Social insects hydrocarbons

Blomquist, G. J., Tillman J. A., Mpuru S. and Seybold, S. J. (1998) The cuticle and cuticular hydrocarbons of insects structure, function and biochemistry. In Pheromone Communication in Social Insects, eds R. K. Vander Meer, M. Breed, M. Winston and C. Espelie pp. 34-54. Westview Press, Boulder, CO. 

In addition to providing a thorough up-to-date compilation of current data, this book gives new perspective in several areas. Chapters 2-9 of this book significantly expand discussion of the chemistry, biochemistry and physiology of cuticular hydrocarbons. Chapter 8 provides the first review of the chemical synthesis of long-chain hydrocarbons. Chapters 11-13 provide new insight into the role of chemical communication in various social insect... 

As stated by Blomquist et al. (1998) in their chapter, the line of demarcation between glandular or cuticular release of semiochemical signals is not always clear . This statement echoes an earlier one by Blum (1985), who reported that insect exocrine glands consisting of modified epidermal cells located throughout the body could perform de novo biosynthesis and secretion of behavioral chemicals. Later, Blum (1987) put forth a unified chemoso-ciality concept proposing that epicuticular lipids carried numerous exocrine compounds and that the cuticle could be compared to a thin layer phase. Nevertheless, it is known that in various non-social insects epicuticular hydrocarbons are synthesized by modified cells often associated with the epidermis, the oenocytes (see above), and that these oenocytes can be located in several sites within insects. 

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... 

Endler, A., Liebig, J., Schmitt, T., Parker, J.E., Jones, G.R., Schreier, P. and Holldobler, B. (2004). Surface hydrocarbons of queen eggs regulate worker reproduction in a social insect. Proc. Natl. Acad. Sci. USA, 101, 2945-2950. 

Nestmate recognition in social insects and the role of hydrocarbons... 

Some of the indirect evidence for the use of hydrocarbons in nestmate recognition comes from social parasites. Since these are able to break the code and integrate into the normally closed colony of a social insect, the recognition cues responsible for their success can be found by studying their chemical profiles. We will give a few examples that serve the purpose of illustration a full review of social parasitism and hydrocarbons is given elsewhere (Lenoir et al., 2001b Nash and Boomsma, 2008 see Chapter 14). 

More recently, some evidence for the use of hydrocarbons in recognition in semi-social insects has been found. In the burying beetles Nicrophorus vespilloides and N. orbicollis a male and female bury a small vertebrate carcass together and defend it against intruders, in order to utilize it for their reproduction (Muller et al., 2003). They will attack any conspecific... 

Direct evidence for the use of hydrocarbons in nestmate recognition in social insects has been accumulating over the last fifteen years. When workers of the subterranean termites Reticulitermes speratus and Coptotermes formosanus were topically supplemented with the purified hydrocarbon profile of the other species, this was followed by an increase of aggression by nestmate soldiers (Takahashi and Gassa, 1995). Similarly, the topical application of (Z)-9-C23 1 onto the cuticle of workers of the ant Camponotus vagus resulted in increased antennation and threat in the form of mandible opening (Meskali et al., 1995b). These examples, however, concern qualitatively different hydrocarbons, and thus not variation in abundance that is typical for colonies of the same species. 

Since individuals within the colony are almost constantly encountering their nestmates, it would not be adaptive to continuously have to compare their profiles with an internal template in the long-term memory. The alternative would be to filter out all this input early in the neural structures and only react to hydrocarbon profiles that are dissimilar to the nestmate ones. With either desensitized antennae or habituated antennal lobes, individuals in the social insect colony would not detect or respond to the hydrocarbon profiles of nestmates (D-present), nor would they actively detect that non-nestmate hydrocarbon patterns are absent (U-absent) when accepting an encountered individual, as proposed by Sherman et al. (1997). Instead, they would only detect cues present on non-nestmates, since only these trigger the antennae or the antennal lobe to respond, and on this basis reject the encountered individual. Social insects would thus use the following as a simple rule of thumb if the receptor neurons are not spiking and/or the pattern of activation in the antennal lobes is not altered (no differences in nestmate recognition cues are detected), the encountered individual is accepted as a nestmate. This results in the same acceptance and rejection outcome... 

Greene, M. J. and Gordon, D.M. (2003). Social insects Cuticular hydrocarbons inform task decisions. Nature, 423, 32. 

Cuticular hydrocarbons are part of the lipid layer of the insect cuticle that protects from desiccation (Lockey, 1988) and are thus present in basically every social insect (see Chapter 6). Insects have the sensory apparatus to detect these profiles. So it is not surprising that they utilize variations in hydrocarbon profiles between individuals within and between species to detect various properties in other individuals, such as species identity, gender, colony membership (Howard and Blomquist, 1982, 2005 and various chapters in Part II of this book). In this chapter I will review the evidence indicating that hydrocarbon profiles are also used in colonies of ants, bees, and wasps for the regulation of reproduction. I will especially focus on patterns of variation in hydrocarbon profiles on the cuticle and the eggs in relation to fertility differences, which has not been done in such detail in previous reviews (Heinze, 2004 Monnin, 2006 Hefetz, 2007 Le Conte and Hefetz, 2008 Peeters and Liebig, 2009). 

The question is whether there is a general mechanism that explains the chemical nature of the reproductive regulation in social insects. Cuticular hydrocarbons may be the basis of such a general mechanism. They fulfill all the requirements needed for such a system, as I will describe in the following paragraphs. 

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