Host location in a specialist parasitoid wasp via olfactory cues – a physiological, behavioural and morphological study

Abstract

For successful host location, parasitoids are thought to have evolved different strategies to filter relevant olfactory cues which indicate the presence of the host. Because of their versatility in their ecology and behaviour, as well as their fine tuned olfactory system to volatile compounds of the host and host plant, they have gained increasing recognition as model organisms to study learning and behaviour in an adaptive ecological context. However, neural and cellular mechanisms of olfactory detection and processing in parasitoids are mainly unknown.
In this thesis physiological, behavioural and morphological experiments were used to determine neural and behavioural mechanisms of host location via olfactory cues in the specialist parasitoid Cotesia vestalis. C. vestalis showed significant antennal responses to a range of odour compounds. Behavioural experiments, however, have demonstrated that only the herbivore-induced plant volatile linalool attracts C. vestalis males and females, but 1-nonanol has a repulsive effect on females. A morphological study of the antennal lobe, the first brain area where olfactory information is processed, revealed 40 ordinary glomeruli in both males and females. In addition, a complex of 2-3 enlarged glomeruli (MGC) was found in males. The courtship behaviour observed in males and the MGC suggest that males could use sex pheromones to locate females. Finally, calcium imaging studies showed glomerular activity to olfactory stimulation in bees but not in parasitoids. In conclusion, the degree of host specialisation in C. vestalis appears to influence olfactory learning in males and females, which favours learning of volatiles related to its host and host plant, as well as the morphological organisation of the antennal lobe. Larger, fewer and possibly specialised glomeruli could enhance processing of odour cues which are important for this parasitoid.

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ORCID for Philip L. Newland: orcid.org/0000-0003-4124-8507

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