The neonicotinoid insecticide imidacloprid, but not salinity, impacts the immune system of Sydney rock oyster, Saccostrea glomerata

Integration of transcriptome, gut microbiota, and physiology reveals toxic responses of the red claw crayfish (Cherax quadricarinatus) to imidacloprid

Imidacloprid enters the water environment through rainfall and causes harm to aquatic crustaceans. However, the potential chronic toxicity mechanism of imidacloprid in crayfish has not been comprehensively studied. In this study, red claw crayfish (Cherax quadricarinatus) were exposed to 11.76, 35.27, or 88.17 μg/L imidacloprid for 30 days, and changes in the physiology and biochemistry, gut microbiota, and transcriptome of C. quadricarinatus and the interaction between imidacloprid, gut microbiota, and genes were studied. Imidacloprid induced oxidative stress and decreased growth performance in crayfish. Imidacloprid exposure caused hepatopancreas damage and decreased serum immune enzyme activity. Hepatopancreatic and plasma acetylcholine decreased significantly in the 88.17 μg/L group. Imidacloprid reduced the diversity of the intestinal flora, increased the abundance of harmful flora, and disrupted the microbiota function. Transcriptomic analysis showed that the number of up-and-down-regulated differentially expressed genes (DEGs) increased significantly with increasing concentrations of imidacloprid. DEG enrichment analyses indicated that imidacloprid inhibits neurotransmitter transduction and immune responses and disrupts energy metabolic processes. Crayfish could alleviate imidacloprid stress by regulating antioxidant and detoxification-related genes. A high correlation was revealed between GST, HSPA1s, and HSP90 and the composition of gut microorganisms in crayfish under imidacloprid stress. This study highlights the negative effects and provides detailed sequencing data from transcriptome and gut microbiota to enhance our understanding of the molecular toxicity of imidacloprid in crustaceans.

Resveratrol alleviates imidacloprid-induced mitochondrial apoptosis, necroptosis, and immune dysfunction in chicken lymphocyte lines by inhibiting the ROS/MAPK signaling pathway

Imidacloprid (IMI) is a neonicotinoid insecticide with the highest global market share, and IMI exposure in the environment can negatively affect many nontarget organisms (a general term for organisms affected by drugs other than target organisms). Resveratrol (RSV), a non-flavonoid polyphenolic organic compound derived from peanuts, grapes, and other plants, has anti-inflammatory and antioxidant effects. It is currently unclear how RSV protects against cell damage caused by IMI. Therefore, we established an experimental model of chicken lymphocyte lines exposed to 110 μg/mL IMI and/or 0.5 μM RSV for 24 h. According to the experimental results, IMI markedly raised intracellular reactive oxygen species levels and diminished the activity of the cellular antioxidant enzymes (CAT, SOD, and GPx), leading to MDA accumulation and decreased T-AOC. JNK, ERK, and P38, the essential components of the mitogen-activated protein kinase (MAPK) signaling pathway, were also expressed more when IMI was present. Additionally, IMI resulted in upregulation of mitochondrial apoptosis (Caspase 3, Caspase 9, Bax, and Cyt-c) and necroptosis (Caspase 8, RIPK1, RIPK3, and MLKL) related factors expression, downregulation of Bcl-2 expression, induction of upregulation of cytokine IL-6 and TNF-α expression, and downregulation of IFN-γ expression. The combined treatment of RSV and IMI significantly reduced cellular oxidative stress levels, inhibited the MAPK signaling pathway, and alleviated IMI-induced mitochondrial apoptosis, necroptosis, and immune dysfunction. To summarize, RSV antagonized IMI-induced mitochondrial apoptosis, necroptosis, and immune dysfunction in chicken lymphocyte lines by inhibiting the ROS/MAPK signaling pathway.

