Development on Infected Citrus over Generations Increases Vector Infection by ‘Candidatus Liberibacter Asiaticus in Diaphorina citri’

Abstract

‘Candidatus Liberibacter asiaticus’ (CLas) is a major causal agent of citrus Huanglongbing (HLB), which is transmitted by Asian citrus psyllid (ACP), Diaphorina citri, causing severe losses in various regions of the world. Vector efficiency is higher when acquisition occurs by ACP immature stages and over longer feeding periods. In this context, our goal was to evaluate the progression of CLas population and infection rate over four ACP generations that continuously developed on infected citrus plants. We showed that the frequency of CLas-positive adult samples increased from 42% in the parental generation to 100% in the fourth generation developing on CLas-infected citrus. The bacterial population in the vector also increased over generations. This information reinforces the importance of HLB management strategies, such as vector control and eradication of diseased citrus trees, to avoid the development of CLas-infected ACP generations with higher bacterial loads and, likely, a higher probability of spreading the pathogen in citrus orchards.

Grove-level analysis of titer and prevalence of “CandidatusLiberibacter asiaticus” andWolbachiainDiaphorina citri,vector of citrus Huanglongbing

“…Vector competency of D. citri populations and individuals varies widely in the field as we have seen through this study and others (Capoor et al 1974;Coy and Stelinski 2015;Hall 2018;Ukuda-Hosokawa et al 2015;Ammar et al 2018;Sétamou et al 2016;Xu et al 1988), in addition to laboratory-kept colonies (Inoue et al 2009;Hosseinzadeh et al 2019b;De Souza Pacheco et al 2020). In agreement with our results, Chu et al (Chu et al 2016) show that three wild populations of D. citri vary in their CLas titer and CLas infection incidence, and that like our study, population (grove site) has the strongest effect on all their models.…”

“…A key assumption of this study is that the majority of trees in all citrus groves of Florida are infected with C Las and thus, all adult psyllids will have fed on C Las-infected citrus as nymphs and are competent transmitters as adults. However, even if this assumption did not hold for every individual in our dataset, multiple studies on vector acquisition rates in the lab have recorded <100% acquisition, despite feeding on known infected material (Pelz-Stelinski et al 2010; De Souza Pacheco et al 2020). Samples that do test positive for C Las are competent transmitters and fall into categories of low to high vector capacity, as determined by their mean C Las titer (Ammar et al 2018).…”

“…However, even if this assumption did not hold for every individual in our dataset, multiple studies on vector acquisition rates in the lab have recorded <100% acquisition, despite feeding on known infected material (Pelz-Stelinski et al 2010;De Souza Pacheco et al 2020). Samples that do test positive for CLas are competent transmitters and fall into categories of low to high vector capacity, as determined by their mean CLas titer (Ammar et al 2018).…”

“…This is undoubtedly due to the vastly increased number of both managed and abandoned infected trees in Florida over the past ten years. A study by De Souza Pacheco et al (De Souza Pacheco et al 2020) shows that when D. citri are raised on C Las-infected citrus for four consecutive generations in a greenhouse setting, the percent-infection and the titer in individuals increased with each generation from 42% to 100% infection incidence, and 47.9 to 5,390 C Las cells per 100 ng of DNA. These results suggest that interruptions in vector generations (such as through regular insecticide applications or during seasons of low flush) in the field may help keep C Las titer and incidence lower in vector populations.…”