Effects of tree species diversity on insect herbivory and leaf defences in Cordia dodecandra

1. It is broadly accepted that plant diversity influences plant–herbivore interactions, yet few studies have separated damage by different herbivore species and simultaneously tested for effects on herbivory and plant defences to elucidate the mechanisms underlying such effects. 2. This study tested for effects of tree species diversity on leaf damage by beetle larvae and caterpillars on Cordia dodecandra in a diversity experiment, and measured leaf chemical and physical traits to assess whether differences in herbivory underlie changes in plant traits. 3. Four year‐old trees were sampled in 21 × 21‐m plots classified as monocultures of C. dodecandra or mixtures of this species plus three other tree species. Herbivory by beetle larvae and caterpillars was estimated, and we subsequently collected undamaged leaves to quantify total phenolics and condensed tannins, trichome density, and specific leaf area. 4. A significant effect of diversity on herbivory by beetle larvae was found, with mixtures exhibiting an 80% lower mean value than monocultures. By contrast, there was no diversity effect on caterpillar herbivory. Additionally, a positive relationship was found between beetle larvae (but not caterpillar) damage and plant chemical defences, yet there was no effect of diversity on defences. Specific leaf area was higher and trichome density tended to be lower in mixtures than in monocultures, but neither trait was associated with herbivory, and damage did not explain diversity effects on these traits. 5. These findings emphasise the importance of separating diversity effects on different herbivore species and measuring plant traits associated with herbivory to better understand controls of diversity on plant–herbivore interactions. Tree diversity had contrasting effects on leaf herbivory by beetle larvae and caterpillars on the tropical tree Cordia dodecandra, negatively affecting the former but not influencing the latter. Diversity altered leaf physical attributes but not chemical defences, and changes in the former were not explained by herbivory but instead probably responded to changes in abiotic conditions with diversity. Contrasting effects on beetles and caterpillars suggest differences in dispersal ability or oviposition. That differences in herbivory levels did not to drive changes defences suggests that diversity effects on herbivory and plant defences operate independently.