Strong Acaricidal Activity Research Articles

In vitro acaricidal activity of essential oils and their binary mixtures against ixodes scapularis (Acari: Ixodidae)

Ixodes scapularis ticks are vectors of infectious agents that cause illness in humans, including Lyme disease. Recent years have seen a surge in tick-borne diseases (TBD) resulting in a high demand for tick management products. Plants offer a valuable source of active compounds for the development of novel, eco-friendly tick control products, reducing potential risks to human and animal health. Essential oils (EOs) have emerged as potential acaricides and repellents against ticks providing an alternative to synthetic chemicals and aiding in the prevention of TBD by lowering the risk of tick bites. We investigated the acaricidal activity of EOs from lemongrass (Cymbopogon citratus), geranium (Pelargonium x asperum), savory thyme (Thymus saturejoides), and white thyme (Thymus zygis) on I. scapularis. The interactions (i.e., synergistic, antagonistic, or additive) of their binary mixtures were also evaluated. EO samples were analyzed via gas chromatography-mass spectrometry to determine their chemical composition. The adult immersion test was used to determine the lethal concentration (LC50) of each EO alone and in mixtures. Quantitative assessment of synergistic, additive, or antagonistic effect of the binary mixtures was performed by calculating the combination index. Strong acaricidal activity was recorded for savory thyme and white thyme EOs, with LC50 values of 28.0 and 11.0 μg/μL, respectively. The LC50 of lemongrass and geranium EOs were 49.0 and 39.7 μg/μL, respectively. Among the tested EOs, savory thyme and white thyme had a strong acaricidal effect on I. scapularis, which might be linked to the presence of carvacrol (26.05 % ± 0.38) and thymol (53.6 % ± 2.31), main components present in savory thyme and white thyme EOs, respectively. The tick killing efficacy of lemongrass and geranium EOs was lower when mixed than when used separately (LC50 of 65.3 µg/µL). The same happened with savory thyme and white thyme EOs, except at 9.75 µg/µL where they had a synergistic effect (LC50 of 58.3 µg/µL). Lemongrass and savory thyme EOs had a synergistic effect at low concentrations, and an antagonistic effect at higher concentrations (LC50 of 95.4 µg/µL). Lemongrass and white thyme EOs had a synergistic effect against ticks from 15 to 120 µg/µL (LC50 of 18.5 µg/µL) similar to white thyme EO. Geranium and savory thyme EOs had an antagonistic effect at all concentrations, with an LC50 of 66.8 µg/µL. Geranium and white thyme EOs also had an antagonistic effect, except at 12.7 µg/µL where they had a synergistic effect (LC50 of 66.8 µg/µL). The interaction observed when combining selected essential oils suggests promising potential for developing acaricidal formulations aimed at controlling ticks and curbing the transmission of tick-borne disease agents.

Transcriptomics and proteomic-based study of the acaricidal mechanism of paeonol against Aleuroglyphus ovatus

ABSTRACTAleuroglyphus ovatus, a common mite harming stored grain, poses a threat to human health. Paeonol is the main component isolated from peony roots and exhibits various medicinal values. In our previous study, we found that paeonol shows strong acaricidal activity. In the present study, the acaricidal mechanism of paeonol against A. ovatus was uncovered through RNA-seq transcriptomics and TMT proteomics. According to the transcriptomics results, paeonol treatment noticeably up-/downregulated genes associated with “oxidoreductase activity” (peptidase activity, ATPase activity, and hydrolase activity). As shown by proteomic analysis, concordant changes were identified in proteins linked with hydrolase activity, serine-type peptidase activity, antioxidant activity, and oxidoreductase activity. Paeonol target proteins were FMO, ACAD8, GPX, CTSL, and PRSS1, as determined by transcriptomics-proteomics correlation analysis. We propose that paeonol may play an acaricidal role by interfering with enzyme activities in A. ovatus, especially serine-type peptidase, thereby causing an imbalance in amino acid ratios and eventually leading to the death of A. ovatus. However, the specific mechanism of action needs to be further studied. In addition, we verified the key enzymes at the transcriptional level.

