Larvicidal potential of essential oils against Musca domestica and Anopheles stephensi

Proteomic analysis suggests that monoterpenes in lemongrass disrupt Ca2+ homeostasis in Haemaphysalis longicornis leading to mitochondrial depolarization and cytotoxicity

Complex mixtures of bioactive ingredients in plant essential oils present complex chemistries which involve different modes of action. An increasing body of scientific reports has recently focused on the acaricidal activities of plant essential oils attributed to their monoterpene components, but information about their underlying molecular mechanism of action is scarce. Here, after the chemical analysis of lemongrass oil, a proteomic analysis of the ovary, salivary gland, and midgut of Haemaphysalis longicornis exposed to Cymbopogon citratus (lemongrass) essential oil was performed via data-independent acquisition mass spectrometry (DIA-MS) technology to further elucidate the molecular mechanisms involved. Pathway analysis reveals the activation of metabolic pathways mediated by oxidoreductases and transferases. Furthermore, the upregulation of various calcium-associated proteins and the upregulation of cytochrome c1, cytochrome c oxidase polypeptide IV, and programmed cell death protein 6-like isoform X1 suggest a cytotoxic mode of action via the formation of reactive oxygen species (ROS), mitochondrial Ca²⁺ overload, mitochondrial uncoupling, and depolarization, and ATP depletion leading to either apoptotic or necrotic death. Morphological alterations observed after the RNAi of a major detoxification enzyme (glutathione S-transferase) merit further investigation. Hence, the cytotoxic mode of action exhibited by C. citratus oil could be vital for the development of eco-friendly acaricide.

Transcriptome profile of Haemaphysalis longicornis (Acari: Ixodidae) exposed to Cymbopogon citratus essential oil and citronellal suggest a cytotoxic mode of action involving mitochondrial Ca2+ overload and depolarization

Haemaphysalis longicornis is an ixodid tick species of medical and veterinary importance. Investigation into the acaricidal activities of botanicals have increased recently but information about their molecular mechanism of action is scarce. Here, RNA-seq analysis of the ticks exposed to Cymbopogon citratus essential oil and citronellal was performed and the responsive genes were identified. More than 6.39 G clean reads with Q₂₀ ≥ 94.88% were obtained for each H. longicornis sample, with an average GC content of 50.94%. Using the Trinity method, 166,710 unigenes with a mean length of 869 bp and a maximum contig length of 29,156 bp were obtained. The upregulation of genes was concentration-dependent in most of the treated groups. Many genes responsive to C. citratus oil and citronellal were stress-related and they include genes associated with adrenergic signaling/calcium channels, cGMP-PKG signaling, apoptosis, focal adhesion, ECM-receptor interaction, ubiquitin-mediated proteolysis, mTOR signaling pathway, and longevity regulating pathway. The upregulation of genes (CACNAID, ADCY9, TPM1, and MYH6) associated with calcium channels suggests a neurotoxic mode of action, whereas, the upregulation of apoptosis-associated genes (CYC, DRONC, CASP7, CASP9, BCL2L1, bcl-xL, etc.) suggests a cytotoxic mode of action. The metabolism of C. citratus essential oil generates oxidative stress which increases the intra-mitochondrial free Ca²⁺ and triggers the formation of reactive oxygen species (ROS) that culminates to mitochondrial depolarization, ATP depletion, and either necrotic or apoptotic death. The neurotoxic and cytotoxic effects exhibited by the monoterpenes in H. longicornis is vital and could be exploited for the advancement of acaricide development and eco-friendly tick control.

Toxicity of the essential oil from Thymus serpyllum and thymol to larvae and pupae of the housefly Musca domestica L. (Diptera: Muscidae)

The essential oil (EO) of Thymus serpyllum and thymol were evaluated for their insecticidal activity against the housefly (Musca domestica) larvae and pupae. Contact toxicity and fumigation bioassays were used. Chemical composition analysis of T. serpyllum EO by gas chromatographic mass spectrometry (GC-MS) revealed that thymol (41.6%), p-cymene (21.9%), and γ-terpinene (19.2%) were the major components. For larval assays, the LC50 value of T. serpyllum EO was 0.4 μl/cm2 for contact toxicity and 20.9 μl/l for fumigation toxicity. For thymol, the contact toxicity LC50 value was 0.035 μl/cm2 and the fumigation LC50 value was 2.0 μl/l. For the pupal assay, T. serpyllum EO had a percentage inhibition rate (PIR) value of 100% for both contact toxicity (1.0 μl/cm2) and fumigation toxicity assay (25 μl/l), whereas thymol had a PIR of 100% for contact toxicity (0.1 μl/cm2) and fumigation assay (5 μl/l). This study shows that T. serpyllum EO and thymol are toxic to housefly larvae and pupae and have the potential for use in the population control of this species.

