Individuals of different species interact in local communities and can influence each other’s fitness both directly or indirectly through intermediaries. This is particularly true for the interactions among plants, insect herbivores and the natural enemies of these herbivores. Using a combination of field and laboratory experiments, we examined how early season herbivory by beetles on lima bean plants affects plant performance and the abundance and performance of seed predators and their parasitoids, which occur on the plants at the end of the growing season. In addition, we determined the consequences of early herbivore-induced defenses for plant performance. We hypothesized that early-season induction will affect plant reproduction and alter the suitability of seeds for late season seed-eating beetles, and the vulnerability of these seed beetles to parasitoids.
We found strong support for these hypotheses. In the field, early-season herbivory negatively affected plant reproduction and seeds of these plants suffered lower infestation by seed-eating beetles, which in turn suffered less parasitism. Moreover, the progeny of plants whose parents were subjected to herbivory showed significantly lower insect infestation of their seeds. Laboratory assays with field-collected seeds confirmed that the performance of beetles and parasitoids was lower on seeds from plants that had been subjected to early season herbivory. Further analyses revealed that seeds produced by control plants contain larger quantities of two important cyanogenic compounds and had a higher total protein content than seeds from plants subjected to herbivory. Our results provide insight into how direct and indirect interactions between and within different trophic levels affect the dynamics and structure of complex communities.