Ecological cross-effects of induced plant responses towards herbivores and phytopathogenic fungi

Plants are under continuous threat of being challenged by herbivorous insects and pathogenic micro-organisms. How plants respond to multiple antagonists that may co-occur has been investigated by researchers on the ecological, pharmacological, and genetic level. In this review we focus on recent studies of ecological cross-effects between phyllophagous herbivores and phytopathogenic fungi. Interactions between the two types of plant antagonists may be direct, plant-mediated or both. We present studies which describe a) potentially plant-mediated cross-effects but where direct effects cannot be excluded ('direct/plant-mediated effects'), b) plant-mediated cross-effects that are confined to the attacked plant part ('locally plant-mediated effects') and c) plant-mediated cross-effects on a systemic scale ('systemic effects'). Also, studies ate addressed which attempted to directly link plant physiological changes induced by the herbivore and fungal attack with effects on the antagonists. Special attention will be given to spatial and temporal aspects of plant fungal infection and herbivore infestation.