Improved adulticidal activity against Aedes aegypti (L.) and Aedes albopictus (Skuse) from synergy between Cinnamomum spp. essential oils

Adulticidal synergy of two plant essential oils and their major constituents against the housefly Musca domestica and bioassay on non-target species

Single and mixture formulations of lemongrass (Cymbopogon citratus (DC.) Stapf.) and star anise (Illicium verum (J. Presl.)) essential oils (EOs) and their major constituents were assayed for their adulticidal activities against housefly, Musca domestica L., and two non-target species, stingless bee (Tetragonula pegdeni Schwarz) and guppy (Poecilia reticulata Peters). The efficacies of the mixture formulations were compared against those of the single formulations and 1.0% α-cypermethrin, a common synthetic insecticide. GC-MS analysis found that the major constituent of lemongrass EO was geranial (45.23%), and that of star anise EO was trans-anethole (93.23%). Almost all mixture formulations were more effective in adulticidal activity against housefly adults than single formulations and 1.0% α-cypermethrin. A mixture of 1.0% lemongrass EO + 1.0% trans-anethole exhibited the strongest synergistic insecticidal activity with a 100% mortality rate (KT50 of 3.2 min and LT50 of 0.07 h). The relative percentage increase in mortality rate over single formulations was between 1.6 and 91.9%. In addition, it was three times more effective than 1.0% α-cypermethrin. To find the mechanism of adulticidal action, scanning electron microscopy (SEM) was done to find morphological aberrations, such as antennal and mouthpart aberrations, after the houseflies were treated with 1.0% lemongrass EO + 1.0% trans-anethole. The aberrations included deformed and abnormal shape of arista and flagellum, change in labellum pigmentation, and damage to pseudotracheae. Regarding toxicity against non-target species, all single and mixture formulations were not toxic to the two non-target species, while 1.0% α-cypermethrin was highly toxic. To conclude, a mixture of 1.0% lemongrass EO + 1.0% trans-anethole can be an excellent, natural, sustainable housefly adulticidal agent.

Deciphering the antifungal mechanism and functional components of cinnamomum cassia essential oil against Candida albicans through integration of network-based metabolomics and pharmacology, the greedy algorithm, and molecular docking

ETHNOPHARMACOLOGICAL RELEVANCE

Fungal pathogens can cause deadly invasive infections and have become a major global public health challenge. There is an urgent need to find new treatment options beyond established antifungal agents, as well as new drug targets that can be used to develop novel antifungal agents. Cinnamomum cassia is a tropical aromatic plant that has a wide range of applications in traditional Chinese medicine, especially in the treatment of bacterial and fungal infections.

AIM OF THE STUDY

The present study aimed to explore the mechanism of action and functional components of Cinnamomum cassia essential oil (CEO) against Candida albicans using an integrated strategy combining network-based metabolomics and pharmacology, the greedy algorithm and molecular docking.

MATERIALS AND METHODS

CEO was extracted using hydrodistillation and its chemical composition was identified by GC-MS. Cluster analysis was performed on the compositions of 19 other CEOs from the published literature, as well as the sample obtained in this study. The damages of C. albicans cells upon treatment with CEO was observed using a scanning electron microscope. The mechanisms of its antifungal effect at a subinhibitory concentration of 0.1 × MIC were determined using microbial metabolomics and network analysis. The functional components were studied using the greedy algorithm and molecular docking.

RESULTS

A total of 69 compounds were identified in the chemical analysis of CEO, which accounted for 90% of the sample. The major compounds were terpenoids (34.04%), aromatic compounds (4.52%), aliphatic compounds (0.9%), and others. Hierarchical cluster analysis of the compositions of 20 essential oils extracted from Cinnamomum cassia grown in different geographical locations showed a wide diversity of chemical composition with four major chemotypes. CEO showed strong antifungal activity and caused destruction of cell membranes in a concentration-dependent way. Metabolic fingerprint analysis identified 29 metabolites associated with lipid metabolism, which were mapped to 23 core targets mainly involved in fatty acid biosynthesis and metabolism. Six antifungal functional components of CEO were identified through network construction, greedy algorithm and molecular docking, including trans-cinnamaldehyde, δ-cadinol, ethylcinnamate, safrole, trans-anethole, and trans-cinnamyl acetate, which showed excellent binding with specific targets of AKR1B1, PPARG, BCHE, CYP19A1, CYP2C19, QPCT, and CYP51A1.

CONCLUSIONS

This study provides a systematic understanding of the antifungal activity of CEO and offers an integrated strategy for deciphering the potential metabolism and material foundation of complex component drugs.

