Flupyradifurone (Sivanto™) and its novel butenolide pharmacophore: Structural considerations

Small volume solid phase extraction method for comprehensive analysis of neonicotinoids, their metabolites, and related pesticides in water

Neonicotinoid insecticides (NEOs) such as clothianidin, imidacloprid, and thiamethoxam are used worldwide. The occurrence of their degradates, for instance, clothianidin-n-desmethyl (CLO-N-DES), clothianidin-urea (CLOU), imidacloprid urea (IMIU) and olefin (IMIO), as well as thiamethoxam urea (THXU), have seldom been documented in water due to the lack of a sensitive analytical method. In this study, a method only requiring 12 mL of water sample was developed and validated to quantify 8 NEOs, 13 metabolites, and 3 related insecticides using solid phase extraction (SPE) coupled with HPLC-MS/MS. The method demonstrated good linearity (r2 > 0.99), with limits of detection (LOD) ranging from 0.16 to 1.21 ng/L and limits of quantification (LOQ) from 0.54 to 4.03 ng/L in water samples. Validation showed accuracy between 70 and 130 % and precision below 15 % for most analytes. The method's performance was comparable to, or better than, existing methods, with the advantage of requiring much smaller sample volumes. Using this method, we monitored the occurrence and seasonal variability of NEOs and their metabolites in various surface water and groundwaters matrices from across Iowa. For example, analysis of water samples from private wells across three Iowa counties detected several NEOs, with notable findings including the first detection of flupyradifurone (FLU) in Iowa well water. Surface water analysis from five locations revealed frequent detection of NEOs and their metabolites, with some concentrations exceeding U.S. EPA chronic toxicity benchmarks for freshwater invertebrates. In addition, this is the first study to demonstrate the occurrence of CLO-N-DES, CLOU, and THX-U in US surface water. The study helps advance analytical methods for NEOs and their metabolites while also highlighting their widespread occurrence in Iowa waters and associated ecological risks, emphasizing the need for more comprehensive monitoring of these compounds.

Chemical case studies from natural products of recent interest in the crop protection industry

Covering: up to 2024This review showcases selected natural products, which are of high relevance to the craft of crop protection, including in its most recent aspects such as their non-cidal use as biostimulants in plant health. Focussing on the chemistry and associated structure-activity relationships that were disclosed, the review presents case studies from the recent chemical development of important natural products and compounds inspired by them for their use in the crop protection industry.

Bumblebees under stress: Interacting effects of pesticides and heatwaves on colony development and longevity

Pollinator decline is linked to intensified agricultural practices, pathogens, climate change, and several other factors. We investigated the combined impact of heat and pesticide stress on food consumption, survival, and reproductive fitness of bumble bees. As climate change is expected to intensify heatwaves, we simulated a present-day and a future heatwave scenario (as expected in 50 years). In both scenarios, we exposed microcolonies to three widely used pesticides: azoxystrobin (fungicide), flupyradifurone, and sulfoxaflor (both insecticides)-mixed into pollen and nectar in field-realistic concentrations. We found that bees always consumed the least of sulfoxaflor-treated food, whereas consumption did not differ between other treatments or heatwave scenarios. Surprisingly, pesticide-stressed colonies performed slightly better in the future heatwave scenario in terms of reproductive fitness and survival. Sulfoxaflor consistently had the strongest negative effect, reducing survival rates, brood development, and food consumption, although effects were less severe in the future heatwave scenario.

Flupyradifurone activates DUM neuron nicotinic acetylcholine receptors and stimulates an increase in intracellular calcium through the ryanodine receptors

Insect neuronal nicotinic acetylcholine receptors (nAChRs) are transmembrane receptors that play a key role in the development and synaptic plasticity of both vertebrates and invertebrates, and are considered to be major targets of several insecticides. We used dorsal unpaired median (DUM) neurons, which are insect neurosecretory cells, to explore what type of nAChRs are involved in flupyradifurone's (FLU) mode of action, and to study the role of calcium release from intracellular stores in this process. Using whole-cell patch-clamp and fura-2-AM calcium imaging techniques, we found that inhibition of IP3Rs through application of 2-APB reduced FLU inward currents, but did not affect the intracellular calcium release induced by FLU. In contrast, inhibition of RyRs using ryanodine, led to reduction of intracellular calcium increase following FLU pulse application. These results suggested that FLU inward currents are likely due to a combination of the direct effects of FLU on DUM neuron nAChRs and the subsequent calcium release from RyRs.

Monitoring the susceptibility of Bemisia tabaci Middle East-Asia Minor 1 (Hemiptera: Aleyrodidae) to afidopyropen, cyantraniliprole, dinotefuran, and flupyradifurone in south Florida vegetable fields

Bemisia tabaci Middle East-Asia Minor 1 (MEAM1) is a significant pest that damages a wide range of high-value vegetable crops in south Florida. This pest has demonstrated the ability to develop resistance to various insecticide groups worldwide. Monitoring the resistance levels of MEAM1 populations and maintaining baseline susceptibility data are crucial for the long-term effectiveness of insecticide management strategies. We conducted serial dilution bioassays on 15 field populations of MEAM1 collected in south Florida to assess their resistance to 4 key insecticides: afidopyropen, cyantraniliprole, dinotefuran, and flupyradifurone. To quantify resistance levels, resistance ratios (RR) were generated by comparing the LC50 values of field populations to those of a known susceptible MEAM1 colony reared in the laboratory. Our findings reveal that all field-collected populations were susceptible to dinotefuran (RR 1-8) and flupyradifurone (RR 2-8). While over 80% of the populations tested were susceptible to afidopyropen (RR 1-9), 2 populations exhibited low (RR 38) and moderate resistance (RR 51), respectively. In contrast, most of the populations (57%) showed low to moderate resistance to cyantraniliprole (RR 21-78), and the remaining populations were susceptible (RR 3-10). The 2 populations with resistance to afidopyropen also exhibited moderate resistance to cyantraniliprole. Further research in this direction can aid in refining insecticide resistance management programs in Florida and other regions where B. tabaci MEAM1 is a major pest. Exploring the implications of these findings will be essential for insecticide use and integrated pest management strategies in south Florida.

Swift regulation of nicotinic acetylcholine receptors (nAChRs) and glutathione S-transferase (GST) enables the rapid detoxification of thiacloprid in pine sawyer beetles

Thiacloprid, a neonicotinoid insecticide, has become one of the major control agents for the pine sawyer beetle, Monochamus alternatus Hope, however, the mechanism of detoxification is unknown. We demonstrate that glutathione S-transferases (GSTs) and nicotinic acetylcholine receptors (nAChRs) are involved in the rapid detoxification of thiacloprid in M. alternatus larvae. The activity of detoxification enzyme GSTs was significantly higher, while the activity of acetylcholinesterase (AChE) was inhibited under thiacloprid exposure. The inhibition of AChE activity led to lethal over-stimulation of the cholinergic synapse, which was then released by the rapid downregulation of nAChRs. Meanwhile, GSTs were overexpressed to detoxify thiacloprid accordingly. A total of 3 nAChR and 12 GST genes were identified from M. alternatus, among which ManAChRα2 and MaGSTs1 were predicted to confer thiacloprid tolerance. RNA interference (RNAi) was subsequently conducted to confirm the function of ManAChRα2 and MaGSTs1 genes in thiacloprid detoxification. The successful knock-down of the ManAChRα2 gene led to lower mortality of M. alternatus under LC30 thiacloprid treatment, and the suppression of the MaGSTs1 gene increased the mortality rate of M. alternatus. However, the mortality rate has no significant difference with controls when thiacloprid was fed together with both dsMaGSTs1 and dsManAChRα2. Molecular docking modeled the molecular basis for interaction between MaGSTs1/ManAChR and thiacloprid. This study highlights the important roles that ManAChRα2 and MaGSTs1 genes play in thiacloprid detoxification through transcriptional regulation and enzymatic metabolization, and proposes a new avenue for integrated pest management that combines pesticides and RNAi technology as an efficient strategy for M. alternatus control.

