Neonicotinoid-containing insecticide disruption of growth, locomotion, and fertility in Caenorhabditis elegans

Impacts of neonicotinoids on biodiversity: a critical review

Neonicotinoids are the most widely used class of insecticides in the world, but they have raised numerous concerns regarding their effects on biodiversity. Thus, the objective of this work was to do a critical review of the contamination of the environment (soil, water, air, biota) by neonicotinoids (acetamiprid, clothianidin, imidacloprid, thiacloprid, thiamethoxam) and of their impacts on terrestrial and aquatic biodiversity. Neonicotinoids are very frequently detected in soils and in freshwater, and they are also found in the air. They have only been recently monitored in coastal and marine environments, but some studies already reported the presence of imidacloprid and thiamethoxam in transitional or semi-enclosed ecosystems (lagoons, bays, and estuaries). The contamination of the environment leads to the exposure and to the contamination of non-target organisms and to negative effects on biodiversity. Direct impacts of neonicotinoids are mainly reported on terrestrial invertebrates (e.g., pollinators, natural enemies, earthworms) and vertebrates (e.g., birds) and on aquatic invertebrates (e.g., arthropods). Impacts on aquatic vertebrate populations and communities, as well as on microorganisms, are less documented. In addition to their toxicity to directly exposed organisms, neonicotinoid induce indirect effects via trophic cascades as demonstrated in several species (terrestrial and aquatic invertebrates). However, more data are needed to reach firmer conclusions and to get a clearer picture of such indirect effects. Finally, we identified specific knowledge gaps that need to be filled to better understand the effects of neonicotinoids on terrestrial, freshwater, and marine organisms, as well as on ecosystem services associated with these biotas.

Mitochondria in the Spotlight: C. elegans as a Model Organism to Evaluate Xenobiotic-Induced Dysfunction

Mitochondria play a crucial role in cellular respiration, ATP production, and the regulation of various cellular processes. Mitochondrial dysfunctions have been directly linked to pathophysiological conditions, making them a significant target of interest in toxicological research. In recent years, there has been a growing need to understand the intricate effects of xenobiotics on human health, necessitating the use of effective scientific research tools. Caenorhabditis elegans (C. elegans), a nonpathogenic nematode, has emerged as a powerful tool for investigating toxic mechanisms and mitochondrial dysfunction. With remarkable genetic homology to mammals, C. elegans has been used in studies to elucidate the impact of contaminants and drugs on mitochondrial function. This review focuses on the effects of several toxic metals and metalloids, drugs of abuse and pesticides on mitochondria, highlighting the utility of C. elegans as a model organism to investigate mitochondrial dysfunction induced by xenobiotics. Mitochondrial structure, function, and dynamics are discussed, emphasizing their essential role in cellular viability and the regulation of processes such as autophagy, apoptosis, and calcium homeostasis. Additionally, specific toxins and toxicants, such as arsenic, cadmium, and manganese are examined in the context of their impact on mitochondrial function and the utility of C. elegans in elucidating the underlying mechanisms. Furthermore, we demonstrate the utilization of C. elegans as an experimental model providing a promising platform for investigating the intricate relationships between xenobiotics and mitochondrial dysfunction. This knowledge could contribute to the development of strategies to mitigate the adverse effects of contaminants and drugs of abuse, ultimately enhancing our understanding of these complex processes and promoting human health.

Soil microbial gene expression in an agricultural ecosystem varies with time and neonicotinoid seed treatments

Neonicotinoids, a class of systemic insecticides, have been widely used for decades against various insect pests. Previous studies have reported non-target effects of neonicotinoids on some beneficial macro- and micro-organisms. Considering the crucial role the soil microbiota plays in sustaining soil fertility, it is critical to understand how neonicotinoid exposure affects the microbial taxonomic composition and gene expression. However, most studies to date have evaluated soil microbial taxonomic compositions or assessed microbial functions based on soil biochemical analysis. In this study, we have applied a metatranscriptomic approach to quantify the variability in soil microbial gene expression in a 2 year soybean/corn crop rotation in Quebec, Canada. We identified weak and temporally inconsistent effects of neonicotinoid application on soil microbial gene expression, as well as a strong temporal variation in soil microbial gene expression among months and years. Neonicotinoid seed treatment altered the expression of a small number of microbial genes, including genes associated with heat shock proteins, regulatory functions, metabolic processes and DNA repair. These changes in gene expression varied during the growing season and between years. Overall, the composition of soil microbial expressed genes seems to be more resilient and less affected by neonicotinoid application than soil microbial taxonomic composition. Our study is among the first to document the effects of neonicotinoid seed treatment on microbial gene expression and highlights the strong temporal variability of soil microbial gene expression and its responses to neonicotinoid seed treatments.

