Screening for Enhancement of Permethrin Toxicity by Plant Essential Oils Against Adult Females of the Yellow Fever Mosquito (Diptera: Culicidae)

Abstract

<jats:title>Abstract</jats:title> <jats:p>Aedes aegypti L. (Diptera: Culicidae) is one of the most medically important mosquito species, due to its ability to spread viruses of yellow fever, dengue fever, and Zika in humans. In this study, the insecticidal activity of 17 plant essential oils was evaluated via topical application against two strains of Ae. aegypti mosquito, Orlando (insecticide-susceptible) and Puerto Rico (pyrethroid-resistant). Initial screens with the Orlando strain showed that cucumber seed oil (2017 sample) was the most toxic, followed by sandalwood and thyme oil. When the essential oils were mixed with permethrin, they failed to show any significant synergism of insecticidal activity. Sandalwood and thyme oils displayed consistently high mortality against the resistant Puerto Rico strain, with low resistance ratios of 2.1 and 1.4, respectively. In contrast, cucumber seed oil showed significantly less activity against Puerto Rico mosquitoes, with a resistance ratio of 45. Bioactivity-guided fractionation of the 2017 sample of cucumber seed oil sample via flash column chromatography produced 11 fractions, and gas-chromatography/mass spectrometry analysis revealed that the three active fractions were contaminated with 0.33, 0.36, and 0.33% of chlorpyrifos-methyl, an organophosphorus insecticide, whereas inactive fractions did not show any trace of it. These results suggested that the insecticidal activity of cucumber seed oil was probably due to the presence of the insecticide, later confirmed with a clean batch of cucumber seed oil obtained in 2018, which showed negligible insecticidal activity. These findings demonstrate clearly the need for essential oil analysis to confirm purity before any claims are made about pesticidal potency.</jats:p>

Adult Mosquito and Butterfly Exposure to Permethrin and Relative Risk Following ULV Sprays from a Truck-Mounted Sprayer

“…Since interpreting residues measured on mosquitoes following ULV sprays was a goal of the present study, we analyzed permethrin concentrations on the mosquitoes following the toxicity tests to minimize potential errors in the reported effect concentrations. The 24-h LD50 we determined for Aa (81 ng/g) was within the range of toxicity values (17–440 ng/g) determined for Aa strains reported as susceptible to permethrin (Agramonte et al 2017 ; Chansang et al 2018 ; Estep et al 2018 ; Tak et al 2020 ). It was lower than the toxicity values for strains reported as relatively resistant to permethrin (350–6690 ng/g) (Estep et al 2018 ).…”

“…A risk comparison for butterflies and mosquitoes requires data on toxicity and exposure for both insect groups. Several studies have reported 24-h LD50s for adult mosquitoes exposed to permethrin (Pridgeon et al 2008 , Agramonte et al 2017 , Chansang et al 2018 , Estep et al 2018 , Taylor-Wells et al 2018 , Tak et al 2020 and Baker et al 2023 ). The toxicity values reported in those studies ranged from 49 to 6960 ng/g for five different species ( Culex quinquefasciatus Say, Anopheles quadrimaculatus Say, Aedes aegypti Linnaeus, Anopheles gambiae Giles and Aedes albopictus Skuse).…”

Co-Toxicity Factor Analysis Reveals Numerous Plant Essential Oils Are Synergists of Natural Pyrethrins against Aedes aegypti Mosquitoes

“…While this study identified a number of novel synergistic plant essential oils, some apparent differences from other studies were noted. For example, Tak et al [8] showed that 10 μg/female doses of cedarwood, dill, and fennel oils applied in combination with permethrin did not produce statistically significant mortality greater than permethrin alone, whereas cedarwoods, dillweed and dillseed, and fennel oils synergized natural pyrethrins at the specific doses studied here. The greater potential of plant essential oils to increase the toxicity of natural pyrethrins vs. permethrin may result from greater susceptibility of natural pyrethrins to metabolic degradation than permethrin.…”

“…Plant essential oils were obtained from Berje, Inc. (Carteret, NJ, USA). Oils were selected for their novelty compared to what has been screened previously in the literature [6,8,9,[11][12][13][14]. Natural pyrethrins were obtained from Fairfield American Corp. (Newark, NJ, USA).…”

“…Coupled with the recent consumerdriven push for more natural and "green" control strategies, more of these products are now available for purchase than ever before [3,5]. While not as potent as synthetic insecticides, their potential to kill and repel arthropods is appreciable [6][7][8]. Moreover, many oils have been shown to produce potent synergism with various synthetic insecticides, further demonstrating their utility.…”