Insecticide Flonicamid Research Articles

Efficient Biodegradation of the Neonicotinoid Insecticide Flonicamid by Pseudaminobacter salicylatoxidans CGMCC 1.17248: Kinetics, Pathways, and Enzyme Properties.

Nitrile-containing insecticides can be converted into their amide derivatives by Pseudaminobacter salicylatoxidans. N-(4-trifluoromethylnicotinoyl) glycinamide (TFNG-AM) is converted to 4-(trifluoromethyl) nicotinoyl glycine (TFNG) using nitrile hydratase/amidase. However, the amidase that catalyzes this bioconversion has not yet been fully elucidated. In this study, it was discovered that flonicamid (FLO) is degraded by P. salicylatoxidans into the acid metabolite TFNG via the intermediate TFNG-AM. A half-life of 18.7 h was observed for P. salicylatoxidans resting cells, which transformed 82.8% of the available FLO in 48 h. The resulting amide metabolite, TFNG-AM, was almost all converted to TFNG within 19 d. A novel amidase-encoding gene was cloned and overexpressed in Escherichia coli. The enzyme, PmsiA, hydrolyzed TFNG-AM to TFNG. Despite being categorized as a member of the amidase signature enzyme superfamily, PsmiA only shares 20-30% identity with the 14 previously identified members of this family, indicating that PsmiA represents a novel class of enzyme. Homology structural modeling and molecular docking analyses suggested that key residues Glu247 and Met242 may significantly impact the catalytic activity of PsmiA. This study contributes to our understanding of the biodegradation process of nitrile-containing insecticides and the relationship between the structure and function of metabolic enzymes.

Asp-tRNAAsn/Glu-tRNAGln amidotransferase A subunit-like amidase mediates the degradation of insecticide flonicamid by Variovorax boronicumulans CGMCC 4969

The main metabolic product of the pyridinecarboxamide insecticide flonicamid, N-(4-trifluoromethylnicotinyl)glycinamide (TFNG-AM), has been shown to have very high mobility in soil, leading to its accumulation in the environment. Catabolic pathways of flonicamid have been widely reported, but few studies have focused on the metabolism of TFNG-AM. Here, the rapid transformation of TFNG-AM and production of the corresponding acid product N-(4-trifluoromethylnicotinoyl) glycine (TFNG) by the plant growth-promoting bacterium Variovorax boronicumulans CGMCC 4969 were investigated. With TFNG-AM at an initial concentration of 0.86 mmol/L, 90.70 % was transformed by V. boronicumulans CGMCC 4969 resting cells within 20 d, with a degradation half-life of 4.82 d. A novel amidase that potentially mediated this transformation process, called AmiD, was identified by bioinformatic analyses. The gene encoding amiD was cloned and expressed recombinantly in Escherichia coli, and the enzyme AmiD was characterized. Key amino acid residue Val154, which is associated with the catalytic activity and substrate specificity of signature family amidases, was identified for the first time by homology modeling, structural alignment, and site-directed mutagenesis analyses. When compared to wild-type recombinant AmiD, the mutant AmiD V154G demonstrated a 3.08-fold increase in activity toward TFNG-AM. The activity of AmiD V154G was greatly increased toward aromatic L-phenylalanine amides, heterocyclic TFNG-AM and IAM, and aliphatic asparagine, whereas it was dramatically lowered toward benzamide, phenylacetamide, nicotinamide, acetamide, acrylamide, and hexanamid. Quantitative PCR analysis revealed that AmiD may be a substrate-inducible enzyme in V. boronicumulans CGMCC 4969. The mechanism of transcriptional regulation of AmiD by a member of the AraC family of regulators encoded upstream of the amiD gene was preliminarily investigated. This study deepens our understanding of the mechanisms of metabolism of toxic amides in the environment, providing new ideas for microbial bioremediation.

