Nitrogen fertilization enhances growth and development of Cacopsylla chinensis by modifying production of ferulic acid and amino acids in pears

Psyllids feed exclusively on plant sap, which is an unbalanced diet for herbivores due to its low nitrogen content. Therefore, the plant-psyllid-natural enemy interactions can be strongly shaped by the bottom-up forces of N fertilization. Pear psylla Cacopsylla chinensis is a notorious pest in East Asian countries, inflicting devastating damage to pear trees and fruits. However, the bottom-up effects of nitrogen fertilizer on C. chinensis and the mechanisms remain unexplored. Here, we evaluated the performance of C. chinensis larvae over the N application range of 0–1500 mg/kg. The feeding activity and body weight of C. chinensis increased and the developmental duration of C. chinensis decreased significantly when N application increased. Our results indicated that nitrogen application enhanced psyllid fitness on host plant. By analyzing pear leaf metabolites, we found that only ferulic acid increased with the increase of nitrogen fertilizer concentration among phenolics assessed. Exogenously application of ferulic acid accelerated the development of psyllid nymphs. We also found that the concentration of both essential and non-essential amino acids increased significantly when N supply increased, which provided C. chinensis with increased nutrients for their development. The expression levels of several C. chinensis genes in the amino acids synthesis pathway decreased significantly after nitrogen application, indicating that C. chinensis can adjust its amino acid synthesis levels based on its diet. We demonstrated that the enhanced fitness of psyllids under nitrogen supply stems from altered host chemical traits and nutritional quality. The manipulation of nitrogen fertilization has a high potential for use in psyllid IPM programs by reducing psyllid performance.