Nicotinic acetylcholine receptor agonists: a milestone for modern crop protection

Neonicotinoid insecticides in plant-derived Foodstuffs: A review of separation and determination methods based on liquid chromatography

Neonicotinoids (NEOs) are the most widely used insecticides globally. They can contaminate or migrate into foodstuffs and exert severe neonic toxicity on humans. Therefore, lots of feasible analytical methods were developed to assure food safety. Nevertheless, there is a lack of evaluation that the impacts of food attributes on the accurate determination of NEOs. This review aims to provide a comprehensive overview of sample preparation methods regarding 6 categories of plant-derived foodstuffs. Currently, QuEChERS as the common strategy can effectively extract NEOs from plant-derived foodstuffs. Various enrichment technologies were developed for trace levels of NEOs in processed foodstuffs, and multifarious novel sorbents provided more possibility for removing complex matrices to lower matrix effects. Additionally, detection methods based on liquid chromatography were summarized and discussed in this review. Finally, some limitations were summarized and new directions were proposed for better advancement.

Molecular Mechanism Underlying ROS-Mediated AKH Resistance to Imidacloprid in Whitefly

Synthetic insecticides used to control Bemisia tabaci include organophosphorus, pyrethroids, insect growth regulators, nicotinoids, and neonicotinoids. Among these, neonicotinoids have been used continuously, which has led to the emergence of high-level resistance to this class of chemical insecticides in the whitefly, making whitefly management difficult. The adipokinetic hormone gene (AKH) and reactive oxygen species (ROS) play roles in the development of insect resistance. Therefore, the roles of AKH and ROS in imidacloprid resistance in Bemisia tabaci Mediterranean (MED; formerly biotype Q) were evaluated in this study. The expression level of AKH in resistant B. tabaci MED was significantly lower than that in sensitive B. tabaci (MED) (p < 0.05). AKH expression showed a decreasing trend. After AKH silencing by RNAi, we found that ROS levels as well as the expression levels of the resistance gene CYP6CM1 and its upstream regulatory factors CREB, ERK, and P38 increased significantly (p < 0.05); additionally, whitefly resistance to imidacloprid increased and mortality decreased (p < 0.001). These results suggest that AKH regulates the expression of resistance genes via ROS in Bemisia tabaci.

Environmental ameliorations and politics in support of pollinators. Experiences from Europe: A review

At least 87% of angiosperm species require animal vectors for their reproduction, while more than two-thirds of major global food crops depend on zoogamous pollination. Pollinator insects are a wide variety of organisms that require diverse biotic and abiotic resources. Many factors have contributed to a serious decrease in the abundance of populations and diversity of pollinator species over the years. This decline is alarming, and the European Union has taken several actions aimed at counteracting it by issuing new conservation policies and standardizing the actions of member countries. In 2019, the European Green Deal was presented, aiming to restore 100% of Europe's degraded land by 2050 through financial and legislative instruments. Moreover, the Common Agricultural Policies have entailed greening measures for the conservation of habitats and beneficial species for more than 10 years. The new CAP (CAP 23-27) reinforces conservation objectives through strategic plans based on eco-schemes defined at the national level by the member countries, and some states have specifically defined eco-schemes for pollinator conservation. Here, we review the framework of EU policies, directives, and regulations, which include measures aimed at protecting pollinators in agricultural, urban, and peri-urban environments. Moreover, we reviewed the literature reporting experimental works on the environmental amelioration for pollinators, particularly those where CAP measures were implemented and evaluated, as well as studies conducted in urban areas. Among CAP measures, several experimental works have considered the sowing and management of entomophilous plants and reported results important for environmental ameliorations. Some urban, peri-urban and wasteland areas have been reported to host a considerable number of pollinators, especially wild bees, and despite the lack of specific directives, their potential to contribute to pollinator conservation could be enhanced through targeted actions, as highlighted by some studies.

Computational Modeling Oriented Substructure Splicing Application in the Identification of Thiazolidine Derivatives as Potential Low Honeybee Toxic Neonicotinoids

With the aim of identifying novel neonicotinoid insecticides with low bee toxicity, a series of compounds bearing thiazolidine moiety, which has been shown to be low bee toxic, were rationally designed through substructure splicing strategy and evaluated insecticidal activities. The optimal compounds A24 and A29 exhibited LC50 values of 30.01 and 17.08 mg/L against Aphis craccivora, respectively. Electrophysiological studies performed on Xenopus oocytes indicated that compound A29 acted on insect nAChR, with EC50 value of 50.11 μM. Docking binding mode analysis demonstrated that A29 bound to Lymnaea stagnalis acetylcholine binding protein through H-bonds with the residues of D_Arg55, D_Leu102, and D_Val114. Quantum mechanics calculation showed that A29 had a higher highest occupied molecular orbit (HOMO) energy and lower vertical ionization potential (IP) value compared to the high bee toxic imidacloprid, showing potentially low bee toxicity. Bee toxicity predictive model also indicated that A29 was nontoxic to honeybees. Our present work identified an innovative insecticidal scaffold and might facilitate the further exploration of low bee toxic neonicotinoid insecticides.

Discovery and biological characterization of a novel mesoionic insecticide fenmezoditiaz

BACKGROUND

Many piercing-sucking insects have developed resistance or cross-resistance to many insecticides targeting insect neural nicotinic acetylcholine receptor (nAChR). Here we are aiming to present the discovery of a novel mesoionic insecticide, fenmezoditiaz, by BASF through structure-based drug design (SBDD) approaches. It has recently been added to the Insecticide Resistance Action Committee mode of classification (IRAC 4E). It is being developed for plant protection against piercing-sucking pests, especially rice hopper complex.

RESULTS

The soluble acetylcholine binding protein (AChBP) from the sea slug Aplysia californica was modified using site-directed mutagenesis and based on putative aphid nAChR subunit sequences to create soluble insect-like AChBPs. Among them, insect-like β1 AChBP and native aphid membrane preparation showed the highest correlated biochemical affinity toward structurally diverse ligands. This mutant AChBP was used to understand how insect nAChRs structurally interact with mesoionics, which was then utilized to design novel mesoionics including fenmezoditiaz. It is an excellent systemic insecticide with diverse application methods and has a broad insecticidal spectrum, especially against piercing/sucking insects. It lacks cross-resistance for neonicotinoid resistant plant hoppers. Field-collected brown plant hopper populations from Asian countries showed high susceptibility.

CONCLUSIONS

Fenmezoditiaz is a systemic insecticide with a broad spectrum, lack of cross-resistance and it could be an additional tool for integrated pest management and insecticide resistance management, especially for the rice hopper complex. © 2024 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Mutation V65I in the β1 Subunit of the Nicotinic Acetylcholine Receptor Confers Neonicotinoid and Sulfoxaflor Resistance in Insects

Neonicotinoids have been widely used to control pests with remarkable effectiveness. Excessive insecticides have led to serious insect resistance. Mutations of the nicotinic acetylcholine receptor (nAChR) are one of the reasons for neonicotinoid resistance conferred in various agricultural pests. Two mutations, V65I and V104I, were found in the nAChR β1 subunit of two neonicotinoid-resistant aphid populations. However, the specific functions of the two mutations remain unclear. In this study, we cloned and identified four nAChR subunits (α1, α2, α8, and β1) of thrips and found them to be highly homologous to the nAChR subunits of other insects. Subsequently, we successfully expressed two subtypes nAChR (α1/α2/α8/β1 and α1/α8/β1) by coinjecting three cofactors for the first time in thrips, and α1/α8/β1 showed abundant current rapidly. Acetylcholine, neonicotinoids, and sulfoxaflor exhibited different activation capacities for the two subtypes of nAChRs. Finally, V65I was found to significantly reduce the binding ability of nAChR to neonicotinoids and sulfoxaflor through electrophysiology and computer simulations. V104I caused a decrease in agonist affinity (pEC50) but an increase in the efficacy (Imax) of nAChR against neonicotinoids and reduced the binding ability of nAChR to sulfoxaflor. This study provides theoretical and technical support for studying the molecular mechanisms of neonicotinoid resistance in pests.

Typical neonicotinoids and organophosphate esters, but not their metabolites, adversely impact early human development by activating BMP4 signaling

Recent studies have highlighted the presence of potentially harmful chemicals, such as neonicotinoids (NEOs) and organophosphate esters (OPEs), in everyday items. Despite their potential threats to human health, these dangers are often overlooked. In a previous study, we discovered that NEOs and OPEs can negatively impact development, but liver metabolism can help mitigate their harmful effects. In our current research, our objective was to investigate the toxicity mechanisms associated with NEOs, OPEs, and their liver metabolites using a human embryonic stem cell-based differentiation model that mimics early embryonic development. Our transcriptomics data revealed that NEOs and OPEs significantly influenced the expression of hundreds of genes, disrupted around 100 biological processes, and affected two signaling pathways. Notably, the BMP4 signaling pathway emerged as a key player in the disruption caused by exposure to these pollutants. Both NEOs and OPEs activated BMP4 signaling, potentially impacting early embryonic development. Interestingly, we observed that treatment with a human liver S9 fraction, which mimics liver metabolism, effectively reduced the toxic effects of these pollutants. Most importantly, it reversed the adverse effects dependent on the BMP4 pathway. These findings suggest that normal liver function plays a crucial role in detoxifying environmental pollutants and provides valuable experimental insights for addressing this issue.

