Most studies of the interactions between plants and gall-inducing (galling) insects have focused on the entomological aspects, few having addressed the diversity of galls in relation to the characteristics of the host plants. The objective of this study was to analyze the richness and composition of the community of host plants of galls in areas of cerrado (savanna) in the state of Goiás, Brazil. To that end, we inventoried the galls in different regions of the state and within various types of vegetation formations, between 2005 and 2007. We registered 80 gall morphotypes in 58 species of host plants (30 families and 47 genera). The host family with highest diversity of galls was Fabaceae, with 17 morphotypes, followed by Styracaceae, with seven. In the cerrado, Fabaceae is the plant family with the highest number of species. Our results show that the composition of a plant community is a determinant of the distribution of galling insects. At the family or genus level, the presence of certain taxa increases the species richness of the population of galling insects.

Impacts of forest fragmentation and edge effect on plant-herbivores interactions are relatively unknown, and the relationships between galling insects and their host plants are very susceptible to environmental variations. The goal of our study was to test the edge effect hypothesis for galling insects associated with Styrax pohlii (Styracaceae) host plant. Samplings were conducted at a fragment of semi-deciduous forest in Goiânia, Goiás, Brazil. Thirty host plant individuals (15 at fragment edge and 15 in its interior) were sampled in July of 2007; in each plant, 10 apical branches were collected at the top, middle and bottom crown levels. Our results supported the prediction of greater richness of gall morphotypes in the edge habitat compared with remnant interior. In a similar way, gall abundance and frequency of attacked leaves were also greater in the fragment edge. These findings consequently suggest a positive response of galling insect diversity to edge effect; in the Saint-Hilaire forest, this effect probably operates through the changes in microclimatic conditions of edge habitats, which results in an increased hygrothermal stress, a determinant factor to distribution patterns of galling insects. We also concluded that these organisms could be employed as biological indicators (i) because of their host-specificity, (ii) they are sensitive to changes in plant quality, and (iii) present dissimilar and specific responses to local variation in habitat conditions. Rev. Biol. Trop. 59 (4): 1589-1597. Epub 2011 December 01.