Semi-purified Antimicrobial Proteins from Oyster Hemolymph Inhibit Pneumococcal Infection

Pneumococcal infections caused by Streptococcus pneumoniae are a leading cause of morbidity and mortality globally, particularly among children. The ability of S. pneumoniae to form enduring biofilms makes treatment inherently difficult, and options are further limited by emerging antibiotic resistance. The discovery of new antibiotics, particularly those with antibiofilm activity, is therefore increasingly important. Antimicrobial proteins and peptides (AMPs) from marine invertebrates are recognised as promising pharmacological leads. This study determined the in vitro antibacterial activity of hemolymph and unique protein fractions from an Australian oyster (Saccostrea glomerata) against multi-drug-resistant S. pneumoniae. We developed a successful method for hemolymph extraction and separation into 16 fractions by preparative HPLC. The strongest activity was observed in fraction 7: at 42 µg/mL protein, this fraction was bactericidal to S. pneumoniae and inhibited biofilm formation. Proteomic analysis showed that fraction 7 contained relatively high abundance of carbonic anhydrase, cofilin, cystatin B-like, and gelsolin-like proteins, while surrounding fractions, which showed lower or no antibacterial activity, contained these proteins in lower abundance or not at all. This work supports traditional medicinal uses of oysters and contributes to further research and development of novel hemolymph/AMP-based treatments for pneumococcal infections.

Immunotoxicity of microplastics and polychlorinated biphenyls alone or in combination to Crassostrea gigas

Microplastics (MPs) and polychlorinated biphenyls (PCBs) are pervasive pollutants in the marine environment, exerting adverse effects on marine organisms. While it is suggested that their exposure may compromise the immune responses of marine organisms, the cumulative immunotoxic effects remain uncertain. Additionally, the intricate mechanisms underlying the immunotoxicity of PCBs and MPs in marine organisms are not yet fully comprehended. To illuminate their combined biological impacts, Crassostrea gigas were exposed to 50 μg/L MPs (30-μm porous) alone, as well as 10 or 100 ng/L PCBs individually or in combination with 50 μg/L of MPs for 28 days. Our data demonstrated that oysters treated with the pollutants examined led to decreased total haemocyte count, inhibited phagocytosis of haemocytes, enhanced the intracellular contents of reactive oxygen species, lipid peroxidation and DNA damage, reduced lysozyme concentration and activity, gave rise to superoxide dismutase. Catalaseand glutathione S-transferaseactivity. The expression of three immune-related genes (NF-κB, TNF-α, TLR-6) was drastically suppressed by the PCBs and MPs treatment, while the apoptosis pathway-related genes (BAX and Caspase-3) showed a significant increase. In addition, compared to oysters treated with a single type of pollutant, coexposure to MPs and PCBs exerted more severe adverse impacts on all the parameters investigated, indicating a significant synergistic effect. Therefore, the risk of MPs and PCBs chemicals on marine organisms should be paid more attention.

Aquatic ecological risk assessment of imidacloprid and thiacloprid in an urban river of Qingdao, China

Imidacloprid and thiacloprid, two neonicotinoid insecticides that are extensively used in urban areas, are potentially toxic to non-target aquatic organisms. In this study, the concentrations of imidacloprid and thiacloprid in surface runoff after rainfall were 20.79-43.77 ng/L and 25.13-63.84 ng/L, respectively, whereas the levels for the Licun River were 10.78-41.70 ng/L and 2.66-39.68 ng/L, respectively. The acute and chronic criteria for imidacloprid and thiacloprid are 0.865, 0.006, 0.83, and 0.012 μg/L, respectively. Tiered ecological risk assessments revealed the chronic ecological risks of these micropollutants to local aquatic species. There was a moderate chronic toxicity risk associated with imidacloprid and thiacloprid in the Licun River, and the joint probability curves showed a probability of chronic ecological risk to 5 % of the aquatic organisms at 68 %-97 %. The results provide evidence of urban surface runoff transporting micropollutants from surface into rivers and estuaries, highlighting the ecological risks to aquatic ecosystems.

