Gustatory responsiveness to pyrrolizidine alkaloids in the Senecio specialist, Tyria jacobaeae (Lepidoptera, Arctiidae)

.  Electrophysiological recordings from taste sensilla of the caterpillar Tyria jacobaeae with the pyrrolizidine alkaloids, characteristic compounds from their host plants, demonstrated sensitivity of a pyrrolizidine alkaloid‐sensitive cell in the lateral galeal sensilla at concentrations as low as 1 × 10 −11  M. Another pyrrolizidine alkaloid‐sensitive cell in the medial galeal sensilla responded at higher concentrations. Both pyrrolizidine alkaloid‐cells were maximally sensitive to seneciphylline N ‐oxide and senecionine N ‐oxide. Seven other pyrrolizidine alkaloids were less stimulating. Monocrotaline N ‐oxide was the least stimulating. Observation experiments demonstrated that differences in sensitivity to different pyrrolizidine alkaloids at the electrophysiological level were correlated with differences in feeding behaviour; the first feeding bout was of longer duration on diet containing seneciphylline N ‐oxide than on diet containing monocrotaline N ‐oxide, and a plain diet was generally not accepted.