Mesoionic pyrido[1,2- a ]pyrimidinones: Discovery of dicloromezotiaz as a lepidoptera insecticide acting on nicotinic acetylcholine receptors 1,2

The discovery of indazapyroxamet: a novel 3-pyridinyl insecticide targeting piercing/sucking insectsa

In recent years, the registrations for a number of commercial insecticides utilized for piercing/sucking insects have been cancelled or restricted. To meet this growing need for new hemipteran controlling agrochemicals, we discovered a 2-(pyridin-3-yl)-thiazole compound, with limited insecticidal activity against cotton/melon aphid (Aphis gossypii). The 2-(pyridin-3-yl)-thiazole moiety offered us a basis to pursue the bicyclic 2-(pyridin-3-yl)-2H-indazole carboxamides. Evaluation of such 2-(pyridin-3-yl)-2H-indazole carboxamides revealed that even analogs containing only simple alkyl amides attached at the 4 or 5 positions possess promising insecticidal activity. Extensive optimization of this novel class of 2-(pyridin-3-yl)-2H-indazole carboxamides led to identifying indazapyroxamet for commercial development. © 2024 Society of Chemical Industry.

Design, Synthesis, and Insecticidal Activity of Pyridino[1,2-a]pyrimidines Containing Indole Moeites at the 1-Position

Research on mesoionic structures in pesticide design has gained significant attention in recent years. However, the 1-position of pyridino[1,2-a]pyrimidine is usually designed with 2-chlorothiazole, 2-chloropyridine, or cyano moieties commonly found in neonicotinoid insecticides. In order to enrich the available pharmacophore library, here, we disclose a series of new pyridino[1,2-a]pyrimidine mesoionics bearing indole-containing substituents at the 1-position. Most of these target compounds are confirmed to have good insecticidal activity against aphids through bioevaluation. In addition, a three-dimensional structure-activity relationship model is established to allow access to optimal compound F45 with an LC50 value of 2.97 mg/L. This value is comparable to the property achieved by the positive control triflumezopyrim (LC50 = 2.94 mg/L). Proteomics and molecular docking analysis suggest that compound F45 has the potential to modulate the functioning of the aphid nervous system through its interaction with neuronal nicotinic acetylcholine receptors. This study expands the existing pharmacophore library for the future development of new mesoionic insecticides based on 1-position modifications of the pyridino[1,2-a]pyrimidine scaffold.

Synthesis, insecticidal activity, and mode of action of novel imidazopyridine mesoionic derivatives containing an amido group

BACKGROUND

In our previous work, we applied a new synthetic strategy to design and synthesize a series of imidazopyridine mesoionic derivatives with an ester group. The newly synthesized compounds had excellent insecticidal activity against aphids; however, insecticidal activity against planthoppers was less than satisfactory. In the present study, we designed and synthesized a series of novel imidazopyridine mesoionic compounds, containing an amido group, and these compounds were found to have improved insecticidal activity against planthoppers.

RESULTS

The bioassay results demonstrated that most of the target compounds had moderate-to-good insecticidal activity against Sogatella furcifera, and some exhibited good-to-excellent insecticidal activity against Aphis craccivora. Among them, compound C6 had the highest insecticidal activity against S. furcifera and A. craccivora, with LC₅₀ values of 10.5 and 2.09 μg mL^-1 , respectively. Proteomic results suggested that the differentially expressed proteins mainly were enriched in the nervous system-related pathways after compound C6 treatment. Enzymatic assay results showed that compound C6 and triflumezopyrim had a certain inhibitory effect on acetylcholinesterase. Molecular docking and real-time quantitative PCR results indicated that compound C6 not only may act on the nicotinic acetylcholine receptor, but also may interact with the α4 and β1 subunits of this receptor.

CONCLUSION

The results reported here contribute to the development of new mesoionic insecticides and further our understanding of the mode-of-action of imidazopyridine mesoionic derivatives. © 2022 Society of Chemical Industry.

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.

