Lingering Effects of Herbivory and Plant Defenses on Pollinators

In order to survive and reproduce, flowering plants must balance the conflicting selective pressures of herbivore avoidance and pollinator attraction. Links between herbivory and reproduction are often attributed to indirect effects of leaf damage on pollination via reductions in floral allocation, or increases in chemical defenses on herbivore-damaged plants. However, the impacts of herbivory on pollinators have the potential to extend beyond initial floral visits when plant defenses impact pollinator health, foraging behavior, and reproductive success. Here, we examine important but underexplored ways in which herbivory may alter floral phenotype and thus impact pollinators. First, we outline genetic and biochemical mechanisms predicted to underlie floral changes following herbivory, as they impact the floral resources (nectar and pollen) sought by pollinators. Next, we discuss how the consumption of secondary compounds might impact pollinator fitness, including carryover effects on subsequent foraging, mating success, and transgenerational effects on offspring. We consider how pollinator health, life history, and coevolutionary history might result in context-dependent impacts of plant defensive chemistry on pollinator fitness. Finally, we call for studies that measure the impact of herbivore-induced plant defenses on the full spectrum of flower visitors, and contrast case studies on conventional pollinators (for example, generalized bees) versus insects whose larvae are herbivores on the same plants that adults pollinate (such as several butterflies and moths). By linking these consequences of herbivory to fitness effects on both herbivores and pollinators, we will better understand how coevolution between plants, herbivores, and pollinators shapes both defensive and reproductive plant traits.