Contact Toxicity Research Articles

Fibrous palygorskite clays as versatile nanocarriers for skin delivery of tea tree oils in efficient acne therapy

This paper presents a facile approach to develop palygorskite (Pal), a fibrous clay mineral, as a delivery system of tea tree oil (TTO) for topical acne therapy. The obtained TTO-Pal composite showed an efficient loading of TTO (27.4%) with a selective accumulation of terpine-4-ol and 1,8-cineole (two major antimicrobial TTO constituents), sustained release of TTO at skin physiological conditions (pH5.4, 32 °C) and superior skin sebum (2.2 g/g) absorbability. In vitro toxicological assessments showed that the Pal incorporation strategy significantly reduced the acute contact toxicity of TTO. The antimicrobial results revealed a preferable bacteriostatic effect for the TTO-Pal system towards opportunistic dermal pathogens (Escherichia coli, Staphylococcus aureus and Propionibacterium acnes) over the beneficial bacterium (Staphylococcus epidermis). Moreover, TTO-Pal based formulations exhibited pronounced clinical therapeutic efficacy in treating facial acne by rapidly reducing inflamed lesions, modulating skin sebum overproduction and restoring barrier function. This is the first report of using fibrous clay as a biocompatible nanocarrier system for topical delivery of essential oils in efficient management of facial acne with both in vitro and in vivo evidences, which may open perspectives for fibrous clay-drug delivery system in topical application and expand the high added value development of this mineral resource in the advanced healthcare fields.

Toxicity and context-dependent repellency of temporarily granted repellents under new biocidal products regulations in South Korea against Drosophila melanogaster (Diptera: Drosophilidae)

• Repellents for miniscule flying insects is now under legal control in South Korea. • Several compounds were temporarily graced from registration processes. • Contact toxicity and repellent activity of those granted compounds were examined. • Several compounds were either effective or nonactive based on test methods. In South Korea, control agents for small flying insects are subjected to approval under newly enforced Act on biocidal products by the Ministry of Environment starting from 2019, along with other conventional household insecticides. The present study aimed to evaluate 18 compounds for their toxicity and repellency in various contexts. A tube assay revealed the greatest toxicity of synthetic repellent DEET. Interestingly, spatial repellency of several plant essential oils was greater than those of conventional repellent, indicating their suitability for temporal grants. Meanwhile, unlike conventional repellents, botanical oils often lost their choice repellency in gaseous unsaturable condition. Spatial repellency was positively correlated to the evaporation rate of the compounds while choice repellencies were negatively correlated regardless of their gaseous saturability. Our results are expected to provide implications for both the regulation process and product development.

The synergistic effects of rosehip oil and matrine against Icerya aegyptiaca (Douglas) (Hemiptera: Coccoidea) and the underlying mechanisms.

Icerya aegyptiaca (Douglas) is an important agricultural pest that has a protective wax shell. Insecticides generally fail to achieve the desired control of I. aegyptiaca because of difficulties penetrating this wax shell. Plant essential oils are rich in terpenoids and have strong penetrability and expansibility, which can enable the rapid penetration and absorption of insecticides, thereby improving the control effect. Matrine is a botanical insecticide with contact and stomach toxicity, low toxicity toward non-target organisms and is environmentally friendly. In this study, we tested the insecticidal activity of rosehip oil (Ro)/matrine combinations and revealed the synergistic mechanism of Ro and its components with matrine in terms of physiology and biochemistry. Ro/matrine combinations have strong penetrating power, enabling matrine to quickly penetrate the wax shell of I. aegyptiaca and enter the insect body. This improves the insecticidal activity and enhances inhibition of acetylcholinesterase activity. Ro and its main chemical constituents, cineole and (+)-camphor, showed synergistic effects on matrine with synergic ratios of 4.79, 3.49 and 4.21, respectively. Combinations of Ro, cineole and (+)-camphor with matrine have good insecticidal effects on I. aegyptiaca while remaining safe to the environment. These combinations of biological insecticides have excellent development prospects and provide a new reference for the pest management of scale insects. © 2022 Society of Chemical Industry.

