First record of double-edged sword effect of caterpillar-induced plant volatiles in nature

Plants release volatiles in response to caterpillar feeding that attract natural enemies of the herbivores, a tri-trophic interaction which has been considered an indirect plant defence against herbivores. The caterpillar-induced plant volatiles have been reported to repel or attract conspecific adult herbivores. Apple seedlings infested with Pandemis pyrusana larvae uniquely release five compounds (benzyl alcohol, benzyl nitrile, phenylacetaldehyde, indole, and (E)-nerolidol). These compounds and other known caterpillar-induced plant volatiles were tested to investigate the response of both herbivores and natural enemies. In field tests, binary blends of benzyl nitrile and acetic acid or 2-phenylethanol and acetic acid attracted a large number of conspecific male and female adult moths. On the other hand, a ternary blend of benzyl nitrile, 2-phenylethanol and acetic acid attracted the largest numbers of the general predator, the common green lacewing, Chrysoperla carnea. This study provides the first record of caterpillar-induced plant volatile attraction to conspecific adult herbivores as well as predators under natural conditions.