Acclimation in intertidal animals reduces potential pathogen load and increases survival following a heatwave

Intertidal animals can experience intense heat during a heatwave, leading to mortality. The causes of death for intertidal animals following heatwaves have often been attributed to a breakdown in physiological processes. This, however, contrasts with research in other animals where heatwave mortality is attributed to existing or opportunistic diseases. We acclimated intertidal oysters to four treatment levels, including an antibiotic treatment, and then exposed all treatments to a 50°C heatwave for 2 h, replicating what can be experienced on Australian shorelines. We found that both acclimation and antibiotics increased survival and reduced the presence of potential pathogens. Non-acclimated oysters had a significant shift in their microbiome, with increasing abundances of bacteria from the Vibrio genera, including known potential pathogens. Our results demonstrate that bacterial infection plays a pivotal role in post-heatwave mortality. We anticipate these findings to inform the management of aquaculture and intertidal habitats as climate change intensifies.

Sex-specific alterations in adaptive responses of Chironomus columbiensis triggered by imidacloprid chronic and acute sublethal exposures

The use of imidacloprid is a common pest control practice in the Neotropical region. However, the imidacloprid unintended sublethal effects on Neotropical aquatic non-target arthropods and undesirable consequences for aquatic environments remain unclear. Here, we assessed the susceptibility of Chironomus columbiensis (Diptera: Chironomidae) larvae to the neonicotinoid imidacloprid and evaluated whether sublethal exposure types would trigger sex-dependent adaptive responses (e.g., emergence, body mass, reproduction, wing morphology). We conducted a concentration-mortality curve (96 h of exposure) and established chronic and acute sublethal exposure bioassays. While chronic sublethal exposures consisted of exposing individuals during their entire larval and pupal stages, the acute sublethal exposures represented a single short duration (24 h) exposure episode during either the first or fourth larval instar. Our results revealed that chronic sublethal exposure reduced the body mass of males, while acute sublethal exposures during the first instar resulted in heavier males than those that were not exposed to imidacloprid. Chronic exposure also reduced the reproduction of males and females, while the acute sublethal exposure only affected the reproduction of individuals that were imidacloprid-exposed on their later larval instar. Chronic and acute sublethal exposures did differentially affect the wing properties of C. columbiensis males (e.g., increased size when chronically exposed and highly asymmetric wings when acutely exposed in early larval phase) and females (e.g., highly asymmetric wings when chronically and acutely exposed). Collectively, our findings demonstrated that imidacloprid can cause unintended sublethal effects on C. columbiensis, and those effects are dependent on sex, exposure type, and developmental stage.

Environmental occurrence, toxicity concerns, and biodegradation of neonicotinoid insecticides

Neonicotinoids (NEOs) are fourth generation pesticides, which emerged after organophosphates, pyrethroids, and carbamates and they are widely used in vegetables, fruits, cotton, rice, and other industrial crops to control insect pests. NEOs are considered ideal substitutes for highly toxic pesticides. Multiple studies have reported NEOs have harmful impacts on non-target biological targets, such as bees, aquatic animals, birds, and mammals. Thus, the remediation of neonicotinoid-sullied environments has gradually become a concern. Microbial degradation is a key natural method for eliminating neonicotinoid insecticides, as biodegradation is an effective, practical, and environmentally friendly strategy for the removal of pesticide residues. To date, several neonicotinoid-degrading strains have been isolated from the environment, including Stenotrophomonas maltophilia, Bacillus thuringiensis, Ensifer meliloti, Pseudomonas stutzeri, Variovorax boronicumulans, and Fusarium sp., and their degradation properties have been investigated. Furthermore, the metabolism and degradation pathways of neonicotinoids have been broadly detailed. Imidacloprid can form 6-chloronicotinic acid via the oxidative cleavage of guanidine residues, and it is then finally converted to non-toxic carbon dioxide. Acetamiprid can also be demethylated to remove cyanoimine (=N-CN) to form a less toxic intermediate metabolite. A few studies have discussed the neonicotinoid toxicity and microbial degradation in contaminated environments. This review is focused on providing an in-depth understanding of neonicotinoid toxicity, microbial degradation, catabolic pathways, and information related to the remediation process of NEOs. Future research directions are also proposed to provide a scientific basis for the risk assessment and removal of these pesticides.