Pyrido [1,2-a] Pyrimidinone Mesoionic Compounds Containing Vanillin Moiety: Design, Synthesis, Antibacterial Activity, and Mechanism

Xanthomonas oryzae pv. oryzicola (Xoo) is a plant pathogen responsible for rice bacterial blight disease that remains challenging for prevention and cure. To discover innovative and extremely potent antibacterial agents, vanillin moiety was introduced to develop a series of novel mesoionic derivatives. Compound 15 demonstrated excellent in vitro antibacterial activity against Xoo, with a 50% effective concentration value (EC₅₀) of 27.5 μg/mL, which was superior to that of the positive control agent thiodiazole copper (97.1 μg/mL) and comparable to that of compound "A11" (17.4 μg/mL). The greenhouse pot experiment also revealed that compound 15 had 38.5% curative and 36.8% protective efficacy against rice bacterial leaf blight in vivo at 100 μg/mL, which was higher than those of thiodiazole copper (31.2 and 32.6%, respectively) and compound "A11" (29.6 and 33.2%, respectively). Compound 15 enhanced the activities of related defense enzymes, increased chlorophyll content, and promoted the resistance of rice to bacterial infection by modulating the photosynthetic pathway. This study provides a basis for the subsequent structural modification and mechanism research of mesoionic derivatives.

Discovery of Pyrido[1,2-a]pyrimidine Mesoionic Compounds Containing Benzo[b]thiophene Moiety as Potential Pesticide Candidates

The increasing evolution of insect resistance has made it challenging for traditional insecticides to control the bean aphid (Aphis craccivora Koch). To address this pending issue, a range of pyrido[1,2-a]pyrimidine mesoionic compounds containing benzo[b]thiophene were designed and synthesized. The biological activity test results of the target compounds indicated that they had moderate to outstanding insecticidal activity against the bean aphid (Aphis craccivora) and moderate insecticidal activity against the white-backed planthopper (Sogatella furcifera). Compound L14 exhibited significant insecticidal activity against A. craccivora, with an LC₅₀ value of 1.82 μg/mL, which was superior to triflumezopyrim (LC₅₀ = 4.76 μg/mL). The results of enzyme activity assay showed that compound L14 had a definite inhibitory effect on ATPase. Moreover, the proteomics and docking findings of compound L14 suggested that it may act on the central nervous system of aphids and interact with nicotinic acetylcholine receptors. Therefore, compound L14 is a potentially novel insecticide candidate for further utilization.

First Discovery of Imidazo[1,2-a]pyridine Mesoionic Compounds Incorporating a Sulfonamide Moiety as Antiviral Agents

The applications of mesoionic compounds and their analogues as agents against plant viruses remain unexplored. This was the first evaluation of the antiviral activities of mesoionic compounds on this issue. Our study involved the design and synthesis of a series of novel imidazo[1,2-a]pyridine mesoionic compounds containing a sulfonamide moiety and the assessment of their antiviral activities against potato virus Y (PVY). Compound A33 was assessed on the basis of three-dimensional quantitative structure-activity relationship (3D-QSAR) model analysis and displayed good curative, protective, and inactivating activity effects against PVY at 500 mg/L, up to 51.0, 62.0, and 82.1%, respectively, which were higher than those of commercial ningnanmycin (NNM, at 47.2, 50.1, and 81.4%). Significantly, defensive enzyme activities and proteomics results showed that compound A33 could enhance the defense response by activating the activity of defense enzymes, inducing the glycolysis/gluconeogenesis pathway of tobacco to resist PVY infection. Therefore, our study indicates that compound A33 could be applied as a potential viral inhibitor.

Dehydrative amination of benzhydrols with electron-withdrawing group-substituted 2-aminopyridines utilizing Au(III)/TPPMS catalyst system in water

We report a method for gold(III)/sodium diphenylphosphinobenzene-3-sulfonate (TPPMS)-catalyzed direct amination of benzhydrols using 2-aminopyridines with poor nucleophilic character in water. Various functional groups such as electron-withdrawing nitro, cyano and halogen groups were tolerated well to form the desired N-benzylated 2-aminopyridine compounds. On the basis of mechanistic studies including kinetic profiles, Hammett study and isotope effects, we propose a pathway in which a Lewis acidic gold cation species activates the sp³ C-O bond of the alcohol in the rate-determining step.

