Papilio machaon - osmetrium

[Martin Dilling]

Hello everybody!

I have some questions about the P. machaon osmetrium:

The host plants for P. m. in central europe are umbelliferae like
Foeniculum vulgare, Anethum graveolens, Daucus carota and so on. These
plants offer anisaldehyde as a substitute 'lure" ingredient for citral,
offered by citrus plants in mediterranean countries.

1. The osmetrium smells like concentrated orange flavor. Is the
anisaldehyde transformed into citral or another molecule by the larvae?
What are the chemical processes within this secondary metabolism?

2. What is the osmetrium good for? Most books say it's a security
mechanism for not being eaten. I saw pictures of P. m. pupae with
entoparasites (wasp larvae) so that 'weapon' doesn't make sense to me.
Is it supposed to work with birds? I don't think so.

3. Does one know when and how evolution decided to give papilionidae
this strange organ?

Thanks for your interest,
bye for now

Martin