Galling impacts of the gall wasp Leptocybe invasa (Hymenoptera: Eulophidae) on Eucalyptus trees vary with plant genotype

Abstract

Impacts of galling on the distributions of plant metabolites can vary greatly with plant genotype. In this study, two Eucalyptus genotypes with different resistance levels were chosen, and the levels of several primary and secondary metabolites, as well as phytohormones in galls and ungalled portions of galled leaves infested by the gall wasp Leptocybe invasa, and gall-free (control) leaves were compared. It was found that galls of both two plant genotypes accumulated higher concentrations of carbon, total phenolics, gibberellins (GA), and abscisic acid (ABA) but had lower chlorophyll content than ungalled portions. However, galls of highly susceptible genotype contained higher nitrogen (N), cytokinins (CK), GA, and chlorophyll content but lower C/N ratio, total phenolics, tannins, and ABA than less susceptible genotype. For both two genotypes, ABA in galls and ungalled portions increased compared with adjacent control leaves. CK and GA levels increased in galls but decreased in ungalled portions of highly susceptible genotype, compared with control leaves. For less susceptible genotype, CK levels increased in both galls and ungalled portions compared with control leaves, but higher levels of tannins, total phenolics, and GA were only detected in galls. Therefore, our study found insufficient evidence that the impact of galling on the distributions of these metabolites and phytohormones extended beyond the attacked leaves, because they varied greatly with plant genotype.