Although ROS have been proposed to be important defenses against microsporidial infections, e.g., infections of the intestinal epithelium of honeybees by Nosema ceranae (12), we did not find that the two major enzymes known to secrete ROS extracellularly, NOX and Duox, appeared to play a role against injected T. ratisbonensis spores. This evidence concerns the gene DUOX1 and infection.