Does herbivore diversity increase induced phytochemical diversity? Testing the pathway co-activation hypothesis

Dual-herbivory by phloem-feeding aphids and leaf-chewing caterpillars on cabbage seedlings increases phytochemical richness and evenness, with evenness rising from caterpillar-only to dual exposure.

• Why it matters: The mechanistic link between multiple herbivory and plant phytochemical diversity as an emergent trait is unclear, limiting tests of how herbivore diversity shapes plant chemistry.
• What they did: In a dual-herbivory experiment on cabbage seedlings, pressures were equalized across treatments and untargeted metabolomics was used; defense phytohormone applications tested the mechanism.
• The result: Phytohormone applications produced similar effects, and glucosinolate and whole-metabolome analyses were consistent with prevalent, but not exclusive, antagonistic JA–SA crosstalk, explaining increased phytochemical evenness under combined exposures.