Laboratory-based toxicity of scale insect pathogen Moelleriella raciborskii (Zimm.) (Hypocreales: Clavicipitaceae) crude extracts and isolated compounds against Tetranychus truncatus Ehara (Acari: Tetranychidae)

Tetranychus truncatus is a phytophagous spider mite that is one of the economic pests of agricultural and economic crops. Its control has been and still is based mainly on the use of chemical controls. Since pesticides compatibility with natural enemies is a main concern for IPM programs, the aim of this study was carried out to explore the toxicity, repellency, oviposition deterrent and eggs hatching inhibition of crude ethyl acetate extract of Moelleriella raciborskii and their secondary metabolites against adults and eggs of T. truncatus. The results indicated that M. raciborskii crude extract at 5% (w/v) had high contact toxicity (89% mortality) on adult females of T. truncatus. The LC50 value was 1.476%, 1.026 and 0.732% after 24, 48 and 72 h posttreatment. Among the two steroidal and two hopane triterpenes separated from the ethyl acetate extract, 3β-acetoxy-15α,22-dihydroxyhopane was identified as the most active compound with LC50 values of 0.232% (w/v), followed by ergosterol, ergosterol 5, 8-endoperoxide with LC50 values of 0.235% and 0.318% at 72 h posttreatment, respectively. In addition, 3β-acetoxy-15α,22-dihydroxyhopane showed strong repellency (70.19%) and ergosterol and ergosterol 5, 8-endoperoxide decreased egg production of T. truncatus by 70.35 and 67.98%, respectively. Strong oviposition deterrent (ODI=100) was noted when 0.5% (w/v) crude extract was applied on half of the leaf disc. The crude ethyl acetate extract of M. raciborskii could have potential for the development of novel acaricides to control T. truncatus for use in an integrated pest management program.

Utilization of Pomelo (Citrus maxima) Peel Waste into Bioactive Essential Oils: Chemical Composition and Insecticidal Properties.

The wastes generated during the post-harvest handling of various agricultural commodities is rather under-utlilized. The peels of citrus fruits are often discarded as waste. Citrus peels are rich in essential oils and exhibit toxicity towards various insect species. The essential oils are also an eco-friendly option for insect pest management. The Citrus maxima peel essential oil (CMEO), a waste product, characterized it, and evaluated its potential for insect pest management. The major terpenoids present in CMEO are Limonene and α-Pinene. The CMEO displayed potentials in controlling the insect pests via contact and fumigant toxicity. Moreover, CMEO showed significant larvicidal activities against Culex tritaeniorhynchus and Aedes aegypti species of mosquitoes; however, Armigeres subalbatus was more resistant. The biological safety of the essential oil was also tested against the stored seeds, where no significant inhibition of seed germination was noticed compared to the control. Utilizing a waste product such as citrus peel for pest management can achieve the dual objective of waste utilization and eco-friendly pest management. Overall, the CMEO is therefore found to be a bioactive essential oil extracted from the wastes of pomelo (C. maxima).

The Insecticidal Efficacy and Physiological Action Mechanism of a Novel Agent GC16 against Tetranychus pueraricola (Acari: Tetranychidae).

Simple SummarySpider mite is major pest in agriculture and have developed resistance to commonly used pesticides. Therefore, it is urgent to discover new pesticides to control the pest. In order to provide alternatives for its management, we evaluated the effectiveness of a new agent GC16 against the spider mite Tetranychus pueraricola. Then, we preliminarily revealed the its acaricidal mechanism of action based on the damage of cuticle and organelles of mites. We confirmed that GC16 has a good controlling effect on T. pueraricola and it is not harmful to Picromerus lewisi and Harmonia axyridis. Our research provides not only an alternative pesticide for the management of spider mites, but also guidance for the application of GC16 in sustainable agriculture.Chemical control plays a crucial role in pest management but has to face challenges due to insect resistance. It is important to discover alternatives to traditional pesticides. The spider mite Tetranychus pueraricola (Ehara & Gotoh) (Acari: Tetranychidae) is a major agricultural pest that causes severe damage to many crops. GC16 is a new agent that consists of a mixture of Calcium chloride (CaCl2) and lecithin. To explore the acaricidal effects and mode of action of GC16 against T. pueraricola, bioassays, cryogenic scanning electron microscopy (cryo-SEM) and transmission electron microscopy (TEM) were performed. GC16 had lethal effects on the eggs, larvae, nymphs, and adults of T. pueraricola, caused the mites to dehydrate and inactivate, and inhibited the development of eggs. GC16 displayed contact toxicity rather than stomach toxicity through the synergistic effects of CaCl2 with lecithin. Cryo-SEM analysis revealed that GC16 damaged T. pueraricola by disordering the array of the cuticle layer crest. Mitochondrial abnormalities were detected by TEM in mites treated by GC16. Overall, GC16 had the controlling efficacy on T. pueraricola by cuticle penetration and mitochondria dysfunction and had no effects on Picromerus lewisi and Harmonia axyridis, indicating that GC16 is likely a new eco-friendly acaricide.

