Nicotinic acetylcholine receptor agonists: a milestone for modern crop protection

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.

Mode of Action of Neonicotinoid Insecticides Imidacloprid and Thiacloprid to the Cockroach Pameα7 Nicotinic Acetylcholine Receptor

The functional expression of the cockroach Pameα7 nicotinic acetylcholine receptor subunit has been previously studied, and was found to be able to form a homomeric receptor when expressed in Xenopus laevis oocytes. In this study, we found that the neonicotinoid insecticide imidacloprid is unable to activate the cockroach Pameα7 receptor, although thiacloprid induces low inward currents, suggesting that it is a partial agonist. In addition, the co-application or 5 min pretreatment with 10 µM imidacloprid increased nicotine current amplitudes, while the co-application or 5 min pretreatment with 10 µM thiacloprid decreased nicotine-evoked current amplitudes by 54% and 28%, respectively. This suggesting that these two representatives of neonicotinoid insecticides bind differently to the cockroach Pameα7 receptor. Interestingly, the docking models demonstrate that the orientation and interactions of the two insecticides in the cockroach Pameα7 nAChR binding pocket are very similar. Electrophysiological results have provided evidence to suggest that imidacloprid and thiacloprid could act as modulators of the cockroach Pameα7 receptors.

Structure Simplification of Natural Products as a Lead Generation Approach in Agrochemical Discovery

Natural products (NPs) have a long history as sources of compounds for crop protection. Perhaps a more important role for NPs has been as models and inspiration for the discovery and development of synthetic crop protection compounds. NPs and their synthetic mimics account for 18% of all crop protection compounds, whereas another 38% of all crop protection compounds have a NP that could have served as a model. Because NPs are often complex molecules, have limited availability, or possess structural features that constrain their suitability for use in agricultural settings, a key element in NP-inspired compounds is the simplification of the NP structure to provide a synthetically accessible molecule that possesses the physicochemical properties needed for use in crop protection. Herein we review a series of examples of NP mimics that demonstrate the structural or synthetic simplification of NPs as a guide for the discovery of future NP-inspired agrochemicals focused on fungicides, herbicides, and insecticides.

Robust functional expression of insect nicotinic acetylcholine receptors provides new insights into neonicotinoid actions and new opportunities for pest and vector control

Neonicotinoids are selective modulators of insect nicotinic acetylcholine receptors (nAChRs). These widely deployed insecticides interact with the orthosteric sites of nAChRs, not only to activate nAChRs on their own, but also to block the desensitizing component of nAChR responses. To date recombinant vertebrate or insect/vertebrate hybrid nAChRs have been deployed to understand the mechanism of selectivity and diversity of neonicotinoid actions as well as to show that both α/α and α/non-α interfaces are involved in the interactions with neonicotinoids. However, many of the fine details of insecticide interactions with sites on nAChRs remain to be resolved. The breakthrough of functional expression of insect nAChRs allows such questions to be addressed, not only for neonicotinoids but for other insecticides targeting insect nAChRs. © 2020 Society of Chemical Industry.

Synthesis, crystal structure, and biological evaluation of a novel eight-membered dinitration neonicotinoid analogues

In the studies on dihydroxy intermediate synthesis, a serendipitous reaction of introducing nitro group from nitromethylene has been observed. Instead of expected dihydroxy compounds, dinitration structures with nitromethylene analogues were prepared under mild conditions by using a metal-free catalyst B(OH)₃. In this reaction, the extra nitro group was suggested to be from starting material. Bioassays indicated that compound 3a showed good insecticidal activities against cowpea aphid (Aphis craccivora) and armyworm (Mythimna separata), with LC₅₀ values were 4.9 mg/L and 7.1 mg/L, respectively.

A toxicogenomics approach reveals characteristics supporting the honey bee (Apis mellifera L.) safety profile of the butenolide insecticide flupyradifurone

Flupyradifurone, a novel butenolide insecticide, selectively targets insect nicotinic acetylcholine receptors (nAChRs), comparable to structurally different insecticidal chemotypes such as neonicotinoids and sulfoximines. However, flupyradifurone was shown in acute toxicity tests to be several orders of magnitude less toxic to western honey bee (Apis mellifera L.) than many other insecticides targeting insect nAChRs. The underlying reasons for this difference in toxicity remains unknown and were investigated here. Pharmacokinetic studies after contact application of [¹⁴C]flupyradifurone to honey bees revealed slow uptake, with internalized compound degraded into a few metabolites that are all practically non-toxic to honey bees in both oral and contact bioassays. Furthermore, receptor binding studies revealed a lack of high-affinity binding of these metabolites to honey bee nAChRs. Screening of a library of 27 heterologously expressed honey bee cytochrome P450 enzymes (P450s) identified three P450s involved in the detoxification of flupyradifurone: CYP6AQ1, CYP9Q2 and CYP9Q3. Transgenic Drosophila lines ectopically expressing CYP9Q2 and CYP9Q3 were significantly less susceptible to flupyradifurone when compared to control flies, confirming the importance of these P450s for flupyradifurone metabolism in honey bees. Biochemical assays using the fluorescent probe substrate 7-benzyloxymethoxy-4-(trifluoromethyl)-coumarin (BOMFC) indicated a weak, non-competitive inhibition of BOMFC metabolism by flupyradifurone. In contrast, the azole fungicides prochloraz and propiconazole were strong nanomolar inhibitors of these flupyradifurone metabolizing P450s, explaining their highly synergistic effects in combination with flupyradifurone as demonstrated in acute laboratory contact toxicity tests of adult bees. Interestingly, the azole fungicide prothioconazole is only slightly synergistic in combination with flupyradifurone - an observation supported by molecular P450 inhibition assays. Such molecular assays have value in the prediction of potential risks posed to bees by flupyradifurone mixture partners under applied conditions. Quantitative PCR confirmed the expression of the identified P450 genes in all honey bee life-stages, with highest expression levels observed in late larvae and adults, suggesting honey bees have the capacity to metabolize flupyradifurone across all life-stages. These findings provide a biochemical explanation for the low intrinsic toxicity of flupyradifurone to honey bees and offer a new, more holistic approach to support bee pollinator risk assessment by molecular means.

