Discovery of Potential Neonicotinoid Insecticides by an Artificial Intelligence Generative Model and Structure-Based Virtual Screening

The identification of neonicotinoid insecticides bearing novel scaffolds is of great importance for pesticide discovery. Here, artificial intelligence-based tools and virtual screening strategy were integrated to discover potential leads of neonicotinoid insecticides. A deep generative model was successfully constructed using a recurrent neural network combined with transfer learning. The model evaluation showed that the pretrained model could accurately grasp the SMILES grammar of drug-like molecules and generate potential neonicotinoid compounds after transfer learning. The generated molecules were evaluated by hierarchical virtual screening, hits were subjected to a similarity search, and the most similar structures were purchased for the bioassay. Compounds A2 and A5 displayed 52.5 and 50.3% mortality rates against Aphis craccivora at 100 mg/L, respectively. The docking study indicated that these two compounds have similar binding modes to neonicotinoids, which were verified by further molecular dynamics simulations.

Identification and Coexposure of Neonicotinoid Insecticides and Their Transformation Products in Retail Cowpea (Vigna unguiculata)

There is growing evidence that the transformation products of emerging contaminants in foodstuffs may pose a health risk to humans. However, the exact identities, levels, and estimated dietary intake (EDI) of neonicotinoid transformation products in crops remain poorly understood. We established an extended suspect screening strategy to investigate neonicotinoid insecticides and their transformation products in retail cowpea from 11 cities in Hainan Province, China. Forty-nine transformation products were identified in retail cowpea, of which 22-36 were found in 98.6% of the samples. Notably, 31 new transformation products were derived from new processes or a combination of different transformation processes. The mean concentrations of neonicotinoids and nine of the transformation products (with authentic standards) were in the ranges of 0.0824-5.34 and 0.0636-1.50 ng/g, respectively. The cumulative EDIs of the quantified transformation products were lower than those of parent neonicotinoids with the exception of clothianidin desmethyl, which had a ratio of 1157%. However, the coexistence of the other 40 transformation products (without authentic standards) in cowpea suggested that the exposure risk from all of the transformation products might be higher. This study demonstrated that pesticide transformation products should be considered in food chain risk assessments and included in future regulatory management.

Design, Synthesis, and Insecticidal Evaluation of Neonicotinoids with Conjugated Diene

Neonicotinoid insecticides acting on the insect nicotinic acetylcholine receptors (nAChRs) play an essential role in contemporary pest control. In the present study, a series of novel neonicotinoid analogues with conjugated diene were synthesized. Bioassays indicated that compounds A3 and A12 had LC₅₀ values of 1.26 and 1.24 mg/L against Myzus persicae, respectively, which were comparable to that of imidacloprid (IMI, LC₅₀ = 0.78 mg/L). Density functional theory (DFT) calculations were performed to explain the differences in the insecticidal activities of target compounds. Molecular docking results indicate that compounds A3 and A12 interact favorably with Lymnaea stagnalis AChBP. The hydrolysis experiments confirmed that the stability of compounds A3 and A12 was enhanced in water.

The Fungus Nosema ceranae and a Sublethal Dose of the Neonicotinoid Insecticide Thiamethoxam Differentially Affected the Health and Immunity of Africanized Honey Bees

Honey bees (Apis mellifera L.) are affected by different biotic and abiotic stressors, such as the fungus Nosema ceranae and neonicotinoid insecticides, that negatively impact their health. However, most studies so far conducted have focused on the effect of these stressors separately and in European honey bees. Therefore, this study was conducted to analyze the impact of both stressors, singly and in combination, on honey bees of African descent that have demonstrated resistance to parasites and pesticides. Africanized honey bees (AHBs, Apis mellifera scutellata Lepeletier) were inoculated with N. ceranae (1 × 10⁵ spores/bee) and/or chronically exposed for 18 days to a sublethal dose of thiamethoxam (0.025 ng/bee) to evaluate their single and combined effects on food consumption, survivorship, N. ceranae infection, and immunity at the cellular and humoral levels. No significant effects by any of the stressors were found for food consumption. However, thiamethoxam was the main stressor associated to a significant decrease in AHB survivorship, whereas N. ceranae was the main stressor affecting their humoral immune response by upregulating the expression of the gene AmHym-1. Additionally, both stressors, separately and combined, significantly decreased the concentration of haemocytes in the haemolymph of the bees. These findings indicate that N. ceranae and thiamethoxam differentially affect the lifespan and immunity of AHBs and do not seem to have synergistic effects when AHBs are simultaneously exposed to both stressors.