Chemo-Selective Single-Cell Metabolomics Reveals the Spatiotemporal Behavior of Exogenous Pollutants During Xenopus Laevis Embryogenesis

In-depth profiling of embryogenesis-associated endogenous and exogenous metabolic changes can reveal potential bio-effects resulting from human-made chemicals and underlying mechanisms. Due to the lack of potent tools for monitoring spatiotemporal distribution and bio-transformation behavior of dynamic metabolites at single-cell resolution, however, how and to what extent environmental chemicals may influence or interfere embryogenesis largely remain unclear. Herein, a zero-sample-loss micro-biopsy-based mass spectrometric platform is presented for quantitative, chemo-selective, high-coverage, and minimal-destructive profiling of development-associated cis-diol metabolites, which are critical for signal transduction and epigenome regulation, at both cellular level and tissue level of Xenopus laevis. Using this platform, three extraordinary findings that are otherwise hard to achieve are revealed: 1) there are characteristically different cis-diol metabolic signatures among oocytes, anterior and posterior part of tailbud-stage embryos; 2) halogenated cis-diols heavily accumulate at the posterior part of tailbud-stage embryos of Xenopus laevis; 3) dimethachlon, a kind of exogenous fungicide that is widely used as pesticide, may be bio-transformed and accumulated in vertebrate animals in environment. Thus, this study opens a new avenue to simultaneously monitoring intercellular and intraembryonic heterogeneity of endogenous and exogenous metabolites, providing new insights into metabolic remolding during embryogenesis and putting a warning on potential environmental risk.

Dual mutations in the whitefly nicotinic acetylcholine receptor β1 subunit confer target-site resistance to multiple neonicotinoid insecticides

Neonicotinoid insecticides, which target insect nicotinic acetylcholine receptors (nAChRs), have been widely and intensively used to control the whitefly, Bemisia tabaci, a highly damaging, globally distributed, crop pest. This has inevitably led to the emergence of populations with resistance to neonicotinoids. However, to date, there have been no reports of target-site resistance involving mutation of B. tabaci nAChR genes. Here we characterize the nAChR subunit gene family of B. tabaci and identify dual mutations (A58T&R79E) in one of these genes (BTβ1) that confer resistance to multiple neonicotinoids. Transgenic D. melanogaster, where the native nAChR Dβ1 was replaced with BTβ1A58T&R79E, were significantly more resistant to neonicotinoids than flies where Dβ1 were replaced with the wildtype BTβ1 sequence, demonstrating the causal role of the mutations in resistance. The two mutations identified in this study replace two amino acids that are highly conserved in >200 insect species. Three-dimensional modelling suggests a molecular mechanism for this resistance, whereby A58T forms a hydrogen bond with the R79E side chain, which positions its negatively-charged carboxylate group to electrostatically repulse a neonicotinoid at the orthosteric site. Together these findings describe the first case of target-site resistance to neonicotinoids in B. tabaci and provide insight into the molecular determinants of neonicotinoid binding and selectivity.

Use of double-stranded RNA targeting β2 divergent nicotinic acetylcholine receptor subunit to control pea aphid Acyrthosiphon pisum at larval and adult stages

BACKGROUND

In recent years, the use of the RNA interference technology (RNAi) has emerged as one of the new strategies for species-specific control of insect pests. Its specificity depends on the distinctiveness of the target gene sequence for a given species. In this work, we assessed in the pea aphid Acyrthosiphon pisum (A. pisum) the use of a double-stranded RNA (dsRNA) that targets the β2 divergent nicotinic acetylcholine receptor (nAChR) subunit (dsRNA-β2), which shares low sequence identity with other subunits, to control populations of this pest at different developmental stages. Because nAChRs are targeted by neonicotinoid insecticides such as imidacloprid, we also assessed the effect of dsRNA-β2 coupled to this insecticide on aphid survival. Finally, because the effect of a control agent on beneficial insect must be considered before any use of new pest management strategies, the acute toxicity of dsRNA-β2 combined with imidacloprid was evaluated on honeybee Apis mellifera.

RESULTS

In this work, we demonstrated that dsRNA-β2 alone has an insecticidal effect on aphid larvae and adults. Moreover, dsRNA-β2 and imidacloprid effects on aphid larvae and adults were additive, meaning that dsRNA-β2 did not alter the efficacy of imidacloprid on these two developmental stages. Also, no obvious acute toxicity on Apis mellifera was reported.

CONCLUSION

Using RNAi that targets β2 divergent nAChR subunit is effective alone or combined with imidacloprid to control A. pisum at larval and adult stages. Because no obvious Apis mellifera mortality has been reported, this RNAi-based pest management strategy should be considered to control insect pest. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Effect of Acetamiprid, a Neonicotinoid Insecticide, on Locomotor Activity of the American Cockroach

Toxicological studies have shown that the American cockroach Periplaneta americana (Linnaeus) is a classical model for studying the mode of action of commonly used insecticides. In a previous study, we demonstrated that thiamethoxam and clothianidin decreased locomotor activity in an open-field-like apparatus. Here, we tested the effect of the neonicotinoid acetamiprid when applied orally, topically, or injected into the haemolymph. We found that acetamiprid was also able to impair locomotor activity in the open-field-like apparatus. When treated with acetamiprid, a strong alteration in locomotor activity was observed 1 h, 24 h, and 48 h after haemolymph and topical applications. Oral application induced an impairment of locomotor activity at 24 h and 48 h. A comparison of the present data with our previously published results showed that neonicotinoids were more active when injected into the haemolymph compared to oral and topical applications. These findings increased our understanding of the effect of neonicotinoid insecticides on insect locomotor activity, and demonstrated that the cyano-substituted neonicotinoid, acetamiprid, was able to alter cockroach locomotor activity.

Discovery of novel thiazolyl anthranilic diamide derivatives as insecticidal candidates

BACKGROUND

Agricultural pests have caused huge losses in agricultural production and threaten global food security. Synthetic insecticides remain the major control method. However, with the rapid development of pest resistance and the increasingly stringent regulations on pesticide usage, the development of efficient insecticides with novel structures is particularly urgent.

RESULTS

Twenty-six novel anthranilic diamide derivatives containing the thiazole moiety were designed based on the scaffold hopping strategy. Bioassay results indicated that compound 6e exhibited excellent insecticidal activity against a susceptible strain of diamondback moth (Plutella xylostella) with a median lethal concentration (LC50 ) of 0.65 mg L-1 , which was similar to chlorantraniliprole (LC50  = 0.53 mg L-1 ). Compound 6e showed marginally lower (LC50  = 50.45 mg L-1 ) insecticidal activity than chlorantraniliprole (LC50  = 31.98 mg L-1 ) on chlorantraniliprole-resistant P. xylostella larvae, suggesting a cross-resistance of compound 6e with chlorantraniliprole (resistance ratios, 77.6-fold and 60.3-fold, respectively). Compound 6e also showed good insecticidal activity against fall armyworm and beet armyworm with pest mortalities of 74% and 64%, respectively, at 5 mg L-1 concentration. In addition, compounds 6e and 12a showed delayed toxicity against red imported fire ant with mortality rates of 84% and 85% (respectively) after 5 days of treatment at 1.0 mg L-1 , which were superior to that of chlorantraniliprole.

CONCLUSION

The introduction of thiazole into anthranilic diamide scaffolds resulted in insecticidal leads 6e and 12a with excellent insecticidal activities and potential application in controlling red imported fire ants. The work also guides the discovery of insecticidal molecules with thiazole-containing anthranilic diamide scaffold. © 2023 Society of Chemical Industry.