Fragment-Based Local Coupled Cluster Embedding Approach for the Quantification and Analysis of Noncovalent Interactions: Exploring the Many-Body Expansion of the Local Coupled Cluster Energy

Herein, we introduce a fragment-based local coupled cluster embedding approach for the accurate quantification and analysis of noncovalent interactions in molecular aggregates. Our scheme combines two different expansions of the domain-based local pair natural orbital coupled cluster (DLPNO-CCSD(T)) energy: the many-body expansion (MBE) and the local energy decomposition (LED). The low-order terms in the MBE are initially computed in the presence of an environment that is treated at a low level of theory. Then, LED is used to decompose the energy of each term in the embedded MBE into additive fragment and fragment-pairwise contributions. This information is used to quantify the total energy of the system while providing at the same time in-depth insights into the nature and cooperativity of noncovalent interactions. Two different approaches are introduced and tested, in which the environment is treated at different levels of theory: the local coupled cluster in the Hartree-Fock (LCC-in-HF) method, in which the environment is treated at the HF level; and the electrostatically embedded local coupled cluster method (LCC-in-EE), in which the environment is replaced by point charges. Both schemes are designed to preserve as much as possible the accuracy of the parent local coupled cluster method for total energies, while being embarrassingly parallel and less memory intensive. These schemes appear to be particularly promising for the study of large and complex molecular aggregates at the coupled cluster level, such as condensed phase systems and protein-ligand interactions.

Synthetic approaches to the 2015-2018 new agrochemicals

In this review, the synthesis of 33 agrochemicals that received an international standardization organization (ISO) name between January 2015 and December 2018 is described. The aim is to showcase the broad range and scope of reactions, reagents and intermediates used to discover and produce the latest active ingredients addressing the crop protection industry's needs.

Zeolitic imidazolate framework-8 decorated with gold nanoparticles for solid-phase extraction of neonicotinoids in agricultural samples

A composite built with aminated zeolitic imidazolate framework and gold nanoparticles (AuNPs) for solid-phase extraction (SPE) of neonicotinoids in agricultural samples is presented. The composite was prepared through the assembly of AuNPs onto the surface of metal-organic framework based on the strong interaction between the amino group and AuNP. These metallic surfaces provided additional interactions based on the affinity of amino and cyano groups present in the target compounds. The composite was characterized by scanning electron microscopy, powder X-ray diffraction, Fourier-transform infrared spectroscopy, and surface area measurements. Regarding the SPE protocol, several parameters that can influence the extraction performance were optimized, such as sample volume or composition of elution solvent, among others. After elution, the analytes were determined via HPLC with diode-array detection. Under the selected conditions, satisfactory recoveries of five pesticides (thiamethoxan, clothianidin, imidacloprid, acetamiprid, and thiacloprid) were obtained (between 80 and 110%) in real samples, whereas the limits of detection ranged from 0.019 to 0.041 μg L^-1 in aqueous samples and 0.3 to 0.8 μg g^-1 in solid samples.

Imidacloprid-mediated alterations on the salivary glands of the Neotropical brown stink bug, Euschistus heros

The management of the Neotropical brown stinkbug Euschistus heros (Hemiptera: Pentatomidae) in soybean fields has been heavily dependent on the application of neonicotinoid insecticides. Neonicotinoids act primarily by impairing the function of the nicotinic acetylcholine receptors of the nervous system. These compounds also target specific organs (e.g., salivary glands), which may potentiate their insecticidal efficacy. Here, we evaluated whether the exposure to the neonicotinoid imidacloprid would cause cytomorphological changes in the salivary glands of E. heros. First, we determined the lethal concentrations (LCs) of imidacloprid through contact and ingestion. Subsequently, the cytomorphology of the salivary glands were evaluated in insect groups that survived exposure to the LC₅ (3.75 mg a.i./L), LC₅₀ (112.5 mg a.i./L), or LC₇₅ (375.0 mg a.i./L, equivalent to the recommended field rate) doses. Imidacloprid induced apoptosis and necrosis in the salivary gland cells according to the insecticide concentration and salivary gland region. All concentrations increased apoptosis and injured cells (e.g., vacuolization, chromatin condensation, swelling of organelles, and plasma membrane rupture) in the principal and accessory salivary glands. Individuals that survived exposure to the highest concentrations (i.e., LC₅ and LC₅₀) were more affected, and exhibited several necrotic cells on their main principal salivary glands. Collectively, our results indicate that imidacloprid exerts toxic effects on the non-target organs, such as the salivary glands, which increases the efficacy of this compound in the management of stink bug infestations.

The Effects of Exposure to Flupyradifurone on Survival, Development, and Foraging Activity of Honey Bees (Apis mellifera L.) under Field Conditions

Flupyradifurone (FPF) is a novel systemic nAChR agonist that interferes with signal transduction in the central nervous system of sucking pests. Despite claims that FPF is potentially "bee-safe" by risk assessments, laboratory data have suggested that FPF has multiple sub-lethal effects on individual honey bees. Our study aimed to expand the studies to the effects of field-realistic concentration of FPF. We found a statistically significant decrease in the survival rate of honey bees exposed to FPF, whereas there were no significantly negative effects on larvae development durations nor foraging activity. In addition, we found that the exposed foragers showed significantly higher expression of ApidNT, CYP9Q2, CYP9Q3, and AmInR-2 compared to the CK group (control group), but no alteration in the gene expression was observed in larvae. The exposed newly emerged bees showed significantly higher expression of Defensin and ApidNT. These results indicate that the chronic exposure to the field-realistic concentration of FPF has negligible effects, but more important synergistic and behavioral effects that can affect colony fitness should be explored in the future, considering the wide use of FPF on crops pollinated and visited by honey bees.

