1. Many plants are simultaneously attacked by arthropod herbivores and phytopathogens.
These may affect each other directly and indirectly, enhancing or reducing the amount of plant
resources they each consume. Ultimately, this may reduce or enhance plant performance relative
to what should be expected from the added impacts of herbivore and pathogen when they
attack alone.
2. Previous studies have suggested synergistic and antagonistic impacts on plant performance
from certain combinations of arthropods and pathogens, for example, synergistic impacts from
necrotrophic pathogens together with wounding arthropods because of facilitated infection
and antagonistic impacts from induction of pathogen resistance by sucking herbivores.
3. We compiled published studies on the impact of plant–herbivore–pathogen interactions on
plant performance and used meta-analysis to search for consistent patterns of impacts among
plant, herbivore and pathogen characteristics and experimental conditions, and to test the
suggested hypotheses on synergistic or antagonistic impacts.
4. None of the hypotheses based on proximate interactions between arthropods and pathogens
were supported by our analysis; in contrast, the patterns we found were related to plant traits
and experimental conditions.
5. Our results suggest that immediate loss of resources from interactions between arthropod
herbivores and pathogens is generally moderated by compensation to an extent where there
are no interactive effects on plant performance. However, as interactive impacts also differed
among environments and parasite manipulation methods, this suggests that the ability of
plants to compensate such losses may depend on environmental conditions and probably also
overall infection load.