The insecticidal activity of essential oil constituents against pyrethroid-resistant Anopheles funestus (Diptera: Culicidae)

Malaria vector control relies on the use of insecticides for indoor residual spraying and long-lasting bed nets. However, insecticide resistance to pyrethroids among others, has escalated. Anopheles funestus, one of the major African malaria vectors, has attained significant levels of resistance to pyrethroids. Overexpressed P450 monooxygenases have been previously identified in pyrethroid resistant An. funestus. The escalating resistance against conventional insecticides signals an urgent need for identification of novel insecticides. Essential oils have gained recognition as promising sources of alternative natural insecticides. This study investigated six essential oil constituents, farnesol, (-)-α-bisabolol, cis-nerolidol, trans-nerolidol, methyleugenol, santalol (α and β isomers) and essential oil of sandalwood, for the adulticidal effects against pyrethroid-resistant An. funestus strain. The susceptibility against these terpenoids were evaluated on both pyrethroid-susceptible and resistant An. funestus. Furthermore, the presence of overexpressed monooxygenases in resistant An. funestus was confirmed. Results showed that both the pyrethroid-susceptible and resistant An. funestus were susceptible to three EOCs; cis-nerolidol, trans-nerolidol and methyleugenol. On the other hand, the pyrethroid-resistant An. funestus survived exposure to both farnesol and (-)-α-bisabolol. This study however does not show any direct association of the overexpressed Anopheles monooxygenases and the efficacy of farnesol and (-)-α-bisabolol. The enhanced activity of these terpenoids against resistant An. funestus that has been pre-exposed to a synergist, piperonyl butoxide, suggests their potential effectiveness in combination with monooxygenase inhibitors. This study proposes that cis-nerolidol, trans-nerolidol and methyleugenol are potential agents for further investigation as novel bioinsecticides against pyrethroid-resistant An. funestus strain.

Ovicidal toxicity of plant essential oils and their major constituents against two mosquito vectors and their non-target aquatic predators

Plant essential oil (EO) is a natural alternative to synthetic chemical insecticides for mosquito control. EOs from Citrus aurantium L., Cymbopogon citratus (Stapf.), and Cinnamomum verum (J. Presl.) were selected for topical assay of their ovicidal activity against Aedes aegypti (Linnaeus) and Aedes albopictus (Skuse). Their efficacy was compared to that of 1% (w/w) temephos. In addition, their non-toxicity against aquatic mosquito predators, Poecilia latipinna and Poecilia reticulata, was tested. Found by GC-MS analysis, the major constituent of C. verum EO was trans-cinnamaldehyde, of C. aurantium EO was D-limonene, and of C. citratus EO was geranial. Both C. verum EO and trans-cinnamaldehyde at a high concentration (30,000 ppm) exhibited high ovicidal activity against Ae. aegypti and Ae. albopictus eggs after 48 h of incubation with an inhibition rate of 91.0-93.0% for C. verum EO and 96.7-95.2% for trans-cinnamaldehyde. The combination of C. verum EO + geranial exhibited the strongest synergistic inhibition activity (100%) against the two mosquito vectors and was five times more effective than temephos. Moreover, they were not toxic to the non-target fishes. As a safe ovicidal agent for mosquito egg control, the combination of C. verum EO + geranial has excellent potential.

Phytochemical Profiles and Biological Studies of Selected Botanical Dietary Supplements Used in the United States

Based on their current wide bioavailability, botanical dietary supplements have become an important component of the United States healthcare system, although most of these products have limited scientific evidence for their use. The most recent American Botanical Council Market Report estimated for 2020 a 17.3% increase in sales of these products when compared to 2019, for a total sales volume of $11,261 billion. The use of botanical dietary supplements products in the United States is guided by the Dietary Supplement Health and Education Act (DSHEA) from 1994, enacted by the U.S. Congress with the aim of providing more information to consumers and to facilitate access to a larger number of botanical dietary supplements available on the market than previously. Botanical dietary supplements may be formulated for and use only using crude plant samples (e.g., plant parts such as the bark, leaves, or roots) that can be processed by grinding into a dried powder. Plant parts can also be extracted with hot water to form an "herbal tea." Other preparations of botanical dietary supplements include capsules, essential oils, gummies, powders, tablets, and tinctures. Overall, botanical dietary supplements contain bioactive secondary metabolites with diverse chemotypes that typically are found at low concentration levels. These bioactive constituents usually occur in combination with inactive molecules that may induce synergy and potentiation of the effects observed when botanical dietary supplements are taken in their different forms. Most of the botanical dietary supplements available on the U.S. market have been used previously as herbal remedies or as part of traditional medicine systems from around the world. Their prior use in these systems also provides a certain level of assurance in regard to lower toxicity levels. This chapter will focus on the importance and diversity of the chemical features of bioactive secondary metabolites found in botanical dietary supplements that are responsible for their applications. Many of the active principles of botanical dietary substances are phenolics and isoprenoids, but glycosides and some alkaloids are also present. Biological studies on the active constituents of selected botanical dietary supplements will be discussed. Thus, the present chapter should be of interest for both members of the natural products scientific community, who may be performing development studies of the products available, as well as for healthcare professionals who are directly involved in the analysis of botanical interactions and evaluation of the suitability of botanical dietary supplements for human consumption.