Novel Insecticidal Butenolide-Containing Methylxanthine Derivatives: Synthesis, Crystal Structure, Biological Activity Evaluation, DFT Calculation and Molecular Docking

The design of novel agrochemicals starting from bioactive natural products is one of the most effective ways in the discovery and development of new pesticidal agents. In this paper, a series of novel butenolide-containing methylxanthine derivatives (Ia-Ir) were designed based on natural methylxanthine caffeine and stemofoline, and the derivatized insecticide flupyradifurone of the latter. The structures of the synthesized compounds were confirmed via 1H-NMR, 13C NMR, HRMS and X-ray single crystal diffraction analyses. The biological activities of the compounds were evaluated against a variety of agricultural pests including oriental armyworm, bean aphid, diamondback moth, fall armyworm, cotton bollworm, and corn borer; the results indicated that some of them have favorable insecticidal potentials, particularly toward diamondback moth. Among others, Ic and Iq against diamondback moth possessed LC50 values of 6.187 mg ⋅ L-1 and 3.269 mg ⋅ L-1, respectively, - 2.5- and 4.8-fold of relative insecticidal activity respectively to that of flupyradifurone (LC50=15.743 mg ⋅ L-1). Additionally, both the DFT theoretical calculation and molecular docking with acetylcholine binding protein were conducted for the highly bioactive compound (Ic). Ic and Iq derived from the integration of caffeine (natural methylxanthine) and butenolide motifs can serve as novel leading insecticidal compounds for further optimization.

Recent developments in fluorine-containing pesticides

To ensure ongoing sustainability, the modern agrochemical industry is faced with enormous challenges. These arise from provision of high-quality food to increasing water use and environmental impact as well as a growing world population. The loss of previous agrochemicals due to consumer perception, changing grower needs and ever-changing regulatory requirements is higher than the number of active ingredients that are being introduced into the crop protection market. Therefore, the development of novel agrochemicals is essential to provide improved efficacy and environmental profiles. In this context, the introduction of fluorine atoms and fluorine-containing motifs into a molecule is an important method to influence its physicochemical properties. These include, for example, small difluoro- and trifluoromethyl, or trifluoromethoxy groups at aryl or heterocyclic aryl moieties but also fragments like 2,2,2-trifluoroethoxycarbonyl, trifluoromethylsulfonyl, trifluoroacetyl, as well as the so far unusal rest like heptafluoro-iso-propyl. This review gives an overview of recent developments of fluorine-containing pesticides launched over the past 7 years and describes a selection of current fluorine-containing development candidates. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Following Regulation, Imidacloprid Persists and Flupyradifurone Increases in Nontarget Wildlife

After regulation of pesticides, determination of their persistence in the environment is an important indicator of effectiveness of these measures. We quantified concentrations of two types of systemic insecticides, neonicotinoids (imidacloprid, acetamiprid, clothianidin, thiacloprid, and thiamethoxam) and butenolides (flupyradifurone), in off-crop nontarget media of hummingbird cloacal fluid, honey bee (Apis mellifera) nectar and honey, and wildflowers before and after regulation of imidacloprid on highbush blueberries in Canada in April 2021. We found that mean total pesticide load increased in hummingbird cloacal fluid, nectar, and flower samples following imidacloprid regulation. On average, we did not find evidence of a decrease in imidacloprid concentrations after regulation. However, there were some decreases, some increases, and other cases with no changes in imidacloprid levels depending on the specific media, time point of sampling, and site type. At the same time, we found an overall increase in flupyradifurone, acetamiprid, thiamethoxam, and thiacloprid but no change in clothianidin concentrations. In particular, flupyradifurone concentrations observed in biota sampled near agricultural areas increased twofold in honey bee nectar, sevenfold in hummingbird cloacal fluid, and eightfold in flowers after the 2021 imidacloprid regulation. The highest residue detected was flupyradifurone at 665 ng/mL (parts per billion [ppb]) in honey bee nectar. Mean total pesticide loads were highest in honey samples (84 ± 10 ppb), followed by nectar (56 ± 7 ppb), then hummingbird cloacal fluid (1.8 ± 0.5 ppb), and least, flowers (0.51 ± 0.06 ppb). Our results highlight that limited regulation of imidacloprid does not immediately reduce residue concentrations, while other systemic insecticides, possibly replacement compounds, concurrently increase in wildlife. Environ Toxicol Chem 2024;43:1497-1508. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Flupyradifurone negatively affects survival, physical condition and mobility in the two-spotted lady beetle (Adalia bipunctata)

Lady beetles play a crucial role in natural ecosystems and agricultural settings. Unfortunately, these insects and more specifically the two-spotted lady beetle (Adalia bipunctata) are currently facing a severe decline in populations due to various stressors, with pesticide exposure being a significant threat. Flupyradifurone is a relatively newly introduced insecticide and as existing research is mainly elucidating its effects on bees there remains a limited understanding of its effects on non-hymenopteran insects, including lady beetles. In this study we investigated the impact of acute orally applied flupyradifurone doses on survival and sublethal parameters such as physical condition and mobility on A. bipunctata. Our findings revealed a significant increase in mortality among individuals subjected to flupyradifurone doses of 19 ng/individual (corresponding to >1.5-2.0 ng active substance (a.s.)/mg body weight (bw). The calculated LD50 of flupyradifurone at 48 h was 2.11 ng a.s./mg bw corresponding to an amount of 26.38 ng/individual. Sublethal consequences were observable immediately after pesticide application. Even at doses as low as 2 ng/individual (corresponding to >0.0-0.5 ng a.s./mg bw), flupyradifurone induced trembling and temporary immobility in treated animals. Furthermore, pesticide intoxication led to hypoactivity, with less distance covered and a decline in straightness of locomotion. In conclusion, our study underscores the harmful effects of flupyradifurone on the two-spotted lady beetle at doses notably lower than those affecting bees. These findings stress the importance of additional research to attain a more holistic understanding of pesticide impacts not only on a broader range of non-target arthropods species, but also on various exposure routes as well as lethal and sublethal effects.

Biophoton emission-based approach of the effects of systemic insecticides on the survival of Eurydema ventralis Kolenati, 1846 (Hemiptera: Pentatomidae) and on the photosynthetic activity of oilseed rape

The choice of effective crop protection technologies is a key factors in the economical production of oilseed rape. Insecticides belonging to the group of active substances butenolides and diamides are active substances available as seed treatments in oilseed rape and promising control tools in the crop protection technologies. Our laboratory experiment demonstrated that the experimental insecticides flupyradifurone and cyantraniliprole are both effective against Eurydema ventralis (Hemiptera: Pentatomidae) when used as a seed and in-crop treatments, but there is a fundamental difference in their insect mortality inducing effects. Flupyradifurone was found to have a total mortality 96 h after application based on basipetal translocation. In the case of cyantraniliprole, the insecticidal effect of the same treatment was 27% less. The experiment showed that the acropetal translocation of the tested active substances after seed treatment did not induce efficacy comparable to that of the basipetal translocation. The study of the biophoton emission of the plants demonstrated a verifiable correlation between the different application methods of the insecticides and the photon emission intensity per unit plant surface area. In conclusion, the systematic insecticides tested, in addition to having the expected insecticidal effect, interfere with plant life processes by enhancing photosynthetic activity.

