Topological structure of a tritrophic network composed of host plants, gall-inducing insects and parasitoids in a restinga area in Brazil

Plants, insect herbivores and parasitoids can form tritrophic networks that are species rich and complex in interactions. In the present study, we describe the network structure of an assemblage composed of host plants, cecidomyiid gall midges and hymenopteran parasitoids in a restinga in Brazil. We used data collected between 1992 and 2011 to build plant-galling and galling-parasitoid networks. In total we recorded 44 species of host plants, 79 species of gall midges and 70 taxa of parasitoids. The network of host plants and gall midges was very specialized, being characterized by 79 distinct interactions, low connectance, low linkage density and high modularity. This specialized pattern is because all species of gall midges have been monophages. In contrast, galling-parasitoid interactions were more numerous (203 distinct interactions) and were more connected, and less modular than expected based on the null model. The occurrence of generalist parasitoids (i.e. 35.7% of parasitoid species occurring on two or more hosts) is the main factor that explains this lower specialization in the galling-parasitoid network when compared to the plant-galling network. Our findings corroborate previous studies indicating high specialization for the interactions of gall midges with their plants but indicate a slightly smaller specialization of the parasitoids in relation to the gall midge species.

Automated summary

The tritrophic network in a restinga in Brazil consisted of diverse interactions among plants, gall midges, and parasitoids. The network between host plants and gall midges was highly specialized, while the interactions between galling and parasitoid species were more numerous and less modular, driven by the presence of generalist parasitoids.