Pesticide occurrence in an agriculturally intensive and ecologically important coastal aquatic system in Australia

Coastal agricultural practices are often located in catchments upstream of ecologically important aquatic systems. Here, we investigate the occurrence of pesticides in a coastal creek flowing into a habitat-protected area within the Solitary Islands Marine Park, Australia. Water samples were collected from six sites along a creek transect during three sampling periods. Samples were analysed for 171 pesticide analytes, including organochlorines, organophosphates, herbicides, and fungicides. Five insecticides, two herbicides, and two fungicides were detected. The neonicotinoid imidacloprid was detected at 5 out of 6 sites, with concentrations reaching 294 μg L^-1, the highest yet detected in Australian waterways. The organophosphate insecticide dimethoate was detected at 4 sites, which occurred at the 2nd highest detected concentration in the study (12.8 μg L^-1). The presence of these pesticides in the aquatic environment downstream of horticulture in this and other regions may have serious implications for stream biota and ecologically important marine ecosystems.

Enantioselective bioaccumulation and toxicity of rac-sulfoxaflor in zebrafish (Danio rerio)

Sulfoxaflor is a fourth-generation neonicotinoid insecticide mainly used to control sap-feeding pests. In this study, four stereoisomers of sulfoxaflor were separated using HPLC, and the absolute configurations of three stereoisomers were identified via single-crystal X-ray diffraction. First, the stability and isomerization of the four enantiomers and rac-sulfoxaflor in water and seven organic solvents were investigated. All enantiomers were extremely unstable in water with isomerization rates above 20%. The racemate did not isomerize in any of the solutions and was stable in water (degradation rate less than 7%). Therefore, we studied the acute toxicity, enantioselective behavior, and enzymatic activities of rac-sulfoxaflor in zebrafish. The bioaccumulation experiment demonstrated that the bioconcentration of sulfoxaflor in zebrafish was enantioselective, and the four enantiomers accumulated in zebrafish in the order (+)-2S,3S-sulfoxaflor > (-)-2R,3R-sulfoxaflor > (+)-2R,3S-sulfoxaflor > (-)-2S,3R-sulfoxaflor. The effect of rac-sulfoxaflor on the enzymatic activities of zebrafish showed that superoxide dismutase and glutathione-S-transferase activities and malondialdehyde content were significantly enhanced as compared to those in control, whereas acetylcholinesterase was significantly reduced in the sulfoxaflor exposure treatment (p < 0.05), indicating that sulfoxaflor caused oxidative lesions and induced enzymatic activity in zebrafish. This study provides important information on the enantioselective behavior and toxic effects of sulfoxaflor, which can help assess the potential ecological risk of chiral pesticides to aquatic organisms.

Bivalve Haemocyte Subpopulations: A Review

Bivalve molluscs stand out for their ecological success and their key role in the functioning of aquatic ecosystems, while also constituting a very valuable commercial resource. Both ecological success and production of bivalves depend on their effective immune defence function, in which haemocytes play a central role acting as both the undertaker of the cellular immunity and supplier of the humoral immunity. Bivalves have different types of haemocytes, which perform different functions. Hence, identification of cell subpopulations and their functional characterisation in immune responses is essential to fully understand the immune system in bivalves. Nowadays, there is not a unified nomenclature that applies to all bivalves. Characterisation of bivalve haemocyte subpopulations is often combined with 1) other multiple parameter assays to determine differences between cell types in immune-related physiological activities, such as phagocytosis, oxidative stress and apoptosis; and 2) immune response to different stressors such as pathogens, temperature, acidification and pollution. This review summarises the major and most recent findings in classification and functional characterisation of the main haemocyte types of bivalve molluscs.

