Galhas de insetos: um micro-laboratório de estudos de interações multitróficas e não-tróficas

Abstract

Galling insects are one of the most specialized guilds, feeding on neo-formed and complex plant organs, metabolically dependent on their continuous chemical and/or mechanical food stimuli. Thus, any change in the behavior of the gall due to the effect of natural enemies may reflect on the anatomical and chemical configuration of the gall. While some insects use mature plant organs to form their microhabitats, galling insects depend on reactive sites for oviposition. The availability of sites in plants for the induction of galls, however, depends on the phenology of the host plant and, therefore, a synchronization of the phenophases of the galling insect is necessary for compatibility between the emergence of reactive plant sites and oviposition by the galling organisms. Therefore, all organisms that interact directly or indirectly with each galling insect, after the development of their galls, depend on this synchrony of phenophases, and can also adapt their life histories to interact with the galls at certain stages. The galls provide the natural enemies of galling insects with food resources, also functioning as microhabitats for a variety of arthropods that can escape adverse abiotic conditions using the gall structure. Some galling insects also establish non-trophic facilitating interactions in the ecosystems in which they occur through the availability of these microhabitats after emergence. Galls induced at axillary bud sites, for example, can remain for long periods, even years, on host plants. Therefore, the taxa of galling insects and the organ where galls are induced determine their histological characteristics and, as a result, the permanency of these microhabitats in plants after senescence. In this Thesis we investigate galls as microhabitat in different contexts of trophic and non-trophic interactions. Galls induced by Cecidomyiidae on Piptocarpha macropoda (DC.) Baker (Asteraceae) responds to parasitoid wasps Platygaster sp. and, since an individual of Cecidomyiidae supports many parasitoids, we hypothesized that an intense consumption of nutrients by the parasitized galling insect would affect the gall size, the number of cells in each compartment of gall tissues, as well as the histochemical profile. In a multitrophic system established in Macairea radula (Melastomataceae) (involving the galls induced by Palaeomystella oligophaga (Lepdoptera: Momphidae) and its direct and indirect natural enemies) we analyzed how this system is influenced by biotic conditions. And finally, also in galls of M. radula-P. oligophaga, we evaluated why these galls remain attached to the host plant even after the emergence of the galling insect, and also which opportunistic arthropods use the structure of these galls as a micro-habitat.