Phytoplasma infection renders cranberries more susceptible to above- and belowground insect herbivores.

While phytoplasma infections in plants are known to affect their interactions with aboveground herbivores, the impact of different genotypes on these infections and their effects on belowground herbivores remains largely unexplored. In cranberry (Vaccinium macrocarpon), infection by the phytoplasma Candidatus Phytoplasma sp. subgroup 16SrIII-Y leads to false blossom disease. This study investigates whether cranberry infection by this phytoplasma affects the performance and feeding behavior of a foliar feeder (spongy moth, Lymantria dispar) and a root feeder (oriental beetle, Anomala orientalis). Using phytoplasma-infected and uninfected cranberries of two genotypes ("Ben Lear" and "Crimson Queen"), the survival, growth and consumption of L. dispar and A. orientalis larvae were measured. To assess the effects on plant morphological and chemical traits, we also examined the impact of phytoplasma infection on shoot and root growth, carbon and nitrogen content, and the levels of defensive compounds such as proanthocyanidins (PACs). Results indicate that larvae of L. dispar and A. orientalis generally showed larger size and more efficient tissue consumption on infected plants, with these effects varying by cranberry genotype, possibly due to differences in phytoplasma titer. Phytoplasma infection was associated with stunted growth, elevated nitrogen content, and lower PAC levels in both shoots and roots of infected cranberry plants compared to uninfected ones. These findings indicate that phytoplasma infection potentially manipulates plant chemical composition by increasing nutrient levels and decreasing defensive compounds, enhancing herbivore performance both above and belowground. This study sheds light on the intricate interplay among plants, phytoplasma infection, and insect herbivore communities.