Unraveling individual host-guest interactions in molecular recognition from first principles quantum mechanics: Insights into the nature of nicotinic acetylcholine receptor agonist binding

Drug binding to a protein target is governed by a complex pattern of noncovalent interactions between the ligand and the residues in the protein's binding pocket. Here we introduce a generally applicable, parameter-free, computational method that allows for the identification, quantification, and analysis of the key ligand-residue interactions responsible for molecular recognition. Our strategy relies on Local Energy Decomposition analysis at the "gold-standard" coupled cluster DLPNO-CCSD(T) level. In the study case shown in this paper, nicotine and imidacloprid binding to the nicotinic acetylcholine receptor, our approach provides new insights into how individual amino acids in the active site determine sensitivity and selectivity of the ligands, extending and refining classical pharmacophore hypotheses. By inference, the method is applicable to any kind of host/guest interactions with potential applications in industrial biocatalysis and protein engineering.

Responses of Aquatic Nontarget Organisms in Experiments Simulating a Scenario of Contamination by Imidacloprid in a Freshwater Environment

Several studies have indicated the presence of the neonicotinoid insecticide imidacloprid (IMI) in aquatic ecosystems in concentrations up to 320.0 µg L^-1. In the present study, we evaluated the effects of the highest IMI concentration detected in surface water (320.0 µg L^-1) on the survival of Chironomus sancticaroli, Daphnia similis, and Danio rerio in three different scenarios of water contamination. The enzymatic activities of glutathione S-transferase (GST), catalase (CAT), and ascorbate peroxidase (APX) in D. rerio also were determined. For this evaluation, we have simulated a lotic environment using an indoor system of artificial channels developed for the present study. In this system, three scenarios of contamination by IMI (320.0 µg L^-1) were reproduced: one using reconstituted water (RW) and the other two using water samples collected in unpolluted (UW) and polluted (DW) areas of a river. The results indicated that the tested concentration was not able to cause mortality in D. similis and D. rerio in any proposed treatment (RW, UW, and DW). However, C. sancticaroli showed 100% of mortality in the presence of IMI in the three proposed treatments, demonstrating its potential to impact the community of aquatic nontarget insects negatively. Low IMI concentrations did not offer risks to D. rerio survival. However, we observed alterations in GST, CAT, and APX activities in treatments that used IMI and water with no evidence of pollution (i.e., RW and UW). These last results demonstrated that fish are more susceptible to the effects of IMI in unpolluted environments.

Pesticide risk assessment at the molecular level using honey bee cytochrome P450 enzymes: A complementary approach

Honey bee (Apis mellifera) first-tier pesticide risk assessment is largely based on standardized laboratory toxicity bioassays after both acute and chronic exposure. Recent research on honey bee cytochrome P450 monooxygenases (P450s) uncovered CYP9Q3 as the molecular determinant mediating neonicotinoid insecticide selectivity and explaining why certain neonicotinoids such as thiacloprid show > 1000-fold lower acute toxicity than others (e.g. imidacloprid). Here this knowledge is leveraged for mechanistic risk assessment at the molecular level using a fluorescence-based high-throughput in vitro assay, predicting the interaction of diverse pesticidal chemotypes, including azole fungicides, with recombinantly expressed honey bee CYP9Q enzymes, known to metabolize thiacloprid, acetamiprid and tau-fluvalinate. Some azole fungicides were shown to be synergistic in combination with certain insecticides, including neonicotinoids and pyrethroids, whereas others such as prothioconazole were not. We demonstrate that biochemical CYP9Q2/CYP9Q3 inhibition data of azoles revealed a striking correlation with their synergistic potential at the organismal level, and even allow to explain combined toxicity effects observed for tank mixtures under field conditions. Our novel toxicogenomics-based approach is designed to complement existing methods for pesticide risk assessment with unprecedented screening capacity, by utilizing honey bee P450 enzymes known to confer pesticide selectivity, in order to biochemically address issues of ecotoxicological concern.

Status and outlook for acaricide and insecticide discovery

To guarantee sustainability and progress, the agrochemical industry is faced with several major challenges. Currently, loss of active ingredients due to consumer perception, changing grower needs and ever-changing regulatory requirements is far higher than the number being introduced into the market. Therefore, there is a need to develop new products that can provide improved efficacy, selectivity and favorable environmental profiles. Strategies to achieve these goals are the search for acaricides and insecticides with new modes of action, or the discovery of novel molecules with activity on the most attractive target sites having resistance breaking properties against pest species. In this context, the introduction of halogen atoms or asymmetric centers into an active ingredient remains an important tool to modulate their properties, but so too is the pro-pesticide concept. This review gives an overview of agrochemicals launched over the past 8 years, reflects new insights into known mechanisms of action, and describes the status and outlook for acaricide and insecticide discovery.

Binding properties to nicotinic acetylcholine receptors can explain differential toxicity of neonicotinoid insecticides in Chironomidae