Potential Toxic Mechanisms of Neonicotinoid Insecticides in Rice: Inhibiting Auxin-Mediated Signal Transduction

Inappropriate application of pesticides not only causes sub-lethal effects on ecosystem service providers but also reduces crop yield and quality. As a xenobiotic signal molecule, pesticides may interact with signal transduction receptors in crops, resulting in oxidative damage and even metabolic perturbations. We discovered that three neonicotinoid insecticides (NIs), namely, imidacloprid, thiamethoxam, and clothianidin, at 0.06-0.12 kg ai/ha significantly inhibited the auxin signal pathway in rice leaves, thereby reducing the intracellular auxin (IAA) content. Molecular simulation further confirmed that NIs occupied the binding site where auxin transporter-like proteins 1 (LAX11) and 2 (LAX12), in which Thr253 and Asn66 of LAX11, as well as Thr244 and Asn57 of LAX12, were bound to the nitroguanidine of NIs via H-bonds. Meanwhile, Asn66 of LAX11 and Asn57 of LAX12 interacted with nitroguanidine via aromatic H-bonds. Moreover, phenylpropanoid biosynthesis was significantly disturbed because of the inhibited auxin signal pathway. Notably, peroxidase-coding genes were downregulated with a maximum value greater than 10-fold, resulting in decreased antioxidant metabolites flavone (37.82%) and lignin content (20.15%). Ultimately, rice biomass was reduced by up to 25.41% due to the decline in IAA content and antioxidant capacity. This study deeply explored the molecular mechanism of metabolic perturbations in crops stressed by pesticides, thus providing a scientific basis for pesticide environmental risk assessment and agricultural product safety.

Determination of Neonicotinoid Insecticides in Environmental Water by the Enrichment of MIL-53 Mixed Matrix Membrane Coupled with High Performance Liquid Chromatography

Metal organic framework based mixed matrix membranes (MOF-MMMs) were synthesized and applied for dispersive membrane extraction (DME) of four neonicotinoid insecticides (nitenpyram, thiacloprid, imidacloprid, and acetamiprid) in environmental water, combined with high performance liquid chromatography (HPLC) for determination. Several experimental conditions were optimized in detail, involving dosage percentage of MOF, extraction time, sample pH, salinity, type and volume of eluent, and elution time. High sensitivity with limits of detection and quantification were achieved as 0.013-0.064 μg L^-1 and 0.038-0.190 μg L^-1, respectively, and good precision with relative standard deviations were obtained as 3.07-12.78%. The proposed method has been successfully applied to determine four neonicotinoid insecticides in tap water, surface water, and seawater, satisfactory recoveries of spiked water samples were between 72.50 and 117.98%. Additionally, the MOF-MMMs showed good reusability with the extraction efficiencies almost remaining stable after 14 cycles. The MOF-MMMs based DME followed by the HPLC method can be a promising utility for the determination of neonicotinoid insecticides in environmental water samples, with high sensitivity and convenient operation.

Neonicotinoid Insecticides and Their Metabolites Can Pass through the Human Placenta Unimpeded

Studies on neonicotinoid (NEO) exposure in pregnant women and fetuses are scarce, and transplacental transfer of these insecticides is unknown. In this study, parent NEOs (p-NEOs) and their metabolites (m-NEOs) were determined in 95 paired maternal (MS) and cord serum (CS) samples collected in southern China. Imidacloprid was the predominant p-NEO in both CS and MS samples, found at median concentrations of 1.84 and 0.79 ng/mL, respectively, whereas N-desmethyl-acetamiprid was the most abundant m-NEO in CS (median: 0.083 ng/mL) and MS (0.13 ng/mL). The median transplacental transfer efficiencies (TTEs) of p-NEOs and m-NEOs were high, ranging from 0.81 (thiamethoxam, THM) to 1.61 (olefin-imidacloprid, of-IMI), indicating efficient placental transfer of these insecticides. Moreover, transplacental transport of NEOs appears to be passive and structure-dependent: cyanoamidine NEOs such as acetamiprid and thiacloprid had higher TTE values than the nitroguanidine NEOs, namely, clothianidin and THM. Multilinear regression analysis revealed that the concentrations of several NEOs in MS were associated significantly with hematological parameters related to hepatotoxicity and renal toxicity. To our knowledge, this is the first analysis of the occurrence and distribution of NEOs in paired maternal-fetal serum samples.

Survival Rate of the Neotropical Stingless Bees Nannotrigona perilampoides and Frieseomelitta nigra after Exposure to Five Selected Insecticides, under Controlled Conditions

Insecticides used in agricultural pest management pose survival risks to the stingless bees that forage on crops in tropical and subtropical regions. In the present study, we evaluated, under laboratory conditions, the acute oral toxicity of five selected insecticides (dinotefuran, imidacloprid, flupyradifurone, spirotetramat, and cyantraniliprole) to two species of neotropical stingless bees: Nannotrigona perilampoides and Frieseomelitta nigra. At field recommended doses, dinotefuran, imidacloprid, and flupyradifurone caused the highest mortality in both bee species. These insecticides also caused the largest decrease in the survival rate when exposed to a 10-fold dilution of the field recommended doses. Notably, dinotefuran exerted a high effect even at 100-fold dilution (100% mortality). In contrast, cyantraniliprole had a low effect and spirotetramat was virtually nontoxic. These results suggest that some insecticides used to control sap-sucking insects may have a significant negative impact on the communities of stingless bees.

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

BACKGROUND

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.

RESULTS

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.

CONCLUSION

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.

