We investigated herbivore suitability, foliar chemistry, and seedling growth of blight-susceptible pure American chestnut, Castanea dentata (Marsh.) Borkh., and a blight-resistant Chinese chestnut, Castanea mollisima Blume × American chestnut hybrid, using supplemental fertilizer and ectomycorrhizal inoculation to affect nutrient availability and nutrient uptake, and the gypsy moth, Lymantria dispar (L.), to measure herbivore suitability. Gypsy moth performance was best on fertilized hybrid seedlings, and was lowest on untreated American chestnut seedlings. Foliar carbohydrates were greatest, and tannin levels were lowest, in mycorrhizae-inoculated American chestnut. Foliar nitrogen was also high in mycorrhizal American chestnut, and was equivalent to that found in fertilized seedlings of both species. American chestnut seedlings had greater height and diameter growth than hybrids, regardless of soil amendments. Our results suggest that blight resistance may exact a cost in plant growth and productivity for this chestnut hybrid, and may enhance plant suitability for a generalist herbivore. Additionally, enhanced gypsy moth performance on blight-resistant chestnut hybrids has implications with respect to the restoration of chestnut to eastern deciduous forests, because intense herbivore pressure could compromise seedling growth and survival, and play a role in sustaining potentially damaging gypsy moth populations. The implications of this work within the context of current theories addressing herbivore–plant relations are discussed.