Insecticidal activity of essential oils: octopaminergic sites of action

In vitro acaricidal activity of several natural products against ibex-derived Sarcoptes scabiei

In this study we analysed the effect of the temperature, diverse strains of Bacillus thuringiensis, Lysinibacillus sphaericus and nanoformulations with essential plant oils (EONP) on the survival of Sarcoptes scabiei mites derived from naturally-infested Iberian ibex (Capra pyrenaica). In general, mites maintained at 12ºC survived more than those maintained at 35ºC (40.7 hr and 31.2 hr, respectively). Mites with no treatment survived 27.6 h on average. Mites treated with B. thuringiensis serovar. konkukian and geranium EONP showed significant reduction in their survival. Despite the fact that these agents seem to be promising candidates for controlling sarcoptic mange in the field, further research is still needed to get stable, efficient and eco-friendly acaricides.

Nitrogen-mediated volatilisation of defensive metabolites in tomato confers resistance to herbivores

Plants synthesise a vast array of volatile organic compounds (VOCs), which serve as chemical defence and communication agents in their interactions with insect herbivores. Although nitrogen (N) is a critical resource in the production of plant metabolites, its regulatory effects on defensive VOCs remain largely unknown. Here, we investigated the effect of N content in tomato (Solanum lycopersicum) on the tobacco cutworm (Spodoptera litura), a notorious agricultural pest, using biochemical and molecular experiments in combination with insect behavioural and performance analyses. We observed that on tomato leaves with different N contents, S. litura showed distinct feeding preference and growth and developmental performance. Particularly, metabolomics profiling revealed that limited N availability conferred resistance upon tomato plants to S. litura is likely associated with the biosynthesis and emission of the volatile metabolite α-humulene as a repellent. Moreover, exogenous application of α-humulene on tomato leaves elicited a significant repellent response against herbivores. Thus, our findings unravel the key factors involved in N-mediated plant defence against insect herbivores and pave the way for innovation of N management to improve the plant defence responses to facilitate pest control strategies within agroecosystems.

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.

Comparative analysis of essential oil efficacy against the Asian longhorned tick Haemaphysalis longicornis (Acari: Ixodidae)

This study evaluated the potential repellent and acaricidal effects of 4 essential oils (clove, eucalyptus, lavender, and mint) against the Asian longhorned tick Haemaphysalis longicornis, a vector of various tick-borne diseases in medical and veterinary contexts. Selected for their potential repellent and acaricidal properties, the 4 essential oils were tested on adult and nymph H. longicornis ticks at different concentrations. The experiment assessed mortality rates and repellency, particularly during tick attachment to host skin. There was a significant increase (p<0.05) in tick mortality and repellency scores across all groups. At a 1% concentration, adult tick mortality ranged from 36% to 86%, while nymph mortality ranged from 6% to 97%. Clove oil exhibited notable efficacy, demonstrating high mortality rates of nymphs and adults. Clove oil also displayed strong repellency properties, with a repellency index of 0.05, surpassing those of mint, eucalyptus, and lavender oils. Clove oil showed the highest effectiveness in deterring nonattached adult ticks (90%) and nymphs (95%) when applied to skin. Clove oil was the most effective against adult and nymph ticks, achieving mortality rates of 86% and 97%, respectively, and led to the highest nonattachment rates when applied to skin. In conclusion, essential oils such as clove, eucalyptus, lavender, and mint oils present promising results for tick population control.

The Potential of Plant-Based Biorational Products for the Drosophila suzukii Control: Current Status, Opportunities, and Limitations

Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) is an invasive species that causes serious damage to soft-skinned fruits. The use of plant-based biorational insecticides (plant extracts and essential oils) to control this pest has grown extensively. We conducted a systematic review and meta-analysis to examine the current status, trends, and perspectives of these studies, with a focus on the plant families and major compounds used as insecticides to control D. suzukii. The first article in this research field was published in 2015, and there has been exponential growth in subsequent years. Thirty-six botanical families were studied in these articles, with a prevalent interest in Myrtaceae and Lamiaceae plant species. The major constituents of these plant-based biorational molecules belong to monoterpenoids, followed by monoterpenes, benzene derivatives, and others. Geranial was the most frequent major constituent of these plant-based compounds. Our analysis revealed a few crucial consequences of the bias provided by the investigations using plant-based biorational insecticides for controlling D. suzukii. Firstly, there is a major focus on the pest species, with little or no attention paid to undesired effects on non-target beneficial organisms (e.g., pollinator bees, predators; parasitoids) and non-target pests. Secondly, the poor knowledge of how these plant-based biorational insecticides act on target and non-target organisms. Finally, there is a need to assess the efficacy of these substances under field conditions. Thus, attention is needed to address these gaps so that plant-based biorational insecticides can become a viable pest management tool for controlling D. suzukii.

Alpha- and beta-pinene isomers act differently to control Rhipicephalus microplus (Acari: Ixodidae)

The cattle tick Rhipicephalus microplus is an ectoparasite of high importance in veterinary medicine and public health. Since synthetic chemicals used to control these ticks can select resistant strains and cause toxic effects in their hosts, there is a need to identify effective substances with fewer adverse effects. For this reason, we investigated the effects of alpha- and beta-pinene, known for their various biological effects, on the mortality and reproductive performance of R. microplus engorged female ticks. The products were diluted in a 2% Tween 80 aqueous solution. The ticks were first weighed and then immersed in the test solutions for five minutes. Then, they were dried with paper towels and fixed dorsoventrally in Petri dishes, totalling five treatment groups for each pinene and a control group treated with the solvent alone. The ticks were monitored daily for mortality, and their eggs were collected and weighed. The larval hatching rate was estimated, and the pre-oviposition and incubation periods were determined. From these data, the following parameters were calculated: egg production index, fertility rate, estimated reproduction rate, percentages of reduction in oviposition and hatching, and product efficacy. Alpha-pinene showed better results at higher concentrations, unlike beta-pinene, which was more effective at lower concentrations. The effectiveness of alpha-pinene was 74% at a concentration of 14.0 μL/mL, while beta-pinene showed 78% efficacy at 2.0 μL/mL. The results indicated for the first time different effects of two isomers in ticks, suggesting that these compounds act on R. microplus females in different ways.

Antioxidant, Antimicrobial, and Insecticidal Properties of Chemically Characterized Essential Oils Extracted from Mentha longifolia: In Vitro and In Silico Analysis

The present study aimed to explore the phytochemical profile, and evaluate the antioxidant, antimicrobial, and insecticidal properties, of Moroccan Mentha longifolia L. essential oil (ML-EO) using in vitro and in silico assays. Noteworthily, as chromatography (GC-MS/MS) revealed that ML-EO is majorly composed of piperitenone oxide (53.43%), caryophyllene (20.02%), and (-) germacrene D (16.53%). It possesses excellent antioxidant activity with an IC50 of 1.49 ± 0.00 for DPPH and 0.051 ± 0.06 μg/mL for ABTS. Moreover, the RP and TAC activities were 0.80 ± 0.01 μg/mL and 315.532 ± 0.00 mg EAA/g, respectively. ML-EO exhibited a potent antimicrobial effect, specifically against Pseudomonas aeruginosa. It also exhibited strong antifungal ability, especially against Candida albicans. Regarding insecticidal activity, for ML-EO, a dose of 20 µL/mL produced a complete reduction in fecundity, fertility, and emergence of adult C. maculatus with mortality rates reaching 100%. In silico results showed that the antioxidant activity is mostly attributed to α-Cadinol, the antibacterial efficiency is attributed to piperitenone oxide, and antifungal capacity is related to cis-Muurola-4(15),5-diene and piperitenone oxide. Accordingly, ML-EO has high potential to be used as an alternative for preserving food and stored grain and protecting them against microbes and insect pests in the food and pharmaceutical sectors.

