Cuticular lipids

A sequence of reptilian studies tracked down the likely signal for mating in Canadian Red-sided Garter snakes. Males respond to products on the female s skin surface, which turn out to be related both to insect cuticular lipids and to those of mammalian skin. These integumentary... 

Kolattukudy PE, Ettinger WF, Sebastian J (1987) Cuticular lipids in plant-microbe interactions. In Stumpf PK, Mudd BD, Ness WD (eds) The metabolism, structure, and function of plant lipids. Plenum Publishing, New York, p 473... 

Another contact sex pheromone was identified as a component of the cuticular lipids of females of Psacothea hilaris [350,351]. Extracts of the elytra contained (Z)-21-methyl-8-pentatriacontene 189. The synthetic compounds (both enantiomers were synthesized [352,353]) induced precopulatory behaviour in males, however, its biological activity was considerably lower than that of the natural extract. 

Another group of compounds unique to spiders, namely propyl esters of long-chain, multiply branched fatty acids, have been found in the cuticular lipids of the spider A. eximus (Bagneres et al., 1997). 

It has become widely recognized over the past several decades that cuticular lipids, especially the hydrocarbons, function in chemical communication in many insect species (Howard, 1993 Nelson and Blomquist, 1995 Blomquist et al., 1998). Semiochemical functions attributed to hydrocarbons include sex attractants... 

Table 8.1 Cuticular lipids which function in chemical communication in Diptera... 

The other long understood and, indeed, fundamental function of insect cuticular lipids is to restrict water loss to prevent a lethal rate of desiccation (Hadley, 1984 Noble-Nesbitt, 1991 Nelson and Blomquist, 1995). Conservation of water is a primary challenge faced by terrestrial animals with high surface area to volume ratio such as insects. The anti-desiccatory function of the cuticular waxes is crucial in meeting this need, and makes them a focused target for insect control. 

Methyl-branched alkanes function as an arrestant in the housefly pheromone (Adams and Holt, 1987 Nelson el al., 1981). They are abundant components of the insect cuticular lipids (Nelson and Blomquist, 1995) where they function in waterproofing (Gibbs, 1998) and serve in chemical communication (Blomquist et al., 1993, 1998). 

Gibbs A. G. (1998) Water-proofing properties of cuticular lipids. American Zool. 38, 471 182. 

Uebel E. C., Sonnet P. E., Menzer R. E., Miller R. W. and Lusby W. R. (1977) Mating-stimulant pheromone and cuticular lipid constituents of the little housefly, Fannia canicularis (L.). J. Chem. Ecol. 3, 269-278. 

The eggs of B. germanica contain the same types of hydrocarbons as the hemolymph, HDLp, and cuticle of the adult female. Only 150 pg of hydrocarbons accumulate on the epicuticular surface whereas up to 450 pg accumulate within the female during the period of egg maturation (Fan et al., 2002). The internal hydrocarbons are divided primarily between the ovaries, fat body, and 150 pg of HDLp-bound hydrocarbons in the hemolymph. During oocyte maturation ovarian hydrocarbons increase by more than 65-fold - from 3.5 pg on day-1 to 232 pg on day-8 (Fan et al., 2002). However, after oviposition on day-9, ovarian hydrocarbons decline to only 8.2 pg, demonstrating that hydrocarbons were associated with the ovulated oocytes. Radiotracing results indicate that they serve as components of the cuticular lipids of the embryos and first instars (Fan and Schal, unpublished results). 

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). 

Blomquist, G.J. and Dillwith, J.W. (1985). Cuticular lipids. In Comprehensive Insect Physiology, Biochemistry and Pharmacology, ed. G.A. Kerkut and L.I. Gilbert, Vol. 3. Integument, Respiration, and Circulation. Oxford Pergamon, pp.117-154. 

Blomquist, G.J., Nelson, D.R. and de Renobales, M. (1987). Chemistry, biochemistry, and physiology of insect cuticular lipids. Arch. Insect Biochem. Physiol., 6, 227-265. 

Hadley N.F. (1981). Cuticular lipids of terrestrial plants and arthropods a... 

Jackson, L.L. (1972). Cuticular lipids of insects IV. Hydrocarbons of the cockroaches Periplaneta japonica and Periplaneta americana compared to other cockroach hydrocarbons. Comp. Biochem. Physiol., 41B, 331-336. 

Jackson, L.L. and Blomquist, G.J. (1976b). Cuticular lipids of insects VIII - Alkanes of the mormon cricket Anabrus simplex. Lipids, 11, 77-79. 

Figure 2.1 Structures of major hydrocarbons present in insect cuticular lipids.

Baker, J.E., Sukkestad, D.R., Nelson, D. R. and Fatland, C.L. (1979). Cuticular lipids of larvae and adults of the cigarette beetle, Lasioderma serricorne. Insect Biochem., 9, 603-611. 

It is generally accepted that insects synthesize a majority of their cuticular hydrocarbons (Nelson and Blomquist, 1995), although studies have shown that dietary hydrocarbons are incorporated into cuticular lipids (Blomquist and Jackson, 1973a). However, for most species it appears that dietary lipid accounts for very small amounts of insect cuticular hydrocarbon. Some inquilines, which use cuticular hydrocarbons in chemical mimicry, synthesize hydrocarbons with a composition very similar to those of their host termites (Howard et al., 1980 see also Chapter 14). A number of studies with widely diverse insect species have established that the major site of hydrocarbon biosynthesis occurs in the cells... 

Blomquist, G.J. and Jackson, L.L. (1973a). Incorporation of labelled dietary n-alkanes into cuticular lipids of the grasshopper Melanoplus sanguinipes. J. Insect Physiol., 19, 1639-1647. 

Eliyahu, D., Nojima, S., Capracotta, S.S., Comins, D.L. and Schal, C. (2008). Identification of cuticular lipids eliciting interspecific courtship in the German cockroach, Blattella germanica. Naturwissenschaften, 95,403 112. 

The transport of hydrocarbons by social insects can be involved in creating the hydrocarbon signature . Evidence was first obtained in the termite Zootermopsis nevaden-sis (Sevala et al., 2000). Comparison of cuticular lipids with internal and hemolymph hydrocarbons in different castes showed that, as in other species, the content was qualitatively similar. However, quantitative differences were observed between hemolymph and cuticular hydrocarbon profiles. Sevala et al. (2000) showed that hemolymph hydrocarbons were associated with a dimeric high-density lipoprotein (HDLp) lipophorin, similar to those described from other insects (see above). This lipoprotein consisted... 

---