The Asiatic citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), is the main vector of the Asiatic form of huanglongbing (HLB), the putative cause of which is a phloem-limited bacterium ‘Candidatus Liberibacter asiaticus' (‘CLas') (α-Proteobacteria). Nymphal and adult D. citri prefer to feed on young leaves of their host plants. Adults feeding on mature leaves are not considered very important by some Chinese farmers in the management of HLB. This study examined feeding by adult D. citri on ‘CLas'-infected citrus leaves of several maturity stages. Diaphorina citri adults from a ‘CLas'-free colony were tested for feeding behavior and the efficiency of their acquisition of ‘CLas' from new shoots, and young and mature leaves. Probing and feeding behavior were monitored using the electrical penetration graph (EPG) technique, and pathogen acquisition efficiencies were tested by qPCR. The results showed that some EPG variables were significantly influenced by host-plant leaf maturity. The duration of waveform C (pathway phase) on new shoots was significantly longer than that on young leaves and mature leaves. In contrast, the duration of waveform E2 (phloem ingestion) was significantly shorter on new shoots and young leaves than on mature leaves. However, the duration taken for stylets of adult D. citri to reach the phloem and commence ingestion was not related to leaf maturity status. The qPCR results indicated that 23 of the 24 adults for which E2 waveforms were recorded harbored ‘CLas'. In addition, the minimum period of E2 waveform of these individuals was only 2 min. Proportions of ‘CLas'-positive adults feeding on mature leaves, young leaves and new shoots, were 55%, 40% and 35%, respectively. The main EPG variables were not significantly different between the males and females. Our results suggest that the acquisition of ‘CLas' by adult D. citri is highly efficient, even when feeding on mature leaves. Therefore to effectively manage both vector and pathogen, D. citri populations should be monitored carefully, even when the trees stop producing new growth.