Ovicidal and repellent activities of several plant essential oils against Periplaneta americana L. and enhanced activities from their combined formulation

Natural ovicidal and repellent agents against Periplaneta americana L. are urgently needed, and plant essential oils (EOs) can assume this role quite readily. In this study, ovicidal and repellent activities against Periplaneta americana of EOs from Cymbopogon citratus (Stapf.), Cinnamomum verum (J. Presl.), Eucalyptus globulus (Labill.), Illicium verum (Hook.f.), and Zanthoxylum limonella (Alston) in soybean oil and in ethyl alcohol were determined by topical and dual-choice assays, as well as 10% cypermethrin and a combined formulation of 5% C. verum EO + 5% I. verum EO. Cypermethrin at 10% provided the highest toxicity (100% inhibition rate) against the eggs, but only slightly higher than that (99.3%) provided by the combined EO formulation, while the highest repellent activity against the adults was provided by the combined formulation (89.5% repelled cockroaches at 48 h after treatment). In addition, all EO formulations in soybean oil provided higher ovicidal and repellent activities than those in ethyl alcohol. To conclude, the combined EO formulation in soybean oil can replace cypermethrin because their efficacy was nearly equivalent, but the combination should be much safer to use.

Combinations of plant essential oils and their major compositions inducing mortality and morphological abnormality of Aedes aegypti and Aedes albopictus

Extensive uses of synthetic insecticides to control mosquito's populations have induced the insects to develop resistance against them, rendering them ineffective today. Moreover, they cause serious impacts on human health and the ecosystem. Therefore, safe and effective natural alternatives are needed. This study evaluated the larvicidal and pupicidal activities of essential oils (EOs) from Illicium verum and Zanthoxylum limonella and the major constituents against Aedes aegypti and Aedes albopictus mosquitoes as well as recorded their morphological aberrations at death. The GC-MS analysis showed that trans-anethole was the major constituent of I. verum EO, and limonene was the major constituent of Z. limonella EO. Both were more effective against the larvae and pupae of Ae. aegypti than those of Ae. albopictus. A 2.5% I. verum EO + 2.5% trans-anethole combination showed the highest larvicidal and pupicidal effects against Ae. aegypti and Ae. albopictus with an LT₅₀ ranging from 0.2-6.9 h. Between the two tested constituents, trans-anethole exhibited stronger larvicidal and pupicidal activities (LC₅₀ ranging 2.4–3.4%) against the two tested mosquito species than d-limonene (LC₅₀ ranging 2.5–3.7%). Most importantly, 5% trans-anethole, 5% d-limonene, and 2.5% I. verum EO + 2.5% trans-anethole were more effective (LT₅₀ ranging 0.1–0.3 h) than 1% (w/w) temephos (LT₅₀ ranging 2.9–3.1 h). Morphological aberrations at death observed were such as color pigment and thorax shape abnormalities. To conclude, trans-anethole, d-limonene, and a combination of I. verum EO + trans-anethole, are natural compounds that not only are as effective as temephos at the time of this study, but should be also be much safer to human health.

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Trans-anethole and limonene are strongly insecticidal against two mosquito species.

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I. verum EO + trans-anethole was very strong larvicide and pupicide.

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I. verum EO + trans-anethole was much more effective than temephos.

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All formulations effected some morphological changes at time of death.

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These long-used natural compounds should be much safer than temephos.

