Mechanism of Excessive Nitrogen Fertilization Aggravates the Damage of Cacopsylla Chinensis to Pear

Abstract Cacopsylla chinensis (Hemiptera: Psyllidae) is one of the most important pests on pear trees. Although nitrogen fertilization is known to often benefit the performance of many herbivores including psyllids, physiochemical and molecular mechanisms of how psyllids respond to excessive nitrogen application remain unclear. Study showed that nitrogen fertilizer concentrations significantly impacted phenolic acids compositions in pear leaves, there was an upward trend in ferulic acid concentration when increasing nitrogen fertilizers. The increased ferulic acid concentration accelerated the C. chinensis development. Moreover, high nitrogen fertilization also caused a significant increase in psyllid honeydew secretion and several amino acids concentrations in honeydew. The increased amino-acid content in pear leaves under high nitrogen fertilization improved the feed intakes of psyllid, however decreased more significantly the expression levels of several C. chinensis genes in amino-acid synthesis pathways. The mechanism of excessive nitrogen fertilization aggravating the damage of C. chinensis to pear trees was defined preliminarily.