Crotalaria pallida chemical defence and ant attendance

The efficiency of different plant defences is expected to vary depending on the combination and abundance of herbivores. Effectiveness of ant-mediated defences can also depend on ant activity and local ant assemblage, which can vary due to human activities such as intensive grazing. We used the plant Crotalaria pallida (Fabaceae), its two pod-boring herbivores and the ants that visit the extrafloral nectaries (EFNs) to understand how chemical defence and ant-plant associations affect plant damage. We hypothesised causal relationships between plant chemical defence, ant presence on plants and herbivore damage in scenarios of constitutive and induced plant defences and tested the different possible relationships using path analysis. The constitutive model explained the data more adequately, and each plant defence had different effects on each herbivore species. First, chemical defence significantly reduced damage by the generalist pod borer Etiella zinckenella but not by the specialist Ut...