Asian citrus psyllid adults inoculate huanglongbing bacterium more efficiently than nymphs when this bacterium is acquired by early instar nymphs

Authors: Ammar, Eldesouky; George, Justin; Sturgeon, Kasie; STELINSKI, LUKASZ - University Of Florida; Shatters, Robert

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/11/2020
Publication Date: 10/26/2020
Citation: Ammar, E., George, J., Sturgeon, K.L., Stelinski, L.L., Shatters, R.G. Asian citrus psyllid adults inoculate huanglongbing bacterium more efficiently than nymphs when this bacterium is acquired by early instar nymphs. Scientific Reports. 10:18244. 2020. https://doi.org/10.1038/s41598-020-75249-5.
DOI: https://doi.org/10.1038/s41598-020-75249-5

Interpretive Summary: The Asian citrus psyllid (Diaphorina citri) transmits the bacterium ‘Candidatus Liberibacter asiaticus’ (CLas), which causes huanglongbing (citrus greening) disease by ingesting the bacterium from infected trees and then delivering them to uninfected trees when they move to this tree and start feeding again. Understanding how the insect acquires and then delivers the bacterium from and to citrus plants is important information that will aid in developing solutions to this devastating disease. We compared CLas inoculation efficiency of D. citri nymphs (immature insects) and adults into healthy (uninfected) citron leaves when both insect stages were reared from eggs on infected plants. The proportion of CLas-positive leaves was 2.5% for nymphs and 36.3% for adults. For the insect to be able to inoculcate a plant with the CLas bacterium, it is assumed that the bacterium must move from the gut to the salivary glands of the insect. We found that the Clas bacterium moved into the head region of the insect (location of the salivary glansd) in 26.7–30.0% of nymphs and 37–45% of adults. Also, in those insects that did have detectable CLas bacterium in the head, the amount of bacterium present was higher in the adults than in the nymphs. Our results suggest that following acquisition of CLas by early instar D. citri nymphs, emerging adults inoculate the bacteria into citrus more efficiently than nymphs because adults are afforded a longer period necessary (after acquisition) for multiplication and/or translocation of CLas into the salivary glands from the gut. We propose that CLas uses D. citri nymphs mainly for pathogen acquisition and multiplication, and their adults mainly for pathogen inoculation and spread.

Technical Abstract: The Asian citrus psyllid (Diaphorina citri) transmits the bacterium ‘Candidatus Liberibacter asiaticus’ (CLas), which causes huanglongbing (citrus greening) disease, in a circulative-propagative manner. We compared CLas inoculation efficiency of D. citri nymphs and adults into healthy (uninfected) citron leaves when both vector stages were reared from eggs on infected plants. The proportion of CLas-positive leaves was 2.5% for nymphs and 36.3% for adults. CLas acquisition by early instar nymphs followed by dissections of adults and 4th instar nymphs revealed that CLas bacterium had moved into the head-thorax section (containing the salivary glands) in 26.7–30.0% of nymphs and 37–45% of adults. Mean Ct values in these sections were 31.6–32.9 and 26.8–27.0 for nymphs and adults, respectively. Therefore, CLas incidence and titer were higher in the head-thorax of adults than in nymphs. Our results suggest that following acquisition of CLas by early instar D. citri nymphs, emerging adults inoculate the bacteria into citrus more efficiently than nymphs because adults are afforded a longer latent period necessary for multiplication and/or translocation of CLas into the salivary glands of the vector. We propose that CLas uses D. citri nymphs mainly for pathogen acquisition and multiplication, and their adults mainly for pathogen inoculation and spread.