Insecticidal and Repellent Activity of Thymus quinquecostatus Celak. Essential Oil and Major Compositions against Three Stored-Product Insects

Chemical profiling and bioactivities of essential oils from Thymus capitatus and Origanum compactum against Tribolium castaneum

The use of essential oils has emerged as an ecofriendly solution for controlling different pests, particularly insects of stored products. Essential oils (EOs) from Thymus capitatus (TC) and Origanum compactum (OC) have received less attention for these bioactivities. Therefore, our study aimed to assess the repellent, antifeedant and contact toxicity of their EOs against a major stored product pest Tribolium castaneum. Besides, GC-MS was also carried out to determine the compounds responsible for the observed bioactivities. Regarding contact toxicity, LC50 values were 0.58 and 0.35 μL/cm2 for TC and OC after 24 h of exposure, respectively. For the repellent effect, the percentage of repellency (PR) was variable across different concentrations and exposure durations. TC exhibited the best PR (98%) after 3 h of exposure at 0.031 μL/cm2. For prolonged repulsive effect (24 h), TC sustained its repulsive efficacy with a PR of 90% at 0.062 μL/cm2 followed by OC with a PR of 88% at 0.125 μL/cm2. As for the antifeedant effect, both EOs had a significant impact on nutritional indexes, especially the feeding deterrent index and relative consumption rate. OC displayed a notable effect, causing 59% of feeding deterrence at 1.92 μL/pellet. These multifaced effects can be explained by the high content of carvacrol in both EOs (OC: 90% and TC: 78%). These multifaced effects demonstrated through different exposure routes and bioassays promote the use of T. capitatus and O. compactum EOs as a sustainable management strategy to control T. castaneum.

Multi-dimensional preparation of Thymus quinquecostatus Celak. by normal-phase flash chromatography coupled to counter-current chromatography

In this study, a multi-dimensional chromatography system was developed by integrating normal-phase flash chromatography and counter-current chromatography to isolate flavonoids, phenylpropanoids, and thymol from the aerial parts of Thymus quinquecostatus Celak. In the online multi-dimensional switching system, a normal-phase flash chromatograph packed with 1.2 g of dry homogeneous silica gel mixture (containing 600 mg of methanol extract) was connected to counter-current chromatography via a six-port valve. Two two-dimensional separations were performed using n-heptane-ethyl acetate-methanol-water (6:4:6:4, v/v) and ethyl acetate-water solvent systems sequentially to separate the constituents of Thymus quinquecostatus Celak. The upper phase of the former solvent system was utilized as both elution solvent for flash chromatography and the stationary phase for counter-current chromatography, while the lower phase of the latter solvent system containing 10 mM trifluoroacetic acid was employed as elution solvent for flash chromatography and one mobile phase in pH gradient counter-current chromatography. Thymol (7) and xanthomicrol (8), two hydrophobic ingredients, were purified in the initial two-dimensional separation. The subsequent two-dimensional separation yielded six hydrophilic compounds, namely dihydrokaempferol-7-O-D-glucopyranoside (1), lithospermic acid (2), luteolin-7-O-glucuronide (3), rosmarinic acid (4), messerschmidin (5) and apigenin-7-O-D-glucuronide (6). This study represents the first documented use of online multi-dimensional normal-phase flash chromatography coupled to counter-current chromatography for separating constituents from Thymus quinquecostatus Celak.

Bioactivity of Deverra tortuosa essential oil, its nanoemulsion, and phenylpropanoids against the cowpea weevil, a stored grain pest with eco-toxicological evaluations

The essential oil (EO) was hydrodistilled from of Deverra tortuosa aerial parts. Fifty-six components amounting 99.3% were identified in EO through using gas chromatography-flame ionization detection (GC-FID) and (GC-MS). Phenylpropanoids, dillapiole (41.6%), elemicin (7.3%) and myristicin (5.1%), and the monoterpene, sabinene (4.2%) were identified as the major terpenes. An oil-in-water nanoemulsion (particle size 70.3 nm) was developed from EO adopting a low-energy method. The EO products showed insecticidal and biochemical effects against the cowpea weevil Callosobruchus maculatus. Based on a 48-h exposure period, the oil nanoemulsion exhibited a superior contact bioactivity (LC₅₀ = 10.3 µg/cm²), followed by EO (LC₅₀ = 23.1 µg/cm²), dillapiole (LC₅₀ = 27.8 µg/cm²), and myristicin (LC₅₀ = 37.1 µg/cm²). Upon fumigation, nanoemulsion and EO were superior as fumigants (LC₅₀ after 48 h were 6.9 and 14.3 µl/l, respectively). Test materials showed a residual bioactivity against C. maculatus, where EO, dillapiole, and myristicin showed the strongest grain protecting activity. EO products significantly inhibited acetylcholinesterase (AChE) activity of C. maculatus adults. Test products were safe toward the non-target earthworms and did not alter the viability of cowpea seeds. There are evidences for the potential of using EO of D. tortuosa and its nanoemulsion and phenylpropanoids as natural grain protectants against C. maculatus.

