Chemoreception of phenolic acids and flavonoids in larvae of two species of Pieris

Abstract

1. Chemosensory responses in lateral and medial maxillary sensilla styloconica to stimulation with phenolic acids and flavonoids were studied using electrophysiological methods in caterpillars of Pieris brassicae L. and Pieris rapae L. (Lepidoptera: Pieridae). 2. Of the 5 phenolic acids tested, those possessing ortho-substituted phenolic groups (chlorogenic and protocatechuic acids) were the most effective stimulants. 3. Of the 7 flavonoids examined, catechin was the most effective stimulant in the lateral sensillum of both species, while 3 others did not evoke a response at any of the concentrations tested. 4. Responses generally increased with increasing stimulus concentrations in the range tested (0.2–5.0 mm). P. rapae generally exhibited higher sensitivity thresholds. 5. Mixture experiments suggested that in the lateral sensillum of P. brassicae one cell and in the medial sensillum two cells were especially sensitive. 6. The anthocyanin cyanin chloride caused inhibition of spiking activity in several neurones. 7. Caterpillars reared on an artificial diet showed reduced sensitivity compared to caterpillars reared on a host plant. 8. Chemosensory activity was reflected in preference behaviour in dual choice situations. 9. Dose-response relations combined with phytochemical data permit the conclusion that naturally occurring levels of phenolic acids and flavonoids are stimulatory to some chemosensory neurones and can cause inhibition of activity in others.