Impact of imidacloprid exposure on the biochemical responses, transcriptome, gut microbiota and growth performance of the Pacific white shrimp Litopenaeus vannamei

The widespread use of neonicotinoid insecticides, such as imidacloprid, in agriculture is one of the key factors for the drop in the survival of invertebrates, including decapod crustaceans. However, there is currently a lack of comprehensive studies on the chronic toxicity mechanisms in decapod crustaceans. Here, the concentration-dependent effects of imidacloprid on the physiology and biochemistry, gut microbiota and transcriptome of L. vannamei , and the interaction between imidacloprid, gut microbiota and genes were studied. Imidacloprid caused oxidative stress, leading to reduced growth and to immunity and tissue damage in L. vannamei . Imidacloprid increased the gut pathogenic microbiota abundance and broke the steady state of the gut microbiota interaction network, resulting in microbiota function disorders. Chronic imidacloprid exposure induced overall transcriptome changes in L. vannamei . Specifically, imidacloprid caused a large number of differentially expressed genes (DEGs) to be significantly downregulated. The inhibition of autophagy-related pathways revealed the toxic process of imidacloprid to L. vannamei . The changes in phase I and II detoxification gene expression clarified the formation of a detoxification mechanism in L. vannamei . The disturbance of circadian rhythm (CLOCK) caused by imidacloprid is one of the reasons for the increase in gut pathogenic microbiota abundance.

Marine heatwaves have minimal influence on the quality of adult Sydney rock oyster flesh

Marine heatwaves (MHWs) are impacting marine biodiversity, including fisheries and aquaculture. However, it is largely unknown which species will be able to endure MHWs and at what price. Here, we applied elevated temperature (2 °C above ambient) and two different heatwave scenarios to adults of the economically important Sydney rock oyster (SRO, Saccostrea glomerata), and evaluated the impact on nutritional properties, gene expression profiles and immune health indicators. We found that elevated temperature (23 °C) and a variable heatwave (VHW) during winter caused some significant differences in the micronutrient and trace elements levels in oyster flesh. There was an increase of lead under VHW and a decrease in chromium, barium and aluminium under elevated temperature. Conversely, gene expression profiles and other physiological parameters, including flesh protein, fatty acid profiles and hemocyte numbers, were not affected by MHWs. These results indicate that adult SRO are reasonably resilient, and should continue to provide high-quality seafood, under near-future ocean warming and moderate heatwave scenarios.

Effects of long-term exposure of Mytilus galloprovincialis to thiacloprid: A multibiomarker approach

Thiacloprid is a neonicotinoid insecticide widely exploited in agriculture and easily mobilized towards aquatic environments by atmospheric agents. However, little information about its toxicological effects on aquatic invertebrate bioindicators is available. In this study, specimens of the mussel Mytilus galloprovincialis were exposed to thiacloprid at environmental (4.5 μg L^-1) and 100 times higher than environmental (450 μg L^-1) concentrations for 20 days. Thiacloprid affected haemolymph biochemical parameters, cell viability in the digestive gland, antioxidant biomarkers and lipid peroxidation in the digestive gland and gills at environmentally relevant concentrations (4.5 μg L^-1). In addition, thiacloprid exposure caused histological damage to the digestive gland and gills. Interestingly, the pesticide was detected at levels equal to 0.14 ng g^-1 in the soft tissues of sentinels exposed for 20 days to 450 μg L^-1 thiacloprid in seawaterμ. Due to its harmful potential and cumulative effects after long-term exposure of M. galloprovincialis, thiacloprid may pose a potential risk to nontarget aquatic organisms, as well as to human health. This aspect requires further in-depth investigation.

