Resistência induzida em Bauhinia brevipes Vog. (fabaceae) e interações com insetos de diferentes guildas

Abstract

In interactions such as herbivory the consumption of plant tissue by herbivore insects promotes several impacts on vegetative and reproductive performance of host plants. Defense mechanisms induced as hypersensitive response (HR) are observed in several species and is directly related to the specificity of herbivore insects and host plants. However, the ability to develop HR varies according to genotype and phenotype of plant hosts and with environmental disturbances such as fire. Thus, we aimed evaluate the performance of Bauhinia brevipes, the ability to evolve induced defenses against gall insect Schizomyia macrocapillata and herbivory rates by free-living insects. We analyzed these interactions in the context of phenotypic variation of resistance and environmental disturbances as fire. Then, in the first chapter, we evaluated the performance of mature plants and offspring according to the phenotypic resistance (resistant and susceptible) to S. macrocapillata attacks. Thus, we evaluate vegetative performance as architecture and reproductive performance as number of seeds (female component), the number of fruits (male component) and the nutritional quality (macro and micronutrients in leaves) on resistant and susceptible individuals. In addition, we evaluated the performance of the offspring in three stages of development: seeds, seedlings and juveniles. There were no differences in vegetative and reproductive performances of mature plants from resistant and susceptible phenotypes. Besides, there was no relationship between macro and micronutrients and the resistance factor. Germination rates and investments in shoot and root portion in the offspring of different phenotypes were similar. We believe that the low incidence of S. macrocapillata on the population of B. brevipes contributed to the similar performance between phenotypes. Moreover, strategies such as tolerance to herbivory should be analyzed in this gall insect / plant host system. In the second chapter, we evaluate the differences in responses to fire effects in relation to interactions between herbivore insects and host plants in and induced defenses (HR and silicon content). We detected an individual variation in response to fire as resprouting and non-resprouting plants in the population of B. brevipes. Non-resprouting plants showed higher rates of herbivory by chewing insects and lower silicon content in relation to resprouting. Contrasting, resprouting presented greater attack rate by S. macrocapillata, but exhibited larger amounts of HR than non- resprouting. We believe that resprouting of B. brevipes can be better defended, since allocate more nutrients such as nitrogen for growth and silicon which reduces the performance of chewing insects. HR can also be increased by the allocation of resources post-fire, which lead to the greatest defenses rates among resprouting plants. This study provided evidences about the role of fire in the interactions between host plants and insects of different guilds and possible changes in the behavior of chewing insects.