Abstract: The Asian citrus psyllid, Diaphorina citri (Hemiptera: Psyllidae), is a general pest causing economic losses in orchards, mainly feeds on the highly osmotic sap of citrus phloem and transmits pathogen Candidatus Liberibacter asiaticus to induce a devastating disease of citrus named huanglongbing (HLB). The osmotic pressure of phloem sap is a challenge for hemipteran insects, which is regulated by a set of osmoregulation mechanisms evolved in insects. The excessive sugars are converted into long chain oligosaccharides and excreted outside of insects as honeydew. In this article, the behavior of honeydew excretion, composition of honeydew and factors affecting honeydew excretion of D. citri are summarized, and the functions of osmoregulatory genes involved are overviewed. The studies show that the behavior of honeydew excretion and the color, texture and composition of honeydew were different among male and female adults and nymphs of D. citri. The host plants, insecticides, pathogenic microorganisms and compounds secreted by natural enemies were demonstrated as the main factors affecting the excretion behavior of D. citri. In addition, the pivotal osmoregulatory genes encoding α-glucoside hydrolases, aquaporins and sugar transporters were considered as the potential genes involved in the regulation of honeydew excretion. This review may provide a reference for further studying honeydew excretion behavior of D. citri and exploring the new targets for developing new insecticides for the control of this insect.

Key words: Diaphorina citri, honeydew excretion, behavior, composition, osmoregulatory gene, osmoregulation, molecular mechanism