Three-way interactions between pathogens, plants and herbivores: consequences for herbivore feeding, disease development and plant fitness.
Tamara van Mölken
Department of Agriculture and Ecology, University of Copenhagen, Denmark.
Under natural conditions plants are often simultaneously exposed to pathogen attack and damage by insect herbivores. As a consequence of sharing the same host plant, interactions between pathogens and herbivores are bound to occur. The plant plays a central role in mediating such interactions, whereby pathogen induced changes in the host plant can affect herbivory and vice versa. Mechanisms underlying these effects include pathogen induced changes in: secondary metabolite levels; nutritional value; plant volatile emissions; and crosstalk between defence pathways. In turn, these biochemical changes may affect herbivore feeding and behaviour. Given that both pathogens and herbivores can impair plant performance, reciprocal effects between pathogens and herbivores are expected to result in altered plant growth and reproduction. To gain more insight into the ecological implications of pathogen infection for plant-herbivore interactions, we need a better understanding of the tripartite interactions between plants originating from wild populations and their naturally associated pathogens and herbivores. Barbarea vulgaris is well studied for its chemical defences against a range of herbivores. This herbaceous plant is susceptible to Phyllotreta nemorum flea beetles and the oomycete pathogen Albugo candida which both occur in wild B. vulgaris populations. In a series of experiments we have addressed the following questions: (i) does infection with the oomycete have an effect on flea beetle induced changes in plant nitrogen, glucosinolate and saponin levels; (ii) what are the effects of the pathogen on herbivore preference, consumption and fitness; and (iii) how do biochemical changes and variation in pathogen and herbivore damage affect plant growth, development and fitness?
