Acaricidal Activity and Synergistic Effect of Thyme Oil Constituents against Carmine Spider Mite (Tetranychus Cinnabarinus (Boisduval))

Management potentiality of emulsions based on essential oil of Piper macedoi and Piper arboreum for spider mite: a possible alternative for agroecological control

Tetranychus urticae, popularly known as spider mite, is a pest that causes several economic losses to crops. Thus, this work evaluated the effect of essential oils from the leaves of Piper macedoi and Piper arboreum on managing T. urticae. The chemical compounds present in essential oils were identified by gas chromatography. Tests were carried out to evaluate the acaricidal activity by fumigation effect and direct contact with T. urticae. The results showed that LC50 values for the essential oils of P. macedoi and P. arboreum in the fumigation effect were 16.15 and 50.53 µL L-1 air, respectively. Using the contact application route, the LC50 values for the essential oil of P. macedoi was 17.16 µL mL-1, and for P arboreum, it was 15.17 µL mL-1. So, this work showed that essential oils of Piper macedoi and Piper arboreum could be used as possible alternative to managing T. urticae.

Chitinase from Streptomyces mutabilis as an Effective Eco-friendly Biocontrol Agent

Blood sucking parasites not only cause economic loss but also transmit numerous diseases. Dermanyssus gallinae, an obligatory blood feeding ectoparasite causes huge production loss to the poultry industry. Mosquitoes act as vector for transmitting several viral and parasitic diseases in humans. Acaricide resistance limits the control of these parasites. The present study was aimed to control the parasites using chitinase that have selective degradation of chitin, an important component in exoskeleton development. Chitinase was induced in Streptomyces mutabilis IMA8 with chitin extracted from Charybdis smithii. The enzyme showed more than 50% activity at 30-50 °C and the optimum activity at 45 °C. The enzyme activity of chitinase was highest at pH 7.0. The kinetic parameters Km and Vmax values of chitinase were determined by non-linear regression using Michaelis-Menten equation and its derivative Hanes-Wolf plot. The larvicidal effect of different concentrations of chitinase was evaluated against all instar larvae (I-IV) and pupae of An. stephensi and Ae. aegypti after 24 h of exposure. The percentage of mortality was directly proportional to the chitinase concentration. Bioassay for miticidal activity showed that chitinase had excellent miticidal activity (LC50 = 24.2 ppm) against D. gallinae. The present study suggested the usage of Streptomyces mutabilis for preparation of chitinase in mosquito and mite control.

Discovery of 3-Formyl-N-(un)Substituted Benzylindole Pyrimidines as an Acaricidal Agent and Their Mechanism of Action

To discover the pronounced acaricide candidate, herein, a series of 3-formyl-N-(un)substituted benzylindole pyrimidines were prepared by structural modification of indoles at the N-1 and C-3 positions via the successive Vilsmeier-Haack-Arnold (VHA), aldol condensation, and cyclization reactions. The steric structures of nine compounds were undoubtedly confirmed by X-ray single-crystallography. Against Tetranychus cinnabarinus Boisduval, compounds V-15, V-31, V-34, V-42, V-44, and V-60 exhibited promising acaricidal activity with LC50 values of 0.299-0.481 mg/mL. In particular, compound V-34 displayed 4.2 times the acaricidal activity of its precursor 6-methylindole. Scanning electron microscopy (SEM) imaging revealed that the construction of the cuticle layer of V-34-treated T. cinnabarinus was seriously destroyed. Furthermore, RNA-Seq analysis indicated that compound V-34 could regulate the homeostasis metabolism of T. cinnabarinus through arachidonic acid and linoleic acid metabolism and lysosome pathways. These results suggested that compound V-34 can be further studied as a lead acaricidal agent.

Desiccant Dusts, With and Without Bioactive Botanicals, Lethal to Rhipicephalus (Boophilus) microplus Canestrini (Ixodida: Ixodidae) in the Laboratory and on Cattle

