The costs and effectiveness of chemical defenses in herbivorous insects: a meta‐analysis
Level 1 - systematic review of randomized trials
Meta-analysis of ecological studies (graded by design analogy, not clinical CEBM)
OpenAlex W2176150191 · doi:10.1890/15-0911.1
What was done
The authors conducted a meta-analysis evaluating the effectiveness (measured as prey survival across 159 publications) and costs (measured as performance reduction across 33 publications) of chemical defenses in plant-feeding insects. The dataset encompassed 140 herbivore species and 124 natural enemy species across diverse prey–predator interactions.
What was found
The abstract reports no numerical effect sizes or confidence intervals. Chemically defended herbivores showed effective protection against generalist predators, no protection against specialist predators or generalist parasitoids, and an increased risk of parasitism by specialist parasitoids. Defenses were more effective against vertebrates (especially birds) than invertebrates. De novo synthesized compounds and plant-derived sequestered compounds yielded similar effect magnitudes. Specialist herbivores had more effective defenses than generalists. Aposematic coloration enhanced effectiveness specifically against vertebrate predators. No physiological costs were identified across 22 evaluated herbivore species, though cost results varied strongly by measurement method.
Why it matters
This synthesis indicates that evolutionary trade-offs in insect chemical defenses are governed primarily by ecological costs (such as heightened vulnerability to specialist natural enemies) rather than physiological resource costs.
Limits
The abstract reports no exact numerical effect sizes, variances, or p-values. Assessment of physiological costs was restricted to a smaller subset of 22 herbivore species and exhibited substantial variability depending on the assay methodology employed.
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