Chemical composition and larvicidal activity against Aedes mosquitoes of essential oils from Arisaema fargesii

Essential Oil and Waste Hydrosol of Ocimum Tenuiflorum L.: A Low-Cost Raw Material Source of Eugenol, Botanical Pesticides, and Therapeutic Potentiality

In this study, essential oils and waste hydrosols of leaves of Ocimum tenuiflorum in four different geographical locations were extracted by hydrodistillation method and using gas chromatography/mass spectrometry (GC/MS) for chemical composition analysis. All four essential oil samples contained the main components (E)-β-caryophyllene (27.8-49.0 %), trans-β-elemene (20.3-37.1 %) and eugenol (9.0-44.0 %). Three of the four hydrosol samples had eugenol in absolute content (94.5-98.6 %), while the remaining hydrosol sample had two main components, elemicin (77.8 %) and eugenol (14.2 %). Essential oils and hydrosols demonstrated larvicidal activities against four important disease-transmitting mosquito species including Aedes aegypti, Aedes albopictus, Culex quinquefasciatus, and Culex fuscocephala with 24-h LC50 values in the range 15.42-56.01 μg/mL and 53.88-97.80 μg/mL for the essential oils and the hydrosols, respectively. Essential oils and hydrosols strongly inhibited the acetylcholinesterase (AChE) enzyme of electric eels with IC50 values in the range of 25.35-107.19 μg/mL. Microemulsion (ME) can be considered as a sustainable pesticide formulation over 300 days and has improved larvicidal activity compared to free essential oil. The O. tenuiflorum in Vietnam can be considered a low-cost source of eugenol, botanical pesticides that control disease-transmitting mosquitoes, as well as having therapeutic potential to be further investigated.

Lemongrass essential oil and its major component citronellol: evaluation of larvicidal activity and acetylcholinesterase inhibition against Anopheles sinensis

Mosquito-borne diseases, such as malaria, dengue fever, and the Zika virus, pose significant global health challenges, affecting millions annually. Due to increasing insecticide resistance, there is a growing interest in natural alternatives for mosquito control. Lemongrass essential oil, derived from Cymbopogon citratus, has shown promising repellent and larvicidal properties against various mosquito species. In this study, we investigated the larvicidal effect of lemongrass oil and its major compounds on Anopheles sinensis, the primary malaria vector in China. GC-MS analysis identified the major compounds of lemongrass oil as ( +)-citronellal (35.60%), geraniol (21.84%), and citronellol (13.88%). Lemongrass oil showed larvicidal activity against An. sinensis larvae, with an LC50 value of 119.20 ± 3.81 mg/L. Among the major components, citronellol had the lowest LC50 value of 42.76 ± 3.18 mg/L. Moreover, citronellol demonstrated inhibitory effects on acetylcholinesterase (AChE) activity in An. sinensis larvae, assessed by homogenizing larvae at different time points following treatment. Molecular docking studies further elucidated the interaction between citronellol and AChE, revealing the formation of hydrogen bonds and Pi-Sigma bonds. Aromatic amino acid residues such as Tyr71, Trp83, Tyr370, and Tyr374 played a pivotal role in these interactions. These findings may contribute to understanding lemongrass oil's larvicidal activity against An. sinensis and the mechanisms underlying these effects.

The contact toxicity and toxic mechanism of essential oils from Pimenta racemosa and Eugenia caryophyllata against Haemaphysalis longicornis (Acari: Ixodidae)

Haemaphysalis longicornis, which is widely distributed in China, can transmit various tick-borne diseases such as severe fever with thrombocytopenia syndrome, babesiosis, rickettsia disease and so on, and do great harm to human health and the development of animal husbandry. Chemical acaricides are the most traditional tick control method, but because of its many shortcomings, there is an urgent need to find a substitute with high efficiency, environmental protection and low toxicity. It has been found that some plant essential oils (EOs) have good insecticidal activity and environmental safety. In this study, the components of EOs from Pimenta racemosa and Eugenia caryophyllata were analyzed by gas chromatography-mass spectrometry (GC-MS), and their potential for application in the control of Haemaphysalis longicornis were studied. Gas chromatography-mass spectrometry analysis showed that the main components of P. racemosa EO were eugenol (64.07%), those of E. caryophyllata EO were Hexadecanoic acid, 2-methylpropyl ester (51.84%) and eugenol (39.76%). Larval packet test showed that the EOs of P. racemosa and E. caryophyllata had significant acaricidal activity against unfed larvae of H. longicornis, with LC50 values of 1.20 mg/mL and 0.47 mg/mL and LC90 values of 8.76 mg/mL and 2.91 mg/mL, respectively. The P. racemosa EO, E. caryophyllata EO and eugenol showed significant acaricidal activity against unfed nymph H. longicornis, with LC50 values of 1.65 mg/mL, 2.29 mg/mL and 0.93 mg/mL and LC90 values of 5.03 mg/mL, 11.01 mg/mL and 4.77 mg/mL, respectively. The P. racemosa EO, E. caryophyllata EO and eugenol showed significant acaricidal activity against unfed adults H. longicornis, with LC50 values of 0.51 mg/mL, 2.57 mg/mL and 1.83 mg/mL and LC90 values of 2.44 mg/mL, 11.44 mg/mL and 2.54 mg/mL, respectively. Enzyme assays revealed that the E. caryophyllata EO and eugenol significantly inhibited the activity of carboxylesterase (CarE), eugenol significantly inhibited the activity of catalase (CAT), and two EOs and eugenol had no significant effect on acetylcholinesterase (AchE) (p < 0.05). The above results suggest that the essential oils from P. racemosa and E. caryophyllata have great potential for use as alternatives to synthetic acaricides for tick control.

