Neonicotinoids disrupt memory, circadian behaviour and sleep

Exposure to neonicotinoid pesticides induces physiological disorders and affects color performance and foraging behavior in goldfish

We investigated the effects of neonicotinoid pesticides (NEOs) on the spontaneous swimming and foraging behavior, as well as the morphological and physiological changes of goldfish. Most fish reared in thiamethoxam (THM)-sprayed rice fields showed the scales easily peeled off, and increased ascites. Some individuals showed decreased bio-defense activity and low plasma Ca2+. Similar changes were found in the exposure test to THM (1.0 and 20.0 μg/L) and dinotefuran (1.2 and 23.5 μg/L). Next, the effects of a low concentration of THM (1.0 μg/L) on the spontaneous swimming and foraging behavior of fish were examined. Fish exposed to THM for 1 week became restless and had increased the swimming performance, especially under natural light, white LED lighting and blue LED lighting. Goldfish exposed to THM had also increased intake of shiny white beads under green LED illumination. These results indicate that the exposure to NEO, even for a short period and at low levels, not only suppressed bio-defense activities and metabolic abnormalities, but also stress response, the swimming and foraging behavior of the fish are likely to be significantly suffered.

Avian migration clocks in a changing world

Avian long-distance migration requires refined programming to orchestrate the birds' movements on annual temporal and continental spatial scales. Programming is particularly important as long-distance movements typically anticipate future environmental conditions. Hence, migration has long been of particular interest in chronobiology. Captivity studies using a proxy, the shift to nocturnality during migration seasons (i.e., migratory restlessness), have revealed circannual and circadian regulation, as well as an innate sense of direction. Thanks to rapid development of tracking technology, detailed information from free-flying birds, including annual-cycle data and actograms, now allows relating this mechanistic background to behaviour in the wild. Likewise, genomic approaches begin to unravel the many physiological pathways that contribute to migration. Despite these advances, it is still unclear how migration programmes are integrated with specific environmental conditions experienced during the journey. Such knowledge is imminently important as temporal environments undergo rapid anthropogenic modification. Migratory birds as a group are not dealing well with the changes, yet some species show remarkable adjustments at behavioural and genetic levels. Integrated research programmes and interdisciplinary collaborations are needed to understand the range of responses of migratory birds to environmental change, and more broadly, the functioning of timing programmes under natural conditions.

Unravelling nicotinic receptor and ligand features underlying neonicotinoid knockdown actions on the malaria vector mosquito Anopheles gambiae

With the spread of resistance to long-established insecticides targeting Anopheles malaria vectors, understanding the actions of compounds newly identified for vector control is essential. With new commercial vector-control products containing neonicotinoids under development, we investigate the actions of 6 neonicotinoids (imidacloprid, thiacloprid, clothianidin, dinotefuran, nitenpyram and acetamiprid) on 13 Anopheles gambiae nicotinic acetylcholine receptor (nAChR) subtypes produced by expression of combinations of the Agα1, Agα2, Agα3, Agα8 and Agβ1 subunits in Xenopus laevis oocytes, the Drosophila melanogaster orthologues of which we have previously shown to be important in neonicotinoid actions. The presence of the Agα2 subunit reduces neonicotinoid affinity for the mosquito nAChRs, whereas the Agα3 subunit increases it. Crystal structures of the acetylcholine binding protein (AChBP), an established surrogate for the ligand-binding domain, with dinotefuran bound, shows a unique target site interaction through hydrogen bond formation and CH-N interaction at the tetrahydrofuran ring. This is of interest as dinotefuran is also under trial as the toxic element in baited traps. Multiple regression analyses show a correlation between the efficacy of neonicotinoids for the Agα1/Agα2/Agα8/Agβ1 nAChR, their hydrophobicity and their rate of knockdown of adult female An. gambiae, providing new insights into neonicotinoid features important for malaria vector control.

