Psyllid nymphs are dorso-vent rally flattened, are less mobile than adults, and are often found congregating. Nymphs of some psyllid species are covered with white waxy secretions and others are gall formers. World-wide there are over 3000 described species of psyllids which feed mostly on woody dicotyledonous plants. Psyllids can damage their host plants by feeding on the sap or injecting toxic saliva that may cause plant galling, malformations, or necroses. Both adults and nymphs are plant feeding.
Some species are also capable of transmitting plant diseases.
Psyllid feeding can also result in the production of honeydew. This substance is high in sugars and serves as a substrate for fungi which can subsequently reduce photosynthesis in the plant. Identification of psyllids is based primarily on the morphology of the adults. Structural differences of the head, wing venation, antennal length, and genitalia are some of the characters that are used for comparative purposes. In the past few years, greater emphasis is being placed on nymphal morphology for species identification.