Occurrence and ecological risks of flonicamid and its metabolites in multiple substrates from intensive rice–vegetable rotations in tropical China

Rice–vegetable rotations are dominant in (sub)-tropical agriculture worldwide. However, fate and risks of the insecticide flonicamid (FLO) and its main degradates (collectively called FLOMs) in multiple substrates from those cropping systems remain largely unknown. In this study, we characterized residual concentrations, driving factors, transport, and potential ecological risks of FLOMs in different substrates in 28 tropical rice–vegetable rotations. Concentrations (median) of FLOMs were 0.013–3.03 (0.42) ng g−1 in plants, 0.012–1.92 (0.23) ng g−1 in soil, 0.029–0.63 (0.126) μg L−1 in water, and 0.002–0.398 (0.055) ng g−1 in sediments. Flonicamid and its metabolite N-(4-trifluoromethylnicotinoyl) glycine were the dominant species in the four substrates (84.1 % to 88.5 %). Plants had the highest levels of FLOMs, with the highest bioconcentration factor in peppers. According to boosted regression trees coupled with a partial least squares structural equation model, levels and composition of FLOMs showed high spatiotemporal and crop-related patterns in different substrates, with patterns highly codetermined by agricultural practices (e.g., crop type and FLO/neonicotinoid/pyrethroid applications), substrate parameters (e.g., pH, organic matter or total organic carbon), and climate features (e.g., wet/dry seasons). Moreover, a fugacity method indicated differences in transport and partitioning patterns in different substrates during rice and vegetable planting periods. Integrated substrate risk assessment of FLOMs contamination was conducted based on species-sensitive distributions and substrate weight index. Although overall risks of FLOM contamination in tropical rice–vegetable rotations were negligible to low, the highest risks were in soils, vegetable planting periods, and a central intensively planted area.

Novel biodegradation pathway of insecticide flonicamid mediated by an amidase and its unusual substrate spectrum.

The insecticide flonicamid (FLO) and its main degradation intermediate 4-trifluoromethylnicotinamide (TFNA-AM) are hazardous to the environment and animals. Microbial transformation of FLO has been well studied, but no study has yet reported on TFNA-AM degradation by a microorganism. Here, Pseudomonas stutzeri CGMCC 22915 effectively degraded TFNA-AM to 5-trifluoromethylnicotinic acid (TFNA). P. stutzeri CGMCC 22915 degraded 60.0% of TFNA-AM (1154.44μmol/L) within 6h with a half-life of just 4.5h. Moreover, P. stutzeri CGMCC 22915 significantly promoted TFNA-AM decomposition in surface water. The reaction was catalyzed by an amidase, PsAmiA. PsAmiA is encoded in a novel nitrile-converting enzyme gene cluster. The enzyme shared only 20-44% identities with previously characterized signature amidases. PsAmiA was successfully expressed in Escherichia coli and its enzymatic properties were investigated using TFNA-AM as the substrate. PsAmiA was more active toward amides without hydrophilic groups, and did not hydrolyze another amide metabolite of FLO, N-(4-trifluoromethylnicotinoyl)glycinamide (TFNG-AM), which is structurally very similar to TFNA-AM. Molecular docking of PsAmiA and TFNA-AM indicated that hydrophobic residues Leu148, Ala150, Ala195, Ile225, Trp341, Leu460, and Ile463 may affect its substrate spectrum. This study provides new insights of the environmental fate of FLO at the molecular level and the structure-function relationships of amidases.

