Asian citrus psyllid

Alert

Asian citrus psyllid is a notifiable disease.

Under Queensland legislation, if you suspect the presence of this disease in any species of animal, you must report it to Biosecurity Queensland on 13 25 23 or contact the Emergency Disease Watch Hotline on 1800 675 888.

Like the African citrus psyllid, the Asian citrus psyllid (Diaphorina citri Kuwayama) is a sap-sucking insect that can transmit one of the world's most serious bacterial diseases of citrus, huanglongbing, also known as 'citrus greening disease'. The disease is caused by Candidatus Liberibacter bacteria.

Asian citrus psyllid can transmit all 3 strains of the bacterium.

Asian citrus psyllid, African citrus psyllid and huanglongbing are not found in Australia.

Cause

Asian citrus psyllid is a small insect known as Diaphorina citri.

Other names

  • Asiatic citrus psyllid
  • Oriental citrus psyllid
  • Citrus psylla

Description

Adult

  • Small (3–4 mm long), brownish, sap-sucking insects.
  • Forewings are distinctively patterned with mottled brown patches.
  • Abdomen has a pointed shape when viewed from above.
  • Has a distinctive feeding posture, with the head down, almost touching the plant surface, and the body lifted at 45 degrees.

Nymphs

  • Dull orange with red eyes.
  • Can secrete white, string-like honeydew that may melt to form droplets at temperatures above 36°C.
  • Can be difficult to see because they are small, flat, and close to the surface of twigs and leaves.
  • Are mainly found on buds, leaves and stems of young flushing growth less than 50mm long.

Eggs

  • Bright yellow-orange and almond-shaped.
  • Are laid in groups on buds, and young flushing tips less than 10mm long.

Plant stage and plant parts affected

  • Found mostly in young flushing leaves and shoots of host plants.

Plant damage

In the Americas, high numbers of nymphs feeding can cause leaves and shoots to distort, giving them a twisted or curled appearance. Leaves can also appear to have notches. Death of new plant growth has also been reported. These symptoms are not common in Asia.

The honeydew produced by Asian citrus psyllid can lead to sooty mould growth on plants.

May be confused with

Common sap sucking insects such as citrus leaf miner and aphids can also cause leaf distortion and sooty mould to develop. If you find leaf distortion and sooty mould, look for the insect causing the damage. Psyllids are active insects and will jump if disturbed. Asian citrus psyllid nymphs could be confused with soft scale insects.

The feeding posture of an adult Asian citrus psyllid is distinctive, with its head down, almost touching the leaf, and the rest of its body raised at a 45 degree angle is distinctive.

If you suspect Asian citrus psyllid, don't hesitate to report it.

Distribution

Asian citrus psyllid occurs throughout Asia, and in parts of North, South and Central America, and some islands off Africa. Closer to Australia, it is found in Indonesia (including Papua), East Timor and north-western Papua New Guinea.

Asian citrus psyllid was detected near Darwin in 1915 and was eradicated. There have been no detections in Australia since then.

Hosts

All citrus cultivars are hosts of the psyllid (e.g. orange, grapefruit, mandarin, tangelo, lemon, lime, kumquat, pomelo, trifoliate orange and native citrus species). Some species and varieties are better hosts than others, with Murraya spp. (native and ornamental forms of mock orange, orange jasmine and curry leaf) favoured hosts.

Asian citrus psyllid can also feed on:

  • Afraegle spp. (Gabon powder-flask, Nigerian powder-flask)
  • Atalantia buxifolia (Chinese box-orange)
  • Balsamocitrus dawei (Uganda powder-flask)
  • Citropsis spp. (west African cherry-orange, Gillet's cherry-orange)
  • Limonia acidissima (wood apple, elephant apple)
  • Merrillia caloxylon (Malay lemon)
  • Naringi crenulata (hesperethusa)
  • Pamburus missionis
  • Swinglea glutinosa (tabog)
  • Triphasia trifolia (lime berry)
  • Clausena spp. (e.g. wampee)
  • Toddalia asiatica (orange-climber, forest pepper)
  • Vepris lanceolata (white ironwood).

Life cycle

  • Females prefer to lay their eggs in the growing tips of young host plants.
  • The eggs hatch into wingless nymphs.
  • The nymphs moult 4 times, gradually getting bigger with each moult as they transition through the 5 nymphal stages (instars).
  • From the fifth instar stage, the nymph changes into a winged adult.
  • There is no pupal stage.
  • Adults are reported to live 1–2 months.

Impacts

Citrus is an important crop in Australia, there are over 28,000 hectares of citrus planted and around 1,900 growers. Citrus production for the year ending June 2017 was valued at $724.4 million, with Queensland the largest producer of mandarins (Source: Citrus Australia).

Overseas, when populations of Asian citrus psyllid are high, the psyllid can cause defoliation and dieback of citrus trees. The sooty mould growth resulting from excess honeydew production can also affect the plants ability to photosynthesize, which can affect overall plant health. Production costs would increase as a result of the need to control this pest and market access would be disrupted. The nursery industry would also be affected.

The economic impact of the Asian citrus psyllid would be significantly increased if the serious citrus disease huanglongbing was also present. Huanglongbing causes citrus tree death and is readily spread by the Asian citrus psyllid.

Home gardeners would also be affected as citrus and Murraya spp. are common backyard plants.

Legal requirements

Asian citrus psyllid is a prohibited plant pest under the Biosecurity Act 2014.

Report suspected Asian citrus psyllid to Biosecurity Queensland immediately on 13 25 23 or contact the Exotic Plant Pest Hotline on 1800 084 881.

If you think you have found Asian citrus psyllid, you must take all reasonable and practical steps under your control to minimise any associated risks. This is called a general biosecurity obligation (GBO).

Further information