Nutrient inputs alter host–pathogen–herbivore interactions in cranberry

Nutrient availability plays a critical role in shaping bottom-up effects on
plant–pathogen–herbivore interactions, with important implications for pest management in
agroecosystems. While numerous studies have examined the impact of pathogen-infected plants
on insect herbivores, relatively few have explored how nutrient availability influences these
interactions. In this study, we investigated the effects of fertilization on interactions between a
phytoplasma responsible for false blossom disease in cranberries and three insect herbivores: the
vector blunt-nosed leafhopper (Limotettix vaccinii) and two non-vector species, Sparganothis
fruitworm (Sparganothis sulfureana) and spongy moth (Lymantria dispar). We conducted a 4×2
factorial greenhouse experiment using four fertilizer regimes (0, ¼×, 1×, and 2× the standard
rate) and two disease levels (non-infected and infected plants). Herbivore
performance—measured by mortality and weight—was assessed alongside plant chemical traits,
including defense compounds (total phenolics and proanthocyanidins) and nutrient status
(carbon-to-nitrogen ratio). Results showed that both increased fertilizer application and
phytoplasma infection generally enhanced herbivore performance, driven by elevated nitrogen
levels and reduced levels of plant defense compounds. These findings provide new insights into
how nutrient availability modulates plant–pathogen–herbivore interactions and suggest practical
considerations for managing insect pests and diseases in agroecosystems.