Differences in Selection Behaviors and Chemical Cues of adult Asian Citrus Psyllids, Diaphorina citri, on Healthy and Huanglongbing-Infected Young Shoots of Citrus Plants

The pathogen Candidatus Liberibacter asiaticus (Las) causes devastating citrus huanglongbing in many parts of Asia. The host selection behavior of the Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera- Sternorrhyncha- Psyllidae), the only known Las vector, is critical to its epidemics. Las-infected citrus plants attract adult psyllids by altering their color and chemical cues. However, it is unclear whether any changes in selection behavior or chemical cues occur in young shoots. Selection behavior bioassays showed the number of adults and eggs on Las-infected shoots was significantly higher than on healthy shoots. Significantly more adults responded to the odor of Las-infected shoots than to that of uninfected shoots. GC-MS analysis of volatile constituents showed that the quantitatively dominant constituents were Beta-elemene and Beta-phellandrene in both samples, (+)-epi-bicyclosesquiphellandrene was only detected in Las-infected shoots, but ocimene, germacrene D, ?-cadinene, d-longifolene, and ?-sinensal were detected only in healthy shoots. Analysis of the concentrations of surface-soluble carbohydrates indicated that the levels of sucrose, fructose, and glucose were significantly higher on the surfaces of Las-infected shoots than on the surfaces of healthy shoots. Alteration of volatile compounds and soluble surface carbohydrates of young shoots after Las infection could be attributed to the preference of Asian citrus psyllids for Las-infected young shoots. The knowledge obtained from this investigation may contribute to novel control measures for plant diseases transmitted by insect vectors.