Development of CHARMM compatible force field parameters and molecular dynamics simulations for the pesticide flupyradifurone

Flupyradifurone (FLU) is a novel butenolide insecticide with partial agonist activity for insect nicotinic acetylcholine receptors. Its safety for non-target organisms has been questioned in the literature, despite initial claims of its harmlessness. Detailed understanding of its toxicity and related molecular mechanisms remain under discussion. Thus, in this work, an optimized set of CHARMM compatible parameters for FLU is presented. CHARMM General Force Field program was used as a starting point while the non-bonded and bonded parameters were adjusted and optimized to reproduce MP2/6-31G(d) accuracy level results. For the validity assessment of these parameters, infrared spectrum, water-octanol partition coefficient, and normal modes were computed and compared to experimental values found in the literature. Several MD simulations of FLU in water and FLU in complex with an acetylcholine-binding protein were performed to estimate the ability of the optimized parameters to correctly describe its torsional space and reproduce observed crystallographic trends respectively.

Toxicity risk assessment of flupyradifurone for the predatory pirate bug, Orius strigicollis (Poppius) (Heteroptera: Anthocoridae), a biological control agent of Diaphorina citri Kuwayama (Hemiptera: Liviidae)

Diaphorina citri Kuwayama (Hemiptera: Liviidae), commonly known as the Asian citrus psyllid, is a prominent citrus tree pest that serves as a vector for Asian huanglongbing (HLB). The substantial costs incurred by the citrus industry as a consequence of this disease have spurred considerable interest in the combined control of D. citri using insecticides and natural enemies. However, the successful implementation of such integrated pest management strategies is dependent on ensuring the compatibility of using natural enemies in the presence of insecticides. In this regard, we evaluated the lethal and sublethal effects of flupyradifurone on Orius strigicollis (Poppius) (Heteroptera: Anthocoridae), an important predatory biological control agent, in which we assessed the risk of exposure to flupyradifurone under both in- and off-field scenario. The median lethal rate (LR50) value of flupyradifurone against O. strigicollis (9.089 g a.i. ha-1), was found to be significantly lower than the maximum field recommended rate (MFRR, 170 g a.i. ha-1). Additionally, at 0.254 g a.i. ha-1, flupyradifurone was established to significantly prolong the developmental duration of O. strigicollis from the first to third instar nymphs. Although we detected no significant difference in the survival of immature O. strigicollis subjected to 0.064 g a.i. ha-1 and control treatments, survival was significantly lower in 0.127 and 0.254 g a.i. ha-1 treatments. Moreover, whereas there were no significant differences in adult longevity between the 0.127 g a.i. ha-1 and control treatments, we recorded a significant reduction in fecundity. Furthermore, there were reductions in peak life expectancy, reproductive value, finite rate of increase, intrinsic rate of increase, and net reproduction rate in response to exposure to increasing flupyradifurone rate. Additionally, at 0.127 g a.i. ha-1, the mean generation time was significantly longer than that under control conditions. Following simulated exposure to flupyradifurone for 100 days, population of O. strigicollis in the 0.064 g a.i. ha-1 and control treatments were found to be significantly larger than those exposed to 0.127 g a.i. ha-1. On the basis on LR50 evaluations, whereas the risk of exposure risk was unacceptable for O. strigicollis under in-field scenario, it remained acceptable off-field. Nonetheless, the sublethal effect of prolonged exposure to residual flupyradifurone could pose an unacceptable off-field risk to O. strigicollis (e.g., in adjacent habitats). Consequently, the effects of different flupyradifurone exposure scenarios on O. strigicollis should be thoroughly assessed, and reducing the dosage of flupyradifurone could be advantageous for the control of D. citri when combine with augmentative release of O. strigicollis.

The effect of temperature on toxicokinetics and the chronic toxicity of insecticides towards Gammarus pulex

A comprehensive understanding of chemical toxicity and temperature interaction is essential to improve ecological risk assessment under climate change. However, there is only limited knowledge about the effect of temperature on the toxicity of chemicals. To fill this knowledge gap and to improve our mechanistic understanding of the influence of temperature, the current study explored toxicokinetics and the chronic toxicity effects of two insecticides, imidacloprid (IMI) and flupyradifurone (FPF), on Gammarus pulex at different temperatures (7-24 °C). In the toxicokinetics tests, organisms were exposed to IMI or FPF for 2 days and then transferred to clean water for 3 days of elimination at 7, 18, or 24 °C. In the chronic tests, organisms were exposed to the individual insecticides for 28 days at 7, 11, or 15 °C. Our research found that temperature impacted the toxicokinetics and the chronic toxicity of both IMI and FPF, while the extent of such impact differed for each insecticide. For IMI, the uptake rate and biotransformation rate increased with temperature, and mortality and food consumption inhibition was enhanced by temperature. While for FPF, the elimination rate increased with temperature at a higher rate than the increasing uptake rate, resulting in a smaller pronounced effect of temperature on mortality compared to IMI. In addition, the adverse effects of the insecticides on sublethal endpoints (food consumption and dry weight) were exacerbated by elevated temperatures. Our results highlight the importance of including temperature in the ecological risk assessment of insecticides in light of global climate change.

Spirotetramat resistance in Myzus persicae (Sulzer) (Hemiptera: Aphididae) and its association with the presence of the A2666V mutation

BACKGROUND

Chemicals are widely used to protect field crops against aphid pests and aphid-borne viral diseases. One such species is Myzus persicae (Sulzer), a global pest that attacks a broad array of agricultural crops and transmits many economically damaging plant viruses. This species has evolved resistance to a large number of insecticide compounds as a result of widespread and repeated chemical use in many parts of the world. In this study, we investigated the evolution of resistance to a new plant protection product, spirotetramat, following reported chemical control failures.

RESULTS

Our study provides clear phenotypic and genotypic evidence of spirotetramat resistance in populations of M. persicae from Australia. We show there is cross-resistance to other insecticides within the same chemical group, namely spiromesifen and spirodiclofen. We also demonstrate that resistance is associated with the previously reported mutation, A2226V in the target site of spirotetramat, acetyl-CoA carboxylase. Our genetic analysis found all resistant M. persicae populations belong to the same multi-locus clonal type and carry the A2226V mutation, which appears to be inherited as a dominant trait in this species.

