A taste receptor neurone dedicated to the perception of pyrrolizidine alkaloids in the medial galeal sensillum of two polyphagous arctiid caterpillars

Abstract

It is shown that pyrrolizidine alkaloids are phagostimulants for the caterpillars of two polyphagous arctiid caterpillars, Estigmene acrea and Grammia geneura. The caterpillars will also eat dry glass-fibre discs containing only pyrrolizidine alkaloid - an example of pharmacophagy. The tip-recording technique is used to demonstrate that each species has a neurone in the medial galeal styloconic taste sensillum responding to pyrrolizidine alkaloids, although the species differ in their sensitivities. This neurone responds to at least four different pyrrolizidine alkaloids and their N-oxides, and experiments indicate that it is dedicated to perception of these compounds. The sensory response is phasic-tonic and during the tonic phase remains unchanged for at least 500ms, resembling the type of response often seen in neurones that are sensitive to plant secondary compounds producing deterrent effects.