title: Antioxidants in the midgut fluids of a tannin-tolerant and a tannin-sensitive caterpillar: effects of seasonal changes in tree leaves.
abstract: The seasonal decline in foliar nutritional quality in deciduous trees also effects the availability of essential micronutrients, such as ascorbate and alpha-tocopherol, to herbivorous insects. This study first examined whether there are consistent patterns of seasonal change in antioxidant concentrations in deciduous tree leaves. Alpha-tocopherol concentrations increased substantially through time in late summer in sugar maple (Acer saccharum), red oak (Quercus rubra), and trembling aspen (Populus tremuloides). However, seasonal change in the concentrations of other antioxidants differed between each species: P. tremuloides had higher levels of ascorbate and glutathione in the spring, Q. rubra had higher levels of glutathione but lower levels of ascorbate in the spring, and A. saccharum had lower levels of both ascorbate and glutathione in the spring. To test the hypothesis that tannin-tolerant caterpillars maintain higher concentrations of antioxidants in their midgut fluids than do tannin-sensitive species, we measured antioxidants in Orgyia leucostigma (a spring- and summer-feeding, tannin-tolerant species) and Malacosoma disstria (a spring-feeding, tannin-sensitive species) that were fed tree leaves in the spring and summer. The midgut fluids of O. leucostigma larvae generally had higher concentrations of antioxidants in the summer than did those of M. disstria, and were significantly higher overall. The results of this study are consistent with the hypothesis that higher concentrations of antioxidants form an important component of the defenses of herbivores that feed on mature, phenol-rich tree leaves. Some limitations of the interpretation of total antioxidant capacity are also discussed.
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, Michigan 48109-1048, USA. rvb@umich.edu
authors.forename: Raymond V
authors.initials: RV
authors.lastname: Barbehenn
authors.forename: Ann C
authors.initials: AC
authors.lastname: Walker
authors.forename: Farhan
authors.initials: F
authors.lastname: Uddin
mesh_terms: D031002:Acer / Q000737:chemistry*; D000222:Adaptation, Physiological; D000818:Animals; D000975:Antioxidants / Q000032:analysis* / Q000378:metabolism; D001205:Ascorbic Acid / Q000032:analysis* / Q000378:metabolism; D004064:Digestive System / Q000737:chemistry; D004068:Digestive System Physiological Phenomena; D005247:Feeding Behavior; D007814:Larva / Q000502:physiology; D009036:Moths / Q000502:physiology*; D018515:Plant Leaves / Q000737:chemistry; D032107:Populus / Q000737:chemistry*; D029963:Quercus / Q000737:chemistry*; D012621:Seasons; D013634:Tannins / Q000494:pharmacology*; D024502:alpha-Tocopherol / Q000032:analysis* / Q000378:metabolism
chemical_list: D000975:Antioxidants; D013634:Tannins; D024502:alpha-Tocopherol; D001205:Ascorbic Acid