Prolonged phloem ingestion by Diaphorina citri nymphs compared to adults is correlated with increased acquisition of citrus greening pathogen

Authors: GEORGE, JUSTIN - University Of Florida; AMMAR, EL-DESOUKY - Oak Ridge Institute For Science And Education (ORISE); Hall, David; Shatters, Robert - Bob; Lapointe, Stephen

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/22/2018
Publication Date: 7/9/2018
Citation: George, J., Ammar, E., Hall, D.G., Shatters, R.G., Lapointe, S.L. 2018. Prolonged phloem ingestion by Diaphorina citri nymphs compared to adults is correlated with increased acquisition of citrus greening pathogen. Scientific Reports. 8:10352. https://doi.org/10.1038/s41598-018-28442-6.
DOI: https://doi.org/10.1038/s41598-018-28442-6

Interpretive Summary: Citrus greening disease (huanglongbing) is the most destructive disease of citrus worldwide. The bacterial pathogen is transmitted by a tiny insect, the Asian citrus psyllid. Immature psyllids (nymphs) are known to pick up the pathogen during feeding from infected plants much more efficiently than adult psyllids for unknown reasons. Psyllid mouthparts are similar to mosquitoes and feed by sucking plant sap from leaf veins. We performed 42 hours-long electrical recordings of the feeding behavior of psyllid adults and nymphs feeding on infected or healthy citrus plants. Our results support the hypothesis that increased frequency and duration of phloem ingestion by psyllid nymphs may be a major factor in the greater ability of nymphs to acquire Candidatus Liberibacter asiaticus (CLas) from infected citrus plants compared with adults. This is the first study comparing psyllid nymphs and adults on healthy and infected citrus plants in relation to pathogen acquisition. Our findings constitute an important step towards understanding the epidemiology of this most serious worldwide disease of citrus.

Technical Abstract: Citrus greening disease (huanglongbing) is currently the most destructive disease of citrus worldwide. The putative pathogen, Candidatus Liberibacter asiaticus (CLas), is a phloem-limited bacterium transmitted by the Asian citrus psyllid Diaphorina citri (Hemiptera: Liviidae) in a circulative-propagative manner. Nymphs are known to acquire CLas from infected plants much more efficiently than adults, but the reasons are unknown. We performed 42 hour-long electrical penetration graph (EPG) to study the feeding behavior of Diaphorina citri adults and 4th or 5th instar nymphs feeding on CLas-infected or healthy citron plants. Following these EPG recordings, quantitative polymerase chain reaction (qPCR) was performed on each insect to determine if they had acquired CLas during the recording period. We present evidence that supports the hypothesis that increased frequency and duration of the phloem ingestion phase (E2 waveform) by Diaphorina citri nymphs may be a major factor in the greater ability of nymphs to acquire CLas from infected citrus plants compared with that of adults. This is the first EPG study comparing nymphs and adults of Diaphorina citri on healthy and infected citrus plants in relation to CLas acquisition. Our findings constitute an important step towards understanding the epidemiology of this most serious worldwide disease of citrus.