Neonicotinoids are neuroactive insecticides commonly detected in freshwater ecosystems. Recent studies have indicated that these compounds are markedly toxic to Chironomidae, a widespread family of ecologically important aquatic insects. However, despite their sensitivity, the pharmacological mechanisms driving neonicotinoid toxicity have yet to be characterized in these insect species. Here, we used a combination of saturation and competition binding studies to characterize neonicotinoid binding properties to nicotinic acetylcholine receptors (nAChR) in two different Chironomidae (Chironomus riparius and Chironomus dilutus) at two different life stages (larval and adult). Using radiolabeled imidacloprid ([³H]-IMI), we characterized and compared receptor density (B_max), imidacloprid binding affinity (K_D), and receptor binding affinity (K_i) to three different neonicotinoid competitors (imidacloprid, clothianidin, and thiamethoxam). We then compared receptor density and binding affinity parameters derived for Chironomidae to data previously generated for other dipterans and agricultural pests. We found that there were limited differences in neonicotinoid binding between C. riparius and C. dilutus, with both organisms demonstrating high affinities for imidacloprid (K_D = 0.22-0.87 nM) and high receptor densities (B_max = 0.92-6.53 pmol/mg). However, there were significant differences between life-stages, with larvae expressing higher densities of nicotinic acetylcholine receptors and higher imidacloprid affinities than adults. Moreover, there were compound-specific differences in receptor affinity, with larval stages displaying relative affinities (K_i) that generally correlated with acute neonicotinoid toxicity (e.g. clothianidin ≥ imidacloprid >>> thiamethoxam). Finally, compared to other dipterans and agricultural pests, Chironomidae display very high densities of high affinity nicotinic acetylcholine receptors, which likely contribute to their sensitivity. Results indicated that receptor-level differences in neonicotinoid binding may be responsible for ecotoxicological differences amongst distinct insect species, and they likely play a role in life stage-, and compound-level toxicity differences previously observed for Chironomidae. Overall, this study highlights the value of understanding the toxicological mechanisms of action of neonicotinoids in sensitive, non-target aquatic insects, to better predict adverse effects associated with unintentional neonicotinoid exposure.

Neonicotinoid Insecticides: Molecular Targets, Resistance, and Toxicity

Neonicotinoids have been used to protect crops and animals from insect pests since the 1990s, but there are concerns regarding their adverse effects on nontarget organisms, notably on bees. Enhanced resistance to neonicotinoids in pests is becoming well documented. We address the current understanding of neonicotinoid target site interactions, selectivity, and metabolism not only in pests but also in beneficial insects such as bees. The findings are relevant to the management of both neonicotinoids and the new generation of pesticides targeting insect nicotinic acetylcholine receptors.

Effects of Nosema ceranae (Dissociodihaplophasida: Nosematidae) and Flupyradifurone on Olfactory Learning in Honey Bees, Apis mellifera (Hymenoptera: Apidae)

The health of insect pollinators, particularly the honey bee, Apis mellifera (Linnaeus, 1758), is a major concern for agriculture and ecosystem health. In response to mounting evidence supporting the detrimental effects of neonicotinoid pesticides on pollinators, a novel 'bee safe' butenolide compound, flupyradifurone (FPF) has been registered for use in agricultural use. Although FPF is not a neonicotinoid, like neonicotinoids, it is an excitotoxic nicotinic acetylcholine receptor agonist. In addition, A. mellifera faces threats from pathogens, such as the microsporidian endoparasite, Nosema ceranae (Fries et al. 1996). We therefore sought 1) to increase our understanding of the potential effects of FPF on honey bees by focusing on a crucial behavior, the ability to learn and remember an odor associated with a food reward, and 2) to test for a potential synergistic effect on such learning by exposure to FPF and infection with N. ceranae. We found little evidence that FPF significantly alters learning and memory at short-term field-realistic doses. However, at high doses and at chronic, field-realistic exposure, FPF did reduce learning and memory in an olfactory conditioning task. Infection with N. ceranae also reduced learning, but there was no synergy (no significant interaction) between N. ceranae and exposure to FPF. These results suggest the importance of continued studies on the chronic effects of FPF.

Efficacy of Fludora® Fusion (a mixture of deltamethrin and clothianidin) for indoor residual spraying against pyrethroid-resistant malaria vectors: laboratory and experimental hut evaluation

Background

A new generation of IRS insecticides which can provide improved and prolonged control of pyrethroid-resistant malaria vector populations are being developed. Fludora® Fusion is a new IRS insecticide containing a mixture of deltamethrin and clothianidin, a neonicotinoid.

Methods

The efficacy of Fludora® Fusion IRS was evaluated over 11–12 months on concrete and mud substrates in laboratory bioassays and experimental huts against wild free-flying pyrethroid-resistant Anopheles gambiae (sensu lato) in Cové, Benin. A comparison was made with the two active ingredients of the mixture; clothianidin and deltamethrin, applied alone. CDC bottle bioassays were also performed to investigate resistance to clothianidin in the wild vector population.

Results

Fludora® Fusion induced > 80% laboratory cone bioassay mortality with both susceptible and pyrethroid-resistant An. gambiae (s.l.) for 7–9 months on concrete block substrates and 12 months on mud block substrates. The vector population at the experimental hut site was fully susceptible to clothianidin in CDC bottle bioassays. Overall mortality rates of wild free-flying pyrethroid-resistant An. gambiae (s.l.) entering the experimental huts during the 11-month trial were < 15% with deltamethrin and significantly higher with Fludora® Fusion (69–71%) and clothianidin alone (72–78%). Initial high experimental hut mortality rates with Fludora® Fusion (> 80%) only declined by 50% after 8 months. Monthly in situ wall cone bioassay mortality of susceptible mosquitoes was > 80% for 9–12 months with Fludora® Fusion and clothianidin alone. Fludora® Fusion induced significantly higher levels of early exiting of mosquitoes compared to clothianidin alone (55–60% vs 37–38%, P < 0.05).

Conclusions

Indoor residual spraying with Fludora® Fusion induced high and prolonged mortality of wild pyrethroid-resistant malaria vectors for 7–10 months mostly due to the clothianidin component and substantial early exiting of mosquitoes from treated huts due to the pyrethroid component. Fludora® Fusion is an important addition to the current portfolio of IRS insecticides with the potential to significantly reduce transmission of malaria by pyrethroid-resistant mosquito vectors.