Dinotefuran exposure alters biochemical, metabolomic, gut microbiome, and growth responses in decapoda pacific white shrimp Penaeus vannamei

Dinotefuran, a neonicotinoid insecticide, may impact nontarget organisms such as Decapoda P. vannamei shrimp with nervous systems similar to insects. Exposing shrimp to low dinotefuran concentrations (6, 60, and 600 μg/L) for 21 days affected growth, hepatosomatic index, and survival. Biomarkers erythromycin-N-demethylase, alanine aminotransferase, and catalase increased in all exposed groups, while glutathione S-transferase is the opposite; aminopyrin-N-demethylase, malondialdehyde, and aspartate aminotransferase increased at 60 and 600 μg/L. Concentration-dependent effects on gut microbiota altered the abundance of bacterial groups, increased potentially pathogenic and oxidative stress-resistant phenotypes, and decreased biofilm formation. Gram-positive/negative microbiota changed significantly. Metabolite differences between the exposed and control groups were identified using mass spectrometry and KEGG pathway enrichment. N-acetylcystathionine showed potential as a reliable dinotefuran metabolic marker. Weighted correlation network analysis (WGCNA) results indicated high connectivity of cruecdysone in the metabolite network and significant enrichment at 600 μg/L dinotefuran. The WGCNA results revealed a highly significant negative correlation between two key metabolites, caldine and indican, and the gut microbiota within co-expression modules. Overall, the risk of dinotefuran exposure to non-target organisms in aquatic environments still requires further attention.

Critical roles of nicotinic acetylcholine receptors in olfactory memory formation and retrieval in crickets

Acetylcholine (ACh) is a major excitatory neurotransmitter in the insect central nervous system, and insect neurons express several types of ACh receptors (AChRs). AChRs are classified into two subgroups, muscarinic AChRs and nicotinic AChRs (nAChRs). nAChRs are also divided into two subgroups by sensitivity to α-bungarotoxin (α-BGT). The cricket Gryllus bimaculatus is one of the useful insects for studying the molecular mechanisms in olfactory learning and memory. However, the roles of nAChRs in olfactory learning and memory of the cricket are still unknown. In the present study, to investigate whether nAChRs are involved in cricket olfactory learning and memory, we tested the effects of two different AChR antagonists on long-term memory (LTM) formation and retrieval in a behavioral assay. The two AChR antagonists that we used are mecamylamine (MEC), an α-BGT-insensitive nAChR antagonist, and methyllycaconitine (MLA), an α-BGT-sensitive nAChR antagonist. In crickets, multiple-trial olfactory conditioning induced 1-day memory (LTM), whereas single-trial olfactory conditioning induced 1-h memory (mid-term memory, MTM) but not 1-day memory. Crickets injected with MEC 20 min before the retention test at 1 day after the multiple-trial conditioning exhibited no memory retrieval. This indicates that α-BGT-insensitive nAChRs participate in memory retrieval. In addition, crickets injected with MLA before the multiple-trial conditioning exhibited MTM but not LTM, indicating that α-BGT-sensitive nAChRs participate in the formation of LTM. Moreover, injection of nicotine (an nAChR agonist) before the single-trial conditioning induced LTM. Finally, the nitric oxide (NO)-cGMP signaling pathway is known to participate in the formation of LTM in crickets, and we conducted co-injection experiments with an agonist or inhibitor of the nAChR and an activator or inhibitor of the NO-cGMP signaling pathway. The results suggest that nAChR works upstream of the NO-cGMP signaling system in the LTM formation process.