Physiological Effects of Neonicotinoid Insecticides on Non-Target Aquatic Animals-An Updated Review

In this paper, we review the effects of large-scale neonicotinoid contaminations in the aquatic environment on non-target aquatic invertebrate and vertebrate species. These aquatic species are the fauna widely exposed to environmental changes and chemical accumulation in bodies of water. Neonicotinoids are insecticides that target the nicotinic type acetylcholine receptors (nAChRs) in the central nervous systems (CNS) and are considered selective neurotoxins for insects. However, studies on their physiologic impacts and interactions with non-target species are limited. In researches dedicated to exploring physiologic and toxic outcomes of neonicotinoids, studies relating to the effects on vertebrate species represent a minority case compared to invertebrate species. For aquatic species, the known effects of neonicotinoids are described in the level of organismal, behavioral, genetic and physiologic toxicities. Toxicological studies were reported based on the environment of bodies of water, temperature, salinity and several other factors. There exists a knowledge gap on the relationship between toxicity outcomes to regulatory risk valuation. It has been a general observation among studies that neonicotinoid insecticides demonstrate significant toxicity to an extensive variety of invertebrates. Comprehensive analysis of data points to a generalization that field-realistic and laboratory exposures could result in different or non-comparable results in some cases. Aquatic invertebrates perform important roles in balancing a healthy ecosystem, thus rapid screening strategies are necessary to verify physiologic and toxicological impacts. So far, much of the studies describing field tests on non-target species are inadequate and in many cases, obsolete. Considering the current literature, this review addresses important information gaps relating to the impacts of neonicotinoids on the environment and spring forward policies, avoiding adverse biological and ecological effects on a range of non-target aquatic species which might further impair the whole of the aquatic ecological web.

Contemporary Oyster Reef Restoration: Responding to a Changing World

Globally, there is growing interest in restoring previously widespread oyster reefs to reinstate key ecosystem services such as shoreline protection, fisheries productivity and water filtration. Yet, since peak expiration of oysters in the 1800s, significant and ongoing environmental change has occurred. Estuaries and coasts are undergoing some of the highest rates of urbanization, warming and ocean acidification on the planet, necessitating novel approaches to restoration. Here, we review key design considerations for oyster reef restoration projects that maximize the probability that they will meet biological and socio-economic goals not only under present-day conditions, but into the future. This includes selection of sites, and where required, substrates and oyster species and genotypes for seeding, not only on the basis of their present and future suitability in supporting oyster survival, growth and reproduction, but also based on their match to specific goals of ecosystem service delivery. Based on this review, we provide a road map of design considerations to maximize the success of future restoration projects.

Imidacloprid induces locomotion impairment of the freshwater crayfish, Procambarus clarkii via neurotoxicity and oxidative stress in digestive system

Imidacloprid (IMI) is used in integrated farming like the rice-crayfish co-culture system to prevent water weevil. However, the toxic effect of IMI on the freshwater crayfish Procambarus clarkii is unknown. In the current study, the effects of IMI on the locomotion, antioxidative status, digestion and intestinal microbiota of P. clarkii were investigated. The results showed that IMI caused locomotion impairment with reduced crawl velocity, and attenuated their dark preference, aggressiveness and reversal ability. Inhibited AChE in muscle and hepatopancreas indicates the neurotoxicity of IMI which may directly lead their locomotion dysfunction. The increase of antioxidative enzymes activity and MDA level were found after 25 μg/L and 250 μg/L exposure. Significant up-regulation of several antioxidative and immune-related genes, including CZ-SOD, CAT, GPx, GST, AFL, proPO, HSP27 and HSP70 confirmed that oxidative stress was induced in all treatments when exposed to IMI. In addition, there was significant increase of LDH, indicating the different energy allocation during the exposure. Meanwhile, results from DNA damage analysis showed elevated OTM value and 8-OHdG level in hepatopancretic cells. On the other hand, decreases of alpha-amylase, lipase and increase of trypsin in hepatopancreas was observed at 25 and 250 μg/L. In addition, significant changes of composition of intestinal microbiota at both phylum and genus levels were observed according to the 16S rRNA sequencing results. Increase of pathogenic genera and decrease of beneficial bacterial communities revealed the disequilibrium of intestinal flora of crayfish. In summary, results in the present study suggest that IMI at environmentally realistic concentration could induce AChE inhibition and oxidative stress, conjointly leading the locomotion impairment in crayfish. IMI also affected the digestive functions by enzymes inhibition and gut microbiota dysbiosis.

