Contact Toxicity Research Articles

Contact Toxicity and Repellent Activity of a Powder Extracted from Tridax Daisy (Tridax procumbens) against Maize Weevil (Coleoptera: Curculionidae)1

Abstract The maize weevil (Sitophilus zeamais Motschulsky) is a significant pest affecting stored seeds and grains, leading to substantial losses in both quantity and quality. Utilizing crushed plant powders derived from specific natural plants offers a promising alternative to synthetic insecticides, which pose risks to both consumers and the environment. This study aimed to evaluate the contact toxicity of Tridax daisy (Tridax procumbens L.) plant powder derived from its aerial parts against S. zeamais when incorporated into jasmine brown rice, Oryza sativa L., grains. Laboratory experiments were conducted at 30°C ± 5°C and 70% ± 5% relative humidity following a completely randomized design with four replications and five treatments. Jasmine brown rice grains were treated with different application rates of 0 (control), 20, 40, 60, and 80 g/kg, with five pairs/replicate of 7-d-old S. zeamais. Results showed that T. procumbens powder exhibited a contact toxicity of 93.08 g/kg of grain after 12 d, resulting in a mortality of 27.5%. Additionally, the F1 generation comprised 51 adults, indicating an 85% reduction in adult progeny emergence. These findings demonstrate the potential of T. procumbens powder as a natural grain protectant to control S. zeamais populations in storage.

The toxicity, repellent, and biochemical effects of four wild plant extracts against Aphis gossypii Glover and Phenacoccus solenopsis Tinsley: HPLC analysis of phenolic compounds

AbstractThe insecticidal and repellent activities of the four wild plant extracts: stinging nettle, Urtica dioica L., white henbane, Hyoscyamus albus L., camphorweeds, Pluchea dioscoridis L., and cocklebur, Xanthium strumarium L. were tested compared to the insecticide spirotetramat against the 3rd nymphal instar of Aphis gossypii Glover and adult females of Phenacoccus solenopsis Tinsley after 24 and 48 h of treatment. Their effects on acetylcholinesterase (AChE) and glutathione-S-transferase (GST) enzyme activities were also assessed to explore their possible mechanisms of action. The phenolic compounds of the plant extracts were investigated by high-performance liquid chromatography (HPLC) analysis. The most abundant compounds in the methanol extract from P. dioscoridis were gallic acid (14.45 µg/mL), and cinnamic acid (11.44 µg/mL); from U. dioica were caffeic acid (15.32 µg/mL) and syringic acid (13.47 µg/mL); from H. albus were syringic acid (7.12 µg/mL) and catechol (5.33 µg/mL); and from X. strumarium were p-coumaric acid (24.53 µg/mL) and pyrogallol (18.35 µg/mL). According to the LC50 values, the contact toxicity of U. dioica, H. albus, P. dioscoridis, and X. strumarium against A. gossypii was 40.3, 60.6, 56.2, and 32.3 mg/L, whereas, the contact toxicity against P. solenopsis was 56.4, 67.5, 64.3, and 36.2 mg/L, compared to the spirotetramat (17.2 and 24.5 mg/L), respectively, at 48 h of treatment. The highest repellency rates were observed with LC50 values for X. strumarium (63.2 and 60.3%), followed by U. dioica (46.2 and 43.5%), P. dioscoridis (45.3 and 42.8%), and H. albus extract (38.8 and 35.2%) compared to the spirotetramat (78.5 and 76.2%) against A. gossypii and P. solenopsis at 24 h, but decreased with time. The AChE and GST activities in pests were significantly inhibited, compared to control and spirotetramat, with dose and time-dependent effects. These findings indicate that tested wild extracts may be suggested as viable alternatives for aphids and mealybugs control.