Sex-Dependent Environmental Health Risk Analysis of Flupyradifurone

Pesticides are used in agricultural production worldwide, resulting in widespread environmental pollution. Many diseases are closely related to exposure to pesticide residues. In this study, the association between exposure to the pesticide flupyradifurone (FPF), a substitute for neonicotinoids, and sex-dependent thyroid dysfunction was explored for the first time. Exposure using rat models revealed that the FPF metabolism is sex-dependent, with males preferring N-dealkylation and hydrolytic metabolism and females preferring hydroxylation. In particular, novel chloropyridine-site hydroxylation I and II metabolic pathways of FPF were discovered. More importantly, differential metabolic pathways of FPF induced sex-based dysregulation of the hypothalamic-pituitary-thyroid axis, in which females exhibited subclinical hyperthyroidism, while males displayed abnormal hypothyroidism. This may be attributed to the potential agonistic or antagonistic effect of FPF sex-dependent metabolites on liver thyroid hormone receptors. Furthermore, FPF exposure further mediated sex-specific dysregulation of cellular lipid homeostasis, with abnormal fatty acid β-oxidation and excessive energy expenditure in females and the risk of excessive accumulation of triglycerides in males. These results illustrate the potential risk of sex-related thyroid metabolic diseases caused by FPF and provide an important basis and support for further studies of FPF on human health and as an environmental pollutant.

Imidacloprid treatments induces cyanobacteria blooms in freshwater communities under sub-tropical conditions

Imidacloprid is one of the most used neonicotinoid insecticides all over the world and is considered as a contaminant of concern due to its high toxicity potential to aquatic organisms. However, the majority of the studies that have evaluated the effects of imidacloprid on aquatic organisms were conducted under temperate conditions. In the present study, a mesocosm experiment was conducted under sub-tropical conditions to assess the effects of imidacloprid on the structure (macroinvertebrates, zooplankton and phytoplankton) and functional endpoints of an aquatic ecosystem and to compare the results with similar temperate and (sub-)tropical mesocosm studies. Imidacloprid (0, 0.03, 0.3 and 3 µg/L) was applied to 13 mesocosms weekly over a period of 4 weeks, followed by a one month recovery period. At the community level a lowest NOEC_community of 0.03 µg/L was calculated for the zooplankton, phytoplankton and macroinvertebrate communities. The highest sensitivity to imidacloprid (NOEC < 0.03 µg/L) were observed for Gerris sp., Diaptomus sp. and Brachionus quadridentatus. Imidacloprid induced population declines of the larger zooplankton species (Diaptomus sp. and Ostracoda) resulted in increased rotifer abundances and shifted the phytoplankton community to a graze resistant gelatinous cyanobacteria dominated ecosystem. These cyanobacteria blooms occurred at all different concentrations and could pose an important public health and environmental concern. Although there are some differences in species and community sensitivity between the present and the other (sub-)topical mesocosm studies, it can be observed that all show a similar general community response to imidacloprid. Under (sub-)tropical conditions, the toxic effects of imidacloprid occur at lower concentrations than found for temperate ecosystems.

Myzus persicae Management through Combined Use of Beneficial Insects and Thiacloprid in Pepper Seedlings

Simple Summary

Myzus persicae is a worldwide pest causing significant economic loss, especially to vegetables. However, the mainly applied insecticides were not effective, whilst also endangering the safety of pollinators. Harmonia axyridis and Aphidoletes aphidimyza are predators of aphids, but they are costly and affected by temperature and insecticides. We conducted toxicity tests and greenhouse trails to make an effective combination of neonicotinoid insecticides and predators. Both H. axyridis and A. aphidimyza effectively controlled aphids whether combined with thiacloprid or not, at above 20 °C temperature condition. Our results indicated that it is it is necessary to choose H. axyridis or A. aphidimyza to control aphids based on economic and thermal considerations. Practically, thiacloprid could be used either as an emergency option to control aphids’ abundance alone or in combination with natural enemies.

Abstract

Excessive insecticide application has posed a threat to pollinators and has also increased insecticide resistance of Myzus persicae Sulzer. Therefore, it is urgent to develop an economical and effective strategy, especially for greenhouse vegetables. Firstly, we selected a neonicotinoid insecticide that is specifically fatal to M. persicae but relatively safe to predators and bumblebees by laboratory toxicity tests and risk assessments. Then, we tested the effectiveness of the neonicotinoid insecticide under different temperature conditions. According to the LC₅₀ values and the hazard quotients, thiacloprid met the requirements. Greenhouse trails indicated that thiacloprid was quite efficient, while control dropped to 80% without the application of thiacloprid. As for biological control, Harmonia axyridis effectively controlled 90% of aphids with thiacloprid or not. However, Aphidoletes aphidimyza performed better above 20 °C. Our results indicated that it is cost-effective to control M. persicae with A. aphidimyza in suitable temperature conditions and H. axyridis was more effective at low temperatures. Practically, thiacloprid could be used either as an emergency option to control aphids’ abundance alone or in combination with natural enemies.