Target Enzymes of Origanum majorana and Rosmarinus officinalis Essential Oils in Black Cutworm (Agrotis ipsilon): In Vitro and In Silico Studies

In this study, in vitro and in silico approaches were employed to assess the toxicity of marjoram (Origanum majorana) and rosemary (Rosmarinus officinalis) essential oils (EOs) to A. ipsilon larvae. The study determined the activities of ATPases in the larvae after treatment with the LC20 and LC70 of each EO. α-esterase and glutathione-S-transferase (GST) activities were also determined after treatment with LC10 and LC30 of each EO. Furthermore, molecular docking was employed to determine the binding affinity of terpinene-4-ol and α-pinene, the major constituents of O. majorana, and R. officinalis EOs, respectively, compared to the co-crystallized ligand of α-esterase, diethyl hydrogen phosphate (DPF). Toxicity assays revealed that O. majorana EO was more toxic than R. officinalis EO to the A. ipsilon larvae at 96 h post-treatment. However, the LC20 and LC70 of the latter significantly inhibited the activity of the Na+-K+ pump at almost all intervals. The same concentrations significantly inhibited the Mg2+/Ca2+-ATPase and Ca2+ pump at 96 h post-treatment. In contrast, O. majorana EO showed a variable effect on the Na+-K+ pump across different time intervals. On the other hand, LC10 and LC30 of both EOs showed varied effects on α-esterase and GST over time. Molecular docking revealed energy scores of -4.51 and -4.29 kcal/mol for terpinene-4-ol and α-pinene, respectively, compared to a score of -4.67 for PDF. Our study demonstrated the toxicity of the tested EOs to A. ipsilon, suggesting their potential efficacy as insecticides.

Towards Sustainable Pest Management: Toxicity, Biochemical Effects, and Molecular Docking Analysis of Ocimum basilicum (Lamiaceae) Essential Oil on Agrotis ipsilon and Spodoptera littoralis (Lepidoptera: Noctuidae)

Over the last decade, essential oils (EOs) have become potential ingredients for insecticide formulations due to their widespread availability and perceived safety. Therefore, this study aimed to evaluate the toxicity and biochemical efficacy of basil (Ocimum basilicum) (Lamiaceae) against two destructive pests Noctuidae, Agrotis ipsilon (Hufnagel) and Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae). In addition, a molecular docking study was performed to gain insight into the binding pattern between glutathione S-transferase (GST) and linalool, the main component of EO. GC-MS analysis of O. basilicum EO revealed that linalool is the most abundant compound (29.34%). However, the toxicity tests showed no significant difference between the values of LC50 of O. basilicum EO to A. ipsilon and S. littoralis. On the other hand, the sublethal experiments indicated that treating the second instar larvae with LC15 or LC50 values of O. basilicum EO significantly prolonged the larval duration in both insects, compared to the control. Regarding the biochemical effect of O. basilicum EO, the treatments significantly impacted the activity of detoxification enzymes. A notable elevation in glutathione S-transferase (GST) activity was recorded in A. ipsilon larvae compared with a reduction in S. littoralis larvae. The molecular docking analysis revealed that linalool bonded with the amino acid serine (SER 9) of GST, indicating its binding affinity with the enzyme. The obtained results could offer valuable insights into the mode of action of O. basilicum and can encourage the adoption of sustainable pest control practices that incorporate essential oils.