Bio-Pesticidal Potential of Nanostructured Lipid Carriers Loaded with Thyme and Rosemary Essential Oils against Common Ornamental Flower Pests

The encapsulation of essential oils (EOs) in nanostructured lipid carriers (NLCs) represents a modern and sustainable approach within the agrochemical industry. This research evaluated the colloidal properties and insecticidal activity of NLCs loaded with thyme essential oil (TEO-NLC) and rosemary essential oil (REO-NLC) against three common arthropod pests of ornamental flowers: Frankliniella occidentalis, Myzus persicae, and Tetranychus urticae. Gas chromatography–mass spectrometry (GC-MS) analysis identified the major chemical constituents of the EOs, with TEO exhibiting a thymol chemotype and REO exhibiting an α-pinene chemotype. NLCs were prepared using various homogenization techniques, with high shear homogenization (HSH) providing the optimal particle size, size distribution, and surface electrical charge. A factorial design was employed to evaluate the effects of EO concentration, surfactant concentration, and liquid lipid/solid lipid ratio on the physicochemical properties of the nanosuspensions. The final TEO-NLC formulation had a particle size of 347.8 nm, a polydispersity index of 0.182, a zeta potential of −33.8 mV, an encapsulation efficiency of 71.9%, and a loading capacity of 1.18%. The REO-NLC formulation had a particle size of 288.1 nm, a polydispersity index of 0.188, a zeta potential of −34 mV, an encapsulation efficiency of 80.6%, and a loading capacity of 1.40%. Evaluation of contact toxicity on leaf disks showed that TEO-NLC exhibited moderate insecticidal activity against the western flower thrips and mild acaricidal activity against the two-spotted spider mite, while REO-NLC demonstrated limited effects. These findings indicate that TEO-NLCs show potential as biopesticides for controlling specific pests of ornamental flowers, and further optimization of the administration dosage could significantly enhance their effectiveness.

Contact toxicity of insecticides against honeybees, Apis mellifera L. under laboratory conditions

Contact toxicity of insecticides against honeybees, Apis mellifera L. under laboratory conditions

Chemical Characterization and Insecticidal Activities of the Essential Oils from the Different Parts of Ocimum gratissimum var. suave (Willd.) Hook. f.

In this research, the essential oils (EOs) from different parts of Ocimum gratissimum var. suave were chemically characterized and evaluated for insecticidal activity, especially against two common storage pests of Chinese herbal medicines: Tribolium castaneum and Liposcelis bostrychophila. Ocimum gratissimum is a plant with several medicinal values in traditional Chinese medicine. In the study, EOs were successfully extracted from inflorescences (OGI) and stem-leaf (OGLS) parts of O. gratissimum by steam distillation and 16 compounds were identified by gas chromatography-mass spectrometry (GC-MS), of which eugenol was the major constituent in both extracts. In fumigation toxicity tests against both pests, the EOs showed limited toxicity against T. castaneum but showed better toxicity against L. bostrychophila. Contact toxicity tests showed that OGLS had better insecticidal potential than OGI, while the insecticidal effect of eugenol sometimes exceeded that of EOs. In addition, repellency experiments showed that O. gratissimum EOs repelled the pests to varying degrees, with the effect being influenced by concentration and exposure time. The results suggest that O. gratissimum EOs could be a promising alternative to synthetic insecticides for sustainable utilization.

Toxicity and Repellent Effect of Three Plant Based Essential Oils against the Red Flour Beetle <i>Tribolium castaneum</i> (Herbst)

In this study jasmine (Jasminum officinale), lemon grass (Cymbopogon citratus), and sandalwood (Santalum album) essential oils were investigated for their efficacy against the red flour beetle Tribolium castaneum. Sandalwood oil consistently showed the highest contact toxicity, with LD50 values decreasing over time. Jasmine and lemon grass oils ranked lower but still exhibited toxicity. The order of contact toxicity was sandalwood > jasmine > lemon grass at each exposure period. Fumigation treatments revealed sandalwood’s initial superiority, though jasmine surpassed it at 48 hr. The order of fumigation toxicity shifted to jasmine > sandalwood > lemon grass at this extended exposure time. Repellency tests showed dose and time-dependent responses for both larval and adult stages, with occasional fluctuations. Sandalwood’s significance differed for adult beetles between time intervals, and jasmine exhibited insignificance in its efficacy for larvae at certain intervals. This study provides insights into the potential of these essential oils as alternatives for pest control.

