The influence of individual cuticular hydrocarbons on nestmate recognition in the European hornet, Vespa crabro L., was investigated. We observed the behavioural response of workers towards differently treated dead conspecifics in a bioassay. Dummies were extracted with dichloromethane and extracts were spiked with microgram amounts of synthetic hydrocarbons naturally occurring on the cuticle of V. crabro. These modified extracts were reapplied to extracted workers that were subsequently tested in the bioassay. Non-spiked nestmate dummies (negative control) and untreated non-nestmate dummies (positive control) were tested in control experiments. The addition of only heneicosane or a mixture of heneicosane, tricosane, and (Z)-9-tricosene to the extracts led to a significant increase of agonistic behaviour in workers leaving the nest for foraging flights. Returning workers reacted much less aggressively than those leaving. This is one of the first behavioural proofs that manipulation of cuticular hydrocarbon profiles can be perceived by a social insect species. The results support the hypothesis that colony-specific cuticular hydrocarbon profiles are involved in the phenomenon of nestmate recognition among social insects.

In order to elucidate nestmate recognition in the European hornet Vespa crabro L. (Hymenoptera, Vespidae) the behavioral response of workers towards dead nestmates and non-nestmates was tested in a bioassay. The testing arena was integrated in a socially and physically intact nest, in an effort to ensure natural behavior of the extremely sensitive wasps. The hornets responded to dead non-nestmates with aggressive behavior, whereas dead nestmates were tolerated or ignored. Solvent extraction of non-nestmate dummies resulted in significant decrease of agonistic behavior of the responding workers. Their behavior towards extracted non-nestmate dummies was no longer statistically distinguishable from the behavior towards nestmate dummies treated in the same way. Treatment of extracted nestmate dummies with cuticular extracts of non-nestmates induced aggressive behavior in the responding workers, whereas treatment of the extracted non-nestmate dummies with cuticular extracts of nestmates lead to a significant decrease of agonistic behavior, when compared with untreated non-nestmates.A statistical comparison of the two colonies with regard to the chemical composition of the cuticular extracts revealed that relative peak areas of 5 monoenes, 4 methyl branched alkanes, 1 terpenoid ester, and 2 n-alkanes differed significantly. The chemical analysis of the Dufour's gland revealed that all 16 compounds identified in the gland were also present in the cuticular extracts.The results strongly indicate that particular mixtures of cuticular lipids play an important role in nestmate recognition of V. crabro.

Foragers of the two cavity-nesting vespines, Vespa crabro and Vespula vulgaris, lay and follow chemical trails in their nest cavities. In our experiments 75 % of V. crabro and 72% of V. vulgaris foraging workers followed a trail arranged in a direction to which they were not accustomed. In experiments with trails taken in from conspecific alien colonies, 21 % of V. crabro foragers and 65 % of V. vulgaris foragers followed the trails. These behavioural responses indicate that the trail of V. crabro is colony-specific whereas that of V. vulgaris is not.