Insecticidal Activity of Essential Oils and Their Synergistic Effect on Improving the Efficacy of β-Cypermethrin against Blattella germanica

We screened the contact activity of 32 commercial essential oils (EOs) and their synergistic effect with β-cypermethrin against Blattella germanica. Results showed that the most effective EOs against B. germanica were from Illicium verum, Syzygium aromaticum, and Cinnamomum camphora, with LD50 values of less than 500 μg/insect. The most potent synergistic effects of β-cypermethrin on B. germanica were from Dysphania ambrosioides and Mentha canadensis. Both oils have a co-toxic factor of 133.33. The results of the major compound testing of the EOs showed that trans-anisaldehyde and thymol have the best insecticidal activity against B. germanica, with LD50 values of 141.30 and 138.61 μg/insect, respectively. The compounds with the best synergistic effect on β-cypermethrin were γ-terpinene and linalool at a concentration of 0.5%. The co-toxic factors for γ-terpinene and linalool were 150 and 133.33, respectively, which were similar to the synergistic effect observed with 2% piperonyl butoxide.

Essential oil and fenchone extracted from Tetradenia riparia (Hochstetter.) Codd (Lamiaceae) induce oxidative stress in Culex quinquefasciatus larvae (Diptera: Culicidae) without causing lethal effects on non-target animals

We investigated the larvicidal activity of the essential oil (EO) from Tetradenia riparia and its majority compound fenchone for controlling Culex quinquefasciatus larvae, focusing on reactive oxygen and nitrogen species (RONS), catalase (CAT), glutathione S-transferase (GST), acetylcholinesterase (AChE) activities, and total thiol content as oxidative stress indicators. Moreover, the lethal effect of EO and fenchone was evaluated against Anisops bouvieri, Diplonychus indicus, Danio rerio, and Paracheirodon axelrodi. The EO and fenchone (5 to 25 µg/mL) showed larvicidal activity (LC50 from 16.05 to 18.94 µg/mL), followed by an overproduction of RONS, and changes in the activity of CAT, GST, AChE, and total thiol content. The Kaplan-Meier followed by Log-rank (Mantel-Cox) analyses showed a 100% survival rate for A. bouvieri, D. indicus, D. rerio, and P. axelrodi when exposed to EO and fenchone (262.6 and 302.60 µg/mL), while α-cypermethrin (0.25 µg/mL) was extremely toxic to these non-target animals, causing 100% of death. These findings emphasize that the EO from T. riparia and fenchone serve as suitable larvicides for controlling C. quinquefasciatus larvae, without imposing lethal effects on the non-target animals investigated.

A new cytotoxic disaccharide glycoside from the tubers of Arisaema franchetianum

A new disaccharide glycoside, franchoside A (1), and 17 known compounds were isolated from the tubers of Arisaema franchetianum Engler. The chemical structure of the previously undescribed compound 1 was elucidated on the basis of detailed spectroscopic analyses. Compounds 1, 2, 6, 10, 14 and 18 showed significant cytotoxic activities at varying IC50 values in the range of 4.0-10.6 μM against five cancer cell lines. Compounds 8, 10, 13 and 17 (10 μM) exhibited moderate anti-inflammatory activities by inhibiting the NF-κB signaling pathway and the release of NO from RAW264.7 macrophages induced by lipopolysaccharide (LPS), while compounds 1, 9, 14, 15 and 16 showed weak anti-inflammatory activities.

Efficiency of plant-based acaricide gels compared to fluvalinate-impregnated strips for control of Varroa destructor in honey bee colonies

The Varroa mite is one of the most important pests of honey bee colonies. This study compares the efficiency of thymol-based acaricides with the tau-fluvalinate-based commercial treatment to control this mite species. Two experiments were conducted: (1) in the Fall, thymol-based gel was compared with a widely used acaricide, fluvalinate-impregnated strips (Apistan®), and (2) in the Spring, gels containing thymol-only, thymol + menthol + eucalyptus essential oil, and thymol + thyme essential oil were compared with fluvalinate-impregnated strips. In the first experiment, both treatments reduced Varroa mite infestation levels significantly after 70 days of their application compared to the control treatment. The results of the second experiment showed that thymol + thyme essential oil gel, thymol + menthol + eucalyptus essential oil gel, and Apistan strips had always higher efficiency on decreasing mite infestation levels of the selected colonies compared to the control treatment and thymol-only gel during their 7-week application. The results of this study demonstrate that plant-based acaricides for controlling Varroa mites in honey bee colonies have similar efficiency compared to the chemical control methods. Therefore, it is better to use these selected acaricides to reduce mite resistance to chemical control treatments in honey bee colonies.

