The innate immune system of the Asian citrus psyllid (Diaphorina citri)

While the innate immune system of insect vectors of human diseases has been studied extensively, hemipteran vectors of agricultural diseases have been largely neglected. In those hemipterans studied, the pea aphid, Acyrthosiphon pisum, was seen to have a drastically reduced immune system, while the brown plant hopper, Nilaparvata lugens, has an immune system similar to other insects. Expanding these studies to other hemiperans will further the understanding of transmission parameters of insect vectored agricultural diseases and aid in the development of novel control methods. In this study, the innate immune system of the Asian citrus psyllid, Diaphorina citri, was investigated. D. citri is the vector of Candidatus Liberibacter asiaticus, the putative causal agent of citrus greening which is considered the most severe disease threatening citrus. The immune genes of D. citri were identified by searching the current draft genome using tblastx against innate immune associated genes from D. melanogaster, A. gambiae, A. pisum, and A. mellifera. Genes that did not return results were searched for using available sequences from additional insects. Results indicate that D. citri are similar to A. pisum and lack most components of the Imd pathway, PGRPs, and antimicrobial peptides. The reduced immune system of D. citri is apparent with high mortality observed after oral exposure or septic injections of non-virulent bacteria. The reduced immune system of D. citri could play a direct role in their ability to transmit the citrus greening pathogen.