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New research from West Lafayette, Purdue University in India, has found that plant-based essential oils can be deadly to bed bugs, especially when combined with deltamethrin. Purdue University’s AgSEED program, the Urban and Industrial Pest Control Center, and the Bilsland Dissertation Fellowship supported this research as part of the PhD thesis for then PhD student Sudip Gaire, who published two articles on the results (both in the journal) Pesticide Biochemistry and – physiologie, 2020 and 2021) with Purdue entomologist Dr. Ameya Gondhalekar and other team members. Dr. Gaire is now a postdoctoral fellow at the University of Kentucky, Lexington, Ky.
“Our results show that essential oils can kill bed bugs, but the combination of essential oils and pyrethroid insecticides has a synergistic effect,” said Dr. Gondhalekar in a Purdue article.
Drs. Gaire and Gondhalekar first tested the pyrethroid insecticide deltamethrin and a range of essential oil compounds on non-resistant bed bugs and a resistant bed bug strain in Knoxville, Tennessee. According to the press release:
The active ingredients in essential oils – thymol from thyme, carvacrol from oregano and thyme, eugenol from cloves and others – worked equally against resistant and non-resistant insects. A dose that was supposed to kill 25 percent killed so many of each type.
Dr. Gondhalekar said that the beetles’ nervous system normally opens and closes sodium channels to pass signals through neurons. Deltamethrin binds to these sodium channels and keeps them open so neurons can’t stop firing. This repeated shooting quickly depletes the beetle’s energy and kills it.
However, resistant bed bugs have several mechanisms to resist pyrethroids, including overactive levels of an enzyme called cytochrome P450, which breaks down deltamethrin. The essential oil compounds, Drs. Gaire and Gondhalekar reported, bind and deactivate this enzyme and allow deltamethrin to do its job in the bed bug’s nervous system.
Drs. Gaire and Gondhalekar combined a single dose of deltamethrin with a single dose of essential oil compounds, which are expected to kill 25 to 50 percent of resistant bed bugs. Instead, more than 90 percent of the resistant bed bugs were killed.
“When we treated the resistant Knoxville bed bugs with various essential oils and tested them for cytochrome P450, we found that these enzymes were inhibited,” said Dr. Gaire. “The essential oil compounds were able to neutralize these enzymes and allow the deltamethrin to do its job.”
According to the press release, Dr. Gondhalekar, continues to research possible formulations of essential oils with additional pyrethroid insecticides and to test them in the laboratory and on site.