CONCLUSION

Our findings provide new insight into the resistance conferred by A2226V and have implications for the control of M. persicae in Australia and worldwide. A diagnostic assay developed in this study should serve as a valuable tool for future resistance monitoring and to support the implementation of pest management strategies. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Comparing the acute and chronic toxicity of flupyradifurone and imidacloprid to non-target aquatic arthropod species

Flupyradifurone (FPF) is a new type of butenolide insecticide. It was launched on the market in 2015 and is considered an alternative to the widely used neonicotinoids, like imidacloprid (IMI), some of which are banned from outdoor use in the European Union. FPF is claimed to be safe for bees, but its safety for aquatic organisms is unknown. Its high water solubility, persistence in the environment, and potential large-scale use make it urgent to evaluate possible impacts on aquatic systems. The current study assessed the acute and chronic toxicity of FPF for aquatic arthropod species and compared these results with those of imidacloprid. Besides, toxicokinetics and toxicokinetic-toxicodynamic models were used to understand the mechanisms of the toxicity of FPF. The present study results showed that organisms take up FPF slower than IMI and eliminate it faster. In addition, the hazardous concentration 5th percentiles (HC₀₅) value of FPF derived from a species sensitivity distribution (SSD) based on acute toxicity was found to be 0.052 µmol/L (corresponding to 15 µg/L), which was 37 times higher than IMI (0.0014 µmol/L, corresponding to 0.36 µg/L). The chronic 28 days EC₁₀ of FPF for Cloeon dipterum and Gammarus pulex were 7.5 µg/L and 2.9 µg/L, respectively. For G. pulex, after 28 days of exposure, the no observed effect concentration (NOEC) of FPF for food consumption was 0.3 µg/L. A toxicokinetic-toxicodynamic (TKTD) model parameterised on the acute toxicity data well predicted the observed chronic effects of FPF on G. pulex, indicating that toxicity mechanisms of FPF did not change with prolonged exposure time, which is not the case for IMI.

Exposure to the novel insecticide flupyradifurone impairs bumblebee feeding motivation, learning, and memory retention

Bees are vital pollinators of crops and wildflowers and as such, wild bee declines threaten food security and functioning ecosystems. One driver of bee declines is the use of systemic insecticides, such as commonly used neonicotinoids. However, rising pest resistance to neonicotinoids, and restrictions on their use in the EU, has increased the demand for replacement insecticides to control crop pests. Flupyradifurone is a novel systemic insecticide that is thought to be relatively 'bee safe' although it can be present in the nectar and pollen of bee-attractive crops. Bumblebees rely on learning to forage efficiently, and thus detriments to learning performance may have downstream consequences on their ability to forage. While neonicotinoids negatively influence bumblebee learning and memory, whether this is also the case for their replacements is unclear. Here, we exposed bumblebees (Bombus impatiens) to an acute, field-realistic dose of flupyradifurone before training them to learn either an olfactory or colour association. We found that flupyradifurone impaired bumblebees' learning and memory performance in both olfactory and visual modalities. Flupyradifurone-treated bees were also less motivated to feed. Given the similarity between the detriments to cognition found here and those previously reported for neonicotinoids, this implies that these insecticides may have similar sub-lethal effects on bees. Restrictions on neonicotinoid use are therefore unlikely to benefit bees if novel insecticides like flupyradifurone are used as an alternative, highlighting that current agrochemical risk assessments are not protecting bees from the unwanted consequences of pesticide use. Sub-lethal assessments on non-Apis bees should be made mandatory in agrochemical regulation to ensure that novel insecticides are indeed 'bee safe'.

Synthesis and medicinal chemistry of tetronamides: Promising agrochemicals and antitumoral compounds

Butenolides and tetronic acids occupy a prominent position in synthetic chemistry due to their ubiquitous distribution in nature. This has stimulated investigations firstly in the synthesis of such systems and, laterly, the interest has turned to the understanding of the quantum structure of such systems, allowing a deeper understanding of the mechanism and reactivity of this cyclic scaffold. In contrast, tetronamides, which consist of compounds bearing a 4-aminofuran-2(5H)-one backbone, are relatively rare in nature and synthetic routes to such compounds are poorly explored. This review highlights both the importance of the tetronamide scaffold in medicinal chemistry and the most relevant recondite synthetic strategies for obtaining compounds of this class.

Acute oral toxicity and risks of four classes of systemic insecticide to the Common Eastern Bumblebee (Bombus impatiens)

The Common Eastern Bumblebee (Bombus impatiens) is native to North America with an expanding range across Eastern Canada and the USA. This species is commercially produced primarily for greenhouse crop pollination and is a common and abundant component of the wild bumblebee fauna in agricultural, suburban and urban landscapes. However, there is a dearth of pesticide toxicity information about North American bumblebees. The present study determined the acute oral lethal toxicity (48-h LD50) of: the butenolide, flupyradifurone (>1.7 μg/bee); the diamide, cyantraniliprole (>0.54 μg/bee); the neonicotinoid, thiamethoxam (0.0012 μg/bee); and the sulfoximine, sulfoxaflor (0.0177 μg/bee). Compared with published honey bee (Apis mellifera) LD50 values, the present study shows that sulfoxaflor and thiamethoxam are 8.3× and 3.3× more acutely toxic to B. impatiens, whereas flupyradifurone is more acutely toxic to A. mellifera. The current rule of thumb for toxicity extrapolation beyond the honey bee as a model species, termed 10× safety factor, may be sufficient for bumblebee acute oral toxicity. A comparison of five risk assessment equations suggested that the Standard Risk Approach (SRA) and Fixed Dose Risk Approach (FDRA) provide more nuanced levels of risk evaluation compared to the Exposure Toxicity Ratio (ETR), Hazard Quotient (HQ), and Risk Quotient (RQ), primarily because the SRA and FDRA take into account real world variability in pollen and nectar pesticide residues and the chances that bees may be exposed to them.

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.

Revisiting pesticide pollution: The case of fluorinated pesticides

Fluorinated pesticides acquired a significant market share in the agrochemical sector due to the surge of new fluoroorganic ingredients approved in the last two decades. This growing trend has not been accompanied by a comprehensive scientific and regulatory framework entailing all their potential negative impacts for the environment, especially when considering the hazardous properties that may result from the incorporation of fluorine into organic molecules. This review aims to address the safe/hazardous dichotomy associated with fluorinated pesticides by providing an updated outlook on their relevancy in the agrochemical sector and how it leads to their role as environmental pollutants. Specifically, the environmental fate and distribution of these pesticides in the ecosystems is discussed, while also analysing their potential to act as toxic substances for non-target organisms.

Flupyradifurone resistance in Myzus persicae populations from peach and tobacco in Greece

BACKGROUND

Myzus persicae has evolved resistance to various insecticides in Greece. Here we examine the effectiveness of the insecticide flupyradifurone against aphid clones collected from tobacco and peach in Greece during 2017-2020. Furthermore, we monitored the frequency of the neonicotinoid resistance mutation R81T in the sampled clones, and the association between the responses to flupyradifurone and acetamiprid.

RESULTS

Of 43 clones tested with flupyradifurone, 6.977%, 60.465% and 32.558% showed low (10-14), moderate (19-89) and high (104-1914) resistance factor (RF) values, respectively. Resistance was higher in clones from peach than from tobacco with 42.308% and 17.647% of clones (respectively) failing into the high RF category (median RF values 67.5 and 36.4 for clones from peach and tobacco, respectively). Acetamiprid resistance was detected in clones collected in 2019-2020, in line with our previous study in Greece. The analysis of the whole dataset (54 clones collected during 2017-2020) revealed that all tobacco clones had RF < 7.5, whereas 55.263%, 18.421% and 26.316% of the peach clones exhibited low (<12), moderate (20-48) and high (100-145) RF values, respectively. A significant but moderate association between flupyradifurone and acetamiprid responses was detected (r = 0.513, P < 0.001). The R81T mutation was detected in aphids from peach (5.6% and 32.6% as homozygotes and heterozygotes, respectively) and in one aphid specimen (heterozygote) from tobacco. R81T was partially associated with the resistance to both insecticides, but many highly resistant clones did not possess the mutation, indicating the possible operation of one or more alternative underlying resistance mechanisms.