Functional orthologs of honeybee CYP6AQ1 in stingless bees degrade the butenolide insecticide flupyradifurone

Flupyradifurone (FPF), a novel butenolide insecticide binding to nicotinic acetylcholine receptors (nAChRs), has been shown to be less acutely toxic to western honey bees (Apis mellifera) than other insecticides such as neonicotinoids sharing the same target-site. A previous study revealed that this is due to enhanced oxidative metabolism of FPF, mediated by three cytochrome P450 monooxygenases (P450s), including CYP6AQ1. Therefore, we followed a toxicogenomics approach and investigated the potential role of functional CYP6AQ1 orthologs in FPF metabolism from eight different bee species, including stingless bees (Tribe: Meliponini). We conducted a phylogenetic analysis on four stingless bee species, including Frieseomelitta varia, Heterotrigona itama, Melipona quadrifasciata and Tetragonula carbonaria to identify CYP6AQ1-like functional orthologs. Three non-Meliponini, but tropical bee species, i.e., Ammobates syriacus, Euglossa dilemma and Megalopta genalis were analyzed as well. We identified candidate P450s in all (neo)tropical species with greater than 61% and 67% predicted protein sequence identities when compared to A. mellifera CYP6AQ1 and Bombus terrestris CYP6AQ26, respectively. Heterologous expression in High Five insect cells of these functional orthologs revealed a common coumarin substrate profile and a preference for the O-debenzylation of bulkier substrates. Competition assays using the fluorescent probe substrate 7-benzyloxymethoxy-4-trifluoromethylcoumarin (BOMFC) with these enzymes indicated inhibition of BOMFC metabolism by increasing concentrations of FPF. Furthermore, UPLC-MS/MS analysis revealed the capacity of all CYP6AQ1-like orthologs to metabolize FPF by hydroxylation in vitro at various levels, indicating a conserved FPF detoxification potential in different (neo)tropical bee species including Meliponini. This research, employing a toxicogenomics approach, provides important insights into the potential of stingless and other tropical bee species to detoxify FPF, and highlights the significance of investigating the detoxification mechanisms of insecticides in non-Apis bee species by molecular tools to inform risk assessment and conservation efforts.

Isosteric Ring Exchange as a Useful Scaffold Hopping Tool in Agrochemistry

Replacing one ring in a molecule by a different carba- or heterocycle is an important scaffold hopping manipulation, because biologically active compounds and their analogues, which underwent such a transformation, are often similar in size, shape, and physicochemical properties and, therefore, likely in their potency as well. This review will demonstrate, how isosteric ring exchange led to the discovery of highly active agrochemicals and which ring interchanges have proven to be most successful.

Ring Closure and Ring Opening as Useful Scaffold Hopping Tools in Agrochemistry

Ring closing acyclic parts of a molecular scaffold or the opposite manipulation, opening rings to produce pseudo-ring structures, is an important scaffold hopping manipulation. Analogues derived from biologically active compounds through the utilization of such strategies are often similar in shape and physicochemical properties and, therefore, likely to exhibit similar potency. This review will demonstrate how several different ring closure techniques, such as replacing carboxylic functions by cyclic peptide mimics, incorporating double bonds into aromatic rings, tying back ring substituents to a bicyclic structure, cyclizing adjacent ring substituents to an annulated ring, bridging annulated ring systems to tricyclic scaffolds, and exchanging gem-dimethyl groups by cycloalkyl rings, but also ring opening led to the discovery of highly active agrochemicals.

Monitoring of imidacloprid residues in fresh fruits and vegetables from the central parts of Jordan

Imidacloprid pesticide is widely utilized in agriculture due to its effectiveness in controlling a broad spectrum of insect pests. However, its usage has raised concerns about potential environmental impacts, and requires careful monitoring and responsible application to ensure sustainable agricultural practices. Thus, Gas chromatography-mass spectrometry (GC-MS) was utilized to analyze imidacloprid in 300 vegetable and fruit samples obtained from 15 major wholesalers in four regions of Amman, Jordan's capital city. Among the examined samples, 39.7 % were found to be contaminated with imidacloprid residues. Imidacloprid levels in different edible fruits and vegetables ranged from less than the Limit of Quantification (LOQ) to 0.40 mg kg-1. Significantly, eggplant and apples exhibited the highest average values (0.40 and 0.25 mg kg-1, respectively). Lower levels were detected in bananas (0.04 mg kg-1), potatoes (0.05 mg kg-1), grapes (0.07 mg kg-1), and cabbage (0.07 mg kg-1). Imidacloprid was below the method detection limit (BD) in samples of okra, peaches, apricots, and carrots. Overall, 25 samples (8.3 %) exceeded the Codex maximum residue limit (MRL) for imidacloprid. Moreover, 8 out of the 300 samples (2.7 %) exceeded the MRL established by the Pest Management Regulatory Agency (PMRA). Notably, the fruits of eggplant and apple contained the highest residual levels (1.30 and 0.83 mg kg-1, respectively), markedly exceeding the CODEX and PMRA MRLs. Additionally, the maximum detected imidacloprid residue concentration in bananas (0.25 mg kg-1) was 500 % higher than the CODEX MRLs. The estimated average daily intake (EDI) of the Amman population varied from 0.00 to 0.144 μg kg-1 body weight day-1 across various products. The hazard index (HI) for imidacloprid ranged from 0.00 to 0.24, all of which were below unity in all samples (<1). In conclusion, this investigation reveals low HI levels of imidacloprid residues in commonly consumed fruits and vegetables. However, the significant presence of imidacloprid residues in some samples highlights the urgent need for comprehensive measures to limit potential health hazards to consumers.

The modes of action of ion-channel-targeting neurotoxic insecticides: lessons from structural biology

Insecticides are indispensable tools for plant protection in modern agriculture. Despite having highly heterogeneous structures, many neurotoxic insecticides use similar principles to inhibit or deregulate neuronal ion channels. Insecticides targeting pentameric ligand-gated channels are structural mimetics of neurotransmitters or manipulate and deregulate the proteins. Those binding to (pseudo-)tetrameric voltage-gated(-like) channels, on the other hand, are natural or synthetic compounds that directly block the ion-conducting pore or prevent conformational changes in the transmembrane domain necessary for opening and closing the pore. The use of a limited number of inhibition mechanisms can be problematic when resistances arise and become more widespread. Therefore, there is a rising interest in the development of insecticides with novel mechanisms that evade resistance and are pest-insect-specific. During the last decade, most known insecticide targets, many with bound compounds, have been structurally characterized, bringing the rational design of novel classes of agrochemicals within closer reach than ever before.

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.

Screening of Toxic Effects of Neonicotinoid Insecticides with a Focus on Acetamiprid: A Review

Recently, neonicotinoids have become the fastest-growing class of insecticides in conventional crop protection, with extensive usage against a wide range of sucking and chewing pests. Neonicotinoids are widely used due to their high toxicity to invertebrates, simplicity, flexibility with which they may be applied, and lengthy persistence, and their systemic nature ensures that they spread to all sections of the target crop. However, these properties raise the risk of environmental contaminations and potential toxicity to non-target organisms. Acetamiprid is a new generation insecticide, which is a safer alternative for controlling insect pests because of its low toxicity to honeybees. Acetamiprid is intended to target nicotinic acetylcholine receptors in insects, but its widespread usage has resulted in negative impacts on non-target animals such as mammals. This review summarizes in vivo and in vitro animal studies that investigated the toxicity of specific neonicotinoids. With summarized data, it can be presumed that certain concentrations of neonicotinoids in the reproductive system cause oxidative stress in the testis; spermatogenesis disruption; spermatozoa degradation; interruptions to endocrine function and Sertoli and Leydig cell function. In the female reproductive system, acetamiprid evokes pathomorphological alterations in follicles, along with metabolic changes in the ovaries.

Gene expression in bumble bee larvae differs qualitatively between high and low concentration imidacloprid exposure levels

Neonicotinoid pesticides negatively impact bumble bee health, even at sublethal concentrations. Responses to the neonicotinoid imidacloprid have been studied largely at individual adult and colony levels, focusing mostly on behavioral and physiological effects. Data from developing larvae, whose health is critical for colony success, are deficient, particularly at the molecular level where transcriptomes can reveal disruption of fundamental biological pathways. We investigated gene expression of Bombus impatiens larvae exposed through food provisions to two field-realistic imidacloprid concentrations (0.7 and 7.0 ppb). We hypothesized both concentrations would alter gene expression, but the higher concentration would have greater qualitative and quantitative effects. We found 678 genes differentially expressed under both imidacloprid exposures relative to controls, including mitochondrial activity, development, and DNA replication genes. However, more genes were differentially expressed with higher imidacloprid exposure; uniquely differentially expressed genes included starvation response and cuticle genes. The former may partially result from reduced pollen use, monitored to verify food provision use and provide additional context to results. A smaller differentially expressed set only in lower concentration larvae, included neural development and cell growth genes. Our findings show varying molecular consequences under different field-realistic neonicotinoid concentrations, and that even low concentrations may affect fundamental biological processes.