In Vitro Acaricidal Activity of Silver Nanoparticles (AgNPs) against the Poultry Red Mite (Dermanyssus gallinae)

Dermanyssus gallinae (PRM) is the most common blood-sucking ectoparasite in laying hens and is resistant against numerous acaricides. Silver nanoparticles (AgNPs) represent an innovative solution against PRM. The current study aimed to assess the in vitro acaricidal activity of AgNPs against PRM and describe their potential mechanism of action. Nanoparticles were produced using a wet chemistry approach. Mites were collected using AviVet traps from 18 poultry farms in Greece. Contact toxicity bioassays were carried out for 24 h with negative controls, 20, 40, 60, or 80 ppm AgNPs. Analysis of variance was used to compare the mortality rates of PRM between the control and treatment groups, while LC50, LC90, and LC99 values were estimated using probit regression analysis for the total farms jointly and separately. Nanoparticles displayed strong acaricidal activity, and mortality rates were significantly different between groups and increased by AgNPs concentration. Overall mean LC50, LC90, and LC99 values were 26.5, 58.8, and 112.3 ppm, respectively. Scanning electron microscopy on mites treated with 80 ppm AgNPs revealed cracks in their exoskeleton and limb detachments, presumably resulting from the interaction between AgNPs and the mites' chitin. Future studies should focus on assessing AgNPs residues in chicken tissues before moving into field trials.

Acaricidal and Insecticidal Activities of Essential Oils and Constituents of Tasmannia lanceolata (Poir.) A.C.Sm. (Canellales: Winteraceae) Against Tetranychus urticae Koch (Trombidiformes: Tetranychidae) and Myzus persicae Sulzer (Hemiptera: Aphididae).

The negative side effects of synthetic pesticides have drawn attention to the need for environmentally friendly agents to control arthropod pests. To identify promising candidates as botanical pesticides, we investigated the acaricidal and insecticidal activities of 44 plant-derived essential oils (EOs) against Tetranychus urticae Koch and Myzus persicae Sulzer. Among the tested EOs, Tasmannia lanceolata (Poir.) A.C.Sm. (Tasmanian pepper) essential oil (TPEO) exhibited strong acaricidal and insecticidal activity. Mortality rates of 100% and 71.4% against T. urticae and M. persicae, respectively, were observed with TPEO at a concentration of 2 mg/ml. Polygodial was determined to be the primary active component after bioassay-guided isolation of TPEO using silica gel open-column chromatography, gas chromatography, and gas chromatography-mass spectrometry. Polygodial demonstrated acaricidal activity against T. urticae with mortality rates of 100%, 100%, 61.9%, and 61.6% at concentrations of 1, 0.5, 0.25, and 0.125 mg/ml, respectively. Insecticidal activity against M. persicae was also evident, with mortality rates of 88.5%, 85.0%, 46.7%, and 43.3% at respective concentrations of 1, 0.5, 0.25, and 0.125 mg/ml. Insecticidal and acaricidal activities of TPEO were greater than those of Eungjinssag, a commercially available organic agricultural material for controlling mites and aphids in the Republic of Korea. These findings suggest that TPEO is a promising candidate for mites and aphids control.

AKTIVITAS BIOINSEKTISIDA EKSTRAK DAUN MAJA (Crencentia cujete Linn.) TERHADAP Rhipicephalus sanguineus DARI ANJING LOKAL

Brown tick, Rhicephalus sanguineus generally known as a very adaptive tick, is widely spread on tropical, subtropical, and temperate regions, and infested dogs living on not only rural but urban areas. Synthetic acaricides are the most widely control measures. However, with the development of tick resistance, plant-derived components are highly investigated. The present study aims to investigate the activity of Crecentia cujete Linn. leaves extract on R. sanguineus. Fifty adult R. sanguineus were collected from local dogs and used in this study. Ticks are divided into the control and treatment groups. Aquadest and deltamethrin were sprayed to ticks in the negative and positive control groups, respectively. The three treatment groups were given maja leaves extract of 2.5%, 5%, and 10%. The tick mortality was observed for 12 hours of exposure to the extracts. All extracts exhibited similar lethal effects on R. sanguineus with total mortality (100%) after 4 hours exposure, compared to the standard therapy. The highest extract concentration (10%) reduces ticks faster compare to other concentrations. Thus, this study suggests that strong acaricidal activity and mortality rate was dose-dependent. This finding needs further scientific investigation to prove.

