Editors' ChoicePARASITES

An Acquired Taste for Toxins

Science's STKE  02 Aug 2005:
Vol. 2005, Issue 295, pp. tw278
DOI: 10.1126/stke.2952005tw278

The tiger moth caterpillars Grammia geneura and Estigmene acrea defend themselves against parasites by feeding on plants containing phytochemicals toxic to the parasites: E. acrea eats and sequesters pyrrolizidine alkaloids; G. geneura eats and sequesters iridoid glycosides as well. The caterpillars detect these compounds by means of specialized chemoreceptor gustatory cells that stimulate feeding behavior. Bernays and Singer showed that, compared with control caterpillars, the increase in taste cell firing rate in response to the iridoid catalpol and the pyrrolizidine alkaloid seneciphylline N-oxide was greater in parasitized G. geneura. In contrast, the response of a gustatory cell sensitive to the feeding deterrent caffeine was decreased. There was no difference in the response to sucrose, which is detected through the same gustatory cells as iridoids, indicating that the change affected the iridoid receptor or the subsequent signaling pathway rather than being cell-wide. Similarly, gustatory cells in parasitized E. acrea showed an enhanced response to seneciphylline N-oxide compared with unparasitized caterpillars, a reduced response to the feeding deterrent protocatechuic acid, and an inconsistent response to sucrose. Thus, parasitization appears to alter the sensitivity of caterpillar gustatory cells to promote the ingestion of substances toxic to the parasites and to inhibit the response to substances that inhibit feeding behavior.

E. A. Bernays, M. S. Singer, Insect defences: Taste alteration and endoparasites. Nature 436, 476 (2005). [PubMed]