Biological activity and safety profile of monoterpenes against Plutella xylostella L. (Lepidoptera: Plutellidae)

Plutella xylostella L. is a cosmopolitan pest of wild and cultivated crucifer vegetables worldwide. It has developed resistance to almost all commercial chemicals, making them one of the most problematic field pests in China. The natural plant extracts and essential oils (EOs) could be a safe alternative for agricultural pests. The development and production of EOs decrease the negative effects of synthetic chemicals. In the present study, the fumigation activity of 8 pure monoterpenes against P. xylostella was evaluated. Results from fumigation tests revealed that 8 tested compounds exhibited various degrees of toxicity against adults of the diamondback moth. Cuminaldehyde was the most toxic compound based on the 12-h LC₅₀ (0.17 mg/L) and 24-h LC₅₀ (0.12 mg/L) values, respectively. Also for larvae and eggs, cuminaldehyde was the most toxic compound. The 12-h LC₅₀ value for cuminaldehyde to 1st, 2nd, and 3rd instar larvae was 0.10 mg/L, 0.12 mg/L, and 0.55 mg/L, respectively. The 24-h LC₅₀ value for the different instar larvae was 0.07 mg/L, 0.09 mg/L, and 0.35 mg/L, respectively. The 24-h LC₅₀ value for eggs (endpoint hatching rate) was 1.95 mg/L for cuminaldehyde, followed by carvacrol and eugenol (2.05 mg/L and 2.31 mg/L, respectively). Cuminaldehyde was very friendly to the larvae and adults of Harmonia axyridis and did not cause any mortality. Our results indicated that cuminaldehyde had potential insecticidal activity against P. xylostella and could be utilized in the novel biological pesticide development.

Adulticidal activities of Cymbopogon citratus (Stapf.) and Eucalyptus globulus (Labill.) essential oils and of their synergistic combinations against Aedes aegypti (L.), Aedes albopictus (Skuse), and Musca domestica (L.)

The knockdown and adulticidal activities of individual Cymbopogon citratus and Eucalyptus globulus essential oils (EOs) and their combinations were evaluated against three medical insect pests (Aedes aegypti, Aedes albopictus, and Musca domestica) using a WHO susceptibility test. The knockdown and adulticidal activities against the three medical insect pests of combinations of C. citratus and E. globulus EOs were higher than those of individual EOs alone. Combinations of 7.5% C. citratus + 7.5% E. globulus EOs and 10% C. citratus + 10% E. globulus EOs exhibited the highest efficacy against females of the three species with 100% knockdown and mortality rates at 1 and 24 h after exposure, respectively. Their adulticidal activities were equivalent to that of 10% w/v cypermethrin. In contrast, 70% v/v ethyl alcohol negative control was not effective at all. The combinations of EOs showed a synergistic effect, i.e., their adulticidal activity was improved by 0.2 to 100%, with increased knockdown and mortality rates, compared to individual EOs. The highest synergistic effect on effective knockdown and adulticidal activities against females of the three species was achieved by a combination of 2.5% C. citratus + 2.5% E. globulus EOs, with 36.6 to 100% knockdown rate increase and 33.5 to 98.9% mortality rate increase. This study demonstrates that all tested combinations of C. citratus and E. globulus EOs were effective adulticidal agents against females of Ae. aegypti, Ae. albopictus, and M. domestica and have a high potential for development into a botanical insecticide for controlling populations of Aedes mosquitoes and houseflies.

Lemon Grass Essential Oil Does not Modulate Cancer Cells Multidrug Resistance by Citral-Its Dominant and Strongly Antimicrobial Compound

