METHYL SALICYLATE AND (-)-(1R,5S)-MYRTENAL ARE PLANT-DERIVED REPELLENTS FOR BLACK BEAN APHID, APHIS-FABAE SCOP (HOMOPTERA, APHIDIDAE)

Methyl salicylate and (-)-(1R,5S)-myrtenal stimulate specific olfactory cells in the primary rhinaria on the sixth and fifth antennal segments, respectively, of the black bean aphid, Aphis fabae. In behavioral studies employing a linear track olfactometer, both compounds were repellent to A. fabae and also inhibited attraction to volatiles from its host, broad bean (Vicia faba). Methyl salicylate is associated with secondary metabolite-based defense in plants, and the monoterpenoid (-)-(1R,5S)-myrtenal is metabolically related to (-)-(1S,5S)-alpha-pinene, an abundant component of defensive resins produced by gymnosperms. It is argued that these two compounds are employed by A. fabae as indicators of nutritionally unsuitable or nonhost plants.