Data from: Separate and synergistic anti-herbivore effects of non-glandular trichomes and leaf chemistry in a desert plant

Plant defense phenotypes commonly integrate physical and chemical traits
that may act synergistically against herbivores, but empirical evidence
for synergy as a defense strategy remains limited. We experimentally
tested the separate and combined effects of two common plant defenses,
non-glandular trichomes and leaf chemistry, on the feeding, behavior, and
performance of a generalist herbivore. We conducted choice and no-choice
assays that exposed beet armyworm caterpillars (Spodoptera exigua,
Noctuidae) to desert stingbush (Eucnide urens, Loasaceae) leaves with
manipulated trichome cover and raised caterpillars on a diet containing
factorial combinations of E. urens trichomes and leaf extracts. We
assessed differences in caterpillar behavior, performance, and survival
across treatments. We found a significant interactive effect of trichomes
and leaf chemistry that markedly decreased caterpillar growth, providing
evidence for a defense synergism. Both defenses also reduced caterpillar
performance individually. Leaf extracts contained a high proportion of
putatively defensive compounds, including iridoid glycosides, which were
associated with reduced caterpillar growth and high mortality before
pupation. Barbed trichomes impeded caterpillar movement and, when
consumed, caused mandible damage and reduced eclosion rates compared to
controls. Our results indicate that two commonly co-expressed plant
defenses can synergistically reduce herbivore performance. These findings
provide a rare example of trait synergy as a defense strategy and
represent a step forward in the effort to study plant defense
holistically, as suites or syndromes of defenses, rather than isolated
traits.