The smell of the German wasp Vespula germanica

By Cintia Akemi Oi

Based on the short communication “Cuticular hydrocarbons as cues of caste and sex in the German wasp Vespula germanica” by R.C. da Silva, R.L Brown, F.S. do Nascimento, T. Wenseelers and C.A. Oi in Insectes Sociaux.

One of the most used mechanisms of communication in social insects (ants, bees, wasps and termites) is the chemical one, which occurs through pheromones. Those pheromones are chemical molecules that are produced by glands or specialized cells. We focused our research on characterizing the chemical compounds that cover the insect body. The question we wanted to answer was if within the same species of wasp Vespula germanica, the different castes and sex would have unique chemical signatures, like a badge or ID. This is super interesting because the workers need to know if there is a queen in the colony, males need to recognize virgin queens to mate and vice-versa, for the colony to function cohesively.

Example of pupae (phase that precede the adult phase): (1) male, (2) worker, and (3) virgin queen of Vespula germanica. Black bar represents 5 mm. Photo credits: Rafael C. da Silva.

The class of chemical compounds that was under this investigation are the cuticular hydrocarbons (CHCs). These chemical compounds cover the insect body to prevent water loss and to offer protection. Usually there is a mix of CHCs formed by high molecular weight compounds, composed by long-chain hydrocarbons (molecules of carbon and hydrogen). In social insects, CHCs were co-opted to have a communicative role. CHCs are helpful to differentiate castes, sex, nest membership, task, health condition and even to prevent parasites or water loss. Thus, by touching each other with their antennae, social insects have access to the information reflected by a certain individual.

Cuticular hydrocarbons are found over the surface body of insects in general. In social insects they contribute to chemical communication. Drawing credits: Wesley B. Moser.

To do our research, colonies of V. germanica were collected in Belgium and brought to the lab at KU Leuven University. Then, individuals belonging to the groups males, queens, virgin queens, and workers were separated and stored in the freezer. Those groups are easily recognized because of their body morphology. For the characterization of the smell, each individual was placed in a glass vial that was filled with a solvent (we used hexane to extract the CHC layer). Then, the samples were analysed in a Gas Chromatography-Mass Spectrometer to separate the compounds and to allow us to identify the chemical composition, which we called ‘chemical profile’.

Chemical communication using cuticular hydrocarbons (CHCs) in Vespula germanica. Chemical cues are correlated with caste, sex and nest membership. Drawing credits: Wesley B. Moser.

Among the findings, we show that the chemical profile of males, queens, virgin queens, and workers is similar in number of compounds, but differs in abundance. We can discriminate each of the groups based on their chemical signature. These results indicate that there is a specific chemical badge carried by the adults of V. germanica. In addition to that, CHCs also differ according to their colony origin. Our results are interesting because they can serve as basis to the investigation of the identity of specific queen pheromones (as the commercialized QMP in honeybees) or sexual pheromones (to develop traps where this species is invasive). To confirm whether CHCs have indeed the functions mentioned above, it is important to test them in controlled bioassays using synthetic versions of the candidates. 

(a) Queen of Vespula germanica walking over a comb full of pupae (white closed caps – individuals developing). (b) Ovaries of a mature queen, each white piece represents one oocyte that is developing, which at the end becomes an egg. Photo credits: Cintia A. Oi and Rafael C. da Silva.

Our work has been published as short communication in Insects Sociaux and has been conducted in cooperation between researchers from Brazil (Universidade de São Paulo (USP-Ribeirão Preto)), New Zealand (Manaaki Whenua – Landcare Research) and Belgium (University of Leuven (KU Leuven)).

Also, this work was partially funded from an ongoing bilateral project between Belgium and Brazil (funded by FWO and FAPESP), in which we aim to understand the division of labour in wasps and how hormones affect traits like reproduction, behavioural and chemical communication.

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