Bio-Insecticidal Nanoemulsions of Essential Oil and Lipid-Soluble Fractions of Pogostemon cablin.

The present study aimed to develop nanoemulsions (NEs) of essential oil (EO) and lipid-soluble extract (HE) of Pogostemon cablin leaves using biosurfactant, saponin. Hydro-distilled EO and fat-soluble HE were analyzed using GC-MS, which revealed 38.7 ± 2.7% and 37.5 ± 2.1% patchoulol, respectively. EO and HE were formulated with saponin to prepare corresponding coarse emulsions (CEs); furthermore, high-speed homogenization for 2 min was followed by ultrasonication for 3 min with constant frequency of 50 kHz. of the CEs resulted in respective NEs. NEs were characterized for the physico-chemical properties such as emulsion intrinsic stability, particle size distribution, polydispersity index (PDI), and transmission electron microscopy (TEM) for morphology and accurate nanodroplet diameters. CEs and NEs were investigated for insecticidal efficacy against adults of Tetranychus urticae and larvae of Spodoptera litura. Stable NEs of EO and HE at 500 μg mL−1 concentration exhibited corresponding average particle size of 51.7 and 89.9 nm, while TEM image revealed spherical-shaped droplets with the average droplet diameters of 15.3 and 29.4 nm, respectively. NEs of EO and HE displayed highest efficacy in contact toxicity (LC50 43.2 and 58.4 μg mL−1) after 48 h and fumigant toxicity (LC50 9.3 and 13.6 μg mL−1) after 24 h against T. urticae. In addition, NEs of EO showed considerable antifeedant and feeding deterrent action (AI 99.21 ± 0.74 and FI 99.73 ± 1.24) against S. litura larvae.

A Star Polyamine-Based Nanocarrier Delivery System for Enhanced Avermectin Contact and Stomach Toxicity against Green Peach Aphids.

The unscientific application of synthesized/botanical pesticides has not only brought the resistance of plant pathogens and pests, but also led to serious environmental pollution. In recent years, various nano-delivery systems have been used for the development of environmental-friendly pesticides with improved efficacy. Herein, the current study constructed an efficient avermectin B1a (AVM) nano-delivery system based on a star polyamine (SPc) and focused on the characterization and bioactivity of SPc-loaded AVM at various mass ratios. The hydroxyl groups of AVM could assemble with carbonyl groups of SPc through hydrogen bond and van der Waals forces, and the self-assembly of AVM and SPc formed nearly spherical particles of AVM/SPc complex with nanoscale size. The contact angle of SPc-loaded AVM decreased with the increasing mass ratio of SPc, revealing the easier distribution and spreading of the AVM/SPc complex. Furthermore, the stomach and contact toxicity of AVM/SPc complex also increased along with the increasing SPc mass ratio, which could be attributed to the enhanced systemic transportation in plants, enlarged contact area to insect pests and stronger permeability across the insect cuticle. The current study provides an efficient nano-delivery system for increasing stomach and contact toxicity of pesticides with wide applications in the agricultural field.

Nano-bio interfacial interactions determined the contact toxicity of nTiO2 to nematodes in various soils

The biological effect of soilborne nanoparticles (NPs) is a manifestation of soil-NMs-bio interactions. Soil factors are known to restructure NPs surfaces and thus influence the nanotoxicity. However, the mechanisms by which environmental factors affecting nano-bio interactions to aggravate or alleviate nanotoxicities are poorly understood. Herein, we compared the toxicity of TiO2 NPs (nTiO2) in five soils using the model nematode (Caenorhabditis elegans), and investigated the variation of nano-bio interactions under different conditions. A correlation analysis showed that pH and dissolved organic matter (DOM) were dominant regulators of nTiO2 toxicity. At the nano-bio interface, low pH (5.0) led to nTiO2 adhesion to micron-sized furrows and aggravated dermal wrinkling, while humid acid (HA) alleviated these impacts. Mechanically, low pH increased nTiO2 adhesion through enhanced electrostatic attraction and subsequent stimulation of mucin and collagen synthesis, resulting in a positive feed cycle of pH-dependent contact nanotoxicity. HA not only prevented nTiO2 adhesion onto the epidermis due to its negative charge, but also relieved the overstimulation of stress response pathways, thereby alleviating nanotoxicity. These findings broaden our knowledge of how NPs induce contact toxicity in soil invertebrates through specific biointerfacial interactions, and highlight the important role of DOM in alleviating the combined hazards of NPs and soil acidification.

