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

Patterns of gall-inducing insect diversity tend to be influenced by both
habitat-related and plant-related characteristics. We investigated the
distribution patterns of galling insects in four vegetation types (terra
firme forest, white-sand dry forest, white-sand wet forest, and palm swamp
forest) of the Peruvian Amazon to test if the insect gall diversity 1)
differs among different types of vegetation and 2) depends on host plant
richness. In total, we found 11,579 galls belonging to 249 insect gall
morphotypes, distributed across 30 botanical families and 75 plant
species. Among host plant families, Fabaceae showed the greatest richness
of insect gall morphotypes. We found that galling species richness was
lower in palm swamp forests than in white-sand forests, which can be
explained by the lower richness of plants in this type of vegetation.
However, we found no evidence of greater richness in xeric habitats (e.g.,
white-sand dry forest) than in more mesic vegetation (terra firme forest),
contradicting the hypothesis of hygrothermal stress. We also found that
plant species richness was positively influenced by the richness and
abundance of galling species, regardless of vegetation type. Galling
insect species composition differed significantly between vegetation
types, similarly to the floristic composition. Our findings show that the
diversity of galling insects in the tropical rainforests of the Peruvian
Amazon are mainly influenced by host plant composition and host plant
richness.