In vitro acaricidal activity of essential oil and crude extracts of Laurus nobilis, (Lauraceae) grown in Tunisia, against arthropod ectoparasites of livestock and poultry: Hyalomma scupense and Dermanyssus gallinae

The current study assayed the toxicity of Laurus nobilis essential oil and crude extracts obtained using solvents of increasing polarity (cyclohexane, acetone and ethanol), on two ectoparasites of veterinary importance, i.e., Hyalomma scupense and Dermanyssus gallinae.The major components detected in bay laurel essential oil were dominated by 1.8-cineole (46.56 %), α-terpinenyl acetate (13.99 %), sabinene (7.69), α-pinene (5.75), linalool (5.50), methyleugenol (5.36 %) and β-pinene (3.97). The highest total phenolic and flavonoids contents were present in the ethalonic extract of L. nobilis leaves at an amount of 152.88 mg gallic acid equivalents per gram of dry weight (GAE/g DW) and 21.77 mg quercetin equivalent per gram of dry weight (QE/g DW), respectively.In vitro acaricidal effects of essensial oil and crude extract of L. nobilis against H. scupense were ascertained by adult immersion test of engorged females (AIT) and larval packet test (LPT) compared with a reference drug amitraz.The essential oil exhibited strong acaricidal activity against tick engorged female and inhibition of hatching eggs. After 24 h of exposure, at the highest tested concentration (100 mg/mL) essential oil induced 90.67 % mortality of H. scupense larvae (LC50 = 10.69 mg/mL). Otherwise, essential oil exhibited high acaricidal activity compared to extracts, and among the extract, the ethanolic extract revealed the highest acaricidal efficacy (81.27 % female mortality).Results from mite contact toxicity showed that essential oil and extracts from L. nobilis were toxic to D. gallinae. Bay essential oil was both more toxic to mites, and faster in exerting this toxicity than other tested crude extracts. L. nobilis essential oil concentration leaded to enhance mortality of D. gallinae reaching the highest (100 %) mortality at 12 h with a concentration of 320 mg/mL. While, ethanolic extract acheived this rate after 24 h of exposure at same concentration. Cyclohexanic extract showed weak acaricidal activity.

Development of an efficient antitick natural formulation for the control of acaricide-resistant ticks on livestock

Animal production has a key role in global economic development and food security. Ticks, specifically Rhipicephalus microplus cause substantial economic and health impacts on more than eighty percent of the world cattle population. Though synthetic acaricides play a major role in tick management, their injudicious usage has caused environmental pollution and also promote the establishment of multi-acaricide resistant tick populations which is a matter of great concern. To provide an effective tool for controlling these resistant ticks, the present work was aimed to develop safe and inexpensive antitick natural formulations. Our bioprospection studies of Ageratum conyzoides plant established it as a species potentially having strong acaricidal activity due to the presence of potent acaricidal phyto-chemicals. To develop a suitable antitick natural formulation, 41 samples/fractions/formulations were prepared from the dry powder of the whole aerial part of the A. conyzoides plant using different techniques and delivery matrices. The strongest antitick effect was recorded for formulation ACF6, which demonstrated 87 ± 6% mean mortality with 57 % inhibition of oviposition in treated female ticks. Ticks treated with the ACF6 formulation showed a significant (p < 0.001) reduction in cuticular protein (1.238 ± 0.01 mg/mL) as compared to control ticks (2.928 ± 0.01 mg/mL) but no significant difference in chitin content of treated ticks and control ticks was observed. The formulation was found safe in a rat model as no significant differences in biochemical and haematological parameters among treated and control rats were noted. Histopathological studies indicated no sign of hepatocellular necrosis and no significant changes in the weights of liver and spleen was recorded. The overall in vivo efficacy of the formulation was 85 % for experimentally infested cattle with direct mortality of more than 80 % within 96 h post-application. The lethal effect of the formulation was in the form of drying and dead ticks 1–2 d after application. The developed formulation has the potential to be adopted as an alternative tick control measure in an ecofriendly manner.