Evidence of active oviposition avoidance to systemically applied imidacloprid in the Colorado potato beetle

Agricultural pests can develop behavioral resistance to insecticides by choosing to feed or oviposit on insecticide-free hosts. As young larvae have relatively low mobility, oviposition preferences from female adults may play a critical role in shaping the evolutionary trajectory of pest populations. While oviposition avoidance of insecticide-treated hosts was found in different agriculture pests, it remains unclear whether female adults actively choose to occupy insecticide-free hosts. To address this question, we investigated feeding and oviposition preferences between imidacloprid-treated and imidacloprid-free plants in the Colorado potato beetle, Leptinotarsa decemlineata Say, a major potato pest. We performed behavioral choice assays on two strains that differed in both fecundity and insecticide resistance. We found that one strain preferred to feed on the insecticide-free plants and that this preference is not innate. Meanwhile, the other strain chose plants for feeding and oviposition randomly. Further analyses of the moving patterns of the beetles suggested that the oviposition preference in the first strain is likely due to active learning.

Neonicotinoid insecticide imidacloprid induces chemosensory deficits in a nontarget parasitoid wasp

Chemical pesticides are widely used to manage the population of arthropod pests. Their increasing use in agriculture has raised concerns about their harmful effects on nontarget organisms, particularly some beneficial insects such as parasitoid wasps. To assess the potential risk and ecological safety of chemical pesticides, it is necessary to understand their impacts on the physiology and behaviour of those important natural enemies of arthropod pests. Here, we applied the Drosophila parasitoid Leptopilina drosophilae as a study model to investigate the effects of sublethal doses of imidacloprid, a widely used neonicotinoid insecticide. Our results demonstrated the detrimental effects of imidacloprid on the host-searching behaviour of L. drosophilae females and the courtship behaviour of L. drosophilae males. Comparative transcriptome and functional analysis provided further insights into the potential mechanisms underlying the impaired behaviours, with the downregulated expression of certain chemoreception genes in both female and male exposed wasps. Our findings thus emphasize the importance of understanding the risks associated with the use of chemical pesticides and the need to develop more eco-friendly pest management strategies for a sustainable balance between chemical and biological control.

Systematic analysis of circadian disrupting substances with a high-throughput zebrafish circadian behavior screening approach

Circadian rhythm aligns numerous biological functions in majority of animals. Aside from well-known external factors such as the light-dark cycle and temperature, circadian rhythm can also be regulated by rarely explored factors such as synthetic substances. Here, we established a circadian behavior screening approach utilizing zebrafish larvae model, which integrated high-throughput capabilities with automated batch processing. With this approach, we systematically analyzed the circadian disruptive effects of >60 synthetic substances commonly detected in aquatic environment by assessing both the circadian period length and amplitude of circadian behavior, with an exposure concentration set at 100 μg/L. Among tested substances, a series of circadian disrupting compounds (circadian disruptors) were identified. Several categories of the hit compounds can be recognized, such as phthalate (diisopentyl phthalate (DIPP), with 10.1 % and 49.6 % increases for circadian period length and amplitude, respectively), neuroactive substance (mirtazapine, with 10.6 % and 63.1 % increases, respectively), and biocides (thiamethoxam, with 100.3 % increase for amplitude). Among these compounds, DIPP increased circadian period length and amplitude with a high degree. Aside from DIPP, we further examined eleven other phthalates and demonstrated that benzyl butyl phthalate, diisobutyl phthalate and diisohexyl phthalate could also significantly increase the zebrafish circadian period length by 7.9 %, 3.7 % and 8.5 %, respectively. Collectively, the present findings substantiated the feasibility of this high throughput screening strategy for circadian disruptor's discovery and provided novel insights into understanding of the potential risks of synthetic substances.

