Galls are abnormal plant growths induced by invading organisms which provide resources for gall inducers. Galls act as resource sinks by manipulating nutrients and defense compounds to enhance the suitability of the gall. Several studies have suggested that adjacent leaf material is an important nutrient source for galls produced on plant material. In this study, we evaluated the relationship between chestnut (Castanea spp.) stem galls produced by Dryocosmus kuriphilus (Yasumatsu) and foliage directly attached to the galls (gall leaves). We excised gall leaves and assessed the outcome on gall quality and gall associates. Leaf excision resulted in the development of significantly (P<0.05) smaller galls with reduced chamber linings and higher tannin concentrations. Leaf excision also slightly increased (P<0.1) gall wasp larval mortality, but did not impact parasitism. Galls with leaves excised were also more susceptible to fungal infection and weevil herbivory. Our results corroborate the hypothesis that gall leaves are essential for normal gall development, and are an important resource for defenses against fungal pathogens and herbivory. A second goal was to compare the suitability and preference of gall leaves and normal foliage to gypsy moth (Lymantria dispar) herbivory to determine whether the gall wasp induced defenses in source leaves. Gypsy moth larvae preferred gall leaves over normal foliage in a two-choice preference assay. Fourth instar gypsy moth larvae had increased growth rates and final weight when fed gall leaves. These results suggest that gall leaves do not have enhanced herbivore defenses and may be better utilized for caterpillar growth.