Metabolomic analyses of the haemolymph of the Asian citrus psyllid Diaphorina citri, the vector of huanglongbing

The Asian citrus psyllid Diaphorina citriKuwayama is currently threatening the citrus industry by transmitting the causative agent CandidatusLiberibacter asiaticus (CLas) of huanglongbing. Multiplication of CLas in haemolymph of D. citri indicates that it contains the necessary nutrients for CLas. Although many studies examine D. citri, the haemolymph composition of this dangerous pest remains to be investigated. In the present study, the haemolymph of D. citri is collected using a nanolitre syringe after the removal of one of its forelegs. The haemolymph is either derivatized with methyl chloroformate (MCF) or trimethylsilyl (TMS) derivatizing reagent and analyzed with gas chromatography-mass spectrometry. Nineteen amino acids, two organic acids and seven fatty acids are detected in the haemolymph after MCF derivatization. More metabolites are detected after TMS derivatization. Sugars are the most abundant metabolites in the haemolymph. Glucose and fructose are the main monosaccharides. Trehalose and sucrose are the major disaccharides. Furthermore, three inositol isomers (myo-inositol, scyllo-inositol and chiro-inositol) are detected in the haemolymph. Organic acids are found in low amounts, whereas phosphoric acid is found at a higher concentration. Twenty-four nucleotides and sugar nucleotides, including ATP, ADP and AMP, are detected using high-performance anion-exchange chromatography. Adenine nucleotides are the most abundant nucleotides followed by uridine and guanosine. The adenylate energy charge for the haemolymph is 0.77. Our results show that many metabolites found in the citrus phloem sap are also found in the haemolymph of D. citri.