Phytochemical Characterization, Fumigant and Contact Toxicity Activities of Four Essential Oils Against Eriophyid Gall Mite, Aceria pongamiae Keifer (Acarina: Eriophyidae).

Plant-derived essential oils (EO) offer a natural alternative to chemical pesticides for eco-friendly pest control approaches. Aceria pongamiae Keifer, a notorious pest that affects Pongamia pinnata (L.) Pierre has mainly been controlled using synthetic acaricides leading to resistance development and environmental issues. EOs provide a natural and biodegradable option for pest control, with a unique mode of action. This study evaluates the acaricidal efficacy of EOs-eucalyptus Eucalyptus maculata Hook (EEO), lavender Lavandula angustifola L. (LEO), peppermint Mentha piperita L. (PEO), and black pepper Piper nigrum L. (BPEO) against A. pongamiae for the first time. We investigated the biological activity of EOs using fumigation and contact toxicity assays at concentrations ranging from 0.1 to 1 % and 0.6 to 0.9 % respectively, overexposure periods of 24, 48 and 72 h. Chemical characterization of EOs was performed using GC-MS analysis. Eucalyptol (62.88 %), linalyl acetate (39.11 %), menthol (44.35 %), and caryophyllene (32.77 %) were the main components of EEO, LEO, PEO and BPEO respectively. After 24 h of observation, EEO (LC50=1.01 %) and after 48 and 72 h, PEO had the highest fumigant toxicity (LC50=0.71 and 0.29 % respectively). The BPEO showed the most contact toxicity after 24, 48 and 72 h (LC50=0.92, 0.68 and 0.46 % respectively). This work reinforces the selection of adequate essential oils for implementation in future pest control strategies.

Cell Penetrating Peptide Enhances the Aphidicidal Activity of Spider Venom-Derived Neurotoxin.

HxTx-Hv1h, a neurotoxic peptide derived from spider venom, has been developed for use in commercial biopesticide formulations. Cell Penetrating Peptides (CPPs) are short peptides that facilitate the translocation of various biomolecules across cellular membranes. Here, we evaluated the aphidicidal efficacy of a conjugated peptide, HxTx-Hv1h/CPP-1838, created by fusing HxTx-Hv1h with CPP-1838. Additionally, we aimed to establish a robust recombinant expression system for HxTx-Hv1h/CPP-1838. We successfully achieved the secretory production of HxTx-Hv1h, its fusion with Galanthus nivalis agglutinin (GNA) forming HxTx-Hv1h/GNA and HxTx-Hv1h/CPP-1838 in yeast. Purified HxTx-Hv1h exhibited contact toxicity against Megoura crassicauda, with a 48 h median lethal concentration (LC50) of 860.5 μg/mL. Fusion with GNA or CPP-1838 significantly enhanced its aphidicidal potency, reducing the LC50 to 683.5 μg/mL and 465.2 μg/mL, respectively. The aphidicidal efficacy was further improved with the addition of surfactant, decreasing the LC50 of HxTx-Hv1h/CPP-1838 to 66.7 μg/mL-over four times lower compared to HxTx-Hv1h alone. Furthermore, we engineered HxTx-Hv1h/CPP-1838 multi-copy expression vectors utilizing the BglBrick assembly method and achieved high-level recombinant production in laboratory-scale fermentation. This study is the first to document a CPP fusion strategy that enhances the transdermal aphidicidal activity of a natural toxin like HxTx-Hv1h and opens up the possibility of exploring the recombinant production of HxTx-Hv1h/CPP-1838 for potential applications.