The exotic southern cattle fever tick, Rhipicephalus (Boophilus) microplus (Canestrini) (Ixodida: Ixodidae), since its eradication from the United States in 1943, made a strong incursion into Texas, beginning 2016. The pest is arguably the most economically detrimental ectoparasite of cattle, Bos taurus L., worldwide. Current R. (B.) microplus control mostly relies on conventional synthetic acaricides to which the ixodid has been developing resistance. Our study demonstrates that commercially available desiccant dust products, with and without bioactive botanical additives, are strongly lethal, when applied dry, against larval R. (B.) microplus in the laboratory, and after being released on dust-treated cattle. Deadzone (renamed Celite 610, a diatomaceous earth product), Drione (silica gel + pyrethrins + piperonyl butoxide synergist), and EcoVia (silica gel + thyme oil), each prophylactically prevented larval R. (B.) microplus from attaching to and feeding on stanchioned calves. Desiccant dust-based products are less likely than conventional synthetic acaricides to decline in terms of efficacy as a result of ixodid resistance, and other desiccant dust advantages, including extended residual, flexibility in terms of application methods, environmental, animal, and human safety, and possible compatibility with organic, or 'green', production systems, are discussed. We anticipate that the desiccant dusts we evaluated, and others not included in this study (e.g., kaolin, perlite, and silica gel) will be effective when used with other control tactics in integrated pest management approaches for controlling R. (B.) microplus (and other ixodid species).

High Value-Added Application of Natural Plant Products in Crop Protection: Construction and Pesticidal Activities of Piperine-Type Ester Derivatives and Their Toxicology Study

To discover new potential pesticide candidates, recently, structural modification of natural bioactive products has received much attention. In this work, a series of new piperine-type ester derivatives were regio- and stereoselectively synthesized based on a natural alkaloid piperine isolated from Piper nigrum. Their structures were characterized by IR, mp, ¹H NMR (¹³C NMR), and high-resolution mass spectrometry (HRMS). Against Tetranychus cinnabarinus Boisduval (Acari: Tetranychidae), compounds 4e, 4f, 4u, and 4v displayed the most significant acaricidal activity with LC₅₀ values of 0.155, 0.117, 0.177, and 0.164 mg/mL, respectively. Particularly, compound 4f showed >120-fold higher acaricidal activity than piperine (LC₅₀: 14.198 mg/mL). Notably, the acaricidal activity of 4f was equivalent to that of the commercial acaricide spirodiclofen (LC₅₀: 0.115 mg/mL). Additionally, against Eriosoma lanigerum Hausmann (Hemiptera: Aphididae), compounds 4w and 4b' showed 1.8-fold aphicidal activity of piperine. Furthermore, via the scanning electron microscope (SEM) imaging method, the obvious destruction of the construction of the cuticle layer of 4f-treated T. cinnabarinus was observed. Compound 4f could be further studied as a lead acaricidal agent.

Acaricidal Activity and Field Efficacy Analysis of the Potential Biocontrol Agent Bacillus vallismortis NBIF-001 against Spider Mites

In recent years, spider mites have caused considerable economic losses to global agriculture. However, currently available management strategies are limited because of the rapid development of resistance. In this study, Bacillus vallismortis NBIF-001 was isolated and evaluated for its acaricidal activity. NBIF-001 exhibited a significant lethal effect on spider mites within 48 h. The median lethal concentration (LC₅₀) of the culture powders (3.2 × 10¹⁰ CFU/g) was 50.2 µg/mL for Tetranychus urticae (red form), 18.0 µg/mL for T. urticae (green form), and 15.7 µg/mL for Panonychus citri (McGregor). Cultivation optimisation experiments showed that when the number of spores increased, fermentation toxicity also increased. Moreover, field experiments demonstrated that NBIF-001 performed well in the biocontrol of P. citri, which showed a similar corrected field efficacy with the chemical control (67.1 ± 7.9% and 71.1 ± 6.4% after 14 days). Genomics analysis showed that NBIF-001 contains 231 factors and seven gene clusters of metabolites that may be involved in its acaricidal activity. Further bioassays of the fermentation supernatants showed that 50× dilution treatments killed 72.5 ± 5.4% of the mites in 48 h, which was similar with those of the broth. Bioassays of the supernatant proteins confirmed that various proteins exhibited acaricidal activity. Five candidate proteins were expressed and purified successfully. The bioassays showed that the small protein BVP8 exhibited significant acaricidal activity with an LC₅₀ of 12.4 μg/mL (T. urticae). Overall, these findings suggest that B. vallismortis NBIF-001 is a potential biocontrol agent for spider mite management.

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.