Design, Synthesis, and Insecticidal Activity of Novel Pyrido[1, 2-a]pyrimidinone Mesoionic Compounds Containing an Indole Moiety as Potential Acetylcholine Receptor Insecticides

In this study, a series of novel mesoionic pyrido[1,2-a]pyrimidinone compounds containing a natural skeleton indole were designed and synthesized, and the insecticidal activities of the target compounds were tested. The results showed that the target compounds had good to excellent insecticidal activities against white-backed planthoppers (Sogatella furcifera) and bean aphids (Aphis craccivora). Among them, compound 7 showed outstanding insecticidal activities against both S. furcifera and A. craccivora, with LC₅₀ values of 0.86 and 0.85 μg/mL, respectively. The insecticidal activity against bean aphids (A. craccivora) was superior to that of triflumezopyrim (LC₅₀ = 3.67 μg/mL). Proteomics and quantitative real-time polymerase chain reaction (qRT-PCR) results revealed that compound 7 may interact with α1 and α7 nAChR subunits of S. furcifera. The results of enzyme activities indicated that compound 7 was an inhibitor of AChE in S. furcifera. This study provides new ideas for the discovery of new mesoionic pyrido[1,2-a]pyrimidinone insecticides.

New Synthetic Method and Insecticidal Activities of Novel Imidazopyridine Mesoionic Derivatives Containing an Ester Group

To develop novel insecticides with high efficiency, a new mode of action, and safety to nontarget organisms and the environment, a series of imidazopyridine mesoionic compounds containing an ester group have been designed and synthesized via a new synthetic method discovered by our group. The bioactivity results showed that most of the target compounds exhibited significant insecticidal activities against Aphis craccivora, and some of them showed moderate insecticidal activities against Sogatella furcifera. Among them, compounds C2, C4-C11, and D3 showed excellent insecticidal activities against A. craccivora (LC₅₀ values were lower than 4.5 μg/mL), which were superior to those of pymetrozine (LC₅₀ = 6.19 μg/mL) and triflumezopyrim (LC₅₀ = 4.68 μg/mL). Remarkably, the insecticidal activity of compound C9 was 5.9-fold greater than that of triflumezopyrim with an LC₅₀ value of 0.8 μg/mL. Proteomics and molecular docking results indicated that compound C9 may affect the nervous system of A. craccivora and act on nicotinic acetylcholine receptors like triflumezopyrim.

Structural Biology-Guided Design, Synthesis, and Biological Evaluation of Novel Insect Nicotinic Acetylcholine Receptor Orthosteric Modulators

The development of novel and safe insecticides remains an important need for a growing world population to protect crops and animal and human health. New chemotypes modulating the insect nicotinic acetylcholine receptors have been recently brought to the agricultural market, yet with limited understanding of their molecular interactions at their target receptor. Herein, we disclose the first crystal structures of these insecticides, namely, sulfoxaflor, flupyradifurone, triflumezopyrim, flupyrimin, and the experimental compound, dicloromezotiaz, in a double-mutated acetylcholine-binding protein which mimics the insect-ion-channel orthosteric site. Enabled by these findings, we discovered novel pharmacophores with a related mode of action, and we describe herein their design, synthesis, and biological evaluation.

Discovery of Pyrido[1,2-a]pyrimidinone Mesoionic Compounds Incorporating a Dithioacetal Moiety as Novel Potential Insecticidal Agents

A series of novel mesoionic pyrido[1,2-a]pyrimidinone compounds incorporating a dithioacetal skeleton were designed and synthesized for use as insecticidal agents. The biological activity of the title compounds indicated good to excellent insecticidal activities against bean aphids (Aphis craccivora) and white-backed planthoppers (Sogatella furcifera). Compound 34 showed excellent insecticidal activity against bean aphids (A. craccivora) with an LC₅₀ value of 2.80 μg/mL, exceeding the insecticidal activity of trifluoropyrimidine (LC₅₀ = 4.20 μg/mL). Proteomics and molecular docking results indicated that compound 34 could act on nicotinic acetylcholine receptors. This study provides support for the application of mesoionic pyrido[1,2-a]pyrimidinone compounds containing dithioacetal as novel insecticidal agents.

