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Insect Vector
ASIAN CITRUS PSYLLID
Diaphorina citri Kuwayama
Current Situation in Texas: Primarily present throughout most of Southeast Asia and China, the Asian citrus psyllid (ACP) Diaphorina citri Kuwayama (Hemiptera: Psyllidae) was first found in the U.S. in Florida in June, 1998, and three years later in September 2001 in South Texas. Currently, the pest is reported from most of the southeastern states in the continental U.S. In Texas, ACP is increasingly becoming a significant problem, with infestation levels reaching 100% in many new plantings in the early part of summer. By 2009, the insect was found in 60 of the 110 Texas counties where citrus is found. Although causing direct damage to plants through plant sap uptake during feeding by both nymphs and adults, the Asian citrus psyllid is economically important because it vectors the bacterial causal agent of citrus greening disease.
Host Plants: ACP is a phytophagous insect that feeds exclusively on plants in the Rutaceae family. Recorded host plants belong to 25 genera including all Citrus and closely related genera such as Poncirus and Fortunella and Murraya (orange jasmine). Variable host plant preference has been observed. Lemon, lime and orange jasmine are the most preferred; grapefruit tends to be least preferred; while sweet oranges have moderate preference.
Description and Biology: ACP adults are small insects, 1/8 to 1/6 inch (≈ 3 to 4 mm) in length with a brownish color (Fig. 1). They feed with their heads down and the body lifted off the feeding site at about a 45° angle. Adult lifespan depends on temperature and the nutritional status of the host plant, but averages 30 to 60 days. Adult psyllids are found feeding at the underside of mature leaves, twigs and on new flush growth where reproduction takes place.
Almond-shaped eggs are bright yellow-orange when they are laid on the tips of new flushes or in crevices of unopened leaves (Fig. 3). They are often fixed to the oviposition site by a stalk driven into the tissue. An adult female can lay up to 800 eggs. Eggs turn orange before hatching, usually within 3 to 4 days.
Nymphs are flat, yellowish-orange in color with two red eye-spots (Fig. 4). They are 0.01 to 0.07 inch (0.25 to 1.5 mm) in length. They settle and start feeding very soon after hatching, remaining almost exclusively on new flush growth. Nymphs usually do not move from the initial feeding site, but when disturbed, they can move slowly. Nymphs go through five stages (instars) before turning into adults. Their size gradually increases after each molt, but only the 3rd, 4th and 5th instars have wing pads (Fig. 5). Like many sucking insects, ACP nymphs produce honeydew while feeding but also some white wax-like tubules that direct this honeydew away from their bodies (Figs. 4 & 6). This wax is a distinctive characteristic of ACP. Developmental time of nymphs varies with temperature; usually complete within 15 to 17 days at 77°F (25°C). Survival of nymphs is highest on tender flushes and substantial nymphal mortality may occur as flush shoots harden off.
Damage and Economic Impact: When feeding, nymphs and adults extract substantial amount of plants sap and produce honeydew and wax-like substances on plant tissues. This honeydew promotes the growth of sooty mold on foliage. It is also believed that ACP may inject some salivary toxin while feeding, resulting in twisting and deformation of leaves. Several individuals feeding on a single flush can result in the burning or death of the growing tip (Fig. 7). While mature trees generally tolerate psyllid feeding damage, young plantings can be severely affected, resulting in poor growth and possibly plant death.
While economic damage directly caused by psyllid feeding is usually minor, the transmission of Candidatus Liberibacter, the bacterial pathogen of citrus greening disease or Huanglongbing (HLB) causes substantial crop losses. Trees infected by HLB may live only 3 to 10 years, during which time they produce unmarketable, misshapen fruit with an acrid,bitter taste (See 'The Disease' section). HLB was first found in the Western Hemisphere in Brazil during 2004. In 2005, the disease was also found in Florida, with subsequent detections in South Carolina, Georgia, Louisiana, Mexico and several countries in the Caribbean and in Central America. To date, detection surveys have not found it in Texas.
Detection of Asian citrus psyllid: Early detection is key for successful control. ACP detection and monitoring is conducted by visual inspections of new flush growth and leaves of citrus plants and their relatives. All developmental stages can readily be found on new flush growth but adults will continue feeding at the underside of mature leaves when new flush shoots are not available. A 5× (or higher) hand lens may be required to detect the presence of eggs and 1rst stage nymphs. Because nymphs produce profuse wax-lke substances while feeding, the presence of these white tubules is generally indicative of their infestation. In addition, the development of sooty mold or the presence of ants may be used as clue to look more closely for psyllid. Alternatively, sticky traps (green, lime-green or yellow) can be used for detection and monitoring of adult psyllids.
Preparation of Asian citrus psyllid samples for Testing: Adult psyllids and late stage nymphs (3rd to 5th instars) can transmit the greening bacterium; therefore, these stages can be collected to test for the presence of the greening pathogen. Adults should be collected with an aspirator; nymphs can be collected using a camel hair brush. It is recommended that all specimens be immediately put into vials containing 95 percent alcohol to reduce the risk of artificially spreading either the insect or the disease. A minimum of 5 individuals per developmental stage per sample should be submitted for Candidatus Liberibacter testing. In addition, data on collection site (GPS information, address, host plant type) and collector information should be recorded and submitted with the samples.