Abstract  [Objectives]  To clarify the effects of Beauveria bassiana−maize symbionts (hereafter, symbionts) on the growth and development of the Asian corn borer (Ostrinia furnacalis). [Methods] Symbionts were constructed using the root-irrigation method and fed to O. furnacalis larvae, after which the food consumption, body weight and cumulative survival rate, of larvae were measured and compared. The effect of symbionts on the expression of protective enzymes and key defensive genes was also analyzed, and the ecological mechanisms underlying the effects of symbionts on larvae were clarified. [Results]  There were significant differences in the consumption by larvae of symbionts compared to uninfected plants. The body weight, cumulative survival rate and protective enzyme activities (SOD, POD and CAT) of larvae decreased after feeding on symbionts, expression of immune-related genes was up-regulated, and expression of resistance-related genes was down-regulated. [Conclusion]  Maize colonized by B. bassiana can inhibit the feeding and growth of O. furnacalis larvae. B. bassiana−maize symbionts can regulate insect development by adjusting the protective enzyme activity of insects, and the expression of genes involved in toxin resistance.