Root herbivory can greatly affect the performance of aboveground insects via changes in plant chemistry.
These interactions have been studied extensively in experiments where aboveground and belowground
insects were feeding on the same plant. However, little is known about how aboveground and belowground
organisms interact when they feed on plant individuals that grow after each other in the same soil.
We show that feeding by aboveground and belowground insect herbivores on ragwort (Jacobaea vulgaris)
plants exert unique soil legacy effects, via herbivore-induced changes in the composition of soil fungi.
These changes in the soil biota induced by aboveground and belowground herbivores of preceding plants
greatly influenced the pyrrolizidine alkaloid content, biomass and aboveground multitrophic interactions of
succeeding plants. We conclude that plant-mediated interactions between aboveground and belowground
insects are also important when they do not feed simultaneously on the same plant.