Conifers possess inducible terpenoid defense systems. These systems are associated with the formation of traumatic resin ducts (TRD) and are underpinned by enhanced gene expression and activity of terpene synthases (TPS), enzymes responsible for oleoresin formation. We first determined that Sitka spruce (Picea sitchensis [Bong.] Carriere) had the capacity for TRD formation by mechanically wounding representative trees. We then proceeded to investigate whether the white pine weevil (Pissodes strobi Peck.), a stem-boring insect, can influence the expression of genes encoding monoterpene synthases (mono-tps) in Sitka spruce. We went on to compare this response with the effects of a simulated insect attack by drill wounding. A significant increase in mono-tps transcript level was observed in the leaders of lateral branches of weevil-attacked and mechanically wounded trees. In this study, weevils induced a more rapid enhancement of mono-tps gene expression. A full-length Sitka spruce mono-tps cDNA (PsTPS2) was isolated, expressed in Escherichia coli, and functionally identified as (Ϫ)-pinene synthase. The recombinant (Ϫ)-pinene synthase catalyzes the formation of (Ϫ)-␣-pinene and (Ϫ)--pinene, both of which are known constituents of stem oleoresin in Sitka spruce and increase in abundance after weevil attack. These data suggest that increased (Ϫ)-pinene synthase gene expression is an important element of the direct defense system deployed in Sitka spruce after insect attack.Oleoresin is a complex mixture of monoterpenes, sesquiterpenes, and diterpene resin acids that provide chemical and physical protection of conifer trees against potential herbivores, stem-boring insects, and pathogens (Berryman, 1972; Bohlmann and Croteau, 1999; Phillips and Croteau, 1999; Trapp and Croteau, 2001). In Sitka spruce (Picea sitchensis [Bong.] Carrière), constitutive oleoresin is sequestered in preformed resin ducts in bark, sapwood, and needles. During the initial stages of attack by stem-boring insects, such as weevils (Curculionidae) or bark beetles (Coleopterae), this oleoresin is released and repels insects through intoxication or the formation of physical barriers. Conifers also possess inducible terpenoid defense systems. These include the formation of new traumatic resin ducts (TRD) in phloem and xylem tissue (Cheniclet, 1987; Alfaro, 1995; Nagy et al., 2000; Alfaro et al., 2002) and a hypersensitive response associated with the accumulation of terpenoids, lignin, and phenolics associated with cells surrounding an attack site (Raffa, 1991; Franceschi et al., 1998). Traumatic resinosis can be induced by a range of stimuli, including mechanical wounding, abiotic stress, insect attack, pathogen invasion, elicitor molecules derived from fungal or plant cell walls, or by treatment of trees with methyl jasmonate (MeJA; Croteau et al., 1987; Lieutier and Berryman, 1988; Nagy et al., 2000; Franceschi et al., 2002; Martin et al., 2002). Recent work with Norway spruce (Picea abies) demonstrated that differentiation of TRD in the d...