Selective actions of insecticides on desensitizing and non-desensitizing nicotinic acetylcholine receptors in cockroach (Periplaneta americana) neurons

BACKGROUND

Insect desensitizing nicotinic acetylcholine (nAChD) receptors are desensitized by low concentrations of agonists, including neonicotinoid insecticides, but are essentially insensitive to spinosyns, while non-desensitizing nicotinic acetylcholine (nAChN) receptors are selectively activated by spinosyns and relatively insensitive to neonicotinoids.

RESULTS

The single-electrode voltage-clamp technique was used to measure the actions of newer nicotinic insecticides dinotefuran, sulfoxaflor, triflumezopyrim, spinetoram and GS-ω/k-hexatoxin-Hv1a on cockroach neuronal nAChD and nAChN currents. Like imidacloprid and clothianidin, newer orthosteric nicotinic agonist insecticides dinotefuran and sulfoxaflor act by desensitizing nAChD receptors. The mesoionic insecticide triflumezopyrim selectively inhibited nAChD current with an half maximal inhibitory concentration (IC₅₀ ) of 1.2 nmol L^-1 , with no activation. Unlike other Group 4 insecticides, it did not activate nAChN current, but inhibited it with an IC₅₀ of 3.8 μmol L^-1 , indicating that the compound is a true antagonist. Spinosad and the spinosyn-derived insecticide spinetoram potently and selectively activated nAChN receptors. GS-ω/k-hexatoxin-Hv1a had no effect on nAChN currents and it had a complex action on nAChD currents, inhibiting at sub-nanomolar concentrations and causing some activation and enhancement of ACh-evoked currents at 30 nmol L^-1 and above. Some cells express GS-ω/k-hexatoxin-Hv1a-resistant nAChD receptors.

CONCLUSIONS

Nicotinic acetylcholine receptor competitive modulators (IRAC Group 4) and nicotinic acetylcholine receptor allosteric modulators, site II (hexatoxins, IRAC Group 32) are selective for nAChD receptors, while nicotinic acetylcholine receptor allosteric modulators, site I (spinosyns, IRAC Group 5) are selective for nAChN receptors. It is proposed that IRAC Groups 5 and 32 be re-named non-desensitizing nicotinic acetylcholine receptor allosteric modulators and desensitizing nicotinic acetylcholine receptor allosteric modulators, respectively. © 2021 Society of Chemical Industry.

Recent Research Progress in and Perspectives of Mesoionic Insecticides: Nicotinic Acetylcholine Receptor Inhibitors

Triflumezopyrim exemplifies a new class of mesoionic insecticides and has attracted increasing attention as a result of its unique structure, high level of insecticidal activity, new mechanisms of action, low toxicity toward non-target organisms, and environmental friendliness. It inhibits the nicotinic acetylcholine receptor and has high potency against sucking pests, including the brown planthopper (Nilaparvata lugens), which has developed serious resistance to conventional neonicotinoids and low cross-resistance to some newly developed neonicotinoids. This review focuses on the discovery, synthesis, structure-activity relationships, and mechanism of action of mesoionic insecticides. Finally, potential directions for the development of mesoionic insecticides are discussed.

On the hydrolysis of diethyl 2-(perfluorophenyl)malonate

Diethyl 2-(perfluorophenyl)malonate was synthesized in 47% isolated yield by the reaction of sodium diethyl malonate and hexafluorobenzene. The resulting compound was considered as a starting material for synthesizing 2-(perfluorophenyl)malonic acid by hydrolysis. It was found that the desired 2-(perfluorophenyl)malonic acid could not be obtained from this ester by hydrolysis, neither under basic nor under acidic conditions. Nevertheless, hydrolysis of the ester with a mixture of HBr and AcOH gave 2-(perfluorophenyl)acetic acid in a good preparative yield of 63%. A significant advantage of this new approach to 2-(perfluorophenyl)acetic acid is that handling toxic substances such as cyanides and perfluorinated benzyl halides is avoided.

