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Very interesting - this is really a case for the Lepiforum! If you get an identification of the caterpillar, please let me know. However, it might be necessary to rear it and wait for hatching of the imago to get a sure ID.
In my lectures on poisonous plants, the taxa containing pyrrolizidine alkaloids (PA) play an important role (PA are produced in several families, especially Asteraceae and Boraginaceae), and I mention cases of insect larvae that are able to incorporate the alkaloids for self-defense. So I am, of course, interested in your caterpillar.
There is an interesting book, edited by A. Schaller (2008), Induced Plant Resistance to Herbivory. Chapter 10, written by T. Hartmann and D. Ober, is titled: "Defense by Pyrrolizidine Alkaloids: Developed by Plants and Recruited by Insects". You can google it and perhaps contact the authors. These insect larvae may well be polyphagous but prefer PA plants, among which the widely distributed Senecio species play an important role.
The horse riding centre where I use to go to tries very hard to eradicate the frequent Senecio vernalis on the grazing land, because an uptake of these plants in hay or silage might be fatal. I have never noticed caterpillars on or in the annual Senecio species, however. I shall look more closely in the coming spring!
Good luck for your studies! Sundew