The genus Eucalyptus contains some of the most cultivated hardwood timber species around the world. In Brazil, the area planted with this genus reached in 2012 the amount of 5.1 million hectares. However, eucalypt plantations are often targets of pests. The eucalypt yellow beetle, Costalimaita ferruginea, is an important leaf-eating beetle of Eucalyptus. The adults that emerge after the first rains, clump of eucalypt plants to feed on their leaves and new shoots. In nature, many models of interactions between insect-insect, insect-plant and insect-plant-insect are well known. These models generally are mediated by volatile compounds. The insect-insect and plant-insect interactions have not been analyzed for the C. ferruginea and its host plant. In the first chapter I present an introduction to models of insect-insect interactions described in the literature for the Chrysomelidae family. In the second chapter the volatiles released by adult of C. ferruginea, its host plant and the association between the two were featured and in the third chapter, responses to bioactive compounds within this system were investigated. Thus, two goals were proposed: (i) to describe the volatiles released by eucalypt yellow beetle adults and eucalypts and investigate the qualitative and quantitative differences in the volatiles released during and after herbivory and (ii) to evaluate the response of beetles to possible bioactive compounds released by conspecifics, host plant and the association between both. For the first objective, the volatiles were obtained by the technique of sampling in headspace and analyzed by gas chromatography-mass spectrometry (GC-MS). For the second objective, the response of the antennae of insects was analyzed using the electroanntenographic-gas chromatography technique (EAD-GC). Some compounds emitted by eucalypt yellow beetle were considered strong candidates to an insect pheromone. Two of them were exclusively produced by the female alone or during feeding eucalypts and two others were produced in a similar manner by the male, but such compounds were not identified. The constitution of the volatiles emitted by the plant without attack followed a pattern already observed and reported in the literature, being the Eucalyptol the major constituent. In quantitative terms the insect-plant association altered the rate of emissions of certain compounds emitted by host plant. Electrophysiological responses were observed for six compounds. Of these, four were identified as (3Z)-Hexenyl acetate, Allo-ocimene, Decanal and γ-Cadinene. Males and females responded promptly to all compounds, except Decanal, in which only responses of females were detected. For the two unidentified compounds, one is exclusively released by males alone or in combination with eucalypt, and other the presence was also detected in these volatiles and in the volatiles released by the plant after feeding beetles. These two compounds, plus the γ-Cadinene are strong candidates in the constitution of an aggregation pheromone. (3Z)-Hexenyl acetate and Allo- ocimene are compounds produced by the plant, and in the presence of insects its emission rate was changed and possibly this change is perceived by the insect. Future research should be directed to the importance of these compounds in insect-insect and plant-insect interactions in order to use them in monitoring and controlling the populations of C. ferruginea in eucalypt plantations.
