(Comparison of feeding behaviors and pathogen acquisition rates of adults and the 5th instar nymphs of Diaphorina citri (Hemiptera: Liviidae) on huanglongbing-infected citrus plants)

Aim: The Asiatic citrus psyllid (ACP), Diaphorina citri, is the major vector of ‘Candidatus Liberibacter asiaticus’ (‘CLas’) (α-Proteobacteria), the pathogen that causes the Asiatic form of huanglongbing (HLB), the most devastating disease of citrus. The aims of this study are to determine whether the feeding behaviors of adults and the 5th instar nymphs of D. citri differ, and if so, whether these differences influence pathogen acquisition efficiency, and whether HLB-infected plants influence feeding by the 5th instar nymphs. Methods: The feeding behavior of adults and the 5th instar nymphs of D. citri on immature shoots of HLB-infected Citrus reticulata cv. Sunki was recorded for 10 h with DC-EPG giga-4. The acquisition efficiency of the pathogen by individual adults and nymphs from HLB-infected shoots was determined by qPCR. The feeding behaviors of the 5th instar nymphs on pathogen-free and HLB-infected shoots were also recorded and compared by EPG. Results: The feeding behaviors of adults and the 5th instar nymphs of D. citri on C. reticulata cv. Sunki shoots infected with HLB differed significantly. The 5th instar nymphs started to ingest xylem and phloem sap sooner than adults. Durations of the phloem salivation and ingestion phases of nymphs were significantly longer than those of adults. When feeding on HLB-infected shoots, 37.5% of the 5th instar nymphs acquired ‘CLas’ in contrast 20% of adults. The frequencies of probing and salivation and phloem sap ingestion by the 5th instar nymphs feeding on HLB-infected shoots were significantly lower than those on healthy shoots. However, HLB-infected plants did not influence the duration of phloem salivation and sap ingestion by the 5th instar nymphs. Feeding also commenced sooner in phloem of HLB-infected shoots than in phloem of healthy shoots. Conclusion: The 5th instar nymphs of D. citri feed for longer intervals, ingest more phloem sap, and acquire higher titers of ‘CLas’ than adults. This may be due to that nymphs require more nutrients for their growth and development than adults. They are therefore less inclined to withdraw their stylets from, and re-insert their stylets into ‘CLas’-infected leaf tissues. ‘CLas’-induced changes in host-plant phytochemistry promote feeding by the 5th instar nymphs of D. citri