Chemical profile, characterization and acaricidal activity of essential oils of three plant species and their nanoemulsions against Tyrophagus putrescentiae, a stored-food mite.

Essential oils of Ocimum basilicum (L.), Achillea fragrantissima (Forssk.) and Achillea santolina (L.) were obtained by hydrodistillation and analyzed using gas chromatography (GC) and GC/mass spectrometry (MS). Oil-in-water nanoemulsions (10% active ingredient) were prepared through a high-energy (ultrasonication) emulsification process. Nanoemulsions were characterized by viscosity, pH, thermodynamic stability, droplet size, polydispersity index (PDI) and scanning electron microscopy (SEM) measurements. The plant oils and their nanoemulsions showed considerable acaricidal activity against the mold mite, Tyrophagus putrescentiae (Schrank) (Sarcoptiformes: Acaridae). In a contact toxicity bioassay and 48h post treatment, O. basilicum oil was the most toxic, followed by A. fragrantissima and A. santolina, where LC50 values were 8.4, 14.1 and 21.8µl/cm2, respectively. LC50 for benzyl benzoate, a standard acaricide was 9.8µl/cm2. Upon fumigation, responses also varied according to the test oil. Based on the 48-h LC50 values, the same manner of activity was also observed, where O. basilicum was the most toxic followed by A. fragrantissima and A. santolina. When prepared as nanoemulsions (particle size from 78.5 to 104.6) and tested as fumigants, toxicity of the oils was increased drastically with LC50 values of 2.2, 4.7, and 9.6µl/l air for O. basilicum, A. fragrantissima and A. santolina, respectively. The oils showed a moderate to strong residual acaricidal activity, where O. basilicum oil was the most effective. The results suggest that appropriate nanoemulsions containing the tested oils can be developed to control T. putrescentiae after the required toxicological assessments.

Acaricidal activity of plant-derived essential oil components against Psoroptes ovis in vitro and in vivo

BackgroundTreatment of Psoroptes ovis in cattle is limited to topical acaricides or systemic treatment with macrocyclic lactones. Treatment failure of macrocyclic lactones has been reported. The aim of this study was to evaluate a potential alternative treatment against P. ovis.MethodsThe acaricidal activity against P. ovis of four plant-derived essential oil components, i.e. geraniol, eugenol, 1,8-cineol and carvacrol, was assessed in vitro and in vivo. In vitro contact, fumigation and residual bioassays were performed. In addition, 12 Belgium Blue cattle were artificially infested and treated topically once a week for three successive weeks with carvacrol in Tween-80 (treatment group) or with Tween-80 alone (control). The efficacy of carvacrol was determined by the reduction in lesion size and mite counts. Six additional animals were topically treated with carvacrol to assess local adverse reactions.ResultsThree components showed a concentration-dependent acaricidal activity in a contact assay, with LC50 of 0.56, 0.38 and 0.26% at 24 h for geraniol, eugenol, and carvacrol, respectively. However, 1,8-cineol showed no activity at any of the tested concentrations in a contact bioassay. In a fumigation bioassay, carvacrol killed all mites within 50 min after treatment, whereas geraniol, eugenol and 1,8-cineol needed 90 to 150 min. Following a 72 h incubation period in a residual bioassay, carvacrol killed all mites after 4 h of exposure to LC90, while geraniol and eugenol killed all mites only after 8 h exposure. Based on these results, carvacrol was further assessed in vivo. Mite counts in the treatment group were reduced by 98.5 ± 2.4% at 6 weeks post-treatment, while in the control group the mite population had increased. Topical application of carvacrol only caused mild and transient erythema 20 min after treatment. No other side effects were observed.ConclusionsConsidering the strong acaricidal activity of carvacrol in vitro and in vivo and the mild and transient local side effects, carvacrol shows potential as an acaricidal agent in the treatment of P. ovis in cattle.

