What are the nutritional needs of the pear psylla Cacopsylla pyri?

Phloem sap is the diet of numerous sap-sucking insects, such as aphids or psyllids, which use it as a source of carbon and nitrogen. Cacopsylla pyri is a phloem sap-sucking insect specialised in pear trees that can cause great damage to most pear tree-growing regions. The main goal of our study is to determine the food requirements of C. pyri and to quantify the nutrients uptaken from the plant (sugars and amino acids), with a comparison between the composition of the phloem sap and the composition of the egested honeydew. We highlighted that phloem sap is composed of two sugars, sorbitol and sucrose and both are ingested by C. pyri. Seventeen free amino acids were also found in the phloem sap, including eight essential amino acids, serine, histidine, threonine, arginine alanine, valine, isoleucine, phenylalanine, leucine and lysine. Two essential amino acids were not found in the pear tree phloem sap (methionine and tryptophan), and two other amino acids (asparagine and glutamine) were egested in high amounts by both the adult females and the larvae. This probably indicates that these four amino acids are synthesised by the pear psylla endosymbiont(s). Finally, three amino acids (valine, glutamic acid and aspartic acid) were consumed only by the adults and not by the larvae and probably participate in actions only performed by adults, such as flying, jumping or reproduction.