Submitted to: Popular Publication
Publication Type: Popular Publication
Publication Acceptance Date: November 16, 2005
Publication Date: November 21, 2005
Citation: Hall, D.G. 2005. The Asian citrus psyllid and citrus greening - a closer look at the vector. Florida Grower. November 21, 2005. Available: http://www.floridagrower.net/forging_ahead/20051121_psyllid.html Technical Abstract: The Asian citrus psyllid, Diaphorina citri Kuwayama (Homoptera: Psyllidae), was first found in Florida during June 1998 and is now widespread throughout much of the state. This invasive psyllid vectors the bacterium responsible for huanglongbing (HLB) (greening disease), a serious citrus disease. HLB was found in Florida late August 2005. The presence of D. citri in Florida sets the stage for further spread of the disease in Florida and possibly into other North American areas. D. citri has a restricted host range that includes citrus, orange jasmine and related species of Rutaceae. Continuous flushes produced by jasmine could play a role in psyllid populations in nearby citrus. Orange jasmine is not considered an HLB host, but this deserves confirmation. Adult D. citri are small (2.7 to 3.3mm long) with mottled brown wings and are active, jumping/flying insects that can readily move short distances. Adult flight can occur all day long but may be pronounced during warm, windless, sunny afternoons between 4 and 6 pm; flight is inhibited by windy weather. Speculations are that flying adults could be transported by prevailing winds over a 0.5 to 1 km distance depending on duration of sustained flight. Another psyllid, Trioza eryteae in Africa, may fly 1.5 km with the help of prevailing winds in absence of host plants. Adults on leaves hold their heads to the leaf surface with their bodies at a 30-45° angle to the leaf surface. Eggs are deposited on terminal flush growth and are elongated (0.31mm long) and oval in shape, initially light yellow but at maturity bright orange with two distinct red eye spots. Numerous eggs can be found on flush, each anchored to plant tissue on one end in an upright position. There are five nymphal instars. At 25°C, eggs hatch in 4 days, nymphs develop into adults in 13 days, and new adults reach reproductive maturity within 15 to 17 days for a mean population generation time of 32 to 34 days. Adults live an average of 40 to 48 days, during which females continuously lay eggs if flush is present. Maximum adult longevity ranges from 117 days at 15°C to 51 days at 30°C. A sex ratio of about 1:1 has been reported. Adult females lay an average of 858 eggs on grapefruit. Population fluctuations of D. citri are closely correlated with flush growth because oviposition and development of nymphs take place exclusively on flush. Visual surveys by persons trained to recognize D. citri may be the fastest way to detect an infestation. There is no attractant available for survey purposes. Sticky traps have some value in monitoring adults; their general efficacy depends on color and placement. Information on sampling to estimate infestation densities is available for citrus and jasmine. D. citri in Florida is subjected to natural control by an array of predators and one introduced parasitoid species, Tamarixia radiata. However, notable infestations of the pest continue to occur. Carefully timed insecticides may provide some control of HLB. The HLB pathogen can be acquired by an adult within a 30 min feeding period and transmitted during a 5-7 hr feeding period. Adults can transmit the pathogen many days after acquiring it. Late instar nymphs can also transmit HLB, and they retain the pathogen after becoming adults. Ovarial transmission of the pathogen has been speculated but remains to be confirmed.