Sight unseen: Belowground feeding influences the distribution of an aboveground herbivore

Abstract

Plants are under constant threat from insect herbivores that can consume all types of plant tissue, both aboveground and belowground. Because plants connect aboveground and belowground environments, they are uniquely positioned to mediate indirect herbivore interactions between the two ecosystems. The effects of this mediation may change over time with cascading consequences both aboveground and belowground. We used a system involving the larval belowground (BG) herbivore Diabrotica speciosa (Coleoptera: Chrysomelidae), corn, and the aphid aboveground (AG) herbivore Rhopalosiphum maidis to answer three questions: (1) What effects does belowground herbivory by D. speciosa have on feeding preferences and distributions of the aboveground R. maidis? (2) How do these preferences and distributions change over time? And (3) what are the longer term consequences for R. maidis populations? Adult alate aphids initially preferred corn seedlings with root feeding by D. speciosa, but preference declined over time driven by aphids leaving corn seedlings with root herbivory. Similarly, observations of aphid performance and colony growth indicated negative effects of root herbivory in contrast to previous studies. These results suggest that shifts in plant-mediated aboveground–belowground interactions can have important consequences for long-term distributions of aboveground herbivores.