Relationships among Defoliation, Red Oak Phenolics, and Gypsy Moth Growth and Reproduction

Abstract

This research assessed (1) the relationship between defoliation and phenolic chemistry of red oak trees, and (2) the relationship between food quality, measured in terms of oak phenolic chemistry and defoliation, and aspects of gypsy moth biology that can influence population dynamics. In a field experiment, larvae were reared in mesh bags on red oaks. Measurements of phenolics were made weekly on foliage inside and outside bags of 60 trees, which experienced 7 to 58% tree—wide defoliation by the end of the larval feeding period. We found that the phenological pattern of tree phenolic concentration over 8 wk was unrelated to defoliation or bagging. Bagging itself caused no change in foliar phenolic chemistry. Greater defoliation was associated with higher levels of total phenolics, hydrolyzable tannins, and protein—binding capacity of leaves. Pupal mass and fecundity were negatively correlated with both defoliation and the concentration of total phenolics, hydrolyzable tannins, and protein—binding capacity of the host tree. Additionally, egg mass was negatively correlated with the protein—binding capacity of the mother's diet. Statistical investigation of the relationship between components of food quality (both related and unrelated to damage) and insect performance, indicated that gypsy moth pupal mass was influenced by constitutive phenolic variation (unrelated to defoliation), by damage—induced nonphenolic variation, and by damage—induced phenolic variation. Variation in defoliation and in phenolic concentrations were related to variation in fecundity and egg mass.