Exposure Level of Neonicotinoid Insecticides in the Food Chain and the Evaluation of Their Human Health Impact and Environmental Risk: An Overview

Neonicotinoid insecticides (neonics) were the most rapidly growing class of insecticides over the past few decades, and are used mainly for vegetables, fruits, and grains. Although neonics exhibit lower toxicity in mammals and humans compared to traditional insecticides, increasing numbers of studies are demonstrating that neonics may accumulate in the food chain and environmental media. Long-term exposure to neonics may raise potential risks to animals and even to humans. The present report reviews the development, application, and prohibition of neonics in the farmland ecosystem, and summarizes the exposure level and harmful effects of these insecticides in the food chain. In addition, the present review analyzes and summarizes the evaluation of the human health impact and environmental risk of the neonics, and overviews the unresolved problems and future research directions in this field. The aim of the present report was to review the exposure level, potential toxicity, human health impact, and environmental risk assessment of neonics in various media in order to provide reliable technical support for strengthening the environmental and food safety supervision and green pesticide designing.

Uptake and physiological effects of the neonicotinoid imidacloprid and its commercial formulation Confidor® in a widespread freshwater oligochaete

The neonicotinoid imidacloprid (IMI) is one of the most extensively applied neuro-active insecticides worldwide and continues to enter surface waters in many countries despite a recent ban for outdoor use in the EU. Yet little is known about ecotoxicological effects on non-target benthic freshwater species exposed to environmentally relevant concentrations of IMI and its marketed products. The aim of the present study was to narrow this gap by assessing effects of pure IMI and its commercial formulation Confidor® on the aquatic oligochaete Lumbriculus variegatus, a key species in freshwater sediments. To this end, we determined dose-response relationships in 24 h toxicity tests, bioconcentration during 24 h and 5 d of exposure to 0.1, 1 and 10 μg IMI L^-1, and physiological stress responses by measuring glutathione S-transferase, glutathione reductase and catalase activity in the same conditions. Maximum neonicotinoid concentrations reported from the field were lethal to L. variegatus within 24 h (LC₅₀ of 65 and 88 μg IMI L^-1 in pure form and as active ingredient of Confidor®, respectively). At sub-lethal exposure concentrations, tissue content of IMI significantly increased with exposure time. The observed bioconcentration factors (BCFs) were far above the water octanol coefficient (K_OW), indicating a potentially large underestimation of IMI bioaccumulation when based on K_OW. Activities of biotransformation and antioxidant enzymes indicated attempts of L. variegatus to counter xenobiotic-triggered oxidative stress to very low IMI and Confidor® concentrations. Together, our data add significantly to growing evidence that the continued proliferation of neonicotinoids require increased efforts in environmental risk assessment, especially in view of species-specific differences in sensitivities to the insecticide and possibly to additives of commercial formulations.

Synthesis of highly functionalized thiazolo[3,2-a]pyridine derivatives via a five-component cascade reaction based on nitroketene N,S-acetal

A highly efficient and straightforward synthesis of N-fused heterocyclic compounds including 5-amino-7-(aryl)-8-nitro-N'-(1-(aryl)ethylidene)-3,7-dihydro-2H-thiazolo[3,2-a]pyridine-6-carbohydrazide derivatives is successfully achieved via a five-component cascade reaction utilizing cyanoacetohydrazide, various acetophenones, aromatic aldehydes, 1,1-bis(methylthio)-2-nitroethylene and cysteamine hydrochloride in ethanol at reflux conditions. The new approach involves domino N,S-acetal formation, Knoevenagel condensation, Michael reaction, imine–enamine tautomerization and N-cyclization sequences. The prominent advantages of this protocol include: facility of operation, available and economical starting materials, no need for toxic solvents, high yields and tolerance of a wide variety of functional groups.

Easy construction of novel and highly substituted thiazolo[3,2-a]pyridine hydrazone compounds using keten N,S-acetals.

Cofactor-enabled functional expression of fruit fly, honeybee, and bumblebee nicotinic receptors reveals picomolar neonicotinoid actions

Neonicotinoids acting on insect nicotinic acetylcholine receptors (nAChRs) are deployed for crop protection, but growing evidence for adverse effects on insect pollinators has led to restricted use of some neonicotinoids in the EU. It is therefore vital to understand the target site actions of neonicotinoids in pollinators, but to date the difficulties of heterologous expression of insect nAChRs have hampered progress. We have found that a thioredoxin (TMX3) enables robust functional expression of honeybee, bumblebee, and fruit fly nAChRs in Xenopus laevis oocytes. With this advance, we show that expressed bee nAChRs are more neonicotinoid-sensitive than those of fruit fly, and clothianidin can modulate both honeybee and bumblebee nAChRs at a concentration below that commonly observed in agricultural fields.

The difficulty of achieving robust functional expression of insect nicotinic acetylcholine receptors (nAChRs) has hampered our understanding of these important molecular targets of globally deployed neonicotinoid insecticides at a time when concerns have grown regarding the toxicity of this chemotype to insect pollinators. We show that thioredoxin-related transmembrane protein 3 (TMX3) is essential to enable robust expression in Xenopus laevis oocytes of honeybee (Apis mellifera) and bumblebee (Bombus terrestris) as well as fruit fly (Drosophila melanogaster) nAChR heteromers targeted by neonicotinoids and not hitherto robustly expressed. This has enabled the characterization of picomolar target site actions of neonicotinoids, findings important in understanding their toxicity.

The mechanism of loop C-neonicotinoid interactions at insect nicotinic acetylcholine receptor α1 subunit predicts resistance emergence in pests

Neonicotinoids selectively modulate insect nicotinic acetylcholine receptors (insect nAChRs). Studies have shown that serine with ability to form a hydrogen bond in loop C of some insect nAChR α subunits and glutamate with a negative charge at the corresponding position in vertebrate nAChRs may contribute to enhancing and reducing the neonicotinoid actions, respectively. However, there is no clear evidence what loop C properties underpin the target site actions of neonicotinoids. Thus, we have investigated the effects of S221A and S221Q mutations in loop C of the Drosophila melanogaster Dα1 subunit on the agonist activity of imidacloprid and thiacloprid for Dα1/chicken β2 nAChRs expressed in Xenopus laevis oocytes. The S221A mutation hardly affected either the affinity or efficacy for ACh and imidacloprid, whereas it only slightly reduced the efficacy for thiacloprid on the nAChRs with a higher composition ratio of β2 to Dα1 subunits. The S221Q mutation markedly reduced the efficacy of the neonicotinoids for the nAChRs with a higher composition of the β2 subunit lacking basic residues critical for binding neonicotinoids. Hence, we predict the possibility of enhanced neonicotinoid resistance in pest insect species by a mutation of the serine when it occurs in the R81T resistant populations lacking the basic residue in loop D of the β1 subunit.

