Alkanes

Linear alkanes or n-alkanes (straight chains) normally dominate the cuticular hydrocarbon profile of insects (Blomquist and Dillwith 1985). Alkanes occur as a continuous homologous series of either odd numbered linear alkanes or even numbered linear alkenes across narrow (e.g. C19-C21 in Gnantogenys striatula, Lommelen et al. 2006) or broad (e.g. C21-C37 in Dinoponera quadriceps, Monnin et al. 2002) ranges. Odd linear n-alkanes are always more abundant than the even linear n-alkanes.

Despite being well studied there is little conclusive evidence yet that alkanes are key signalling compounds. Pickett et al. (1982) demonstrated that honeybee olfactory neurons did not respond to C23-C27 alkanes which was supported by calcium imaging studies, where no glomerular (neural) responses in the antennal lobe of honeybees were obtained for alkanes >C10, whereas a wide range of alcohols, aldehydes and ketones elicited strong neural responses (Sachse et al. 1999). This explains why honeybees were unable to learn to discriminate well between alkanes (C27-C31), whereas they learnt and discriminated well between most alkenes (Chaline et al. 2005). These findings are supported by the observation that only altering the alkene and not the alkane profile results in a clear behavioural response in honeybees (Dani et al. 2005), the paper wasp Polistes dominulus (Dani et al. 2001) and ant Formica exsecta (Martin et al. 2008c). However, alkanes can be learnt by honeybees (Chaline et al. 2005) just not very well. They may play a role in nest-mate recognition in Formica japonica (Akino et al. 2004), but the overall lack of behavioural response to alkanes suggests that their primary function is water-proofing.

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