Evaluation of insecticidal efficacy against maize leaf aphid [Rhopalosiphum maidis (Fitch)] under inner terai condition of Nepal

Field experiments were carried out at the National Maize Research Program in Rampur, Chitwan, with the objective of comparing the effectiveness of insecticides in the field for controlling maize leaf aphid (Rhopalosiphum maidis Fitch) during the winter season of 2019 and 2020. The design of the experiment was randomized complete block with four replications. The plot size was 6 rows of 5 m long with the spacing of 60cm × 25cm. Maize hybrid Rampur Hybrid-14 (RML-86/RML-96) was used as experimental variety. The efficacies of five insecticides viz., thiomethoxam 25% w/w 0.2g/L (T1), acetamiprid 20%WP 2g/L (T2), flonicamid 50% WG 0.5g/L (T3), neemix 3ml/L(T4), imidacloprid 0.5ml/L(T5) and untreated control (T6) were used as experimental treatments. The recommended dose of fertilizer was 180: 60: 40 N: P2O5: K2O kg/ ha with farm yard manure 10 t/ha and seed rate was 20kg/ha. Data on aphid incidence, severity, yield and yield components were recorded. All the tested insecticides significantly (P≤0.05) reduced the plant infestation caused by maize aphid, and thereafter increased the grain yield of maize compared to control. However, newer insecticide flonicamid 50% WG 0.5g/L was found as the most effective insecticide with lower aphid colony per plant (2.85), aphid score (2.63), aphid infested plant (7.33%) and higher crop yield (7904.79kg/ha). The application of insecticides prior to their severe infestations is necessary for the efficient control of the maize leaf aphid. The research findings will assist maize farmers in choosing and applying the best insecticide to ensure efficient management of maize leaf aphid with high yield.

Dissipation Kinetics and Safety Evaluation of Flonicamid in Four Various Types of Crops

The chemical insecticide flonicamid is widely used to control aphids on crops. Differences among crops make the universality of detection methods a particularly important consideration. The aim of this study was to establish a universal, sensitive, accurate and efficient method for the determination of flonicamid residues in peach, cucumber, cabbage and cotton. QuEChERS pretreatment was combined with ultrahigh-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). A satisfactory recovery rate of 84.3-99.3% was achieved at three spiking levels, and the relative standard deviation (RSD) was 0.41-5.95%. The limit of quantification (LOQ) of flonicamid in the four matrices was 0.01 mg/kg. The residue and dissipation kinetics of flonicamid in four types of crops in various locations were determined by using the optimized method. The results showed that flonicamid had a high dissipation rate in the four different types of crops and a half-life in the different matrices and locations of 2.28-9.74 days. The terminal residue of flonicamid was lower than the maximum residue limit (MRL). The risk quotient (RQ) of flonicamid was 4.4%, which is significantly lower than 100%. This result shows that the dietary risk presented by using flonicamid at the maximum recommended dose is low and acceptable. The comprehensive long-term dietary risk assessment of flonicamid performed in this study provides a reference for the protection of consumer health and safe insecticide use.

An insecticide target in mechanoreceptor neurons.

Hundreds of neurotoxic insecticides are currently in use. However, only a few direct targets have been identified. Here, using Drosophila and the insecticide flonicamid, we identified nicotinamidase (Naam) as a previous unidentified molecular target for an insecticide. Naam is expressed in chordotonal stretch-receptor neurons, and inhibition of Naam by a metabolite of flonicamid, TFNA-AM (4-trifluoromethylnicotinamide), induces accumulation of substrate nicotinamide and greatly inhibits negative geotaxis. Engineered flies harboring a point mutation in the active site show insecticide resistance and defects in gravity sensing. Bees are resistant to flonicamid because of a gene duplication, resulting in the generation of a TFNA-AM-insensitive Naam. Our results, in combination with the absence of genes encoding Naam in vertebrate genomes, suggest that TFNA-AM and potential species-specific Naam inhibitors could be developed as novel insecticides, anthelmintics, and antimicrobials for agriculture and human health.

