Cockroaches contact pheromones

Fig. 6.1b). Although they are probably present in most cockroach species, sex-specific contact pheromones have been identified in only a few species. They are thought to be distributed throughout the epicuticular surface and are perceived by means of antennal contact and with the mouthparts. Female-produced contact pheromones elicit courtship responses in males however, in some cockroaches, stridulation and hissing may combine with, or operate in place of, contact chemore-ception. In addition, male contact pheromones may function to inhibit courtship in other males. 

Table 6.3. Chemical structures of the principal identified contact sex pheromones of cockroaches, listed by the species and sex that produces it contact pheromones are localized on the cuticular surface... 

A microsomal FAS was implicated in the biosynthesis of methyl-branched fatty acids and methyl-branched hydrocarbon precursors of the German cockroach contact sex pheromone (Juarez et al., 1992 Gu et al., 1993). A microsomal FAS present in the epidermal tissues of the housefly is responsible for methyl-branched fatty acid production (Blomquist et al., 1994). The housefly microsomal and soluble FASs were purified to homogeneity (Gu et al., 1997) and the microsomal FAS was shown to preferentially use methylmalonyl-CoA in comparison to the soluble FAS. GC-MS analyses showed that the methyl-branching positions of the methyl-branched fatty acids of the housefly were in positions consistent with their role as precursors of the methyl-branched hydrocarbons. 

All life stages of the German cockroach produce 3,11-dimethylnonacosane, suggesting that production of a sex-specific contact pheromone may be less dependent on differentiation of sexually dimorphic pheromone glands, as is the case for volatile pheromones, and more so on the endocrine milieu of the adult female. Normally, adult male cockroaches produce much less JH III than do females, and males have a much lower titer of JH III in the hemolymph (Piulachs et al., 1992 reviewed in Tobe and Stay, 1985 Wyatt and Davey, 1996). However, when newly emerged males were exposed to filter papers treated with the JH mimic hydroprene they exhibited a six-fold elevation in female pheromone on their cuticle (Schal, 1988). Although substantial, this limited stimulation indicates... 

Yet another feature distinguishes JH control of contact pheromone production from control of volatile pheromone production in cockroaches. Although based solely on behavioral data, lack of JH III in females completely suppresses production of attractant pheromones, as for instance in S. longipalpa (section 10.7.1). The contact pheromone of B. germanica, on the other hand, is still biosynthesized in allatectomized females, albeit at a lower rate, probably because regulation of contact sex pheromone production operates at several levels, including the regulated production of its 3,11-dimethylnonacosane precursor (section 10.7.2.3). 

Almost a decade before the term pheromone was coined, Roth and Willis (1952) conducted seminal experiments that characterized volatile and contact pheromones in cockroaches. Louis Roth s research integrated studies of endocrinology and behavior, and the influence of this approach was reflected in Barth s early articulation of the interplay between the endocrine system and sexual behavior. In later years cockroaches continued to serve as important models for invertebrate endocrinology (Scharrer, 1987 Tobe and Stay, 1985), but research on pheromones lagged, in part due to technical difficulties in sex pheromone identification. Below, we highlight some of the many issues yet to be resolved in the physiological and behavioral regulation of sex pheromone production and emission in cockroaches. 

While the hydrocarbon fraction of insect cuticular lipids is certainly the most studied and has been shown to play a key role in a wide range of chemical communication, other lipids are often present on the surface of insects. The most common cuticular lipids in addition to hydrocarbons include a variety of types of esters, free fatty acids, primary and secondary alcohols, ketones and sterols. Triacylglycerols and the more polar phospholipids are not common components of insect cuticular lipids. In some cases, hydrocarbons are hydroxylated and metabolized to oxygenated components, and these products include some of the short range and contact pheromones of the housefly (Blomquist, 2003) and the German cockroach (Schal et al., 2003). The oxygenated cuticular lipids are discussed in Chapter 9 (Buckner, this book). 

