There are many compounds that are derived from plants that are used to repel insects. Some of the most effective are citronella (Mahmud), peppermint (Ansari et al. 2000), geraniol (Mullens et al. 2017), and neem (Garboui et al. 2006). The concentrations and methodologies of the scientific studies used to determine the effects vary greatly, but these studies provide extensive evidence to show that plant based fly sprays work. These products provide an alternative to DEET that avoids the potential toxicity of DEET to the environment (Müller et al. 2009). In fact, citronella is made from lemongrass and was first extracted for the perfume industry (Mahmud et al. 2022). Citronella is used as a GRAS food additive, but of course never use fly spray as a food additive!
Natural fly sprays can work surprisingly well. Müller et al. reports a 97% reduction in mosquito feeding activity with a geraniol diffuser compared to a control group. This is a powerful reduction in mosquito activity. Skakya et al. found that neem oil at all the concentrations they studied had excellent tick repellant activity. They recommended neem oil as part of a tick control program.
In conclusion, plant derived fly sprays can work surprisingly well. They can avoid the environmental problems of chemical fly repellants. Citronella, peppermint, geraniol, and neem are all effective essential oils for fly sprays that have scientific research to support their use. In a good formulation they can provide a powerful fly spray that is also safer than many chemicals.
Ansari, M. A., et al. "Larvicidal and mosquito repellent action of peppermint (Mentha piperita) oil." Bioresource technology 71.3 (2000): 267-271.
Garboui, Samira S., Thomas GT Jaenson, and Katinka Pålsson. "Repellency of MyggA® Natural spray (para-menthane-3, 8-diol) and RB86 (neem oil) against the tick Ixodes ricinus (Acari: Ixodidae) in the field in east-central Sweden." Experimental & applied acarology 40.3 (2006): 271-277.
Mahmud, Faiza, et al. "Biological & insecticidal effect of citronella oil: A short review." Clinical Medicine And Health Research Journal 2.6 (2022): 261-265.
Mullens, Bradley A., et al. "Field trials of fatty acids and geraniol applied to cattle for suppression of horn flies, Haematobia irritans (Diptera: Muscidae), with observations on fly defensive behaviors." Veterinary Parasitology 245 (2017): 14-28.
Müller, Günter C., et al. "Efficacy of the botanical repellents geraniol, linalool, and citronella against mosquitoes." Journal of Vector Ecology 34.1 (2009): 2-8.
Shakya, Mukesh, et al. "Assessment of Antitick and Repellent Activity of Azadirachta indica Oil against Adults and Larvae Stages of Rhipicephalus microplus." Psyche: A Journal of Entomology 2024.1 (2024): 2224036.