Impacts of insect herbivores on rare plant populations

► Population-level impacts of insect herbivory on rare plants have been poorly studied. ► Insect herbivores can have strong impacts on rare plant population sizes and vital rates. ► Impacts are strong across herbivore feeding guilds, forms of plant rarity and herbivore specialization. ► Monophagous herbivores of rare plants exist and raise important conservation challenges. ► Positive (plant-) density-dependence in insect attack appears common and could stabilize rare plant populations.