Grove-level analysis of titer and prevalence of “ Candidatus Liberibacter asiaticus” and Wolbachia in Diaphorina citri, vector of citrus Huanglongbing

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Huanglongbing (HLB, or citrus greening disease) affects all citrus varieties world-wide. In the USA, Asia, and South America the causal agent is “ Candidatus Liberibacter asiaticus” ( C Las), a phloem-limited, uncultured, alphaproteobacterium. The hemipteran insect vector, Diaphorina citri (Asian citrus psyllid) acquires and transmits C Las in a circulative, propagative manner. In addition to C Las, D. citri hosts multiple symbiotic bacterial species including Wolbachia (wDi). In D. citri , wDi has been sequenced and studied but specific roles in D. citri biology are unknown. Using well established quantitative PCR methods we measured C Las titer in D. citri collected from four groves in central Florida with distinct HLB management strategies and tested whether C Las and wDi titer were correlated in a sub-set of these insects. Grove site had the largest effect on C Las titer. Sex had no effect on C Las titer, while higher wDi titer was correlated with non-infected insects. Our results suggest that more directed follow-up research is necessary and important to clarify whether field management tactics influence C Las titer in D. citri and to better understand gene-by-environment interactions among D. citri , wDi and C Las. Now that millions of trees in Florida have been treated with injectable formulations of oxytetracycline, which is likely to decrease bacterial populations in D. citri , this study may represent the last biologically meaningful snapshot of grove-level vector-pathogen ecology in the state during the HLB epidemic.