Development and evaluation of test methods for commercial spatial repellent products using the common fruit flies in laboratory and simulated-use scenarios

Fruit flies and other miniscule flying insects often cause a nuisance in the kitchen areas of our dwellings. To mitigate the invasion of indoor insect pests, behavioral modifications using spatial repellents containing natural products are emerging as alternatives to chemical insecticides especially around the kitchens and food storage areas. However, the absence of standardized testing methods for spatial repellency has undermined the reliability of these products. We introduced three distinct laboratory-scale repellency assays and their relevancy to simulated-use conditions. Out of eleven commercial products tested, five showed effectiveness in laboratory assays, and three of these were further proven effective in simulated-use tests as well. Another issue limiting the utility of commercially available spatial repellents was the lack of clear and comprehensive use instructions on product labels, potentially leading to ineffective applications. We observed that increasing the applied quantity improved the efficacy of one product that was initially determined to be ineffective in a simulated-use test. Based on our findings, we propose three strategies for regulations of spatial repellents: 1) consideration of mixture effects beyond single active ingredients especially using the natural products as their active ingredients, 2) the use of multiple testing systems, while acknowledging the limitations of laboratory assays in predicting real-world efficacy, and 3) ensuring product labels provide detailed and clear instructions for effective use.