Where are they now? Establishment and impact reports of bark beetle biocontrol agents with a case study of introduced parasitoids from Southeast Queensland, Australia

Abstract Efforts to expand the management options for conifer‐infesting bark beetle pests in invaded regions have led to the mobilisation of biocontrol agents on a global scale. However, records of agent establishment and impacts from introduced regions are sparse. Reports of 24 global bark beetle‐oriented biocontrol programmes, involving 41 distinct biocontrol agent introductions revealed that 36.6% of agents successfully established, 43.9% failed to establish and the establishment status of 19.5% was not assessed post‐release. Of those that were successfully established, 9.8% were considered effective, 12.2% had low outcomes and the impact of 34.1% of introductions remains unassessed. Predator impacts, when quantified, generally reflected ecological and operational‐level outcomes. In contrast, parasitism impacts were inadequately reported from introduced ranges, for example, in Australia, where the parasitoids Roptrocerus xylophagorum and Dendrosoter sulcatus were introduced to manage Ips grandicollis . In our case study, surveys of field‐collected I. grandicollis infested pine billets from southeast Queensland in the spring/summer of 2024 revealed collective, apparent brood‐level parasitism to range from 0% to 5% among sites. Model‐estimated marginal means for I. grandicollis densities ranged from 0.65 (Site 2) to 11.15 (Site 3) beetles per 100 cm 2 of bark area. Collectively, our results suggest that overall, introduced parasitoids showed low rates of parasitism relative to host densities under our study conditions. Presenting model‐derived parasitism and I. grandicollis densities concurrently improved the inference of natural enemy impact in our study. We emphasise the significance of post‐release assessments in providing accurate data to drive biocontrol agent selection and deployment.