Flubendiamide, the first phthalic acid diamide insecticide, impairs neuronal calcium signalling in the honey bee's antennae

Cardiotoxicity of the diamide insecticide chlorantraniliprole in the intact heart and in isolated cardiomyocytes from the honey bee

In honey bees, circulation of blood (hemolymph) is driven by the peristaltic contraction of the heart vessel located in the dorsal part of the abdomen. Chlorantraniliprole (CHL) is an insecticide of the anthranilic diamide class which main mode of action is to alter the function of intracellular Ca2+ release channels (known as RyRs, for ryanodine receptors). In the honey bee, it was recently found to be more toxic when applied on the dorsal part of the abdomen, suggesting a direct cardiotoxicity. In the present study, a short-term exposure of semi-isolated bee hearts to CHL (0.1-10 µM) induces alterations of cardiac contraction. These alterations range from a slow-down of systole and diastole kinetics, to bradycardia and cardiac arrest. The bees heart wall is made of a single layer of semi-circular cardiomyocytes arranged concentrically all along the long axis of tube lumen. Since the heart tube is suspended to the cuticle through long tubular muscles fibers (so-called alary muscle cells), the CHL effects in ex-vivo heart preparations could result from the modulation of RyRs present in these skeletal muscle fibers as well as cardiomyocytes RyRs themselves. In order to specifically assess effects of CHL on cardiomyocytes, for the first time, intact heart cells were enzymatically dissociated from bees. Exposure of cardiomyocytes to CHL induces an increase in cytoplasmic calcium, cell contraction at the highest concentrations and depletion of intracellular stores. Electrophysiological properties of isolated cardiomyocytes were described, with a focus on voltage-gated Ca2+ channels responsible for the cardiac action potentials depolarization phase. Two types of Ca2+ currents were measured under voltage-clamp. Exposure to CHL was accompanied by a decrease in voltage-activated Ca2+ currents densities. Altogether, these results show that chlorantraniliprole can cause cardiac defects in honey bees.

Residual Pattern of Chlorantraniliprole, Thiamethoxam, Flubendiamide and Deltamethrin in Tomato Fruit and Soil

Tomato, Lycopersicon esculentum L. is grown widely as an important day-to-day demand vegetable. The crop is attacked by various polyphagous insect pests like tomato fruit borer, stink bug, cabbage looper, flea beetle, aphids, whitefly, two-spotted spider mite, etc., and oligophagous insects like leaf-miner, five-spotted hawkmoth, etc. To combat the damage and yield loss, various chemical insecticides were sprayed on tomatoes under field conditions. The residual pattern of insecticides like chlorantraniliprole, thiamethoxam, flubendiamide, and deltamethrin residues was studied following applications of chlorantraniliprole 18.5% SC (Coragen) @ 30 g a.i./ha, thiamethoxam 25% WG (Actara) @ 50 g a.i./ha, flubendiamide 39.35 M/M SC (Fame) @ 48 g a.i./ha and deltamethrin 2.8% EC (Decis 100) @ 12.5 g a.i./ha using Reverse Phase High-Performance Liquid Chromatography (RP-HPLC). Fruit samples were collected at 0 (1 h after application), 1, 2, 3, 5, 7 days and at harvest time. All the residues of insecticides such as chlorantraniliprole (0.09 mg kg- 1), thiamethoxam (0.03 mg kg- 1), flubendiamide (0.02 mg kg- 1), and deltamethrin (0.01 mg kg- 1) were persisted up to 5th day. There were no residues found at harvest time. The residues of chlorantraniliprole and deltamethrin persisted up to 3rd day of spraying whereas the residues of flubendiamide and thiamethoxam were not detected on the same day in the soil.

Identification of sex pheromone of red swamp crayfish Procambarus clarkii and exploration of the chemosensory mechanism of their antennae

Red swamp crayfish, Procambarus clarkii, is a globally invasive species, which has caused great damage to biodiversity, agriculture, and fishing. Therefore, the development of effective management methods, such as pheromone control, is necessary for biological control and biodiversity protection. However, the components of P. clarkii sex pheromones have not yet been explored, and the chemosensory mechanism of the P. clarkii antennae after stimulation by sex pheromone also remains unknown. In this study, we isolated and identified the candidate bioactive component of the female P. clarkii sex pheromone using ultrafiltration centrifugation, semi-preparative liquid phase separation and omics technologies and conducted bioassays to determine its attraction ability. Meanwhile, RNA-Seq technology was used to analyze the potential chemosensory mechanism of antennae. Our results indicated that the male P. clarkii were uniaxially attracted to the female crude conditioned water (FCW), medium fraction (MF, isolated by ultrafiltration centrifugation), and preparative fragment 6 of females (PFF6, isolated by semi-preparative liquid phase separation). Metabolomic analysis revealed the presence of 18 differential metabolites between the PFF6 and PFM6 samples, among which 15 were significantly upregulated in the PFF6 sample. Bioassay test also showed that mestranol, especially at concentrations of 10-5-10-2 mol∙l-1, could significantly attract P. clarkii males; therefore, mestranol was identified as the candidate sex pheromone component of P. clarkii females. Furthermore, RNA-Seq results showed that most differentially expressed genes (DEGs) enriched in lipid metabolism and signal transduction pathways were up-regulated in P. clarkii males. In addition, high expressions of Ca2+-binding protein and ion transporting ATPases may enhance the sensitivity of the antennae of P. clarkii males towards sex pheromones. Our study provides data on P. clarkii sex pheromone composition and reveals the molecular mechanism of sex pheromone response in P. clarkii. Moreover, our study provides a referable method for the isolation of candidate bioactive molecules from the P. clarkii sex pheromone.

