The African citrus psyllid, Trioza erytreae, is a sap-sucking insect, a hemipteran

Hemiptera

Hemiptera is an order of insects most often known as the true bugs , comprising around 50,000–80,000 species of cicadas, aphids, planthoppers, leafhoppers, shield bugs, and others...

 bug in the family, Triozidae

Triozidae

Triozidae is one of seven families collectively referred to as jumping plant lice. They have traditionally been considered part of a single family, Psyllidae, but recent classifications divide the group into a total of seven families; most of the genera remain in the Psyllidae, but Triozidae is...

. It is an important pest of citrus

Citrus

Citrus is a common term and genus of flowering plants in the rue family, Rutaceae. Citrus is believed to have originated in the part of Southeast Asia bordered by Northeastern India, Myanmar and the Yunnan province of China...

 being one of only two known vectors of the serious citrus disease, Huanglongbing or greening disease. It is widely distributed in Africa. The other vector is the Asian citrus psyllid, Diaphorina citri

Diaphorina citri

The Asian citrus psyllid, Diaphorina citri, is a sap-sucking, hemipteran bug in the family, Psyllidae. It is an important pest of citrus being one of only two known vectors of the serious citrus disease, Huanglongbing or greening disease. It is widely distributed in southern Asia and has spread to...

.

Distribution

The citrus psyllid is found in Cameroon, Comoros, Ethiopia, Kenya, Madagascar, Malawi, Mauritius, Réunion, Rwanda, South Africa, St. Helena, Sudan, Swaziland, Tanzania, Uganda, Zaire, Zambia and Zimbabwe. It is also found in Saudi Arabia, Yemen and the Atlantic island of Madeira. It is sensitive to hot dry conditions and favours cool, moist areas above 500 metres.

Description

The adult psyllid is at first pale but darkens later to a light-brown colour. The female is larger than the male and has a sharply pointed abdomen as compared to the male's blunt one. It typically adopts a distinctive stance when feeding, with head down sucking sap and body raised at an angle of about 35 degrees.

Life cycle

T. erytreae is confined to host plants in the family Rutaceae

Rutaceae

Rutaceae, commonly known as the rue or citrus family, is a family of flowering plants, usually placed in the order Sapindales.Species of the family generally have flowers that divide into four or five parts, usually with strong scents...

. It occurs on wild plants such as Clausena anisata, horsewood, and Vepris lanceolata

Vepris lanceolata

Vepris lanceolata is a large, evergreen tree of South Africa.-External links:*...

, white ironwood, as well as on citrus, especially lemon

Lemon

The lemon is both a small evergreen tree native to Asia, and the tree's ellipsoidal yellow fruit. The fruit is used for culinary and non-culinary purposes throughout the world – primarily for its juice, though the pulp and rind are also used, mainly in cooking and baking...

s and lime

Lime (fruit)

Lime is a term referring to a number of different citrus fruits, both species and hybrids, which are typically round, green to yellow in color, 3–6 cm in diameter, and containing sour and acidic pulp. Limes are a good source of vitamin C. Limes are often used to accent the flavors of foods and...

s. A female psyllid can lay up to 2000 eggs

Egg (biology)

An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...

 over the course of a four to seven week period. Eggs are laid on the margins of new leaf growth and are anchored by short stalks. They hatch after seven to fourteen days and the first instar

Instar

An instar is a developmental stage of arthropods, such as insects, between each molt , until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or assume a new form. Differences between instars can often be seen in altered body proportions, colors, patterns, or...

 nymphs

Nymph (biology)

In biology, a nymph is the immature form of some invertebrates, particularly insects, which undergoes gradual metamorphosis before reaching its adult stage. Unlike a typical larva, a nymph's overall form already resembles that of the adult. In addition, while a nymph moults it never enters a...

 starts to feed on the underside of the leaves where they begin to form gall

Gall

Galls or cecidia are outgrowths on the surface of lifeforms caused by invasion by other lifeforms, such as parasites or bacterial infection. Plant galls are abnormal outgrowths of plant tissues and can be caused by various parasites, from fungi and bacteria, to insects and mites...

s. The feeding of a large number of nymphs causes curling of the leaves, distortion of shoots and even cessation of growth. The nymphs moult five times before becoming winged adults. The nymphal development stage lasts between twenty and forty days depending on temperature.

Damage and control

T. erytreae is one of only two vectors of the causative agents of greening disease, the phloem

Phloem

In vascular plants, phloem is the living tissue that carries organic nutrients , in particular, glucose, a sugar, to all parts of the plant where needed. In trees, the phloem is the innermost layer of the bark, hence the name, derived from the Greek word "bark"...

-restricted, gram-negative bacteria, Candidatus

Candidatus

Candidatus is in scientific classification a component of the taxonomic name for a bacterium that cannot be maintained in a Bacteriology Culture Collection. It is an interim taxonomic status for noncultivable organisms. An example would be "Candidatus Phytoplasma allocasuarinae"...

 Liberibacter spp. The Asian form, L. asiaticus is heat tolerant and symptoms of the disease can develop at temperatures of up to 35ºC. The African form, L. africanum, is heat sensitive and symptoms only develop when the temperature is in the range 20-25ºC. Although T. erytreae is the natural vector of African citrus greening and D. citri the natural vector of Asian citrus greening, either psyllid can in fact transmit either of the greening agents under experimental conditions.

Associated with T. erytreae in Rhodesia are two primary parasitoid

Parasitoid

A parasitoid is an organism that spends a significant portion of its life history attached to or within a single host organism in a relationship that is in essence parasitic; unlike a true parasite, however, it ultimately sterilises or kills, and sometimes consumes, the host...

s and a number of secondary and tertiary hyperparasitoids. One of the primary parasitoids, Terrastichus radiatus remains external to the psyllid host whereas the other, Psyllaephagus pulvinatus, is an internal parasitoid. The major secondary hyperparasitoid is Aphidencyrtua cassatus, which was recorded in large numbers and which attacks both of the primary parasitoids.