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 x 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.