Volatile Metabolomic Composition of Vitex Species: Chemodiversity Insights and Acaricidal Activity.

The Vitex genus (Lamiaceae) produces a plethora of metabolites that include ecdysteroids and terpenoids, some of which have demonstrated insect repellent properties. The volatile composition of several members of this genus has not been chemically defined, as many taxa are endemic to remote ecosystems. In this study, leaves were collected from the northeast of Brazil from Vitex capitata, V. megapotamica, V. gardneriana, and V. rufescens plants and examined for their chemical profile via GC-MS/FID of essential oil extracts. The analyses showed a diversity of terpenoids. Of particular note were seven-member ring sesquiterpenes which were present in great abundance; a dendrogram showed clades separating by the production of bicyclogermacrene, aromadendrane and 5,10-cycloaromadendrane sesquiterpenoids for the four species. Comparison of volatile metabolite profiles to 13 other Vitex species showed strong similarities in the production of some monoterpenes, but varied by their production of larger terpenes, especially those with gem-dimethylcyclopropyl subunits on seven-member ring compounds. From this work, we suggest that the sesquiterpene skeleton with seven member rings is a good chemosystematic biomarker candidate for the Vitex genus. Separation using this biomarker was then validated using Inter-Simple Sequence Repeat profiling. Lastly, experiments examining the toxicity of these four oils against the coconut mite Aceria guerreronis showed that only the oil of V. gardneriana had strong acaricidal activity, with an LC50 of 0.85 mg/mL, thus demonstrating its potential for use as a natural pesticide.

Acaricidal active fractions from acetone extract of Aloe vera L. against Tetranychus cinnabarinus and Panonychus citri

This study aimed to isolate acaricidal active fractions from acetone extract of Aloe vera L. and investigate the toxicity of these fractions against Tetranychus cinnabarinus (T. cinnabarinus) and Panonychus citri (P. citri). Acetone extract of A. vera L. was isolated by immersing in acetone for 72 h, and diverse fractions were fractionated by column chromatography. The acaricidal activity of each fractions was evaluated by corrected mortality of T. cinnabarinus through slide-dip bioassay. The 8th and 13th fractions of acetone extract with good acaricidal activity were indentified by LC/MS, and the toxicity of these two fractions to T. cinnabarinus and P. citri was identified by regression analysis. Acetone extract of A. vera L. exhibited obvious acaricidal activity, from which a total of 18 fractions were isolated. The 8th and 13th fractions with strong acaricidal activity against T. cinnabarinus were identified to be 3-O-alpha-d-mannopyranosyl-d-mannopyranose (OAMM) and aloe emodin. When compared with spirodiclofen, both OAMM and aloe emodin exhibited higher toxicity to T. cinnabarinus, while only OAMM exhibited a higher toxicity to P. citri (P < 0.05). OAMM and aloe emodin isolated from acetone extract of A. vera L. exhibited obvious acaricidal activities against T. cinnabarinus and P. citri.

Synergistic inhibitory effect of scopoletin and bisdemethoxycurcumin on Tetranychus cinnabarinus (Boisduval) (Acari: Tetranychidae).