The Chemical Composition and Biological Activities of Essential Oil from Korean Native Thyme Bak-Ri-Hyang (Thymus quinquecostatus Celak.)

Thymus quinquecostatus Celak. (Korean name: bak-ri-hyang) is an important medicinal and aromatic herb in Korea, which is named for the spread of its fragrance over a distance of approximately 40 km. In traditional Korean systems of medicine, T. quinquecostatus has been used to treat cancer, constipation, hepatic disease, arteriosclerosis, poor circulation in women, constipation, and menstrual irregularities. At present, T. quinquecostatus is used only for ornamental and ground cover purposes. A literature search was conducted to retrieve information regarding the essential oil composition and biological properties of T. quinquecostatus from PubMed, Science Direct, Wiley, Springer, Taylor and Francis, Wiley, and other literature databases. T. quinquecostatus can be divided into different chemotypes, such as γ-terpinene, thymol, phenol, carvacrol, and geraniol, according to the presence of major components in its essential oil. Further, the essential oil from T. quinquecostatus has been reported to possess various therapeutic properties such as antioxidant, antimicrobial, anticancer, anti-inflammatory, analgesic, sleep prolonging, soothing, skin protection and whitening, anti-aging, anti-obesity, and anti-acne properties. In conclusion, this review will be helpful for utilizing the T. quinquecostatus plant in different industries including food, pharmaceuticals, pesticides, perfumery, and cosmetics.

Chemical Profiles and Insecticidal Potential of Essential Oils Isolated from Four Thymus Species against Rhyzopertha dominica (F.)

Although chemical pesticides have been efficiently used to manage insect pest, their overuse has led to environmental contamination and threats to human health, enticing researchers to introduce eco-friendly and effective agents. In this study, the insecticidal effectiveness of essential oils isolated from Thymus species, including T. eriocalyx, T. kotschyanus, T. fallax, and T. vulgaris, was evaluated against the adults of Rhyzopertha dominica. The terpenes p-cymene, 1,8-cineole, linalool, α-terpineol, and carvacrol were the prominent compounds in the hydrodistilled essential oils. All essential oils produced significant fumigant at 24, 48, and 72-exposure times. The energy reserves protein by all essential oils, glycogen by T. kotschyanus and T. vulgaris, and lipid by T. fallax and T. vulgaris were significantly decreased compared to control. All essential oils except T. vulgaris affected the amylolytic and proteolytic activity of the pest. The pest increased the α- and β-esterase enzyme activity in response to the essential oils. Nutritional indices of adults were also affected by essential oils, in which feeding deterrence index was calculated from 20.41% to 61.11%. Accordingly, based on lethal and extensive sub-lethal insecticidal activities, T. eriocalyx, T. kotschyanus, T. fallax, and T. vulgaris essential oils can be considered as efficient agents for R. dominica management.

Toxics or Lures? Biological and Behavioral Effects of Plant Essential Oils on Tephritidae Fruit Flies

The family Tephritidae (Diptera) includes species that are highly invasive and harmful to crops. Due to globalization, international trade, and human displacement, their spread is continuously increasing. Unfortunately, the control of tephritid flies is still closely linked to the use of synthetic insecticides, which are responsible for detrimental effects on the environment and human health. Recently, research is looking for alternative and more eco-friendly tools to be adopted in Integrated Pest Management (IPM) programs. In this regard, essential oils (EOs) and their main compounds represent a promising alternative to chemical insecticides. EOs are made up of phytoconstituents formed from the secondary metabolism of many plants and can act as attractants or toxics, depending on the dose. Because of this unique characteristic, EOs and their main constituents are promising tools that can be used both in Sterile Insect Technique (SIT) programs and in the "lure and kill" technique, exploiting the attractiveness of the product in the former case and its toxicity in the latter. In this article, current knowledge on the biological and behavioral effects of EOs and their main constituents on tephritid fruit flies is reviewed, mainly focusing on species belonging to the Anastrepha, Bactrocera, Ceratitis, and Zeugodacus genera. The mechanisms of action of EOs, their real-world applications, and challenges related to their use in IPM are critically discussed.