Shared phytochemicals predict efficacy of essential oils against western flower thrips (Frankliniella occidentalis) in the greenhouse

Western flower thrips (Frankliniella occidentalis; Thysanoptera: Thripidae), or WFT, are a global pest of commercial crops, particularly those grown in greenhouses. Current management recommendations often involve judicious use of pesticides to which WFT have evolved multiple resistance phenotypes. Essential oils (EOs) have shown promise as a less toxic alternative for WFT greenhouse management. However, challenges remain in predicting which EOs are most likely to be insecticidal to WFT and ensuring that the efficacy of EOs under bioassay conditions reflect performance in whole-plant application scenarios. To address these challenges, 9 EOs were tested for contact toxicity against WFT in small container assays, then gas chromatography–mass spectroscopy (GC–MS) profiles of each EO were used to quantify concentrations of 22 chemicals shared by at least 5 or more of the plant species. Of these, 13 compounds were positively correlated with thrips mortality. Effective compounds were a mixture of sesquiterpenes, cyclic monoterpenes, and noncyclic monoterpenes. Interestingly, no bicyclic monoterpenes shared among the essential oils tested correlated with thrips mortality. Whole-plant assays of the four best EOs from the container assay showed significant reduction in the number of thrips per plant, although mortality in EO treatments in the whole plant assay was lower than in the container assay. In addition, all four EOs were as efficacious as the conventional insecticide flonicamid. Identifying other EOs with high concentrations of the efficacious compounds that were identified in this study and using container assays to screen these oils for WFT thrip mortality and phytotoxicity could help integrated pest management (IPM) practitioners and greenhouse staff to more rapidly accumulate a suite of EOs as low toxicity alternatives for management of WFT in greenhouse settings.Graphical

Characterization of nitrilases from Variovorax boronicumulans that functions in insecticide flonicamid degradation and β-cyano-L-alanine detoxification.

To characterize the functions of nitrilases of Variovorax boronicumulans CGMCC 4969 and evaluate flonicamid (FLO) degradation and β-cyano-L-alanine (Ala(CN)) detoxification by this bacterium. Variovorax boronicumulans CGMCC 4969 nitrilases (NitA and NitB) were purified, and substrate specificity assay indicated that both of them degraded insecticide FLO to N-(4-trifluoromethylnicotinoyl)glycinamide (TFNG-AM) and 4-(trifluoromethyl)nicotinol glycine (TFNG). Ala(CN), a plant detoxification intermediate, was hydrolysed by NitB. Escherichia coli overexpressing NitA and NitB degraded 41.2 and 93.8% of FLO (0.87 mmol·L-1 ) within 1h, with half-lives of 1.30 and 0.25 h, respectively. NitB exhibited the highest nitrilase activity towards FLO. FLO was used as a substrate to compare their enzymatic properties. NitB was more tolerant to acidic conditions and organic solvents than NitA. Conversely, NitA was more tolerant to metal ions than NitB. CGMCC 4969 facilitated FLO degradation in soil and surface water and utilized Ala(CN) as a sole nitrogen source for growth. CGMCC 4969 efficiently degraded FLO mediated by NitA and NitB; NitB was involved in Ala(CN) detoxification. This study promotes our understanding of versatile functions of nitrilases from CGMCC 4969 that is promising for environmental remediation.

Infectivity of Entomopathogenic Fungal Isolates Against Tarnished Plant Bug Lygus lineolaris (Hemiptera: Miridae).

Twelve isolates of entomopathogenic fungi belonging to Metarhizium robertsii, M. pinghaense, M. brunneum, Beauveria bassiana, and Isaria fumosorosea were screened against tarnished plant bug. All isolates were pathogenic, causing mortality from 28.8 ± 3.4 to 96.3 ± 2.7%. The LT50 values ranged from 2.7 to 6.0 d while the LT90 values varied between 6.6 and 15.0 d. Metarhizium robertsii isolate CPD6 (will be under the trade name NoVil) was among the isolates that caused high mortality within shorter times and was selected for study on developmental stages and greenhouse trial. The third-, fourth-, and fifth-instar nymphs, and adults were inoculated with 106, 107, and 108 conidia per ml of NoVil. All the stages were susceptible to fungal infection. However, third and fourth instars were the most susceptible with no significant differences in mortality across the three concentrations. On the other hand, mortality was dose-dependent with fifth-instar nymph and adult stages. The LT50 and LT90 values were also dose-dependent, with higher concentrations having shorter lethal-time values as compared to the lower concentrations. In the greenhouse, pepper plants were sprayed with NoVil and chemical insecticide Flonicamid (as industrial standard), before releasing adult tarnished plant bug. Mortality of 37.3, 75.5, and 76.3% was recorded in the control, NoVil, and Flonicamid, respectively. This study has identified NoVil as a potential mycoinsecticide candidate for the control of tarnished plant bug under greenhouse conditions. Further field testing on juvenile and adults is needed to evaluate the potential for in-field control.