Highly Efficient Removal of Neonicotinoid Insecticides by Thioether-Based (Multivariate) Metal-Organic Frameworks

Circumventing the impact of agrochemicals on aquatic environments has become a necessity for health and ecological reasons. Herein, we report the use of a family of five eco-friendly water-stable isoreticular metal-organic frameworks (MOFs), prepared from amino acids, as adsorbents for the removal of neonicotinoid insecticides (thiamethoxam, clothianidin, imidacloprid, acetamiprid, and thiacloprid) from water. Among them, the three MOFs containing thioether-based residues show remarkable removal efficiency. In particular, the novel multivariate MOF {Sr^IICu^II₆[(S,S)-methox]_1.5[(S,S)-Mecysmox]_1.50(OH)₂(H₂O)}·36H₂O (5), featuring narrow functional channels decorated with both -CH₂SCH₃ and -CH₂CH₂SCH₃ thioalkyl chains-from l-methionine and l-methylcysteine amino acid-derived ligands, respectively-stands out and exhibits the higher removal efficiency, being capable to capture 100% of acetamiprid and thiacloprid in a single capture step under dynamic solid-phase extraction conditions-less than 30 s. Such unusual combination of outstanding efficiency, high stability in environmental conditions, and low-cost straightforward synthesis in 5 places this material among the most attractive adsorbents reported for the removal of this type of contaminants.

Chronic low-dose exposure to imidacloprid potentiates high fat diet-mediated liver steatosis in C57BL/6J male mice

Hepatic steatosis is known to precede a continuum of events that lead to hepatic metabolic dysfunction, inflammation and carcinogenesis. Recently, studies have linked xenobiotic exposures to hepatic steatogenesis and its associated metabolic disorders; however, the underlying mechanisms remain elusive. This study aimed to elucidate the mechanistic role of imidacloprid in the prevalence of high fat diet (HFD)-induced liver steatosis, using a C57BL/6J mice model. Mice (3 weeks old) were fed with HFD and treated with 0.6 mg/kg bw/day (one-tenth of the NOAEL) of imidacloprid through water or diet, for 24 weeks. In a controlled group, mice were fed with only HFD. At the end of the study, imidacloprid treatment significantly potentiated HFD-induced body weight gain in mice. Also, imidacloprid increased the liver weights of mice, with complimentary reductions in mesenteric and gonadal white adipose tissue weights. Histopathological analysis of liver revealed a drastic steatosis in imidacloprid treated mice. Following a real-time qPCR analysis, imidacloprid upregulated transcriptions of hepatic fatty acid biosynthesis-related transcription factors and genes. Imidacloprid also induced hepatic expression of the gene encoding pregnane X receptor; but had no significant effect on hepatic expressions of liver X receptor and aryl hydrocarbon receptor. The imidacloprid treatment further enhanced serum alanine aminotransferase levels but downregulated hepatic antioxidant mRNA expressions. Ultimately, this study suggested an imidacloprid-potentiation effects on prevalence of HFD-induced liver steatosis via transcriptional modulations of the hepatic FA biosynthesis pathway.

Magnetic Solid Phase Extraction Based on Nanostructured Magnetic Porous Porphyrin Organic Polymer for Simultaneous Extraction and Preconcentration of Neonicotinoid Insecticides From Surface Water

In this study, a magnetic porphyrin-based porous organic polymer (MP-POP) nanocomposite was successfully synthesized according previous studies and applied as an adsorbent for simultaneous extraction and preconcentration of four neonicotinoid insecticides from surface river water. The MP-POP was characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy/energy dispersive x-ray spectroscopy (SEM/EDS), N₂-adsorption/desorption analysis, Fourier Transform infrared spectroscopy (FTIR). The neonicotinoid insecticides were quantified using high performance chromatography coupled with diode array detector (HPLC-DAD). The MP-POP shown to have a high surface area, highly porous structure and strong affinity toward the investigated analytes. The adsorption capacities were 99.0, 85.5, 90.0, and 79.4 mg g⁻¹ for acetamiprid, clothiandin, thiacloprid and imidacloprid, respectively. The influential parameters affecting the magmatic μ-solid phase extraction (M-μ-SPE) procedure were investigated using fractional factorial design and surface response methodology (RSM). Under optimum conditions, the method exhibited relatively low limit of detection in the range of 1.3–3.2 ng L⁻¹, limit of quantification in the range of 4.3–11 ng L⁻¹ and wide linearity (up to 600 μg L⁻¹). The intraday and interday precision, expressed as the relative standard deviation (RSD) were <5%. The percentage recoveries for the four target analytes ranged from 91 to 99.3% for the spiked river water samples. The method was applied for determination of neonicotinoids in river water samples and concentrations ranged from 0 to 190 ng L⁻¹.

An Eco-Friendly Hydrophobic Deep Eutectic Solvent-Based Dispersive Liquid-Liquid Microextraction for the Determination of Neonicotinoid Insecticide Residues in Water, Soil and Egg Yolk Samples

A green, simple and sensitive hydrophobic DES-based dispersive liquid–liquid microextraction coupled with high-performance liquid chromatography (HPLC) was developed for the analysis of neonicotinoid insecticide residues in various samples. A hydrophobic deep eutectic solvent (DES) was synthesized using decanoic acid as a hydrogen bond donor and tetrabutylammonium bromide (TBABr) as a hydrogen bond-acceptor. DESs were synthesized and characterized by Fourier transform-infrared (FTIR) spectroscopy. Two disperser solvents were substituted with surfactants and acetonitrile, which could afford more effective emulsification and make the extraction relatively greener. The hydrophobic DES extraction phase occurred 10 min after centrifugation, being easy to be collected for analysis. Several parameters were investigated and optimized. Under the optimum condition, the calibration curve of this method was linear in the range of 0.003–1.0-µg·mL⁻¹, with a correlation coefficient (R²) higher than 0.99 and a good repeatability, with the relative standard deviations (RSDs) were less than 5.00%. The limits of detection were in the range of 0.001–0.003 µg·mL⁻¹; the limits of quantitation were in the range of 0.003–0.009 µg·mL·mL⁻¹. Finally, the presented method was implemented to determine the neonicotinoid insecticide residues in water, soil, egg yolk samples and acceptable recoveries were obtained.

