Hole Size Matters: An Indirect Method for Measuring Gall Wasp Community Emergence?

Quantifying the abundance and diversity of small insects, especially those with specific environmental associations or hidden habitats, can be challenging using direct methods. Galls are specialized microhabitats that host a wide range of interactions between species. However, assessing their abundance and associated community diversity takes time and effort. In this study, we propose an indirect approach using the size of gall emergence holes to estimate the abundance of gall wasps (Cynipini) and their associated wasp species. We examined eight different types of gall structures collected in the temperate forest of Mexico. We identified every gall-emerging individual, classifying them as gall inducer, inquiline, or parasitoid. Kruskal-Wallis tests, correlation analysis and a mixed linear model (LMM) were used to evaluate differences between mesosoma size and gall hole size for each emerged species in each gall type. Our results showed that mesosoma and hole size significantly differed between Cynipini wasps and their associated wasp species. LMM showed a significant relationship between the size of the mesosoma and the diameter of the emergence hole among the analyzed wasp species. Upon validating the method, a low emergence rate and low abundance of the studied Cynipini wasps were observed, attributed to negative interactions and inadequate development of the wasps. We emphasize the potential of gall emergence hole size as an indicator of species abundance and emergence rates within Cynipini gall complexes. Furthermore, strategies are discussed to improve their effectiveness and reliability in future studies to increase our understanding of the ecological dynamics and evolutionary processes of gallforming wasps.