Sonochemical degradation of neonicotinoid pesticides in natural surface waters. Influence of operational and environmental conditions

Neonicotinoids sonochemical oxidation at high-frequency ultrasound (MHz range) has been carried out in ultrapure and natural surface-water matrices (river, reservoir and wastewater treatment plant effluent). To evaluate the influence of the operating variables, that is initial pollutant concentration, ultrasound frequency, ultrasound power, and pulse-stop time a Box-Behnken experimental design was planned. Optimal results were obtained using a frequency of 578 kHz, a power of 40 W L^-1, with a pollutant concentration of 1 μM (for each pesticide), and using a pulse-stop time of 100 ms. The experimental data adjustment using the Langmuir-Hinshelwood heterogeneous kinetic model showed that neonicotinoids oxidation was carried out in the bubble-liquid interface by the attack of hydroxyl radicals. Experiments performed in the presence of radical scavengers, that is, methanol, ethanol and tert-butyl alcohol corroborated this reaction mechanism. The influence of some environmental conditions such as pH, presence of soluble inorganic species (Cl^-, SO₄^2-, NO₃^-, HPO₄^2-, HCO₃^-) and soluble organic species (humic acids content) were established. Finally, the aqueous matrix's influence was investigated for three natural surface water cases, and the results were rationalized according to the main water physicochemical characteristics.

Comparison of imidacloprid, propiconazole, and nanopropiconazole effects on the development, behavior, and gene expression biomarkers of the Pacific oyster (Magallana gigas)

Coastal areas are final recipients of various contaminants including pesticides. The effects of pesticides on non-target organisms are often unclear, especially at environmentally relevant concentrations. This study investigated the impacts of insecticide imidacloprid (IMI) and fungicide propiconazole (PRO), some of the most detected pesticides in the Arcachon Bay in France. This work also included the research of propiconazole nanoformulation (nanoPRO). The effects were assessed studying the development of the early life stages of the Pacific oyster (Magallana gigas). Oyster embryos were exposed for 24, 30, and 42 h (depending on the endpoint) at 24 °C to environmentally relevant concentrations of the two pesticides as well as to nanoPRO. The research focused on sublethal endpoints such as the presence of developmental malformations, alterations of locomotion patterns, or changes in the gene expression levels. No developmental abnormalities were observed after exposure to environmental concentrations detected in the Arcachon Bay in recent years (maximal detected concentration of IMI and PRO were 174 ng/L and 29 ng/L, respectively). EC₅₀ of PRO and nanoPRO were comparable, 2.93 ± 1.35 and 2.26 ± 1.36 mg/L, while EC₅₀ of IMI exceeded 200 mg/L. IMI did not affect larval behavior. PRO affected larval movement trajectory and decreased average larvae swimming speed (2 μg/L), while nanoPRO increased the maximal larvae swimming speed (0.02 μg/L). PRO upregulated especially genes linked to reactive oxygen species (ROS) production and detoxification. NanoPRO effects on gene expression were less pronounced - half of the genes were altered in comparison with PRO. IMI induced a strong dose-response impact on the genes linked to the detoxification, ROS production, cell cycle, and apoptosis regulation. In conclusion, our results suggest that current pesticide concentrations detected in the Arcachon Bay are safe for the Pacific oyster early development, but they might have a small direct effect via altered gene expressions, whose longer-term impacts cannot be ruled out.

