# Repellency of Veratraldehyde (3,4-Dimethoxy Benzaldehyde) against Mosquito Females and Tick Nymphs
## 4 Discussion  
Veratraldehyde is a derivative of vanillin, from which it is prepared by methylation [30]. Vanillin is a repellent synergism against mosquitoes. Mixtures of vanillin with insect repellents containing DEET prolonged the protection time by more than 100% compared to that of DEET alone [31], and its addition to plant essential oils such as celery oil (_Apium graveleus_) and xanthoxylum oil (_Zanthoxylum armatum_) increased both repellency and duration [16; 32]. In this study, veratraldehyde and its 10% formulation, WJ-1041, provided more than 2 h of complete protection time against _A. albopictus_, _C. pipiens pallens_ and _H. longicornis_ nymphs. The repellent effectiveness and duration of chemicals depend on a variety of factors, including the type of active ingredient, the frequency and formulation of application, test conditions such as mosquito species and involved volunteers, loss due to removal by perspiration and abrasion, intrinsic water loss and the numerical density of mosquitoes [33; 34]. DEET formulations (23.8%) give 5 h of complete protection against _A. aegypti_ bites [35], but IR3535 (7.5%), which is another synthetic insect repellent and has been used in Europe for more than 30 years, yielded poor complete protection time (22.9 min) against _A. aegypti_ bites, and some citronella-based repellents, except for a soybean oil-based repellent showing a 1.5 h protection time, also showed very short durations of repellent activity ranging from approximately 3 to 20 min [35]. A number of products based on plant essential oils, such as citronella, fennel, geranium, lavender and rosemary oils, have been commercialized, but their repellency duration was less than 1 h under field conditions [15]. In addition, MossZero(r) aerosol and cream products containing 5 and 8% fennel oil, respectively, and MeiMei(r) cream containing citronella and geranium oils produced 84, 70 and 57% repellency at 90 min after exposure, respectively, whereas Repellan S(r) aerosol containing 19% DEET produced 89% repellency at 210 min [36]. In addition to active ingredients and formulation type, the concentration contained in a repellent formulation may also be an important factor for repellency. The protection provided by DEET depends mainly on both dose and formulation concentration, and its duration reaches a plateau at a concentration of approximately 50% [37]. However, a higher concentration of DEET contained in a formulation does not necessarily mean better repellency. For instance, three \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Collection Time**} & \multicolumn{3}{c}{**Conc. (ng/mL, Mean \(\pm\) SE)**} \\ \cline{2-4}  & **G1 a** & **G2** & **G3** \\ \hline
0 & 0 \(\pm\) 0 & 0 \(\pm\) 0 & 0.99 \(\pm\) 1.71 \\
0.25 & NA & NA & NA \\
1 & NA & 0.1 \(\pm\) 0.23 & 0.5 \(\pm\) 0.88 \\
2 & NA & 0.5 \(\pm\) 0.86 & 0 \(\pm\) 0 \\
4 & 0.2 \(\pm\) 0.40 & 0 \(\pm\) 0 & 0.04 \(\pm\) 0.07 \\
6 & NA & 0 \(\pm\) 0 & 0 \(\pm\) 0 \\
8 & NA & 0 \(\pm\) 0 & 0 \(\pm\) 0 \\
10 & NA & 0 \(\pm\) 0 & 0.04 \(\pm\) 0.07 \\
12 & NA & 0 \(\pm\) 0 & 0 \(\pm\) 0 \\
24 & NA & 0 \(\pm\) 0 & 0 \(\pm\) 0 \\
48 & NA & 0.4 \(\pm\) 0.69 & 0.1 \(\pm\) 0.15 \\
72 & NA & 1.2 \(\pm\) 2.06 & 0 \(\pm\) 0 \\ \hline \hline \multicolumn{4}{l}{C\({}_{\text{max}}\), ng/mL b  \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Plasma concentration versus time profiles for veratraldehyde after percutaneous application (G1\(\sim\)G3) of veratraldehyde. DEET-based repellents containing 33, 42 and 75% DEET provided similar protection effects after application in different climatic regimens (tropical forest, tropical open and basic hot environments) against _A. aegypti_, _A. taeniorhynchus_ and _Anopheles stephensi_, whereas there was no difference in the protection period against _Anopheles albimanus_[38]. Similarly, the 7% veratraldehyde ethanol solution showed higher repellency (97%) than 10 and 15% solutions at 5 h after treatment in the arm-in-cage test.