Glutathione Transferase and Cytochrome P450 (General Oxidase) Activity Levels in Candidatus Liberibacter Asiaticus-Infected and Uninfected Asian Citrus Psyllid (Hemiptera: Psyllidae)

CandidatusLiberibacter asiaticus (Las) has been reported to increase the susceptibility of theAsian citrus psyllid,Diaphorina citriKuwayama (Hemiptera: Psyllidae), to selected insecticides. Reduced general esterase activity in Las-infected, compared with uninfected, D. citri has been proposed as a possible explanation for this difference in insecticide susceptibility. The current study was conducted to quantify glutathione transferase (GST) and cytochrome P450 (general oxidase) activities in Las-infected D. citri to further explain the possible mechanisms for altered susceptibility to insecticides due to Las infection. GST and cytochrome P450 activities (indirectly through general oxidase levels) were quantiÞed in Las-infected and uninfected D. citri nymphs and adults. Mean ( SEM)GST activity was signiÞcantly lower in Las-infected (468.23 26.87 mol/min/mg protein) than uninfected (757.63 59.46 mol/min/mg protein) D. citri adults. Likewise, mean cytochrome P450 activity was signiÞcantly lower in Las-infected (0.23 0.02 equivalent units [EU] cytochrome P450/mg protein) than uninfected (0.49 0.05 EU cytochrome P450/mg protein) D. citri adults. Immature stages (second andÞfth instars)were characterizedby signiÞcantly lowerGSTactivity than adults for uninfected D. citri. However, cytochrome P450 activity was signiÞcantly higher in second instar nymphs than adults and Þfth-instar nymphs for uninfectedD. citri. Lower activities of GST and general oxidase in Las-infected D. citri indicate that infection with Las alters D. citri physiology in a manner that could increase insecticide susceptibility. The reduced activities of these detoxifying enzymes due to Las infection may be explained by examining expression levels of associated genes in Las-infected and uninfected D. citri.