WEST LAFAYETTE, Ind. —Bed bugs hide in dark, invisible spaces and multiply rapidly, making them difficult to control. This job has become even more difficult in recent years, as pests have developed resistance to insecticides long used to eradicate them from homes, hotel rooms and other spaces.
Vegetable essential oils are usually fatal bedbugs, but it is not clear how to use them most effectively. Now Purdue University Entomologist Ameya Gondhalekar and his former doctorate. Student, Sudip equipment, discovered how essential oil compounds act on the physiology of bedbugs and showed how they can improve the lethality of pyrethroids, a class of commercial and household insecticides.
“We have seen that we can kill resistant bed bugs with traditional pyrethroid insecticides, but we have to use more and more quantities. Applying them at these levels is a problem, ”said Gondhalekar, associate professor of entomology research. “Our results show that essential oils can kill bedbugs, but the combination of essential oils and pyrethroid insecticides has a synergistic effect.”
Gaire and Gondhalekar first tested the pyrethroid insecticide deltamethrin and a series of essential oil compounds on non-resistant bedbugs and a resistant Knoxville bedbug strain. A single dose of deltamethrin believed to kill 25% of bedbugs killed as many non-resistant bedbugs, but it took 70,000 times more to kill 25% of the Knoxville strain.
“Deltamethrin is so ineffective against the Knoxville strain of bedbugs that if you use it in the field, even in high doses, you will have almost no control,” Gaire said.
The active ingredients in essential oils – thyme thymol, oregano and thyme carvacrol, clove eugenol and others – have worked the same against resistant and non-resistant insects. One dose meant to kill 25% killed as many of each type.
Gondhalekar said the nervous systems of insects normally open and close sodium channels to transmit signals through neurons. Deltamethrin binds to these sodium channels and keeps them open so neurons cannot stop functioning. This repeated shot quickly uses up the insect’s energy and kills it.
But resistant bed bugs have multiple mechanisms to resist pyrethroids, including overactive levels of an enzyme called cytochrome P450, which breaks down deltamethrin. The essential oil compounds, reported by Gaire and Gondhalekar, bind to this enzyme and deactivate it and allow deltamethrin to do its job on the bedbug nervous system.
Gaire and Gondhalekar combined a single dose of deltamethrin with a single dose of essential oil compounds that are expected to kill 25 to 50 percent of resistant bed bugs. Instead, it killed over 90 percent of resistant bed bugs.
“When we treated the resistant Knoxville bed bugs with different essential oils and tested for cytochrome P450, we found that these enzymes were inhibited,” Gaire said. “The essential oil compounds were able to neutralize these enzymes, allowing deltamethrin to do its job.”
Gondhalekar’s lab will continue to research potential formulations of essential oils with pyrethroid insecticides and test them in the lab and in the field to maximize pest control. The AgSEED program at Purdue University, the Center for Urban and Industrial Pest Management, and the Bilsland Dissertation Fellowship supported this research as part of Gaire’s thesis.
Writer: Brian Wallheimer; 765-532-0233; [email protected]
Sources: Ameya Gondhalekar; 765-494-3839
Sudip Gair; [email protected]
Drawing pins, Cimex lectularius L., with metabolic and target site resistance to deltamethrin are sensitive to vegetable essential oils
Sudip Gaire, Cari D. Lewis, Warren Booth, Michael E. Scharf, Wei Zheng, Matthew D. Ginzel, Ameya D. Gondhalekar
Resistance to pyrethroids has been a major obstacle limiting the effective control of bedbugs (Cimex lectularius L.). Alternative approaches that include the use of vegetable essential oils (EST) have been proposed for effective management of bedbugs. However, no comparison of EO resistance levels between susceptible and pyrethroid resistant bed bug populations has been done previously. The objective of this study was twofold: (i) to determine the levels of resistance to deltamethrin and the associated resistance mechanisms in the Knoxville strain collected in the field and (ii) to quantify the resistance levels of the Knoxville strain at five ET (thyme, oregano, clove, geranium and coriander), their main insecticidal constituents (thymol, carvacrol, eugenol, geraniol and linalool) and an EO-based product (EcoRaider®). First, we found that the Knoxville strain was 72,893 and 291,626 times more resistant to topically applied deltamethrin compared to the LD-sensitive Harlan strain.25 and LD50 lethal dose levels, respectively. Synergistic bioassays and enzyme detoxification assays revealed significantly higher activity of cytochrome P450 and esterase enzymes in the resistant Knoxville strain. In addition, Sanger sequencing revealed the presence of the L925I mutation in the voltage-sensitive sodium channel subunit gene. The Knoxville strain which possesses both enzyme resistance and resistance to target site deltamethrin, however, showed no resistance to EOs, their main insecticidal constituents and EcoRaider® in topical bioassays (resistance report d ‘about 1). In conclusion, this study demonstrated that a strain of bedbugs resistant to deltamethrin is sensitive to EOs and their insecticidal constituents.
The constituents of vegetable essential oils increase the toxicity of deltamethrin in a resistant population of bedbugs (Cimex lectularius L.) by inhibiting cytochrome P450 enzymes
Sudip Gaire, Wei Zheng, Michael E. Scharf, Ameya D. Gondhalekar
Plant essential oils (EO) are secondary metabolites derived from aromatic plants that are composed of complex mixtures of chemical constituents. EOs have been proposed as one of the alternative methods for bedbugs (Cimex lectularius L.) control. In insecticide-resistant mosquitoes and tobacco cutworm, EOs act synergistically on pyrethroid toxicity by inhibiting detoxification enzymes. However, if EOs and their constituents increase the toxicity of pyrethroids in C. lectularius remained unknown. Therefore, this study was designed to (i) determine the effects of binary mixtures of deltamethrin (a pyrethroid insecticide) with EOs or constituents of EO or EcoRaider® (an EO product) on the mortality of insecticide resistant and sensitive bedbugs, and (ii) assess the effects of pretreatment of EO constituents on the enzymatic detoxification activities of resistant and susceptible populations. Topical bioassays with binary mixtures of individual deltamethrin and EO (eg, thyme, oregano, clove, geranium, or coriander oils) or their major constituents (eg, thymol, carvacrol, eugenol, geraniol, or linalool) or EcoRaider® at doses that kill approximately 25% of bedbugs have caused significant increases in resistant bedbug mortality. However, in the susceptible population, only coriander oil, EcoRaider®, thymol and carvacrol significantly increased the toxicity of deltamethrin. Enzymatic detoxification tests with extracts of bed bug proteins pretreated with EO constituents suggested a selective inhibition of cytochrome P450 activity in the resistant population, but no impact was observed on the activities. esterase and glutathione transferase in either population. Inhibition of P450 activity by EO constituents therefore appears to be one of the mechanisms for increasing the toxicity of deltamethrin in resistant bedbugs.
Agricultural communications: 765-494-8415;
Maureen Manier, Head of Department, [email protected]