With strong antimicrobial properties, citral has been repeatedly reported to be the dominant component of lemongrass essential oil. Here, we report on a comparison of the antimicrobial and anticancer activity of citral and lemongrass essential oil. The lemongrass essential oil was prepared by the vacuum distillation of fresh Cymbopogon leaves, with a yield of 0.5% (w/w). Citral content was measured by gas chromatography/high-resolution mass spectrometry (GC-HRMS) and determined to be 63%. Antimicrobial activity was tested by the broth dilution method, showing strong activity against all tested bacteria and fungi. Citral was up to 100 times more active than the lemongrass essential oil. Similarly, both citral and essential oils inhibited bacterial communication and adhesion during P. aeruginosa and S. aureus biofilm formation; however, the biofilm prevention activity of citral was significantly higher. Both the essential oil and citral disrupted the maturated P. aeruginosa biofilm with the IC₅₀ 7.3 ± 0.4 and 0.1 ± 0.01 mL/L, respectively. Although it may seem that the citral is the main biologically active compound of lemongrass essential oil and the accompanying components have instead antagonistic effects, we determined that the lemongrass essential oil-sensitized methicillin-resistant S. aureus (MRSA) and doxorubicin-resistant ovarian carcinoma cells and that this activity was not caused by citral. A 1 mL/L dose of oil-sensitized MRSA to methicillin up to 9.6 times and a dose of 10 µL/L-sensitized ovarian carcinoma to doxorubicin up to 1.8 times. The mode of multidrug resistance modulation could be due to P-glycoprotein efflux pump inhibition. Therefore, the natural mixture of compounds present in the lemongrass essential oil provides beneficial effects and its direct use may be preferred to its use as a template for citral isolation.

Essential Oils Extracted from Different Species of the Lamiaceae Plant Family as Prospective Bioagents against Several Detrimental Pests

On the basis of the side effects of detrimental synthetic chemicals, introducing healthy, available, and effective bioagents for pest management is critical. Due to this circumstance, several studies have been conducted that evaluate the pesticidal potency of plant-derived essential oils. This review presents the pesticidal efficiency of essential oils isolated from different genera of the Lamiaceae family including Agastache Gronovius, Hyptis Jacquin, Lavandula L., Lepechinia Willdenow, Mentha L., Melissa L., Ocimum L., Origanum L., Perilla L., Perovskia Kar., Phlomis L., Rosmarinus L., Salvia L., Satureja L., Teucrium L., Thymus L., Zataria Boissier, and Zhumeria Rech. Along with acute toxicity, the sublethal effects were illustrated such as repellency, antifeedant activity, and adverse effects on the protein, lipid, and carbohydrate contents, and on the esterase and glutathione S-transferase enzymes. Chemical profiles of the introduced essential oils and the pesticidal effects of their main components have also been documented including terpenes (hydrocarbon monoterpene, monoterpenoid, hydrocarbon sesquiterpene, and sesquiterpenoid) and aliphatic phenylpropanoid. Consequently, the essential oils of the Lamiaceae plant family and their main components, especially monoterpenoid ones with several bioeffects and multiple modes of action against different groups of damaging insects and mites, are considered to be safe, available, and efficient alternatives to the harmful synthetic pesticides.

Efficacy of Origanum vulgare essential oil and carvacrol against the housefly, Musca domestica L. (Diptera: Muscidae)

The toxicity of Origanum vulgare essential oil to the housefly Musca domestica L. was evaluated. The major constituents of the O. vulgare essential oil by gas chromatographic mass spectrometry (GC-MS) analysis were carvacrol (58.13%), p-cymene (17.85%), thymol (8.15%), γ-terpinene (4.96%), and linalool (3.69%). Toxicity of O. vulgare essential oil against larvae and pupae was evaluated using fumigation and contact assays. The contact toxicity (LC₅₀) of O. vulgare essential oil and carvacrol for larvae was 0.23 and 0.03 μL/cm², respectively. The fumigation toxicity (LC₅₀) of O. vulgare essential oil and carvacrol for larvae was 9.52 and 2.78 μL/L, respectively. Pupal toxicity was evaluated by percentage inhibition rate (PIR). PIR of O. vulgare essential oil at 0.25 μL/cm² was 90.9% for the contact assay and 100% at 20 μL/L for the fumigation assay. PIR of carvacrol was 29.5% (0.025 μL/cm²) and 81.8% (1.25 μL/L) for the contact toxicity and fumigation assay, respectively. O. vulgare essential oil and carvacrol have significant toxicity to the housefly and are potential insecticides for housefly control.

Preparation of Retinoyl-Flavonolignan Hybrids and Their Antioxidant Properties

Antioxidants protect the structural and functional components in organisms against oxidative stress. Most antioxidants are of plant origin as the plants are permanently exposed to oxidative stress (UV radiation, photosynthetic reactions). Both carotenoids and flavonoids are prominent antioxidant and anti-radical agents often occurring together in the plant tissues and acting in lipophilic and hydrophilic milieu, respectively. They are complementary in their anti-radical activity. This study describes the synthesis of a series of hybrid ester conjugates of retinoic acid with various flavonolignans, such as silybin, 2,3-dehydrosilybin and isosilybin. Antioxidant/anti-radical activities and bio-physical properties of novel covalent carotenoid-flavonoid hybrids, as well as various mixtures of the respective parent components, were investigated. Retinoyl conjugates with silybin—which is the most important flavonolignan in silymarin complex—(and its pure diastereomers) displayed better 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity than both the parent compounds and their equimolar mixtures.

