Honeydew sugar composition of the phloem sap feeder, the Asian citrus psyllid, Diaphorina citri (Homoptera: Psyllidae) on citrus host plants

The Asian citrus psyllid, Diaphorina citri Kuwayama (Homoptera: Psyllidae) damages plants directly through its feeding activities on phloem sap. More importantly, D. citri is the vector of citrus Huanglongbing (HLB). Using gas chromatography-mass spectrometry (GC-MS), we studied the honeydew composition of D. citri. Honeydew samples were collected from D. citri adults reared on one-year Valencia trees. Dried samples (1 mg) were mixed with 30 μL of methoxyamine hydrochloride solution in pyridine (2%). The mixture was incubated for 17 h at the ambient temperature. After methoximation, silylation reactions were induced by adding 80 μL of N-methyl-N-(trimethylsilyl) trifluoracetamide (MSTFA) for 2 h at the ambient temperature and 0.5 μL of derivatized sample was injected into the GC-MS running in the full scan mode. To check for amino acids, a 10 mg of alkaline honeydew sample was reacted with methylchloroformate (MCF) in a mixture of pyridine and methanol. The MCF derivatives were extracted with chloroform and analyzed with GC-MS. The moisture content was determined by drying the honeydew samples to a constant weight at a 100 °C. The major honeydew components were as follows: sucrose 74.5 ± 2.8, D-fructose12.4 ± 0.5, mannose 6.4 ± 3.0, trehalose1.8 ± 0.6, myo-inositol 2.8 ± 0.8, ribitol 0.5 ± 1, galactose 0.4 ± 0.2, quinic acid 0.4± 0.3, and malic acid 0.3 ± 0.1. The moisture content of honeydew was 22.6 ± 2.6. No amino acids were detected as TMS or as MCF derivatives. Information obtained from this study will help in understanding how D. citri interacts with its plant host.