Asian citrus psyllid (ACP, figure 1),

Diaphorina citri, is a new, exotic insect pest

of citrus in Alabama that belongs to the

Order Hemiptera and Family Psyllidae (also called

jumping plant lice). ACP is similar in form to common

pest psyllids that are well known in fruit orchards,

such as the pear psylla (Psylla pyricola) and apple

sucker (Psylla mali). This insect has been responsible

for extensive damage to citrus orchards in China,

India, Brazil, and the state of Florida by spreading,

or “vectoring,” Citrus Greening Disease, also called

Huanglongbing or Yellow Dragon. Citrus Greening

Disease causes tree decline, reduced fruit production,

sour fruit, and tree death. ACP is a piercing-sucking

insect that damages citrus trees directly by removing

plant sap, distorting leaves, and causing defoliation;

the insect causes indirect damage as a disease vector.

It was detected at seven home garden sites in Baldwin

County, Alabama, in 2008; therefore, commercial

citrus producers as well as home owners should

be on high alert for this pest. A quarantine on the

movement of plant materials is in effect in Baldwin

County, and many other counties in Alabama, to

prevent the spread of the ACP to uninfested areas.

Wind and tropical weather systems could also

disperse the psyllids to uninfested areas.

First Detection ACP was first reported in the United States in

1998 in Palm Beach County, Florida. Within 3 years, it spread to thirty-one counties in Florida, causing major problems for citrus orchards. Although the adult ACPs are capable of short flights, the dispersal of this insect pest was greatly aided by the movement of infested nursery plants. As a result, ACP quarantine programs are currently active in several southern, western, and southwestern states. Details about the current Alabama quarantine regulations can be found on the Alabama Department of Agriculture and Industries Web site.

Host PlantsACP is capable of infesting most species of

Rutaceous plants (citrus crops), including sweet orange, tangelo, and mandarins. All citrus grown in Alabama is at risk of becoming a host for ACP. Studies suggest orange jasmine (Murraya paniculata), a commonly grown tropical ornamental plant, as an alternative and preferred host plant for ACP. Between 1985 and 2003, there have been 170 interceptions of live ACPs at U.S. ports on infested orange jasmine and citrus plants shipped from Asia.

Identification of Life Stages

Eggs

Female ACP lays eggs in natural depressions on host plants, preferring new shoot tips. Deformed leaves caused by adult feeding provide additional oviposition (egg laying) sites on citrus leaves. Eggs are elliptical, about 0.3 mm (0.01 inch) in length, and

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Asian Citrus Psyllid

Figure 1. Details of the Asian citrus psyllid, Diaphorina citri (Photo courtesy of Pest and Diseases Image Library, Bugwood.org.)

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white when freshly laid. Eggs can be laid singly or in small clusters on tender new growth. Eggs turn bright orange or yellow as they mature. Research indicates that female psyllids are capable of producing over 748 eggs under favorable conditions.

Nymphs or Crawlers

The newly emerged nymph is less than 0.3 mm (<0.01 inch) in length and grows about five times larger before it becomes an adult. There are five nymphal instars (growth stages), all of which look similar to the adult psyllid, except nymphs lack wings. The nymph is orange and stays flat against the plant surface. A handheld magnifying lens may be adequate to observe details of the late instar nymphs and adult psyllids. nymphs produce long, waxy filaments that direct honeydew (sugary excretion) away from their bodies. The waxy filaments serve as a defense mechanism to avoid predation. nymphs move readily if disturbed but generally spend most of their time feeding on plant juices close to the site where they were born, using piercing-sucking mouth parts. nymphs have four multisegmented needles that are thrust into leaf tissue during feeding. Research indicates that the optimal temperature range for egg and nymph development is 77o to 82oF. Temperatures below 50oF and over 92oF appear to be unfavorable for development.

