Cockroaches volatile pheromones

There are no published reports on the neuroendocrine control of pheromone production in female P. americana, but preliminary observations (in Barth and Lester, 1973 C. Schal, unpublished data) indicated that removal of the CA completely abolished pheromone production. Pheromone production resumed in alla-tectomized females rescued with either implantation of active CA or topical application of a JH analog. Successful copulation also suppressed the production of the volatile pheromone (Wharton and Wharton, 1957), as in some other cockroaches (see below). However, Sass (1983) stated that virgin females carrying partheno-genetically produced egg cases maintained the same level of pheromone as females without egg cases. 

Tsai, C.-W. and Lee, H.-J. (1997). Volatile pheromone detection and calling behavior exhibition secondary mate-finding strategy of the German cockroach, Blattella germanica (L.). Zoological Studies 36 325-332. 

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). 

P. americana (Persoons et al., 1979 Still, 1979), and only one additional female volatile sex pheromone has been identified outside the Periplaneta group, in S. longipalpa (Charlton et al., 1993 Leal et al., 1995). Obviously, more cockroach sex pheromones need to be identified to provide material for comparative studies on biosynthetic pathways and their endocrine and neural control. It would be of particular interest to identify sex pheromones of solitary, nocturnal cockroach species that do not associate with humans. They are most likely to communicate with volatile sex pheromones over longer distances. Indeed, field studies have shown that calling occurs in a variety of tropical species representing two of the largest cockroach families, Blattellidae and Blaberidae (Schal and Bell, 1985). 

Table 6.2. Chemical structures of the principal identified volatile sex pheromones of cockroaches, listed by the species and the sex that produces it for most pheromones common names are also listed.

Liang D. and Schal C. (1993b) Volatile sex pheromone in the female German cockroach. Experientia 49, 324—328. 

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. 

Gemeno C., Snook K., Benda N. and Schal C. (2003) Behavioral and electrophysiological evidence for volatile sex pheromones in Parcoblatta wood cockroaches. J. Chem. Ecol. 29, 37-54. 

Schal, C., Fan, Y. and Blomquist, G. J. (2003). Regulation of pheromone biosynthesis, transport, and emission in cockroaches. In Insect Pheromone Biochemistry and Molecular Biology - The Biosynthesis and Detection of Pheromones and Plant Volatiles, ed. G. J. Blomquist and R. G. Vogt. London Elsevier, pp. 283-322. 

The //-alkanes usually range in chain length from 21 to 31 or 33 carbons. Hydrocarbons with fewer than 20 carbons commonly occur as pheromones, defensive compounds and intermediates to pheromones and defensive compounds, but their volatility makes them unsuited to function as cuticular components, n-Alkanes have been found on almost every insect species analyzed, and can range from less than one percent of the total hydrocarbons, as in tsetse flies (Nelson and Carlson, 1986 Nelson et al., 1988) to almost all of the hydrocarbon fraction, as in the adult tenebrionid beetle, Eurychora sp. (Lockey, 1985). Depending upon the species, they can consist of essentially only one major component, such as n-pentacosane in the American cockroach, Periplaneta americana (Jackson, 1972) to a series of //-alkanes, such as the series from C23 to C33 in the housefly, Musca domes-tica (Nelson et al., 1981), with trace amounts to C37 (Mpuru et al., 2001). In all cases, the odd-numbered alkanes predominate, due to their formation from mostly two carbon units followed by a decarboxylation (Blomquist, Chapter 3, this book). Small amounts of even-numbered carbon chain //-alkanes often occur, and presumably arise from chain initiation with a propionyl-CoA rather than an acetyl-CoA. Occasionally, gas chromatographic analyses reveal similar amounts of even-numbered chain //-alkanes and odd-numbered chain components. This is a red flag that the samples must be checked for contamination. 

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