Interaction of Varroa destructor and Sublethal Clothianidin Doses during the Larval Stage on Subsequent Adult Honey Bee (Apis mellifera L.) Health, Cellular Immunity, Deformed Wing Virus Levels and Differential Gene Expression

Honeybees (Apis mellifera L.) are exposed to many parasites, but little is known about interactions with abiotic stressors on their health, particularly when affected as larvae. Larvae were exposed singly and in combination to the parasitic mite Varroa destructor and three sublethal doses of the neonicotinoid insecticide clothianidin to evaluate their effects on survivorship, weight, haemocyte counts, deformed wing virus (DWV) levels and gene expression of the adult bees that subsequently developed. Clothianidin significantly reduced bee weight at the highest dose and was associated with an increase in haemocyte counts at the lowest dose, whereas V. destructor parasitism increased DWV levels, reduced bee emergence, lowered weight and reduced haemocyte counts. An interaction between the two stressors was observed for weight at emergence. Among the differentially expressed genes (DEGs), V. destructor infestation resulted in broader down-regulatory effects related to immunity that was often shared with the combined stressors, while clothianidin resulted in a broader up-regulatory effect more related to central metabolic pathways that was often shared with the combined stressors. Parasites and abiotic stressors can have complex interactions, including additive effects on reduced weight, number of up-regulated DEGs and biological pathways associated with metabolism.

Spatial and temporal distribution, degradation, and metabolism of three neonicotinoid insecticides on different parts, especially pests' target feeding parts of apple tree

BACKGROUND

Neonicotinoid insecticides (NIs) have been recently banned in some countries because of increased pest resistance and deleterious risks to non-target organisms. Recent studies considered all parts of crops as a whole part in plant protection. However, there are few reports focused on the distribution and metabolic trends of NIs on target feeding sites of different pests in apple orchards.

RESULTS

The spatial and temporal distribution, absorption, degradation, and metabolism of three NIs, imidacloprid, acetamiprid, and thiamethoxam, on different parts of apple trees were studied under foliar spray and root irrigation treatments. In the spray treatment, the initial average concentration ratios (TCRs) were 31.6% for lower shoots, 23.3% for upper leaves, 23.2% for upper shoots, 21.0% for lower leaves, and 0.5% and 0.4% for upper and lower fruits, respectively. The average half-lives of the three NIs were 2.9 days for shoots, 7.4 days for leaves, and 10.8 days for fruits. The degradation rate of shoots was 2.5 times that of leaves, and 3.6 times that of fruits. Imidacloprid olefin and N-methyl acetamiprid were two of the main metabolites. In the root treatment, both roots and soils had high TCRs during the whole sampling period. Only imidacloprid was transmitted to above-ground parts of the plants, with TCRs of 0.38-50.94%.

CONCLUSION

This study found significant differences in spatial and temporal distribution, degradation, metabolism, and trends of NIs on different pest target sites of apple trees. The data obtained may help promote scientific control of target pests and evaluation of safety for non-target species in orchards. © 2020 Society of Chemical Industry.

An Overview on the Effect of Neonicotinoid Insecticides on Mammalian Cholinergic Functions through the Activation of Neuronal Nicotinic Acetylcholine Receptors

Neonicotinoid insecticides are used worldwide and have been demonstrated as toxic to beneficial insects such as honeybees. Their effectiveness is predominantly attributed to their high affinity for insect neuronal nicotinic acetylcholine receptors (nAChRs). Mammalian neuronal nAChRs are of major importance because cholinergic synaptic transmission plays a key role in rapid neurotransmission, learning and memory processes, and neurodegenerative diseases. Because of the low agonist effects of neonicotinoid insecticides on mammalian neuronal nAChRs, it has been suggested that they are relatively safe for mammals, including humans. However, several lines of evidence have demonstrated that neonicotinoid insecticides can modulate cholinergic functions through neuronal nAChRs. Major studies on the influence of neonicotinoid insecticides on cholinergic functions have been conducted using nicotine low-affinity homomeric α7 and high-affinity heteromeric α4β2 receptors, as they are the most abundant in the nervous system. It has been found that the neonicotinoids thiamethoxam and clothianidin can activate the release of dopamine in rat striatum. In some contexts, such as neurodegenerative diseases, they can disturb the neuronal distribution or induce oxidative stress, leading to neurotoxicity. This review highlights recent studies on the mode of action of neonicotinoid insecticides on mammalian neuronal nAChRs and cholinergic functions.