Adult Psyllids

Both sexes of ACP are winged and capable of flying considerable distances. Adult psyllids (figure 2) are 3 to 4 mm (0.1 to 0.2 inch) in length, with a brown body. Their body usually rests at a slant or 45-degree angle to the host leaf or stem, which is a distinguishing feature. Forewings have a brown band all around the periphery, and there is a reduction in the number of wing veins. Antennae are prominent on the head. mouth parts (beak) are directed downward and contain large muscles to facilitate sucking of plant juices. Saliva injected into the plant at the initiation of feeding is toxic to the host. Adult psyllids may look like aphids; however, psyllids are fast-moving jumpers and lack cornicles (tail pipes). They may be found on either the upper or lower surface of the leaf, or along the stem, but are almost exclusively found on new growth. Peak emergence and activity of adults could occur suddenly in orchards, creating a high-risk situation. The complete life cycle of ACP ranges from 15 to 47 days.

2 Alabama Cooperative Extension System

Cold ToleranceReports from Florida suggest prolonged survival

of this insect at 23oF (-5oC). However, overwintering capability of ACP in Alabama is unknown.

Plant DamageInitial infestations of ACP are clustered on

newly formed citrus leaves (figure 3). High populations of psyllid nymphs and adults can cause significant sap removal and permanent deformation of leaves and shoots.

Honeydew produced by nymphs and adults allows growth of sooty mold that coats leaves and further reduces photosynthesis in plants. Ants, attracted by the honeydew, may be observed visiting ACP-infested terminal shoots.

Figure 2. Adult psyllid rests on leaf with head close to the citrus leaf. Note the small size of this insect compared to the entire leaf.

Figure 3. Leaf discoloration due to Citrus Greening Disease (Photo courtesy of J. M. Bové, INRA Centre de Recherches de Bordeaux, Bugwood.org.)

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Asian Citrus Psyllid 3

The greatest threat of ACP is that it can transmit or vector Citrus Greening Disease, also known as citrus chlorosis in Java and Huanglongbing or Yellow Dragon Disease in China. It is caused by the bacterium Candidatus Liberobacter spp. Research indicates that once the bacterium gets inside the body of an ACP, it rapidly multiplies within the insect and enters salivary glands. The bacterium is injected into the citrus plants along with saliva by the insect vector. The bacterium can inhibit phloem channels in susceptible plant hosts, severely reducing vigor. Citrus Greening Disease has also been reported to cause major production losses within 5 to 8 years after tree planting. Symptoms of Citrus Greening Disease may resemble plant nutritional disorders, especially zinc deficiency. General indicators of Citrus Greening Disease include yellow shoots, mottling, and chlorosis of leaves. leaf chlorosis due to Citrus Greening Disease is seen beyond leaf veins and may affect an entire leaf (unlike micronutrient deficiencies that are generally delineated by leaf veins). As the disease progresses, entire twigs may die back and fruits may show lopsided internal development. Peel color of affected citrus fruit often remains green on the blossom-end (hence the name “citrus greening”). Internally, the fruit may be discolored and contain small, dark-colored aborted seeds.

Risk Categories for ACPOrchards or homeowners with citrus in Alabama

are in a low-risk category if the insect has not been identified on their trees or on citrus trees within 2.5 miles of their trees. Citrus trees in this low-risk category should be actively managed for other foliage and fruit feeding insects in an integrated approach; this will offer some protection from ACP infestation. If ACP is found on citrus trees in an orchard or home in Alabama, or if neighboring trees within 2.5 miles are infested, citrus tree owners should consider their trees to be in a high-risk category for ACP buildup. High-risk orchards and home plantings should adopt a preventative, chemical control program based on year-round insecticide sprays, except during fruit harvest. ACP can be managed by quarantines, exclusion with insect screen, natural insect predators or parasitoids, cultural control tactics (like sanitation, removal of alternative host, and selection of clean stock), and chemical treatment. Individuals setting out new trees in orchards or home plantings should

only purchase nursery stock grown entirely (including the root stock) in their own county or that bears a “compliance agreement” tag approved by the state or federal government, which verifies that the tree received appropriate chemical treatment prior to sale. It is important that state quarantine laws be obeyed in order to prevent introduction of Citrus Greening Disease into Alabama. For quarantine-related questions, please contact the Alabama Department of Agriculture and Industries at (334) 240-7225.

Insect Management Versus Disease Management

Early detection of ACP is central to management programs. Psyllid infestations can be managed by a combination of cultural control and insecticide-based tactics. However, Citrus Greening Disease is difficult to control once it establishes in a plant because visual symptoms of this disease only appear after the vascular infection is in advanced stages. Highly mobile adult ACPs can rapidly spread the disease from infected trees to uninfected ones. Therefore, disease management relies on the use of clean stock, removal of infected plant parts, and good vector (ACP) control.

