Submitted to: Annals of the Entomological Society of America
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/26/2011
Publication Date: 5/9/2011
Citation: Ammar, E., Shatters, R.G., Lynch, C., Hall, D.G. 2011. Detection and relative titer of Candidatus Liberibacter asiaticus in the salivary glands and alimentary canal of Diaphorina citri (Hemiptera: Psyllidae) vector of citrus Huanglongbing Disease. Annals of the Entomological Society of America. 104:526-533. Interpretive Summary: Candidatus Liberibacter asiaticus (Las) is believed to be the causative agent of huanglongbing or citrus greening, the most devastating citrus disease worldwide. Here, we provide the first quantitative-PCR confirmation of Ca L. asiaticus in the alimentary canal and salivary glands of the psyllid vector D. citri. Additionally, our results strongly suggest that the salivary glands constitute a major transmission barrier to Ca L. asiaticus in the psyllid vector, and also suggest that Las may replicate or accumulate in both the alimentary canal and salivary glands of D. citri.
Technical Abstract: Candidatus Liberibacter asiaticus has been strongly implicated as the causative agent of huanglongbing (HLB), or citrus greening, which is currently the most devastating citrus disease worldwide. In the Americas and Asia, HLB is transmitted by the Asian citrus psyllid Diaphorina citri in a persistent manner, and Ca L. asiaticus has been previously detected by polymerase chain reaction (PCR) in whole nymphs and adults of D. citri that fed on HLB-diseased citrus. Here, we used quantitative (Q) PCR to detect Ca L. asiaticus (CLas) in dissected organs of individual D. citri adults collected from HLB-infected citrus trees in Florida between October 14 and December 14, 2009. The mean proportion of CLas-positive organs, was 72% for the alimentary canals, 47% for the salivary glands, and 79 % for the rest of the insect body (N=80). Statistical analysis (ANOVA) indicated that the proportion of infected salivary glands was significantly lower (P <0.001) than those of the alimentary canal or other body parts, with no significant difference in this regard between males and females or between sampling dates. Additionally, the relative copy number of CLas genomes, compared to psyllid genomic DNA in each sample, was significantly higher (P< 0.001) in both the salivary gland and alimentary canal compared to that in the rest of the insect body for both males and females. These results provide the first PCR confirmation of Ca L. asiaticus in the alimentary canal and salivary glands of D. citri, and strongly suggest that the salivary glands constitute a major transmission barrier to Ca L. asiaticus in the psyllid vector. Our results also suggest that CLas may replicate or accumulate in both the alimentary canal and salivary glands of D. citri.