The Neglected Link: Psyllid–Plant Interactions as the Central Bottleneck in Huanglongbing

Huanglongbing (HLB), a disease of citrus associated with several species of ‘ Candidatus Liberibacter’, remains the most severe biotic threat to global citrus production. Since the emergence of the disease in the Americas in the early 2000s, particularly in Brazil and the United States, research investment and coordinated programmes involving research, technology development and extension have intensified dramatically. Hundreds of millions of dollars have been allocated to HLB‐related research and management efforts, yet no effective, sustainable and scalable solution has emerged. This letter argues that a substantial part of this failure is not due to insufficient resources, but rather to a persistent conceptual error in research prioritisation. HLB has been predominantly approached as a classical plant–pathogen interaction, with strong emphasis on bacterium‐centred strategies and long‐term genetic improvement. However, HLB is fundamentally a vector‐driven pathosystem, sustained by the interaction among ‘ Candidatus Liberibacter’ spp., the psyllid vectors Diaphorina citri and Trioza erytreae , and the citrus hosts. I critically examine the current state of knowledge of these interactions and highlight the major experimental and conceptual limitations that have hindered progress. Furthermore, I discuss why reliance on conventional breeding is unlikely to deliver timely solutions. Finally, I propose a strategic reorientation of research investment toward transmission‐focused approaches that target vector competence. By prioritising interventions capable of disrupting acquisition and transmission rather than attempting to cure infected trees, future research efforts may achieve meaningful epidemiological impact.