Preparation of Thymus vulgaris (L.) essential oil nanoemulsion and its chitosan encapsulation for controlling mosquito vectors

Here, we report a novel comparative assessment of preparation and characterization of thyme oil nanoemulsion and its chitosan encapsulation using high energy approach for the management of three major mosquito species viz., Anopheles stephensi (Liston,1901), Aedes aegypti (Linn., 1762) and Culex tritaeniorhynchus (Giles, 1901). The synthesized formulations were analysed for thermodynamic stability, indicating 1:0.5 (oil: surfactant) ratio to be the most stable of thyme oil nanoemulsion while 1:1 (nanoemulsion: chitosan solution) ratio of its chitosan encapsulation. These were further characterized by dynamic light scattering and transmission electron microscopy which revealed the size and morphology of the droplets which measured 52.18 ± 4.53 nm for thyme oil nanoemulsion and 50.18 ± 2.32 nm for its chitosan encapsulation. All the droplets were well dispersed with distinct flower-shaped nanoemulsion and somewhat mitochondria like chitosan encapsulation. In-vitro release study of thyme essential oil from its nanoemulsion and chitosan encapsulation showed that 91.68% and 73.41% of the total oil concentration in water was released respectively to the environment after 48 h clearly depicting controlled release in the encapsulation. Assessment of insecticidal potential against selected mosquito species revealed that both the nanoemulsion and its chitosan encapsulation were effective on the major mosquito species. Maximum activity of thyme oil nanoemulsion was noticed against C. tritaeniorhynchus (LC₅₀—22.58 ppm) after 24 h of exposure while it was observed that its chitosan encapsulation was most effective on A. stephensi (LC₅₀—18.88 ppm) after 24 h of exposure. Consistent morphological alterations could be noticed in the larvae of mosquito species. Hence, these nanoemulsions and encapsulations could be further tested for their applications against other insect pests in agriculture.

Comprehensive Evaluation on the Use of Thymus vulgaris Essential Oil as Natural Additive against Different Serotypes of Salmonella enterica

Essential oils were proposed as natural additives to ensure food safety and quality in a more sustainable approach. The chemical composition of Thymus vulgaris essential oil (TV-EO) collected from Morocco, its antioxidant and antimicrobial activity against different serotypes of Salmonella enterica subsp. enterica was investigated. A mathematical model was implemented to predict the Salmonella behavior when exposed to TV-EO. In situ antimicrobial activity and sensory influence were tested in minced poultry meat experimentally contaminated with Salmonella and treated with TV-EO. Hydrodistillation was used to extract TV-EO, and gas chromatography-mass spectrometry (GC-MS) analysis found thymol as the most representative compound. Results of the antioxidant activity showed an IC50 of 0.29 ± 0.04 mg/mL, EC50 of 0.74 ± 0.08 mg/mL, and RC50 of 0.59 ± 0.06 mg/mL. All the Salmonella strains were susceptible to TV-EO with performing results for the disc diffusion method (inhibition diameters ranged between 24 ± 0.4 mm and 32 ± 0.6 mm), determination of minimum inhibitory concentration (MIC; 0.5%) and minimum bactericidal concentration (MBC; 1%), sublethal-injured cells (7.99 ± 0.08%), in situ activity (growth inhibition after 3 days), and meat sensory preservation (up to 1 week). The implemented mathematical model well fitted the Salmonella growth curve. TV-EO with significant antioxidant and antibacterial activities was suitable to ensure food safety and quality consistent with the new sustainable trends in the food field.

Lethal Effects of a Silica Gel + Thyme Oil (EcoVia) Dust and Aqueous Suspensions on Amblyomma americanum (Ixodida: Ixodidae) Larvae and Nymphs

Ixodids suck blood from host animals and transmit pathogens that cause important medical and veterinary diseases. As synthetic conventional acaricide resistance becomes increasingly common, alternative tactics are likely to enhance control efforts. Laboratory bioassays assessed the lethality of CimeXa, a commercial silica gel desiccant dust, and EcoVia, a commercial product containing silica gel + thyme oil, against lone star tick, Amblyomma americanum (L.), larvae and nymphs. Both life stages were completely killed by CimeXa by 24 h, and EcoVia achieved total larval mortality within 1 h when they were initially immersed in the dusts and when they crawled across treated substrate. Larvae were killed faster than nymphs. Temporary immersion of A. americanum larvae and nymphs in aqueous suspensions of the dusts were less effective than exposure to the dusts applied dry. Larval and nymphal mortality associated with crawling on dried aqueous suspensions of the products was also not as strong as when the immature life stages crawled across substrate treated with dry dusts, and EcoVia was not more efficient than CimeXa. CimeXa and EcoVia can likely be used to protect cattle in a prophylactic context because silica gel does not degrade, and EcoVia might be effective at eliminating ticks that are feeding on cattle as well. We suggest that the two dust products be assessed for efficacy against other ixodid species, such as the southern cattle fever tick, Rhipicephalus microplus (Canestrini), which transmits the causal agents of babesiosis to cattle.