Contact and Fumigant Activities of Citrus aurantium Essential Oil against the Stable Fly Stomoxys calcitrans (Diptera: Muscidae).

The stable fly, Stomoxys calcitrans (L.), is a cosmopolitan hematophagous fly of medical and veterinary importance. It is widely considered a major livestock pest that can cause significant economic losses. This study aimed to evaluate the insecticidal activity of Citrus aurantium (L.) essential oil against S. calcitrans based on contact and fumigant toxicity tests. Chemical analysis by gas chromatography-mass spectrometry of the essential oil showed the dominance (93.79%) of limonene in the total essential oil composition. Furthermore, the insecticidal test results showed that the mortality of flies increased with concentration and time within 24 h of exposure. In the contact toxicity test, the median lethal dose was 105.88 µg/fly, while the 90% lethal dose was 499.25 µg/fly. As for the fumigant toxicity test, the median lethal concentration was 13.06 mg/L air, and the 90% lethal concentration was 43.13 mg/L air. These results indicate that C. aurantium essential oil exhibits insecticidal activity against S. calcitrans. Therefore, it can be used as an alternative to synthetic insecticides for achieving stable fly control.

Biological activities and gene expression of detoxifying enzymes in Tribolium castaneum induced by Moutan cortex essential oil

ABSTRACT Tribolium castaneum is one of the most harmful storage pests in the world. The aim of this study was to determine the chemical composition, repellent, and contact activities of Moutan cortex essential oil against this insect pest. In addition, the effects of Moutan cortex were examined on the expressions of three major detoxifying enzyme genes in T. castaneum. Four components were identified in this essential oil by gas chromatography-mass spectrometry (GC-MS), which was predominantly paeonol (99.13%). Paeonol exerted significant repellent activity against T. castaneum, which was more potent than the positive control N.N-diethyl-meta-toluamide (DEET). The most significant contact toxicity was observed at 24 h after exposure to paeonol. Further, quantitative real-time PCR (qRT-PCR) was used to assess expression changes in three detoxification enzyme genes in T. castaneum, including carboxylesterase (CarE), glutathione S-transferase (Gst) and cytochrome P4506BQ8 (Cyp6bq8). Among these, Gst was most highly up-regulated after treatment with paeonol with the highest expression level of 4.9-fold (Rps18 as internal reference gene) greater than control at 24 h following treatment. Data indicated that Gst might play a critical role in metabolic detoxification of toxic xenobiotics. Taken together, our findings might lay a foundation for development of paeonol as a potential natural repellent or pesticide to control storage pests.

A retrospective analysis of honey bee (Apis mellifera) pesticide toxicity data.

Current USEPA ecological risk assessments for pesticide registration include a determination of potential risks to bees. Toxicity data are submitted to support these assessments and the USEPA maintains a large database containing acute and chronic toxicity data on adult and larval honey bees (Apis mellifera), which USEPA considers a surrogate for Apis and non-Apis bees. We compared these toxicity data to explore possible trends. This analysis indicated a significant correlation between acute contact and oral median lethal dose (LD50) values for adult honey bees (ρ = 0.74, p <0.0001). Using default EPA modeling assumptions, where exposure for an individual bee is roughly 12x lower through contact than through ingestion, the analysis indicates that the oral LD50 is similarly if not more protective of the contact LD50 for the majority of pesticides and modes of action evaluated. The analysis also provided evidence that compounds with a lower acute toxicity for adults through contact and oral exposure pathways may still be acutely toxic for larvae. The acute toxicity of herbicides and fungicides was higher for larvae relative to oral and contact toxicity for adult honey bees for the same compounds and the no observed adverse effect level (NOAEL) from chronic toxicity studies were lower for larvae relative to adults, indicating increased sensitivity of larvae. When comparing 8-day LD50 values between single dose larval acute studies to those derived from repeat dose 22-day larval chronic toxicity studies, the LD50 values derived from chronic studies were significantly lower than those from acute toxicity tests (Z = -37, p = 0.03).

