Evaluation of Candidatus Liberibacter asiaticus acquisition by Tamarixia radiata, a nymphal parasitoid of Asian citrus psyllid, on residential citrus of south Texas

The US citrus industry must contend with the Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), spreading huanglongbing (HLB) among residential citrus and from residential landscapes into nearby groves. The nymphal parasitoid, Tamarixia radiata Waterston (Hymenoptera: Eulophidae), was introduced as a biocontrol agent for D. citri in all major regions of US citrus production because biological control is the most viable approach for suppressing D. citri populations and slowing HLB spread in urban landscapes. Transmission of Candidatus Liberibacter asiaticus (CLas), the putative causal agent of HLB, typically occurs horizontally via D. citri acquiring the bacterium during feeding on infected plants or vertically as offspring from infected females. However, recent laboratory studies reported that T. radiata acquires CLas during immature development on CLas-positive nymphs of D. citri and resulting female wasps can horizontally transmit CLas while probing healthy nymphs. Tamarixia radiata is now widely established in urban areas of South Texas but it would diminish T. radiata’s benefit as a biological control agent if this parasitoid contributes to HLB spread. Presently, the extent of this phenomenon under field conditions is unknown. From March to December 2022, we collected different life stages of T. radiata or D. citri from HLB-symptomatic citrus trees in urban neighborhoods of South Texas and tested these life stages and trees for CLas. We detected CLas among only 4% of immature or adult wasps collected on trees that tested positive for CLas. For South Texas, likelihood of CLas acquisition by T. radiata appears to be very low.