Chemical Composition, Larvicidal and Molluscicidal Activity of Essential Oils of Six Guava Cultivars Grown in Vietnam

Diseases transmitted by mosquitoes and snails cause a large burden of disease in less developed countries, especially those with low-income levels. An approach to control vectors and intermediate hosts based on readily available essential oils, which are friendly to the environment and human health, may be an effective solution for disease control. Guava is a fruit tree grown on a large scale in many countries in the tropics, an area heavily affected by tropical diseases transmitted by mosquitoes and snails. Previous studies have reported that the extracted essential oils of guava cultivars have high yields, possess different chemotypes, and exhibit toxicity to different insect species. Therefore, this study was carried out with the aim of studying the chemical composition and pesticide activities of six cultivars of guava grown on a large scale in Vietnam. The essential oils were extracted by hydrodistillation using a Clevenger-type apparatus for 6 h. The components of the essential oils were determined using gas-chromatography-mass-spectrometry (GC-MS) analysis. Test methods for pesticide activities were performed in accordance with WHO guidelines and modifications. Essential oil samples from Vietnam fell into two composition-based clusters, one of (E)-β-caryophyllene and the other of limonene/(E)-β-caryophyllene. The essential oils PG03 and PG05 show promise as environmentally friendly pesticides when used to control Aedes mosquito larvae with values of 24 h LC50-aegypti of 0.96 and 0.40 µg/mL while 24 h LC50-albopictus of 0.50 and 0.42 µg/mL. These two essential oils showed selective toxicity against Aedes mosquito larvae and were safe against the non-target organism Anisops bouvieri. Other essential oils may be considered as molluscicides against Physa acuta (48 h LC50 of 4.10 to 5.00 µg/mL) and Indoplanorbis exustus (48 h LC50 of 3.85 to 7.71 µg/mL) and with less toxicity to A. bouvieri.

Mosquito Larvicidal Activity and Cytotoxicity of the Extracts of Aromatic Plants from Malaysia

Despite ongoing control efforts, the mosquito population and diseases vectored by them continue to thrive worldwide, causing major health concerns. There has been growing interest in the use of botanicals as alternatives to insecticides due to their widespread insecticidal properties, biodegradability, and adaptability to ecological conditions. In this study, we investigated the larvicidal activity and cytotoxicity effects of solvent extracts from three aromatic plants-Curcuma longa (turmeric), Ocimum americanum (hoary basil), and Petroselinum crispum (parsley)-against Aedes albopictus. Subsequently, we examined the phytochemical composition of the extracts through gas chromatography-mass spectrometry (GC-MS) analysis. Results revealed that the hexane extracts of O. americanum and P. crispum exhibited the greatest larvicidal activity with the lowest median lethal concentration (LC₅₀) values (<30 µg/mL) at 24 h post-treatment, with the former found to be significantly less toxic towards African monkey kidney (Vero) cells. The GC-MS analysis of the said extract indicated the presence of different classes of metabolites, including phenylpropanoids, very long-chain alkanes, fatty acids and their derivatives, and terpenes, with the most abundant component being methyl eugenol (55.28%), most of which, have been documented for their larvicidal activities. These findings provide valuable insights into the potential use and development of bioinsecticides, particularly from O. americanum.

Environmental emissions and pollution characteristics of mosquitocides for the control of dengue fever in a typical urban area

Mosquitocides are frequently used to control the spread of dengue fever in tropical and sub-tropic urban regions worldwide, resulting in their discharge into the environment via rainfall runoff, causing adverse effects on ecological health. This study quantitatively evaluated mosquitocide emissions and environmental pollution in a typical urban district in China affected by the dengue fever epidemic, using a method combining market surveys, monitoring campaigns and SWMM (storm water management model) modelling tools. During the assessment period, the total mosquitocide usage in the urban district reached 6334 kg, with an estimated load of 56.55 g entering the receiving environment via rainfall runoff, 91.04 % of which occurred in the rainy season. Monitoring results indicated that the initial 0.5-1 h was the main period of mosquitocide wash off into the receiving water. Environmental mosquitocide pollution levels were found to be affected by the mosquitocide type and the time interval between mosquitocide application and precipitation events. The measured environmental concentrations of mosquitocides in this study were generally higher than those areas unaffected by the dengue fever epidemic. The modelled mosquitocide concentrations were in accordance with monitoring results. The finding of this study are important for assessing the environmental impact of dengue fever control activities, while also providing valuable baseline data for the effective environmental management of mosquitocides.

