Sexual Communication with Pheromones

Among the insect groups in which chemical attraction is a major means of 

Chemical Ecology of Insects. Edited by William J. Bell and Ring T. Card6 1984 Chapman and Hall Ltd. 

In the Coleoptera, most knowledge of sexual communication pertains to bark beetles, family Scolytidae (discussed in detail by Birch, Chapter 12), where one of the sexes, depending on the species, initiates aggregation by boring into host trees. The blend of pheromone plus host-tree volatiles attracts predominantly 

In both species, the male accomplishes copulation while the female is arrested and feeding on the male s dorsal abdominal cuticule. Hence, a dual system of sexual aggregation is found also in the order Orthoptera. Both males and females take part in a chemical dialog that reduces spacing and results in mating. 

Lekking males are also found in some tropical Drosophila species, in which pheromone apparently attracts females into the group whereupon one male may mate with her (Spieth, 1968). 

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Card6, R. T. and Baker, T. C. (1984). Sexual communication with pheromones. In... 

Some lepidopteran species secret methyl-branched chemicals for their sexual communication. These have been abbreviated with Me to indicate the position of the methyl group. Disparlure (Me2,epo7-18 H) is a well-known pheromone identified from Lymantria dispar [3] and two other species in the same genus, L.fumida [95] and L. monacha [96]. L. monacha also secrets an... 

Contrary to the structure similarity of the pheromones secreted by taxonomical related moths, some differences are necessary for their sexual communication systems to play an important role in their reproductive isolation. In addition to further modifications of the various structures, diversity of the lepidopteran sex pheromones is generated by blending multiple components. Innumerable pheromone blends are based not only on combinations of different components but also on variations in the mixing ratio. A pioneer study with Adoxophyes spp. (Tortricidae Tortricinae) had already proposed this concept in the early 1970s. While the smaller tea tortrix (A. honmai) and the Japanese summerfruit tortrix (A. oranafasciata) had been considered to be variant strains with different host preferences in the same species, Tamaki et al. found that females of the former pest insect in the tea garden secreted Z9-14 OAc and Zll-14 OAc in a ratio of 7 4 but females of the latter defoliator of apple trees secreted them in a ratio of 13 4 [127,128]. Furthermore, two other components (Ell-14 OAc and MelO-12 OAc) were subsequently identified from the former species [129]. 

Another way to control the proliferation of insects is to modify their behavior through the use of pheromones, which are volatile organic molecules that insects release to communicate with one another. Each insect species produces its own set of pheromones, some as warning signals and others as sexual attrac-tants. Sexual pheromones synthesized in the laboratory can be used to lure harmful insects to localized insecticide deposits, thereby reducing the need for spraying an entire field, as depicted in Figure 15.34. 

The first system again makes use of yeast. It has been known for some time that S. cerevisiae can exist as two sexual types, a cells and a cells, which communicate with each other via sex pheromones, a-factor and a-factor. The receptors for these two pheromones are members of the 7-transmembrane family, although their amino acid sequences are quite distinct from their mammahan counterparts. The consequence of the binding of the pheromone to its receptor is to set in motion a complex set of biochemical events that lead, ultimately, to mating of the two opposite cell types. However, there are two principal events that can readily be detected. The cells undergo rapid, but transient, cell cycle arrest and express on their ceU surface a variety of proteins that aid in fusion of the mating types. Unlike their mammalian counterparts, the intracellular signal is transmitted via the (3- and -subunits of the trimeric G-protein complex and not by the a-subunit. A detailed description of this pathway... 

Many insects metabolize terpenes they have received with their plant food to growth hormones and pheromones. Pheromones are luring and signal compounds (sociohormones) that insects and other organisms excrete in order to communicate with others like them, e.g. to warn (alarm pheromones), to mark food resources and their location (trace pheromones), as well of assembly places (aggregation pheromones) and to attract sexual partners for copulation (sexual pheromones). Harmless to the environment, pheromones may replace conventional insecticides to trap harmful and damaging insects such as bark beetles. 

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