Peripheral neuropathy, protein aggregation and serotonergic neurotransmission: Distinctive bio-interactions of thiacloprid and thiamethoxam in the nematode Caenorhabditis elegans

Due to worldwide production, sales and application, neonicotinoids dominate the global use of insecticides. While, neonicotinoids are considered as pinpoint neurotoxicants that impair cholinergic neurotransmission in pest insects, the sublethal effects on nontarget organisms and other neurotransmitters remain poorly understood. Thus, we investigated long-term neurological outcomes in the decomposer nematode Caenorhabditis elegans. In the adult roundworm the neonicotinoid thiacloprid impaired serotonergic and dopaminergic neuromuscular behaviors, while respective exposures to thiamethoxam showed no effects. Thiacloprid caused a concentration-dependent delay of the transition between swimming and crawling locomotion that is controlled by dopaminergic and serotonergic neurotransmission. Age-resolved analyses revealed that impairment of locomotion occurred in young as well as middle-aged worms. Treatment with exogenous serotonin rescued thiacloprid-induced swimming deficits in young worms, whereas additional exposure with silica nanoparticles enhanced the reduction of swimming behavior. Delay of forward locomotion was partly caused by a new paralysis pattern that identified thiacloprid as an agent promoting a specific rigidity of posterior body wall muscle cells and peripheral neuropathy in the nematode (lowest-observed-effect-level 10 ng/ml). On the molecular level exposure with thiacloprid accelerated protein aggregation in body wall muscle cells of polyglutamine disease reporter worms indicating proteotoxic stress. The results from the soil nematode Caenorhabditis elegans show that assessment of neurotoxicity by neonicotinoids requires acknowledgment and deeper research into dopaminergic and serotonergic neurochemistry of nontarget organisms. Likewise, it has to be considered more that different neonicotinoids may promote diverse neural end points.

Review of the toxicity and potential molecular mechanisms of parental or successive exposure to environmental pollutants in the model organism Caenorhabditis elegans

Environmental pollutants such as heavy metals, nano/microparticles, and organic compounds have been detected in a wide range of environmental media, causing long-term exposure in various organisms and even humans through breathing, contacting, ingestion, and other routes. Long-term exposure to environmental pollutants in organisms or humans promotes exposure of offspring to parental and environmental pollutants, and subsequently results in multiple biological defects in the offspring. This review dialectically summarizes and discusses the existing studies using Caenorhabditis elegans (C. elegans) as a model organism to explore the multi/transgenerational toxicity and potential underlying molecular mechanisms induced by environmental pollutants following parental or successive exposure patterns. Parental and successive exposure to environmental pollutants induces various biological defects in C. elegans across multiple generations, including multi/transgenerational developmental toxicity, neurotoxicity, reproductive toxicity, and metabolic disturbances, which may be transmitted to progeny through reactive oxygen species-induced damage, epigenetic mechanisms, insulin/insulin-like growth factor-1 signaling pathway. This review aims to arouse researchers' interest in the multi/transgenerational toxicity of pollutants and hopes to explore the possible long-term effects of environmental pollutants on organisms and even humans, as well as to provide constructive suggestions for the safety and management of emerging alternatives.