Baccharis Species Essential Oils: Repellency and Toxicity against Yellow Fever Mosquitoes and Imported Fire Ants

Essential oils from five Baccharis species were screened for their toxicity and biting deterrence/repellency against yellow fever mosquito, Aedes aegypti (L.), and imported fire ants, including Solenopsis invicta Buren (RIFA), Solenopsis richteri Forel (BIFA) and their hybrids (HIFA). Baccharis microdonta DC. and B. punctulata DC. at 10 µg/cm2 showed biting deterrence similar to DEET, N, N-diethyl-meta-toluamide at 25 nmol/cm2, whereas the repellency of B. pauciflosculosa DC., B. sphenophylla Dusén ex Malme and B. reticularioides Deble & A.S. Oliveira essential oils was significantly lower than DEET against mosquitoes. Two major compounds from the active essential oils, kongol and spathulenol, also exhibited biting deterrence similar to DEET against mosquitoes. The highest toxicity exhibited against mosquitoes was by Baccharis punctulata essential oil (LC50 = 20.4 ppm), followed by B. pauciflosculosa (LC50 = 31.9 ppm), B. sphenophylla (LC50 = 30.8 ppm), B. microdonta (LC50 = 28.6 ppm), kongol (LC50 = 32.3 ppm), spathulenol (LC50 = 48.7 ppm) and B. reticularioides essential oil (LC50 = 84.4 ppm). Baccharis microdonta essential oil showed repellency against RIFA, BIFA and HIFA at 4.9, 4.9 and 39 µg/g, respectively. Baccharis microdonta essential oil also showed toxicity with LC50 of 78.9, 97.5 and 136.5 µg/g against RIFA, BIFA and HIFA, respectively, at 24 h post treatment.

Plants and Their Derivatives as Promising Therapeutics for Sustainable Control of Honeybee (Apis mellifera) Pathogens

The most important pollinator for agricultural crops is the Western honeybee (Apis mellifera). During the winter and summer seasons, diseases and stresses of various kinds endanger honeybee numbers and production, resulting in expenses for beekeepers and detrimental effects on agriculture and ecosystems. Researchers are continually in search of therapies for honeybees using the resources of microbiology, molecular biology, and chemistry to combat diseases and improve the overall health of these important pollinating insects. Among the most investigated and most promising solutions are medicinal plants and their derivatives. The health of animals and their ability to fight disease can be supported by natural products (NPs) derived from living organisms such as plants and microbes. NPs contain substances that can reduce the effects of diseases by promoting immunity or directly suppressing pathogens, and parasites. This literature review summarises the advances that the scientific community has achieved over the years regarding veterinary treatments in beekeeping through the use of NPs. Their impact on the prevention and control of honeybee diseases is investigated both in trials that have been conducted in the laboratory and field studies.

Challenges encountered by natural repellents: Since obtaining until the final product

Vector-borne diseases, particularly the arboviruses dengue, Zika, chikungunya, and yellow fever caused by the Aedes aegypti mosquito, have been driving the use of repellents worldwide. The most representative synthetic repellent, DEET stands out as the market's oldest and most efficient repellent. It is considered a reference standard but presents considerable toxicity, not recommended for children up to 6 months old and pregnant women. For this reason, alternatives have been sought, and natural repellents derived mainly from essential oils have been studied, highlighting the essential oils of lemon (Corymbia citriodora), citronella (Cympobogon sp.), Andiroba (Carapa guianensis). However, the development and commercialization of products containing natural repellents are significantly lower when compared to DEET and other synthetic repellents. In order to understand the reasons, aspects related to safety, mechanism of action, efficacy as well development and complexity of the products were evaluated. It is concluded that, as for safety, there is lacking information in the literature regarding the effects on non-target organisms and robust toxicity data. The mechanism of action is based on theories, with less information on the exact mode of action, molecular targets, and interaction with the olfactory and taste receptors of insects. Despite being a current trend to search for actives from natural sources highly present in essential oils, however they reduced action time because due to rapid evaporation after application to the skin, thus requiring repellent vehicles. The development and complexity related to these products bring challenging aspects, beginning on the plant cultivation and extraction processes to produce essential oils with a more homogeneous chemical composition towards the formulation stabilization processes due to fast evaporation and short action time, with the use of pharmaceutical technology such as encapsulation techniques.

Insecticidal potential of a Consolida ajacis extract and its major compound (ethyl linoleate) against the diamondback moth, Plutella xylostella

The diamondback moth (Plutella xylostella) is one of the most destructive lepidopteran pests of cruciferous vegetables. However, DBM has developed resistance to current chemical and biological insecticides used for its control, indicating the necessity for finding new insecticides against it. Bio-insecticides derived from plant extracts are eco-friendly alternatives to synthetic pesticides. The aims of this study were to evaluate the insecticidal activity of Consolida ajacis seed extracts against DBM, the underlying mechanism of the control effect of promising extracts, and the identification of the main insecticidal compounds of these extracts. The results showed that ethyl acetate extract of C. ajacis seed exhibited strong contact toxicity (LC50: 5.05 mg/mL), ingestion toxicity, antifeedant, and oviposition deterrent activities against DBM, among the extracts evaluated. At 72 h, glutathiase, acetylcholinesterase, carboxylesterase, peroxidase, and superoxide dismutase activities were inhibited, but catalase activity was activated. The main compound identified from the extract was ethyl linoleate, which had the most significant insecticidal activity on the diamondback moths. This study's findings provide a better understanding of the insecticidal activity of ethyl acetate extract obtained from C. ajacis and its main component (ethyl linoleate). This will help in the development of new insecticides to control DBM.

Synergism in Two-Component Insecticides with Dillapiole against Fall Armyworm

The fall armyworm (Spodoptera frugiperda), a polyphagous insect pest, is a major threat to food production, rapidly spreading through all the tropical areas in the world. Resistance has developed to the control protocols used so far (pyrethroids, organophosphorus, and genetically modified plants), and alternative strategies must be found. The bioactivity in essential oils is usually associated with the major constituents, but synergistic interactions among the constituents (even minor ones) can improve the levels of activity considerably. Herein, we tested the insecticidal activity of several constituents of the essential oil from Piper aduncum, an Amazonian Piperaceae, both separately and as binary mixtures, through their application on the dorsal side of the larva pronotum. Dillapiole proved to be, isolated, the most active compound in this oil (LD50 = 0.35 ppm). In binary mixtures, a strong synergistic effect was observed for the pairs of dillapiole with β-caryophyllene (LD50 = 0.03 ppm), methyl eugenol (LD50 = 0.05 ppm), and α-humulene (LD50 = 0.05 ppm). In some cases, however, antagonism was recorded, as for dillapiole + β-pinene (LD50 = 0.44 ppm). The use of binary mixtures of essential oil constituents as low-environmental-toxicity insecticides allows a fine tuning of the insecticidal activity, and the exploitation of synergy effects.

Evaluating the Sublethal Effects of Origanum vulgare Essential Oil and Carvacrol on the Biological Characteristics of Culex pipiens biotype molestus (Diptera: Culicidae)

Culex pipiens is a mosquito species complex spread worldwide that poses a serious threat to human health as the primary vector of West Nile virus. Its control is mainly based on larvicidal applications with synthetic insecticides on mosquito breeding sites. However, the excessive use of synthetic larvicides may provoke mosquito resistance issues and negative side effects to the aquatic environment and human health. Plant-derived essential oils, including those from the Lamiaceae family, can be eco-friendly alternative larvicidal agents causing acute larval toxicity and/or growth inhibitory effects on the developmental stages of mosquitoes through different modes of action. In the current laboratory study, we evaluated the sublethal effects of carvacrol-rich oregano essential oil and pure carvacrol on Cx. pipiens biotype molestus, the autogenous member of the Cx. pipiens species complex, after the exposure of 3rd-4th instar larvae to LC₅₀ concentrations. The short-term (24 h) larvicidal treatment with the sublethal concentrations of both tested materials exhibited an acute lethal effect on the exposed larvae as well as significant delayed mortality for surviving larvae and pupae. Larvicidal treatment with carvacrol reduced the longevity of the emerged males. In addition, the morphological abnormalities that were observed at the larval and pupal stage along with failed adult emergence indicate the potential growth inhibitory properties of the tested bioinsecticides. Our findings suggest that carvacrol and carvacrol-rich oregano oil are effective plant-based larvicides at doses lower than the acute lethal ones, thus promoting an environmentally friendly and more affordable perspective for their use against the WNV vector Cx. pipiens biotype molestus.