CONCLUSIONS

The use of flupyradifurone and acetamiprid in IPM/IRM should be based on further ongoing susceptibility monitoring. © 2021 Society of Chemical Industry.

Statement on the active substance flupyradifurone

Flupyradifurone is a novel butenolide insecticide, first approved as an active substance for use in plant protection products by Commission Implementing Regulation (EU) 2015/2084. Following concerns that this substance may pose high risks to humans and the environment, the French authorities, in November 2020, asked the Commission to restrict its uses under Article 69 of Regulation (EC) No 1107/2009. To support this request, competent Authorities from France cited a series of literature papers investigating its hazards and/or exposure to humans and the environment. In addition, in June 2020, the Dutch Authorities notified the Commission, under Article 56 of Regulation (EC) No 1107/2009, of new information on flupyradifurone on the wild bee species Megachile rotundata. This notification is also referred to in the French notification on flupyradifurone. Consequently, the EFSA PPR Panel was mandated to quantify the likelihood of this body of evidence constituting proof of serious risks to humans or the environment. Therefore, the EFSA PPR Panel evaluated the likelihood of these studies indicating new or higher hazards and exposure to humans and the environment compared to previous EU assessments. A stepwise methodology was designed, including: (i) the initial screening; (ii) data extraction and critical appraisal based on the principles of OHAT/NTP; (iii) weight of evidence, including consideration of the previous EU assessments; (iv) uncertainty analysis, followed, whenever relevant, by an expert knowledge elicitation process. For the human health, only one study was considered relevant for the genotoxic potential of flupyradifurone in vitro. These data did not provide sufficient information to overrule the EU assessment, as in vivo studies already addressed the genotoxic potential of flupyradifurone. Environment: All available data investigated hazards in bee species. For honey bees, the likelihood of the new data indicating higher hazards than the previous EU assessment was considered low or moderate, with some uncertainties. However, among solitary bee species - which were not addressed in the previous EU assessment - there was evidence that Megachile rotundata may be disproportionately sensitive to flupyradifurone. This sensitivity, which may partially be explained by the low bodyweight of this species, was mechanistically linked to inadequate bodily metabolisation processes.

Discovery of novel iminosydnone compounds with insecticidal activities based on the binding mode of triflumezopyrim

Triflumezopyrim (TFM) is a new mesoionic insecticide developed by DuPont. Like other neonicotinoid insecticides, it binds to the orthosteric site of the nicotinic acetylcholine receptor (nAChR), but the binding mode has not been reported. Nicotinic acetylcholine binding proteins (nAChBPs) are ideal alternative structure for nAChRs. In this study, molecular docking, molecular dynamics (MD) simulations, binding free energy calculation, and per-residue binding free energy decomposition were used to study the binding modes of TFM and other 12 mesoionic insecticides. By comparing the binding free energy and the insecticidal activity, it was found that the sub-pocket around the benzyl group of the mesoionic insecticide is the key area for maintaining its activity, which is composed of A: Val116, A: Met124, A: Ile126, B: Trp155 and B: Val156. In order to verify the druggability of the sub-pocket, a series of iminosydnone compounds were designed and synthesized based on the structure of the sub-pocket. The lethality rate of compound 1 against Mythimna separata were 100% at 500 mg/L. Our research provides a basis for designing new mesoionic insecticides based on structure.

Sulfoxaflor Alters Bemisia tabaci MED (Hemiptera: Aleyrodidae) Preference, Feeding, and TYLCV Transmission

Many damaging agricultural pests can, in addition to their direct feeding damage, acquire and transmit plant pathogens. Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) is considered a 'supervector' of disease-causing plant pathogens and viruses. One of the most damaging of these is Tomato yellow leaf curl virus (TYLCV), a circulatively transmitted begomovirus than can extensively damage field and greenhouse crops. Because sustained feeding periods are necessary to acquire and transmit circulatively transmitted viruses, pesticides that, in addition to their direct lethality, suppress feeding in surviving individuals may be particularly effective in decreasing viral transmission. We assessed the impact of sulfoxaflor, a sulfoximine insecticide, on the settling preference, feeding, and viral transmission of TYLCV-carrying B. tabaci on tomato. We found that viruliferous B. tabaci avoided both settling and feeding on sulfoxaflor-treated plants, and that sulfoxaflor virtually eliminated the transmission of TYLCV by B. tabaci. The antifeedant properties of sulfoxaflor have previously been reported in other pest systems; our results document similar effects on viruliferous B. tabaci and demonstrate that this pesticide can reduce TYLCV transmission by surviving individuals.

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.

A Piperine-Based Scaffold as a Novel Starting Point to Develop Inhibitors against the Potent Molecular Target OfChtI

The insect chitinase OfChtI from the agricultural pest Ostrinia furnacalis (Asian corn borer) is a promising target for green insecticide design. OfChtI is a critical chitinolytic enzyme for the cuticular chitin degradation at the stage of molting. In this study, piperine, a natural amide compound isolated from black pepper, Piper nigrum L., was discovered for the first time to have inhibitory activity toward OfChtI. The compound-enzyme interaction was presumed to take place between the piperine benzo[d][1,3] dioxole skeleton and subsite -1 of the substrate-binding pocket of OfChtI. Hence, on the basis of the deduced inhibitory mechanism and crystal structure of the substrate-binding cavity of OfChtI, compounds 5a-f were designed and synthesized by introducing a butenolide scaffold into the lead compound piperine. The enzymatic activity assay indicated that compounds 5a-f (K_i = 1.03-2.04 μM) exhibited approximately 40-80-fold higher inhibitory activity than the lead compound piperine (I) (K_i = 81.45 μM) toward OfChtI. The inhibitory mechanism of the piperonyl butenolide compounds was elucidated by molecular dynamics, which demonstrated that the introduced butenolide skeleton improved the binding affinity to OfChtI. Moreover, the in vivo activity assay indicated that these compounds also displayed moderate insecticidal activity toward O. furnacalis. This work introduces the natural product piperine as a starting point for the development of novel insecticides targeting OfChtI.

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.

Long-term field-realistic exposure to a next-generation pesticide, flupyradifurone, impairs honey bee behaviour and survival

The assessment of pesticide risks to insect pollinators have typically focused on short-term, lethal impacts. The environmental ramifications of many of the world's most commonly employed pesticides, such as those exhibiting systemic properties that can result in long-lasting exposure to insects, may thus be severely underestimated. Here, seven laboratories from Europe and North America performed a standardised experiment (a ring-test) to study the long-term lethal and sublethal impacts of the relatively recently approved 'bee safe' butenolide pesticide flupyradifurone (FPF, active ingredient in Sivanto®) on honey bees. The emerging contaminant, FPF, impaired bee survival and behaviour at field-realistic doses (down to 11 ng/bee/day, corresponding to 400 µg/kg) that were up to 101-fold lower than those reported by risk assessments (1110 ng/bee/day), despite an absence of time-reinforced toxicity. Our findings raise concerns about the chronic impact of pesticides on pollinators at a global scale and support a novel methodology for a refined risk assessment.