A homoisoflavonoid and a fatty acid in common purslane (Portulaca oleracea L.) synergistically inhibit growth of Spodoptera litura larvae

BACKGROUND

Portulaca oleracea L., common purslane, is an insecticidal plant that has been documented as a 'Chinese indigenous pesticide', and it is seldom visited by insects in the field. However, identification of anti-insect compounds and mechanisms of action are still unclear.

RESULTS

Interplanting purslane with Chinese cabbage demonstrated that purslane may contain secondary compounds that S. litura avoids eating. Four compounds were isolated from P. oleracea by directed anti-insect activity, and their chemical structures were identified by NMR spectra as (9Z,11E,15Z)-13-hydroxyoctadeca-9,11,15-trienoic acid (1), portulacanone A (2), portulacanone D (3), and a new natural product 2,4'-dihydroxy-3',5'-dimethoxychalcone (4). A combination of compound 1 and 2 possessed stronger activity than other combinations (compounds 1 + 3; 1 + 4; 2 + 3; 2 + 4; 3 + 4). Both active compounds were detected in all samples from 23 regions in China, and concentrations in samples collected from 17 regions were generally above 500 μg/kg. Concentrations of compounds 1 and 2 fluctuated greatly from April to November, and reached maximum concentrations of 45 951.44 μg/kg for compound 1 and 3739.09 μg/kg for compound 2 in November. The combination of these compounds (1 + 2) caused mid-gut structural deformation and tissue decay as determined by mid-gut histopathology of S. litura.

CONCLUSION

In general, these active compounds coexisting contributed to partly protect purslane from insects. This research also provides new insights into the use of purslane as important ingredient of botanical pesticide alternatives to traditional chemical pesticides. © 2019 Society of Chemical Industry.

Synergistic Toxicity Interactions between Plant Essential Oil Components Against the Common Bed Bug (Cimex lectularius L.)

Management of the common bed bug (Cimex lectularius L.) necessitates the use of multiple control techniques. In addition to synthetic pesticides and mechanical interventions, plant-derived essential oils represent one of the control options. Mixtures of two or more essential oil components (monoterpenoids) exhibit synergistic toxicity effects against insects due to increased cuticular penetration. Monoterpenoids, such as carvacrol, eugenol and thymol, are neurologically active and inhibit the nerve firing activity of C. lectularius. However, the effects of mixtures of these monoterpenoids on their toxicity and neuroinhibitory potential against C. lectularius are not known. In this study, the toxicity levels of a tertiary mixture of carvacrol, eugenol and thymol (1:1:1 ratio) and a binary mixture of synthetic insecticides, bifenthrin and imidacloprid (1:1 ratio) were evaluated against C. lectularius through topical bioassays and electrophysiology experiments. Both a mixture of monoterpenoids and the mixture of synthetic insecticides exhibited synergistic effects in topical bioassays. In electrophysiology experiments, the monoterpenoid mixture led to greater neuroinhibitory effects, whereas a mixture of synthetic insecticides caused higher neuroexcitatory effects in comparison to single compounds. This study shows evidence for neurological mechanisms of synergistic interactions between monoterpenoids and provides information regarding the utilization of natural compound mixtures for C. lectularius management.

Synergistic terpene combinations as larvicides against the dengue vector Aedes aegypti Linn

Most of the essential oils (EO) known for mosquitocidal activity contain terpenes as part of their chemical constituents. In this study, four monoterpenes namely γ-terpinene (T), R-(+)-limonene (L), carvacrol (C), and trans-anethole (A) were screened against late third instar Aedes aegypti Linn. larvae singly and in combination to find out the synergistic interaction. The monoterpenes γ-terpinene, R-(+)-limonene, trans-anethole, and carvacrol showed larvicidal activity with LC₅₀ values of 9.76, 11.88, 50.19, 48.57 ppm and LC₉₀ values of 16.99, 17.78, 65.21, 75.02 ppm, respectively for Ae. aegypti when tested individually. Prepared binary combinations at LC₂₀ values and studied the synergistic interactions based on cotoxicity factor (CTF) and found that all the binary combinations showed synergistic interactions (CTF > 20). Further, the binary (1:1), ternary (1:1:1), and quaternary (1:1:1:1) terpene combinations on equal weight basis were prepared, evaluated against Ae. aegypti larvae and synergistic interactions were studied by Wadley's method. Among the eight combinations two combinations viz. LC (LC₅₀ 10.42 ppm) and LA (LC₅₀ 11.86 ppm) were showing synergistic interactions (R > 1.5) and others were exhibiting additive effect (1.5 ≥ R > 0.5) and none of the combinations showed antagonism (R < 0.5). Among the two methods used the Wadley's method found suitable when combinations were made on an equal weight basis. The two binary combinations found in this study are promising synergistic mixtures which has scope in designing mosquito larvicidal EOs by enriching the EOs with terpenes or by producing EO combinations with these terpenes as chemical constituents in the correct proportions.