Identification of CYCLE targets that contribute diverse features of circadian rhythms in the mosquito Culex pipiens

Culex pipiens demonstrates robust circadian rhythms in adult eclosion, flight activity, mating, and development. These rhythmic patterns are believed to be controlled by the endogenous light-entrainable circadian clock that consists of positive and negative regulators working in a transcription-translation feedback loop. Moreover, these mosquitoes undergo seasonal diapause in exposure to the short photoperiod of late summer or early fall. However, the exact genetic and cellular mechanism behind the clock gene-mediated activity pattern, seasonal time measurement, and subsequent diapause initiation still need to be unraveled. To determine the possible linkage between clock genes and downstream processes, here we employed ChIP-sequencing to identify the direct targets of one of the core clock proteins, Cycle (CYC). The nearest genes with peaks mapping to their 1Kb upstream region of the transcription start site were extracted and scanned for consensus E box sequences, resulting in a dataset comprising the target genes possibly regulated by CYC. Based on the highest fold enrichment and functional relevance, we identified genes relating to five gene categories of potential interest, including peptide/receptors, neurotransmission, olfaction, immunity, and reproductive growth. Of these, we validated fourteen genes with ChIP-qPCR and qRT-PCR. These genes showed a significantly high expression in dusk compared to dawn in concert with the activity level of the CYC transcription factor and are thus strong candidates for mediating circadian rhythmicity and possibly regulating seasonal shifts in mosquito reproductive activity.

Proteomic responses in the human dopaminergic LUHMES cell line to imidacloprid and its metabolites imidacloprid-olefin and desnitro-imidacloprid

Neonicotinoids (neonics) are amongst the most commonly used class of pesticides globally. In the United States, imidacloprid (IMI) is extensively used for agriculture and in other common applications such as house-hold pest control. Regular exposure to IMI, and several of its known metabolites including IMI-olefin and desnitro-imidacloprid (DN-IMI), has been shown to be harmful to many organisms including mammals, birds, and fish. Studies show that neonics bind human nicotinicacetylcholine receptors (nAChRs) and cause cellular toxicity. In the dopaminergic Lund human mesencephalic (LUHMES) cell line, IMI and other neonics (10-100 μM) have been recently shown to activate intracellular calcium signaling through nAChRs. Thus, we examined proteomic responses of LUHMES cells to a 48-h treatment with 50 μM IMI, IMI-olefin, or DN-IMI. Our findings show differential effects of these neonics on cellular protein expression. Bioinformatic analysis of significantly altered proteins indicates an effect of IMI, IMI-olefin, and DN-IMI on protein synthesis and ribosomal function. These findings suggest a role for protein synthesis and transcriptional regulation in neonic-mediated dopaminergic neurotoxicity.

Prolonged darkness attenuates imidacloprid toxicity through the brain-gut-microbiome axis in zebrafish, Danio rerio

The present study investigated the toxic effects of IMI on brain and gut of zebrafish (Danio rerio) by a combination of transcriptome and microbiome analysis. In addition, the involvement of light/dark period was also evaluated. An acute toxic test was conducted on adult zebrafish weighing 0.45 ± 0.02 g with 4 experimental groups (n = 15): 1) IMI group (Light: Dark = 12: 12 h), 2) prolonged light group (Light: Dark = 20: 4 h), 3) prolonged darkness group (Light: Dark = 4: 20 h) which received 20 mg/L of IMI, and 4) control group, which was not treated with IMI (Light: Dark = 12: 12 h). The results showed that prolonged darkness improved the survival rate of zebrafish upon IMI exposure for 96 h. In the sub-chronic test, zebrafish were divided into the same 4 groups and exposed to IMI at 1 mg/L for 14 d (n = 30). The results showed that IMI induced oxidative stress in both IMI and prolonged light groups by inhibition of antioxidant activities and accumulation of oxidative products. Transcriptome analysis revealed a compromise of antioxidation and tryptophan metabolism pathways under IMI exposure. Several genes encoding rate-limiting enzymes in serotonin and melatonin synthesis were all inhibited in both IMI and LL groups. Meanwhile, significant decrease (P < 0.5) of serotonin and melatonin levels was observed. However, there's remarkable improvement of biochemical and transcriptional status in prolonged darkness group. In addition, microbiome analysis showed great alteration of gut bacterial community structure and inhibition of tryptophan metabolism pathway. Similarly, the gut microbiota dysbiosis induced by IMI was alleviated in prolonged darkness. In summary, sub-chronic IMI exposure induced neurotoxicity and gut toxicity in zebrafish by oxidative stress and impaired the brain-gut-axis through tryptophan metabolism perturbation. Prolonged darkness could effectively attenuate the IMI toxicity probably through maintaining a normal tryptophan metabolism.