Lethal and Sublethal Effects of Flupyradifurone on Bemisia tabaci MED (Hemiptera: Aleyrodidae) Feeding Behavior and TYLCV Transmission in Tomato

Pesticides primarily affect target organisms via direct toxicity, but may also alter the feeding behaviors of surviving individuals in ways that alter their effect on host plants. The latter impact is especially important when pests can transmit plant pathogens. The Mediterranean (MED) population of the sweetpotato whitefly Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) transmits Tomato yellow leaf curl virus (TYLCV), a pathogen that can be economically devastating in field and greenhouse cropping systems. We first assessed the impact of sublethal (LC15) and label concentrations of flupyradifurone, a butenolide-derived insecticide, on the feeding behavior of TYLCV-infected MED on tomato. We next measured the effect of flupyradifurone on plant TYLCV load, vector transmission efficiency, and MED survival. Both the LC15 and label flupyradifurone concentrations dramatically altered MED feeding and caused the near cessation of both salivation and phloem ingestion (necessary for viral transmission and acquisition, respectively). Both concentrations also significantly reduced plant TYLCV load, and the label rate of flupyradifurone sharply decreased TYLCV transmission while killing >99% of MED. As the first report of pesticide-induced changes in the feeding behavior of viruliferous Bemisia, our findings highlight the potential importance of chemically driven feeding cessation in the control of TYLCV and other Bemisia-transmitted plant pathogens.

Evaluation of flupyradifurone for the management of the Asian citrus psyllid Diaphorina citri via dripping irrigation systems

BACKGROUND

Chemical control is the most used and effective method to control Diaphorina citri, the vector of the phloem-limited bacteria associated with citrus huanglongbing (HLB) disease. The objectives of this study were to determine the effectiveness of flupyradifurone applied via dripping irrigation systems on D. citri. Bioassays were conducted using leaves harvested on various dates post treatment, and insecticide residue in leaf tissue was quantified.

RESULTS

The drip application of flupyradifurone on citrus trees provided high-level and long-term control against D. citri adult, and the median lethal concentration (LC₅₀ ) for ingestion of flupyradifurone in D. citri was 22.22 mg kg^-1 (fresh leaf). Flupyradifurone residue was detected in leaf tissue within 3 days after treatment. The measured level of flupyradifurone peaked on day 40 day after application, and then showed a steady decline in subsequent days for all three applied dosages. The amounts of flupyradifurone in upper, middle, and lower leaves were similar, and trends in the change in concentration of flupyradifurone were consistent.

CONCLUSIONS

The results demonstrate that flupyradifurone can be a valuable new tool for D. citri management programs, and drip-applied flupyradifurone provides an extended period of control efficacy. This paper could provide a reference to reduce the dependence on foliar-applied insecticides, with associated benefits for non-target exposure to workers and pollinators. © 2021 Society of Chemical Industry.

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.

Assessment of the effects of novel insecticides on green peach aphid (Myzus persicae) feeding and transmission of Turnip mosaic virus (TuMV)

BACKGROUND

Laboratory bioassays using treated leaf disks of peach were conducted to determine the efficacy of nine insecticides against the green peach aphid (GPA), Myzus persicae (Sulzer). The effects of these insecticides on aphid feeding behaviors and rates of transmission of Turnip mosaic virus (TuMV) to potted rutabaga plants were also determined.

RESULTS

Median lethal concentration (LC₅₀ ) values after 48 h feeding varied considerably, ranging from lows of 1.5 and 4.6 μg a.i./L for sulfoxaflor and λ-cyhalothrin, respectively, to 97.2 and 167.9 μg a.i./L for flonicamid and spirotetramat. LC₅₀ values were lowest and roughly equivalent for λ-cyhalothrin (1.2) acetamiprid (2.1), sulfoxaflor (0.23) and flupyradifurone (2.3) after 72 h feeding. Electrical penetration graph (EPG) recordings showed modest effects on feeding behaviors for certain insecticides, with sulfoxaflor, spirotetramat, and acetamiprid non-significant reduction in feeding duration and number of pathway and potential drop phases occurring during the first 5 min compared with the control. However, greenhouse experiments carried out to investigate the effect of these insecticides on rates of transmission of TuMV, which is transmitted non-persistently by GPA, resulted in only modest non-significant reductions in infection rates for acetamiprid, pymetrozine, λ-cyhalothrin, and flonicamid of 27%, 23%, 20%, and 17%, respectively.

CONCLUSION

All test materials were efficacious to GPA at differing levels, and some such as sulfoxaflor and acetamiprid non-significantly reduced the duration and number of pathways and potential drop phases of feeding within the first 5 min. None, however, resulted in significant reductions in rates of transmission of TuMV. © 2020 Her Majesty the Queen in Right of Canada. Pest Management Science © 2020 Society of Chemical Industry.

An update of the Worldwide Integrated Assessment (WIA) on systemic insecticides. Part 1: new molecules, metabolism, fate, and transport

With the exponential number of published data on neonicotinoids and fipronil during the last decade, an updated review of literature has been conducted in three parts. The present part focuses on gaps of knowledge that have been addressed after publication of the Worldwide Integrated Assessment (WIA) on systemic insecticides in 2015. More specifically, new data on the mode of action and metabolism of neonicotinoids and fipronil, and their toxicity to invertebrates and vertebrates, were obtained. We included the newly detected synergistic effects and/or interactions of these systemic insecticides with other insecticides, fungicides, herbicides, adjuvants, honeybee viruses, and parasites of honeybees. New studies have also investigated the contamination of all environmental compartments (air and dust, soil, water, sediments, and plants) as well as bees and apicultural products, food and beverages, and the exposure of invertebrates and vertebrates to such contaminants. Finally, we review new publications on remediation of neonicotinoids and fipronil, especially in water systems. Conclusions of the previous WIA in 2015 are reinforced; neonicotinoids and fipronil represent a major threat worldwide for biodiversity, ecosystems, and all the services the latter provide.

Characterization of flupyradifurone resistance in the whitefly Bemisia tabaci Mediterranean (Q biotype)

BACKGROUND

Bemisia tabaci is one of most notorious pests on various crops worldwide and many populations show high resistance to different types of insecticides. Flupyradifurone is a novel insecticide against sucking pests. B. tabaci resistance to flupyradifurone has been detected in the field, however the mechanism of flupyradifurone resistance has rarely been studied.

RESULTS

The flupyradifurone-resistant strain (FLU-SEL) was selected from the susceptible strain of B. tabaci (MED-S) using flupyradifurone for 24 generations. The FLU-SEL strain exhibited 105.56-fold resistance to flupyradifurone, and moderate cross-resistance to imidacloprid, but no cross-resistance to other tested neonicotinoids. Synergism tests and metabolic enzyme assays suggested that FLU-SEL resistance can be attributed to enhanced detoxification mediated by glutathione S-transferase (GST) and P450 monooxygenase (P450). Compared with MED-S strain, CYP6CX4 and GSTs2 were significantly overexpressed in FLU-SEL, and silencing CYP6CX4 or GSTs2 increased the mortality of whiteflies to flupyradifurone challenge in FLU-SEL. In addition, silencing CYP6CX4 also increased the mortality of whiteflies exposed to imidacloprid.

CONCLUSION

Overexpression of CYP6CX4 and GSTs2 was associated with flupyradifurone resistance, as confirmed by RNA interference. Our findings suggested that metabolic resistance to flupyradifurone might be mediated by P450s and GSTs. © 2020 Society of Chemical Industry.

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.

