Chemical communication is the oldest form of communication, spreading across all forms of life. In insects, cuticular hydrocarbons (CHC) function as chemical cues for the recognition of mates, species, and nest-mates in social insects. Although much is known about the function of individual hydrocarbons and their biosynthesis, a phylogenetic overview is lacking. Here, we review the CHC profiles of 241 species of Hymenoptera, one of the largest and most important insect orders, which includes the Symphyta (sawflies), the polyphyletic Parasitica (parasitoid wasps), and the Aculeata (wasps, bees, and ants). We investigated whether these taxonomic groups differed in the presence and absence of CHC classes and whether the sociality of a species (solitarily vs. social) had an effect on CHC profile complexity. We found that the main CHC classes (i.e., n-alkanes, alkenes, and methylalkanes) were all present early in the evolutionary history of the Hymenoptera, as evidenced by their presence in ancient Symphyta and primitive Parasitica wasps. Throughout all groups within the Hymenoptera, the more complex a CHC the fewer species that produce it, which may reflect the Occam’s razor principle that insects’ only biosynthesize the most simple compound that fulfil its needs. Surprisingly, there was no difference in the complexity of CHC profiles between social and solitary species, with some of the most complex CHC profiles belonging to the Parasitica. This profile complexity has been maintained in the ants, but some specialization in biosynthetic pathways has led to a simplification of profiles in the aculeate wasps and bees. The absence of CHC classes in some taxa or species may be due to gene silencing or down-regulation rather than gene loss, as demonstrated by sister species having highly divergent CHC profiles, and cannot be predicted by their phylogenetic history. The presence of highly complex CHC profiles prior to the vast radiation of the social Hymenoptera indicates a ‘spring-loaded’ system where the diversity of CHC needed for the complex communication systems of social insects were already present for natural selection to act upon, rather than having evolved independently. This diversity may have aided the multiple independent evolution of sociality within the Aculeata.Electronic supplementary materialThe online version of this article (doi:10.1007/s10886-015-0631-5) contains supplementary material, which is available to authorized users.
Abstract. Cuticular hydrocarbons (CHCs) are expressed on an insect's cuticle and are one of the major factors allowing insects to identify members of their own species, colony and gender. As a result of their species-specificity, CHCs are increasingly used to delimit species in addition to more conventional methods, such as morphology or genetic markers, and so play an important role in chemotaxonomy. Species vary in the type of CHCs that they produce, as well as in the relative quantities of shared compounds. This review summarizes not only how taxonomists may differentiate between species based on CHC profiles, but also the incentive for using CHC composition as taxonomic tool. Benefits regarding the identification of cryptic species and early signs of reproductive isolation are then discussed, giving examples from studies of taxonomy, behaviour and biosynthesis. For taxonomic characters to reliably indicate species boundaries, their limitations need to be known. Potential problems caused by environmental effects, intra-species variation in profiles and other technical issues are highlighted, and suggestions are made regarding their avoidance. It remains a challenge to determine the variation beyond which two species can be called independent; a problem shared by most methods of delimitation. Recently, there has been a shift towards using a combination of different taxonomic tools, both molecular and non-molecular, to test observed species differences.
Social insects are defined by their ability to divide labor among their numerous nestmates. This is achieved via a complex system of chemical communication that allows colonies to organize task activity so as to maximize the productivity of the colony. However, the mechanism by which social insects distinguish task groups among morphologically identical individuals remains unknown. Using the honey bee, Apis mellifera, as our model species, we investigated the presence of task-specific patterns in the cuticular lipids (n-alkanes, fatty acids, and alkenes) of bees. Cuticular lipids are known to play an essential role in the recognition processes of insects. We found task-specific features in the n-alkane and alkene profiles of bees, but no task-specific patterns in the fatty acid profile. Foragers, in particular, had elevated levels of n-alkanes relative to nurse and newly emerged bees, suggesting increased waterproofing. Newly emerged bees had low levels of cuticular lipids, supporting the Blank Slate theory and potentially explaining their acceptance into foreign colonies.
-Social insect colonies provide a stable and safe environment for their 34 members. Despite colonies been heavily guarded, parasites have evolved numerous 35 strategies to invade and inhabit these hostile places. Two common strategies are chemical 36 mimicry via biosynthesis of the hosts' odour or chemical camouflage were compounds 37 are acquired straight from the host. The ectoparasitic mite Varroa destructor feeds on the 38 heamolymph of its honeybee host Apis mellifera and uses chemical mimicry to remain 39 undetected as it lives on the adult host during its phoretic phase or while reproducing on 40 the honeybee brood.. During the mite life cycle it switches between host adults and 41 brood, which requires it to adjust its profile to mimic the very different odours of 42 honeybee brood and adults. In a series of transfer experiments using adult bees and 43 pupae, we tested whether V. destructor does this by synthesising compounds or using 44 chemical camouflage. We show that V. destructor required direct access to the host 45 cuticle to mimic its odour and was unable to synthesise host-specific compounds itself. destructor was adjusted within three to nine hours after switching hosts, demonstrating 49 that passive camouflage is a highly efficient, fast and flexible way for the mite's to adapt 50 to a new host's profile when moving between different host life stages, or host colonies.
Abstract. In social insects, the integrity of a colony is maintained by recognising and
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