Novel Approach for a Controlled Delivery of Essential Oils during Long-Term Maize Storage: Clove Bud and Pennyroyal Oils Efficacy to Control Sitophilus zeamais, Reducing Grain Damage and Post-Harvest Losses

Maize grains represent a significant contribution for assuring food safety all over the globe. Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae), also known as the maize weevil, is one of the most destructive pests in stored maize, causing qualitative and quantitative losses. To control S. zeamais populations in maize storage sites, synthetical chemical insecticides are applied. However, these are often used wastefully, have environmental implications, and can induce the development of resistant populations. In this work, the insecticidal and grain protecting efficacy of an innovative macro-capsule delivery device, loaded with essential oils from Clove bud and Pennyroyal, as well as their combined solutions, was tested against naturally S. zeamais-infested maize grains. The blend of both compounds incorporated in a controlled release device reduced losses by more than 45% over a long storage period of twenty weeks, diminishing the survivability of maize weevils by over 90%. The usage of the blend at a concentration of 370 μL⋅Lair-1 with an antioxidant showed the best results, however, by halving the concentration (185 μL⋅Lair-1), a significant control of S. zeamais populations was still achieved.

Salvia sclarea Essential Oil Chemical Composition and Biological Activities

Salvia sclarea essential oil (SSEO) has a long tradition in the food, cosmetic, and perfume industries. The present study aimed to analyze the chemical composition of SSEO, its antioxidant activity, antimicrobial activity in vitro and in situ, antibiofilm, and insecticidal activity. Besides that, in this study, we have evaluated the antimicrobial activity of SSEO constituent (E)-caryophyllene and standard antibiotic meropenem. Identification of volatile constituents was performed by using gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS) techniques. Results obtained indicated that the main constituents of SSEO were linalool acetate (49.1%) and linalool (20.6%), followed by (E)-caryophyllene (5.1%), p-cimene (4.9%), a-terpineol (4.9%), and geranyl acetate (4.4%). Antioxidant activity was determined as low by the means of neutralization of the DDPH radical and ABTS radical cation. The SSEO was able to neutralize the DPPH radical to an extent of 11.76 ± 1.34%, while its ability to decolorize the ABTS radical cation was determined at 29.70 ± 1.45%. Preliminary results of antimicrobial activity were obtained with the disc diffusion method, while further results were obtained by broth microdilution and the vapor phase method. Overall, the results of antimicrobial testing of SSEO, (E)-caryophyllene, and meropenem, were moderate. However, the lowest MIC values, determined in the range of 0.22–0.75 µg/mL for MIC50 and 0.39–0.89 µg/mL for MIC90, were observed for (E)-caryophyllene. The antimicrobial activity of the vapor phase of SSEO (towards microorganisms growing on potato) was significantly stronger than that of the contact application. Biofilm analysis using the MALDI TOF MS Biotyper showed changes in the protein profile of Pseudomonas fluorescens that showed the efficiency of SSEO in inhibiting biofilm formation on stainless-steel and plastic surfaces. The insecticidal potential of SSEO against Oxycarenus lavatera was also demonstrated, and results show that the highest concentration was the most effective, showing insecticidal activity of 66.66%. The results obtained in this study indicate the potential application of SSEO as a biofilm control agent, in the shelf-life extension and storage of potatoes, and as an insecticidal agent.

Toxicological and molecular adverse effect of Illicium verum fruit constituents toward Bradysia procera

BACKGROUND

Bradysia procera, a ginseng stem fungus gnat, is one of the most serious insect pests of Korean ginseng (Panax ginseng), causing significant damage to plant growth. The goal of this study was to determine the toxicity and mechanism of action of phenylpropanoids (trans-anethole and estragole) isolated from the methanol extract and hydrodistillate of Illicium verum fruit against third-instar larvae and eggs of Bradysia procera.

RESULTS

The filter-paper mortality bioassay revealed that estragole [median lethal concentration (LC₅₀ ) = 4.68 g/cm² ] has a significant fumigant effect, followed by trans-anethole (LC₅₀ = 43.92 g/cm² ). However, estragole had the lowest toxic effect when compared to commercially available insecticides. After 7 days, estragole and trans-anethole at 75 g/cm² inhibited egg hatchability up to 97% and 93%, respectively. At 0.09 g/cm² , insecticides had an inhibitory effect on egg-hatching ability ranging from 88% to 94%. Furthermore, in both closed and open containers, these active constituents were able to consistently induce vapor-phased toxicity. Both estragole and trans-anethole have the ability to inhibit acetylcholinesterase (AChE), which is involved in neurotransmitter function. However, the active constituent estragole from I. verum fruit acted as a potent AChE inhibitor and had a slightly lower effect on cyclic adenosine monophosphate (AMP) than octopamine alone.

CONCLUSION

This finding suggests that estragole may influence Bradysia procera neurotransmitter function via both the AChE and octopaminergic receptors. More research is needed to demonstrate the potential applications of I. verum fruit-derived products as potential larvicides and ovicides for Bradysia procera population control. © 2022 Society of Chemical Industry.

Specificity of Monoterpene Interactions with Insect Octopamine and Tyramine Receptors: Insights from in Silico Sequence and Structure Comparison

Octopamine and tyramine receptors (OARs/TARs) are interesting targets for new insecticide development due to their unique roles in insects' physiological and cellular response and their specificity to invertebrates. Monoterpene compounds that bear resemblance to the natural ligands have been shown to bind to the OARs/TARs but elicit varied responses in different insect species. Using in silico methods, we attempt to investigate the molecular basis of monoterpene interactions and their specificity in different OARs and TARs of damaging or beneficial insects. Sequence and structure comparison revealed that the OARs/TARs studied generally have more similarities in terms of structure rather than sequence identity. Together with clustering and network analyses, we also revealed that the role of IL3 might be crucial in the identification of OAR and TAR and their unique function. Among the 35 monoterpenes subjected to ensemble docking, carvacrol had the most negative average binding energies with the target insect OARs and TARs. The differences in the key interacting residues of carvacrol with insect OARs and TARs could be the origin of variation in the responses of insect species to this monoterpene. Results suggest that carvacrol may be a potential natural-product-based insecticide, targeting multiple insect pests while being nonharmful to honeybees and Asian swallowtail butterflies. This work could provide insights into the development of effective species-specific natural-product-based insecticides that are more environmentally friendly than conventional insecticides.

Cymbopogom Citratus Essential Oils: A Promising Source of Antifungals Against Panax Notoginseng-Associated Pathogenic Fungi

Due to the great threat of chemical pesticides to the ecosystem environment, it is a long-term goal to find environmentally friendly green pesticides. Essential oils (EOs) are considered weapons in plant chemical defense and are important sources of green pesticides. Therefore, the antifungal effects and action mechanisms of Cymbopogom citratus (C. citratus) EOs against seven kinds of Panax notoginseng (P. notoginseng) pathogenic fungi were investigated. Oxford Cup results showed that C. citratus EOs had an excellent detraction effects against seven fungi of P. notoginseng. Gas chromatography-mass spectrometry (GC-MS) was used to construct the chemical profiles of C. citratus EOs, disclosed that the main categories are terpenes and oxygenated terpenes. In addition, compared with the hymexazol, the minimum inhibitory concentration (MIC) showed that EOs and their main components had strong antifungal activities. Besides, EOs had a synergistic effect with hymexazol (a chemical pesticide). The antifungal mechanism of C. citratus EOs was studied by using Fusarium oxysporum (F. oxysporum) as the dominant pathogen. C. citratus EOs may affect the metabolism of fungi and induce mycotoxins to destroy the cell wall to achieve antifungal effects. Finally, EOs were found to significantly retard P. notoginseng infection by F. oxysporum. According to our research, C. citratus EOs are potential green antifungal agent that can be used in the cultivation of P. notoginseng.

