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Outbreaks of bronze birch borer, Agrilus anxius, a North American wood-boring beetle, have occurred periodically over the last 100 years, causing extensive tree mortality. Little is known about mechanisms underlying tree resistance to wood-boring insects, but previous studies have suggested that secondary metabolites and wound periderm (callus) tissue may play a role. North American birches (Betula spp.) are much more resistant to bronze birch borer than exotic species that lack a coevolutionary history. We compared patterns of constitutive phenolic chemistry and the rate of wound periderm formation in phloem tissues of North American paper birch (B. papyrifera) to exotic European white birch (B. pendula). Six phenolic compounds were in higher concentrations in phloem of paper birch than in European white birch and might be involved in resistance. There were no interspecific differences in rate of wound periderm formation.