Biological control of arthropods emerged as a scientific enterprise in the late nineteenth century and the orchard industry of California was an early centre of expertise. In 1900, as the Australian colonies prepared for federation, each had a government entomologist attached to its agriculture department. The hiring of George Compere from California by the Western Australian Department of Agriculture began a controversial chapter in the early history of biological control that was linked to a late, local popularization of acclimatization. Compere became known as the ‘travelling entomologist’ and for a decade brought ‘parasites’ of pest insects from overseas and released them in Perth. His antagonistic disciplinary rhetoric and inflated claims for the ‘parasite theory’ created conflict with his counterparts in the eastern states. The resulting inter-state entomological controversy was played out in the press, revealing the political use of science for institutional and even state identity. It is a story of transnational exchanges, chance discoveries and popular public science: popular because of the promise of a simple, natural solution to agricultural insect pests and because of the public nature of the disputes it generated between the experts. This microcosm contributes to the global historiography of acclimatization, biological control, scientific exposition and the professionalization of agricultural science.