Sublethal effects of oregano essential oil and its major compound carvacrol on biological parameters of Aedes albopictus (Diptera: Culicidae)

Mosquito management programs rely basically on the use of conventional synthetic larvicides. However, frequent applications and misuse of some synthetic insecticides have led to problems related to mosquito resistance development, harmful effects on human health and unacceptable environmental effects on non-target organisms. Recently, a growing number of phytochemicals has been tested as more eco-friendly larvicides against various mosquito species, exerting high efficacy with multiple modes of action. In the laboratory, we investigated for the first time the sublethal effects of oregano oil and its major compound carvacrol, against Aedes albopictus (Asian tiger mosquito), a mosquito of great medical importance. We determined the effects of short term (24h) exposure of 3rd- 4th larvae to LC₅₀ concentrations on survival and development of survived larvae until adulthood, as well as on fecundity, fertility, longevity and wing length of emerged adults. Only half of 24h survived larvae from oregano oil and carvacrol treatment finally reached adulthood. Abnormal shapes of dead larvae and pupae, and failed adult emergence were also observed, indicating a potential growth inhibitory activity of the tested materials. No particular effects from exposure to larvicidal LC₅₀ concentrations were recorded on life cycle parameters of successfully emerged adults. These findings suggest the tested oregano oil and carvacrol as sufficiently effective larvicides against Ae. albopictus at lower than the acutely toxic concentrations, promoting a more eco-friendly and less costly profile for these biopesticides.

Resistance induction and nematicidal activity of certain monoterpenes against tomato root-knot caused by Meloidogyne incognita

This research was performed to evaluate the potential of carvone, cuminaldehyde, cineole, and linalool for the control of root-knot of tomato. The tested control agents were evaluated for their ability to stimulate systemic resistance to Meloidogyne incognita in tomato by monitoring the transcription levels of defense-related genes. Moreover, the ability of the tested agents to induce nematicidal activity concerning second-stage juveniles (J2) hatching and mortality was evaluated. Furthermore, the effect of the tested agents on certain tomato growth and yield parameters was assessed. The tested monoterpenes showed high nematicidal activity against M. incognita concerning J2 hatching inhibition and mortality. Carvone, cuminaldhyde, linalool, and cineole had LC50 values of 123.5, 172.2, 354.9, 466.4, and 952.3 μg/mL, respectively. Carvone was found to be the most efficient hatching inhibitor. The tested monoterpenes showed a high potential against root-knot under greenhouse and field conditions with respect to root-galling, egg masses, and the number of J2. Carvone was the most effective treatment. The growth and yield characters of treated tomato were significantly increased in monoterpenes treatments compared to untreated control. Treated tomato plants showed expression of defense-related genes (PR1 and PAL) 5-8 folds higher than the control. The results also showed that cuminaldhyde, followed by carvone, linalool, and cineole, had the greatest levels of expression in tomato plants. Taken together, the selected monoterpenes could be used as alternatives to control the root-knot of tomato.

Direct and Indirect Effects of Essential Oils for Sustainable Crop Protection

Plant essential oils (EOs) are gaining interest as biopesticides for crop protection. EOs have been recognized as important ingredients of plant protection products including insecticidal, acaricidal, fungicidal, and nematicidal agents. Considering the growing importance of EOs as active ingredients, the domestication and cultivation of Medicinal and Aromatic Plants (MAPs) to produce chemically stable EOs contributes to species conservation, provides the sustainability of production, and decreases the variations in the active ingredients. In addition to these direct effects on plant pests and diseases, EOs can induce plant defenses (priming effects) resulting in better protection. This aspect is of relevance considering that the EU framework aims to achieve the sustainable use of new plant protection products (PPPs), and since 2020, the use of contaminant PPPs has been prohibited. In this paper, we review the most updated information on the direct plant protection effects of EOs, focusing on their modes of action against insects, fungi, and nematodes, as well as the information available on EOs with plant defense priming effects.

Preparation of geranium oil formulations effective for control of phenotypic resistant cattle tick Rhipicephalus annulatus

The aim of the present study was to evaluate in vitro and in vivo the acaricidal activity of two forms of geranium (Pelargonium graveolens) (PG). These two forms were the P. graveolens essential oil nanoemulsion (PGN), and the PG in combination with the sesame oil (SO), PGSO). These forms were first evaluated in vitro for their adulticidal, ovicidal, and larvicidal activities against the different stages of acaricide-resistant Rhipicephalus annulatus (Say). Geranium nanoemulsion was prepared and then characterized by UV-Vis spectrophotometer, and zeta droplet size measurement. The results revealed that LC₅₀ of the PG against the adult ticks was attained at concentration of 7.53% while it was decreased to 1.91% and 5.60% for PGSO and PGN, respectively. Also, the LC₅₀ of PGN and PGSO were reached at concentrations of 1.688 and 0.944%, respectively against the larvae while the LC₅₀ of the PG was reached at concentration of 3.435% for. The combination of PGN with PG exhibited non-significant ovicidal effect meanwhile PGSO showed significant ovicidal effect even at the low concentration (2.5%). The PGSO and PGN formulations were applied in a field trial to control the ticks of the naturally infested cattle. PGSO and PGN significantly reduced the tick burden to 74.83% and 87.97%, respectively at 3 weeks post-application with performance better than the deltamethrin (29.88%). In conclusion, the two PG forms can be used as suitable alternatives to control R. annulatus tick and they need further modifications for effective field application.

Synergistic Effect of Bioactive Monoterpenes against the Mosquito, Culex pipiens (Diptera: Culicidae)

Mosquitoes represent one of the most important vectors and are responsible for the transmission of many arboviruses that affect human and animal health. The chemical method using synthetic insecticides disturbs the environmental system and promotes the appearance of resistant insect species. Therefore, this study investigated the insecticidal effect of some binary monoterpene combinations (1,8 cineole + α-pinene and carvone + R (+)-pulegone) using a mixture design approach. The fumigant toxicity was evaluated against Culex pipiens female adults using glass jars. The results show that the toxicity varies according to the proportions of each compound. Indeed, Mixture 1 (1,8-cineole + α-pinene) displayed a strong toxic effect (51.00 ± 0.86% after 24 h and 100.00 ± 0.70% after 48 h) when the pure compounds were tested at 0.25/0.75 proportions of 1,8-cineole and α-pinene, respectively. Nevertheless, the equal proportion (0.5/0.5) of carvone and R (+)-pulegone in Mixture 2 exhibited a toxic effect of 54.35 ± 0.75% after 24 h and 89.96 ± 0.14% after 48 h, respectively. For Mixture 1, the maximum area of mortality that the proposed model indicated was obtained between 0/1 and 0.25/0.75, while the maximum area of mortality in the case of Mixture 2 was obtained between 0.25/0.75 and 0.75/0.25. Moreover, the maximum possible values of mortality that could be achieved by the validated model were found to be 51.44% (after 24 h) and 100.24% (after 48 h) for Mixture 1 and 54.67% (after 24 h) and 89.99% (after 48 h) for Mixture 2. It can be said that all purev molecules tested through the binary mixtures acted together, which enhanced the insecticide’s effectiveness. These findings are very promising, as the chemical insecticide (deltamethrin) killed only 19.29 ± 0.01% and 34.05 ± 1.01% of the female adults after 24 h and 48 h, respectively. Thus, the findings of our research could help with the development of botanical insecticides that might contribute to management programs for controlling vectors of important diseases.

Acaricidal and anthelmintic efficacy of Ocimum basilicum essential oil and its major constituents estragole and linalool, with insights on acetylcholinesterase inhibition

The present study evaluated the acaricidal and anthelmintic action of Ocimum basilicum essential oil and its main components against ticks and helminth parasites as well as to relate these activities to acetylcholinesterase inhibition. The in vitro acaricidal activity against Hyalomma scupense was evaluated by Adult Immersion Test (AIT) and Larval Packet Test (LPT), while the in vivo nematocidal potential was assessed in laboratory mice infected with Heligmosomoides polygyrus using fecal egg count reduction (FECR) and total worm count reduction (TWCR). Chemical analyzes were performed by gas chromatography coupled to mass spectrometry (GC-MS). Estragole (80.87%) and linalool (16.12%) were the major compounds detected in O. basilicum essential oil. In the AIT assay for H. scupense tick, LC₅₀ of estragole, O. basilicum oil and linalool were 0.73, 0.81 and 0.97 mg/mL, respectively. In LPT, estragole, linalool and essential oil showed LC₅₀ of 0.22, 1.11 and 1.19 mg/mL, respectively. Against He. polygyrus, the highest activity was observed with estragole administered at 100 mg/kg body weight (bwt), which resulted in a FECR of 90.86% and a TWCR of 82.91%. The O. basilicum essential oil, estragole and linalool inhibited the enzyme acetylcholinesterase (AChE) extracted from both parasites species. Estragole was found the most active AChE inhibitor with IC₅₀ of 0.176 mg/mL for H. scupense and IC₅₀ of 0.138 mg/mL for He. polygyrus larvae. The results of the present study pointed out the importance of the traditional use of O. basilicum as an eco-friendly alternative against endo and ectoparasites. In vivo trials should also be conducted to confirm the above-mentioned activities and to assure the safe use of natural plants.

