Changes in galling insect community on Caryocar brasiliense trees mediated by soil chemical and physical attributes

Abstract

The nutrient stress hypothesis predicts that galling insects prevail on host plants growing in habitats with soils of low nutritional quality. Caryocar brasiliense (Caryocaraceae) is host to four different leaf-galling insects. These insects have the potential to cause a reduction in the production of C. brasiliense fruits, an important source of income for many communities in Brazil. We studied the effects of soil physical and chemical characteristics on the abundance, species richness, and diversity of galling insects and their natural enemies on C. brasiliense trees growing under three different soil conditions. Our data corroborate the hypothesis that in nutritionally poor (e.g., lower phosphorus content) and worse physical textures (e.g., sandy) soils, host plants support higher species richness and diversity of galling insects. However, the abundance of Eurytoma sp. (the most common gall in C. brasiliense), was correlated with a higher phosphorus concentration in the soil (better nutritional condition). The percentage of galled leaflets and the area of leaflets occupied by Eurytoma sp galls were higher in the more fertile soil. In this soil, there was greater abundance, species richness, and diversity of parasitoids of Eurytoma sp. (e.g., Sycophila sp.) and predators (e.g., Zelus armillatus). Our data indicate the importance of habitat quality in the composition of the galling insect community and the impact of soil properties in mediating the distribution of these insects in C. brasiliense.

Plant species richness, not hygrothermal stress, is the main predictor of gall‐inducing insect richness in Peruvian Amazon forests

“…The main mechanisms responsible for the high galling species richness in stressed environments are thought to be related to nutritional flexibility and relationships with natural enemies (Fernandes & Price, 1988; Fleck & Fonseca, 2007). Plants under environmental stress tend to be more sclerophyllous (Fagundes et al., 2020; Poorter et al., 2009) and accumulate higher levels of chemical compounds (Fagundes et al., 2018; Leite et al., 2022). Galling insects have adaptive advantages in xeric habitats because they sequester secondary metabolites in gall tissue as a mechanism of protection against natural enemies (Stone & Schönrogge, 2003).…”