Efficacy and safety of catnip (Nepeta cataria) as a novel filth fly repellent*

Catnip (Nepeta cataria) is known for its pseudo‐narcotic effects on cats. Recently, it has been reported as an effective mosquito repellent against several Aedes and Culex species, both topically and spatially. Our laboratory bioassays showed that catnip essential oil (at a dosage of 20 mg) resulted in average repellency rates of 96% against stable flies, Stomoxys calcitrans (L.) and 79% against houseflies, Musca domestica (L.), respectively. This finding suggested that the application of repellent could be used as part of filth fly management. Further evaluations of catnip oil toxicity were conducted to provide a broad‐spectrum safety profile of catnip oil use as a potential biting and nuisance insect repellent in urban settings. Acute oral, dermal, inhalation, primary dermal and eye irritation toxicity tests were performed. The acute oral LD₅₀ of catnip oil was found to be 3160 mg/kg body weight (BW) and 2710 mg/kg BW in female and male rats, respectively. The acute dermal LD₅₀ was > 5000 mg/kg BW. The acute inhalation LD₅₀ was observed to be > 10 000 mg/m³. Primary skin irritation tested on New Zealand white rabbits showed that catnip oil is a moderate irritant. Catnip oil was classified as practically non‐irritating to the eye. In comparison with other U.S. Environmental Protection Agency‐approved mosquito repellents (DEET, picaridin and p‐menthane‐3,8‐diol), catnip oil can be considered as a relatively safe repellent, which may cause minor skin irritation.