The Neonicotinoid Imidacloprid Impairs Learning, Locomotor Activity Levels, and Sucrose Solution Consumption in Bumblebees (Bombus terrestris)

Bumblebees carry out the complex task of foraging to provide for their colonies. They also conduct pollination, an ecosystem service of high importance to both wild plants and entomophilous crops. Insecticides can alter different aspects of bumblebee foraging behavior, including the motivation to leave the hive, finding the right flowers, handling flowers, and the ability to return to the colony. In the present study, we assessed how the neonicotinoid imidacloprid affects bumblebees' foraging behavior after exposure to four different treatment levels, including field-realistic concentrations (0 [control], 1, 10, and 100 μg/L), through sucrose solution over 9 days. We observed the behavior of several free-flying bumblebees simultaneously foraging on artificial flowers in a flight arena to register the bees' complex behavior postexposure. To conduct a detailed assessment of how insecticides affect bumblebee locomotor behavior, we used video cameras and analyzed the recordings using computer vision. We found that imidacloprid impaired learning and locomotor activity level when the bumblebees foraged on artificial flowers. We also found that imidacloprid exposure reduced sucrose solution intake and storage. By using automated analyses of video recordings of bumblebee behavior, we identified sublethal effects of imidacloprid exposure at field-realistic doses. Specifically, we observed negative impacts on consumption of sucrose solution as well as on learning and locomotor activity level. Our results highlight the need for more multimodal approaches when assessing the sublethal effects of insecticides and plant protection products in general. Environ Toxicol Chem 2023;42:1337-1345. © 2023 SETAC.

Sex-specific alterations in adaptive responses of Chironomus columbiensis triggered by imidacloprid chronic and acute sublethal exposures

The use of imidacloprid is a common pest control practice in the Neotropical region. However, the imidacloprid unintended sublethal effects on Neotropical aquatic non-target arthropods and undesirable consequences for aquatic environments remain unclear. Here, we assessed the susceptibility of Chironomus columbiensis (Diptera: Chironomidae) larvae to the neonicotinoid imidacloprid and evaluated whether sublethal exposure types would trigger sex-dependent adaptive responses (e.g., emergence, body mass, reproduction, wing morphology). We conducted a concentration-mortality curve (96 h of exposure) and established chronic and acute sublethal exposure bioassays. While chronic sublethal exposures consisted of exposing individuals during their entire larval and pupal stages, the acute sublethal exposures represented a single short duration (24 h) exposure episode during either the first or fourth larval instar. Our results revealed that chronic sublethal exposure reduced the body mass of males, while acute sublethal exposures during the first instar resulted in heavier males than those that were not exposed to imidacloprid. Chronic exposure also reduced the reproduction of males and females, while the acute sublethal exposure only affected the reproduction of individuals that were imidacloprid-exposed on their later larval instar. Chronic and acute sublethal exposures did differentially affect the wing properties of C. columbiensis males (e.g., increased size when chronically exposed and highly asymmetric wings when acutely exposed in early larval phase) and females (e.g., highly asymmetric wings when chronically and acutely exposed). Collectively, our findings demonstrated that imidacloprid can cause unintended sublethal effects on C. columbiensis, and those effects are dependent on sex, exposure type, and developmental stage.

Knockdown of the Nicotinic Acetylcholine Receptor β1 Subunit Decreases the Susceptibility to Five Neonicotinoid Insecticides in Whitefly (Bemisia tabaci)

The sweet potato whitefly, Bemisia tabaci, (Gennadius) (Hemiptera:Aleyrodidae) is a global pest of crops. Neonicotinoids are efficient insecticides used for control of this pest. Insecticidal targets of neonicotinoids are insect nicotinic acetylcholine receptors (nAChRs). Here, we characterized and cloned the full length of the nAChR β1 subunit (BTβ1) in B. tabaci and confirmed the consistency of BTβ1 in B. tabaci MEAM1 and MED. Expression levels of BTβ1 in different developmental stages and body parts of adults were investigated and compared in B. tabaci MED. dsRNA was prepared to knock down BTβ1 in adult B. tabaci and significantly decreases the susceptibility to five neonicotinoid insecticides, including imidacloprid, clothianidin, thiacloprid, nitenpyram, and dinotefuran. This study indicated BTβ1 as a notable site influencing the susceptibility of B. tabaci to neonicotinoids.

Functional impact of subunit composition and compensation on Drosophila melanogaster nicotinic receptors-targets of neonicotinoids

Neonicotinoid insecticides target insect nicotinic acetylcholine receptors (nAChRs) and their adverse effects on non-target insects are of serious concern. We recently found that cofactor TMX3 enables robust functional expression of insect nAChRs in Xenopus laevis oocytes and showed that neonicotinoids (imidacloprid, thiacloprid, and clothianidin) exhibited agonist actions on some nAChRs of the fruit fly (Drosophila melanogaster), honeybee (Apis mellifera) and bumblebee (Bombus terrestris) with more potent actions on the pollinator nAChRs. However, other subunits from the nAChR family remain to be explored. We show that the Dα3 subunit co-exists with Dα1, Dα2, Dβ1, and Dβ2 subunits in the same neurons of adult D. melanogaster, thereby expanding the possible nAChR subtypes in these cells alone from 4 to 12. The presence of Dα1 and Dα2 subunits reduced the affinity of imidacloprid, thiacloprid, and clothianidin for nAChRs expressed in Xenopus laevis oocytes, whereas the Dα3 subunit enhanced it. RNAi targeting Dα1, Dα2 or Dα3 in adults reduced expression of targeted subunits but commonly enhanced Dβ3 expression. Also, Dα1 RNAi enhanced Dα7 expression, Dα2 RNAi reduced Dα1, Dα6, and Dα7 expression and Dα3 RNAi reduced Dα1 expression while enhancing Dα2 expression, respectively. In most cases, RNAi treatment of either Dα1 or Dα2 reduced neonicotinoid toxicity in larvae, but Dα2 RNAi enhanced neonicotinoid sensitivity in adults reflecting the affinity-reducing effect of Dα2. Substituting each of Dα1, Dα2, and Dα3 subunits by Dα4 or Dβ3 subunit mostly increased neonicotinoid affinity and reduced efficacy. These results are important because they indicate that neonicotinoid actions involve the integrated activity of multiple nAChR subunit combinations and counsel caution in interpreting neonicotinoid actions simply in terms of toxicity.

Rapid quantification of seven major neonicotinoids and neonicotinoid-like compounds and their key metabolites in human urine

Neonicotinoids and neonicotinoid-like compounds (NNIs) are frequently used insecticides worldwide and exposure scenarios can vary widely between countries and continents. We have developed a specific and robust analytical method based on liquid chromatography-electrospray tandem mass spectrometry coupled to online-SPE (online-SPE-LC-ESI-MS-MS) to analyze the seven most important NNIs from a global perspective together with nine of their key metabolites in human urine. The method also includes the neonicotinoid-like flupyradifurone (FLUP), an important future substitute for classical neonicotinoids, and two of its major human metabolites, 5-hydroxy- and N-desfluoroethyl-FLUP. Validation of the method was carried out using pooled urine samples from low-dose human metabolism studies and spiked urine samples with a wide range of creatinine concentrations. Depending on the analyte, the limits of quantitation were between 0.06 and 2.1 µg L^-1, the inter-day and intra-day imprecisions ≤6%, and the mean relative recoveries between 89% and 112%. The method enabled us to successfully quantify NNIs and their metabolites at current environmental exposures in 34 individuals of the German general population and 43 pregnant women from Brazil with no known occupational exposures to NNIs.

Meta-analysis of neonicotinoid insecticides in global surface waters

Neonicotinoids (NEOs) are a class of insecticides that have high insecticidal activity and are extensively used worldwide. However, increasing evidence suggests their long-term residues in the environment and toxic effects on nontarget organisms. NEO residues are frequently detected in water and consequently have created increasing levels of pollution and pose significant risks to humans. Many studies have focused on NEO concentrations in water; however, few studies have focused on global systematic reviews or meta-analyses of NEO concentrations in water. The purpose of this review is to conduct a meta-analysis on the concentration of NEOs in global waters based on published detections from several countries to extend knowledge on the application of NEOs. In the present study, 43 published papers from 10 countries were indexed for a meta-analysis of the global NEO distribution in water. Most of these studies focus on the intensive agricultural area, such as eastern Asia and North America. The order of mean concentrations is identified as imidacloprid (119.542 ± 15.656 ng L^-1) > nitenpyram (88.076 ± 27.144 ng L^-1) > thiamethoxam (59.752 ± 9.068 ng L^-1) > dinotefuran (31.086 ± 9.275 ng L^-1) > imidaclothiz (24.542 ± 2.906 ng L^-1) > acetamiprid (23.360 ± 4.015 ng L^-1) > thiacloprid (11.493 ± 5.095 ng L^-1). Moreover, the relationships between NEO concentrations and some environmental factors are analyzed. NEO concentrations increase with temperature, oxidation-reduction potential, and the percentage of cultivated crops but decrease with stream discharge, pH, dissolved oxygen, and precipitation. NEO concentrations show no significant relations to turbidity and conductivity.