Larvicidal Activity of Methyl Benzoate, a Volatile Organic Compound, Against the Mosquitoes Aedes albopictus and Culex pipiens (Diptera: Culicidae)

Methyl benzoate (MBe) is a volatile organic molecule found in various plants; it is used as an insect semiochemical. MBe also has a biorational insecticidal effect against various agricultural and urban arthropod pests. The present study was the first to assess the larvicidal potential of MBe against fourth-instar larvae of the mosquitoes Aedes albopictus (Skuse) and Culex pipiens (L.). A positive association was observed between MBe concentrations and larval mortality in both the species. The highest mortality recorded was 100% for Ae. albopictus and 56% for Cx. pipiens after 24 h of exposure to 200 ppm MBe. The lethal median concentration (LC50) values of MBe against fourth-instar larvae of Ae. albopictus and Cx. pipiens were 61 ppm and 185 ppm, respectively. These results suggest that MBe has great potential for use as an environmentally friendly larvicidal agent for mosquito control.

The essential oil of Schinus terebinthifolius and its nanoemulsion and isolated monoterpenes: investigation of their activity against Culex pipiens with insights into the adverse effects on non-target organisms

BACKGROUND

The house mosquito, Culex pipiens L. is a harmful species, widespread in urban areas, and considered the primary enzootic vector of West Nile arbovirus. Widespread insecticide resistance in mosquito populations and the environmental risks and toxicity hazards of chemical pesticides make insecticides an inadequate mosquito control strategy. Seeking ecofriendly tools for mosquito control tools has become necessary.

RESULTS

Essential oil (EO) was hydrodistilled from the fruits of Brazilian pepper, Schinus terebinthifolius Raddi and analyzed using gas chromatography-flame ionization detection and gas chromatography-mass spectrometry. An oil-in-water nanoemulsion (particle size 41.3 nm) was developed and characterized from EO using a green low-energy approach. EO, its nanoemulsion and monoterpenes showed mosquitocidal, repellent and acetylcholinesterase inhibitory activities against Cx. pipiens. A nanoemulsion concentration of 30 μl L^-1 caused 100% larval mortality after 24 h of exposure, whereas EO, d-limonene and α-phellandrene at 60 μl L^-1 caused 100%, 92.4% and 88.2% larval mortality, respectively. The concentration that killed 50% of organisms (LC₅₀ ) for larvae after 24 h ranged between 6.8 and 40.6 μl L^-1 . Upon fumigation, 15.0 μl L^-1 of nanoemulsion killed 94.5% of adults after 24 h of exposure. LC₅₀ values against adults ranged between 5.3 and 31.2 μl L^-1 . EO products exhibited repellence activity at concentrations between 0.5 and 4.0 μl cm^-2 . Test materials effectively inhibited the acetylcholinesterase activity of mosquito and were safe toward the non-target organisms Gambusia affinis and Eisenia fetida.

CONCLUSION

There is a potential for using S. terebinthifolius EO, its nanoemulsion and monoterpenes as ecofriendly natural mosquitocides.

Bioactivity and safety evaluations of Cupressus sempervirens essential oil, its nanoemulsion and main terpenes against Culex quinquefasciatus Say

The essential oil (EO) of Cupressus sempervirens was obtained by hydrodistillation and analysed using gas chromatography-flame ionization detection (GC-FID) and gas chromatography-mass spectrometry (GC-MS). Two monoterpenes, α-pinene (49.1%) and δ-3-carene (21.4%), and one sesquiterpene hydrocarbon, α-cedrol (5.1%), were isolated as the EO major terpenes. An oil-in-water nanoemulsion (particle size 71.2 nm) was produced from the EO through a low-energy method. The EO, its nanoemulsion and its main constituents showed mosquitocidal and biochemical effects against Culex quinquefasciatus Say, the common vector of lymphatic filariasis parasites. All treatments showed dose-dependent bioactivity, and adults were more susceptible to the EO products than the larvae. The nanoemulsion showed superior activity, followed by the crude EO and α-cedrol. At 40 μg/ml, the nanoemulsion caused 100% larval mortality, while the EO and α-cedrol required twice this concentration to achieve the same larval mortality. The LC₅₀ values were 8.4, 16.1, 15.1, 30.7 and 53.4 μg/ml at 24 h after exposure for the nanoemulsion, crude oil, α-cedrol, δ-3-carene and α-pinene, respectively. For adults, 20.0 μl/l nanoemulsion caused 100% mortality, while twice this concentration of the EO was required to achieve the same effect. The LC₅₀'s against adults ranged between 6.2 and 40.4 μl/l. EO products prominently repelled mosquitoes at concentrations between 0.75 and 6.0 μl/cm². The EO products caused remarkable inhibition of Cx. quinquefasciatus acetylcholinesterase activity but were safer towards the non-target aquatic species Gambusia affinis. These results recommend the use of C. sempervirens EO, its nanoemulsion and main terpenes as natural tools to control Cx. quinquefasciatus.

