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

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.

Spatial Distribution and Development of Sequential Sampling Plans for Diaphorina citri Kuwayama (Hemiptera: Liviidae)

“…For D. citri-citrus-Ca. Liberibacter asiaticus, such threshold is not applicable because studies have shown low transmission associated with a single D. citri adult [11] and even more when nymphal development occurs in healthy plants [9,13,67]. Furthermore, there are diverse natural enemies contributing to the reduction in the vector population [68][69][70][71] that would potentially and naturally assist the prevention of the vector from reaching efficient transmission levels.…”

“…[3,4,6,7]. Characteristically, CLas is transmitted by the Asian citrus psyllid (ACP) Diaphorina citri Kuwayama (Hemiptera: Liviidae) [1,5,[8][9][10]. ACP adults that developed on infected trees were positive for CLas at a rate of 68%, while those that developed on healthy plants were positive at a rate of only 5% [11,12].…”

“…ACP adults that developed on infected trees were positive for CLas at a rate of 68%, while those that developed on healthy plants were positive at a rate of only 5% [11,12]. For transmission, the bacterium must be acquired during the nymphal stage [9][10][11][12][13]. When the ACP acquires the bacteria as an adult, the rate of acquisition is low and the time for inoculation is long, both of which result in low infection rates [11].…”

Improving Suppression of Hemipteran Vectors and Bacterial Pathogens of Citrus and Solanaceous Plants: Advances in Antisense Oligonucleotides (FANA)

“…In Brazil, the CLam species is dominant, while CLas occurs globally in many citrus growing countries (Hall et al, 2013;Wang et al, 2017a,b;Ammar et al, 2020b). The pathogens replicate and circulate systemically in both the plant and the psyllid host tissues (Ammar et al, 2011(Ammar et al, , 2016(Ammar et al, , 2020aCoy et al, 2014;Ramsey et al, 2015;Kruse et al, 2017Kruse et al, , 2018, which facilitates their effective, rapid spread and persistence (Inoue et al, 2009;Ebert, 2019;Jiang et al, 2019;Huang et al, 2020).…”

The molecular interplay of the establishment of an infection – gene expression of Diaphorina citri gut and Candidatus Liberibacter asiaticus

“…CLas was also demonstrated to alter the host plant transcriptional profile [ 23 – 25 ]. We also learned CLas infects salivary glands and the midgut of vectors, tissues that are often recognized as natural barriers to circulative, propagative pathogens as they can prevent translocation of pathogens within the vector host [ 17 , 22 , 26 , 27 ]. Differential gene expression analysis of CLas-infected psyllids also demonstrated CLas alters the gene expression profile of of the gut, salivary glands and whole-body of D. citri [ 19 , 28 – 30 ].…”