Biomarkers of imidacloprid toxicity in Japanese quail, Coturnix coturnix japonica

The in vivo effect of the oral sublethal doses of 3.014 mg kg^-1 of IMI (1/25 LD₅₀) for 1, 7, 14, and 28 days every other day on Japanese quail was investigated. The results revealed that certain biomarkers in the selected tissues of the quail such as acetylcholinesterase (AChE), butyrylcholinesterase (BuChE), aminotransaminases (alanine aminotransferase, ALT, and aspartate aminotransaminase, AST), phosphatases (acid phosphatase, ACP, and alkaline phosphatase, ALP), lactate dehydrogenase (LDH), adenosine-triphosphatase (ATPase), glutathione-S-transferase (GST), lipid peroxidation (LPO), and blood glucose showed significant inductions, while significant reductions in the levels of glutathione-reduced (GSH), deoxyribonucleic acid (DNA), and ribonucleic acid (RNA) were noticed. In this study, the molecular mechanisms of the toxic effects of imidacloprid on quails were elucidated regarding neurotoxicity, hepatotoxicity, oxidative stress, lipid peroxidation, antioxidant activity, and genotoxicity. Because IMI induced alterations in the levels of these biomarkers in Japanese quail; therefore, Japanese quail as a wild avian can be used as a suite bioindicator to detect imidacloprid toxicity.

Defining the Biologically Plausible Taxonomic Domain of Applicability of an Adverse Outcome Pathway: A Case Study Linking Nicotinic Acetylcholine Receptor Activation to Colony Death

For the majority of developed adverse outcome pathways (AOPs), the taxonomic domain of applicability (tDOA) is typically narrowly defined with a single or a handful of species. Defining the tDOA of an AOP is critical for use in regulatory decision-making, particularly when considering protection of untested species. Structural and functional conservation are two elements that can be considered when defining the tDOA. Publicly accessible bioinformatics approaches, such as the Sequence Alignment to Predict Across Species Susceptibility (SeqAPASS) tool, take advantage of existing and growing databases of protein sequence and structural information to provide lines of evidence toward structural conservation of key events (KEs) and KE relationships (KERs) of an AOP. It is anticipated that SeqAPASS results could readily be combined with data derived from empirical toxicity studies to provide evidence of both structural and functional conservation, to define the tDOA for KEs, KERs, and AOPs. Such data could be incorporated in the AOP-Wiki as lines of evidence toward biological plausibility for the tDOA. We present a case study describing the process of using bioinformatics to define the tDOA of an AOP using an AOP linking the activation of the nicotinic acetylcholine receptor to colony death/failure in Apis mellifera. Although the AOP was developed to gain a particular biological understanding relative to A. mellifera health, applicability to other Apis bees, as well as non-Apis bees, has yet to be defined. The present study demonstrates how bioinformatics can be utilized to rapidly take advantage of existing protein sequence and structural knowledge to enhance and inform the tDOA of KEs, KERs, and AOPs, focusing on providing evidence of structural conservation across species. Environ Toxicol Chem 2023;42:71-87. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Metal-Organic Frameworks as Potential Agents for Extraction and Delivery of Pesticides and Agrochemicals

Pesticide contamination is a global issue, affecting nearly 44% of the global farming population, and disproportionately affecting farmers and agricultural workers in developing countries. Despite this, global pesticide usage is on the rise, with the growing demand of global food production with increasing population. Different types of porous materials, such as carbon and zeolites, have been explored for the remediation of pesticides from the environment. However, there are some limitations with these materials, especially due to lack of functional groups and relatively modest surface areas. In this regard, metal-organic frameworks (MOFs) provide us with a better alternative to conventionally used porous materials due to their versatile and highly porous structure. Recently, a number of MOFs have been studied for the extraction of pesticides from the environment as well as for targeted and controlled release of agrochemicals. Different types of pesticides and conditions have been investigated, and MOFs have proved their potential in agricultural applications. In this review, the latest studies on delivery and extraction of pesticides using MOFs are systematically reviewed, along with some recent studies on greener ways of pest control through the slow release of chemical compounds from MOF composites. Finally, we present our insights into the key issues concerning the development and translational applications of using MOFs for targeted delivery and pesticide control.

Immunohistochemical distribution of Bcl-2 and p53 apoptotic markers in acetamiprid-induced nephrotoxicity

Pesticides, which adversely affect the critical metabolic processes of organisms, disrupt the physiological balance by specifically targeting enzymes and may lead to such consequences that may lead to death. It provides benefits in agricultural activities. The p53 protein antagonizes bcl-2, an anti-apoptotic protein character, and induces apoptosis by causing mitochondrial membrane permeability. This study aims to show the effect of acetamiprid, which is an insecticide from the neonicotinoid class, on bcl-2 and p53 immunoreactivity, which has an important place in the apoptotic mechanism in kidney tissue. A total of four groups including control and three experimental groups (the acetamiprid was administered 5, 10, and 15 mg kg−1) were formed in the study. After acetamiprid was administered via gavage for 14 days, the kidney tissues taken from the mice, which were sacrificed by cervical dislocation, were fixed in 10% formaldehyde solution for histological and immunohistochemical analyses, and as a result of routine tissue follow-up, the sections were blocked in paraffin and stained with haematoxylin–eosin and immunostaining. The histopathological examinations revealed that while the kidney tissue had a normal structure in the control group, degeneration in the distal and proximal tubules, glomerular degeneration, increase in the capsular area, glomerular atrophy, and haemorrhage were determined in the acetamiprid groups at increasing severity and frequency depending on the dose of the applied substance. In the kidney tissue, Bcl-2 and p53 immunoreactivity was observed in glomerular cells, sinusoidal epithelium, and proximal and distal tubule cells. The acetamiprid caused pathological changes in the kidneys in the dose range used. This effect also affects the expression of bcl-2 and p53 genes, which are biomarkers in the apoptotic mechanism. As acetamiprid accumulates in tissues, it increases the expression of p53 from cell death receptors, while suppressing the anti-apoptotic bcl-2 expression.

Review on effects of some insecticides on honey bee health

Insecticides, one of the main agrochemicals, are useful for controlling pests; however, the indiscriminate use of insecticides has led to negative effects on nontarget insects, especially honey bees, which are essential for pollination services. Different classes of insecticides, such as neonicotinoids, pyrethroids, chlorantraniliprole, spinosad, flupyradifurone and sulfoxaflor, not only negatively affect honey bee growth and development but also decrease their foraging activity and pollination services by influencing their olfactory sensation, memory, navigation back to the nest, flight ability, and dance circuits. Honey bees resist the harmful effects of insecticides by coordinating the expression of genes related to immunity, metabolism, and detoxification pathways. To our knowledge, more research has been conducted on the effects of neonicotinoids on honey bee health than those of other insecticides. In this review, we summarize the current knowledge regarding the effects of some insecticides, especially neonicotinoids, on honey bee health. Possible strategies to increase the positive impacts of insecticides on agriculture and reduce their negative effects on honey bees are also discussed.

Impact of the nicotinic acetylcholine receptor mutation R81T on the response of European Myzus persicae populations to imidacloprid and sulfoxaflor in laboratory and in the field

Sulfoxaflor (Isoclast™ active) is a sulfoximine insecticide that is active on a broad range of sap-feeding insects, including species that exhibit reduced susceptibility to currently available insecticides. Colonies of Myzus persicae (green peach aphid) were established from aphids collected in the field from peach (Prunus persica) and nectarine (Prunus persica var. nucipersica) orchards in France, Italy and Spain. The presence of the nicotinic acetylcholine receptor (nAChR) point mutation R81T was determined for all the colonies. Eight of the 35 colonies collected were susceptible relative to R81T (i.e., R81T absent), three of the colonies were found to be homozygous for R81T while 24 colonies had R81T present in some proportion (heterozygous). Sulfoxaflor and imidacloprid were tested in the laboratory against these M. persicae field colonies, which exhibited a wide range of susceptibilities (sulfoxaflor RR = 0.6 to 61, imidacloprid RR = 0.7 to 986) (resistance ratios, RR) to both insecticides. Although sulfoxaflor was consistently more active than imidacloprid against these field collected M. persicae, there was a statistically significant correlation across all colonies between the RRs for imidacloprid and sulfoxaflor (Pearson's r = 0.939, p < 0.0001). However, when a larger group of the colonies from Spain possessing R81T were analyzed, there was no correlation observed for the RRs between imidacloprid and sulfoxaflor (r = 0.2901, p = 0.3604). Thus, consistent with prior studies, the presence of R81T by itself is not well correlated with altered susceptibility to sulfoxaflor. In field trials, sulfoxaflor (24 and 36 gai/ha) was highly effective (~avg. 88-96% control) against M. persicae, demonstrating similar levels of efficacy as flonicamid (60-70 gai/ha) and spirotetramat (100-180 gai/ha) at 13-15 days after application, in contrast to imidacloprid (110-190 gai/ha) and acetamiprid (50-75 gai/ha) with lower levels of efficacy (~avg. 62-67% control). Consequently, sulfoxaflor is an effective tool for use in insect pest management programs for M. persicae. However, it is recommended that sulfoxaflor be used in the context of an insecticide resistance management program as advocated by the Insecticide Resistance Action Committee involving rotation with insecticides possessing other modes of action (i.e., avoiding rotation with other Group 4 insecticides) to minimize the chances for resistance development and to extend its future utility.

