**5. Conclusions**

Mosquitoes and ticks are considered to be the most important vectors in the transmission of human and animal disease-causing pathogens. The vast array of pathogens includes viruses, bacteria, protozoa, and nematodes. Pathogens' acquisition and transmission largely depend on the ability of the pathogens to evade not only the arthropod's immune response but also their physiology. ROS are an integral part of the cellular physiology of any organism. In hematophagous arthropods, high amounts of ROS are produced by heme released during the digestion of blood meals. Moreover, several biological activities such as embryonic and larval development and flight activity augment ROS production. ROS have dual functions and are essential mediators of varieties of biological functions, including immune responses, cell signaling, and maintenance of the natural microbiome. ROS are also crucial in maintaining the natural microbiota in ticks. On the other hand, high amounts of ROS could result in redox imbalance, causing lipid peroxidation and DNA damage, and eventually death. ROS have pivotal roles in the effectiveness of mosquito resistance to insecticides. As pathogens have co-evolved with the arthropods that transmit them, the pathogens have devised ways to adapt to the physiological responses of the arthropods, even making use of their antioxidant response to evade ROS attacks of the host.

For the reasons mentioned above, it is important to consider the antioxidants or the antioxidant system as a potential target group in the development of drugs, vaccines, or other biological and chemical means to control the arthropods and their associated pathogens. In addition to the control aspects, this novel approach would address the vectorial capacity of these arthropods as well as their resistance to insecticides/acaricides. The use of phytochemicals has been a step in the right direction, but further understanding of the mechanism on how these phytochemicals work may be necessary to enable mass production globally.

**Author Contributions:** Conceptualization, E.P.H., T.T., N.T. and T.H.; writing, review, and editing, E.P.H., A. and M.A.A.; review and editing of final manuscript, H.K., K.D.K., D.L., Y.K., T.I., S.S., F.M. and M.M. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported by JSPS KAKENHI Grant Numbers 20F20093 and 20H03001.

**Conflicts of Interest:** The authors declare no conflict of interest.
