Galling inducing insects associated with a tropical shrub: The role of resource concentration and species interactions

Abstract

Gall-forming insects are sophisticated sedentary herbivores that present high level of specifcity with host plant, but their performance can be affected by biotic and abiotic factors. In this study we have tested two predictions: a) plants that have a greater number of conspecifc neighbors have greater richness and abundance of gall-forming insects, and b) interspecifc competition is a force capable of shaping the organization of gall-forming insect communities in super-host plants. We used the Copaifera oblongifolia (Fabaceae)/galling insects’ system to test these predictions. Fieldwork was carried out in areas of Cerrado (Brazilian Savanna) in northern Minas Gerais, Brazil. To test the frst hypothesis, we evaluated with generalized linear mixed models, the effects of the number of conspecifc neighbors on the richness and abundance of galls associated with 67 C. oblongifolia individual plants belonging to two populations. To test the second hypothesis, we used null models to evaluate whether a plant of C. oblongifolia colonized by a species of gall is preferred or avoided by another species of gall. A total of 2901 gall-forming insects belonging to 15 species were collected from the host plant C. oblongifolia. We observed negative relationships between the number of conspecifc neighbors and the abundance and richness of gall-forming insects associated C. oblongifolia. Thus, our data did not support the resource concentration hypothesis. Instead, we used the resource dilution theory to explain the negative relation between resource concentration and frequency of attack by galling insects. Our results also showed that the co-occurrence pattern of gall-forming insects in the host plant did not differ from those expected by chance. Therefore, the structure of the gall-forming insect community associated to single C. oblongifolia plants cannot be attributed to deterministic factors such as interspecifc competition. https://doi.org/10.25260/EA.19.29.1.0.751