# Triple-Olfactory Mechanism Synergy: Development of a Long-Lasting DEET–Botanical Composite Repellent Against Aedes albopictus

## TL;DR

This study developed a long-lasting mosquito repellent by combining DEET with plant-based oils, offering better protection than single-ingredient repellents.

## Contribution

A novel hybrid repellent formulation combining DEET and botanical oils for extended mosquito protection.

## Key findings

- A blend of 15% DEET, 15% citronella oil, and 10% camphor oil in alcohol provided 9.45 hours of protection against Aedes albopictus.
- The composite formulation outperformed single-agent repellents like 15% DEET and 10% citronella oil in duration of protection.
- Catnip oil did not significantly enhance repellency in the tested formulation.

## Abstract

Mosquitoes serve as vectors for serious diseases such as dengue fever. However, conventional chemical repellents may contain ingredients that pose risks to human health and the environment. To devise an alternative formulation, this study combined a commonly used chemical repellent with natural plant-derived oils. Mixtures of DEET, citronella oil (derived from lemongrass), camphor oil, and catnip oil were tested to determine the optimal formulation for repelling Aedes albopictus. Using scientific blending methodologies, it was found that a blend consisting of 15% DEET, 15% citronella oil, and 10% camphor oil in alcohol demonstrated the greatest repellent efficacy. In laboratory arm-in-cage tests, this mixture provided protection against mosquito bites for 9.45 h, which was significantly longer than that of repellents such as 15% DEET or 10% citronella oil used alone. Notably, this optimized formulation demonstrates enhanced effectiveness through the synergistic combination of DEET with botanical oils. This novel formula presents a hybrid mosquito repellent formulation combining synthetic and botanical actives, demonstrating extended protection time under controlled laboratory conditions. If proven effective and safe in field scenarios, it could assist communities in preventing mosquito-borne diseases.

Mosquito-borne diseases, including dengue fever, chikungunya, and Zika, continue to pose a substantial global public health challenge. This is largely attributable to the absence of effective vaccines and the expanding distribution of vectors such as Aedes albopictus (Ae. albopictus). Repellents, therefore, remain a critical component of prevention strategies for disease prevention. However, existing formulations have notable limitations. Synthetic repellents such as DEET provide broad-spectrum efficacy but may raise safety concerns, especially at high concentrations. In contrast, botanical repellents, such as citronella and camphor oils, offer more favorable safety profiles but are restricted by short protection durations due to their high volatility. To overcome these drawbacks, this research developed a composite mosquito repellent through the strategic combination of DEET (5–15%), citronella oil (10–20%), and camphor oil (5–15%). This formulation leverages interactions across multiple olfactory pathways to simultaneously enhance efficacy and reduce the DEET concentration. Orthogonal experimental optimization identified an optimized formulation, Mix-3 (consisting of 15% DEET, 15% citronella oil, and 10% camphor oil in 75% ethanol), which achieved a mean complete protection time of 9.45 h. Mix-3 provided longer protection than 7% DEET (mean difference = 5.50 h, p < 0.001), 4.5% IR3535 (2.83 h, p < 0.001), 10% citronella oil (3.58 h, p < 0.001), and 15% DEET (6.50 h, p < 0.001). Catnip oil did not contribute significantly to repellency (p = 0.895). This study demonstrates that the rational combination of synthetic and botanical repellents effectively overcomes the limitations of single-agent formulations, providing a long-lasting and scalable approach for vector control.