Simultaneous analysis of current-use pesticides and their transformation products in water using mixture-sorbent solid phase extraction and high-performance liquid chromatography-tandem mass spectrometry

Pesticides have posed significant threats to aquatic ecosystems, yet little is known about their transformation products. The challenge is to simultaneously analyze various pesticides and transformation products in water as they have distinct physicochemical properties. A mix-mode solid phase extraction method was established to simultaneously analyze current-use pesticides and their transformation products using a mixture of hydrophile-lipophile balance, weak anion, and cation exchange resins (2:1:1, w/w/w) in combination with high-performance liquid chromatography and tandem mass spectrometry for chemical quantification. Neutral, acidic, and alkaline methanol were used as the elution solvent. Box-Behnken design was applied to optimize extraction conditions. Optimal conditions were as follows: sorbent mass, 200 mg; volume of elution solvent, 5 mL × 3; pH 4. The method was validated for compounds at concentrations from 20 to 1000 ng/L in different types of water samples, with recovery being from 43.5 ± 3.1 to 141 ± 35%. Low method detection limits (0.02-5.6 ng/L) implied that the developed method was sensitive. Finally, the method was applied to monitor current-use pesticides and their transformation products in natural waters. Frequent detection of transformation products of pesticides indicated that their contribution to aquatic risk should not be ignored.

The Toxic Effects of Sulfoxaflor Induced in Earthworms (Eisenia fetida) under Effective Concentrations

Sulfoxaflor is a new kind of neonicotinoid insecticide that is used to control sap-feeding insect pests. In this study, a hazard assessment of sulfoxaflor on soil invertebrate earthworms was performed under effective concentrations. The results showed that different exposure times and doses had significant influence on the toxicity of sulfoxaflor. Sulfoxaflor degraded quickly in artificial soil with a degradation rate of 0.002–0.017 mg/(kg·d) and a half-life of 12.0–15.4 d. At 0.5 mg/kg and 1.0 mg/kg, the ·OH⁻ content, antioxidant enzyme activeities, thiobarbituric acid reactive substances (TBARS) content and 8-OHdG content had significant differences compared to those in the control group. On the 56th day, significant differences were only observed in the Glutathione S-transferase enzyme (GST) activity and 8-OHdG content at 1.0 mg/kg compared to those in the control group due to the degradation of sulfoxaflor. This indicated that the risk of sulfoxaflor to earthworms was reduced because it was easily degraded in soil. However, because sulfoxaflor is a super toxic pollutant to earthworms, high concentrations of sulfoxaflor should not be released into the soil environment.

Interactions between Imidacloprid and Thiamethoxam and Dissolved Organic Matter Characterized by Two-Dimensional Correlation Spectroscopy Analysis, Molecular Modeling, and Density Functional Theory Calculations

The heavy application of neonicotinoid insecticides in agricultural production has burdened the environment. In the present study, interactions of two neonicotinoid insecticides imidacloprid and thiamethoxam with dissolved organic matter (DOM) were investigated by spectroscopic techniques, molecular modeling, and density functional theory (DFT) calculations. The static mechanism of imidacloprid and thiamethoxam quenching the endogenous fluorescence of DOM was assessed through time-resolved analyses. During the binding process, a protein-like substance binds imidacloprid and thiamethoxam later than a humic-like substance, as analyzed by two-dimensional correlation spectroscopy, but more strongly than the humic-like substance, as suggested by molecular modeling and DFT calculations. The conformational changes of DOM are attributed to imidacloprid and thiamethoxam, as assessed with three-dimensional spectra. Fourier transform infrared spectroscopy indicated that DOM binds imidacloprid and thiamethoxam by hydroxyl, aliphatic C-H, amide I, and carboxyl to form stable DOM-imidacloprid and DOM-thiamethoxam complexes. Understanding the changes in the structural conformation of humic-like and protein-like substances with imidacloprid and thiamethoxam helps further understand the fate of the neonicotinoids in the environment.

β-Cyclodextrin Assisted Liquid-Liquid Microextraction Based on Solidification of the Floating Organic Droplets Method for Determination of Neonicotinoid Residues

An efficient and environment-friendly microextraction method, namely, β-cyclodextrin assisted liquid–liquid microextraction, based on solidification of the floating organic droplets method coupled with HPLC is investigated for the sensitive determination of trace neonicotinoid pesticide residues. In this method, β-cyclodextrin is used as a disperser solvent, while 1-octanol is selected as an extraction solvent. β-cyclodextrins was found to decrease interfacial tension and increase the contact area between the organic and water phases with the help of centrifugation. A cloudy solution was rapidly formed and then centrifuged to complete phase separation. Various key parameters influencing extraction efficiency were systematically investigated and optimized; they include salt addition, concentration of β-cyclodextrin, and volume of extraction solvent (1-octanol). Under optimum conditions, good linearity was obtained with coefficient for determination (R²) greater than 0.99. A low limit of detection, high enrichment factor, and good recovery (83 – 132) were achieved. This proves that the proposed method can be applied to determine trace neonicotinoid pesticide residues in natural surface water samples.

