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Title: Ultrastructure of the salivary glands, alimentary canal and bacteria-like organisms in the Asian citrus psyllid, vector of citrus huanglongbing-disease bacteria

Author
item AMMAR, EL-DESOUKY - Oak Ridge Institute For Science And Education (ORISE)
item Hall, David
item Shatters, Robert - Bob

Submitted to: Journal of Microscopy and Ultrastructure
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/26/2016
Publication Date: 3/1/2017
Citation: Ammar, E.D., Hall, D.G., Shatters, R.G. 2017. Ultrastructure of the salivary glands, alimentary canal and bacteria-like organisms in the Asian citrus psyllid, vector of citrus huanglongbing-disease bacteria. Journal of Microscopy and Ultrastructure. 5(1):9-20.

Interpretive Summary: The Asian citrus psyllid (ACP) is the principal vector of Candidatus Liberibacter asiaticus, ‘Las’, the putative bacterial causal agent of huanglongbing (HLB) or citrus greening, currently the most serious citrus disease worldwide. Candidatus Liberibacter asiaticus (Las) is transmitted in a persistent propagative manner by ACP, and the salivary glands and midgut have been suggested as transmission barriers that can impede translocation of Las within the vector. In this study, we describe the ultrastructure of the salivary glands, alimentary canal, and other organs and tissues of ACP. Furthermore, in addition to two ultrastructurally different apparently symbiotic bacteria found in the bacteriome, other morphological types of bacteria were found in the gut epithelial cells and salivary glands of both Las-infected and non-infected ACP. This shows the importance of immunolabeling or other labeling techniques that must be used before identifying any bacteria-like structures in ACP as Las or other possible agents of HLB. This study should help future work on the cellular and subcellular aspects of pathogen-psyllid relationships including the question of transmission barriers of Las and other pathogens within their psyllid vectors.

Technical Abstract: Several psyllids (Hemiptera: Psylloidea) are known as vectors of some economically important viral and bacterial plant pathogens. The Asian citrus psyllid (ACP, Diaphorina citri, Hemiptera, Liviidae) is the principal vector of ‘Candidatus Liberibacter asiaticus’ (Las), the putative bacterial causal agent of huanglongbing (HLB) or citrus greening, currently the most serious citrus disease worldwide. Las is transmitted in a persistent propagative manner by ACP, and the salivary glands and midgut have been suggested as transmission barriers that can impede translocation of Las within the vector. However, no detailed ultrastructural studies have been done on these organs in this or other psyllid species, although some bacteria-like structures have been described in them and assumed to be the causal agents of hunaglongbing (HLB). In this study, we describe the ultrastructure of the salivary glands, filter chamber, other parts of the alimentary canal, and other organs and tissues of ACP including the compound ganglionic mass and the bacteriome. Furthermore, in addition to two ultrastructurally different apparently symbiotic bacteria found in the bacteriome, other morphological types of bacteria were found in the gut epithelial cells and salivary glands of both Las-infected (quantitative polymerase chain reaction (PCR positive) and non-infected (qPCR negative) ACP. This shows the importance of immunolabeling, fluorescence in situ hybridization (FISH) or other labeling techniques that must be used before identifying any bacteria-like structures in ACP as Las or other possible agents of HLB. This study should help future work on the cellular and subcellular aspects of pathogen-psyllid relationships including the question of transmission barriers of Las and other pathogens within their psyllid vectors.