Contact exposure to neonicotinoid insecticides temporarily suppresses the locomotor activity of Pardosa lugubris agrobiont wolf spiders

Exposure to numerous chemicals disrupts the spiders' locomotion. Spiders, particularly epigeic spiders, are dependent on their locomotory activities to search for prey, hide from their enemies, and perform sexual reproduction and subsequent parental care. Among the best-known compounds that inhibit the locomotion of arthropods are neonicotinoids. Despite spiders are less affected by the neonicotinoids than insects due to the sequence differences in their acetylcholine receptors, they are not resistant to these compounds. We hypothesized that acute exposure to a broad spectrum of neonicotinoids suppresses the traveled distance, mean velocity, and maximum velocity in epigeic spiders. As a model species, we used adults of Pardosa lugubris. We tested commercial formulations of thiamethoxam, acetamiprid, and thiacloprid. We tested each of the neonicotinoids in the maximum and minimum concentrations recommended for foliar applications. We applied them under controlled conditions dorsally by spraying them directly on the spiders or exposing the spiders to the tarsal contact with neonicotinoid residues. Control groups consisted of 31 individuals; treated groups consisted of 10–21 individuals. We found that a broad spectrum of neonicotinoids temporarily suppresses the traveled distance in epigeic spiders. At 1 h after application, all the three tested neonicotinoid insecticides induced declines in the traveled distance, but this effect mostly disappeared when tested at 24 h after the application. The decrease in the traveled distance was associated with substantial temporary decreases in the mean and maximum velocities. Despite differences among modalities, all three insecticides caused multiple adverse effects on the locomotory parameters in any tested concentrations. It remains to test what would be the lowest safe concentration for the chronic exposure to neonicotinoids in epigeic spiders.

Low Doses of Imidacloprid Induce Oxidative Stress and Neural Cell Disruption in Earthworm <i>Eisenia fetida</i>

Imidacloprid is a widely used pesticide that belongs to the class of neonicotinoids. There is a piece of rising evidence that neonicotinoids exert cytotoxic effects in non-target organisms including vertebrate species such as mammals. Nevertheless, dose-limiting toxicity and molecular mechanisms of neonicotinoids' deleterious effects are still poorly understood. In accord to imidacloprid fate in the environment, the most of used pesticide is absorbed in the soil. Therefore, earthworms, which are prevailing soil organisms, could be considered as a target of neonicotinoids toxicity. The earthworm’s simple nervous system is a prospective model for neurotoxicological studies. We exposed earthworms to imidacloprid in a paper contact test with a doses range of 0.1‑0.4 µg/cm2 for 14 days. In the present work, we studied the imidacloprid effect on oxidative stress generation and neuronal marker neuron-specific enolase (NSE) expression. The exposure to imidacloprid induced a dose-dependent decrease in NSE. Both reactive oxygen species production and lipid peroxidation level were upregulated as well. Observed NSE decline suggests imidacloprid-caused disturbance in earthworm neuron cells. Obtained data have shown that relatively low doses of imidacloprid are potent to induce cytotoxicity in neurons. Furthermore, neurotoxicity could be recognized as one of an individual scenario of the general imidacloprid toxicity. Thus, presented results suggest the cytotoxicity of imidacloprid low doses in non-target organisms and hypothesize that NSE downregulation could be estimated as a biomarker of neonicotinoid cytotoxicity in a nervous system of non-insect species.

Low Doses of Imidacloprid Induce Oxidative Stress and Neural Cell Disruption in Earthworm <i>Eisenia fetida</i>

Imidacloprid is a widely used pesticide that belongs to the class of neonicotinoids. There is a piece of rising evidence that neonicotinoids exert cytotoxic effects in non-target organisms including vertebrate species such as mammals. Nevertheless, dose-limiting toxicity and molecular mechanisms of neonicotinoids' deleterious effects are still poorly understood. In accord to imidacloprid fate in the environment, the most of used pesticide is absorbed in the soil. Therefore, earthworms, which are prevailing soil organisms, could be considered as a target of neonicotinoids toxicity. The earthworm’s simple nervous system is a prospective model for neurotoxicological studies. We exposed earthworms to imidacloprid in a paper contact test with a doses range of 0.1‑0.4 µg/cm2 for 14 days. In the present work, we studied the imidacloprid effect on oxidative stress generation and neuronal marker neuron-specific enolase (NSE) expression. The exposure to imidacloprid induced a dose-dependent decrease in NSE. Both reactive oxygen species production and lipid peroxidation level were upregulated as well. Observed NSE decline suggests imidacloprid-caused disturbance in earthworm neuron cells. Obtained data have shown that relatively low doses of imidacloprid are potent to induce cytotoxicity in neurons. Furthermore, neurotoxicity could be recognized as one of an individual scenario of the general imidacloprid toxicity. Thus, presented results suggest the cytotoxicity of imidacloprid low doses in non-target organisms and hypothesize that NSE downregulation could be estimated as a biomarker of neonicotinoid cytotoxicity in a nervous system of non-insect species.