When Scent Becomes a Weapon—Plant Essential Oils as Potent Bioinsecticides

Crop protection still mostly relies on synthetic pesticides for crop pest control. However, the rationale for their continued use is shaded by the revealed adverse effects, such as relatively long environmental persistence that leads to water and soil contamination and retention of residues in food that brings high risks to human and animal health. As part of integrated pest management, biopesticides may provide crop protection, being eco-friendly and safe for humans and non-target organisms. Essential oils, complex mixtures of low-molecular-weight, highly volatile compounds, have been highlighted as major candidates for plant-derived bioinsecticides that are up to the sustainable biological standard. In this review, we screened the insecticidal activity of essential oils or their purified compounds, with focus given to their modes of action, along with the analyzed advantages and problems associated with their wider usage as plant-derived insecticides in agriculture.

Defining the mechanisms of action and mosquito larva midgut response to a yeast-encapsulated orange oil larvicide

BACKGROUND

Yeast-encapsulated orange oil (YEOO) is a novel, ingestible larvicide that combines the benefits of a low-cost essential oil with yeast, an attractive food source for mosquito larvae. In this work, we investigated the underlying mechanisms of action associated with YEOO ingestion by Aedes aegypti larvae.

METHODS

Aedes aegypti third-stage larvae (L3) were treated with sublethal or lethal concentrations of YEOO. Genes associated with apoptosis, autophagy and innate immune responses were investigated by RT-qPCR in guts and carcasses dissected from treated and control larvae. Differential expression of cytochrome P450 genes in the CYP6 and CYP9 families were also investigated. Confocal and transmission electron microscopy were used to assess damage caused by YEOO throughout the larval alimentary canal. TUNEL was used to assess apoptosis via DNA fragmentation.

RESULTS

The apoptosis genes IAP1 and IAP2 in larvae displayed opposing effects following exposure to lethal doses of YEOO, with a 26-fold induction of IAP1 at 8 h post YEOO ingestion. The effector caspase CASPS8 displayed a 6.7-fold induction in the gut and concomitant 70-fold induction in the carcass at 8 h post YEOO ingestion. The midgut epithelia regenerator, Vein, had an 11-fold induction in the gut after 4 h and was repressed 7.6-fold in the carcass at 24 h. Sublethal concentrations (< LC₅₀) led to significant differential expression of CYP6 and CYP9 genes. Midgut epithelial damage was highlighted by the destruction of microvilli, vacuolization of midgut cells and damage to cell junctions and basal lamina as early as 30 min. Larval type 2 peritrophic matrix structural integrity and porosity remain unchanged.

CONCLUSION

Our results strongly suggest that the robust larvicidal activity of YEOO is due to a generalized broad-acting mechanism combining epithelial damage and apoptosis, with concomitant expression of multiple innate response genes involved in epithelial regeneration and detoxification. YEOO's amenability for use as part of an integrated vector management program makes this novel larvicide a practical approach for mosquito larval control in the future.

Pesticidal Activity and Mode of Action of Monoterpenes

Synthetic pesticides are often associated with issues such as pest resistance, persistent residue, nontarget toxicity, and environmental issues. Therefore, the research and development of novel, safe, and effective pesticides has become a focus in pesticide discovery. Monoterpenes are secondary plant metabolites that commonly have multiple action targets and have been used in aromatherapy, alternative medicine, and food industries. Some are highly potent and stereoselective. They can potentially be botanical pesticides and serve as lead candidates for the design and synthesis of new monoterpenoid pesticides for agricultural applications. This article reviews publications and patents found in SciFinder Scholar between 2000 and May 2021 on monoterpenes and mainly focuses on pesticidal activities of frequently studied monoterpenes and their modes of action. The presented information and our views are hopefully useful for the development of monoterpenes as biopesticides and monoterpenoid pesticides.

Mosquitoes Larvicidal Activity of Ocimum kilimandscharicum Oil Formulation under Laboratory and Field-Simulated Conditions

Simple Summary

Mosquitoes are vectors of many severe diseases, notably malaria, yellow as well as dengue fever, and lymphatic filariasis. Vector control with synthetic chemical insecticides has been associated with resistance development and undesirable human and ecological effects. Ocimum kilimandscharicum oil formulation was evaluated for larvicidal activity against third instar mosquito larvae in the laboratory. The formulation was then compared with Bacillus thuringiensis subsp. israelensis (Bti) granules on An. gambiae larvae under field-simulated field trials. The LC₅₀ for O. kilimandscharicum oil after 24 h against third instar larvae of An. gambiae was 0.74 ppm while for the emulsified O. kilimandscharicum oil formulation against third instar larvae of An. gambiae and An. arabiensis was 0.07 and 0.31 ppm, respectively. The high bioactivity and sublethal toxic effects to offspring of treated mosquito larvae in terms of the disruption of larval morphological aspects suggest its high potential as a botanical larvicide for the control of disease vectors. The bioactive formulation had the advantage of high solubility in aqueous media; it is also easily produced, ecofriendly, and low-cost. Moreover, because O. kilimandscharicum can easily be widely cultivated and has high EO yields, it may provide a valuable alternative for the effective and eco-friendly control of disease vectors among developing and developed communities.

Abstract

Mosquitoes are vectors of many severe diseases, including malaria, yellow as well as dengue fever, and lymphatic filariasis. The use of synthetic chemical insecticides for mosquito control has been associated with resistance development and detrimental human, and ecological effects. For a safer alternative, the emulsified Ocimum kilimandscharicum oil formulation was evaluated for its larvicidal activity. The oil was analyzed by GC and GC/MS. The formulations were evaluated against third instar mosquito larvae in the laboratory and later compared with Bacillus thuringiensis subsp. israelensis against An. gambiae under field-simulated conditions. Thirty-nine compounds were identified in the oil, the main ones being D-camphor (36.6%) and limonene (18.6%). The formulation showed significant larval mortalities against An. gambiae and An. arabiensis larvae with LC₅₀ of 0.07 and 0.31 ppm, respectively, at 24 h. Under the field-simulated trial, within 24 h, the formulation showed 98% mortality while Bti had achieved 54%. On day three, it caused 100% mortality while Bti achieved 76.5%. The high bioactivity and sublethal toxic effects to offspring of treated mosquito larvae, in terms of disruption of larval morphological aspects, suggest the high potential of the formulation as a botanical larvicide. The formulation, thus, may provide a valuable alternative for the effective and eco-friendly control of disease vectors.

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.

Plant-Based Bioinsecticides for Mosquito Control: Impact on Insecticide Resistance and Disease Transmission

Simple Summary

Mosquito-borne diseases cause millions of deaths each year. There has been an increase in the use of insecticides to combat disease transmission caused by mosquitoes. Synthetic insecticides have been effectively used to protect humans from mosquito bites through insecticide-treated mosquito nets, fabrics, and indoor sprays. Despite the considerable progress made in reducing mosquito borne diseases, extensive usage of insecticides has caused serious health problems to humans and animals, insecticide resistance or insensitivity in mosquitoes, and environmental damage. A success in the fight with mosquito disease transmission can only be accomplished by adequate and effective implementation of insecticide resistance monitoring and management programs globally. For this purpose, extensive research focuses on exploring insecticide resistance mechanisms in mosquitoes and how they get resistant to chemical applications over time. The search also focuses on novel compounds that are more effective, safer, and eco-friendly for improved management of mosquito vectors. In this review, we provide the current literature on the synthetic insecticides and how mosquitoes develop resistance to them, with further emphasis on bioinsecticides that could replace conventional synthetic insecticides. In this context, plant-based compounds are explained in detail with their potential applications to control mosquitoes.

