Heatwave‐Resilient Cuticular Microbiota Protect the Leaf Beetle Plagiodera versicolora From Fungal Infection

The increasing frequency and intensity of heatwaves—extreme thermal events characterized by prolonged supra‐optimal temperatures—exert profound impacts on global ecosystem stability and species interactions. While the disruptive effects of thermal stress on host physiology and gut microbiota are well documented, the role of cuticular microbiota in host defense under heatwaves remains poorly characterized. Here, we show that the cuticular microbiota of the willow leaf beetle Plagiodera versicolora may serve as a thermostable protective barrier against the entomopathogenic fungus Beauveria bassiana . Using microbiota‐manipulated larval models, we found that cuticular microbiota significantly bolstered host survival under both control (27°C) and simulated heatwave (32°C) regimes. High‐throughput 16S rRNA sequencing revealed a dramatic microbial regime shift: Pantoea dominated at control temperatures, whereas Enterobacter proliferated and became predominant during simulated heatwaves. Both genera exhibited potent antifungal activity that markedly increased with rising temperature, suggesting a potential functional compensation property whereby thermally adaptive taxa may maintain host defensive capacity under climatic perturbations. Recolonization experiments confirmed that cuticle‐isolated Enterobacter gergoviae and Pantoea anthophila are sufficient to reduce the increased fungal susceptibility of germ‐free larvae. Mechanistically, these symbionts appear to inhibit fungal germination through direct antagonism and modulate host immune responses by upregulating antimicrobial peptide effectors while potentially reducing excessive immune recognition signaling. These findings highlight the resilience of cuticular defensive symbioses in the face of climate change and provide new insights into the adaptive mechanisms that sustain host–microbe–pathogen dynamics in a warming world.