Synthesis of new tetronamides displaying inhibitory activity against bloom-forming cyanobacteria

BACKGROUND

The increasing frequency and intensity of cyanobacterial blooms pose a serious threat to aquatic ecosystems. These blooms produce potent toxins that can contaminate drinking water and endanger the life of wild and domestic animals as well as humans. Consequently, the development of effective methods for their control is a matter of high priority. We have previously shown that some γ-benzylidenebutenolides, related to the rubrolide family of natural products, are capable of inhibiting the photosynthetic electron transport chain (Hill reaction), a target of commercial herbicides. Here we report the synthesis and biological properties of a new class of rubrolide-inspired molecules featuring a tetronamide motif.

RESULTS

A total of 47 N-aryl tetronamides, including 38 aldol adducts, were prepared bearing phenyl, biphenyl, naphthyl, aliphatic and heteroaromatic groups. Some of the aldol adducts were dehydrated to the corresponding γ-benzylidenetetronamides, although satisfactory yields were obtained in only three cases (52-97%). None of the synthesized compounds were capable of blocking the Hill reaction. This notwithstanding, several aldol adducts equipped with a biphenyl substituent displayed excellent inhibitory activity against Synechococcus elongatus and other cyanobacterial strains (IC₅₀  = 1-5 μM). Further, these tetronamides were found to be essentially inactive against eukaryotic microorganisms.

CONCLUSION

Several newly synthesized biphenyl-containing tetronamides were shown to display potent and selective inhibitory activity against cyanobacteria. These compounds appear to exert their biological effects without interfering with the Hill reaction. As such, they represent novel leads in the search of environmentally benign agents for controlling cyanobacterial blooms. © 2019 Society of Chemical Industry.

Consequences of a short time exposure to a sublethal dose of Flupyradifurone (Sivanto) pesticide early in life on survival and immunity in the honeybee (Apis mellifera)

Dramatic losses of pollinating insects have become of global concern, as they threaten not only key ecosystem services but also human food production. Recent research provided evidence that interactions between ecological stressors are drivers of declining pollinator health and responsible for observed population collapses. We used the honeybee Apis mellifera and conducted a series of experiments to test for long-term effects of a single short exposure to the agricultural pesticide flupyradifurone to a second environmental stressor later in life. To do this, we exposed individuals during their larval development or early adulthood to sublethal dosages of flupyradifurone (0.025 μg for larvae and 0.645 μg for imagos), either pure or as part of an agricultural formulation (Sivanto). We afterwards exposed bees to a second ecological stressor infecting individuals with 10,000 spores of the fungal gut parasite Nosema ceranae. We found that pesticide exposures significantly reduced survival of bees and altered the expression of several immune and detoxification genes. The ability of bees to respond to these latter effects differed significantly between colonies, offering opportunities to breed bees with elevated levels of pesticide tolerance in the future. We conclude that short episodes of sublethal pesticide exposures during development are sufficient to trigger effects later in life and could therefore contribute to the widespread declines in bee health.

Combined nutritional stress and a new systemic pesticide (flupyradifurone, Sivanto®) reduce bee survival, food consumption, flight success, and thermoregulation

Flupyradifurone (FPF, Sivanto®) is a new butenolide insecticide that, like the neonicotinoids, is a systemic nicotinic acetylcholine receptor (nAChR) agonist. However, FPF is considered bee-safe (according to standard Risk Assessment tests), and is thus a potential solution to the adverse effects of other pesticides on beneficial insects. To date, no studies have examined the impact of nutritional stress (decreased food diversity and quality) and FPF exposure on bee health although both stressors can occur, especially around agricultural monocultures. We therefore tested the effects of a field-realistic FPF concentration (4 ppm, FPF_{daily dose} = 241 ± 4 ng/bee/day, 1/12 of LD₅₀) and nutritional stress (nectar with low-sugar concentrations) on honey bee (Apis mellifera L.) mortality, food consumption, thermoregulation, flight success (unsuccessful vs. successful), and flight ability (duration, distance, velocity). Flight and thermoregulation are critical to colony health: bees fly to collect food and reproduce, and they thermoregulate to increase flight efficiency and to rear brood. We studied the effects across seasons because seasonality can influence bee sensitivity to environmental stress. We demonstrate that, depending upon season and nutritional stress, FPF can reduce bee survival (-14%), food consumption (-14%), thermoregulation (-4%, i.e. hypothermia), flight success (-19%), and increase flight velocity (+13%). Because pesticide exposure and nutritional stress can co-occur, we suggest that future studies and pesticide risk assessments consider both seasonality and nutritional stress when evaluating pesticide safety for bees.

A simple and robust LC-ESI single quadrupole MS-based method to analyze neonicotinoids in honey bee extracts

Over the past years, neonicotinoids such as thiacloprid and flupyradifurone have gained considerable scientific and public interest. These molecules used as active compounds in pesticides are known due to cause drastic negative long-time effects on pollinators and even human health. Therefore, determining trace amounts of neonicotinoid in different environmental matrices by liquid chromatography coupled with mass selective detectors (LC-MS/MS or LC-Q-TOF/MS) has become an important methodology. However, not every scientific group has unlimited access to high-resolution mass-selective detectors (e.g., MS/MS). It becomes more apparent that the analytics of neonicotinoids are already a global issue. Research groups and organizations with a limited financial budget often depend on using cheap and robust equipment to do their analytical work. We demonstrate a single-quadrupole (Q) MS-based method with single-class residue methods (SRMs) for the analysis of neonicotinoids, applicable without the requirement of a high-end MS system. For an adequate sample clean-up strategy, QuEChERS (Quick, Easy, Cheap, Efficient, Rugged, safe) extraction and purification methods were modified and applied to eliminate residual matrix after honey bee extraction steps to analyze thiacloprid and flupyradifurone. •Simple liquid chromatography electro-spray ionization (LC-ESI) single-quadrupole mass selective (MS) method for neonicotinoid analysis.•Efficient sample pretreatment by a modified QuEChERS extraction and purification method.•Limit of detection (LOD) and limit of quantification (LOQ) for thiacloprid was 19.72 ng g^-1 and 7.61 ng g^-1, for flupyradifurone 65.73 ng g^-1 and 25.36 ng g^-1, respectively.

Lethal and sublethal synergistic effects of a new systemic pesticide, flupyradifurone (Sivanto®), on honeybees

The honeybee ( Apis mellifera L.) is an important pollinator and a model for pesticide effects on insect pollinators. The effects of agricultural pesticides on honeybee health have therefore raised concern. Bees can be exposed to multiple pesticides that may interact synergistically, amplifying their side effects. Attention has focused on neonicotinoid pesticides, but flupyradifurone (FPF) is a novel butenolide insecticide that is also systemic and a nicotinic acetylcholine receptor (nAChR) agonist. We therefore tested the lethal and sublethal toxic effects of FPF over different seasons and worker types, and the interaction of FPF with a common SBI fungicide, propiconazole. We provide the first demonstration of adverse synergistic effects on bee survival and behaviour (poor coordination, hyperactivity, apathy) even at FPF field-realistic doses (worst-case scenarios). Pesticide effects were significantly influenced by worker type and season. Foragers were consistently more susceptible to the pesticides (4-fold greater effect) than in-hive bees, and both worker types were more strongly affected by FPF in summer as compared with spring. Because risk assessment (RA) requires relatively limited tests that only marginally address bee behaviour and do not consider the influence of bee age and season, our results raise concerns about the safety of approved pesticides, including FPF. We suggest that pesticide RA also test for common chemical mixture synergies on behaviour and survival.