Toxicity of the essential oil from Tetradenia riparia (Hochstetter.) Codd (Lamiaceae) and its principal constituent against malaria and dengue vectors and non-target animals

Malaria and dengue are diseases transmitted by mosquitoes of the genera Anopheles and Aedes resistant to commercial insecticides, which are toxic to non-target animals. Alternatively, eco-friendly strategies have focused on searching for essential oil (EO) from plants to control these mosquitoes. In this aspect, this study was carried out to investigate the toxicity of the EO from Tetradenia riparia and its main constituent against Anopheles and Aedes larvae and non-target animals Toxorhynchites haemorrhoidalis and Gambusia affinis. The mechanism of the larvicidal action of the EO and its main compound was investigated by the acetylcholinesterase (AChE) inhibition. The EO from T. riparia was extracted by hydrodistillation with yield of 1.4 ± 0.17%. The analysis of the EO by GC-MS and GC-FID revealed fenchone (38.62%) as the main compound. The EO (100 ppm) showed larvicidal activity against Anopheles and Aedes larvae (91 to 100% of mortality) (LC₅₀ from 29.31 to 40.76 ppm). On the other hand, fenchone (10 ppm) showed more activity (89 to 100% of mortality) (LC₅₀ from 5.93 to 7.00 ppm) than the EO. The EO and fenchone caused the inhibition of AChE (IC₅₀ from 1.93 to 2.65 ppm), suggesting the inhibition of this enzyme as a possible mechanism of larvicidal action. Regarding toxicity, the EO (1000 ppm) and fenchone (100 ppm) showed low toxicity against T. haemorrhoidalis and G. affinis (9 to 74% of mortality) (LC₅₀ from 170.50 to 924.89 ppm) (SI/PSF from 17.99 to 31.91) than the α-cypermethrin (0.52 ppm) which was extremally toxic against these non-target animals (100% of mortality, LC₅₀ from 0.22 to 0.29 ppm). This significant larvicidal activity of the T. riparia EO and its main constituent, along with the low toxicity towards non-target organisms indicate these samples as a possible eco-friendly alternative for the control of malaria and dengue vectors.

Ultrasound-assisted nanoemulsion of Trachyspermum ammi essential oil and its constituent thymol on toxicity and biochemical aspect of Aedes aegypti

Aedes aegypti is the main vector of yellow fever, chikungunya, Zika, and dengue worldwide and is managed by using chemical insecticides. Though effective, their indiscriminate use brings in associated problems on safety to non-target and the environment. This supports the use of plant-based essential oil (EO) formulations as they are safe to use with limited effect on non-target organisms. Quick volatility and degradation of EO are a hurdle in its use; the present study attempts to develop nanoemulsions (NE) of Trachyspermum ammi EO and its constituent thymol using Tween 80 as surfactant by ultrasonication method. The NE of EO had droplet size ranging from 65 ± 0.7 to 83 ± 0.09 nm and a poly dispersity index (PDI) value of 0.18 ± 0.003 to 0.20 ± 0.07 from 1 to 60 days of storage. The NE of thymol showed a droplet size ranging from 167 ± 1 to 230 ± 1 nm and PDI value of 0.30 ± 0.03 to 0.40 ± 0.008 from 1 to 60 days of storage. The droplet shape of both NEs appeared spherical under a transmission electron microscope (TEM). The larvicidal effect of NEs of EO and thymol was better than BEs (Bulk emulsion) of EO and thymol against Ae. aegypti. Among the NEs, thymol (LC₅₀ 34.89 ppm) had better larvicidal action than EO (LC₅₀ 46.73 ppm). Exposure to NEs of EO and thymol causes the shrinkage of the larval cuticle and inhibited the acetylcholinesterase (AChE) activity in Ae. aegypti. Our findings show the enhanced effect of NEs over BEs which facilitate its use as an alternative control measure for Ae. aegypti.

Biochemical and insecticidal effects of plant essential oils on insecticide resistant and susceptible populations of Musca domestica L. point to a potential cross-resistance risk