The study aimed to investigate the synergistic activity of scopoletin and bisdemethoxycurcumin (BDMC) against the carmine spider mite Tetranychus cinnabarinus. The acaricidal activities of mixtures of scopoletin and BDMC against T. cinnabarinus female adults were measured via slide dipping and leaf disc dipping. A mathematical model was established by SPSS software. Bioassays for multiple effects including contact, ovicidal, cowpea root intake, repellency and oviposition inhibitory activity were carried out. The optimal mass ratio of the mixture of scopoletin and BDMC (at their respective LC(50)), the median lethal concentration (LC(50)) and the co-toxicity coefficient were 7:6, 0.19 mg/mL and 129, respectively. LC(50) values of contact activities of the mixture at optimal ratio against adults, nymphs, larvae, and eggs were 0.19, 0.18, 0.06, and 1.52 mg/mL, respectively. LC(50) values of cowpea root intake activity against adults and nymphs were 5.62 and 6.52 mg/mL, respectively. The highest repellent rates against adults and nymphs were 69.5% and 72.5%, respectively. The mixture of scopoletin and BDMC at the optimal mass ratio possessed strong acaricidal activity against T. cinnabarinus at various developmental stages.

Acaricidal activity of extracts from Ligularia virgaurea against the Sarcoptes scabiei mite in vitro.

The aim of the present study was to investigate the acaricidal activity of Ligularia virgaurea. An extract was prepared by refluxing with ethanol and steam distillation, and its toxic effect was tested in vitro against Sarcoptes scabiei. The data from the toxicity tests were analyzed using a complementary log-log (CLL) model. The ethanol extract exhibited strong acaricidal activity against these mites; at a concentration of 2 g/ml it killed all S. scabiei within 2 h and at 1 g/ml it killed all S. scabiei within 6 h. Similarly, 2, 1, 0.5 and 0.25 g/ml concentrations of the extract had strong toxicity against S. scabiei, with median lethal time (LT50) values of 0.716, 1.741, 2.968 and 4.838 h, respectively. The median lethal concentration (LC50) values were 1.388, 0.624, 0.310 and 0.213 g/ml for Scabies mite in 1, 2, 4 and 6 h, respectively. The results indicate that the L. virgaurea extract has strong acaricidal activity and may be exploited as a novel treatment for the effective control of acariasis in animals.

Acaricidal activity of 9-oxo-10,11-dehydroageraphorone extracted from Eupatorium adenophorum in vitro

The acaricidal activity of the 9-oxo-10,11-dehydroageraphorone (euptox A), a cadenine sesquiterpene from Eupatorium adenophorum (E. adenophorum) against Sarcoptes scabiei and Psoroptes cuniculi was tested in vitro. A complementary log–log (CLL) model was used to analyze the data of the toxicity tests in vitro. The results showed euptox A had strong toxicity against mites, killing all S. scabiei at 3 and 4mg/ml (m/v) concentration, while 4mg/ml euptox A was also found to kill all P. cuniculi within a 4h period. Similarly, 2, 3 and 4mg/ml concentration of euptox A had strong toxicity against S. scabiei, with median lethal time (LT50) values at 0.687, 0.526, 0.326h, respectively. 3mg/ml and 4mg/ml showed strong acaricidal action against P. cuniculi; the LT50 values were 0.693 and 0.493h, respectively. The median lethal concentration (LC50) values were 1.068mg/ml for Scabies mite and 0.902mg/ml for P. cuniculi in 2h. The results indicate that euptox A has strong acaricidal activity and may exploit as novel drugs for the effective control of animal acariasis.

Isolation and identification of acaricidal compounds in Eupatorium adenophorum petroleum ether extract and determination of their acaricidal activity against Psoroptes cuniculi

We used multiple silica gel column chromatography and thin-layer chromatography coupled with 1H nuclear magnetic resonance (NMR) and 13C NMR to separate and identify the active acaricidal ingredients in Eupatorium adenophorum petroleum ether extract. The acaricidal activity of each compound was tested against Psoroptes cuniculi in vitro. Three compounds had strong acaricidal activity against P. cuniculi in vitro. The insecticidal effect of 0.5% compound 9β-hydroxy-ageraphorone was better than the insecticidal effect of fenvalerate, and compounds 9-oxo-ageraphorone and 9-oxo-10,11-dehydro-ageraphorone exhibited higher insecticidal effects than 9β-hydroxy-ageraphorone. Thus, the E. adenophorum petroleum ether extract contains an effective composition of acaricides that could potentially be developed as a promising plant-origin acaricide.

