BACKGROUND: In the present investigation, the effect of Candidatus Liberibacter asiaticus (Las), a bacterium considered to be responsible for causing huanglongbing (HLB) disease in citrus, on the physiology of its vector, the Asian citrus psyllid (ACP) Diaphorina citri Kuwayama, was determined. Specifically, the effects of Las infection on the susceptibility of ACP to selected insecticides were determined. Furthermore, total protein content and general esterase activity were quantified in Las-infected and uninfected ACP to gain insight into the possible mechanism(s) responsible for altered susceptibility to insecticides owing to Las infection. RESULTS: LC(50) values were significantly lower in Las-infected than in uninfected ACP adults for chlorpyrifos and spinetoram. Furthermore, there was a general trend towards lower LC(50) values for three other insecticides for Las-infected ACP; however, the differences were not statistically significant. Total protein content (µg mL(-1)) was significantly lower in Las-infected (23.5 ± 1.3 in head + thorax; 27.7 ± 1.9 in abdomen) than in uninfected (29.7 ± 2.1 in head + thorax; 35.0 ± 2.3 in abdomen) ACP. Likewise, general esterase enzyme activity (nmol min(-1) mg(-1) protein) was significantly lower in Las-infected (111.6 ± 4.5 in head + thorax; 109.5 ± 3.7 in abdomen) than in uninfected (135.9 ± 7.5 in head + thorax; 206.1 ± 23.7 in abdomen) ACP. CONCLUSION: Susceptibility of ACP to selected insecticides from five major chemistries was greater in Las-infected than in uninfected ACP. The lower total protein content and reduced general esterase activity in Las-infected than in uninfected ACP may partly explain the observed higher insecticide susceptibility of Las-infected ACP.