Essential oils (EOs) can provide important alternatives to chemical insecticides in the control of pests. In this study, 12 EOs of native plant species from Iran were evaluated for their adulticidal activity against the house fly. In addition, we examined the insecticidal activity of Zataria multiflora and Rosmarinus officinalis EOs on adult female house flies from pyrethroid and organophosphate resistant and susceptible populations, using both fumigant and topical bioassays. The involvement of detoxification enzymes in susceptibility was investigated with synergism experiments in vivo, while the inhibitory effects of R. officinalis and Zataria multiflora EOs on the activities of cytochrome P450-dependent monooxygenases (P450s), carboxylesterases (CarEs) and glutathione S-transferases (GSTs) were determined by enzymatic inhibition assays in vitro. The EOs of Z. multiflora, Mentha pulegium, R. officinalis and Thymus vulgaris were the most effective against adults in contact topical assays, while oils extracted from Eucalyptus cinerea, Z. multiflora, Citrus sinensis, R. officinalis, Pinus eldarica and Lavandula angustifolia where the most effective in fumigant assays. Rosmarinus officinalis and Z. multiflora EOs were selected for further investigation and showed higher toxicity against a susceptible population, compared to two insecticide-resistant populations. Correlation analysis suggested cross-resistance between these EOs and pyrethroids in the resistant populations. The toxicity of both EOs on the resistant populations was synergized by three detoxification enzyme inhibitors. Further, in vitro inhibition studies showed that R. officinalis and Z. multiflora EOs more effectively inhibited the activities of the detoxification enzymes from flies of the susceptible population compared to those of the pyrethroid resistant populations. Synergistic and enzymatic assays further revealed that increased activities of P450s, GSTs, and CarEs are possibly involved in the cross-resistance between EOs and pyrethroids. Investigating the molecular mechanisms of P450s, GSTs, and CarEs in the resistance to EOs should be subject to further studies.

A comprehensive review of research progress on the genus Arisaema: Botany, uses, phytochemistry, pharmacology, toxicity and pharmacokinetics

ETHNOPHARMACOLOGICAL RELEVANCE

The genus Arisaema belongs to the family Araceae, which includes Chinese herbal medicines with wide-ranging pharmacological functions, including those useful for the treatment of stubborn phlegm, cough, epilepsy, tetanus, snakebite, rheumatoid arthritis, and other ailments.

AIM OF THE STUDY

The current study aimed to comprehensively review the botany, uses, phytochemistry, pharmacology, toxicity, quality control and pharmacokinetics of plants in the genus Arisaema and to provide novel insights to develop future research in this field.

MATERIALS AND METHODS

Relevant information on the genus Arisaema was obtained from published scientific materials (including materials from PubMed, Elsevier, Web of Science, Google Scholar, Baidu Scholar, CNKI, and Wiley) and other literature sources (e.g., the Chinese Pharmacopoeia, 2020 edition; Chinese herbal books and PhD and MSc thesis).

RESULTS

The application information complied with this review and included processing techniques, traditional uses, clinical applications and classic prescriptions. Approximately 260 compounds, including flavonoids, alkaloids, saccharides, steroids, fatty acids, amino acids and volatile oils, have been separated and identified from the genus Arisaema. The isolated compounds exhibit wide-ranging pharmacological activities such as antitumor activity, analgesic and sedative activity, antioxidant activity and anti-inflammatory activity. The toxicity and irritant impacts, quality control, and pharmacokinetics are also discussed in this review.

CONCLUSIONS

Plants in the genus Arisaema are valuable resources with therapeutic potential for a broad spectrum of ailments. Based on the limited literature, this review comprehensively and systematically summarizes current knowledge regarding the genus Arisaema for the first time. However, there have been insufficient studies on the active ingredients and germplasm and insufficient in-depth mechanistic studies. Therefore, isolation and identification of additional effective components and through research on the germplasm, pharmacodynamic mechanisms, and toxicology should be conducted to assess effectiveness and safety and to ensure the quality of the related drugs.

Densovirus Oil Suspension Significantly Improves the Efficacy and Duration of Larvicidal Activity against Aedes albopictus

Aedes albopictus is the sole vector for various mosquito-borne viruses, including dengue, chikungunya, and Zika. Ecofriendly biological agents are required to reduce the spread of these mosquito-borne infections. Mosquito densoviruses (MDVs) are entomopathogenic mosquito-specific viruses, which can reduce the capacity of isolated vectors and decrease mosquito-borne viral disease transmission. However, their variable pathogenicity restricts their commercial use. In the present study, we developed a series of novel larvicide oil suspensions (denoted Bacillus thuringiensis (Bti) oil, Ae. albopictus densovirus (AalDV-5) oil, and a mixture of AalDV-5+Bti oil), which were tested against Ae. albopictus larvae under experimental semi-field and open-field conditions. The effect of AalDV-5 on non-target species was also evaluated. The combined effect of AalDV-5+Bti was greater than that of individual toxins and was longer lasting and more persistent compared with the laboratory AalDV-5 virus strain. The virus was quantified on a weekly basis by quantitative polymerase chain reaction (qPCR) and was persistently detected in rearing water as well as in dead larvae. Wildtype densovirus is not pathogenic to non-target organisms. The present findings confirm the improved effect of a mixed microbial suspension (AalDV-5+Bti oil) larvicide against Ae. albopictus. The development and testing of these products will enable better control of the vector mosquitoes.

