Vegetative induction increases plant resistance to antagonistic insect frugivores

Abstract

Plant fitness is shaped by interactions with insect mutualists and antagonists. Vegetative (leaf) herbivory often results in increased allocation of resources to defense in order to deter further damage. This allocation to defense can reduce floral or reproductive allocation. Reductions in floral allocation can have negative effects on pollinator attraction and therefore decrease plant fitness. However, defense-induced changes in reproductive tissues may also be protective against antagonistic fruit-feeding insects (frugivores). This may have important implications for plant fitness when plants experience multiple types of insect damage, but the potential protective effect of herbivory against frugivory is not well-understood. In this study, we tested the prediction that herbivory mediates interactions between plants and their antagonistic frugivores. In the greenhouse, we manipulated vegetative induction in Physalis pubescens (Solanaceae) and measured the effects on plant fitness via changes in floral and fruit allocation, herbivore resistance in the next generation, and deterrence of an antagonistic frugivore (Chloridea virescens (Lepidoptera)). Vegetative induction in P. pubescens enhanced plant resistance to Chloridea virescens frugivores with minimal negative effects on plant reproductive traits. Vegetative induction reduced C. virescens larval growth rate on fruits. Chloridea virescens also avoided induced plants for larval fruit feeding and oviposition. While leaf induction reduced flower size, induction did not negatively affect fruit size, seed set, or seed germination. Furthermore, offspring of induced plants showed increased resistance to Manduca sexta leaf herbivory. These findings indicate that herbivore-induced resistance may benefit plant fitness when plants are under simultaneous pressure from herbivores and frugivores.