The phloem-sap feeding mealybug (Ferrisia virgata) carries 'Candidatus Liberibacter asiaticus' populations without transmitting disease

Authors: Pitino, Marco; Hoffman, Michele; ZHOU, LIJUAN - University Of Florida; STOCKS, IAN - Florida Department Of Agriculture And Consumer Services; Duan, Ping

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2014
Publication Date: 3/14/2014
Publication URL: http://10.1371/journal.pone.0092757
Citation: Pitino, M., Hoffman, M.T., Zhou, L., Stocks, I.C., Duan, Y. 2014. The phloem-sap feeding mealybug (Ferrisia virgata) carries 'Candidatus Liberibacter asiaticus' populations without transmitting disease. PLoS One. 9(3):e92757. https://doi.org/10.1371/journal.pone.0092757.
DOI: https://doi.org/10.1371/journal.pone.0092757

Interpretive Summary: Citrus huanglongbing (HLB), caused by three species of 'Candidatus Liberibacter’, is one of the most devastating diseases of citrus worldwide. HLB bacteria are primarily transmitted by three psyllid species Diaphorina citri (Hemiptera: Liviidae), Cacopsylla citrisuga (Hemiptera: Psyllidae), and Trioza erytreae (Hemiptera: Triozidae). We found that another hemipteran, the striped mealybug Ferrisia virgata, was able to acquire and retained Las bacteria. Since this mealybug is also a phloem-sap feeding insect with a broad host range of 150 genera in 68 families including citrus and periwinkle, we investigated the acquisition and transmission efficiencies of ‘Ca. Liberibacter asiaticus’ (Las) by the striped mealybugs, and using Las-specific molecular markers to differentiate different Las populations present in F. virgata and D. citri. The bacterial titer was positively correlated with the confinement time on Las-infected leaf discs. However, Las populations transmitted by the mealybugs did not cause disease in host plants. We discovered that prophage/phage populations of Las in the mealybugs and psyllids were different using Las prophage specific molecular markers. Different Las populations found in these two distinct insect hosts may explain why the bacteria transmitted by mealybugs did not cause disease in host plants. Understanding the factors in Las prophage(s) affecting Las transmission by insect vectors may lead to new HLB management tactics.

Technical Abstract: Candidatus Liberibacter asiaticus (Las) is the primary causal agent of huanglongbing (HLB), the most devastating disease of citrus worldwide. Currently the known insect vectors of the HLB-associated bacteria are three species of psyllids, Diaphorina citri (Hemiptera: Sternorrhyncha: Psyllidae), Trioza erytreae (Sternorrhyncha: Triozidae), and Cacopsylla (Psylla) citrisuga (Sternorrhyncha: Psyllidae). We found that another hemipteran, the striped mealybug Ferrisia virgata, was able to acquire and retained Las bacteria. The bacterial titer was positively correlated with the confinement time on Las-infected leaf discs, and after two weeks Ct value ranged from 23.1 to 36.1 (8.24 x 107 to 1.07 x 104 Las cells per mealybug). As in the psyllids, Las bacteria moved through the insect gut wall to salivary glands after being ingested by the mealybug. However, Las populations transmitted by the mealybugs did not cause disease in host plants. We further discovered that prophage/phage populations of Las in the mealybugs and psyllids were different using Las prophage specific molecular markers for type A, B, and D. Type D population of Las bacteria did not survive in vector psyllids but became dominant in the mealybugs. This is first evidence of genetic variations in Las prophages/phages contributed to acquisition and transmission of Las bacteria by insect vectors.