Parasitoids of leaf herbivores enhance plant fitness and do not alter caterpillar-induced resistance against seed beetles

1. Organisms of the third trophic level can indirectly interact with plants. However, whether parasitoids of herbivores have a positive effect on plant fitness has been controversial. In addition to possible effects on plant fitness, parasitoid-mitigated herbivory can modify plant physiological responses and thereby alter the plant-mediated indirect interactions between different herbivore species. These types of indirect multitrophic interactions remain largely unexplored. Thus, to understand the full effect of the third trophic level on plants, it is necessary to consider the context of the community of interacting species, both herbivores and their enemies.

2. Here, we investigated if parasitoids of leaf-feeding caterpillars affect plant fitness (seed quantity and quality) and the consequences for seed-dwelling insects at the second and third trophic levels through plant mediated effects. To test this, we exposed lima bean plants (Phaseolus lunatus), under controlled field conditi...