Rapid direct cathodic voltammetric determination of insecticide flonicamid by renewable silver-amalgam film electrode

ABSTRACT The voltammetric characterisation and determination of insecticide flonicamid (N-cyanomethyl-4-(trifluoromethyl)nicotinamide) were performed for the first time using a simple electrochemical sensor, renewable silver-amalgam film electrode (Hg(Ag)FE). During the development of the direct cathodic square wave voltammetric method (SWV) for the determination of flonicamid, a voltammetric behaviour of a target analyte in aqueous Britton-Robinson buffer solution from pH 2.0 to pH 11.98 was examined. In the investigated pH range, the peak which appeared in the potential span between −0.86 V and −1.56 V vs. saturated calomel electrode depending on the applied pH value was chosen for analytical purposes. As optimal pH for the determination of flonicamid, pH 2.5 was selected. Cyclic voltammetric measurements at pH 2.5 confirmed that the electrode reaction mechanism is an irreversible reduction controlled by the diffusion of flonicamid at Hg(Ag)FE. The optimised Hg(Ag)FE-SWV method resulted in good linearity in the concentration range of 1.96–41.2 µg mL−1 while the relative standard deviation of the method was 0.30%. Flonicamid was successfully determined in commercial formulation Teppeki 500 WG® and spiked river water sample by the developed method using the standard addition procedure. The average value of flonicamid amount found in a commercial formulation based on three repetitions was 497.8 ± 0.9 g kg−1, which is in good agreement with the manufacturer’s declaration (500 ± 25 g kg−1) and with comparative high-performance liquid chromatographic measurements with diode array detection where a found average value of flonicamid content was 497.5 ± 11.5 g kg−1. The obtained results also indicate that the developed SWV procedure using Hg(Ag)FE was appropriate for the determination of flonicamid in a spiked river water sample with the recovery of 92.86% and RSD of 6.19%.

Characterizing the exposure of streams in southern Ontario to agricultural pesticides

Aquatic communities can be exposed to pesticides transported from land. Characterizing this exposure is key to predicting potential toxic effects. In this study, samples of streamwater from 21 sites were used to characterize pesticide exposure to aquatic communities. Sites were in agricultural areas of southwestern Ontario, Canada and were sampled monthly from 2012 to 2019 from April to November. Samples were analyzed for a suite of hundreds of pesticides and pesticide degradation products and other water quality indicators (e.g., nutrients). Frequently detected pesticides included herbicides (2,4-D; bentazon; MCPP; metolachlor) and neonicotinoid insecticides (NNIs) (clothianidin; thiamethoxam) which were detected in >50% of samples collected between 2015 and 2019. Non-metric multidimensional scaling (NMDS) was used to explore connections between pesticide concentrations and upstream land use and crop type. Detectable concentrations of the NNI clothianidin and many herbicides were related to corn, soybean, and grain/cereal crops while concentrations of the NNI imidacloprid, insecticide flonicamid, and fungicide boscalid were related to greenhouse/nursery land use. Potential toxicity to aquatic communities was assessed by comparing pesticide concentrations to Pesticide Toxicity Index (PTI) values. Few samples exceeded levels where acute (1% of samples) or chronic toxicity (10.5%) would be expected. The diamide insecticide chlorantraniliprole was detected in several streamwater samples at levels that may cause toxicity to aquatic invertebrates, highlighting the need for continued toxicity research into this pesticide class. The number of pesticides detected was positively correlated with nutrient and total suspended solids levels, underscoring the multiple stressors aquatic communities are exposed to in these habitats.

