**1. Introduction**

Every year more than 700,000 individuals die from diseases transmitted by hematophagous arthropods, of which malaria, dengue, human African trypanosomiasis, leishmaniasis, Chagas disease, yellow fever, Japanese encephalitis, onchocerciasis, and tick-borne encephalitis are particularly detrimental [1]. Hematophagous arthropods such as mosquitoes, triatomine bed bugs, sandflies, blackflies, midges, and ticks derive their nutritional requirement

**Citation:** Hernandez, E.P.; Anisuzzaman; Alim, M.A.; Kawada, H.; Kwofie, K.D.; Ladzekpo, D.; Koike, Y.; Inoue, T.; Sasaki, S.; Mikami, F.; et al. Ambivalent Roles of Oxidative Stress in Triangular Relationships among Arthropod Vectors, Pathogens and Hosts. *Antioxidants* **2022**, *11*, 1254. https://doi.org/10.3390/ antiox11071254

Academic Editor: Serge Ankri

Received: 10 May 2022 Accepted: 21 June 2022 Published: 25 June 2022

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from blood feeding. While some of them are facultative blood feeders such as the female mosquitoes that need blood to trigger oogenesis; others, such as ticks, are obligate blood feeders that solely depend on blood meals from their hosts for their propagations, molting, development, and survival [2–7]. Most of them ingest huge amounts of blood in a single meal ranging from three to ten times their body weight to up to several hundred times their unfed body weight [8,9]. Due to this unique feeding behavior, these arthropods have become efficient bridging agents between vector-borne pathogens and their hosts. Therefore, the control of these vectors could also lead to the control of these diseases. Among blood-feeding arthropods, mosquitoes and ticks are recognized as the most important vectors of pathogens affecting animals or humans. Of the arthropod-borne diseases, only the mosquito-borne pathogens cause high morbidity and mortality globally and the collective global burden of mosquito-borne diseases is not less than that of AIDS. Malaria, a mosquito-borne protozoan disease, alone attributes to 45 million disability-adjusted life years (DALYs) per year and is considered one of the "big three" along with AIDS and tuberculosis [10]. On the other hand, ticks are only second to mosquitoes in terms of their potential to transmit a wide array of devastating pathogens, posing a global threat to both human and animal health. Therefore, the control of these vectors is of public health and veterinary concern [11].

Blood is an excellent source of nutrients for hematophagous arthropods; however, its components including heme, iron, amino acids, and even water could be deleterious for the attacking vectors themselves. Heme and free iron lead to the formation of reactive oxygen species (ROS), resulting in oxidative stress. Previous works of literature have already shed some light into the mechanisms of how vectors are engaged in the neutralization of oxidative stresses for their survival [8,12–14]. In this review, we describe the roles of ROS in mosquitoes and ticks, particularly in vector competency and the development of insecticide/acaricide resistance.
