The potential for pre-emptive biological control of Diaphorina citri (EPPO A1 List) using Tamarixia radiata
Why
Pre-emptive biological control can be considered for plant pests prior to a pest establishing and becoming widespread in a country at risk. Potential biological control agents (BCAs) can be identified in advance of the pest arriving and some initial screening can be conducted on their safety and suitability for the EPPO region. Diaphorina citri (Hemiptera: Psyllidae) is a vector of the causal agent of citrus huanglongbing disease (‘Candidatus Liberibacter asiaticus’, ‘Candidatus Liberibacter americanus’, and ‘Candidatus Liberibacter africanus’ - all EPPO A1 List), under natural conditions. Huanglongbing disease is currently absent from the EPPO region, however, D. citri has recently been reported in the EPPO region (Israel, 2021 transient; Cyprus 2023 present, few occurrences). The potential economic impact of huanglongbing to the citrus industry in the Mediterranean basin is huge. Having a biological control agent ready for use in case of an outbreak of D. citri can help to reduce the spread of the pest and the pathogens it can vector and contain outbreaks.
Potential biocontrol agents
Tamarixia radiata (Hymenoptera: Eulophidae) is an ectoparasitic wasp originally from southern Asia (e.g. Pakistan), which has been utilised as a biological control agent against D. citri in a number of regions with varying levels of success. The biological control agent has been introduced into Guadelupe, Indonesia, Martinique, Mauritius, Philippines, Reunion, Saudi Arabia, Taiwan, USA (California and Florida). In the EPPO region, T. radiata has recently been released (2024) in Cyprus and monitoring is ongoing to assess its impact and establishment (Melifronidou-Pantelidou et al., 2025).
Biology and ecology
Tamarixia radiata females deposit 166 to 300 eggs during their life-span of 14 to 24 days. The development time from egg to adult is 12 days under a 25 °C and 14 hours of light:10 hours of dark regime. T. radiata completes development at temperatures varying from 15 to 32 °C, with an optimum of 25 °C. The lowest developmental threshold is estimated to be 11 °C for the whole life cycle.
Feeding and efficacy
Adult T. radiata feed on D. citri 1st – 3rd instar nymphs and eggs and the females parasitise the 4th and 5th instar nymphs of the psyllid. High levels of parasitism have been recorded at 25 and 30°C (84.17 and 72.50%, respectively). A female’s total parasitism capacity ranges from 20 to 168 nymphs. A low parasitism rate was observed at 15°C.
Safety
Tamarixia radiata has a narrow host range and is highly host specific to D. citri, with just one non-target species, Bactericera cockerelli (Hemiptera: Triozidae, EPPO A1 List), which is parasitised at low levels (< 5 %). There is no evidence of adverse negative impacts of T. radiata.
History of use as a biocontrol agent
In Florida (USA), T. radiata has established though parasitism rates are lower than those reported in some other regions where it has been introduced i.e. Reunion Island, Guadeloupe and Puerto Rico (USDA, 2010). In the late 1970s, T. radiata was released in Reunion Island and the population of D. citri was significantly reduced with T. radiata attacking 60 to 70 % of D. citri nymphs. USDA (2010) detail that the use of the BCA in South-East Asia has not achieved a good level of control, probably due to hyperparasites. T. radiata is considered a key natural enemy of D. citri and in urban citrus in southern California (Irvin & Hoddle, 2021), this introduced ectoparasitoid has resulted in a 70% reduction in D. citri densities since its initial release and establishment (Kistner et al., 2016a; Kistner et al., 2016b; Milosavljević et al., 2021).
Climatic suitability
Souza et al. (2023) provides an assessment of the current global distribution of T. radiata along with future projections using CLIMEX. Under the current climate, the model projects some suitability for the Mediterranean region. Under climate change scenarios, the suitability increases in both magnitude and overall area.
Recommendations of the Joint EPPO/IOBC Panel on Biological Control Agents
The Joint EPPO/IOBC Panel on Biological Control Agents recommends that countries at risk of D. citri and huanglongbing follow the progress of biological control programmes using T. radiata, and consider joining regional consortiums for preparedness against the pest.
Sources
Aidoo OF, Souza PGC, Silva RS, Júnior PAS, Picanço MC, Heve WK, Duker RQ, Ablormeti FK, Sétamou M, Borgemeister C (2023) Modeling climate change impacts on potential global distribution of Tamarixia radiata Waterston (Hymenoptera: Eulophidae). Science of the total environment. 864.
Chen X, Stansly PA (2014) Biology of Tamarixia radiata (Hymenoptera: Eulophidae), Parasitoid of the Citrus Greening Disease Vector Diaphorina citri (Hemiptera: Psylloidea): A Mini Review. Florida Entomologist 97 4.
EPPO (2020) PM 9/27 (1) ‘Candidatus Liberibacter’ species that are causal agents of Huanglongbing disease of citrus and their vectors: procedures for official control. EPPO Bulletin 50, 122-141.
Hoddle M, Pandey RR (2014) Host Range Testing of Tamarixia radiata (Hymenoptera: Eulophidae) Sourced from the Punjab of Pakistan for Classical Biological Control of Diaphorina citri (Hemiptera: Liviidae: Euphyllurinae: Diaphorinini) in California. Journal of Economic Entomology 107, 125-136.
Irvin NA & Hoddle MS (2021) The effects of floral nectar, extrafloral nectar and hemipteran honeydew on the fitness of Tamarixia radiata (Hymenoptera: Eulophidae), a parasitoid of Diaphorina citri, Biological Control 163, 104753.
Kistner EJ, Amrich R, Castillo M, Stroke V, Hoddle MS (2016a) Phenology of Asian citrus psyllid (Hemiptera: Liviidae), with special reference to biological control by Tamarixia radiata, in the residential landscape of southern California. Journal of Economic Entomology 109, 1047-1057.
Kistner EJ, Melhem N, Carpenter E, Castillo M, Hoddle MS (2016b) Abiotic and biotic mortality factors affecting Asian citrus psyllid (Hemiptera: Liviidae) demographics in southern California. Annals of the Entomological Society of America. 109, 860-871.
Melifronidou‐Pantelidou A, Urbaneja A, Tena A, Seraphides N, Stavrinides M, Koukkoularidou D, Georgiades M (2025) Eradication campaign for Diaphorina citri in Cyprus. EPPO Bulletin 55(2), 305-311
Parra JRP, Alves GR, Diniz AJF, Vieira JM (2016) Tamarixia radiata (Hymenoptera: Eulophidae) 3 Diaphorina citri (Hemiptera: Liviidae): Mass Rearing and Potential Use of the Parasitoid in Brazil. Journal of Integrated Pest Management 5, 1-11.
Pluke RWH, Qureshi JA, and Stansly PA (2008) Citrus flushing patterns, Diaphorina citri (Hemiptera: Psyllidae) populations and parasitism by Tamarixia radiata (Hymenoptera: Eulophidae) in Puerto Rico. Florida Entomologist 91, 36–42.
Souza PGC, Aidoo OF, Farnezi PKB et al., (2023) Tamarixia radiata global distribution to current and future climate using the climate change experiment (CLIMEX) model. Scientific Reports 13, 1823
USDA (2010) Proposed release of a Parasitoid (Tamarixia radiata Waterston) for the Biological Control of Asian Citrus Psyllid (Diaphorina citri Kuwayama) in the Continental United States. Environmental Assessment. https://aphis-direct.stg.platform.usda.gov/sites/default/files/tamarixia-radiata-acp.pdf