Phytochemical defences and performance of specialist and generalist herbivores: a meta‐analysis

Abstract

1. Phytochemical coevolution theory, a long-standing paradigm in plant-insect interactions, predicts that specialist herbivores are less negatively affected by the allelochemicals of their host plants than are generalist herbivores. Although this theory is prevalent in plant-insect science, it is not always supported by empirical studies measuring the performance of specialist and generalist insects in response to allelochemicals.2. The present study aimed to investigate: (i) whether there a difference between specialist and generalist performance in response to allelochemicals and (ii) whether the effect of allelochemicals on specialists and generalists depend upon allelochemical class or insect order.3. A meta-analysis was conducted incorporating 76 effect sizes drawn from studies that directly compared the performance of specialist and generalist insects in response to treatment and control diets. Most of the effect sizes were related to the performance metric growth, the insect order Lepidoptera, and the allelochemical class nitrogen-containing compounds. 4. As predicted by phytochemical coevolution theory, specialist insects responded less negatively to allelochemicals of their hosts than generalist insects in terms of growth. There were no significant differences in terms of fecundity or survival, or among allelochemical classes or insect orders. 5. These results support the prediction of phytochemical coevolution theory that specialist insects respond less negatively to allelochemicals of their hosts than generalists, although only in terms of growth.

Cardenolides, toxicity, and the costs of sequestration in the coevolutionary interaction between monarchs and milkweeds

“…For example, how do plants respond to highly specialized herbivores, and are such adapted consumers immune to plant defenses? On average, specialists are less impacted by particular plant defense compounds than generalists (1,2), but does this mean that further coevolution is not possible? Even highly specialized herbivores must contend with plant defenses if coevolutionary interactions are proceeding (3).…”

Degree of dietary specialization on furanocoumarin-containing hostplants in a newly invasive species, Depressaria depressana (Lepidoptera: Depressariidae)

“…Additionally, the terms 'generalist' and 'specialist' may also oversimplify a continuous spectrum of insect diet breadth (Loxdale and Harvey 2016). Rothwell and Holeski (2020) conducted a meta-analysis incorporating 45 studies and found evidence that specialist insects do outperform generalists in terms of growth, but not fecundity or survival. However, the need remains for further consideration of insects occupying the middle portion of the diet breadth spectrum.…”

Genotypic Variation in Plant Traits, Chemical Defenses, and Resistance Against Insect Herbivores in Avocado (Persea americana) Across a Domestication Gradient

“…be better adapted to the secondary metabolites of their host plants than generalist herbivores (Stamp, 2003;Loxdale et al, 2011), although this prediction has been increasingly debated in recent years (Ali and Agrawal, 2012;Smilanich et al, 2016;Rothwell and Holeski, 2019). To our surprise, the generalist S. frugiperda performed better on some of the landraces that had higher phenolic content, whereas the specialist C. multifenestrata performed best on the cultivated "Hass."…”