Abstract

The use of synthetic insecticides has been a solution to reduce mosquito-borne disease transmission for decades. Currently, no single intervention is sufficient to reduce the global disease burden caused by mosquitoes. Problems associated with extensive usage of synthetic compounds have increased substantially which makes mosquito-borne disease elimination and prevention more difficult over the years. Thus, it is crucial that much safer and effective mosquito control strategies are developed. Natural compounds from plants have been efficiently used to fight insect pests for a long time. Plant-based bioinsecticides are now considered a much safer and less toxic alternative to synthetic compounds. Here, we discuss candidate plant-based compounds that show larvicidal, adulticidal, and repellent properties. Our discussion also includes their mode of action and potential impact in mosquito disease transmission and circumvention of resistance. This review improves our knowledge on plant-based bioinsecticides and the potential for the development of state-of-the-art mosquito control strategies.

PaOctβ2R: Identification and Functional Characterization of an Octopamine Receptor Activating Adenylyl Cyclase Activity in the American Cockroach Periplaneta americana

Biogenic amines constitute an important group of neuroactive substances that control and modulate various neural circuits. These small organic compounds engage members of the guanine nucleotide-binding protein coupled receptor (GPCR) superfamily to evoke specific cellular responses. In addition to dopamine- and 5-hydroxytryptamine (serotonin) receptors, arthropods express receptors that are activated exclusively by tyramine and octopamine. These phenolamines functionally substitute the noradrenergic system of vertebrates Octopamine receptors that are the focus of this study are classified as either α- or β-adrenergic-like. Knowledge on these receptors is scarce for the American cockroach (Periplaneta americana). So far, only an α–adrenergic-like octopamine receptor that primarily causes Ca²⁺ release from intracellular stores has been studied from the cockroach (PaOctα1R). Here we succeeded in cloning a gene from cockroach brain tissue that encodes a β-adrenergic-like receptor and leads to cAMP production upon activation. Notably, the receptor is 100-fold more selective for octopamine than for tyramine. A series of synthetic antagonists selectively block receptor activity with epinastine being the most potent. Bioinformatics allowed us to identify a total of 19 receptor sequences that build the framework of the biogenic amine receptor clade in the American cockroach. Phylogenetic analyses using these sequences and receptor sequences from model organisms showed that the newly cloned gene is an β2-adrenergic-like octopamine receptor. The functional characterization of PaOctβ2R and the bioinformatics data uncovered that the monoaminergic receptor family in the hemimetabolic P. americana is similarly complex as in holometabolic model insects like Drosophila melanogaster and the honeybee, Apis mellifera. Thus, investigating these receptors in detail may contribute to a better understanding of monoaminergic signaling in insect behavior and physiology.

Biochemical evaluation and molecular docking assessment of Cymbopogon citratus as a natural source of acetylcholine esterase (AChE)- targeting insecticides

Acetylcholinesterase (AChE) has been an effective target for insecticide development which is a very important aspect of the global fight against insect-borne diseases. The drastic reduction in the sensitivity of insects to AChE-targeting insecticides like organophosphates and carbamates have increased the need for insecticides of natural origin. In this study, we used Drosophila melanogaster as a model to investigate the insecticidal and AChE inhibitory potentials of Cymbopogon citratus and its bioactive compounds. Flies were exposed to 100 and 200 mg/mL C. citratus leaf extract for a 3-h survival assay followed by 45 min exposure for negative geotaxis and biochemical assays. Molecular docking analysis of 45 bioactive compounds of the plant was conducted against Drosophila melanogaster AChE (DmAChE). Exposure to C. citratus significantly reduced the survival rate of flies throughout the exposure period and this was accompanied by a significant decrease in percentage negative geotaxis, AChE activity, catalase activity, total thiol level and a significant increase in glutathione-S-transferase (GST) activity. The bioactive compounds of C. citratus showed varying levels of binding affinities for the enzyme. (+)-Cymbodiacetal scored highest (−9.407 kcal/mol) followed by proximadiol (−8.253 kcal/mol), geranylacetone (−8.177 kcal/mol), and rutin (−8.148 kcal/mol). The four compounds occupied the same binding pocket and interacted with important active site amino acid residues as the co-crystallized ligand (1qon). These compounds could be responsible for the insecticidal and AChE inhibitory potentials of C. citratus and they could be further explored in the development of AChE-targeting insecticides.

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Cymbopogon citratus reduced the AChE activity, catalase activity, total thiol level in Drosophilia melanogaster.

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The bioactive compounds of Cymbopogon citratus displayed considerable binding affinities for Drosophila melanogaster AChE and the four top-scoring compounds are (+)-Cymbodiacetal, proximadiol, geranylacetone, and rutin.

•

(+)-Cymbodiacetal showed the highest binding affinity to AChE (DmAChE).

Chemical composition, antibacterial, antioxidant and insecticidal activities of moroccan Thapsia transtagana essential oil

INTRODUCTION

The use of chemical products to neutralize microorganisms has always been a subject of discussion and research for alternative solutions, indeed, the use of essential oils has been a promising natural methodology.

METHODS

In our study we used the essential oils from different parts of Thapsia transtagana (Apiaceae), obtained by hydrodistillation, were identified and using Gas chromatography-mass spectrometry (GC-MS) and Gas Chromatography-Flame Ionization Detection (GC/FID) methods and evaluated against several bacteria of Gram- and Gram + bacteria. Disk diffusion, Minimum Inhibitory Concentration (MIC) and Minimum Microbicidal Concentration (MMC) methods have been used. Free radical-scavenging activity and insecticidal activity of Thapsia transtagana essential oils were also identified.

RESULTS

Majority products from different parts of Thapsia transtagana essential oil identified by GC-MS and GC/FID methods are 2,6-Dimethylnaphthalene, Pinane and Hexahydrofarnesyl acetone. The highest activity was found against Staphylococcus aureus using inflorescence essential oil with minimal inhibitory concentration value for 0,56 μg/μL. Insecticidal activity was also the subject of this study, roots and inflorescence essential oils demonstrated to have a remarkable potent against Acanthoscelides obtectus and Sitophilus oryzae using contact assessment, inhalation assessment and ingestion assessment tests. Insecticidal activity assay results showed a significant enhancement of mortality in both test insect pest on increasing the dose and exposure period. In the other hand, the different essential oils of Thapsia transtagana were evaluated for their radical scavenging activities by means of the 2,2-diphenyl-1-picryl-hydrazyl (DPPH) assay. The strongest scavenging activity was observed in inflorescences essential oil fraction scavenged radicals effectively at 100% using 500 mgL-1 concentration.

CONCLUSION

Its essential oils were proved to have strong antimicrobial, insecticidal and antioxidant activities that allows it to be used by the pharmaceutical and cosmetic industries as natural preservative.

Combination of cypermethrin and thymol for control of Rhipicephalus microplus: Efficacy evaluation and description of an action mechanism

The cattle tick Rhipicephalus microplus is one of the most important ectoparasites in the tropical and subtropical regions of the world. Synthetic pyrethroids are widely used to control this tick, and the selection of resistant populations is a huge problem worldwide. The activity of thymol, a natural monoterpene, free or in combination with other compounds, has been demonstrated against different species of ticks. However, the mode of action is not fully understood. The present study aimed to evaluate the efficacy and the potential mode of action of the combination of cypermethrin and thymol on ticks from two populations with different levels of susceptibility to cypermethrin (low and high susceptibility). The isolated acaricidal activity of cypermethrin and thymol on larvae was carried out in different concentrations. The combination with different concentrations of cypermethrin and fixed concentrations of thymol (1300 µg/mL for the low susceptibility population; 690 µg/mL for the high susceptibility population) were performed. Adult engorged females were divided into five experimental groups (n = 20): 1) Control group untreated; 2) Control group: 2.0% (v/v) DMSO; 3) Thymol group: 1300 µg/mL thymol; 4) Cypermethrin group: 3700 µg/mL cypermethrin; 5) Association of cypermethrin (3700 µg/mL) + thymol (1300 µg/mL). A subgroup was used to study the efficacy of the reproductive parameters and another subgroup, with ten adults from each treatment, was used to quantify thymol and cypermethrin by HPLC chromatographic analysis. All compounds tested were effective on larvae from both populations, and the combination with thymol decreased the LC₅₀ of cypermethrin (232.4 to 52.7 µg/mL) on the low-susceptibility population. The combination of thymol and cypermethrin was effective in both populations of R. microplus (reproductive performance of engorged females) when compared to the untreated control group, even with higher percent control values (pop. 1: 93.5 ± 5.6% and pop. 2: 92.7 ± 1.1%) than the group treated only with cypermethrin (pop. 1: 87.3 ± 7.3% and pop. 2: 83.5 ± 1.2%). From the HPLC analyzes, a higher concentration of cypermethrin (pop. 1: 30.3 ± 6.9 and pop. 2: 45.4 ± 17.7 ng/mg) was detected in the tissues of engorged females treated with the combination compared to analyte concentrations in groups treated with cypermethrin only (pop. 1: 12.4 ± 4.4 pop. 2: 25.5 ± 9.4 ng/mg). This was the first study to investigate the acaricidal efficacy of the combination of thymol + cypermethrin on R. microplus and demonstrate that the presence of thymol increases the concentration of cypermethrin in the internal tissues of engorged females through a possible mechanism for increasing the penetration of cypermethrin at the cuticular level.

