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The Asian citrus psyllid, Diaphorina citri Kuwayama and the African citrus psyllid, Trioza erytreae (del Guercio) are two of the most serious pests of citrus in the world. The Asian citrus psyllid is of particular importance to Florida because it is already established in South and Central America as far north as Honduras (Burckhardt 1994), and is now known from Florida (June 1998).
The Asian citrus psyllid causes damage to the crop primarily by transmission of the pathogen that causes greening, or "huang long bing", which means "yellow dragon disease" in Chinese. Huang long bing has been loosely translated as yellow shoot disease in English language publications because of characteristic yellow shoots caused by the disease. As well as yellow shoots, the disease causes chlorosis resembling zinc deficiency, twig dieback and reduced fruit size and quality. Fruit do not color up properly, leading to the name greening. The disease complex may be the most devastating of graft and insect transmissible pathogens of citrus in the world. The pathogen, Liberobacter asiaticum, is a phloem limited bacteria. Fortunately, it has not been found in the Western Hemisphere, and no disease resembling greening or huang long bing has been reported in citrus in South or Central America.
The interaction between the vector and the pathogen is poorly known. Acquisition times of 30 minutes for Asian psyllids (Roistacher 1991) and 24 hours for African psyllids (Buitendag and von Broembsen 1993) have been reported. The pathogen evidently multiplies in the vector (Aubert 1987). Adults and fourth and fifth instar Asian citrus psyllid nymphs are able to transmit the pathogen after 8 - 12 days (Roistacher 1991). A considerably shorter latent period of 24 hours has been reported for African greening (Buitendag and von Broembsen 1993). There are conflicting reports as to whether Liberobacter spp. are transovarially transmitted (Buitendag and von Broembsen 1993; Roistacher 1991).
Adult Asian citrus psyllids are small (3-4 mm). They have mottled brown wings (Fig. 1). Characteristically,
they sit at an angle to the shoot or leaf on which they feed. Adults are very active jumping insects. Eggs are bright yellow and deposited on newly emerging "feather flush". Nymphs are green or dull orange. They feed on leaves and stems and can be very difficult to see. Asian citrus
psyllids are most likely to be found on new shoots, and population increase occurs during periods of active plant
growth.
Asian citrus psyllids evidently are restricted to citrus and closely related Rutaceae. The preferred host is Murraya paniculata, an ornamental that is widely grown in southern Florida. Populations on this plant can be extremely high (Fig. 2). Inspection of this plant may be the best way to survey for Asian citrus psyllids. Any psyllids found on citrus or close citrus relatives should be reported immediately to the Division of Plant Industry.
Literature cited:
Aubert, B. 1987. Trioza erytreae Del Guercio and Diaphorina citri Kuwayama (Homoptera: Psylloidea), the two vectors of citrus greening disease: Biological aspects and possible control stragegies. Fruits 42:149-162.
Buitendag, C.H. and von Broembsen, L.A. 1993. Living with citrus greening in South Africa. Pages 269-273 in P. Moreno, J.V. daGraça and L.W. Timmer, Eds. Proceedings of the Twelfth Conference of the International Organization of Citrus Virologists.
Burckhardt, D. 1994. Generic key to Chilean jumping plant-lice (Homoptera: Psylloidea) with inclusion of potential exotic pests. Rev. Chilean Ent. 21:57-67.
Roistacher, C.N. 1991. Techniques for biological detection of specific citrus graft transmissible diseases, pages
35-45 (Greening). FAO, Rome
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