Insecticidal properties of Clausena austroindica leaf essential oil and its major constituent, trans-anethole, against Sitophilus oryzae and Tribolium castaneum

In this study, the chemical profile of the leaf essential oil of hitherto uninvestigated shrub Clausena austroindica B.C.Stone & K.K.N.Nair and its insecticidal potential against two stored product pests, Sitophilus oryzae (L.) and Tribolium castaneum (Herbst) are being investigated. Essential oils from the leaves of C. austroindica collected from two locations in south India were isolated by hydrodistillation and analyzed by gas chromatography-flame ionization detector (GC-FID) and gas chromatography-mass spectrometry (GC-MS). Six to eight compounds comprising 99.41–99.44% were characterized with trans-anethole (phenyl propanoid) as the major component (95.12–97.44%) in leaf essential oils. Trans-anethole was isolated from the leaf oil by column chromatography, characterized by Fourier Transform Infrared (FT-IR), ultraviolet-visible (UV-Vis), 1H-, 13C- and distortionless enhancement by polarization transfer (DEPT 135) nuclear magnetic resonance (NMR) spectroscopy, and quantified by external standardization. Insecticidal activity of C. austroindica leaf oil and trans-anethole were assessed against the rice weevil (S. oryzae) and red flour beetle (T. castaneum) by contact and fumigant toxicity assays. Mammalian cell toxicity of C. austroindica leaf oil and trans-anethole was also tested against L929 cell lines using (3-(4,5-dimethylthiazol-2-yl)−2,5-diphenyltetrazolium bromide) MTT assay and quantification of reactive oxygen species (ROS). C. austroindica leaf oil and trans-anethole demonstrated superior contact and fumigant toxicities against adult beetles of S. oryzae and T. castaneum. C. austroindica leaf oil and trans-anethole showed potential fumigant toxicity against S. oryzae (lethal concentration 50 (LC50) 38.80 & 76.98 µL/L) and T. castaneum (LC50 35.65 & 29.10 µL/L). Relatively less prominent viz., S. oryzae: LC50 leaf oil 469.70 µL/L, trans-anethole 2543.20 µL/L; T. castaneum: LC50 leaf oil, 1090.70 µL/L, trans-anethole 2050.84 µL/L, but significant contact toxicities were displayed by the leaf oil and trans-anethole against the two stored product pests. Both C. austroindica leaf oil and trans-anethole (< 2.0 µg/mL) have not demonstrated any mammalian cell (L929 cell line) toxicity. Our study demonstrates the potential of C. austroindica leaf essential oil as a new botanical insecticide for controlling stored product pests. Its major component, trans-anethole, also showed prominent insecticidal activity.

Chemical Composition and Insecticidal Properties of Essential Oil Obtained from Artemesia songarica Schrenk

Artemisia songarica Schrenk is a dominant sand fixation plant growing in the People's Republic of China. At present, there are rare studies on the chemical composition and biological activity of A. songarica. The chemical composition of the original oil was analyzed by gas chromatography-mass spectrometry, and 16 compounds were determined. The main compounds were bisabolol oxide II (28.7%), nerolidol (18.6%), bisabolol (12.9%), bisaboloxide A (10.0%), and spathulenol (6.0%). The contact toxicity and repellent activity of A. songarica essential oil and four selected compounds (bisabolol, geranyl butyrate, nerolidol, and santalol) were assessed against Tribolium castaneum Herbst and Liposcelis bostrychophila Badonnel. Bioassays showed that the crude essential oil exhibited strong insecticide and repellent activities against both pests. Santalol possessed the strongest contact toxicity (50% lethal dose [LD50] = 1.29 μg per adult) against T. castaneum. Nerolidol, santalol, and geranyl butyrate showed fair contact activity against L. bostrychophila. In particular, geranyl butyrate exhibited outstanding activity (LD50 = 11.53 μg/cm2). In addition, all of the four compounds did not detect a difference between compounds and the positive control (P > 0.05) against two pests at five tested concentrations. These results indicated that A. songarica and its selected compounds could be used as prospective insecticidal and repellent agents for further development and use.

