and sex pheromones have been identified from virgin female moths of more than 600 species. The chemical structures are simple, but diverse, because species-specific pheromones play an important role in the reproductive isolation of each species. The pheromone content in each female is quite low, and gas chromatography coupled to mass spectrometry (GC-MS) is most frequently utilized to reveal the chemical structure. Almost all pheromone components are straight-chain compounds and are classified into two major groups [i.e. unsaturated C
10-C
18 fatty alcohols and their derivatives (Type I) and C
17-C
23 polyenyl hydrocarbons and their epoxides (Type II)]. In addition to the unbranched compounds, some species secrete methyl-branched compounds (e.g., 2-ketones). For the identification of these compounds, determining the positions of the double bond, the epoxy ring, and the methyl group is an important key step. Copious spectral information measured by electron-impact ionization (70 eV) has been accumulated for these compounds. This review therefore deals with their spectral characteristics, namely, diagnostic ions, to apply them to pheromone studies on new target insects.
9 Chiral methyl-branched pheromones.
Insect pheromones are some of the most interesting natural products because they are utilized for interspecific communication between various insects, such as beetles, moths, ants, and cockroaches. A large number of compounds of many kinds have been identified as pheromone components, reflecting the diversity of insect species. While this review deals only with chiral methyl-branched pheromones, the chemical structures of more than one hundred non-terpene compounds have been determined by applying excellent analytical techniques. Furthermore, their stereoselective syntheses have been achieved by employing trustworthy chiral sources and ingenious enantioselective reactions. The information has been reviewed here not only to make them available for new research but also to understand the characteristic chemical structures of the chiral pheromones. Since biosynthetic studies are still limited, it might be meaningful to examine whether the structures, particularly the positions and configurations of the branched methyl groups, are correlated with the taxonomy of the pheromone producers and also with the function of the pheromones in communication systems.
10 Semiochemicals containing lepidopteran sex pheromones: Wonderland for a natural product chemist.
Since the first identification of bombykol, sex pheromones of about 700 moth species have been elucidated. Additionally, field evaluations of synthetic pheromones and their related compounds have revealed the male attraction of another 1,300 species. These pheromones and attractants are listed on the web-sites, “Pheromone Database, Part I.” Pheromone components are classified according to their chemical structures into two major groups (Types I and II) and miscellaneous. Based on our previous review published in 2004, studies reported during the last two decades are highlighted here to provide information on the structure characteristics of newly identified pheromones, current techniques for structure determination, new enantioselective syntheses of methyl-branched pheromones, and the progress of biosynthetic research. Besides the moth sex pheromones, various pheromones and allomones from many arthropod species have been uncovered. These semiochemicals are being collected in the“Pheromone Database, Part II.” The chemical diversity provides a wonderland for natural product chemists.
