Abstract:The objective of this study was to determine the effects of gall induction on leaf phenolic compounds and their indirect effects on the subsequent attack of folivorous insects in Achatocarpus gracilis, Cordia alliodora, Guapira macrocarpa, Guettarda elliptica and Ruprechtia fusca that occur in both hillside and riparian sites at Chamela-Cuixmala tropical dry forest in western Mexico. There are differences in soil water content between riparian and hillside sites where trees in the first are mainly evergreen and deciduous in the second. A few tree species occur in both sites and their intraspecific phenological response is also different between sites. In this case, trees of a given species that occur in riparian sites will be evergreen whereas trees on hillsides of the same species will be deciduous. Four plant species had significantly greater total phenol concentrations in galled than ungalled leaves in both deciduous hillside and riparian sites. In three plant species associated with galls, host total phenol concentrations were significantly greater in short than in tall plants. The frequency and amount of folivore damage were greater in leaves without galls than leaves with galls in these four plant species. These results indicate that galling insect species may directly affect leaf phenolic concentrations and indirectly may affect the incidence and consumption of folivorous insects in tropical plant species. This may have important consequences on the preference of leaves by folivorous insects that might be excluded by galling insect species in this dry tropical system.

Background: Gall-inducing insects make up a guild of highly specialized endophagous herbivores. The cynipids (Hymenoptera: Cynipidae: Cynipini) are highly diversified gall-inducing wasps that are largely associated with oaks (Fagaceae: Quercus). Mexico is one of the centers of diversification for the Quercus genus with 161 described species, of which 109 are endemic. Questions / hypothesis: The present study aims to identify the gall richness, gall morphological variation and degree of specificity to oaks in Mexico. Methods: An intensive collection was conducted from March to September each year from 2008 to 2012 for a total of 80 oak species in 120 localities in Mexico. Results: A total of 224 morphologically distinct galls associated with 73 of the 80 oak species were found. The largest number of morphotypes was found in leaves (125), followed by branches (37), buds (31), petioles (20), catkins (5), acorns (3) and roots (3). The degree of specificity between the gall-inducing wasps and their hosts was highly variable; between one to 20 distinct gall morphotypes were found in each species. Only 23 oak species had a single gall morphotype associated. Conclusions: This study demonstrates the important interaction between oaks and gall-inducing wasps, which is a very complex co-evolutionary process. It also shows the relevance of basic taxonomic studies of little-known groups such as gall-inducing wasps, especially in a highly biodiverse country such as Mexico.