Assessment of lipid profile in fat body and eggs of Rhipicephalus microplus engorged females exposed to (E)-cinnamaldehyde and α-bisabolol, potential acaricide compounds

In the present study, the lipid profile from the fat body and eggs of Rhipicephalus microplus was evaluated after exposure of engorged females to (E)-cinnamaldehyde and α-bisabolol, substances which have acaricide potential according to the literature. Engorged females collected from artificially infested cattle were immersed in a concentration of 10.0 mg/mL of each substance. Dissection of the female fat bodies was performed at different times (72 h and 120 h), for subsequent lipid extraction. In addition, on the fifth day of oviposition, were collected 50.0 ml50.0 mL aliquots of the egg mass of each treatment to perform the same lipid extraction procedure. To assess the lipid profiles, the samples were submitted to the thin layer chromatography (TLC) and gas chromatography-mass spectrometry (GCMS) analysis. Furthermore, an in silico analysis was performed using PASS online® software to predict the possible molecular targets of (E)-cinnamaldehyde and α-bisabolol. As result, the main lipids identified from the fat body were triacylglycerides, fatty acids, and cholesterol, whereas, triacylglycerides (TAG), fatty acids (FA), and cholesterol (CHO) and cholesterol esters (CHOE), were identified in the eggs. The results also showed a significant increase (p < 0.05) of CHO in the fat body in the group exposed to (E)-cinnamaldehyde at 72 h (0.12 μg/fat body) and 120 h (0.46 μg/fat body), in the eggs from females treated with this same substance, there was a significant reduction (p < 0.05) in the amount of CHO (0.21 μg), compared to the water control group (0.45 μg). In the GCMS technique, 5 chemical classes were found, and variations were observed between these substances, mainly hydrocarbons and steroids, in the different groups, and (E)-cinnamaldehyde promoted the greatest changes. From the predictions of the in silico study, 38 and 20 targets were selected, respectively, which are mainly related to alterations in lipid metabolism, immune system and nervous system. This study provides the first report of changes in lipid metabolism of R. microplus exposed to (E)-cinnamaldehyde and α-bisabolol, as well as presenting possible activity on the molecular targets of these substances, expanding knowledge for the potential use of these compounds in the development of botanical acaricides.

Acaricidal and Repellent Effects of Essential Oils against Ticks: A Review

Tick control is a priority in order to prevent the transmission of vector-borne diseases. Industrial chemical acaricides and repellents have been the most efficient tools against hard ticks for a long time. However, the appearance of resistances has meant the declining effectiveness of the chemicals available on the market. The trend today is to develop alternative control methods using natural products to replace nonefficient pesticides and to preserve the efficient ones, hoping to delay resistance development. Traditional in vitro evaluation of acaricidal activity or resistance to synthetic pesticides have been reviewed and they mainly focus on just one species, the one host tick (Rhipicephalus (Boophilus) microplus (Acari: Ixodidae)). Recent reports have called for the standardization of natural product components, extraction techniques, and experimental design to fully discover their acaricidal potential. This study reviews the main variables used in the bibliography about the efficiency of natural products against ticks, and it proposes a unification of variables relating to ticks, practical development of bioassays, and estimation of ixodicidal activity.

Nematicidal Activity of Essential Oil from Lavandin (Lavandula × intermedia Emeric ex Loisel.) as Related to Chemical Profile

Essential oils (EOs) from lavandin are known for a large spectrum of biological properties but poorly and contrastingly documented for their activity against phytoparasitic nematodes. This study investigated the toxicity of EOs from three different lavandin cultivars, Abrialis, Rinaldi Cerioni, and Sumiens, either to juveniles (J2) and eggs of the root-knot nematode Meloidogyne incognita and to infective stages of the lesion nematode Pratylenchus vulnus. The suppressive activity of treatments with EOs from the three lavandin cultivars in soil infested by M. incognita was also investigated in a greenhouse experiment on potted tomato. The compositional profiles of tested EOs were also analyzed by GC-FID and GC-MS. Linalool was the major component of all the three EOs, as accounting for about 66%, 48%, and 40% of total EO from cv Rinaldi Cerioni, Sumiens, and Abrialis, respectively. Linalool acetate was the second most abundant compound in the EOs from cv Abrialis (18.3%) and Sumiens (14.9%), while significant amounts of camphor (11.5%) and 1,8-cineole (12.1%) were detected in cv Rinaldi Cerioni and Sumiens EOs, respectively. The mortality of M. incognita J2 peaked 82.0%, 95.8%, and 89.8% after a 24 h treatment with 100 mg·mL⁻¹ solutions of cv Abrialis, Rinaldi Cerioni, and Sumiens EOs, respectively. Infective specimens of P. vulnus were largely more sensitive than M. incognita J2, as there were peak mortality rates of 65.5%, 67.7%, and 75.7% after 4 h of exposure to Abrialis, Rinaldi Cerioni, and Sumiens EO, respectively. All three lavandin EOs significantly affected also M. incognita egg hatchability, which reduced to 43.6% after a 48 h egg mass exposure to a 100 µg·mL⁻¹ solution of cv Rinaldi Cerioni EO. Soil treatments with the three lavandin EOs strongly reduced, according to a dose–effect relationship, density of M. incognita eggs, and J2 both on tomato roots and in soil, as well as significantly reduced gall formation on tomato roots. Finally, almost all soil treatments with the lavandin EOs also resulted in a positive impact on tomato plant growth.

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.

Development of nano-emulsions based on Ayapana triplinervis essential oil for the control of Aedes aegypti larvae

Ayapana triplinervis is a plant species used in traditional medicine and in mystical-religious rituals by traditional communities in the Amazon. The aim of this study are to develop a nano-emulsion containing essential oil from A. triplinervis morphotypes, to evaluate larvicidal activity against Aedes aegypti and acute oral toxicity in Swiss albino mice (Mus musculus). The essential oils were extracted by steam dragging, identified by gas chromatography coupled to mass spectrometry, and nano-emulsions were prepared using the low energy method. Phytochemical analyses indicated the major compounds, expressed as area percentage, β-Caryophyllene (45.93%) and Thymohydroquinone Dimethyl Ether (32.93%) in morphotype A; and Thymohydroquinone Dimethyl Ether (84.53%) was found in morphotype B. Morphotype A essential oil nano-emulsion showed a particle size of 101.400 ± 0.971 nm (polydispersity index = 0.124 ± 0.009 and zeta potential = -19.300 ± 0.787 mV). Morphotype B essential oil nano-emulsion had a particle size of 104.567 ± 0.416 nm (polydispersity index = 0.168 ± 0.016 and zeta potential = -27.700 ± 1.307 mV). Histomorphological analyses showed the presence of inflammatory cells in the liver of animals treated with morphotype A essential oil nano-emulsion (MAEON) and morphotype B essential oil nano-emulsion (MBEON). Congestion and the presence of transudate with leukocyte infiltration in the lung of animals treated with MAEON were observed. The nano-emulsions containing essential oils of A. triplinervis morphotypes showed an effective nanobiotechnological product in the chemical control of A. aegypti larvae with minimal toxicological action for non-target mammals.