Acaricidal activity of Aloe vera L. leaf extracts against Tetranychus cinnabarinus (Boisduval) (Acarina: Tetranychidae)

Four different extracts of Aloe vera L. leaves were evaluated for acaricidal activity against female adults of carmine spider mite, Tetranychus cinnabarinus (Boisduval), by slide-dip bioassay. At 72 h after treatment, the acetone extract showed the strongest acaricidal activity with LC 50 value of 90 ppm. The LC 50 values for ethyl acetate, water, and ethanol extracts were 113, 340, and 391 ppm, respectively. The acetone extract was fractionated using a silica gel column. Among the twenty-two fractions obtained the fifth, tenth, eleventh, twelfth, fifteenth, and seventeenth fractions showed strong acaricidal activity, causing 80.39 to 92.16% mortality at 72 h after treatment. The tenth and eleventh fractions had the strong activity, with LC 50 values of 44 ppm and 33 ppm, respectively. The results suggested that A. vera has a great potential for development as a botanical acaricide for T. cinnabarinus control.

Acaricidal and quantitative structure activity relationship of monoterpenes against the two-spotted spider mite, Tetranychus urticae

The acaricidal activity of 12 monoterpenes against the two-spotted spider mite, Tetranychus urticae Koch, was examined using fumigation and direct contact application methods. Cuminaldehyde and (-)-linalool showed the highest fumigant toxicity with LC(50)=0.31 and 0.56mg/l, respectively. The other monoterpenes exhibited a strong fumigant toxicity, the LC(50) values ranging from 1.28 to 8.09mg/l, except camphene, which was the least effective (LC(50)=61.45mg/l). Based on contact activity, the results were rather different: menthol displayed the highest acaricidal activity (LC(50)=128.53mg/l) followed by thymol (172.0mg/l), geraniol (219.69mg/l) and (-)-limonene (255.44mg/l); 1-8-cineole, cuminaldehyde and (-)-linalool showed moderate toxicity. At 125mg/l, (-)-Limonene and (-)-carvone caused the highest egg mortality among the tested compounds (70.6 and 66.9% mortality, respectively). In addition, the effect of molecular descriptors was also analyzed using the quantitative structure activity relationship (QSAR) procedure. The QSAR model showed excellent agreement between the estimated and experimentally measured toxicity parameter (LC(50)) for the tested monoterpenes and the fumigant activity increased significantly with the vapor pressure. Comparing the results of the fumigant and contact toxicity assays of monoterpenes against T. urticae with the results of acetylcholinesterase (AChE) inhibitory effect revealed that some of the tested compounds showed a strong acaricidal activity and a potent AChE inhibitory activity, such as cuminaldehyde, (-)-linalool, (-)-limonene and menthol. However, other compounds such as (-)-carvone revealed a strong fumigant activity but a weak AChE inhibitory activity.

Methyl Palmitate, an Acaricidal Compound Occurring in Green Walnut Husks

Walnut, Juglans regia L., is known for its insecticidal activities to a range of herbivores and microbes. Isolation and identification of bioactive compounds from walnut is a potential approach for the development of new pesticides. Laboratory experiments were carried out to investigate the acaricidal activities of green husk extracts of walnut. Bioassay-guided fractionation of petroleum-ether extracts of walnut led to the identification of a common plant-borne fatty acid ester, methyl palmitate (MP), which produced strong acaricidal activity (62.8% mortality) at 1 mg/ml at 24 h. The structure of MP was characterized with infrared spectrum and NMR, and the identification of MP confirmed using an authentic standard on high-performance liquid chromatography. Based on a slide dip bioassay, 10 mg/ml MP provided 97.9% mortality against adults of Tetranychus cinnabarinus (Boisduval) (Acari: Tetranychidae), whereas mortality against eggs was much lower (57.2%).