In addition to 3,1 l-dimethylnonacosan-2-one (M12) and 3,1 l-dimethylheptacosan-2-one, products of u>-oxidation, that is, 29-hydroxy-3,ll-dimethylnonacosan-2-one and 19,27-dimethyl-28-oxononacosanal (M37) as well as the two corresponding C27 compounds are components of a multicomponent contact pheromone contained in the cuticula of sexually mature females of the German cockroach B. germanica932... 

German cockroach (Blattella germanka). The female produces the contact pheromone shown in Figure 4.11 with the specific chirality at the two carbon centers shown [20]. Note that this is a very big molecule (the subscript 17 denotes a 17-carbon chain) and is not volatile, so it must be touched (tasted ) to be effective. The male German cockroach, it seems, doesn t care about chirality, as he is attracted to all four possible isomers RR, RS, SR, and SS. Further amazing insect stories await the reader of the additional references listed at the end of this chapter. 

P americana is one of just a few species of insects in which both peripheral and central olfactory processing have been studied. In contrast to many short-lived lepidopterans, in which the male antenna is highly specialized for sex pheromone reception, the antennae of male cockroaches contain numerous food-responsive sensilla. In addition to olfactory sensilla, the antennae also house mechano-, hygro-and thermoreceptors, as well as contact chemoreceptors (Schaller, 1978 review Boeckh et al., 1984). Extensive ultrastructural and electrophysiological evidence has demonstrated that morphologically defined sensillum types house receptor cells of specific functional types (Sass, 1976, 1978, 1983 Schaller, 1978 Selzer, 1981, 1984 review Boeckh and Ernst, 1987). Boeckh and Ernst (1987) defined 25 types of cell according to their odor spectra, but of the 65 500 chemo- and mechanosensory sensilla on the antenna of adult male P. americana, an estimated 37 000 house cells that respond to periplanone-A and periplanone-B. 

Gu, X., Quilici, D., Juarez, P, Blomquist, G. J. and Schal, C. (1995). Biosynthesis of hydrocarbons and contact sex pheromone and their transport by lipophorin in females of the German cockroach (Blattella germanica). Journal of Insect Physiology 41 257-267. 

Jurenka, R. A., Schal, C Burns, E., Chase, J. and Blomquist, G. J. (1989). Structural correlation between cuticular hydrocarbons and female contact sex pheromone of German cockroach Blattella germanica (L.). Journal of Chemical Ecology 15 939-949. 

In contrast, the hydrocarbon contact sex pheromone of the German cockroach is synthesized in Class II oenocytes associated with the abdominal stemites (Young et al., 1999 Fan et al., 2002). These large oenocytes, ranging up to 50 p in in diameter in B. germanica, have abundant mitochondria and extensive smooth endoplasmic reticulum (Fan et al., 2002). Although the oenocytes are associated with abdominal stemites, the hydrocarbons are released into the hemolymph and loaded, probably across a plasma membrane reticular system, into high-density lipophorin. The lipophorin then likely transports the hydrocarbon to epidermal cells for release onto the cuticle (Fan et al., 2002). 

Figure 10.1 Metabolic pathways for the biosynthesis of 3,11-dimethylnonacosan-2-one and related sex pheromone components of the female contact sex pheromone of the German cockroach, Blattella germanica.

Transport of pheromones. Two major routes for translocation of pheromones have been considered in this chapter (a) from the secretory cell directly through the cuticle overlying it and (b) indirectly through the hemolymph. Cockroaches share with even the most studied lepidopterans an almost complete lack of information on the former pathway. Transport of hydrocarbons and contact sex pheromones, on the other hand, has been extensively studied in cockroaches, commencing with the work of Chino and colleagues. It has... 

Schal C., Burns E. L. and Blomquist G. J. (1990a) Endocrine regulation of female contact sex pheromone production in the German cockroach, Blattella germanica. Physiol. Entomol. 15, 81-91. 

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