Forest Stand Susceptibility to the Gypsy Moth (Lepidoptera: Lyman triidae): Species and Site Effects on Foliage Quality to Larvae

Abstract

In the northeastern United States, forest stands on xeric sites, such as ridgetops and steep upper slopes, generally experience more gypsy moth, Lymantria dispar (L.), defoliation than those on mesic lowland sites. To address whether foliage quality from a site could contribute to forest stand susceptibility, we reared gypsy moth larvae on chestnut oak, Quercus prinus (L.), and northern red oak, Quercus rubra (L.), foliage collected from two xeric and two mesic forest sites. Food quality 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 had greater measures of phenolics than red oak and produced heavier male and female pupae and more fecund females. Foliage from xeric sites was likely to have greater measures of phenolics, but only male pupal weights were greater for larvae reared on xeric site foliage. Larval development 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 fecundities were negatively correlated with measures of red oak hydrolyzable tannins, but there was no relationship between chestnut oak phenolics and gypsy moth success. The greater frequency of gypsy moth outbreaks on xeric sites may be more a function of tree species composition than site induced differences in foliage quality.