Eucalyptus globulus (Labill.) : un arbre à essence aux mille vertus

Eucalyptus globulus (Labill.) [Myrtaceae] est originaire de Tasmanie en Australie et pousse surtout dans les régions chaudes. L’eucalyptus commun ou gommier bleu est un arbre sempervirent qui peut croître jusqu’à 30–55 m de haut. Ses feuilles sont la principale source de son huile essentielle (HE). Utilisée pour ses vertus médicinales, notamment antitussives et expectorantes, elle n’en a pas moins des propriétés fébrifuges, toniques, astringentes, antiseptiques, hémostatiques et vermifuges. Parmi ces composés, le 1,8- cinéole ou eucalyptol (50 à 80 %) est sans doute le plus connu, car c’est un expectorant qui peut soulager la toux et lutter contre les problèmes des voies respiratoires. En outre, pinène, limonène et au moins 250 autres composés dont citronellal, cryptone, pipéritone viendront étoffer la liste des nombreux composés aux vertus médicinales de l’eucalyptus. En phytoaromathérapie, l’essence d’eucalyptus officinal pourra trouver une place comme désinfectant atmosphérique en milieu hospitalier afin de lutter contre les infections nosocomiales et les contaminations aéroportées. Elle aide aussi à lutter contre l’asthme et peut être utilisée pour la désinfection de plaies. Notre travail se veut une revue de la littérature des propriétés thérapeutiques, préventive et/ou curative, de cet arbre à parfum et les potentiels utilisations de son HE en phytoaromathérapie anti-infectieuse ou encore comme ingrédient actif dans les préparations pharmaceutiques.

Lethal and Repellent Effects of the Botanical p-Anisaldehyde on Musca domestica (Diptera: Muscidae)

The house fly, Musca domestica L., is a globally distributed nuisance and disease-carrying urban and livestock pest. Control mostly relies on synthetic insecticides but resistance to them has become problematic. p-Anisaldehyde, a compound found in many edible plants, was assessed for its effects on different life stages of M. domestica. Whereas p-anisaldehyde, applied as an adult contact spray, caused >80% mortality by 30 min at a 30% concentration, egg mortality on treated substrate was complete at 0.1%, and the LC90 was 0.024%. Only 0.5 and 1 ml of 1.5% p-anisaldehyde mixed into 100 g of cow manure curtailed pupation. When the amount of p-anisaldehyde was increased to 2 ml, 0.75% p-anisaldehyde reduced pupation by 95.5%. In static air olfactometer tubes, 0.075% p-anisaldehyde repelled substantial numbers of adult M. domestica within 30 min. Repellency of 60-78% was maintained throughout the 4-h bioassay. This study demonstrates that p-anisaldehyde is strongly bioactive against M. domestica in terms of lethal and nonlethal effects.

Repellency potential of essential oils against housefly, Musca domestica L

In present study, the essential oils such as Mentha piperita (mentha oil, M.O), Cymbopogan citratus (lemongrass oil, LG.O), Citrus sinensis (orange oil, O.O), and Eucalyptus globulus (eucalyptus oil, E.O) were evaluated for repellency against housefly (Musca domestica) in a specially designed chamber. Further, to study any synergistic effect, essential oil combinations, i.e., M.O + LG.O, M.O + O.O, and M.O + E.O, were screened at 50:50 and 70:30 ratios. The results showed superior repellency of mentha and mentha + lemongrass (70:30) with RC₉₅ value of 0.009 μl/cm³. The other oils and combinations showed higher values of RC₉₅ (0.010-0.041 μl/cm³). The order of repellency was observed to be mentha = mentha + lemongrass (70:30) > mentha + lemongrass (50:50) = lemongrass = mentha + orange (50:50) = mentha + orange (70:30) > mentha + eucalyptus (70:30) > orange > mentha + eucalyptus (50:50) > eucalyptus. Chemical composition of selected essential oils indicated various monoterpenes as active components for efficient repellency. The essential oil of mentha marked the presence of menthol (38%) and menthone (27%) in major fractions, whereas citral (49%) was found dominating in lemongrass oil. Eucalyptus and orange oils showed the presence of 1,8-cineole (85%), and limonene (87%), respectively, as major components of oils. Further, monoterpenes (menthol and limonene) were also evaluated for repellency against housefly. The data showed 90 ± 5 and 60 ± 5% repellency from menthol and limonene, respectively, after 1 h, indicating the vital role of monoterpenes in overall efficacy of essential oil.