The effect of inactivated bacteria on the redox status of larvae of the wax moth Galleria mellonella

Insects' defences can be directed at both live and inactivated pathogens. Recognition of pathogen‐associated structures leads to modulation of innate immune responses and oxidative stress in the host. The article presents results of experiments showing that inactivated vegetative cells of Bacillus thuringiensis , B. subtilis and B. cereus can modulate immune responses in Galleria mellonella in the absence of damage to the tissues of the midgut. In the first hours after feeding on Bacillus spp., an increase in the number of immunocompetent haemocytes was observed. Phenoloxidase activity in the haemolymph of wax moth larvae was inhibited, which is confirmed by the suppression of the production of reactive oxygen species (ROS) in haemolymph. In addition, it was found that the antioxidant response to the bacterial inoculation in the midgut and haemolymph is different. Probably, the local antioxidant defence system is configured in such a way that the level of (ROS) increases rapidly to perform useful biological functions and decreases just as quickly, minimising oxidative damage.