Effects of essential oil components exposure on biological parameters of Caenorhabditis elegans

The extensive use of essential oil components in an increasing number of applications can substantially enhance exposure to these compounds, which leads to potential health and environmental hazards. This work aimed to evaluate the toxicity of four widely used essential oil components (carvacrol, eugenol, thymol, vanillin) using the in vivo model Caenorhabditis elegans. For this purpose, the LC₅₀ value of acute exposure to these components was first established; then the effect of sublethal concentrations on nematodes' locomotion behaviour, reproduction, heat and oxidative stress resistance and chemotaxis was evaluated. The results showed that all the components had a concentration-dependent effect on nematode survival at moderate to high concentrations. Carvacrol and thymol were the two most toxic compounds, while vanillin had the mildest toxicological effect. Reproduction resulted in a more sensitive endpoint than lethality to evaluate toxicity. Only pre-exposure to carvacrol and eugenol at the highest tested sublethal concentrations conferred worms oxidative stress resistance. However, at these and lower concentrations, both components induced reproductive toxicity. Our results evidence that these compounds can be toxic at lower doses than those required for their biological action. These findings highlight the need for a specific toxicological assessment of every EOC application.

Insect Epigenetic Mechanisms Facing Anthropogenic-Derived Contamination, an Overview

Currently, the human species has been recognized as the primary species responsible for Earth's biodiversity decline. Contamination by different chemical compounds, such as pesticides, is among the main causes of population decreases and species extinction. Insects are key for ecosystem maintenance; unfortunately, their populations are being drastically affected by human-derived disturbances. Pesticides, applied in agricultural and urban environments, are capable of polluting soil and water sources, reaching non-target organisms (native and introduced). Pesticides alter insect's development, physiology, and inheritance. Recently, a link between pesticide effects on insects and their epigenetic molecular mechanisms (EMMs) has been demonstrated. EMMs are capable of regulating gene expression without modifying genetic sequences, resulting in the expression of different stress responses as well as compensatory mechanisms. In this work, we review the main anthropogenic contaminants capable of affecting insect biology and of triggering EMMs. EMMs are involved in the development of several diseases in native insects affected by pesticides (e.g., anomalous teratogenic reactions). Additionally, EMMs also may allow for the survival of some species (mainly pests) under contamination-derived habitats; this may lead to biodiversity decline and further biotic homogenization. We illustrate these patterns by reviewing the effect of neonicotinoid insecticides, insect EMMs, and their ecological consequences.

Nicotinic receptor targeting in physiological and environmental vulnerability: A whole of biosphere perspective

We propose a biosphere model of convergent interactions between nicotine and neonicotinoids (neonics) within a related framework of nicotinic receptor targeting agents (NrTA) across the globe. We explore how rising global trends in the use nicotine as well as neonics impacts vulnerability, within and across species, and posit that evolutionary conservation at the nicotinic acetylcholine receptor (nAChR) provides an operational strategy map for pathogens and disease. Furthermore, we examine the effects of NrTA exposure on balance within extant and developing ecological niches, food chains, and human societies. We advocate for a global strategy for biomonitoring across agriculture, wildlife, and human centers. Such a strategy would relate emergent pathogenic and infectious diseases, amongst others, along a tractable biological stress pathway. This new framework aims to better prepare society in the face of emergent pandemics through 1. identifying primary chemical drivers that can impact emergent diseases; 2. outlining data-driven strategy options for health and environmental policy decision makers.