Insecticidal activity of chlorine dioxide gas by inducing an oxidative stress to the red flour beetle, Tribolium castaneum

Chlorine dioxide (ClO₂) is a commercial bleaching and disinfection agent. Its fumigant formulation at 200 ppm for 24 h exposure gave a complete lethality to both larvae and adults of the red flour beetle, Tribolium castaneum. This study set up a hypothesis that oxidative stress induced by ClO₂ treatment is a main factor to kill the beetles. To test this hypothesis, two antioxidant enzymes (superoxide dismutase (SOD) and thioredoxin-peroxidase (Tpx)) were annotated from the insect genome and analyzed in their functional links to oxidative stress. An oxidative stress to T. castaneum was simulated by an immune challenge. Gene expressions of both SOD and Tpx were upregulated in the larvae challenged by bacteria. Similarly, an exposure to ClO₂ gas significantly induced the larvae to up-regulate the gene expressions of both SOD and Tpx. Either RNA interference of SOD or Tpx using specific double-stranded RNAs significantly enhanced the lethal activity of the ClO₂ gas treatment. Reactive oxygen species (ROS) amounts were significantly enhanced by the bacterial challenge or ClO₂ treatment. These results suggest that ClO₂ gas induces an oxidative stress by generating ROS, which can be detoxified by the antioxidant activities of SOD and Tpx of T. castaneum. Thus, the excessive oxidative stress derived from a lethal concentration of ClO₂ is an insecticidal factor against T. castaneum.