Direct and indirect defense response of Lima bean ("Phaseolus lunatus") to herbivory: implications for tritrophic interactions

In the nature plants are exposed to a huge amount of interactions with species from different guilds from mutualistic to antagonistic, and during the last 10 years researchers have been trying to underlying the ecological and evolutionary mechanisms that plants use to respond against this complex web of interactions. Plant traits such as chemical defenses after damage can affect not only the performance of the insect herbivores that feed on the plants but also the availability of them to their predators / parasitoids. The aim of my Phd thesis was in one side, to test whether in each specific community herbivores and their natural enemies will have adapted to the plant defenses induced by earlier herbivores. We tested that by determining the extent to which damage on leaves and seeds of Lima bean plants (<i>Phaseolus lunatus</i>) by the leaf beetle (<i>Cerotoma ruficornis</i>) and the bean pod weevil (<i>Apion godmani</i>) affects the performance and choice behavior of the Mexican bean weevil (<i>Zabrotes subfasciatus</i>) which arrive later in the season. In parallel we also studied how such effects affected the next trophic level (parasitoids). In the other side, we showed that in Lima bean there is a potential conflict between attracting defending ants and pollinators. This conflict could only be detected in situations of an increased production of extrafloral and floral nectar by plants induced with JA. By integrating the results regarding both direct and indirect defenses in Lima bean we can conclude that the complexity of the plant responses is driven by hormonal control. As soon as the first visitor arrives to the plant it triggers a series of responses that will affect not only the next visitor’s choice but also will affect the plant defense in the next generation.

Thèse de doctorat : Université de Neuchâtel, 2015