Persistent susceptibility of Aedes aegypti to eugenol

Botanical insecticides are preferred for their environment and user-friendly nature. Eugenol is a plant-based monoterpene having multifarious biocidal activities. To understand whether eugenol would persistently work against Aedes aegypti, we performed larvicidal bioassays on thirty successive generations and determined median lethal concentration (LC50) on each generation. Results showed no apparent differences between LC50 at F0 (63.48 ppm) and F30 (64.50 ppm) indicating no alteration of susceptibility toward eugenol. To analyze, if eugenol has any effect on metabolic detoxification-associated enzymes, we measured esterases (alpha and beta), cytochrome P450, and GST activities from the survived larvae exposed to LC50 concentration from F0–F30. Results revealed a decrease of esterases, GST, and cytochrome P450 activities at the initial 4–8 generations and then a gradual increase as the generations progressed. GST activity remained significantly below the control groups. Synergists (TPP, DEM, and PBO) were applied along with eugenol at F30 and LC50 concentration, and the said enzyme activities were recorded. Results showed a noticeable decrease in LC50 and enzyme activities indicating effective inhibitions of the respective enzymes. Overall, present results inferred that eugenol would effectively work as a larvicide for a longer period in successive generations without initiating rapid resistance and therefore could be advocated for controlling A. aegypti.

Acaricidal activity of Cinnamomum cassia (Chinese cinnamon) against the tick Haemaphysalis longicornis is linked to its content of (E)-cinnamaldehyde

Background

The tick Haemaphysalis longicornis (Neumann) is a well-known vector of numerous pathogens of veterinary and medical importance. Various control strategies, including the use of synthetic pesticides, have been developed to control this tick species. However, demand for effective and safe alternative pesticides is increasing due to the adverse effects associated with the intensive and injudicious use of synthetic pesticides, which include undesirable effects on non-target species and environmental pollution. Hence, the acaricidal activity of the extract and the essential oil of Cinnamomum cassia (Chinese cinnamon) and their major components, and the underlying mechanisms of this activity, were evaluated against unfed larvae and nymphs of H. longicornis.

Methods

The components of the extract and essential oil of C. cassia were determined by gas chromatography-mass spectrometry, and their larvicidal and nymphicidal activity were evaluated using the larval and nymphal packet test. The underlying detoxification mechanism was elucidated by targeting in vivo esterase and monooxygenase activity, and the toxicological effect was assessed on non-target Tenebrio molitor and Harmonia axyridis by topical application in open Petri dishes.

Results

(E)-cinnamaldehyde was the predominant component of the extract (50.79%) and essential oil (89.95%). The 50% lethal concentration (LC₅₀) for larvae and nymphs treated with the extract was 11.56 and 49.18 mg/mL, respectively. The essential oil, (E)-cinnamaldehyde and fenvalerate exhibited acaricidal activity, with LC₅₀ values of 3.81, 3.15, and 0.14 mg/mL, respectively, against the larvae, and 21.31, 16.93, and 1.89 mg/mL, respectively, against the nymphs. (E)-cinnamaldehyde significantly increased esterase and monooxygenase activity in both larvae and nymphs. Unlike fenvalerate, C. cassia essential oil and (E)-cinnamaldehyde did not cause mortality of T. molitor or H. axyridis adults.

Conclusions

This study demonstrates that C. cassia essential oil and (E)-cinnamaldehyde have the potential to be developed into botanical-based larvicidal and nymphicidal agents for tick control.

Graphical abstract

Chemical Composition, Larvicidal Activity, and Enzyme Inhibition of the Essential Oil of Lippia grata Schauer from the Caatinga Biome against Dengue Vectors

Insect resistance and environmental pollution are among the drawbacks of continuous use of synthetic insecticides against the vectors of dengue, Aedesaegypti and Aedes albopictus. The objective of this study was to analyze the composition of the essential oil of Lippia grata Schauer collected from plants, in three periods of the year, to compare the larvicidal activity and enzymatic inhibition of the dengue vectors. The oilsanalyzed by gas chromatography coupled to mass spectrometry (GC-MS), presented thymol and 1,8-cineole, as the main constituents, in all three periods. This composition was different from that found in previous studies of the species from different places, thus, suggesting a new chemotype of Lippia grata. Larvicidal tests were performed at concentrations of 100, 75, 50, 25, and 12.5 μg.mL⁻¹ and the essential oil from the rainy season showed the best results, with LC₅₀ of 22.79 μg.mL⁻¹ and 35.36 μg.mL⁻¹ against Ae. aegypti and Ae. albopictus, respectively; this result was better than other reports. In the rainy period, however, there was a greater variety of components, which led to a better larvicidal effect, possibly due to synergistic action with minor constituents. Total proteins, amylases, and acetylcholinesterase of both species were inhibited by the oils.