Effectiveness of bio-insecticide incorporated storage bag for safe storage of legumes

India loses 2–6% of total produce due to lack of improper farm storage facilities. A potential novel method ofincorporating the bioinsecticide (azadirachtin 0.15%) into the storage bag was evaluated for its effectiveness in insect control for safe pulse storage at Division of Agricultural Engineering, ICAR-Indian Agricultural Research Institute, New Delhi during 2021. Azadirachtin (2.41%) was incorporated into jute and woven polypropylene bag. The configuration with both sides treated jute and WPP bag produced mortality of 93 and 100% respectively against Callosobruchus maculatus adults. Both the treated bags produced mortality (&gt;75%) within 48 h indicating the efficacy of selected bioinsecticide to contain infestation. The contact toxicity was dependent on porosity and pH of the storage bag material along with exposure time. Incorporation of the bioinsecticide saved more than 30% loss of weight in Bengal gram stored for 6 months. The storage quality of legumes, accessed as percentage of grains with holes and percentage of grains with eggs after storage duration of six months was within the acceptable values. The practice saved a value of `3242/t on stored Bengal gram in Jute bag and `206 in WPP bag respectively. Thus incorporation of azadirachtin could be potential tool for effective post-harvest storage of legumes in a sustainable manner.

Ursane-type triterpenoids, steroids and phenolics from the stem bark and leaves of Nauclea orientalis (L.) L. (Rubiaceae)

Phytochemical investigation of the stem bark and leaf extract of Nauclea orientalis led to the isolation and identification of the three ursane-type triterpenoids rotundic acid, (3β)-3,19,23,24-tetrahydroxyurs-12-en-28-oic acid, 3-oxo-19,23,24-trihydroxyurs-12-en-28-oic acid, the two steroids β-sitosterol, β-sitostenone, the two megastigmane derivatives blumenol A and blumenol A glucoside, the isocoumarine trans-4-hydroxymellein, as well as the flavonole glycoside rutin. From the crude stem bark extract, we performed an anti-bacterial assay against four Gram positive and six Gram negative bacterial strains. An acetylcholinesterase inhibitory assay was performed from the crude extracts and rotundic acid, (3ß)-3,19,23,24-tetrahydroxyurs-12-en-28-oic acid and β-sitostenone. Both assays showed only weak effects. Contact toxicity determined via topical application revealed increased mortality of Spodoptera exigua caterpillars. The chemophenetic significance of ursane-type triterpenoids for the genus Nauclea is discussed briefly.

Contact Toxicity and Ovideterrent Activity of Three Essential Oil-Based Nano-Emulsions against the Olive Fruit Fly Bactrocera oleae

The control strategies for the olive crop key pest, Bactrocera oleae, involve synthetic chemical insecticides and few eco-sustainable alternatives, such as ovideterrents and lures. In the last few decades, the interest concerning the formulation of botanical based biopesticides increased, but little research investigated the suitability of these approaches for B. oleae control. This research aimed to investigate the residual contact toxicity and the oviposition deterrence of three essential oil (EO)-based nano-emulsions (Pimpinella anisum, Foeniculum vulgare, Mentha × piperita) against B. oleae adult flies. All the nano-emulsions possessed optimal physical characteristics, with droplets dimensions ranging from 115 to 152 nm and low PDI values (&lt;0.2), even after 1 year of storage. Although no notable residual contact toxicity was noted, all the tested formulations reduced the number of oviposition puncture in no-choice tests (percent repellence: mint &lt; fennel &lt; anise). In choice trials, olives treated with fennel and anise EO-formulations at the highest concentration (7.5%, 75 g of EO/L) were less attractive respect to control fruits and a significant reduction of olive punctures was recorded. Nano-biopesticides are promising eco-friendly tools to integrate B. oleae pest management programs and to reduce the use of harmful conventional active ingredients.

Green Veterinary Pharmacology for Honey Bee Welfare and Health: Origanum heracleoticum L. (Lamiaceae) Essential Oil for the Control of the Apis mellifera Varroatosis.

