Leaf traits mediate galling insect frequency on woody plants in a Neotropical savanna

Abstract

Galling insects are highly specialized herbivores that exhibit intimate interactions with their host plants. How ever, the role of interspecific variation in plant traits on galling species occurrence has been little explored. Here, we assessed the roles of nutritional (P:N ratio) and defensive (latex, specific leaf area, leaf toughness and extrafloral nectaries) leaf traits in determining galling insect frequency and richness across 50 woody plant species in a Brazilian savanna. Specifically, we tested the hypotheses that nutritional leaf traits attract galling insects, thus increasing their frequency and species richness, while defensive leaf traits reduce galling frequency and richness. Sampling was conducted during the rainy season, resulting in the identification of 82 galling insect species distributed among 42 plant species. We found no relationship between leaf traits and galling species richness. However, latex reduced the frequency of galling insects, whereas the presence of extrafloral nectaries, tougher leaves and higher leaf P:N ratio were positively associated with galling frequency. Our findings indicate that latex plays an important role on the occurrence of galling insects, presumably by hindering oviposition and reducing egg survival and larval hatching. Additionally, the presence of extrafloral nectaries may offer protection against natural enemies, tough leaves can increase leaf longevity and enhance defense against herbivory, and galling species prefer plant with better nutritional quality. In contrast to previous studies, we demonstrate that defensive and nutritional leaf traits do not affect galling species richness; rather, defensive traits influence the frequency of galling insects among savanna plant species.