Thiacloprid exposure perturbs the gut microbiota and reduces the survival status in honeybees

Honeybees (Apis mellifera) offer ecosystem services such as pollination, conservation of biodiversity, and provision of food. However, in recent years, the number of honeybee colonies is diminishing rapidly, which is probably linked to the wide use of neonicotinoid insecticides. Middle-aged honeybees were fed with 50% (w/v) sucrose solution containing 0, 0.2, 0.6, and 2.0 mg/L thiacloprid (a neonicotinoid insecticide) for up to 13 days, and on each day of exposure experiment, percentage survival, sucrose consumption, and bodyweight of honeybees were measured. Further, changes in honeybee gut microbial community were examined using next-generation 16S rDNA amplicon sequencing on day 1, 7, and 13 of the exposure. When compared to control-treatment, continuous exposure to high (0.6 mg/L) and very high (2.0 mg/L) concentrations of thiacloprid significantly reduced percentage survival of honeybees (p <  0.001) and led to dysbiosis of their gut microbial community on day 7 of the exposure. However, during subsequent developmental stages of middle-aged honeybees (i.e. on day 13), their gut microbiome recovered from dysbiosis that occurred previously due to thiacloprid exposure. Taken together, improper application of thiacloprid can cause loss of honeybee colonies, while the microbial gut community of honeybee is an independent variable in this process.

An electroanalytical platform for nereistoxin-related insecticide detection based on DNA conformational switching and exonuclease III assisted target recycling

In this work, an electroanalytical platform for nereistoxin (NRT)-related insecticide detection is proposed on the basis of NRT induced DNA conformational switching and exonuclease III (Exo III) assisted target recycling. NRT-related insecticides were first hydrolyzed and converted into NRT with two thiol groups (-SH). Then, a cytosine-Ag+-cytosine (C-Ag+-C) mismatched base pair was adopted to induce a blunt-ended hairpin configuration of HP DNA. In the presence of converted NRT, it could take up Ag+ from HP DNA to change its conformation from a hairpin to single-stranded structure (HP ssDNA). Thereafter, the obtained HP ssDNA was further hybridized with an H1 hairpin probe on the electrode surface to trigger the Exo III cleavage process, releasing HP ssDNA for recycling leaving the G-quadruplex fragment of H1, which was used for hemin/G-quadruplex complex formation. The reversible redox reaction of Fe(iii)/Fe(ii) of hemin gave a remarkable electrochemical response for quantitative determination of the NRT-related insecticides. As an analytical model, a low detection limit of 3.9 ng L-1 and a wide linear range of 0.01-1500 μg L-1 with excellent selectivity were achieved for cartap detection. The proposed method also displayed great applicability for cartap detection in agricultural products.

The novel butenolide pesticide flupyradifurone does not alter responsiveness to sucrose at either acute or chronic short-term field-realistic doses in the honey bee, Apis mellifera

BACKGROUND

Sublethal exposure to neonicotinoids, a popular class of agricultural pesticides, can lead to behavioral effects that impact the health of pollinators. Therefore, new compounds, such as flupyradifurone (FPF), have recently been developed as 'safer' alternatives. FPF is an excitotoxic nicotinic acetylcholine receptor agonist, similar to neonicotinoids. Given the novelty of FPF, what data exist are focused mostly on assessing the effect of FPF on pollinator mortality. One important avenue for investigation is the potential effect of FPF on the sensitivity of nectar foragers, such as Apis mellifera, to sucrose concentrations. Neonicotinoids can alter this sucrose responsiveness and disrupt foraging. Compounding this effect, neonicotinoid-containing solutions are preferred by A. mellifera over pure sucrose solutions. We therefore conducted four studies, administering FPF under both acute and chronic conditions, and at field-realistic and higher than field-realistic doses, to assess the influence of FPF exposure on sucrose responsiveness and sucrose solutions with FPF in A. mellifera nectar foragers.

RESULTS

We found no evidence that FPF exposure under acute or chronic field-realistic conditions significantly altered sucrose responsiveness, and we did not find that bees exposed to FPF consumed more of the solution. However, at the much higher median lethal dose (48 h), among bees that survived, FPF-exposed foragers responded to significantly lower concentrations of sucrose than controls and responded at significantly higher rates to all concentrations of sucrose than controls.

CONCLUSION

We found no evidence that FPF alters the sucrose responsiveness of nectar foragers at field-realistic doses during winter or early spring, but caution and further investigation are warranted, particularly on the effects of FPF in conjunction with other stressors. © 2019 Society of Chemical Industry.

Acetylcholine and Its Receptors in Honeybees: Involvement in Development and Impairments by Neonicotinoids

Acetylcholine (ACh) is the major excitatory neurotransmitter in the insect central nervous system (CNS). However, besides the neuronal expression of ACh receptors (AChR), the existence of non-neuronal AChR in honeybees is plausible. The cholinergic system is a popular target of insecticides because the pharmacology of insect nicotinic acetylcholine receptors (nAChRs) differs substantially from their vertebrate counterparts. Neonicotinoids are agonists of the nAChR and are largely used in crop protection. In contrast to their relatively high safety for humans and livestock, neonicotinoids pose a threat to pollinating insects such as bees. In addition to its effects on behavior, it becomes increasingly evident that neonicotinoids affect developmental processes in bees that appear to be independent of neuronal AChRs. Brood food (royal jelly, worker jelly, or drone jelly) produced in the hypopharyngeal glands of nurse bees contains millimolar concentrations of ACh, which is required for proper larval development. Neonicotinoids reduce the secreted ACh-content in brood food, reduce hypopharyngeal gland size, and lead to developmental impairments within the colony. We assume that potential hazards of neonicotinoids on pollinating bees occur neuronally causing behavioral impairments on adult individuals, and non-neuronally causing developmental disturbances as well as destroying gland functioning.