Varroatosis, caused by the Varroa destructor mite, is currently the most dangerous parasitic disease threatening the survival of honey bees worldwide. Its adverse effect on the welfare and health of honey bees requires the regular use of specific acaricides. This condition has led to a growing development of resistance phenomena towards the most frequently used drugs. In addition, another important aspect that should not be understated, is the toxicity and persistence of chemicals in the environment. Therefore, the identification of viable and environmentally friendly alternatives is urgently needed. In this scenario, essential oils are promising candidates. The aim of this study was to assess the contact toxicity, the fumigation efficacy and the repellent effect of Origanum heracleoticum L. essential oil (EO) against V. destructor mite. In the contact tests, each experimental replicate consisted of 15 viable adult female mites divided as follows: 5 treated with EO diluted in HPLC grade acetone, 5 treated with acetone alone (as negative control) and 5 treated with Amitraz diluted in acetone (as positive control). The EO was tested at concentrations of 0.125, 0.25, 0.5, 1 and 2 mg/mL. For each experimental replicate, mortality was manually assessed after one hour. The efficacy of EO fumigation was evaluated through prolonged exposure at different time intervals. After each exposure, the 5 mites constituting an experimental replicate were transferred to a Petri dish containing a honey bee larva and mortality was assessed after 48 h. The repellent action was investigated by implementing a directional choice test in a mandatory route. During the repellency tests the behavior of the mite (90 min after its introduction in the mandatory route) was not influenced by the EO. In contact tests, EO showed the best efficacy at 2 and 1 mg/mL concentrations, neutralizing (dead + inactivated) 90.9% and 80% of the mites, respectively. In fumigation tests, the mean mortality rate of V. destructor at maximum exposure time (90 min) was 60% and 84% at 24 and 48 h, respectively. Overall, these results demonstrate a significant efficacy of O. heracleoticum EO against V. destructor, suggesting a possible alternative use in the control of varroatosis in honey bee farms in order to improve Apis mellifera welfare and health and, consequently, the hive productions.

Methyl Benzoate as a Promising, Environmentally Safe Insecticide: Current Status and Future Perspectives

The widespread use of synthetic chemical pesticides beginning in the late 1930s has contributed to the development of insecticide resistance of many important species of pest insects and plants. Recent trends in pesticide development have emphasized the use of more environmentally benign control methods that take into consideration environmental, food safety, and human health. Biopesticides (e.g., naturally occurring pesticidal compounds) are alternative pest management tools that normally have no negative impact on human health or the environment. Here we review methyl benzoate, a relatively new botanical insecticide that occurs naturally as a metabolite in plants, and whose odor is an attractant to some insects. Since 2016, many studies have shown that methyl benzoate is an effective pesticide against a range of different agricultural, stored product, and urban insect pests. Methyl benzoate has several important modes of action, including as a contact toxicant, a fumigant, an ovicidal toxin, an oviposition deterrent, a repellent, and an attractant. In this review, we summarize various modes of action of methyl benzoate and its toxicity or control potential against various kinds of arthropods, including agricultural pests and their natural enemies, and pollinators. We conclude that methyl benzoate is a very promising candidate for use in integrated pest management under either greenhouse or field conditions.

Toxicity, horizontal transfer, and physiological and behavioral effects of cycloxaprid against Solenopsis invicta (Hymenoptera: Formicidae).

The red imported fire ant, Solenopsis invicta Buren, is a significant urban, agricultural, and medical pest with a wide distribution in the world. Surface or mound treatment using contact insecticide is one of the main methods to control S. invicta. In the present study, cycloxaprid, a newly discovered neonicotinoid insecticide, was evaluated for S. invicta control and compared with two referent insecticides, imidacloprid and bifenthrin. Surfaces or sand treated with cycloxaprid, imidacloprid, or bifenthrin caused high mortality of S. invicta workers, and the action of cycloxaprid or imidacloprid was slower than bifenthrin. Like imidacloprid and bifenthrin, cycloxaprid can be horizontally transferred from corpses or live donor ants to recipient ants. In addition, cycloxaprid- or imidacloprid-treated surfaces significantly induced the activities of acetylcholinesterase (AChE) and detoxification enzymes; nevertheless, they had no significant effect on the foraging behaviors of S. invicta workers. Also, sand treated with cycloxaprid or imidacloprid did not negatively affect the digging activities of ants. Interestingly, S. invicta workers excavated significantly more sand containing 0.01 mg/kg cycloxaprid than untreated sand in the no-choice digging bioassays. In addition, extensive nesting activities (sand excavation and stacking) were observed in the flowerpots containing untreated sand or sand treated with cycloxaprid or imidacloprid. On the contrary, bifenthrin significantly reduced the foraging, digging, and nesting activities of S. invicta workers. Cycloxaprid is a slow-acting and nonrepellent insecticide against S. invicta workers, and its contact and horizontal toxicities are slightly higher than imidacloprid. © 2022 Society of Chemical Industry.