Development of novel pesticides in the 21st century

General trends and strategies for novel pesticides are summarized. Global pesticide sales and pesticide discovery research are also briefly reviewed. At least 105 chemical pesticides have been launched during the past decade or are under development: 43 fungicides, 34 insecticides/acaricides, 6 nematicides, 21 herbicides, and 1 herbicide safener. Most of them are safe to humans and environmentally friendly. The most developed fungicides are SDHI (succinate dehydrogenase inhibitors), DMI (demethylation inhibitors), QoI (quinone outside inhibitors), and QiI (quinone inside inhibitors). Due to the development of resistance to fungicides with existing modes of action, many fungicides possessing various novel modes of action have been launched or are under development. The trend of insecticide development is changing from organophosphorus, carbamate, and synthetic pyrethroids to nicotinic and diamide insecticides. During the past decade, compounds possessing a variety of novel modes of action have also been launched or are under development. Flupyradifurone and flupyrimin, exhibiting extremely low honeybee toxicity, have been developed and subjected to practical use. Herbicides possessing varied modes of action, such as acetolactate synthase, p-hydroxyphenylpyruvate dioxygenase, protoporphyrinogen oxidase, and very-long-chain fatty acid elongase inhibition, have been developed, but no herbicides possessing a novel mode action have commercialized in nearly 30 years. It is of interest that cyclopyrimorate, which was recently launched, and tetflupyrolimet, which is under development, have novel modes action: homogentisate solanesyltransferase (HST) and dihydroorotate dehydrogenase (DHODH) inhibition, respectively. The development of useful acaricides and nematicides is also progressing. Some natural product origin pesticides are getting attention.

First Discovery of Novel Pyrido[1,2-a]pyrimidinone Mesoionic Compounds as Antibacterial Agents

Plant bacterial diseases cause tremendous decreases in crop yield and quality, and there is a lack of highly effective and low-risk antibacterial agents. A series of novel pyrido[1,2-a]pyrimidinone mesoionic compounds containing vanillin moieties were synthesized, and the application of these mesoionic compounds as plant antibacterial agents was reported here for the first time. The bioassay results revealed that the mesoionic compounds had good antibacterial activity. Of these compounds, compound 11 showed excellent in vitro activity against Xanthomonas oryzae pv. oryzae, with an EC₅₀ value of 1.1 μg/mL, which was substantially better than that of bismerthiazol (92.7 μg/mL) and thiodiazole copper (105.4 μg/mL). Moreover, greenhouse condition trials indicated that the protective and curative activities of compound 11 against rice bacterial leaf blight were 75.12 and 72.04%, respectively, which were better than those of bismerthiazol (62.24 and 50.83%, respectively) and thiodiazole copper (53.35 and 65.04%, respectively). These results provide a basis for the application of mesoionic vanillin moieties as new antibacterial agents.

Neonicotinoids: molecular mechanisms of action, insights into resistance and impact on pollinators

Neonicotinoids are insecticides that target insect nicotinic acetylcholine receptors (nAChRs), exhibiting high selective toxicity to insects over vertebrates and good systemic activity in crop plants. For these reasons, neonicotinoids currently make up ∼30% of insecticide sales worldwide. However, due to their adverse impact on pollinators such as honey bees and bumble bees, neonicotinoids are being banned from the EU, and other countries may follow. It is therefore crucial to understand the mechanism underlying neonicotinoid actions on pollinators as well as on the nAChRs of pests, with a view to understanding their selectivity. Here we review the molecular mechanisms of neonicotinoid actions at an atomic level, through structural and resistance mechanism studies and propose relevant research topics for further studies on the future of pest management.

Mesoionic Pyrido[1,2-a]pyrimidinone Insecticides: From Discovery to Triflumezopyrim and Dicloromezotiaz