Integrated Pest Management

Scouting and Detection Techniques

Early detection of ACP nymphs in citrus trees is important because the insect has high reproductive capacity and mobility as adults. Tree scouting should focus searching for nymphs on flush growth (new, tender terminal branches) in early spring. A magnifying glass or hand lens should be used to improve detection. Thorough scouting should be performed at least once per week during the growing season, until all flush growth hardens and matures. The relative abundance of natural enemies (see below) can also serve as an indicator of pest problems including ACP. Abundance of the ash-gray lady beetle (Olla v-nigrum) in Florida citrus orchards has been strongly linked to the population density of ACP. Yellow, sticky cards (sold commercially by several manufacturers) are attractive to adult psyllids and can complement tree scouting for nymphs and eggs. note that the use of sticky traps and other monitoring devices only provides evidence of infestation but cannot provide information about the

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Ayanava Majumdar, Extension Specialist, Agronomic Crops and Commercial Horticulture, Auburn University, Monte Nesbitt, Horticulturist, Gulf Coast Research Extension Center, and Henry Fadamiro, Associate Professor, Entomology and Plant Pathology, Auburn University.

For more information, call your county Extension office. look in your telephone directory under your county’s name to find the number.

Use pesticides only according to the directions on the label. Follow all directions, precautions, and restrictions that are listed. Do not use pesticides on plants that are not listed on the label.

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actual damage occurring in the field. Homeowners and commercial gardeners should contact the nearest county Extension office or the Department of Agriculture with samples for correct identification. For identification services, insect samples (dead specimens) should be separated from plant material to prevent decay and damage during transit. Avoid shipping samples over weekends.

Role of Biological Control Agents (BCAs)

limited information is available on the impact of BCAs on psyllid populations under natural conditions. Psyllids have a number of BCAs that could be important at low population levels. BCAs in citrus orchards include assassin bugs, hoverflies, lady beetles, lacewings, and spiders. Predator exclusion studies with the ash-gray lady beetle have suggested populations could increase 120-fold in the absence of natural enemies. Florida has also introduced a parasitic wasp, Tamarixia radiate, which has the unusual ability to lay eggs under psyllid nymphs. These eggs hatch, and the wasp larvae feed on the ACP nymphs. BCAs are often slow-acting and inconsistent in suppressing pest populations. Several insect pathogenic fungi belonging to the genera Cladosporium, Capnodium, and Hirsutella have been observed infecting and killing ACP; however, insect pathogens need specific weather conditions (80 percent humidity and optimum temperature) for significant impact on psyllid populations.

ACP Suppression in Noncommercial Settings

Homeowners with a small number of trees may use petroleum oil sprays (horticultural oil or 435 oil sold under various trade names), insecticidal soap,

products containing neem extract, and malathion for suppression of ACP and other pests. These insecticides have a broad spectrum of activity, and they need to be applied early in an infestation to maximize their effectiveness. Products used in the home garden should contain an approved EPA label that permits use on citrus and/or edible crops. Read insecticides labels carefully and apply them at the recommended rates. Systemic (plant-absorbed) insecticides containing the active ingredient imidacloprid (Provado 1.6F, nuprid 1.6F) are effective against ACP. These chemicals provide an extended period of control. Imidaclopid products are not “restricted use,” and are therefore available to commercial growers and homeowners, although the cost may be prohibitive for use on a small number of trees.

ACP Suppression in Commercial Orchards

Protecting trees with a soil-applied systemic insecticide is a sound approach for commercial growers to manage ACP infestations. Admire Pro is an insecticide containing imidacloprid that can be applied in irrigation systems or as a soil drench to young trees shorter than 6 feet; this will provide protection against ACP for one full growing season. For trees taller than 6 feet, the insecticide aldicarb (Temik) is a similarly effective insecticide, although this is a highly dangerous, restricted-use chemical. Consult your county Extension office for a complete list of all foliar and systemic insecticides recommended for use against ACP and other insects, mites, and diseases in Alabama.

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