Contact Toxicity and Repellent Effects of Essential Oils from Toddalia asiatica Against Two Stored-Product Insects.

Insect infestations continually endanger stored goods, underscoring the significance of discovering eco-friendly insecticides for pest management. Essential oils (EOs) from different parts of Toddalia asiatica (leaf, fruit and branch) were extracted by hydrodistillation and analyzed by GC-MS. Carvene, p-cymene and muurolene are the principal compounds of T. asiatica leaf (TAL), T. asiatica fruit (TAF) and T. asiatica branch (TAB) EO respectively. Our work aimed to assess the contact toxicity and repellent effects of EOs on two storage pests, Tribolium castaneum and Lasioderma serricorne. All tested EOs exhibited obvious contact toxicity, especially, TAL EO against T. castaneum (33.48 μg/adult) and TAF EO against L. serricorne (16.42 μg/adult). Repellency tests revealed that TAL and TAF EOs, at a concentration of 78.63 nL/cm2, achieved nearing 100 % efficiency against T. castaneum. These results suggest that EOs of T. asiatica could be used as effective botanical insecticides for managing stored-product insects.

Repellency, Toxicity, and Chemical Composition of Plant Essential Oils from Myrtaceae against Asian Citrus Psyllid, Diaphorina citri Kuwayama (Hemiptera Liviidae).

Diaphorina citri Kuwayama (D. citri) is one of the major pests in the citrus industry, which spreads Citrus Huanglongbing disease. It has developed resistance to chemical insecticides. Therefore, searching for greener solutions for pest management is critically important. The main aim of this study was to evaluate the repellent and insecticidal efficacy of essential oils (EOs) from four species of Myrtaceae plants: Psidium guajava (PG), Eucalyptus robusta (ER), Eucalyptus tereticornis (ET), and Baeckea frutescens (BF) against D. citri and to analyze their chemical compositions. GC-MS analysis was performed, and the results indicated that the EOs of PG, ER, ET, and BF were rich in terpenoids, ketones, esters, and alcohol compounds. The repellent rate of all four EOs showed that it decreased with exposure time but increased with the concentration of EOs from 80.50% to 100.00% after treating D. citri for 6 h with four EOs at 100% concentration and decreased to 67.71% to 85.49% after 24 h of exposure. Among the compounds from the EOs tested, eucalyptol had the strongest repellent activity, with a 24 h repellency rate of 100%. The contact toxicity bioassay results showed that all EOs have insecticidal toxicity to D. citri; the LC50 for nymphs was 36.47-93.15 mL/L, and for adults, it was 60.72-111.00 mL/L. These results show that when PG is used as the reference material, the ER, ET, and BF EOs have strong biological activity against D. citri, which provides a scientific basis for the further development of plant-derived agrochemicals.

Two Novel Diterpenoid Alkaloids from Aconitum Pendulum.

Two previously uncharacterized compounds, an aconitine-type C19-diterpenoid alkaloid (1) and a napelline-type diterpenoid alkaloid C20-diterpenoid alkaloid (2), as well as ten known compounds (3-12), were isolated from Aconitum pendulum. Their structures were elucidated based on spectroscopic data, including 1D and 2D NMR, IR, HR-ESI-MS, and single-crystal X-ray diffraction analysis. The anti-insecticidal activities of these compounds were evaluated by contact toxicity tests against two-spotted spider mites, and compounds 1, 2, and 9 showed moderate contact toxicity, with LC50 values of 0.86±0.09, 0.95±0.23, and 0.89±0.19 mg/mL, respectively. This study highlights the potential use of diterpenoid alkaloids as natural plant-derived pesticides for the management of plant pests.

