Mosaico de alterações estruturais e potencial sinalizador dos voláteis em galhas induzidas por Thysanoptera em Myrcia spp.

Abstract

Studies on Thysanoptera galls in the Neotropical region are scarce, and many species of inducers are yet to be described. This research presents the description of a new species of galling Thysanoptera, Holopothrips striatus, which induces fold/roll galls on Myrcia retorta. In addition, the comparative study of these galls with those induced by an undescribed species of Thysanoptera on Myrcia splendens describes distinct developmental processes for the two fold/roll galls. The moisaic of alterations observed in these galls, corresponding to areas of hypersensitivity, and compactness and homogenization of mesophyll, which are generated by the impairment of leaf adaxialabaxial polatity in distinct levels. This impairment, most expressive in M retorta, is a result of leaf age by the time of oviposition. for the signaling for the establishmentof the adaxial and abaxial domains originates from the apical meristem and promotes responses in young leaves. As the induction of galls on M. splendens occurs in mature leaves, the alterations are less expressive. Current results show that although the feeding habit is important for the determination of gall shape, it is not the only determinant factor. The constraints imposed by the host plant, the age of the host leaves, as well as the oviposition habits are also crucial for gall development. The observed structural alterations led us to conclude that Myrcia galls are true galls, refuting the concept of pseudogalls, based on the fact that they are permanently open, found only in leaves and do not present the tissue neoformation. Both galls have morphogenetic similarities, plant-dependent processes, and converged in form. In addition, an analysis of the chemical profile of the galls induced on M. splendens points out the role of volatiles in the signaling of stress and attraction or repellency of the gall inducers. Structural alterations are followed by chemical alterations to several signaling pathways, triggering direct and indirect defenses in the host plant. Although considered simple, the Thysanoptera-Myrcia spp. presented in this study, have important structural and chemical alterations and proved to be excellent models for the understanding of the processes of plant development and the chemical potential involved in the gall induction. In addition, galls are potential model for improving the knowledge on Neotropical entomofauna.