Comparison of anatomical structures and physical barriers to Diaphorina citri probing in two species of Citrus (Rutaceae)

Diaphorina citri, the Asian citrus psyllid, is a serious pest of citrus and vector of the plant pathogenic bacterium Candidatus Liberibacter asiaticus, causal agent of citrus greening disease.  Diaphorina citri are oligophagous and feed on many plants within the family Rutaceae.  We performed an electropenetrography (EPG) study combined with feeding site histology on leaves of two Citrus species, C. sinensis (var. valencia) and C. aurantium (var. sour orange), in order to investigate the effect of host plant on D. citri probing behavior.  We quantified durations, frequencies and order of probing behaviors and correlated anatomical structures within leaves that influence ingestion behaviors.   We found several parameters significantly influenced by host plant, most importantly the mean duration necessary for D. citri to access vascular tissues.  Additionally, we found differences in the structure of the fibrous ring and distribution of oil glands within each host plant species.  Differences in D. citri probing behavior on different host plants may be explained, in part, by anatomical differences among host plant species and these anatomical differences may play an important role in host plant resistance to D. citri probing and inoculation of Ca. Liberibacter asiaticus.