Cyto-Genotoxic and Behavioral Effects of Flubendiamide in Allium cepa Root Cells, Drosophila melanogaster and Molecular Docking Studies

Flubendiamide (FLB) is an insecticide that is commonly employed to control pests on a variety of vegetables and fruits, with low toxicity for non-target organisms. However, due to its widespread use, the environmental risks and food safety have become major concerns. In this study, the toxicity potential of FLB was studied in the model organisms, Allium cepa and Drosophila melanogaster. The cyto-genotoxic effects of FLB on the root growth, mitotic index (MI), chromosomal aberrations (CAs) and deoxyribonucleic acid (DNA) damage in A. cepa root meristematic cells were investigated using the root growth inhibition Allium test and Comet assays. FLB caused CAs in the form of disturbed ana-telophase, chromosome laggards, stickiness, anaphase-bridge and polyploidy depending on the concentration and the exposure time. The toxicity and genotoxicity of FLB at various doses (0.001, 0.01, 0.1 and 1 mM) on D. melanogaster were investigated from the point of view of larval weight and movement, pupal formation success, pupal position, emergence success and DNA damage, respectively. FLB exposure led to a significant reduction of the locomotor activity at the highest concentration. While DNA damage increased significantly in the FLB-treated onions depending on the concentration and time, DNA damage in the FLB-treated D. melanogaster significantly increased only at the highest dose compared to that which occurred in the control group. Moreover, to provide a mechanistic insight into the genotoxic and locomotion-disrupting effects of FLB, molecular docking simulations of this pesticide were performed against the DNA and diamondback moth (DBM) ryanodine receptor (RyR) Repeat34 domain. The docking studies revealed that FLB binds strongly to a DNA region that is rich in cytosine-guanine-adenine bases (C-G-A) in the minor groove, and it displayed a remarkable binding affinity against the DBM RyR Repeat34 domain.

Systematic Review of Calcium Channels and Intracellular Calcium Signaling: Relevance to Pesticide Neurotoxicity

Pesticides of different chemical classes exert their toxic effects on the nervous system by acting on the different regulatory mechanisms of calcium (Ca²⁺) homeostasis. Pesticides have been shown to alter Ca²⁺ homeostasis, mainly by increasing its intracellular concentration above physiological levels. The pesticide-induced Ca²⁺ overload occurs through two main mechanisms: the entry of Ca²⁺ from the extracellular medium through the different types of Ca²⁺ channels present in the plasma membrane or its release into the cytoplasm from intracellular stocks, mainly from the endoplasmic reticulum. It has also been observed that intracellular increases in the Ca²⁺ concentrations are maintained over time, because pesticides inhibit the enzymes involved in reducing its levels. Thus, the alteration of Ca²⁺ levels can lead to the activation of various signaling pathways that generate oxidative stress, neuroinflammation and, finally, neuronal death. In this review, we also discuss some proposed strategies to counteract the detrimental effects of pesticides on Ca²⁺ homeostasis.

Elementary calcium release events in the skeletal muscle cells of the honey bee Apis mellifera

Calcium sparks are involved in major physiological and pathological processes in vertebrate muscles but have never been characterized in invertebrates. Here, dynamic confocal imaging on intact skeletal muscle cells isolated enzymatically from the adult honey bee legs allowed the first spatio-temporal characterization of subcellular calcium release events (CREs) in an insect species. The frequency of CREs, measured in x–y time lapse series, was higher than frequencies usually described in vertebrates. Honey bee CREs had a larger spatial spread at half maximum than their vertebrate counterparts and a slightly ellipsoidal shape, two characteristics that may be related to ultrastructural features specific to invertebrate cells. In line-scan experiments, the histogram of CREs’ duration followed a bimodal distribution, supporting the existence of both sparks and embers. Unlike in vertebrates, embers and sparks had similar amplitudes, a difference that could be related to genomic differences and/or excitation–contraction coupling specificities in honey bee skeletal muscle fibres. The first characterization of CREs from an arthropod which shows strong genomic, ultrastructural and physiological differences with vertebrates may help in improving the research field of sparkology and more generally the knowledge in invertebrates cell Ca²⁺ homeostasis, eventually leading to a better understanding of their roles and regulations in muscles but also the myotoxicity of new insecticides targeting ryanodine receptors.

