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Paenibacillus larvae , the causal agent of American foulbrood disease (AFB), affects Apis mellifera larvae and can induce oxidative stress by overproduction of radical oxygen species (ROS). This study aimed to assess the oxidative stress levels in larvae exposed to three different strains of P. larvae through their diet by examining the ascorbyl radical (A) to ascorbate anion (AH¯) ratio. The results revealed that larvae inoculated with P. larvae exhibited a lower value of this index compared to uninoculated ones. Interestingly, the level of A remained constant, while the concentration of AH¯ increased. Said increase correlated with the virulence of the specific P. larvae strain used in the inoculation. These findings suggest a potential link between AH¯ molecules and a defense response in A. mellifera larvae against infection, consistent with their resistance to P. larvae (LD 50). [Display omitted] • Paenibacillus larvae can induce oxidative stress of Apis mellifera larvae. • Oxidative stress was analyzed by ascorbyl radical (A)/ascorbate anion (AH¯) ratio. • The ratio A /AH¯ of larvae inoculated reflected less oxidative stress that uninoculated ones. • The level of A remained unchanged despite AH¯ increased. • The intensity of AH¯ increased was according to larvae resistance (LD 50). [ABSTRACT FROM AUTHOR]