Exploring chemical composition and insecticidal activities of Alpinia calcarata rhizome essential oil against three major storage insects

Alpinia calcarata (Roscoe), generally recognized as snap ginger or lesser galangal of the Zingiberaceae family, undergoes widespread cultivation in tropical nations. It is characterized by its noteworthy pharmacological attributes, such as anti-inflammatory, analgesic, antinociceptive, reproductive, anti-cancer, and gastro-protective effects. Many storage pests now resist traditional chemical pesticides. Transitioning to organic alternatives is a preferable and sustainable solution. This research investigates the insecticidal activity of essential oil from A. calcarata rhizomes, obtained via hydro-distillation. Chemical analysis was conducted, and the study assessed its toxicity and repellent effects on Tribolium castaneum (Herbst), Lasioderma serricorne (F.), and Callosobruchus chinensis (L). A yield of 0.44 ± 0.02 % essential oil was obtained from dry rhizomes. Gas chromatography-mass spectrometry (GC-MS) characterization revealed the major chemical constituents as 1,8-cineole (25.71 %), ethyl iso-allocholate (16.01 %), and fenchyl acetate (15.15 %). The findings from the investigation into the pesticidal characteristics of essential oils derived from the rhizome of A. calcarata unveiled significant contact (LC50 at 24 h was 10.9 mg/cm2 for T. castaneum, 1.0 mg/cm2 for L. serricorne and 0.5 mg/cm2 for C. chinensis) and fumigant toxicity (LC50 at 24 h was 4.05 mg/L air for T. castaneum, 1.75 mg/L air for L. serricorne, and 1.03 mg/L air for C. chinensis). The repellent efficacy was evaluated through an area preference test, revealing robust repellent activity at various concentrations. Undoubtedly, the essential oil extracted from the rhizome of A. calcarata is valuable and has the potential to be a safe, organic pesticide for controlling storage pests.

Insecticidal, physiological, and biochemical effects of Schinus molle essential oil on the adults of Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae)

Rhyzopertha dominica (F.) is considered as a major stored product pest. Conventional insecticides induce adverse effects on the environment. Plant derivative products constitute a promising alternative for pest control. The purpose of our research was to identify the chemical profile of essential oil (EO) extracted from Schinus molle L. (Anacardiaceae) and to evaluate the fumigant and the contact toxicity, and the repellent activity of this oil on adults of Rhyzopertha dominica F. (Coleoptera), a major pest in products that are stored around the world. The effects of this oil were examined on biochemical profile (energy reserves and Proteins), selective biomarkers like acetylcholinesterase (AChE), glutathione S-transferases (GST) and glutathione (GSH), and nucleic acids (DNA and RNA). Digestive enzymes were also investigated. The major chemical compounds identified by the GC-MS were α-phellandrene (16.613%), ß-phellandrene (12.104%), elemol (9.028%) and β-eudesmol (5.872%). Then, we evaluated the repellent activity, and also the effects in nutritional reserves and some biomarkers. This EO exhibited an insecticidal and repellent activity as a function of the exposure time and concentrations. Contact (LC50 at 24 h: 19.99 μL/mL) is the most effective mode of application compared to fumigation (LC50 at 24h: 174.30 μL/L air). S. molle EO was also investigated in digestive enzymes’ activities (α-amylase, lipase, chitinase and protease). Our results revealed a decrease in both α-amylase, lipase, protease and chitinase activities in treated adults compared to controls. In addition, we noticed a neurotoxic activity of S. molle EO traduced by a decrease of AChE. An induction of the detoxification system was observed via a decrease in GSH rate and an increase in GST activity. Moreover, the treatment induces an alteration of biochemical profile of R. dominica adults. Lastly, essential oil was examined on nucleic acids. Results showed an increase in DNA and RNA amount in treated adults when compared with control. Due to their effective source of bioactive compounds, the EO from the studied plant could be used as an alternative strategy for the management of stored product pests.

In-Depth Structural Simplification of Celangulin V: Design, Synthesis, and Biological Activity.

