*Review* **Ambivalent Roles of Oxidative Stress in Triangular Relationships among Arthropod Vectors, Pathogens and Hosts**

**Emmanuel Pacia Hernandez 1, Anisuzzaman <sup>2</sup> , Md Abdul Alim 2, Hayato Kawada 1,3, Kofi Dadzie Kwofie 1,4, Danielle Ladzekpo 1,4,5 , Yuki Koike 3, Takahiro Inoue 3, Sana Sasaki 3, Fusako Mikami 1, Makoto Matsubayashi 6, Tetsuya Tanaka <sup>7</sup> , Naotoshi Tsuji 1,3 and Takeshi Hatta 1,3,\***


**Abstract:** Blood-feeding arthropods, particularly ticks and mosquitoes are considered the most important vectors of arthropod-borne diseases affecting humans and animals. While feeding on blood meals, arthropods are exposed to high levels of reactive oxygen species (ROS) since heme and other blood components can induce oxidative stress. Different ROS have important roles in interactions among the pathogens, vectors, and hosts. ROS influence various metabolic processes of the arthropods and some have detrimental effects. In this review, we investigate the various roles of ROS in these arthropods, including their innate immunity and the homeostasis of their microbiomes, that is, how ROS are utilized to maintain the balance between the natural microbiota and potential pathogens. We elucidate the mechanism of how ROS are utilized to fight off invading pathogens and how the arthropod-borne pathogens use the arthropods' antioxidant mechanism to defend against these ROS attacks and their possible impact on their vector potentials or their ability to acquire and transmit pathogens. In addition, we describe the possible roles of ROS in chemical insecticide/acaricide activity and/or in the development of resistance. Overall, this underscores the importance of the antioxidant system as a potential target for the control of arthropod and arthropod-borne pathogens.

**Keywords:** ticks; mosquitoes; oxidative stress; ROS; microbiome; acaricide; insecticide resistance