Biodegradation of the pyridinecarboxamide insecticide flonicamid by Microvirga flocculans and characterization of two novel amidases involved

Flonicamid (N-cyanomethyl-4-trifluoromethylnicotinamide, FLO) is a new type of pyridinecarboxamide insecticide that exhibits particularly good efficacy in pest control. However, the extensive use of FLO in agricultural production poses environmental risks. Hence, its environmental behavior and degradation mechanism have received increasing attention. Microvirga flocculans CGMCC 1.16731 rapidly degrades FLO to produce the intermediate N-(4-trifluoromethylnicotinoyl) glycinamide (TFNG-AM) and the end acid metabolite 4-(trifluoromethyl) nicotinol glycine (TFNG). This bioconversion is mediated by the nitrile hydratase/amidase system; however, the amidase that is responsible for the conversion of TFNG-AM to TFNG has not yet been reported. Here, gene cloning, overexpression in Escherichia coli and characterization of pure enzymes showed that two amidases—AmiA and AmiB—hydrolyzed TFNG-AM to TFNG. AmiA and AmiB showed only 20–30% identity to experimentally characterized amidase signature family members, and represent novel amidases. Compared with AmiA, AmiB was more sensitive to silver and copper ions but more resistant to organic solvents. Both enzymes demonstrated good pH tolerance and exhibited broad amide substrate specificity. Homology modeling suggested that residues Asp191 and Ser195 may strongly affect the catalytic activity of AmiA and AmiB, respectively. The present study furthers our understanding of the enzymatic mechanisms of biodegradation of nitrile-containing insecticides and may aid in the development of a bioremediation agent for FLO.

Conformational search, structural analysis, vibrational properties, reactivity study and affinity towards DNA of the novel insecticide flonicamid

This work deals with the study of structural properties, vibrational analysis, and reactivity of the novel insecticide flonicamid. Eight different minimum energy conformers were found during a conformational search and subsequent geometry optimizations at different levels of theory. The analysis of the PES leads to eight zones of minimum energy due to the scan of selected dihedral angles, which agrees with the structure of the eight most stable conformers found in the conformational search. The vibrational analysis and a complete assignment of the vibrational modes were performed, evidencing a good correlation with the experimental reported data. Furthermore, to predict the reactivity of flonicamid, different descriptors were analyzed. Finally, results obtained from docking analysis suggested that due to the molecular interaction with a sequence of DNA, the possible carcinogenic effects of flonicamid and three of its most important metabolites must be evaluated experimentally.

Flonicamid and knockdown of inward rectifier potassium channel gene CsKir2B adversely affect the feeding and development of Chilo suppressalis.

The selective insecticide flonicamid shows highly insecticidal activities against piercing-sucking insects and has been widely used for the control of Hemipteran insect pests, whereas its effects on Lepidopteran insect pests remain largely unknown. Recently, inward rectifier potassium (Kir) channel has been verified to be a target of flonicamid, however, functional characterization of Lepidopteran Kir genes is still lacking. Flonicamid shows no insecticidal toxicity against Chilo suppressalis larvae. However, the feeding and growth of larvae were reversibly inhibited by flonicamid (50-1200 mg L-1 ). Flonicamid treatment also remarkably reduced and delayed the pupation and eclosion of Chilo suppressalis. Additionally, five distinct Kir channel genes (CsKir1, CsKir2A, CsKir2B, CsKir3A and CsKir3B) were cloned from Chilo suppressalis. Expression profiles analysis revealed that CsKir2A was predominately expressed in the hindgut of larvae, whereas CsKir2B had high expressions in the Malpighian tubules and hindgut. RNA interference (RNAi)-mediated knockdown of CsKir2B significantly reduced the growth and increased the mortalities of larvae, whereas silencing of CsKir2A had no obvious effects on Chilo suppressalis. Flonicamid exhibits adverse effects on the growth and development of Chilo suppressalis. CsKir2B might be involved in the feeding behavior of Chilo suppressalis. These results provide valuable information on the effects of flonicamid on non-target insects as well as the function of insect Kir channels, and are helpful in developing new insecticide targeting insect Kir channels. © 2020 Society of Chemical Industry.