Effects of cofactors RIC-3, TMX3 and UNC-50, together with distinct subunit ratios on the agonist actions of imidacloprid on Drosophila melanogaster Dα1/Dβ1 nicotinic acetylcholine receptors expressed in Xenopus laevis oocytes

Insect nicotinic acetylcholine receptors (nAChRs) require cofactors for functional heterologous expression. A previous study revealed that TMX3 was crucial for the functional expression of Drosophila melanogaster Dα1/Dβ1 nAChRs in Xenopus laevis oocytes, while UNC-50 and RIC-3 enhanced the acetylcholine (ACh)-induced responses of the nAChRs. However, it is unclear whether the coexpression of UNC-50 and RIC-3 with TMX3 and the subunit stoichiometry affect pharmacology of Dα1/Dβ1 nAChRs when expressed in X. laevis oocytes. We have investigated the effects of coexpressing UNC-50 and RIC-3 with TMX3 as well as changing the subunit stoichiometry on the agonist activity of ACh and imidacloprid on the Dα1/Dβ1 nAChRs. UNC-50 and RIC-3 hardly affected the agonist affinity of ACh and imidacloprid for the Dα1/Dβ1 nAChRs formed by injecting into X. laevis oocytes with an equal amount mixture of the subunit cRNAs, but enhanced current amplitude of the ACh-induced response. Imidacloprid showed higher affinity for the Dβ1 subunit-excess Dα1/Dβ1 (Dα1/Dβ1 = 1/5) nAChRs than the Dα1 subunit-excess Dα1/Dβ1 (Dα1/Dβ1 = 5/1) nAChRs, suggesting that imidacloprid prefers the Dα1-Dβ1 orthosteric site over the Dα1-Dα1 orthosteric site.

Applications of Isosteres of Piperazine in the Design of Biologically Active Compounds: Part 1

Piperazine and homopiperazine are well-studied heterocycles in drug design that have found gainful application as scaffolds and terminal elements and for enhancing the aqueous solubility of a molecule. The optimization of drug candidates that incorporate these heterocycles in an effort to refine potency, selectivity, and developability properties has stimulated the design and evaluation of a wide range of bioisosteres that can offer advantage. In this review, we summarize the design and application of bioisosteres of piperazine and homopiperazine that have almost exclusively been in the drug design arena. While there are ∼100 approved drugs that incorporate a piperazine ring, only a single marketed agricultural product is built on this heterocycle. As part of the review, we discuss some of the potential reasons underlying the relatively low level of importance of this heterocycle to the design of agrochemicals and highlight the potential opportunities for their use in contemporary research programs.

N-Hetaryl-[2(1H)-pyridinyliden]cyanamides: A New Class of Systemic Insecticides

The new chemical class N-hetaryl-[2(1H)-pyridinylidene]cyanamides were inspired by the long known five-ring structure 2-chloro-5-[2-(nitro-methylene)-1-imidazolidinyl]-pyridine (Shell) and the current development candidate flupyrimin (Meiji Seika Pharma) via scaffold hopping and the concept for designing "shortened structures" by omitting the "methylene link" as a structural feature. The most active N-hetaryl-[2(1H)-pyridinylidene]cyanamides can be synthesized on a technical scale by a simple manufacturing procedure. As full nicotinic acetylcholine receptor (nAChR) agonists, the compounds bind with low affinity at the orthosteric binding site of nAChR. In molecular modeling studies, structural differences are visible in the superposition of active N-[6'-(trifluoromethyl)[1(2H),3'-bipyridin]-2-ylidene]cyanamide onto imidacloprid (IMD) and sulfoxaflor (SXF) in bound conformation. On the basis of their physicochemical properties, the most active xylem systemic candidates offer excellent aphicidal activity in vegetables and cotton, when applied as a foliar spray, by soil drench application, or, in particular, as seed dressing for seed treatment uses. Selected candidates show good plant compatibility and reveal a better risk profile with respect to bee pollinators than the majority of currently registered nAChR competitive modulators for seed treatment uses. Applied as a seed dressing in greenhouse profiling, good to excellent control of different aphid species has been observed. In field trials, an interesting level of activity potential against cereal grain aphids (inclusive virus vector control), corn rootworm, and wireworm could be demonstrated. According to molecular modeling investigations (Fukui functions, dipole moments, and electrostatic potentials), there is a broad scope for structure optimization of the chemical class leading to proposals for novel bicyclic insecticides.

Applying a Bioisosteric Replacement Strategy in the Discovery and Optimization of Mesoionic Pyrido[1,2-a]pyrimidinone Insecticides: A Review

Mesoionic pyrido[1,2-a]pyrimidinones are a unique class of heterocyclic compounds. Compounds from this class with a n-propyl group substituted at the 1 position of the mesoionic core were discovered with interesting insecticidal activity in our screen. In this overview, we showcase how a bioisosteric replacement strategy was applied during the discovery and optimization of this class of compounds. Through exploring various substituents at the 1 position, evaluating a variety of mesoionic bicyclic ring scaffolds, and examining substituents on the phenyl group at the 3 position of the mesoionic core as well as substituents on the mesoionic ring skeleton, many compounds were discovered with excellent hopper activity or potent activity against a wide range of Lepidoptera. Ultimately, dicloromezotiaz was identified for commercial development to control a broad spectrum of lepidopteran pests.

Green Design, Synthesis, and Molecular Docking Study of Novel Quinoxaline Derivatives with Insecticidal Potential against Aphis craccivora

An efficient and environmentally friendly method was established for designing novel 3-amino-1,4-dihydroquinoxaline-2-carbonitrile (1) via the reaction of bromomalononitrile and benzene-1,2-diamine under microwave irradiation in an excellent yield (93%). This targeted amino derivative was utilized for the construction of a series of Schiff bases (8-13). A new series of thiazolidinone derivatives (15-20) were synthesized in high yields (89-96%) via treatment of thioglycolic acid with Schiff bases (8-13) under microwave irradiation in high yields (89-96%). Moreover, new pyrimidine derivatives (26-30 and 35-38) were prepared by treatment of compound 1 with arylidenes (21-25) and/or alkylidenemalononitriles (31-34) using piperidine as a basic catalyst under microwave conditions. Based on elemental analyses and spectral data, the structures of the new assembled compounds were determined. The newly synthesized quinoxaline derivatives were screened and studied as an insecticidal agent against Aphis craccivora. The obtained results indicate that compound 16 is the most toxicological agent against nymphs of cowpea aphids (Aphis craccivora) compared to the other synthesized pyrimidine and thiazolidinone derivatives. The molecular docking study of the new quinoxaline derivatives registered that compound 16 had the highest binding score (-10.54 kcal/mol) and the thiazolidinone moiety formed hydrogen bonds with Trp143.

Phylogenomic and functional characterization of an evolutionary conserved cytochrome P450-based insecticide detoxification mechanism in bees

Bee pollinator pesticide risk assessment is a regulatory requirement for pesticide registration and is largely based on experimental data collected for surrogate species such as the western honeybee. Recently, CYP9Q3, a honeybee cytochrome P450 enzyme, has been shown to efficiently detoxify certain insecticides such as the butenolide flupyradifurone and the neonicotinoid thiacloprid. Here we analyzed genomic data for 75 bee species and demonstrated by the recombinant expression of 26 CYP9Q3 putative functional orthologs that this detoxification principle is an evolutionary conserved mechanism across bee families. Our toxicogenomics approach has the potential to inform pesticide risk assessment for nonmanaged bee species that are not accessible for acute toxicity testing.

The regulatory process for assessing the risks of pesticides to bees relies heavily on the use of the honeybee, Apis mellifera, as a model for other bee species. However, the validity of using A. mellifera as a surrogate for other Apis and non-Apis bees in pesticide risk assessment has been questioned. Related to this line of research, recent work on A. mellifera has shown that specific P450 enzymes belonging to the CYP9Q subfamily act as critically important determinants of insecticide sensitivity in this species by efficiently detoxifying certain insecticide chemotypes. However, the extent to which the presence of functional orthologs of these enzymes is conserved across the diversity of bees is unclear. Here we used a phylogenomic approach to identify > 100 putative CYP9Q functional orthologs across 75 bee species encompassing all major bee families. Functional analysis of 26 P450s from 20 representative bee species revealed that P450-mediated detoxification of certain systemic insecticides, including the neonicotinoid thiacloprid and the butenolide flupyradifurone, is conserved across all major bee pollinator families. However, our analyses also reveal that CYP9Q-related genes are not universal to all bee species, with some Megachilidae species lacking such genes. Thus, our results reveal an evolutionary conserved capacity to metabolize certain insecticides across all major bee families while identifying a small number of bee species where this function may have been lost. Furthermore, they illustrate the potential of a toxicogenomic approach to inform pesticide risk assessment for nonmanaged bee species by predicting the capability of bee pollinator species to break down synthetic insecticides.