A Comparative Perspective on Functionally-Related, Intracellular Calcium Channels: The Insect Ryanodine and Inositol 1,4,5-Trisphosphate Receptors

Calcium (Ca²⁺) homeostasis is vital for insect development and metabolism, and the endoplasmic reticulum (ER) is a major intracellular reservoir for Ca²⁺. The inositol 1,4,5- triphosphate receptor (IP₃R) and ryanodine receptor (RyR) are large homotetrameric channels associated with the ER and serve as two major actors in ER-derived Ca²⁺ supply. Most of the knowledge on these receptors derives from mammalian systems that possess three genes for each receptor. These studies have inspired work on synonymous receptors in insects, which encode a single IP₃R and RyR. In the current review, we focus on a fundamental, common question: “why do insect cells possess two Ca²⁺ channel receptors in the ER?”. Through a comparative approach, this review covers the discovery of RyRs and IP₃Rs, examines their structures/functions, the pathways that they interact with, and their potential as target sites in pest control. Although insects RyRs and IP₃Rs share structural similarities, they are phylogenetically distinct, have their own structural organization, regulatory mechanisms, and expression patterns, which explains their functional distinction. Nevertheless, both have great potential as target sites in pest control, with RyRs currently being targeted by commercial insecticide, the diamides.

Toxicity, residue and risk assessment of tetraniliprole in soil-earthworm microcosms

Maize seed treatment with chemicals to control underground pests is a common agricultural practice, but inappropriate use of insecticides poses a considerable threat to plant development and soil nontarget organisms. In this study, the availability of tetraniliprole seed dressing to control the black cutworm Agrotis ipsilon (Lepidoptera: Noctuidae) in the maize seeding stage and its safety to earthworms (Eisenia fetida) were investigated. The selective toxicity (ST) of tetraniliprole between E. fetida and A. ipsilon was greater than 4000. No significant adverse effect of tetraniliprole seed treatment on the germination of maize seeds was observed at concentrations of 2.4-9.6 g a.i. /kg seed. Compared with the untreated control, seed treatment with tetraniliprole at 9.6 g a.i. /kg seed greatly reduced the percentage of damaged plants from 88.73% to 26.67%, and achieved the highest control effect of 69.91%. Tetraniliprole of 2.4 g a.i. /kg seed can effectively inhibit A. ipsilon until 14 days after seed germination, with the lowest mortality rate of 44.44%. During the entire exposure period, the maximum residual concentration of tetraniliprole detected in the soil (5.86 mg/kg) was considerably lower than the LC₅₀ value of tetraniliprole to E. fetida (>4000 mg/kg). According to the low-tier risk assessment, the highest risk quotient (RQ) of tetraniliprole seed treatment to earthworms at test concentrations was 2.8 × 10^-3, which was evaluated as acceptable. This study provided data support for tetraniliprole seed treatment to control underground pests in maize fields.

Determination of 12 insect growth regulator residues in foods of different matrixes by modified QuEChERS and UPLC-MS/MS

An analytical method was developed and validated for the simultaneous determination of 12 insect growth regulators (IGRs) (buprofezin, cyantraniliprole, flubendiamide, flonicamid, tolfenpyrad, chlorantraniliprole, RH-5849, methoxyfenozide, chromafenozide, tebufenozide, pyriproxyfen and fenoxycarb) in foods collected from different matrixes by modified QuEChERS and ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The samples were ultrasonically extracted with acetonitrile containing 0.5% formic acid, and different QuEChERS purification conditions were optimized for different matrixes (vegetable oil, fruit and tea). 12 IGRs were separated on a Plus C18 column, and detected by MS/MS under multiple reaction monitoring (MRM) mode. The developed method was validated in terms of linearity, matrix effect, accuracy and precision. Acceptable recoveries of IGRs in three different substrates (vegetable oil, tea and fruit) at three spiked levels were in the range of 65.47-95.17%, 80.55-110.15%, and 62.02-96.50%, respectively, with RSDs less than 11.58%. The method showed a good linearity (R 2 ≥ 0.9994) for all analytes in the range of 0.2-200 μg L-1. The LODs (S/N = 3) and LOQs (S/N = 10) of the method were 0.04-0.40 μg kg-1, and 0.13-1.24 μg kg-1, respectively. Owing to the advantages of simple operation, high accuracy and sensitivity, this method is suitable for the rapid and simultaneous detection of 12 IGRs in vegetable oil, tea and fruit.