The novel pesticide flupyradifurone (Sivanto) affects honeybee motor abilities

Honeybees and other pollinators are threatened by changing landscapes and pesticides resulting from intensified agriculture. In 2018 the European Union prohibited the outdoor use of three neonicotinoid insecticides due to concerns about pollinators. A new pesticide by the name of "Sivanto" was recently released by Bayer AG. Its active ingredient flupyradifurone binds to the nicotinic acetylcholine receptor (AchR) in the honeybee brain, similar to neonicotinoids. Nevertheless, flupyradifurone is assumed to be harmless for honeybees and can even be applied on flowering crops. So far, only little has been known about sublethal effects of flupyradifurone on honeybees. Intact motor functions are decisive for numerous behaviors including foraging and dancing. We therefore selected a motor assay to investigate in how far sublethal doses of this pesticide affect behavior in young summer and long-lived winter honeybees. Our results demonstrate that flupyradifurone (830 µmol/l) can evoke motor disabilities and disturb normal motor behavior after a single oral administration (1.2 µg/bee). These effects are stronger in long-lived winter bees than in young summer bees. After offering an equal amount of pesticide (1.0-1.75 µg) continuously over 24 h with food the observed effects are slighter. For comparisons we repeated our experiments with the neonicotinoid imidacloprid. Intriguingly, the alterations in behavior induced by this pesticide (4 ng/bee) were different and longer-lasting compared to flupyradifurone, even though both substances bind to nicotinic acetylcholine receptors.

Toxicity and Sublethal Effects of Flupyradifurone, a Novel Butenolide Insecticide, on the Development and Fecundity of Aphis gossypii (Hemiptera: Aphididae)

The cosmopolitan pest Aphis gossypii (Glover) causes considerable economic losses on various crops by its feeding damage and transmitting diseases around the world. Flupyradifurone is a novel butenolide pesticide; its toxicity on A. gossypii parent generation (F0) was estimated following treatment with LC25 concentration for 48 h. The adult longevity and fecundity of the F0 individuals treated by flupyradifurone showed no significant decrease in comparison with the control. Life table method was used to evaluate the sublethal effects on progeny population (F1). Results showed that the development time of the fourth instar and the preadult as well as the total pre-reproductive period were significantly prolonged, while their fecundity was significantly decreased compared with the control. Additionally, the intrinsic rate of increase (r), the finite rate of increase (λ), and the net reproductive rate (R0) of F1 were all significantly lower in the group treated by LC25 than in the control group. These results reveal that the sublethal concentration of flupyradifurone could suppress the population growth of A. gossypii and indicate that this novel insecticide may be as a useful tool in pest management.

Design, synthesis, and insecticidal activity evaluation of novel 4-(N, N-diarylmethylamines)furan-2(5H)-one derivatives as potential acetylcholine receptor insecticides

BACKGROUND

Flupyradifurone is a member of a novel class of insecticides that possess excellent insecticidal activities. Halogen-containing phenyl groups are important and indispensable structural components of many pesticides. However, replacement of the difluoromethyl group of flupyradifurone with halogen-containing phenyl groups has not been reported. Hence, a series of novel butenolide derivatives containing phenyl groups were synthesized and bioassayed to discover novel compounds with excellent insecticidal activities.

RESULTS

Some target molecules exhibited good insecticidal activities against Aphis craccivora. Among the title compounds, 4cc showed the best insecticidal activities with an 50% lethal concentration (LC₅₀ ) value of 1.72 μg mL^-1 , which is superior to that of pymetrozine (LC₅₀  = 6.86 μg mL^-1 ). Molecular docking indicated that 4cc lacks oxidative metabolism by CYP6CM1 and metabolic resistance with imidacloprid. Furthermore, label-free quantitative proteomic analysis indicated that 4cc may be a potential acetylcholine receptor insecticide that acts on the nicotinic acetylcholine receptor. Compound 4cc also decreased the capability for oxidative metabolism, which further supported the molecular docking results.

CONCLUSION

This work can be used to further investigate the mechanism underlying the insecticidal activity of butenolide derivatives and develop potential novel butenolide insecticides. © 2018 Society of Chemical Industry.

Transgenerational hormetic effects of sublethal dose of flupyradifurone on the green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae)

Both inhibitory and stimulatory (known as hormesis) effects of the sublethal flupyradifurone, a butenolide insecticide, on Myzus persicae Sulzer (Hemiptera: Aphididae) were investigated for incorporating it into integrated pest management (IPM). A leaf-dip bioassay showed that flupyradifurone was very toxic against adult M. persicae with a 48 h LC50 of 8.491 mg/L. Using the age-stage two-sex life table approach, we assessed the effects of LC25 of flupyradifurone on adult M. persicae and its progeny (F1 and F2). On the one hand, aphids exposed to flupyradifurone had significantly negative effects on the life history traits acrossing the generations, such as reduced the adult longevity and fecundity of F0, shortened the duration of third instar and fourth instar nymphs, preadult period and the pre-reproductive period of F1, and decreased the reproductive days and adult longevity of F2. On the other hand, stimulatory effects on the duration of pre-adult, adult reproductive days, and reproduction of F1 were observed in the flupyradifurone-treated aphids. Consistently with the stimulation on individual traits, a higher net reproductive rate (R0) of F1 and a shorter mean generation time (T) of F2 were observed in the flupyradifurone-treated aphids, although the other population parameters including the intrinsic rate of increase (r), finite rate of increase (λ) and T of F1 and R0, r and λ of F2 were not significantly affected. These results revealed that adult M. persicae exposed to sublethal concentration of flupyradifurone can induce hormetic effects on F1, and also cause negative effects on F2. Our results would be useful for assessing the overall effects of flupyradifurone on M. persicae and the hormetic effects should take into consideration when use flupyradifurone for control M. persicae.

Cytogenetic alterations induced by flupyradifurone, a new butenolide insecticide, in human lymphocytes

Flupyradifurone (FPD), a member of the new class of butenolide insecticides, acts on nicotinic acetylcholine receptors. Studies on genotoxic and carcinogenic effects of FPD are very limited. This is the first study to investigate the cytotoxic and genotoxic effects of FPD and its metabolites on human lymphocyte cultures with or without a metabolic activation system (S9 mix) using chromosomal aberration (CA) and micronucleus (MN) tests. The cultures were treated with 85, 170, and 340 µg/ml of FPD in the presence (3 h treatment) and absence (48 h treatment) of S9 mix. Dimethyl sulfoxide (DMSO) was used as a solvent control. Statistically significant decreases were detected at the medium and highest concentrations for 48 h treatments while decreases in mitotic index (MI) in the presence of the S9 mix were found statistically significant at all FPD concentrations tested when compared with the solvent control. FPD also decreased the nuclear division index (NDI) at the highest concentration (340 µg/ml) in the absence of S9 mix. When compared with the solvent control, increases in CA frequencies were significant at the medium and highest concentrations. Significantly increased MN frequency was only found at the highest FPD concentration in cultures without S9 mix compared with the solvent control while increases in the MN frequencies in the presence of S9 mix were statistically significant at all FPD concentrations. The results of the present study indicate that FPD and its metabolites can show cytotoxic and genotoxic effects in human lymphocytes. More genotoxicity studies are necessary to make a possible risk assessment in humans.