Efficacy of some insecticides for control of oak lace bug (Corythucha arcuata Say)

The oak lace bug (Corythucha arcuata Say) was introduced to Europe from North America in 2000 and was first recorded in Serbia in 2013. It is a very serious oak pest which has harmful effect in both adult and nymph stages of the insect that feeds by sucking the sap on the lower (abaxial) leaf side. As this is a relatively new pest in our country, the possibility of its control by applying insecticides was tested during 2021. The paper presents the test results of three insecticidal active substances: deltamethrin, flonicamid and acetamiprid for the control of oak lace bugs. The insecticide flonicamid did not show sufficient efficacy in the suppression of the oak lace bug, while deltamethrin and acetamiprid have high efficiency for the suppression of the adults and nymphs of the oak lace bug, which recommended them for this purpose.

Bioinformatics of a Novel Nitrile Hydratase Gene Cluster of the N2-Fixing Bacterium Microvirga flocculans CGMCC 1.16731 and Characterization of the Enzyme.

Microvirga flocculans CGMCC 1.16731 can degrade many cyano group-containing neonicotinoid insecticides. Here, its genome was sequenced, and a novel nitrile hydratase gene cluster was discovered in a plasmid. The NHase gene cluster (pnhF) has gene structure β-subunit 1, α-subunit, and β-subunit 2, which is different from previously reported NHase gene structures. Phylogenetic analysis of α-subunits indicated that NHases containing the three subunit (β1αβ2) structure are independent from NHases containing two subunits (αβ). pnhF was successfully expressed in Escherichia coli, and the purified PnhF could convert the nitrile-containing insecticide flonicamid to N-(4-trifluoromethylnicotinoyl)glycinamide. The enzymatic properties of PnhF were investigated using flonicamid as a substrate. Homology models revealed that amino acid residue β1-Glu56 may strongly affect the catalytic activity of PnhF. This study expands our understanding of the structures and functions of NHases and the enzymatic mechanism of the environmental fate of flonicamid.

Biodegradation of the Insecticide Flonicamid by Alcaligenes faecalis CGMCC 17553 via Hydrolysis and Hydration Pathways Mediated by Nitrilase.

Flonicamid (N-cyanomethyl-4-trifluoromethylnicotinamide, FLO), a novel selective systemic pyridinecarboxamide insecticide, effectively controls hemipterous pests. However, microbial degradation of flonicamid, along with the enzymatic mechanism, has not been studied. Here, bacterial isolate PG13, which converts flonicamid into 4-(trifluoromethyl)nicotinol glycine (TFNG) and N-(4-trifluoromethylnicotinoyl)glycinamide (TFNG-AM), was isolated and identified as Alcaligenes faecalis CGMCC 17553. The genome of CGMCC 17553 contained five nitrilases but no nitrile hydratase, and recombinant Escherichia coli strains harboring CGMCC 17553 nitrilase gene nitA or nitD acquired the ability to degrade flonicamid. Purified NitA catalyzed flonicamid into both TFNG and TFNG-AM, indicating dual functionality, while NitD could only produce TFNG-AM. Three-dimensional homology modeling revealed that aromatic amino acid residues in the catalytic pocket affected nitrilase activity. These findings further our understanding of the enzymatic mechanism of flonicamid metabolism in the environment and may help develop a potential bioremediation agent for the elimination of flonicamid contamination.

