Phytohormones in galls on eucalypt trees and in the gall‐forming wasp Leptocybe invasa (Hymenoptera: Eulophidae)

Abstract

Abstract The role played by phytohormones in insect galls and the mechanisms underlying plant manipulation by gall makers are still unclear. Galls made by Leptocybe invasa on two Eucalyptus species were sampled, the correlations between the levels of nine phytohormones in galls and gall size were analysed, and phytohormone levels in the interior and exterior tissues of galls and L. invasa were determined. During two larval stages, the levels of three forms of cytokinins (CKs) in the galls of the two plant species all showed significantly positive correlations with gall size. Brassinosteroids (BRs) and dihydrozeatin riboside (DHZR) occurred at significantly higher levels in the interior tissues of the galls compared to in the exterior tissues of galls. Isopentenyl adenosine (IPA) was significantly higher in L. invasa larvae themselves, compared to levels in the interior and exterior tissues of galls. However, the levels of DHZR and BR were significantly lower or similar in the L. invasa pupae compared to that in the interior and exterior tissues of the galls. These findings indicate that phytohormones, especially CKs, act as key regulators of L. invasa galls, and that the larvae of L. invasa may themselves be a source of CKs.