Larvicidal activity of selected essential oil in synergized combinations against Aedes aegypti

This study was conducted to attain an alternate plant essential oil (EO) based mosquito larvicide against the dengue vector Aedes aegypti. Here three plants were selected based on their local availability, safety and insecticidal properties. EOs were extracted from Syzygium aromaticum (Myrtaceae) flower buds, fruits of Illicium verum (Schisandraceae) and Trachyspermum ammi (Apiaceae) by hydro-distillation and tested against Ae. aegypti larvae individually and in combinations to find synergistic interactions. Chemical constituent analysis of EOs was done by GC/MS/MS analysis and the main constituents in T. ammi were thymol (93.58%) and terpinen-4-ol (2.16%), in S. aromaticum eugenol 56.32% and caryophyllene 17.91% and in I. verum trans-anethole 53.05% and p-anisaldehyde 12.47%. The EOs from T. ammi, I. verum and S. aromaticum and their top components thymol, trans-anethole and eugenol exhibited larvicidal activity with LC₅₀ values 39.48, 41.30, 66.90, 59.76, 50.19 and 60.89 mgL^-1 respectively against Ae. aegypti larvae. The values for the co-toxicity factors for the binary combinations of the EOs were > 20 showing synergistic interactions among the binary mixtures. The respective LC₅₀ values for the 1:1 binary combinations (S. aromaticum + I. verum), (S. aromaticum + T. ammi) and (I. verum + T. ammi) were 49.07, 48.54 and 27.67 mgL^-1. β-cyclodextrin inclusion complex made with I. verum + T. ammi combination showed an LC₅₀ value of 23.93 mgL^-1. On the whole the outcome of this study draw attention to the capability of synergistic EO combinations to emerge as a safe and environment friendly effective larvicide to control Aedes mosquitoes.

Efficacy of Two Monoterpenoids, Carvacrol and Thymol, and Their Combinations against Eggs and Larvae of the West Nile Vector Culex pipiens

Background: Insect vector control is facing the challenges of resistance development and environmental hazards caused by synthetic pesticides. This has led to a considerable market opportunity for botanical insecticides. In this scenario, our study investigated the potential of selected bioactive monoterpenoids, carvacrol and thymol, as safe and effective tools to control the West Nile vector Culex pipiens. Furthermore, the combined effect of thymol-carvacrol mixtures and their possible interactions were assessed. Methods: For determining larvicidal and ovicidal 50% lethal concentration (LC₅₀), each monoterpenoid was tested at different concentrations (5–500 mg/L). Then, the fixed ratio method was used for evaluating their combinational efficacy. Results: Carvacrol was more toxic against larvae of Cx. pipiens, with a LC₅₀ value of 14 mg/L, whereas thymol exhibited a LC₅₀ value of 49 mg/L. Comparable trends of efficacy were observed when toxicity on Cx. pipiens eggs was investigated, with LC₅₀ values of 7 and 13 mg/L for carvacrol and thymol, respectively. In combinational toxicity assays, the mixture thymol-carvacrol at 1:4 ratio achieved a synergistic effect against larvae of Cx. pipiens, whereas an additive effect was observed on eggs. Other ratios showed antagonistic effects. Conclusions: Overall, our findings pointed out that the 1:4 ratio of thymol-carvacrol blend can enhance the insecticidal efficacy on Cx. pipiens young instars and can be considered further as active ingredient for developing botanical insecticides to be used in mosquito control operations.

Carvacrol and linalool co-loaded in β-cyclodextrin-grafted chitosan nanoparticles as sustainable biopesticide aiming pest control

Pesticides are the main tactics for pest control because they reduce the pest population very fast and their efficiency does not depend on abiotic factors. However, the indiscriminate use of these substances can speed up the development of resistant populations and causing environmental contamination. Therefore, alternative methods of pest control are sought, such as the use of botanical compounds. Nanoencapsulation of volatile compounds has been shown to be an important tool that can be used to overcome the lack of stability of these compounds. In this work, we describe the preparation and characterization of chitosan nanoparticles functionalized with β-cyclodextrin containing carvacrol and linalool. The toxicity and biological activity were evaluated. Decreases of toxicity were observed when the compounds were nanoencapsulated. The nanoparticles presented insecticidal activity against the species Helicoverpa armigera (corn earworm) and Tetranychus urticae (spider mite). In addition, repellent activity and reduction in oviposition were observed for the mites.