Effect of tree fertilization on protein and free amino acid content and feeding rate of pear psylla (Homoptera: Psyllidae)

Abstract

Tree nitrogen, assessed as foliar % N, phloem-cortex free amino acids, and leaf color all increased with tree fertilization, indicating an increase in nitrogen availability to pear psylla, Psylla pyricola Foerster. Free amino acid levels in psyllids increased with tree fertilization rate in orchard and growth room tests. Protein levels, however, were higher in psyllids from seedlings of medium nitrogen content than in those from low- or high-nitrogen seedlings. Psyllids from low-nitrogen seedlings weighed more than those from medium-nitrogen seedlings. Psyllid feeding rate, estimated by honeydew production, was compared on low- and high-nitrogen seedlings. Nymphs on very-low-nitrogen leaves produced more honeydew, suggesting a compensatory feeding response to low dietary nitrogen. Physiological, morphological, and ecological ramifications for pear psylla include effects on (1) adult protein content, (2) adult body size, and (3) nymphal developmental rate.