Terpene based biopesticides as potential alternatives to synthetic insecticides for control of aphid pests on protected ornamentals

Biopesticides based on plant extracts offer a promising alternative to the use of conventional synthetic pesticides. However, biopesticide products must provide acceptable levels of control. To date, few studies have investigated the efficacy of biopesticide products under conditions that reflect commercial practice. Here we report results from three experiments, one completed under glasshouse conditions in 2014 and two completed under polytunnel conditions, in 2015 and 2016, respectively. These experiments tested the efficacy of three terpene based biopesticides used to control two aphid species, peach-potato aphid (Myzus persicae) and melon and cotton aphid (Aphis gossypii), on ornamental crops. The three biopesticide products tested were orange oil (60 g active ingredient per litre, formulated as a soluble liquid), the essential oil from Chenopodium ambrosioides variety nr. ambrosioides (16.75% active ingredient, formulated as an oil dispersion) and neem oil (1% active ingredient, formulated as emulsifiable concentrate). The biopesticides tested were applied as foliar sprays using a water volume of 600 l/Ha and all experiments were done at Harper Adams University, Shropshire, UK.The biopesticide products tested gave statistically similar levels of control of M. persicae populations on pansy plants as the conventional synthetic insecticide flonicamid (500 g/kg active ingredient, formulated as a wettable granule) and spirotetramat (150 g/l active ingredient, formulated as an oil dispersion). All products reduced numbers of aphids by at least 85% during the experimental period. Orange oil also gave a similar speed of kill to flonicamid and was faster acting than spirotetramat, two conventional synthetic insecticides that are widely used to control aphid pests of ornamental crops. Against A. gossypii on Hebe, orange oil gave similar levels of control (90% reduction in aphid numbers) as flonicamid (98% reduction in aphid numbers), when applied with a spray interval of three days (as per label recommendation). The essential oil from Chenopodium ambrosioides variety nr. ambrosioides was not as effective as flonicamid but did significantly reduced (80% reduction in aphid numbers) numbers of A. gossypii on Hebe compared to a water control when applied with a spray interval of five days. Neem oil was not effective against A. gossypii. Importantly, there was little evidence of any phytotoxicity caused by any of the biopesticide products tested. The potential to use these products as part of an Insecticide Resistance Management (IRM) programme are discussed.

Field bioefficacy, phytotoxicity and residue dynamics of the insecticide flonicamid (50 WG) in okra [Abelmoschus esculenta (L) Moench

In India, sucking pests including leafhoppers (Amrasca biguttula biguttula Ishida) and whitefly (Bemisia tabaci Gennadius) cause considerable economic damage to okra cultivation. This study reports the results of field experiments evaluating the bioefficacy, phytotoxicity, and residue dynamics of sprays of flonicamid 50 WG in okra (Abelmoschus esculenta (L.) Moench) crops. Of three doses (50, 75, 100 g a.i ha−1) tested, applications at 75 g a.i ha−1 were equally effective in controlling both leafhoppers and whiteflies with a higher marketable fruit yield of okra under open field conditions. Flonicamid also reduced population of the pest by >85% when compared to untreated controls after three rounds of foliar application at an interval of 10 days. Applications of flonicamid 50 WG did not cause any phytotoxic symptoms. It was also safe to the natural enemies (spiders and rove beetles) prevailing in the okra ecosystem. Initial deposits of flonicamid in okra fruits when applied at the rate of 75 and 150 g a.i. ha−1 were dissipated with half-lives of 3.0 and 3.5 days. Recommendable pre-harvest intervals (PHI) are 16 and 20 days, respectively. The dietary exposure of the measured residues was lower than the maximum permissible intake (MPI) of 0.576 mg person−1 day−1 on all the sampling days at both the doses. These findings are useful in deciding the spray schedule of flonicamid for effective management of sucking pests in okra crop assuring food safety.