Caste- and pesticide-specific effects of neonicotinoid pesticide exposure on gene expression in bumblebees

Social bees are important insect pollinators of wildflowers and agricultural crops, making their reported declines a global concern. A major factor implicated in these declines is the widespread use of neonicotinoid pesticides. Indeed, recent research has demonstrated that exposure to low doses of these neurotoxic pesticides impairs bee behaviours important for colony function and survival. However, our understanding of the molecular-genetic pathways that lead to such effects is limited, as is our knowledge of how effects may differ between colony members. To understand what genes and pathways are affected by exposure of bumblebee workers and queens to neonicotinoid pesticides, we implemented a transcriptome-wide gene expression study. We chronically exposed Bombus terrestriscolonies to either clothianidin or imidacloprid at field-realistic concentrations while controlling for factors including colony social environment and worker age. We reveal that genes involved in important biological processes including mitochondrial function are differentially expressed in response to neonicotinoid exposure. Additionally, clothianidin exposure had stronger effects on gene expression amplitude and alternative splicing than imidacloprid. Finally, exposure affected workers more strongly than queens. Our work demonstrates how RNA-Seq transcriptome profiling can provide detailed novel insight on the mechanisms mediating pesticide toxicity to a key insect pollinator.

Developmental Toxicity of a Neonicotinoid Insecticide, Acetamiprid to Zebrafish Embryos

Agricultural use of neonicotinoid insecticides is increasing worldwide, posing a risk to nontarget organisms. The present study investigated developmental toxicity of a widely used neonicotinoid, acetamiprid, to zebrafish embryos. Sublethal (malformations, hatchability, heart rate, body length, alteration of spontaneous movement and touch responses) and lethal effects were monitored during exposure period from 6 h post fertilization (hpf) to 120 hpf. Zebrafish embryos exhibited significant mortality and teratogenic effects at acetamiprid concentration greater than 263 mg/L, with bent spine being the main malformation. Toxicity spectra were constructed to rank the sensitivity of individual end points to acetamiprid exposure and impaired spontaneous movement was the most sensitive end point of those tested. The present study provides the basis for understanding developmental toxicity of acetamiprid exposure to zebrafish embryos. This information is critical for future studies evaluating aquatic risk from neonicotinoids as little is known regarding adverse effects of neonicotinoids to aquatic vertebrate species.

Ultrasonically Modified Amended-Cloud Point Extraction for Simultaneous Pre-Concentration of Neonicotinoid Insecticide Residues

An effective pre-concentration method, namely amended-cloud point extraction (CPE), has been developed for the extraction and pre-concentration of neonicotinoid insecticide residues. The studied analytes including clothianidin, imidacloprid, acetamiprid, thiamethoxam and thiacloprid were chosen as a model compound. The amended-CPE procedure included two cloud point processes. Triton™ X-114 was used to extract neonicotinoid residues into the surfactant-rich phase and then the analytes were transferred into an alkaline solution with the help of ultrasound energy. The extracts were then analyzed by high-performance liquid chromatography (HPLC) coupled with a monolithic column. Several factors influencing the extraction efficiency were studied such as kind and concentration of surfactant, type and content of salts, kind and concentration of back extraction agent, and incubation temperature and time. Enrichment factors (EFs) were found in the range of 20⁻333 folds. The limits of detection of the studied neonicotinoids were in the range of 0.0003⁻0.002 µg mL−1 which are below the maximum residue limits (MRLs) established by the European Union (EU). Good repeatability was obtained with relative standard deviations lower than 1.92% and 4.54% for retention time (tR) and peak area, respectively. The developed extraction method was successfully applied for the analysis of water samples. No detectable residues of neonicotinoids in the studied samples were found.

Susceptibility of Bemisia tabaci MEAM1 (Hemiptera: Aleyrodidae) to Imidacloprid, Thiamethoxam, Dinotefuran and Flupyradifurone in South Florida

Populations of Bemisa tabaci MEAM1 were established from nineteen locations in south Florida, primarily from commercial tomato fields, and were tested using a cotton leaf petiole systemic uptake method for susceptibility to the nicotinic acetylcholine agonist insecticides imidacloprid, thiamethoxam, dinotefuran and flupyradifurone. Eleven populations produced LC50s for one or more chemicals that were not significantly different from the susceptible laboratory colony based on overlapping fiducial limits, indicating some degree of susceptibility. LC50s more than a 100-fold the laboratory colony were measured in at least one population for each material tested, indicating tolerance. LC50s (ppm) from field populations ranged from 0.901-24.952 for imidacloprid, 0.965-24.430 for thiamethoxam, 0.043-3.350 for dinotefuran and 0.011-1.471 for flupyradifurone. Based on overlapping fiducial limits, there were no significant differences in relative mean potency estimates for flupyradifurone and dinotefuran in relation to imidacloprid and thiamethoxam.

Photodegradation of clothianidin under simulated California rice field conditions

BACKGROUND

Photodegradation can be a major route of dissipation for pesticides applied to shallow rice field water, leading to diminished persistence and reducing the risk of offsite transport. The objective of this study was to characterize the aqueous-phase photodegradation of clothianidin under simulated California rice field conditions.

RESULTS

Photodegradation of clothianidin was characterized in deionized, Sacramento River and rice field water samples. Pseudo-first-order rate constants and DT50 values in rice field water (mean k = 0.0158 min(-1) ; mean DT50 = 18.0 equivalent days) were significantly slower than in deionized water (k = 0.0167 min(-1) ; DT50 = 14.7 equivalent days) and river water (k = 0.0146 min(-1) ; DT50 = 16.6 equivalent days) samples. Quantum yield ϕc values demonstrate that approximately 1 and 0.5% of the light energy absorbed results in photochemical transformation in pure and field water respectively. Concentrations of the photodegradation product thiazolymethylurea in aqueous photolysis samples were determined using liquid chromatography-tandem mass spectrometry and accounted for ≤17% in deionized water and ≤8% in natural water.