Celangulin V is a novel botanical insecticide with significant bioactivity and a unique molecular target, but its complex polyol ester structure hinders its broader application in agriculture. To discover new analogues of celangulin V with a simpler structure and enhanced biological activities, we initiated a research project aimed at simplifying its structure and assessing insecticidal efficacy. In this study, a series of novel 1-tetralone derivatives were designed via a structure-based rational design approach and synthesized by a facile method. The biological activities of the target compounds were determined against Mythimna separata (M. separata), Plutella xylostella, and Rhopalosiphum padi. The results revealed that most of the synthesized compounds exhibited superior activities compared to celangulin V. Remarkably, the insecticidal activity of compound 6.16 demonstrated 102-fold greater stomach toxicity than celangulin V against M. separata. In addition, certain compounds showed significant contact toxicity against M. separata, a finding not reported previously in the structural optimization studies of celangulin V. Molecular docking analysis illustrated that the binding pocket of compound 6.16 with the H subunit of V-ATPase was the same as celangulin V. This study presents novel insights into the structural optimization of botanical pesticides.

The Evaluation of Toxicity Effects of Synthetic Volatile Compounds and Essential Oils on Callosbruchus maculatus L. and its Biology

The biology studies and contact toxicity of synthetic volatile compounds, namely Propionic acid and Benzaldehyde, and essential oils namely, Ocimum basilicum and Mentha piperita, and their different possible combinations evaluated against Callosobruchus maculatus and were carried out at the Department of Entomology, Annamalai University to develop an economically viable and effective alternative to chemical insecticides to manage the stored product insect pests. In the biology study, the egg period was 5±0.07 days. The larval and pupal period together was 21.24±0.67. The total development period recorded from the day of oviposition to adult emergence was 35.03±0.35 days. The maximum contact toxicity was observed in Propionic acid + Benzaldehyde with 8.73 µl LC50. Therefore, in addition to being incorporated into the storage pest management to prevent the development of resistance, combinations of essential oils and synthetic volatiles, such as propionic acid and benzaldehyde, could be used as an alternative to the chemical fumigants that are mostly used to control pests of stored products.

Reduced effectiveness of permethrin-treated military uniforms after prolonged wear measured by contact irritancy and toxicity bioassays with Ixodes scapularis (Acari: Ixodidae) nymphs.

Factory-treated permethrin uniforms are the primary method used by the US Army to prevent arthropod bites and transmission of arthropod-borne diseases. In this study previously worn uniforms were collected from cadets at the United States Military Academy in West Point, NY to determine the amount of permethrin remaining after prolonged wear and subsequent effects on ticks. Six trousers were collected from cadets in the sophomore, junior, and senior classes. A new, unwashed uniform served as a positive control and an untreated maternity uniform served as a negative control. Fabric samples were removed from each trouser and used in bioassays with laboratory-reared Ixodes scapularis Say nymphs. Contact irritancy bioassays measured the nymphs' ability to remain in contact with fabric for a period of 5 min. Toxicity bioassays measured tick survival at 1 and 24 h after contacting uniform samples. liquid chromatography-mass spectrometry was used to quantify the permethrin content (mg/cm2) in each uniform after the bioassays were complete. The results showed significant amounts of permethrin were lost after extended wear and it was related to the cadet year group. The contact irritancy assays found uniforms with less permethrin did not irritate ticks and cause them to dislodge. Mortality was also affected by permethrin levels, with less ticks dying at 24 h on older uniforms. The results from this study show older uniforms lose most of their permethrin and no longer provide the same levels of protection.