Rapid evolution of insecticide resistance and patterns of pesticides usage in agriculture in the city of Yaoundé, Cameroon

BACKGROUND

The practice of agriculture in urban settings contributes to the rapid expansion of insecticide resistance in malaria vectors. However, there is still not enough information on pesticide usage in most urban settings. The present study aims to assess the evolution of Anopheles gambiae (s.l.) population susceptibility to insecticides and patterns of pesticide usage in agriculture in the city of Yaoundé, Cameroon.

METHODS

WHO susceptibility tests and synergist PBO bioassays were conducted on adult An. gambiae (s.l.) mosquitoes aged 3 to 5 days emerging from larvae collected from the field. Seven insecticides (deltamethrin, permethrin, DDT, bendiocarb, propoxur, fenitrothion and malathion) were evaluated. The presence of target site mutation conferring knockdown (kdr) resistance was investigated using TaqMan assay, and mosquito species were identified using SINE-PCR. Surveys on 81 retailers and 232 farmers were conducted to assess general knowledge and practices regarding agricultural pesticide usage.

RESULTS

High resistance intensity to pyrethroids was observed with a high frequency of the kdr allele 1014F and low frequency of the kdr 1014S allele. The level of susceptibility of An. gambiae (s.l.) to pyrethroids and carbamates was found to decrease with time (from > 34% in 2017 to < 23% in 2019 for deltamethrin and permethrin and from 97% in 2017 to < 86% in 2019 for bendiocarb). Both An. gambiae (s.s.) and An. coluzzii were recorded. Over 150 pesticides and fertilizers were sold by retailers for agricultural purposes in the city of Yaoundé. Most farmers do not respect safety practices. Poor practices including extensive and inappropriate application of pesticides as well as poor management of perished pesticides and empty pesticide containers were also documented.

CONCLUSIONS

The study indicated rapid evolution of insecticide resistance and uncontrolled usage of pesticides by farmers in agriculture. There is an urgent need to address these gaps to improve the management of insecticide resistance.

Effects of Thiamethoxam-Dressed Oilseed Rape Seeds and Nosema ceranae on Colonies of Apis mellifera iberiensis, L. under Field Conditions of Central Spain. Is Hormesis Playing a Role?

Simple Summary

The collapse of the honey bee colonies is a complex phenomenon in which different factors may participate in an interrelated manner (e.g., pathogen interactions, exposure to chemicals, beekeeping practices, climatology, etc.). In light of the current debate regarding the interpretation of field and monitoring studies in prospective risk assessments, here we studied how exposure to thiamethoxam affects honey bee colonies in Central Spain when applied as a seed treatment to winter oilseed rape, according to the good agricultural practice in place prior to the EU restrictions. Under the experimental conditions, exposure to thiamethoxam, alone or in combination with other stressors, did not generate and maintain sufficient chronic stress as to provoke honey bee colony collapse. The stress derived from exposure to thiamethoxam and honey bee pathogens was compensated by adjustments in the colony’s dynamics, and by an increase in the worker bee population, a behavior known as hormesis. An analysis of the factors underlying this phenomenon should be incorporated into the prospective risk assessment of plant protection products in order to improve the future interpretation of field studies and management practices.

Abstract

To study the influence of thiamethoxam exposure on colony strength and pathogen prevalence, an apiary (5 colonies) was placed in front of a plot sown with winter oilseed rape (wOSR), just before the flowering phase. Before sowing, the seeds were treated with an equivalent application of 18 g thiamethoxam/ha. For comparison, a second apiary (5 colonies) was located in front of a separate 750 m plot sown with untreated wOSR. Dead foragers at the entrance of hives were assessed every 2–3 days throughout the exposure period, while the colony strength (number of combs covered with adult honey bees and brood) and pathogens were monitored each month until the following spring. Foraging on the wOSR crop was confirmed by melissopalynology determination of the corbicular pollen collected periodically, while the chemical analysis showed that exposure to thiamethoxam was mainly through nectar. There was an increase in the accumulation of dead bees in the apiary exposed to thiamethoxam relating with the control, which was coped with an increment of bee brood surface and adult bee population. However, we did not find statistically significant differences between apiaries (α = 0.05) in terms of the evolution of pathogens. We discuss these results under hormesis perspective.

Interaction of Insecticides and Fungicides in Bees

Honeybees and wild bees are among the most important pollinators of both wild and cultivated landscapes. In recent years, however, a significant decline in these pollinators has been recorded. This decrease can have many causes including the heavy use of biocidal plant protection products in agriculture. The most frequent residues in bee products originate from fungicides, while neonicotinoids and, to a lesser extent, pyrethroids are among the most popular insecticides detected in bee products. There is abundant evidence of toxic side effects on honeybees and wild bees produced by neonicotinoids, but only few studies have investigated side effects of fungicides, because they are generally regarded as not being harmful for bees. In the field, a variety of substances are taken up by bees including mixtures of insecticides and fungicides, and their combinations can be lethal for these pollinators, depending on the specific group of insecticide or fungicide. This review discusses the different combinations of major insecticide and fungicide classes and their effects on honeybees and wild bees. Fungicides inhibiting the sterol biosynthesis pathway can strongly increase the toxicity of neonicotinoids and pyrethroids. Other fungicides, in contrast, do not appear to enhance toxicity when combined with neonicotinoid or pyrethroid insecticides. But the knowledge on possible interactions of fungicides not inhibiting the sterol biosynthesis pathway and insecticides is poor, particularly in wild bees, emphasizing the need for further studies on possible effects of insecticide-fungicide interactions in bees.

Characteristics of neonicotinoid and metabolite residues in Taiwanese tea leaves

BACKGROUND

Neonicotinoids are widely used insecticides, and tea is a popular non-alcoholic beverage in Taiwan. However, the levels of neonicotinoids in Taiwanese tea leaves remain unclear. Therefore, this study aims to understand the characteristics of neonicotinoid and metabolite residues in Taiwanese tea leaves.

METHODS

In this study, 12 tea leaf samples were collected in Taiwan and extracted by solid-phase extraction before analysis by liquid chromatography-tandem mass spectrometry. In addition, the levels of neonicotinoids were compared with the maximum residue level standards from other countries.

RESULTS

In Taiwanese tea leaves, five neonicotinoids and seven metabolites were detected. Different tea species influenced the levels of neonicotinoids and their metabolites in the present study. Moreover, the levels of neonicotinoids and their metabolites in partially fermented leaves were higher than in completely fermented leaves. In Jin-Xuan tea, the levels of neonicotinoids and their metabolites in most winter-harvested teas were lower than in summer-harvested teas.

CONCLUSION

The residue levels of neonicotinoids and their metabolites were detectable in Taiwanese tea leaves. Moreover, different tea species, manufacturing processes, and harvest seasons might influence the levels of these pesticides. Therefore, the government should monitor the use of neonicotinoids. © 2021 Society of Chemical Industry.

Assessment of acetylcholinesterase, catalase, and glutathione S-transferase as biomarkers for imidacloprid exposure in penaeid shrimp

Shrimp aquaculture is a valuable source of quality seafood that can be impacted by exposure to insecticides, such as imidacloprid. Here, adult black tiger shrimp (Penaeus monodon) were used to evaluate the activity of acetylcholinesterase (AChE), catalase (CAT), and glutathione S-transferase (GST) in abdominal, head, gill, and hepatopancreas tissue as biomarkers for imidacloprid exposure. Adult P. monodon were continuously exposed to imidacloprid in water (5 μgL^-1 and 30 μgL^-1) or feed (12.5 μg g^-1 and 75 μg g^-1) for either 4 or 21 days. The imidacloprid concentration in shrimp tissues was determined using liquid chromatography-mass spectrometry after QuEChER extraction, and AChE, CAT, and GST activities were estimated by spectrophotometric assay. Imidacloprid exposure in shrimp elevated the activity of biomarkers, and the enzymatic activity was positively correlated to tissue imidacloprid accumulation, although the effects varied in a tissue-, dose- and time-dependent manner. AChE activity was correlated to imidacloprid concentration in the abdominal tissue of shrimp and was likely related to neural tissue distribution, while the activity of CAT and GST confirmed a generalised anti-oxidant stress response. AChE, CAT, and GST were valuable biomarkers for assessing shrimp response to imidacloprid exposure from dietary or water sources, and the abdominal tissue was the most reliable for exposure assessment. An elevated response in each of these biomarkers during routine monitoring could provide an early warning of shrimp stress, suggesting that investigating potential contamination by neonicotinoid pesticides would be worthwhile.