One of the greatest global challenges is to feed the ever-increasing world population. The agrochemical tools growers currently utilize are also under continuous pressure, due to a number of factors that contribute to the loss of existing products. Mesoionic pyrido[1,2-a]pyrimidinones are an unusual yet very intriguing class of compounds. Known for several decades, this class of compounds had not been systemically studied until we started our insecticide discovery program. This Account provides an overview of the efforts on mesoionic pyrido[1,2-a]pyridinone insecticide discovery, beginning from the initial high throughput screen (HTS) discovery to ultimate identification of triflumezopyrim (4, DuPont Pyraxalt) and dicloromezotiaz (5) for commercialization as novel insecticides. Mesoionic pyrido[1,2-a]pyrimidinones with a n-propyl group at the 1-position, such as compound 1, were initially isolated as undesired byproducts from reactions for a fungicide discovery program at DuPont Crop Protection. Such compounds showed interesting insecticidal activity in a follow-up screen and against an expanded insect species list. The area became an insecticide hit for exploration and then a lead area for optimization. At the lead optimization stage, variations at three regions of compound 1, i.e., side-chain (n-propyl group), substituents on the 3-phenyl group, and substitutions on the pyrido- moiety, were explored with many analogues prepared and evaluated. Breakthrough discoveries included replacing the n-propyl group with a 2,2,2-trifluoroethyl group to generate compound 2, and then with a 2-chlorothiazol-5-ylmethyl group to form compound 3. 3 possesses potent insecticidal activity not only against a group of hopper species, including corn planthopper (Peregrinus maidis (Ashmead), CPH) and potato leafhopper (Empoasca fabae (Harris), PLH), as well as two key rice hopper species, namely, brown planthopper (Nilaparvata lugens (Stål), BPH) and rice green leafhopper (Nephotettix virescens (Distant), GLH), but also against representative lepidoptera species Diamondback moth (Plutella xylostella (Linnaeus), DBM) and fall armyworm (Spodoptera frugiperda (J.E. Smith), FAW). Further optimization based on 3 led to discovery of triflumezopyrim (4), with a 5-pyrimidinylmethyl group, as a potent hopper insecticide for rice usage. Optimization of the substituents on the pyrido- moiety of 3 resulted in discovery of dicloromezotiaz (5) as a lepidoptera insecticide. In this Account, we present the discovery and optimization of mesoionic pyrido[1,2-a]pyrimidinone insecticides toward the identification of triflumezopyrim (4) and dicloromezotiaz (5). We hope that knowledge and lessons derived from this discovery program will provide valuable information for future agrochemical and drug discovery. Our successful discovery and commercialization development of two novel insecticides based on meosoionic pyrido[1,2-a]pyridiminones may also stimulate interests of scientists from other disciplines to adopt this uncommon yet intriguing heterocycle ring system in pharmaceutical and other material science discovery research.

Flupyrimin: A Novel Insecticide Acting at the Nicotinic Acetylcholine Receptors

A novel chemotype insecticide flupyrimin (FLP) [N-[(E)-1-(6-chloro-3-pyridinylmethyl)pyridin-2(1H)-ylidene]-2,2,2-trifluoroacetamide], discovered by Meiji Seika Pharma, has unique biological properties, including outstanding potency to imidacloprid (IMI)-resistant rice pests together with superior safety toward pollinators. Intriguingly, FLP acts as a nicotinic antagonist in American cockroach neurons, and [³H]FLP binds to the multiple high-affinity binding components in house fly nicotinic acetylcholine (ACh) receptor (nAChR) preparation. One of the [³H]FLP receptors is identical to the IMI receptor, and the alternative is IMI-insensitive subtype. Furthermore, FLP is favorably safe to rats as predicted by the very low affinity to the rat α4β2 nAChR. Structure-activity relationships of FLP analogues in terms of receptor potency, featuring the pyridinylidene and trifluoroacetyl pharmacophores, were examined, thereby establishing the FLP molecular recognition at the Aplysia californica ACh-binding protein, a suitable structural surrogate of the insect nAChR. These FLP pharmacophores account for the excellent receptor affinity, accordingly revealing differences in its binding mechanism from IMI.

The invertebrate pharmacology of insecticides acting at nicotinic acetylcholine receptors

The nicotinic acetylcholine receptor (nAChR) is a ligand-gated ion channel composed of 5 protein subunits arranged around a central cation selective pore. Several classes of natural and synthetic insecticides mediate their effect through interacting at nAChRs. This review examines the basic pharmacology of the neonicotinoids and related chemistry, with an emphasis on sap-feeding insects from the order Hemiptera, the principle pest target for such insecticides. Although the receptor subunit stoichiometry for endogenous invertebrate nAChRs is unknown, there is clear evidence for the existence of distinct neonicotinoid binding sites in native insect preparations, which reflects the predicted wide repertoire of nAChRs and differing pharmacology within this insecticide class. The spinosyns are principally used to control chewing pests such as Lepidoptera, whilst nereistoxin analogues are used on pests of rice and vegetables through contact and systemic action, the pharmacology of both these insecticides is unique and different to that of the neonicotinoids.