Citrus psyllids affect trees in different ways, depending on the growth stage and the time of the season. Feeding by adults and nymphs may damage and weaken the season's new flush, that is buds, flowers, tender shoots, and small fruits. The abundant honeydew produced during the feeding on the sugary sap also results in the growth of sooty mold and the reduction of photosynthetic activity of the leaves. Finally, at high population densities, the twisting and curling of new leaves and the reduction of of shoot length often lead to a witches' broom effect. Large populations retard the growth of young trees and cause significant yield reductions. This insect can become extremely damaging because it is also a main vector of the citrus greening pathogen.
The symptoms are caused by the feeding activity of the citrus psyllid, Diaphorina citri. Adults are 3 to 4 mm long with brownish black heads and thorax, light brown abdomen and mottled membranous wings. They may overwinter in sheltered areas of the trunk or on mature leaves. The average lifespan of an adult psyllid depends on the temperature, 20 - 30 °C being optimal. Cooler weather favors longer life spans while hot temperatures shorten them. Females can lay up to 800 orange eggs on the new shoots and buds in spring. Nymphs are flat, usually yellow, and secrete a white waxy coating that protects them. White waxy outgrowths or threads clearly distinguish them from aphids. Compared to adults, nymphs only move over short distances if disturbed. The damage to tissues impairs the ability of the plant to distribute nutrients to all parts.
Predators and parasitoids are more likely to provide sustained control during periods of low psyllid populations, for example during hot, dry weather. Parasitic wasps include Tamarixia radiata or Psyllaephagus euphyllurae. Predatory insects include the pirate bug Anthocoris nemoralis, the lacewing Chrysoperla carnea and the lady beetle Coccinella septempunctata. Insecticidal soaps based on neem oil or horticultural oil also work to control populations but should be applied before the nymphs secrete their protective wax.
Always consider an integrated approach with preventive measures together with biological treatments if available. Timely sprays of insecticides based on dimethoate are effective against psyllids, but should only be used as a last resort. These products should be applied before the insects secrete the protective wax that confers them some resistance. Remember that excessive sprays could easily result in resurgence of psyllids and other pests. Bark can be treated with dimethoate paste (0.03%) to decimate migrating adults moving up and down the tree.