# Repellency of Veratraldehyde (3,4-Dimethoxy Benzaldehyde) against Mosquito Females and Tick Nymphs
## 1 Introduction  
Vector-borne diseases, such as malaria, Zika virus, Lyme disease, rocky mountain spotted fever, encephalitis and West Nile virus (WNV), require a mosquito, tick or other arthropod to transmit them from animals to humans. Mosquito inhabit practically every region of every continent in the world, except Antarctica, and are important as medical insect pests. In particular, _Culex pipiens_ complex mosquitoes play important roles in the transmission of several pathogens that infect humans, including WNV, St. Louis encephalitis virus and filarial worms [1, 2], as well as wildlife pathogens such as bird malaria (_Plasmodium_ spp.) [3]. The adaptation of _C. pipiens_ complex mosquitoes to human-altered environments combined with their mixed feeding patterns on birds and mammals (including humans) greatly increases the transmission of several avian pathogens to humans [4]. Although _C. pipiens pallens_ females mate but do not seek a blood meal under a short photoperiod [5], their stereotype and domestic species _C. pipiens molestus_ thrives in highly polluted sewers, mates in confined spaces, often enters houses and feeds readily on mammals, including humans. The Asian tiger mosquito _Aedes albopictus_ is native to thetropical and subtropical areas of Southeast Asia but has spread to Europe, North and South America and Africa. It has aggressive daytime biting behavior and is a medically important mosquito due to its ability to transmit many human pathogens and parasites (e.g., yellow fever, dengue fever, WNV, Japanese encephalitis, St. Louis encephalitis, chikungunya viruses and filarial nematodes) [6; 7]. _Huemphysalis longicornis_ is known as an obligate blood feeder tick and to have a three-host life cycle and is native to temperate areas such as Korea, Japan, Eastern China and the Russian Far East and was established as an exotic species in Australia, New Zealand and several island nations in the western Pacific Region, including the USA, in 2017 [8; 9; 10]. In East-Northern Asia, _H. longicornis_ transmits severe fever with thrombocytopenia syndrome virus (SFTSV), which causes human hemorrhagic fever [11], and the relationship between the population density of ticks and the number of patients with SFTSV was 40.4% in Korea [12]. In some regions of New Zealand and Australia, this tick can reduce production in dairy cattle by 25% [13]. Most authorities managing arthropod-borne diseases recommend applying insect repellents, wearing protective clothing or avoiding infested habitats to protect against arthropod bites. Insect repellents, such as products containing synthetic chemicals or plants as active ingredients, are currently available to consumers. The most widely marketed insect repellent worldwide is \(n\),_n_-diethyl-meta-toluamide (DEET) because it is a broad-spectrum repellent that is effective against various mosquito species and ticks. However, since treatment with synthetic chemicals such as DEET is associated with human health risks [14], most people hesitate to apply DEET products to their skin or clothing and deliberately look for other DEET-free repellent products. For these reasons, alternative natural repellents are now very appreciated by consumers, and essential oils of aromatic plants are considered the most promising candidates [15; 16]. Essential oils extracted from many plant species have been demonstrated to have repellent activities against arthropods, including mosquitoes, mites and lice, as well as have the potential to provide efficient and safer repellents for humans and the environment [17; 18; 19; 20]. However, essential oils still do not have widespread application due to some limitations, such as their short-lasting repellency, composition variability and strong smell, which is one of the most negative aspects of their use [21]. Thus, to meet the needs of consumers, natural repellents should have a high efficacy against the target arthropod pests coupled with a pleasant smell.