2020 ESA Annual Meeting (August 3 - 6)

COS 177 Abstract - Potential roles for microbes in the interaction between leafcutter bees (Megachile spp.) and plants

Victoria Luizzi1, A. Elizabeth Arnold2 and Judith Bronstein1, (1)Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ, (2)School of Plant Sciences and Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ
Background/Question/Methods

Species interactions are important drivers of species abundance and diversity, trait evolution, and speciation. However, pairwise interactions between macroscopic species do not take place in isolation: both partners usually host communities of microbes that may influence their behavior and/or traits. Such interactions can be especially important when they shape the reproductive success of the species with which they interact. Leafcutter bees (Megachile spp.) are cavity-nesting solitary bees that line their nests with cut leaf discs. Leaves typically harbor diverse microbes on their surfaces (i.e., on the phylloplane). We anticipated that leaf selection by leafcutter bees would be sensitive to phylloplane microbes, as harmful microbes (e.g., pathogens, pollen molds, and saprotrophs) may grow easily in nests made of leaves and organic matter, where they can harm developing larvae directly. Here, we tested the prediction that microbial communities differ between leaves that are and are not cut by leafcutter bees. We collected leaflets from two hybrid cultivars of Rosa spp. immediately after they were cut by leafcutter bees, along with age-matched, adjacent, non-cut leaflets. We sampled epiphytic microbes from these leaves by pressing the adaxial leaf surface on 2% malt extract agar and compared microbial abundance, morphotype richness, and community composition.

Results/Conclusions

Neither microbial abundance nor richness differed between cut and adjacent non-cut leaves. However, microbial community composition differed markedly between cut and non-cut leaves in one of two rose cultivars, potentially reflecting (a) preferential cutting of leaves with specific microbes, (b) avoidance of specific microbes, and/or (c) introduction of microbes by bees when cutting. In our samples, one fungal morphotype (Aspergillus niger, which produces abundant and potent secondary metabolites) was more abundant on cut vs. uncut leaves, accounting for nearly 30% of the community dissimilarity we observed. Whether it is introduced by bees or leads to preferential selection of leaves will be evaluated in future experiments. A second fungal species and one bacterial species were more abundant on uncut leaves, consistent with bees’ avoidance of certain microbes. Leafcutter bees should benefit from building nest environments that promote offspring health and survival. In future work, we will evaluate impacts of microbes on leafcutter bee behavior and fitness, taking into account microbes that may not be cultivable. This work contributes to our understanding of microbial mediation of plant-insect interactions, advancing the study of microbial mediation as a driver of the ecology and evolution of species interactions.