Toxicity of Methyl Benzoate and Analogs to Adult Aedes aegypti

Methyl benzoate is a natural product (floral volatile organic compound) that is currently used as a food flavoring ingredient. This compound has shown to be insecticidal in laboratory studies against agricultural and urban pests, including spotted wing drosophila Drosophila suzukii, brown marmorated stink bug Hyalomorpha halys, the diamondback moth Plutella xylostella, and the common bed bug Cimex lectularius, to name several insect taxa. In this study we topically treated adult Aedes aegypti females with methyl benzoate and analogs and determined their toxicities. We found that among adult females, 4 analogs-butyl benzoate, n-pentyl benzoate, vinyl benzoate, and methyl 3-methoxybenzoate-were more toxic than the parent compound, methyl benzoate.

Acaricidal Efficacy of Jasmine and Lavender Essential Oil or Mustard Fixed Oil against Two-Spotted Spider Mite and Their Impact on Growth and Yield of Eggplants

Simple Summary

The two-spotted spider mite (TSSM) represents the highly polyphagous pest worldwide in protected and open field condition results in a serious economic yield loss (50-100%) in severe infestation conditions. The ecological crisis attributable to the extra-application of acaricides has been an issue of concern in modern decades. It is former to estimate that nearly 2.5 million tons of pesticides are utilized in agricultural production yearly and the global injury evoked by pesticides achieves $100 billion yearly. It is therefore hoped that natural oils can offer alternative options to synthesis acaricides and contribute to pesticide resistance. Application of essential oils of lavender and jasmine, as well as mustard fixed oil, is inducing the plant resistance to TSSM as well as and improving plant growth and yield of eggplants

Abstract

Eggplant is repeatedly attacked by numerous pests, particularly two-spotted spider mite (TSSM), which considerably decline plant productivity. Synthetic acaricides are frequently applied for controlling TSSM, resulting in environmental pollution. The utilization of rational novel substances which repel or prevent TSSM establishment represents a sustainable eco-friendly to reduce the utilization of agrochemicals. A greenhouse investigation was done for assessing the bio-acaricidal activity of mustard (Brassica juncea L.) fixed oil (MFO), jasmine (Jasminum grandiflorum L.) essential oil (JEO), or lavender (Lavandula angustifolia L.) essential oil (LEO), and their influences on eggplant growth and productivity. The results demonstrated that JEO represents the most acaricidal properties against TSSM followed by MFO and/or LEO compared to control. Spraying with natural oils significantly improved eggplant growth, i.e., plant height, number of leaves, and branches/plant, in addition to the leaf area and relative leaf dry mass of the 3rd–5th upper leaves. The JEO had the strongest positive effect compared with other oils or control. Additionally, Natural oils application significantly increased photosynthetic pigment, chlorophyll _a:b ratio, and nitrogen, phosphorus, potassium, ascorbic acid, and phenols. The application of oils increased yield and its quality. In this study, JEO (2.5 mL/l) is shown to be extremely promising for the progress of new eco-friendly acaricides, improving plant growth and increasing eggplant yield.

Molecular Characterization of the β2-like Octopamine Receptor of Helicoverpa armigera

Helicoverpa armigera is a devastating polyphagous and cosmopolitan crop pest. There are reports of this insect being resistant to a variety of pesticides raising concern worldwide. The Octopamine (OA) binding β₂-like receptor (OAR), a GPCR, is widely distributed in the nervous system of the insect and plays essential roles in the physiology and development and thus is an important target for insecticides. Yet, the molecular characterization of the H. armigera OAR (HarmOAR) and rational design of compounds based on this receptor is lacking. As a first step, we performed multiple sequence alignment of all insect OARs, which revealed that the sequences contained all conserved class A GPCR motifs. Phylogenetic studies showed clade-specific variations in the protein sequences primarily arising owing to differences in the ICL3 loop region. Further, a structural model of HarmOAR was built using the inactive human β₂AR as a template. 0.9 µs atomistic simulations revealed conserved inter helical contacts and water molecules of HarmOAR. The detailed binding of octopamine was studied using molecular docking and 0.3 µs atomistic simulations. Twenty-two insecticides active against octopamine receptors of other insects were compiled and docked to HarmOAR followed by rescoring with binding free energies to prioritize them for H. armigera. Our study suggests α-terpineol to be a good candidate as an insecticide or insect repellent for Helicoverpa armigera.

Monoterpenes: Essential Oil Components with Valuable Features

Medicinal plants have a wide range of secondary metabolites including monoterpene. These volatile compounds are the main components of essential oils, belonging to the isoprenoid group and possessing valuable features for plants and humans. This review provides comprehensive information on chemical structures and classification of monoterpenes. It describes their biosynthesis pathways and introduces plant families and species rich in noteworthy monoterpenes. Bio-activities, pharmacological and pesticide effects as well as their mechanism of action are reported. Applications of these compounds in various industries are also included.

Monoterpenes alter TAR1-driven physiology in Drosophila species

Monoterpenes are molecules with insecticide properties whose mechanism of action is, however, not completely elucidated. Furthermore, they seem to be able to modulate the monoaminergic system and several behavioural aspects in insects. In particular, tyramine (TA) and octopamine (OA) and their associated receptors orchestrate physiological processes such as feeding, locomotion and metabolism. Here, we show that monoterpenes not only act as biopesticides in Drosophila species but also can cause complex behavioural alterations that require functional type 1 tyramine receptors (TAR1s). Variations in metabolic traits as well as locomotory activity were evaluated in both Drosophila suzukii and Drosophila melanogaster after treatment with three monoterpenes. A TAR1-defective D. melanogaster strain (TAR1PL00408) was used to better understand the relationships between the receptor and monoterpene-related behavioural changes. Immunohistochemistry analysis revealed that, in the D. melanogaster brain, TAR1 appeared to be mainly expressed in the pars intercerebralis, lateral horn, olfactory and optic lobes and suboesophageal ganglion lobes. In comparison to wild-type D. melanogaster, the TAR1PL00408 flies showed a phenotype characterized by higher triglyceride levels and food intake as well as lower locomotory activity. The monoterpenes, tested at sublethal concentrations, were able to induce a downregulation of the TAR1 coding gene in both Drosophila species. Furthermore, monoterpenes also altered the behaviour in wild-type D. suzukii and D. melanogaster 24 h after continuous monoterpene exposure. Interestingly, they were ineffective in modifying the physiological performance of TAR1-defective flies. In conclusion, it appears that monoterpenes not only act as biopesticides for Drosophila but also can interfere with Drosophila behaviour and metabolism in a TAR1-dependent fashion.

Efficacy of bioactive compounds and their association with different cowpea cultivars against their major stored pest

BACKGROUND

Stored grain insects are controlled with fumigant insecticides which can select resistant insect populations and cause environmental and applicator contamination. Thus, resistant cultivars and chemical constituents of essential oils are an alternative to the almost exclusive use of these insecticides. The effects of the combination of cowpea cultivars Vigna unguiculata (L.) Walp. with chemical constituents of essential oils against Callosobruchus maculatus were determined. Four cowpea cultivars: BRS Tracuateua, BR 17 Gurgueia, Epace 10 and Sempre Verde (insect rearing) untreated were used in the experiments and combined with chemical constituents of essential oil: eugenol, geraniol and trans-anethole. The biological parameters observed were: total egg number and eggs per grain, egg viability (%), insects emerged and insects per grain, immature stage viability (%), instantaneous rate of growth (ri), insect dry weight (mg), grain weight loss (%) and egg-adult period.

RESULTS

When comparing all biological parameters, the cultivars BRS Tracuateua and BR 17 Gurgueia were harmful to C. maculatus. In the toxicity tests, the results showed that LC₃₀ and LC₅₀ of the chemical constituents ranged from 54.77 to 103.48 ppm and 60.99 to 125.18 ppm, respectively. In most of the biological parameters, LC₅₀ had adverse effects significantly higher than LC₃₀ and BR 17 Gurgueia treated were harmful to C. maculatus.

CONCLUSIONS

Overall, the findings showed that BR 17 Gurgueia combined with eugenol and geraniol more significantly affected the biological parameters of C. maculatus than when associated with trans-anethole, reducing egg number, insects emerged and egg viability. © 2020 Society of Chemical Industry.