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 specificity 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 conspecific neighbors have greater richness and abundance of gall-forming insects, and b) interspecific 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 first hypothesis, we evaluated with generalized linear mixed models, the effects of the number of conspecific 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 conspecific 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 interspecific competition.

Diversity of gall-inducing insect associated with a superhost plant species: Plant architecture, resource availability and interspecific interactions

“…Null model analyzes were used to test whether the occurrence of gall-inducing species associated with trees and shrubs plants does not differ from chance. The null hypothesis predicts that the occurrence of one gall-inducing species in one individual plant does not interfere with the occurrence of another species of gall insect in the same plant (Fagundes et al 2019). In this case, the gall-inducing insect community is randomly structured and interspecific interactions cannot be used to explain the structure of galling insect communities in their plants (Ribas and Schoereder 2002;Cornelissen et al 2013).…”

“…Gall-inducing insects are sophisticated herbivores whose immature stages develop within host plant tissues and the adult stage is ephemeral and free-living (Fagundes et al 2019). Females of gall-inducing insects show high oviposition specificity with the taxa and the organ/tissue of the host plant (Carneiro et al 2009).…”

Intraspecific interaction of host plant influences local distribution of specialist herbivores through metabolic alterations in leaves

“…This prediction has been supported by several studies (e.g., Stephens & Myers, 2012;Nerlekar, 2018). On the other hand, the possibility of an inverse distribution pattern, in which herbivores are concentrated on low-density or solitary host plants (Yamamura, 1999;Otway et al, 2005), has been proposed as the resource dilution hypothesis, and these predictions have also been supported by several studies (e.g., Fagundes et al, 2019;Coutinho et al, 2019). These conflicting patterns have been reported for several herbivore species, and some species have even been found to be unresponsive to resource distribution (Rhainds and English-Loeb, 2003;Tuller et al, 2013).…”

Gall-inducing arthropods in a Neotropical savanna area in the EPA of Rio Pandeiros (Bonito de Minas, MG, Brazil): effects of plant species richness and super-host abundance

“…The host-plant species with higher diversity of gall morphotypes also were of family Fabaceae: Copaifera oblongifolia and Andira humilis. Recent studies have pointed Copaifera oblongifolia (Fabaceae) as a super-host plant of galling insects with 15 different gall morphotypes recorded (Coutinho et al, 2019;Fagundes et al, 2019b). Species of the genus Andira have also been listed as important hosts of galling insects in other areas of neotropical savannas, such as Andira paniculata Benth.…”