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Dryad

Data from: A leaf-surface fungus mediates interactions between leafcutter bees and the plants they cut to line their nests

Luizzi, Victoria12; Arnold, A. Elizabeth1; Bronstein, Judith1

Published Sep 03, 2025 on Dryad. https://doi.org/10.5061/dryad.jwstqjqk5

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Abstract

Many arthropods damage leaves, a phenomenon that is foundational to their impacts on terrestrial ecosystems. Leaf traits, including chemistry, shape these interactions. In turn, leaf-surface (phylloplane) microbes can act directly or in concert with chemistry to influence leaf choice, especially by insects whose reproductive success is tied to prolonged contact with leaf surfaces. Leafcutter bees (Megachile spp.) cut discs from leaves to line their nests, with leaves and their associated microbes forming the environment in which bees’ offspring develop. We predicted that phylloplane microbial communities act in concert with leaf chemistry to mediate interactions between the leafcutter bee M. lippiae and the plants they cut. We surveyed phylloplane communities on rose (Rosa × hybrida, Rosaceae) leaflets that were cut vs. not cut by wild M. lippiae. Then, we inoculated rose leaves in the field to test the effect of abundant microbes on cutting. Microbial communities differed between cut and non-cut leaflets. In particular, Aspergillus spp. were over-represented on cut leaflets, and Alternaria sp. and Bacillus sp. were over-represented on non-cut leaflets. When inoculated onto rose leaves, Alternaria and Bacillus did not affect cutting, but Aspergillus resulted in twice as many cuts as sham-inoculated leaves. To test whether Aspergillus could protect bee nests against pathogens, we grew Aspergillus with two pathogenic fungi: the generalist insect pathogen Beauveria bassiania, and three strains of Ascosphaera that cause chalkbrood disease in bee larvae. Aspergillus did not inhibit the growth of Beauveria, but it markedly slowed the growth of Ascophera. To clarify whether these phylloplane microbes reflect differences in leaf chemistry or are instead independent cues that influence leaf cutting, we used liquid chromatography-mass spectroscopy to characterize the metabolome of cut and non-cut leaflets. Chemistry did not differ between cut and non-cut leaflets, nor was it related to microbial community composition. Our results suggest that Aspergillus, a common member of rose phylloplane communities, mediates interactions between leafcutter bees and roses, potentially affecting the fitness of both partners. This study reveals a previously unexplored microbial dimension to plant-insect associations.