Fungicides compatible with entomopathogenic fungi eliminate beneficial symbionts of the brown planthopper, Nilaparvata lugens

BACKGROUND In agricultural pests, both microbial pathogens and partners, that threaten their life and benefit them, respectively, face challenges from fungicides that are ubiquitous to control crop pathogens. However, an integrated understanding of the fungicide‐impacts on pest microbial pathogens and partners, which in turn influence pest management outcomes, remains largely unexplored. RESULTS We investigated the impacts of the most commonly used rice fungicides on an entomopathogenic fungus Cordyceps javanica , a biocontrol agent of rice pest Nilaparvata lugens , as well as the communities of bacteria and fungi within this pest. We found that while traditional fungicides were incompatible with C. javanica , the new generation fungicides Fenoxanil and Thifluzamide did not significantly inhibit its growth. Furthermore, no significant difference was observed in C. javanica infection densities and survival curves of N. lugens individuals exposed to C. javanica spores alone versus in mixtures with Fenoxanil and Thifluzamide, respectively. Subsequently, density measurements of C. javanica on rice seedlings revealed that both Fenoxanil and Thifluzamide did not reduce its habitation, ensuring the sustainable control of N. lugens feeding on rice. Additionally, while Fenoxanil and Thifluzamide did not change the fungal community of N. lugens , they remarkably reshape its bacterial community by eliminating the symbiont Arsenophonus that conferred higher fecundity on N. lugens . CONCLUSION Overall, the new generation fungicides may act as ‘double enemies’ for the pest by being compatible with entomopathogenic fungi and eliminating beneficial symbionts. Our study provides a new avenue for broadening the understanding of the functional effects of fungicides on pest management and highlights their potential to enhance biocontrol effect.