Immunological Responses of Marine Bivalves to Contaminant Exposure: Contribution of the -Omics Approach

The increasing number of data studies on the biological impact of anthropogenic chemicals in the marine environment, together with the great development of invertebrate immunology, has identified marine bivalves as a key invertebrate group for studies on immunological responses to pollutant exposure. Available data on the effects of contaminants on bivalve immunity, evaluated with different functional and molecular endpoints, underline that individual functional parameters (cellular or humoral) and the expression of selected immune-related genes can distinctly react to different chemicals depending on the conditions of exposure. Therefore, the measurement of a suite of immune biomarkers in hemocytes and hemolymph is needed for the correct evaluation of the overall impact of contaminant exposure on the organism's immunocompetence. Recent advances in -omics technologies are revealing the complexity of the molecular players in the immune response of different bivalve species. Although different -omics represent extremely powerful tools in understanding the impact of pollutants on a key physiological function such as immune defense, the -omics approach has only been utilized in this area of investigation in the last few years. In this work, available information obtained from the application of -omics to evaluate the effects of pollutants on bivalve immunity is summarized. The data shows that the overall knowledge on this subject is still quite limited and that to understand the environmental relevance of any change in immune homeostasis induced by exposure to contaminants, a combination of both functional assays and cutting-edge technology (transcriptomics, proteomics, and metabolomics) is required. In addition, the utilization of metagenomics may explain how the complex interplay between the immune system of bivalves and its associated bacterial communities can be modulated by pollutants, and how this may in turn affect homeostatic processes of the host, host–pathogen interactions, and the increased susceptibility to disease. Integrating different approaches will contribute to knowledge on the mechanism responsible for immune dysfunction induced by pollutants in ecologically and economically relevant bivalve species and further explain their sensitivity to multiple stressors, thus resulting in health or disease.

Dynamic changes of transcriptome of fifth-instar spodoptera litura larvae in response to insecticide

Spodoptera litura is a major insect with a cosmopolitan distribution and strong resistance to multiple insecticides. Determining the molecular basis and key candidate genes of the insecticide resistance of S. litura may help in managing this insect. In this study, fifth-instar S. litura larvae were subjected to transcriptome analysis at 6, 12, 24, 48, and 72 h after feeding on an LC20 dose of avermectin. The result showed that genes responding to avermectin changed dynamically with different gene counts and resistance mechanisms at the fifth instar based on a metabolic pathway map. These responses included degrading the insecticide by a series of P450 and glutathione-S-transferase enzymes starting at the 12 h time point, with subsequent increases in the number of genes involved and shifts to TOLL and immune deficiency (IMD) pathways at 48 h after feeding the insecticide. Weighted correlation network analysis (WGCNA) determined a co-expression module related to the avermectin response at 12 and 24 h (r = 0.403, p = 0.0371; r = 0.436, p = 0.023), in which a hub gene (LOC111358940) related to metalloproteinase activity was identified. In addition, Analysis of the genes in the co-expression module further revealed that eight genes encoding UDP-glucuronosyltransferases were directly associated with insecticide response in S. litura. These results provide better understanding of the avermectin response mechanism of S. litura and may be useful in developing improved control strategies for this species.

SUPPLEMENTARY INFORMATION

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Impacts of Neonicotinoids on Molluscs: What We Know and What We Need to Know

The broad utilisation of neonicotinoids in agriculture has led to the unplanned contamination of adjacent terrestrial and aquatic systems around the world. Environmental monitoring regularly detects neonicotinoids at concentrations that may cause negative impacts on molluscs. The toxicity of neonicotinoids to some non-target invertebrates has been established; however, information on mollusc species is limited. Molluscs are likely to be exposed to various concentrations of neonicotinoids in the soil, food and water, which could increase their vulnerability to other sources of mortality and cause accidental exposure of other organisms higher in the food chain. This review examines the impacts of various concentrations of neonicotinoids on molluscs, including behavioural, physiological and biochemical responses. The review also identifies knowledge gaps and provides recommendations for future studies, to ensure a more comprehensive understanding of impacts from neonicotinoid exposure to molluscs.