The establishment of exotic species in novel environments is a major environmental concern, however, few long-term studies have examined the effects of these species on their host environment and community, especially in forest ecosystems. The arrival and subsequent spread of the greater European pine shoot beetle, Tomicus piniperda (L.) (Coleoptera: Curculionidae, Scolytinae), into southern Ontario pine forests provided a natural experiment to assess biotic interactions between an exotic species and its new community over several years. Reproductive success of Tomicus piniperda colonies of various ages was studied between 2001 and 2004. The size and composition of competitor and natural enemy complexes present in these communities were also quantified over time. The impact of the natural enemy complexes on T. piniperda reproduction was assessed, Brood production (no. eggs and galleries/female) by T. piniperda populations rapidly approached those reported from its native range in Europe, with lower densities of parental adults. Thus, reproduction remained consistently above the replacement level for this beetle over all four years of study suggesting that these recently-introduced populations were growing rapidly and at a greater rate than in their country of origin. Tomicus piniperda successfully integrated into a large bark beetle community, and appeared to be capable of displacing native beetles to more marginal bark habitats, however, these competitors were not eliminated during the course of the study. The long-term effect of this marginalization on populations of native beetles is uncertain. Tomicus piniperda rapidly acquired natural enemies in the introduced areas, however, natural enemy-caused mortality did not show a regulating effect on its populations. It seems that intraspecific competition, rather than predation, regulates T. piniperda populations following introduction. The implications of these findings for the establishment and spread of exotic species in forest systems are examined, especially with reference to a prominent theory for success, the Enemy Release Hypothesis. In short, the Enemy Release Hypothesis is not applicable to an exotic species that is not regulated by natural enemies in its native range, and assessments of the Enemy Release Hypothesis should always include a determination of enemy regulation of the exotic in its native range.

The establishment of exotic species in novel environments is a major environmental concern, however, few long-term studies have examined the effects of these species on their host environment and community, especially in forest ecosystems. The arrival and subsequent spread of the greater European pine shoot beetle, Tomicus piniperda (L.) (Coleoptera: Curculionidae, Scolytinae), into southern Ontario pine forests provided a natural experiment to assess biotic interactions between an exotic species and its new community over several years. Reproductive success of Tomicus piniperda colonies of various ages was studied between 2001 and 2004. The size and composition of competitor and natural enemy complexes present in these communities were also quantified over time. The impact of the natural enemy complexes on T. piniperda reproduction was assessed, Brood production (no. eggs and galleries/female) by T. piniperda populations rapidly approached those reported from its native range in Europe, with lower densities of parental adults. Thus, reproduction remained consistently above the replacement level for this beetle over all four years of study suggesting that these recently-introduced populations were growing rapidly and at a greater rate than in their country of origin. Tomicus piniperda successfully integrated into a large bark beetle community, and appeared to be capable of displacing native beetles to more marginal bark habitats, however, these competitors were not eliminated during the course of the study. The long-term effect of this marginalization on populations of native beetles is uncertain. Tomicus piniperda rapidly acquired natural enemies in the introduced areas, however, natural enemy-caused mortality did not show a regulating effect on its populations. It seems that intraspecific competition, rather than predation, regulates T. piniperda populations following introduction. The implications of these findings for the establishment and spread of exotic species in forest systems are examined, especially with reference to a prominent theory for success, the Enemy Release Hypothesis. In short, the Enemy Release Hypothesis is not applicable to an exotic species that is not regulated by natural enemies in its native range, and assessments of the Enemy Release Hypothesis should always include a determination of enemy regulation of the exotic in its native range.