The Phloem-Sap Feeding Mealybug (Ferrisia virgata) Carries ‘Candidatus Liberibacter asiaticus’ Populations That Do Not Cause Disease in Host Plants

Abstract

‘Candidatus Liberibacter asiaticus’ (Las) is the primary causal agent of huanglongbing (HLB), the most devastating disease of citrus worldwide. There are three known insect vectors of the HLB-associated bacteria, and all are members of the Hemiptera: Diaphorina citri (Psyllidae), Trioza erytreae (Triozidae), and Cacopsylla (Psylla) citrisuga (Psyllidae). In this study, we found that another hemipteran, the striped mealybug Ferrisia virgata (Cockerell) (Hemiptera: Pseudococcidae), was able to acquire and retain Las bacteria. The bacterial titers were positively correlated with the feeding acquisition time on Las-infected leaf discs, with a two-weeks feeding period resulting in Ct values ranging from 23.1 to 36.1 (8.24×107 to 1.07×104 Las cells per mealybug). We further discovered that the prophage/phage populations of Las in the mealybugs were different from those of Las in psyllids based on Las prophage-specific molecular markers: infected psyllids harbored the Las populations with prophage/phage FP1 and FP2, while infected mealybugs carried the Las populations with the iFP3 being the dominant prophage/phage. As in the psyllids, Las bacteria were shown to move through the insect gut wall to the salivary glands after being ingested by the mealybug based on a time-course quantitative polymerase chain reaction (qPCR) assay of the dissected digestive systems. However, Las populations transmitted by the mealybugs did not cause disease in host plants. This is the first evidence of genetic difference among Las populations harbored by different insect vectors and difference among Las populations with respect to whether or not they cause disease in host plants.

Effects ofCandidatus Liberibacter asiaticuson the fitness of the vectorDiaphorina citri

“…Similarly, the phloem sap feeding mealybug ( Ferrisia virgata ) can carry Las, but it cannot cause disease in periwinkle or citrus hosts (Pitino et al . ). Therefore, further studies concerning the increase in the Las transmission threshold of ACP transmits to citrus plants, and a better understanding to reveal the mechanism of host plant immunity from these non‐ill feeding of Las‐infected mealybug ( F. virgata ) will also be innovative tactics needed for new HLB management to prevent HLB from spreading.…”

Transcriptome Profiling of Huanglongbing (HLB) Tolerant and Susceptible Citrus Plants Reveals the Role of Basal Resistance in HLB Tolerance

“…To confirm HLB infection on these selected trees, leaf samples with typical HLB symptoms were collected. Genomic DNA was extracted using the DNeasy Plant Mini Kit (Qiagen, Valencia, CA) as described by Pitino et al ( 2014 ). Real-time PCR based on the Las 16S rDNA was used for the titration of Las bacteria in these infected plants (Li et al, 2006 ).…”

Biology and epidemics of Candidatus Liberibacter species, psyllid‐transmitted plant‐pathogenic bacteria

“…Different forms of the prophages also seem to play a role in Ca . L. asiaticus transmission from the insect into the plant (Pitino et al , ), suggesting that the prophage regions encode some factors required in the transmission‐related interactions. It is also possible that those regions contain regulatory genes that function like a general switch, modifying the bacterial gene expression pattern in the psyllid–plant–psyllid host transitions.…”

“…L. asiaticus and to transmit it to periwinkle plants (Zhou et al , ). Although the bacteria transmitted by F. virgata did not cause disease symptoms in the recipient plants (Pitino et al , ), the possibility of mealybugs acting as HLB vectors should not be ignored. In addition to insect dispersal, HLB disease has also been unintentionally propagated by infected nursery productions, and introduced into new areas with contaminated seedlings.…”