Nicotinic acetylcholine receptor modulator insecticides act on diverse receptor subtypes with distinct subunit compositions

Insect nicotinic acetylcholine receptors (nAChRs) are pentameric ligand-gated ion channels mainly expressed in the central nervous system of insects. They are the directed targets of many insecticides, including neonicotinoids, which are the most widely used insecticides in the world. However, the development of resistance in pests and the negative impacts on bee pollinators affect the application of insecticides and have created a demand for alternatives. Thus, it is very important to understand the mode of action of these insecticides, which is not fully understood at the molecular level. In this study, we systematically examined the susceptibility of ten Drosophila melanogaster nAChR subunit mutants to eleven insecticides acting on nAChRs. Our results showed that there are several subtypes of nAChRs with distinct subunit compositions that are responsible for the toxicity of different insecticides. At least three of them are the major molecular targets of seven structurally similar neonicotinoids in vivo. Moreover, spinosyns may act exclusively on the α6 homomeric pentamers but not any other nAChRs. Behavioral assays using thermogenetic tools further confirmed the bioassay results and supported the idea that receptor activation rather than inhibition leads to the insecticidal effects of neonicotinoids. The present findings reveal native nAChR subunit interactions with various insecticides and have important implications for the management of resistance and the development of novel insecticides targeting these important ion channels.

Neonicotinoids and spinosyns account for approximately 24% and 3% of the world market value of insecticides, respectively. However, the negative effects of neonicotinoids on pollinators have led to the development of novel insecticides, such as sulfoxaflor, flupyradifurone and triflumezopyrim. Although all act via insect nicotinic acetylcholine receptors, their modes of action are not fully understood. Our work shows that these insecticides act on diverse receptor subtypes with distinct subunit compositions. This finding could lead to the development of more selective insecticides to control pests with minimal effects on beneficial insects.

The Effects of Structural Alterations in the Polyamine and Amino Acid Moieties of Philanthotoxins on Nicotinic Acetylcholine Receptor Inhibition in the Locust, Schistocerca gregaria

Alterations in the polyamine and amino acid (tyrosine) moieties of philanthotoxin-343 (PhTX-343) were investigated for their effects on the antagonism of nicotinic acetylcholine receptors (nAChRs) isolated from the locust (Schistocerca gregaria) mushroom body. Through whole-cell patch-clamp recordings, the philanthotoxin analogues in this study were shown to cause inhibition of the inward current when co-applied with acetylcholine (ACh). PhTX-343 (IC₅₀ = 0.80 μM at -75 mV) antagonised locust nAChRs in a use-dependent manner, suggesting that it acts as an open-channel blocker. The analogue in which both the secondary amine functionalities were replaced with methylene groups (i.e., PhTX-12) was ~6-fold more potent (IC₅₀ (half-maximal inhibitory concentration) = 0.13 μM at -75 mV) than PhTX-343. The analogue containing cyclohexylalanine as a substitute for the tyrosine moiety of PhTX-343 (i.e., Cha-PhTX-343) was also more potent (IC₅₀ = 0.44 μM at -75 mV). A combination of both alterations to PhTX-343 generated the most potent analogue, i.e., Cha-PhTX-12 (IC₅₀ = 1.71 nM at -75 mV). Modulation by PhTX-343 and Cha-PhTX-343 fell into two distinct groups, indicating the presence of two pharmacologically distinct nAChR groups in the locust mushroom body. In the first group, all concentrations of PhTX-343 and Cha-PhTX-343 inhibited responses to ACh. In the second group, application of PhTX-343 or Cha-PhTX-343 at concentrations ≤100 nM caused potentiation, while concentrations ≥ 1 μM inhibited responses to ACh. Cha-PhTX-12 may have potential to be developed into insecticidal compounds with a novel mode of action.

Association between Haematological Parameters and Exposure to a Mixture of Organophosphate and Neonicotinoid Insecticides among Male Farmworkers in Northern Thailand

Exposure to insecticides may result in various health problems. This study investigated the association between haematological parameters and exposure to a mixture of organophosphate (OP) and neonicotinoid (NEO) insecticides among male farmworkers in Fang district, Chiang Mai province, northern Thailand. Concentrations of urinary dialkylphosphates, non-specific metabolites of OPs, and NEOs and their metabolites and haematological parameters were measured in 143 male farmworkers. The Bayesian kernel machine regression model was employed to evaluate the associations. Exposure to a mixture of insecticides was significantly associated with the mean corpuscular haemoglobin concentration (MCHC) when the concentrations of all the compounds and their metabolites were at the 60th percentile or higher compared with the 50th percentile. Furthermore, exposure to clothianidin (CLO) showed a decreasing association with MCHC when all the other insecticides were at their mean concentrations. CLO was the most likely compound to reduce MCHC, and this was confirmed by sensitivity analysis. These findings suggest that exposure to NEO insecticides, especially CLO, affects the haematological status relating to haemoglobin parameters.

Sulfoxaflor - A sulfoximine insecticide: Review and analysis of mode of action, resistance and cross-resistance

The sulfoximines, as exemplified by sulfoxaflor (Isoclast™active), are a relatively new class of nicotinic acetylcholine receptor (nAChR) competitive modulator (Insecticide Resistance Action Committee [IRAC] Group 4C) insecticides that provide control of a wide range of sap-feeding insect pests. The sulfoximine chemistry and sulfoxaflor exhibits distinct interactions with metabolic enzymes and nAChRs compared to other IRAC Group 4 insecticides such as the neonicotinoids (Group 4A). These distinctions translate to notable differences in the frequency and degree of cross-resistance between sulfoxaflor and other insecticides. Most insect strains exhibiting resistance to a variety of insecticides, including neonicotinoids, exhibited little to no cross-resistance to sulfoxaflor. To date, only two laboratory-based studies involving four strains (Koo et al. 2014, Chen et al. 2017) have observed substantial cross-resistance (>100 fold) to sulfoxaflor in neonicotinoid resistant insects. Where higher levels of cross-resistance to sulfoxaflor are observed the magnitude of that resistance is far less than that of the selecting neonicotinoid. Importantly, there is no correlation between presence of resistance to neonicotinoids (i.e., imidacloprid, acetamiprid) and cross-resistance to sulfoxaflor. This phenomenon is consistent with and can be attributed to the unique and differentiated chemical class represented by sulfoxalfor. Recent studies have demonstrated that high levels of resistance (resistance ratio = 124-366) to sulfoxaflor can be selected for in the laboratory which thus far appear to be associated with enhanced metabolism by specific cytochrome P450s, although other resistance mechanisms have not yet been excluded. One hypothesis is that sulfoxaflor selects for and is susceptible to a subset of P450s with different substrate specificity. A range of chemoinformatic, molecular modeling, metabolism and target-site studies have been published. These studies point to distinctions in the chemistry of sulfoxaflor, and its metabolism by enzymes associated with resistance to other insecticides, as well as its interaction with insect nicotinic acetylcholine receptors, further supporting the subgrouping of sulfoxaflor (Group 4C) separate from that of other Group 4 insecticides. Herein is an expansion of an earlier review (Sparks et al. 2013), providing an update that considers prior and current studies focused on the mode of action of sulfoxaflor, along with an analysis of the presently available resistance / cross-resistance studies, and implications and recommendations regarding resistance management.

Within-Body Distributions and Feeding Effects of the Neonicotinoid Insecticide Clothianidin in Bumblebees (Bombus terrestris)

Bumblebees can be exposed to neonicotinoid pesticides through nectar and pollen collected from treated crops, which can cause lethal and sublethal effects in these nontarget pollinators. However, the body distribution of the compound after exposure to neonicotinoids in bumblebees is not well studied. Bumblebee colonies (Bombus terrestris, n = 20) were exposed to field-realistic concentrations of clothianidin through artificial nectar (3.6-13 µg/L) for 9 d. Comparison of the nominal with the measured exposure in nectar indicated good compliance, confirming the applicability of the method. When quantified, clothianidin showed a concentration-dependent occurrence in the head and body of workers (head: <0.2-2.17 µg/kg; body: <0.2-3.17 µg/kg), and in the body of queens (<0.2-2.49 µg/kg), although concentrations were below those measured in the nectar (bioaccumulation factor = 0.2). Exposure to clothianidin did not affect mortality nor brood production, nor did it have a statistically significant effect on nectar consumption and size of food storage. However, visual inspection suggests higher nectar consumption of nectar with low clothianidin content compared with nectar with no or high clothianidin content. Our results show that dietary clothianidin is taken up in bumblebees, but does not bioaccumulate to elevated levels compared with exposure. Still, clothianidin may elicit responses that affect feeding behavior of the pollinator B. terrestris, although our endpoints were not significantly affected. Environ Toxicol Chem 2021;40:2781-2790. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.