Bio-active essential oils derived from medicinal plants and their insecticidal potential on houseflies and cockroaches

The plant essential oils are intricate blends of semi-volatile and volatile substances. They primarily consist of monoterpenes and sesquiterpenes; however, very trace amounts of diterpenes, triterpenes, and tetraterpenes are also present. In view of environmental concerns, highly aromatic essential oils, exhibit a variety of bioactivities against the targeted species as a novel pest control alternative to synthetic insecticides. As a result, the study aims to evaluate the impact of essential oils (EO) extracted from various plant species: Azadirachta indica, Citrus limon, Eucalyptus globulus, Laurus nobilis, Mentha piperita, and Ocimum tenuiflorum. Gas chromatography and Mass spectrometry (GC–MS) were used to determine the chemical components of these essential oils. Furthermore, the extracted oils were subjected to individual and combination formulations of bio-insecticides, which were assessed on houseflies and cockroaches in comparison to a blank control and the positive control dichlorvos (dimethyl 2, 2-dichlorovinyl phosphate). The findings showed that the maximum essential oil yields from the leaves of A. indica, E. globulus, and O. tenuiflorum were 11.38, 9.64 and 10.41 %, respectively. Compared to DDVP, which killed all insects within the 12-hour period, the combined form of leaf essential oils at 100 % concentration proved to be more effective in controlling insect mortality. It accounted for 98 % of the deaths in houseflies and 76.4 % of the deaths in cockroaches, according to the contact toxicity evaluation. The active insecticidal components in the formulation include eucalyptol, undecane, tetradecane, estragole, pentadecane, and caryophyllene.

Activity of Rosmarinus officinalis (Lamiales: Lamiaceae) Essential Oil and Its Main Constituent, 1,8-Cineole, against Tribolium castaneum (Coleoptera: Tenebrionidae)1

Abstract Rosemary essential oil (EO), from Rosmarinus officinalis L. (Lamiales: Lamiaceae), has potent properties against stored insect pests. This study aimed to evaluate the efficacy of EOs from both manually extracted and commercially produced R. officinalis, as well as the main compound 1,8-cineole, against adults of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae). Chemical analysis of the R. officinalis EOs was conducted using a gas chromatograph–mass spectrometer. Toxicity and repellent effects were assessed through contact and fumigation bioassays in a factorial experimental design with five replicates. Each R. officinalis EO type showed nine major compounds (>90%), with 1,8-cineol as the predominant component (>52%). Contact toxicity bioassays showed 1,8-cineole had a median lethal concentration of 1.12% at 48 h, 1.54% for manually extracted EOs, and 1.64% for commercially produced R. officinalis EOs. Furthermore, 0.5% of 1,8-cineole displayed strong contact efficacy against T. castaneum. Fumigant toxicity was observed at 140.07, 127.28, and 121.52 μl/L air, respectively. Manually extracted EO at 160 μl/L air demonstrated strong fumigant efficacy against T. castaneum, acting as a contact (66–94%) and fumigant (82–69%) repellent within 8 h, outperforming commercially produced EO and 1,8-cineole. These findings highlight the potential of manually extracted EO from R. officinalis as a natural insecticide, effective in both contact and fumigation against T. castaneum. This offers a promising avenue for using plant extracts in storage pest prevention, potentially leading to the development of insecticide products.

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

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

Sublethal Effects of Chlorantraniliprole on the Mobility Patterns of Sitophilus spp.: Implications for Pest Management.

Chlorantraniliprole, an anthranilic diamide insecticide, has emerged as a promising solution for controlling agricultural pests because of its low mammalian toxicity and selectivity towards non-target organisms. This study investigated the sublethal effects of chlorantraniliprole on the mobility behavior of two significant stored-product pests, Sitophilus oryzae (L.) and Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae). Contact toxicity assays revealed varying susceptibility levels between the two species, with S. zeamais showing higher sensitivity. Subsequent analysis of mobility behavior, both in the presence and absence of food, indicated significant differences between chlorantraniliprole-exposed and control groups. While S. oryzae exhibited altered locomotion patterns and a decreased number of food approaches at sublethal concentrations, S. zeamais displayed increased walking time and reduced immobility periods. These findings highlight the importance of considering sublethal effects in understanding the overall impact of chlorantraniliprole on stored-product pests. Further research into the long-term consequences of sublethal exposure is warranted to inform more effective pest management strategies in storage.