Interactive effects of neonicotinoids and natural ultraviolet radiation on yellow perch (Perca flavescens) larvae

Neonicotinoids (NEOCs) are insecticides that are widely used worldwide in the culture of maize and soya. Whereas they specifically target terrestrial insects by acting as agonists of the neurotransmitter acetylcholine in their nervous system, their effects on the cholinergic system of vertebrates is still unclear. Moreover, there is an increasing concern about their effects on aquatic biota because of their high leaching potential. In the agricultural watershed of Lake St. Pierre (LSP) (St. Lawrence River System, Québec, Canada), for example, NEOC concentrations considered toxic for aquatic biota (>8.3 ng L^-1) have frequently been detected. These conditions may affect the yellow perch (Perca flavescens) population in LSP, which collapsed in the mid 1990s and is now experiencing poor recruitment. Moreover, because their larvae are found in shallow waters (<80 cm) near agricultural land, they are also exposed to ultraviolet radiation (UVR), with unknown potential interactions with NEOCs. The objective of this study was to test the synergistic effects of two commonly used NEOCs (imidacloprid and thiamethoxam) with natural UVR on yellow perch larvae using survival analysis and biomarkers to better quantify lethal and sublethal effects. Three common garden experiments were conducted with thiamethoxam and/or imidacloprid and natural UVR following a factorial design. Our results showed an interaction between UVR and thiamethoxam in terms of larval mortality. At the sublethal level, imidacloprid was associated with increased protein content and, in the presence of UVR, with increased acetylcholinesterase activity, thus indicating a cholinergic perturbation like that found in insects. Finally, we also found unexpected reduced lipid peroxidation associated with imidacloprid. A reduction in the overall lipid accumulation is suspected to be behind this puzzling result. These results will open new research avenues related to the effects of NEOCs on proteins and lipid accumulation.

In vitro exposure to thiacloprid-based insecticide formulation promotes oxidative stress, apoptosis and genetic instability in bovine lymphocytes

A proprietary thiacloprid-based neonicotinoid insecticide formulation is widely used in agriculture to protect vegetables and fruit against various pests. However, its effect on animal cells has not been fully elucidated. In this study, bovine peripheral lymphocytes were incubated with different concentrations of this formulation (10; 30; 60; 120 and 240 μg.mL^-1) for 4 h to address the potential cytotoxic and genotoxic effects of the insecticide. Insecticide formulation treatment resulted in decreased cell viability and proliferation, p53-mediated cell cycle arrest at the G₀/G₁ phase, and apoptosis induction accompanied by elevated levels of mitochondrial superoxide and protein carbonylation. Oxidant-based DNA damage and DNA damage response (DDR) were also observed, namely the formation of micronuclei, DNA double-strand breaks and slightly elevated recruitment of p53 binding protein (53BP1) foci. Our results contribute to the elucidation of insecticide effects on animal lymphocyte cultures after short-term exposure. Due to increased application of neonicotinoids worldwide, resulting in both higher yields and adverse effects on non-target animals and humans, further in vivo and in vitro experiments should be performed to confirm their cytotoxic and genotoxic activities during short-term exposure.

Removing constraints to sustainable food production: new ways to exploit secondary metabolism from companion planting and GM

The entire process of agricultural and horticultural food production is unsustainable as practiced by current highly intensive industrial systems. Energy consumption is particularly intensive for cultivation, and for fertilizer production and its incorporation into soil. Provision of nitrogen contributes a major source of the greenhouse gas, N₂ O. All losses due to pests, diseases and weeds are of food for which the carbon footprint has already been committed and so crop protection becomes an even greater concern. The rapidly increasing global need for food and the aggravation of associated problems by the effects of climate change create a need for new and sustainable crop protection. The overall requirement for sustainability is to remove seasonal inputs, and consequently all crop protection will need to be delivered via the seed or other planting material. Although genetic modification (GM) has transformed the prospects of sustainable crop protection, considerably more development is essential for the realisation of the full potential of GM and thereby consumer acceptability. Secondary plant metabolism offers wider and perhaps more robust new crop protection via GM and can be accomplished without associated yield loss because of the low level of photosynthate diverted for plant defence by secondary metabolism. Toxic mechanisms can continue to be targeted but exploiting non-toxic regulatory and signalling mechanisms should be the ultimate objective. There are many problems facing these proposals, both technical and social, and these are discussed but it is certainly not possible to stay where we are in terms of sustainability. The evidence for success is mounting and the technical opportunities from secondary plant metabolism are discussed here. © 2019 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Nicotine promotes atherosclerosis development in apolipoprotein E-deficient mice through α1-nAChR

α1 Nicotinic acetylcholine receptor (α1nAChR) is an important nicotine receptor that is widely distributed in vascular smooth muscle cells, macrophages, and endothelial cells. However, the role of α1nAChR in nicotine-mediated atherosclerosis remains unclear. The administration of nicotine for 12 weeks increased the area of the atherosclerotic lesion, the number of macrophages infiltrating the plaques, and the circulating levels of inflammatory cytokines, such as interleukin-6 and tumor necrosis factor-α, in apolipoprotein E-deficient (ApoE^-/- ) mice fed a high-fat diet. Nicotine also increased α1nAChR, calpain-1, matrix metalloproteinase-2 (MMP-2), and MMP-9 expression in the aortic tissue. Silencing of α1nAChR with an adenoassociated virus decreased the atherosclerotic size, lesion macrophage content, and circulating levels of inflammatory cytokines and suppressed α1nAChR, calpain-1, MMP-2, and MMP-9 expression in the nicotine group. In vitro, nicotine-induced α1nAChR, calpain-1, MMP-2, and MMP-9 expression in mouse vascular smooth muscle cells (MOVAS) and macrophages (RAW264.7), and enhanced the migration and proliferation of these cells. The silencing of α1nAChR inhibited these effects of nicotine MOVAS and RAW264.7 cells. Thus, we concluded that nicotine promoted the development of atherosclerosis partially by inducing the migration and proliferation of vascular smooth muscle cells and macrophages and inducing an inflammatory reaction. The effect of nicotine on atherogenesis may be mediated by α1nAChR-induced activation of the calpain-1/MMP-2/MMP-9 signaling pathway.

