FOREST STAND SUSCEPTIBILITY TO THE GYPSY-MOTH (LEPIDOPTERA, LYMANTRIIDAE) - SPECIES AND SITE EFFECTS ON FOLIAGE QUALITY TO LARVAE

In the northeastern United States, forest stands on xeric sites, such as ridge-tops and steep upper slopes, generally experience more gypsy moth, Lymantria dispar (L.), defoliation than those on mesic lowland s ites. To address whether foliage quality from a site could contribute to forest stand susceptibility, we reared gypsy moth larvae on chestnu t oak, Quercus prinus (L.), and northern red oak, Quercus rubra (L.), foliage collected from two xeric and two mesic forest sites. Food qual ity of foliage was measured as protein and phenolics (hydrolyzable and condensed tannins, total phenolics and protein binding capacity) and was related to measures of gypsy moth success. Chestnut oak foliage ha d greater measures of phenolics than red oak and produced heavier male and female pupae and more fecund females. Foliage from xeric sites wa s likely to have greater measures of phenolics, but only male pupal we ights were greater for larvae reared on xeric site foliage. Larval dev elopment times (days to pupation) were shorter on chestnut oak foliage than on red oak foliage for females and shorter on foliage from mesic sites than from xeric sites for males. Female pupal weights and fecun dities were negatively correlated with measures of red oak hydrolyzabl e tannins, but there was no relationship between chestnut oak phenolic s and gypsy moth success. The greater frequency of gypsy moth outbreak s on xeric sites may be more a function of tree species composition th an site induced differences in foliage quality.