Bottom-up effects of nutrient availability and disease infection on above- and belowground herbivores

Understanding the bottom-up effects of nutrient availability on plant-pathogen-herbivore interactions is important for pest management in agroecosystems. Although many studies have documented the effects of pathogen-infected plants on insect herbivores, only a few have investigated whether these effects are influenced by nutrient availability. Thus, I tested the effects of fertilizer on the interactions between a phytoplasma that causes false blossom disease of cranberries and two insect herbivores: an above-ground herbivore (Sparganothis fruitworm, Sparganothis sulfureana) and a below-ground herbivore (Oriental beetle, Anomala orientalis). In a greenhouse study, I conducted a (4×2) factorial experiment that tested four fertilizer regimes (0, 1/4x, 1x, and 2x of the standard rate) and two disease levels (non-infected and infected). I then assessed the performance, measured by mortality and weights, of S. sulfureana larvae and A. orientalis larvae. The results indicate that, in general, increased fertilizer application and phytoplasma infection had a positive effect on the performance of both insect herbivores. These findings provide novel insights into the bottom-up effects of nutrient availability on plant-pathogen-herbivore interactions and offer practical guidelines for managing insect pests and diseases in agroecosystems.