Trioza erytreae
(African citrus psyllid)

The invasive African psyllid, Trioza erytrea, transmits the causal agent of the African form of citrus huanglongbing (greening) disease, Liberibacter africanum, a very destructive disease of citrus plants. It does this under natural conditions in Africa and the Middle East, and has been shown experimentally to transmit the Asian form, Liberibacter asiaticum. The psyllid itself severely distorts leaves, which become stunted and galled. T. erytreae affects species in the family Rutaceae, occurring on wild hosts as well as on Citrus species.

T. erytreae is listed as an A1 quarantine pest by EPPO (OEPP/EPPO, 1988) and is also a quarantine pest for CPPC and OIRSA. The importation of plants for planting and cut branches of citrus from countries where either citrus greening bacterium or either of its vectors occur has been prohibited (OEPP/EPPO, 1990). T. erytreae occurs in Africa and parts of the Middle East but could probably establish and spread in Mediterranean countries without difficulty.

Besides its role in citrus greening, the psyllid has itself significant damage potential.

The distribution of T. erytreae is wider than that of Liberibacter africanum (the African form of citrus huanglongbing (greening) disease), which is the major pathogen it transmits (EPPO/CABI, 1997). It occurs in the Congo Democratic Republic, St. Helena, Sudan, Uganda, Zambia and, recently, Madeira, where the bacterium has not been recorded.

See also CABI/EPPO (1998, No. 151).

Like the other vector of citrus greening (Diaphorina citri), T. erytreae is listed as an A1 quarantine pest by EPPO (OEPP/EPPO, 1988) and is also a quarantine pest for CPPC and OIRSA. It is primarily a pest in tropical climates and as such could certainly become established in citrus-growing countries in the Americas and Asia. In Asian countries where the Asian form of citrus huanglongbing (greening) disease is present, its presence could facilitate spread and considerably add to the difficulties of huanglongbing control. It could probably also establish and spread without difficulty in citrus-growing countries with a Mediterranean climate. Though biological control may be possible, there is no guarantee that it could keep populations to a sufficiently low level to prevent transmission of huanglongbing. Besides its role in the spread of citrus huanglongbing disease, the psyllid itself has significant damage potential.

T. erytreae affects species in the family Rutaceae, occurring on wild hosts (e.g. Clausena anisata) as well as on Citrus species.

A bibliography of T. erytreae up to 1987 has been compiled by Van den Berg and Fletcher (1988) and a general review has been presented by Van den Berg (1990). T. erytreae has a temperature sensitivity similar to that of Liberibacter africanus (the agent of citrus huanglongbing (greening) in Africa; Schwarz and Green, 1970; Catling, 1973). It is very sensitive to hot, dry weather (the eggs and first-instar nymphs being particularly vulnerable). It is favoured by cooler, moist areas above 500-600 m altitude, where citrus growth flushes tend to be prolonged. Green and Catling (1971) used maximum saturation deficit as an accurate predictor of the geographical distribution of T. erytreae.

Sex ratios fluctuate in the field, but females always predominate. There is a pre-oviposition period of 3-7 days, but this is considerably extended in the absence of young foliage; longevity is also prolonged under such conditions. Mating occurs 2-4 times a day and eggs may be laid immediately. Eggs are supplied with a sharp point that is driven through the leaf epidermis and is thought to be responsible for maintaining a favourable internal water relationship. Females remain fertile for 11-16 days in the absence of males, and maximum egg production occurs towards the middle of their life span, which normally lasts 17-50 days; up to 2000 eggs may be laid per female. There is an incubation period of 6-15 days and nymphal development (five instars) takes 17-43 days, both periods being inversely related to mean temperature and directly related to nutritional value of the leaves. The temperature threshold for nymphal development is around 10-12°C. There is no diapause. Van den Berg et al. (1990) have studied the daily activities and habits of adults, and egg hatching and moulting in T. erytreae, while Van den Berg et al. (1991a) have studied mating, fertility and oviposition.

T. erytreae transmits the causal agent of the African form of citrus huanglongbing (greening) disease, Liberibacter africanus, under natural conditions in Africa and the Middle East (McClean and Oberholzer, 1965). It has been shown experimentally that T. erytreae is also able to transmit the Asian form, Liberibacter asiaticus (Massonie et al., 1976). In Mauritius and Reunion, where both forms occur, T. erytreae probably transmits both.

The presence of small pit galls on young leaves may indicate African citrus psyllid (USDA, 2012).

T. erytreae is similar to Diaphorina citri, the Asian citrus psyllid, which is the vector of citrus huanglongbing (greening) in Asia. The geographical range of the two species did not originally overlap, but they now occur together in Mauritius, Reunion and Saudi Arabia.

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Chemical Control

Insecticides such as dimethoate can be used against T. erytreae, for which there is an active monitoring programme in orchards in South Africa.

Biological Control

In Reunion, T. erytreae has been successfully controlled by the introduction of a parasite, Tamarixia dryi, from South Africa (Aubert et al., 1980). Research on the biological control of the vectors has also been carried out in Mauritius. Aubert (1987) and Van den Berg (1990) report the results for Mauritius and also Reunion. In South Africa, numerous predators occur but have not been found to reduce populations to economically acceptable levels (Van den Berg et al., 1987).

Cultural Practices

T. erytreae enters orchards from indigenous hosts in the surrounding vegetation (Van den Berg et al., 1991b), so it is recommended that these hosts are removed.

Phytosanitary Measures

Because of the difficulty of ensuring freedom from eggs or nymphs, importation of plants for planting and cut branches of citrus from countries where Liberibacter africanum and its vector occur should be prohibited (OEPP/EPPO, 1990). It is possible to fumigate citrus budwood material against T. erytreae (FAO, l983).

27/03/13 Updated by:

Esther Arengo, National Agricultural Research Laboratories, Uganda