Essential oils and their chemical constituents against Aedes aegypti L. (Diptera: Culicidae) larvae

This review focused on the toxicity of essential oils and their constituents against Aedes aegypti L. (Diptera, Culicidae) larvae, a key vector of important arboviral diseases, such as dengue, chikungunya, zika, and yellow fever. This review is based on original articles obtained by searching major databases in the last six years. Our literature review shows that 337 essential oils from 225 plant species have been tested for larvicidal bioactivity. More than 60% of these essential oils were considered active (LC₅₀<100 µg/mL). Most species belong to the families Lamiaceae (19.3%), Lauraceae (9.9%), and Myrtaceae (9.4%). The plants studied for their larvicidal activity against A. aegypti were mainly collected in India and Brazil (30 and 20%, respectively) and the parts of the plants most used were the leaves. Less than 10% of essential oils were evaluated for toxicity against non-target organisms and with the aim to demonstrate safe use. The most used plant parts are leaves and the main compounds of essential oils were described. The most active essential oils are rich in sesquiterpene hydrocarbons, oxygenated sesquiterpenes, and monoterpene hydrocarbons. Here, factors affecting bioactivity (chemical composition, plant parts, and harvesting site) of essential oils and their constituents, as well as safety to non-target organisms are discussed. Essential oils have considerable potential against A. aegypti. This review shows that essential oils might be used to control arboviruses, and further studies on safety and formulations for application in the field should be performed.

Insecticidal and biochemical activity of essential oil from Citrus sinensis peel and constituents on Callosobrunchus maculatus and Sitophilus zeamais

Essential oils are promising substitute for chemical pesticides with the inherent resistance by pests, environmental and health effects on humans. In this study, the chemical composition of essential oil extracted from Citrus sinensis peel was characterized, the insecticidal activities of the oil and its constituents against Callosobrunchus maculatus (Cowpea weevil) and Sitophilus zeamais (maize weevil) were investigated and the underlying insecticidal mechanism were elucidated. The essential oil was extracted by hydro-distillation and characterized using gas chromatography-mass spectrometry (GC-MS). Insecticidal activity was determined by contact and fumigant toxicity assay. The inhibitory effect of the oil and its constituents on acetylcholinesterase (AChE), Na⁺/K⁺-ATPase and glutathione-S- transferase (GST) activity were assayed using standard protocols. The total number of volatile compounds detected in C. sinensis essential oil was eighteen (18). d-limonene (59.3%), terpineol (8.31%) and linalool (6.88%) were the major compounds present in the essential oil. Among the tested essential oil compounds, terpineol showed highest contact toxicity against C. maculatus (LD₅₀ =17.05 μg/adult) while 3-carene showed highest contact toxicity against S. zeamais (LD₅₀ =26.01 μg/adult) at 24 h exposure time. Citral exhibited the highest fumigant toxicity against C. maculatus and S. zeamais with LC₅₀ value 0.19 and 2.02 μL/L air at 24 h respectively. Acetylcholinesterase and Na⁺/K⁺-ATPase activities were significantly inhibited by C. sinensis oil and its constituents in both C. maculatus and S. zeamais as compared to control. This study indicates that C. sinensis essential oil and its constituents have potential to be developed into botanical pesticides.

Larvicidal Activity of Essential Oils Against Aedes aegypti (Diptera: Culicidae)

The Aedes aegypti is responsible for the transmission of arboviruses, which compromise public health. In the search for synthetic product alternatives, essential oils (OEs) have been highlighted by many researchers as natural insecticides. This systematic review (SR) was performed according to PRISMA guidelines (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) and its objective was to evaluate studies addressing OEs with larvicidal properties against Ae. aegypti, through electronic database searches (Pubmed, Science Direct and Scielo), covering an overview of the plant sources OEs, which plant parts were used, the extraction methods, analytical techniques, major and/or secondary constituents with greater percentages, as well as the LC50s responsible for larval mortality. Following study analysis, plants distributed across 32 families, 90 genera and 175 species were identified. The Lamiaceae, Myrtaceae, Piperaceae, Asteraceae, Rutaceae, Euphorbiaceae and Lauraceae families obtained the highest number of species with toxic properties against larvae from this vector. Practically all plant parts were found to be used for OE extraction. Hydrodistillation and steam distillation were the main extraction methods identified, with GC-MS/GC-FID representing the main analytical techniques used to reveal their chemical composition, especially of terpene compounds. In this context, OEs are promising alternatives for the investigation of natural, ecologically correct and biodegradable insecticides with the potential to be used in Ae. aegypti control programs.