Whereas alkanes have one feature, i.e. their chain lengths, alkenes have two added features; the angle formed by the double bond and the lengths of the chains either side of the double bond. This means that a single alkene can have different functions, depending on the position of the double bond. For example, the sex pheromone of the housefly (Musca domestica) is (Z9)-C23:1 with the double bond at the nineth position, whereas (Z7)-C23:1 with the double bond at the seventh position, induces a dose-dependent inhibition of male-male courtship in D. melanogaster (Scott 1986). Therefore, it is essential that the position of all the double bonds in the alkenes is determined e.g. through dimethyldisulfide (DMDS) derivatization (Carlson et al. 1989).

Many other alkenes are found to be involved in sexual communication (Howard and Blomquist 1982), for example, the stable fly, Stomoxys calcitrans uses (Z9)-C311 and (Z9)-C331 as sex pheromones (Sonnet et al. 1979). Among the social insects, honeybees and wasps are much more responsive to alkenes than alkanes (Dani et al. 2001; Dani et al. 2005; Chaline et al. 2005). Furthermore, the proportions of alkenes in three termite (Macrotermes falciger) phenotypes were associated with inter-group aggression levels (Kaib et al. 2002). Alkenes are often found on the cuticle of ants and correlation studies have shown that they may be used as a fertility signal (Monnin 2006). However, there is now direct evidence using bioassays with synthetic compounds that the (Z9)-C231-(Z9)-C291 and (Z9)-C251-(Z9)-C331 alkenes found in Formica japonica (Akino et al. 2004) and F. exsecta (Martin et al. 2008c) ants respectively, act as nest-mate recognition cues in these species.

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