The entomopathogenic fungus Beauveria bassiana employs heterokaryon incompatibility genes in its competitive mechanism against cuticular yeasts of brown planthoppers.

Abstract

BACKGROUND Entomopathogenic fungi (EPF) develop antagonistic strategies to compete with bacteria on the host cuticle surface, facilitating fungal invasion of their host. However, the presence of fungal species on host cuticles and the mechanisms by which EPF compete against cuticular fungi remain unclear. RESULTS Beauveria bassiana is a ubiquitous entomopathogenic fungus with significant potential for biological control of the brown planthopper Nilaparvata lugens. In this study, we demonstrated that three yeast species are dominant on the cuticle surface of N. lugens: Kurtzmaniella quercitrusa, Vanrija humicola and Candida intermedia. These yeasts exhibited significant inhibitory effects on conidial germination but not on blastospore germination. Using K. quercitrusa as a representative species, insect bioassays indicated that conidial virulence was significantly weakened by cuticular yeast compared with blastospores. Notably, the heterokaryon incompatibility gene BbHET-C2 was significantly involved in the resistance of B. bassiana conidia to yeast inhibition. BbHET-C2 played a more significant role in fungal virulence caused by blastospores than by conidia when B. bassiana competed with cuticular yeasts. CONCLUSIONS The current findings reveal that yeasts are dominant on the cuticles of planthoppers and suggest that EPF blastospores are a promising infectious inoculum, with the advantage of competing against fungal defenders in the hosts. These findings provide novel strategies for the development of formulations and strain improvement of insect pathogenic fungi. © 2025 Society of Chemical Industry.