CONCLUSION

Photodegradation rates of clothianidin in flooded rice fields will be controlled by turbidity and light attenuation. Aqueous-phase photodegradation may reduce the risk of offsite transport of clothianidin from flooded rice fields (via drainage) and mitigate exposure to non-target organisms. © 2015 Society of Chemical Industry.

Abiotic partitioning of clothianidin under simulated rice field conditions

BACKGROUND

Clothianidin is registered for pre- and post-flood application in Californian rice fields for control of the rice seed midge, Cricotopus sylvestris, and the rice water weevil, Lissorhoptrus oryzophilus. The objective was to characterize air-water and soil-water partitioning of clothianidin under simulated Californian rice field conditions.

RESULTS

Clothianidin was confirmed to be non-volatile (from water) via the gas purge method, as no loss from the aqueous phase was observed at 22 and 37 °C; an upper-limit KH value was calculated at 2.9 × 10(-11) Pa m(3) mol(-1) (20 °C). Soil-water partitioning was determined by the batch equilibrium method using four soils collected from rice fields in the Sacramento Valley, and sorption affinity (Kd ), sorbent capacity, desorption and organic-carbon-normalized distribution (Koc ) were determined. Values for pH, cation exchange capacity and organic matter content ranged from 4.5 to 6.6, from 5.9 to 37.9 and from 1.25 to 1.97% respectively. The log Koc values (22 and 37 °C) ranged from 2.6 to 2.7, while sorption capacity was low at 22 °C and decreased further at 37 °C. Hysteresis was observed in soils at both temperatures, suggesting that bound residues do not readily desorb.

CONCLUSIONS

Soil-water and air-water partitioning will not significantly reduce offsite transport of clothianidin from flooded rice fields via drainage.

Determination of neonicotinoid insecticides and strobilurin fungicides in particle phase atmospheric samples by liquid chromatography-tandem mass spectrometry

A liquid chromatography-tandem mass spectrometry method has been developed for the determination of neonicotinoids and strobilurin fungicides in the particle phase fraction of atmosphere samples. Filter samples were extracted with pressurized solvent extraction, followed by a cleanup step with solid phase extraction. Method detection limits for the seven neonicotinoid insecticides and six strobilurin fungicides were in the range of 1.0-4.0 pg/m(3). Samples were collected from June to September 2013 at two locations (Osoyoos and Oliver) in the southern Okanagan Valley Agricultural Region of British Columbia, where these insecticides and fungicides are recommended for use on tree fruit crops (apples, pears, cherries, peaches, apricots) and vineyards. This work represents the first detection of acetamiprid, imidacloprid, clothianidin, kresoxim-methyl, pyraclostrobin, and trifloxystrobin in particle phase atmospheric samples collected in the Okanagan Valley in Canada. The highest particle phase atmospheric concentrations were observed for imidacloprid, pyraclostrobin, and trifloxystrobin at 360.0, 655.6, and 1908.2 pg/m(3), respectively.

Quantitative analysis of neonicotinoid insecticide residues in foods: implication for dietary exposures

This study quantitatively measured neonicotinoids in various foods that are common to human consumption. All fruit and vegetable samples (except nectarine and tomato) and 90% of honey samples were detected positive for at least one neonicotinoid; 72% of fruits, 45% of vegetables, and 50% of honey samples contained at least two different neonicotinoids in one sample, with imidacloprid having the highest detection rate among all samples. All pollen samples from New Zealand contained multiple neonicotinoids, and five of seven pollens from Massachusetts detected positive for imidacloprid. These results show the prevalence of low-level neonicotinoid residues in fruits, vegetables, and honey that are readily available in the market for human consumption and in the environment where honeybees forage. In light of new reports of toxicological effects in mammals, the results strengthen the importance of assessing dietary neonicotinoid intakes and the potential human health effects.

Honey bees, neonicotinoids and bee incident reports: the Canadian situation

BACKGROUND

Neonicotinoid insecticides have been the target of much scrutiny as possible causes of recent declines observed in pollinator populations. Although neonicotinoids have been implicated in honey bee pesticide incidents, there has been little examination of incident report data. Here we summarize honey bee incident report data obtained from the Canadian Pest Management Regulatory Agency (PMRA).

RESULTS

In Canada, there were very few honey bee incidents reported in 2007-2011 and data were not collected prior to 2007. In 2012, a significant number of incidents were reported in the province of Ontario, where exposure to neonicotinoid dust during planting of corn was suspected to have caused the incident in up to 70% of cases. Most of these incidents were classified as 'minor' by the PMRA, and only six cases were considered 'moderate' or 'major'. In that same year, there were over three times as many moderate or major incidents due to older non-neonicotinoid pesticides, involving numbers of hives or bees far greater than the number of moderate or major incidents suspected to be due to neonicotinoid poisoning.

CONCLUSIONS

These data emphasize that, while exposure of honey bees to neonicotinoid-contaminated dust during corn planting needs to be mitigated, other pesticides also pose a risk.