Abstract

Eucalyptus globulus (Myrtaceae) plantations in Chile are affected by the gall-inducing species Ophelimus migdanorum (Hymenoptera: Eulophidae). Ophelimus migdanorum induces galls on the mesophyll, midrib, margin, and petioles of adult leaves, and young stems of E. globulus, associated with different inducer phenotypes. The structural and cyto-histometric features of the stem, mesophyll, and midrib O. migdanorum galls were therefore explored in order to determine differences due to the morphogenetic restrictions imposed by the host organ. Additionally, cyto-histometric comparison between stem galls and midrib and mesophyll galls was performed to determine whether O. migdanorum polyphenisms are reflected in the structural gall features. Regardless of the host organ and induction site, the stem and leaf galls are composed of a nutritive tissue surrounded by sclerenchyma cell layers. The outer gall cortex is composed of cortical parenchyma in stem galls, and of palisade and spongy parenchyma in leaf galls. One gall side was always associated with the vascular system of the host organs. The larval chamber diameter and the thickness and cell area of the sclerenchyma were greater in stem galls than in leaf galls, probably determined by the activation of stem vascular cambium. The leaf mesophyll and midrib galls were statistically similar, although the establishment of O. migdanorum in the midrib induced structural changes in the leaves. Ophelimus migdanorum only produces an increase in the stem cortex thickness, due to a greater diameter of the larval chamber. Therefore, the host organ and the induction microsites determine the composition of the outer gall cortex, corroborating the morphogenetic restrictions imposed by the host organ on gall development. Also, the various phenotypes of O. migdanorum are not associated with structural peculiarities of their galls. (c) 2022 SAAB. Published by Elsevier B.V. All rights reserved.