Chemical Composition of Cinnamomum verum Leaf and Flower Essential Oils and Analysis of Their Antibacterial, Insecticidal, and Larvicidal Properties

Cinnamomum verum is widely used in traditional medicines, and the different parts of the plant, such as bark, leaves, and flowers, are used for essential oil production. The present study compared the chemical composition of the essential oil of C. verum extracted from the leaves and flowers. In addition, efficacy of these essential oils against the two common pests Sitophilus oryzae and Callosobruchus maculatus was also evaluated. The results indicated the presence of cinnamaldehyde, eugenol, caryophyllene, and linalool in these essential oils, however, at different concentrations. The leaf essential oil was found to be 10-20% more effective as a fumigant against both the pests. Likewise, the leaf essential oil found to repel these pests even at lower concentrations than that of flower essential oil of C. verum. Besides, these essential oils were also effective in controlling the growth of various gram positive and gram negative microbial pathogens and possibly a safeguard for human health. On contrary, both the essential oils were found to be safe for the application on grains, as indicated by their germination potentials. It was also observed that these essential oils do not cause any significant toxicity to guppy fishes, thus confirming their ecological safety for use as a biopesticide.

Use of Essential Oils for the Control of Anthracnose Disease Caused by Colletotrichum acutatum on Post-Harvest Mangoes of Cat Hoa Loc Variety

Anthracnose disease caused by Colletotrichum spp. makes heavy losses for post-harvest mangoes of Cat Hoa Loc variety during storage, packaging, and transportation. The synthetic fungicides are commonly used to control the disease, but they are not safe for consumers’ health and environment. This study was aimed to investigate the use of essential oils (EOs) as the safe alternative control. Pathogen was isolated from the infected Cat Hoa Loc mangoes and identified by morphology and DNA sequencing of the ITS region. Six EOs (cinnamon, basil, lemongrass, peppermint, coriander, and orange) were chemically analyzed by GC–MS. The antifungal activity of EOs was studied in vitro and in vivo. The results showed that the isolated pathogen was Colletotrichum acutatum. Cinnamon, basil, and lemongrass EOs effectively inhibited the growth of C. acutatum in descending order of cinnamon, basil, and lemongrass. However, they (except basil oil) severely damaged fruit peels. The antifungal activity was closely related to the main compounds of EOs. Basil EOs effectively controlled anthracnose development on Cat Hoa Loc mangoes artificially infected with C. acutatum, and its effectiveness was comparable to that of fungicide treatment. Consequently, basil EOs can be used as a biocide to control anthracnose on post-harvest Cat Hoa Loc mangoes.

Chemical composition of essential oils from Thymus mongolicus, Cinnamomum verum, and Origanum vulgare and their acaricidal effects on Haemaphysalis longicornis (Acari: Ixodidae)

Chemical acaricides are mainly used in traditional tick control, which leads to the emergence of tick resistance and concurrently results in environmental pollution. In the present study, the chemical constituents of essential oils (EOs) from Thymus mongolicus, Cinnamomum verum, and Origanum vulgare was analyzed, and their potential application was evaluated to control the vector tick Haemaphysalis longicornis, which is widely distributed over vast areas of Eurasia, Australia, and New Zealand. Gas chromatography-mass spectrometry analysis revealed that the phenols thymol and carvacrol accounted for 34.66% and 75.72% of the EOs of T. mongolicus and O. vulgare, respectively, whereas trans-cinnamaldehyde (49.42%) was the main constituent of C. verum EO. Immersion tests showed that the EOs of C. verum and O. vulgare had significant acaricidal activity against larval H. longicornis, with the 50% lethal concentration (LC50) being 16.07 and 18.02 mg/mL, respectively, and the 95% lethal concentration (LC95) being 120.37 and 130.09 mg/mL, respectively. The EOs of O. vulgare and T. mongolicus showed significant acaricidal activity against unfed adult H. longicornis, with LC50 being 43.50 and 44.21 mg/mL, respectively, and LC95 being 113.66 and 137.99 mg/mL, respectively. The fumigant toxicity test showed significant acaricidal activity of the three EOs against both unfed and engorged nymphal and adult H. longicornis. Enzyme assays revealed that the EOs of both C. verum and O. vulgare significantly inhibited glutathione S-transferase activity (P < 0.05). In contrast, the activities of carboxylesterase and multifunction oxidases were significantly inhibited by EOs extracted from all three plants (P < 0.05). Taken together, these findings suggest that plant EOs may serve as an environment-friendly alternative for synthetic acaricides in future tick control.