The infection of its insect vector by bacterial plant pathogen “Candidatus Liberibacter solanacearum” is associated with altered vector physiology

Many bacterial and viral plant pathogens are transmitted by insect vectors, and pathogen-mediated alterations of plant physiology often influence insect vector behavior and fitness. It remains largely unknown for most plant pathogens whether, and how, they might directly alter the physiology of their insect vectors in ways that promote pathogen transmission. Here we examined whether the presence of “Candidatus Liberibacter solanacearum” (“Ca. L. solanacearum”), an obligate bacterial pathogen of plants and of its psyllid vector alters the physiochemical environment within its insect vector, the potato psyllid (Bactericera cockerelli). Microelectrodes were used to measure the local pH and oxygen tension within the abdomen of “Ca. L. solanacearum”-free psyllids and those infected with “Ca. L. solanacearum”. The hemolymph of infected psyllids had higher pH at 9.09 ± 0.12, compared to “Ca. L. solanacearum”-free psyllids (8.32 ± 0.11) and a lower oxygen tension of 33.99% vs. 67.83%, respectively. The physicochemical conditions inside “Ca. L. solanacearum”-free and –infected psyllids body differed significantly with the infected psyllids having a higher hemolymph pH and lower oxygen tension than “Ca. L. solanacearum”-free psyllids. Notably, the bacterial titer increased under conditions of higher pH and lower oxygen tension values. This suggests that the vector's physiology is altered by the presence of the pathogen, potentially, resulting in a more conducive environment for “Ca. L. solanacearum” survival and subsequent transmission.