Acute and chronic toxicity of neonicotinoid and butenolide insecticides to the freshwater amphipod, Hyalella azteca

Neonicotinoids are the most widely used insecticides in the world. They are preferentially toxic to insects while displaying a low toxicity toward vertebrates, and this selective toxicity has resulted in the rapid and ubiquitous use of these compounds. However, neonicotinoids have been detected in agricultural surface waters and are known to cause adverse effects in non-target aquatic organisms. A wide range of toxicity has been reported for aquatic crustaceans, but most of the studies focus on the acute effects of imidacloprid, and few data are available regarding chronic effects of other neonicotinoids or neonicotinoid replacements (e.g., butenolides). The objective of this study was to assess the acute and chronic toxicity of six neonicotinoids (imidacloprid, thiamethoxam, acetamiprid, clothianidin, thiacloprid, and dinotefuran) and one butenolide (flupyradifurone) to the freshwater amphipod Hyalella azteca. Chronic (28-d), water-only, static-renewal tests were conducted. Survival was assessed weekly, and growth was measured at the end of the exposure. Effects of neonicotinoids varied depending on the compound. Acute (7-d) LC50s were 4.0, 4.7, 60, 68, 230, and 290 μg/L for clothianidin, acetamiprid, dinotefuran, thiacloprid, imidacloprid, and thiamethoxam, respectively. Chronic (28-d) survival and growth were reduced at similar concentrations to acute (7-d) survival for thiamethoxam, acetamiprid, clothianidin, and dinotefuran. However, chronic survival and growth of amphipods exposed to imidacloprid and thiacloprid were reduced at lower concentrations than acute survival, with respective 28-d LC50s of 90 and 44 μg/L, and EC50s of 4 and 3 μg/L. Flupyradifurone was intermediate in toxicity compared to the neonicotinoids: 7-d LC50, 28-d LC50, and 28-d EC50 were 26, 20, and 16 μg/L, respectively. The concentrations of imidacloprid and clothianidin reported for North American surface waters fall within the effect ranges observed in this study, indicating the potential for these compounds to cause adverse effects to indigenous populations of H. azteca.

Evidence of insecticide resistance selection in wild Anopheles coluzzii mosquitoes due to agricultural pesticide use

BACKGROUND

The wetlands used for some agricultural activities constitute productive breeding sites for many mosquito species. Thus, the agricultural use of insecticide targeting other pests may select for insecticide resistance in malaria mosquitoes. The purpose of this study is to clarify some knowledge gaps on the role of agrochemicals in the development of insecticide resistance in malaria vectors is of utmost importance for vector control.

METHODS

Using the CDC bottle test and the log-probit analysis, we investigated for the first time the resistance levels of Anopheles coluzzii mosquitoes to neonicotinoids, insecticides used exclusively for crop protection in Côte d'Ivoire. The study was conducted in two agricultural regions (Tiassale and Gagnoa) and one non-agricultural region (Vitre) between June and August 2017 using clothianidin, acetamiprid and imidacloprid.

RESULTS

Mosquito populations from Tiassale and Gagnoa (agricultural settings) were determined to be resistant to acetamiprid with mortality rates being < 85% at 24 h post-exposure. In Vitre (non-agricultural area) however, the mosquito population was susceptible to acetamiprid. In all three localities, mosquito populations were resistant to imidacloprid (mortality rates were 60% in Vitre, 37% in Tiassale, and 13% in Gagnoa) and completely susceptible to clothianidin (100% mortality). An. coluzzii represented 100% of mosquito collected in Gagnoa, 86% in Tiassale and 96% in Vitre.

CONCLUSIONS

This study provides strong evidence that agricultural use of insecticides can cause insecticide resistance in malaria vector populations. Insecticide resistance driven by agrochemical usage should be considered when vector control strategies are developed.

Degradation of microplastic seed film-coating fragments in soil

Encapsulating fungicides and/or insecticides in film-coatings applied to agronomic seeds has become a widely accepted method for enhancing seed germination and overall seedling health by protecting against many diseases and early-season insect pests. Despite advancements in seed film-coating technologies, abrasion of the seed coating can occur during handling and mechanical planting operations, resulting in variable amounts of detached fragments entering the soil. The present study investigated the degradation in soil of these plastic-like, small-sized fragments, referred to here as microplastic coating fragments. Degradation of microplastic coating fragments in soil was found to be highly variable. The lowest degradation rate (≤48 days) was observed in fragments detached from seeds coated with a commercial polymer mixture, while fragments from a biodegradable plastic formulation degraded completely within 32 days. When spores of the plant growth-promoting bacterium, Bacillus subtilis, were incorporated into the bioplastic, degradation was even more rapid (≤24 days). The fragment degradation rate was unaffected by incorporating two commonly used neonicotinoid insecticides, imidacloprid or thiacloprid, into either coating formulations, but insecticide dissipation rates in soil were more rapid when added associated with seed coating fragments than when spiked in directly. Half-lives of these two insecticides were reduced by up to 27% in fragments from bioplastic-coated seeds. These results are consistent with variable and not easily predicted soil degradation rates for seed coating fragments, with enhanced dissipation of coating-entrapped pesticides and with a higher degradation rate for biodegradable seed coating incorporating selected microbial strains.