Toxicity and Lethal Effect of Greenhouse Insecticides on Coccinella septempunctata (Coleoptera: Coccinellidae) as Biological Control Agent of Myzus persicae (Hemiptera: Aphididae)

Deltamethrin and imidacloprid are commonly used insecticides for controlling sub-sucking insects in greenhouses. However, their application may cause sublethal effects on the aphid coccinellid predator Coccinella septempunctata (Coleoptera: Coccinellidae). Here, we study (i) the toxicity and the effect of two sublethal doses (LD₁₀ and LD₃₀) of deltamethrin and imidacloprid on C. septempunctata in a laboratory microcosm and (ii) the residual toxicity of the two insecticides in a greenhouse. The results showed that both insecticides reduced fecundity, longevity, the intrinsic rate of increase, the finite rate of increase and the net reproductive rate. However, the developmental time of the fourth instar larvae was prolonged by both insecticides at LD₁₀ and LD₃₀. Deltamethrin residues were toxic 21 DAT (days after treatment) to C. septempunctata fourth instar larvae. In contrast, imidacloprid began in the slightly harmful category (75%) 1 DAT and declined to the harmless category (18.33%) 21 DAT. These results indicate that deltamethrin and imidacloprid have potential risks to C. septempunctata. This study provides information to guide the development of integrated pest management (IPM) strategies in greenhouses.

A neonicotinoid pesticide alters Drosophila olfactory processing

Neonicotinoid pesticides are well-known for their sublethal effects on insect behavior and physiology. Recent work suggests neonicotinoids can impair insect olfactory processing, with potential downstream effects on behavior and possibly survival. However, it is unclear whether impairment occurs during peripheral olfactory detection, during information processing in central brain regions, or in both contexts. We used Drosophila melanogaster to explore the potential for neonicotinoids to disrupt olfaction by conducting electrophysiological analyses of single neurons and whole antennae of flies exposed to varying concentrations of the neonicotinoid imidacloprid (IMD) that were shown to cause relative differences in fly survival. Our results demonstrated that IMD exposure significantly reduced the activity of a single focal olfactory neuron and delayed the return to baseline activity of the whole antenna. To determine if IMD also impacts olfactory-guided behavior, we compared flies' relative preference for odor sources varying in ethanol content. Flies exposed to IMD had a greater relative preference for ethanol-laced pineapple juice than control flies, demonstrating that neuronal shifts induced by IMD that we observed are associated with changes in relative preference. Given the interest in the sensory impacts of agrochemical exposure on wild insect behavior and physiology, we highlight the potential of Drosophila as a tractable model for investigating the effects of pesticides at scales ranging from single-neuron physiology to olfactory-guided behavior.

On-Site Detection of Neonicotinoid Pesticides Using Functionalized Gold Nanoparticles and Halogen Bonding

Neonicotinoid (NN) pesticides have emerged globally as one of the most widely used agricultural tools for protecting crops from pest damage and boosting food production. Unfortunately, some NN compounds, such as extensively employed imidacloprid-based pesticides, have also been identified as likely endangering critical pollinating insects like honey bees. To this end, NN pesticides pose a potential threat to world food supplies. As more countries restrict or prohibit the use of NN pesticides, tools are needed to effectively and quickly identify the presence of NN compounds like imidacloprid on site (e.g., in storage areas on farms or pesticide distribution warehouses). This study represents a proof-of-concept where the colloidal properties of specifically modified gold nanoparticles (Au-NPs) able to engage in the rare intermolecular interaction of halogen bonding (XB) can result in the detection of certain NN compounds. Density functional theory and diffusion-ordered NMR spectroscopy (DOSY NMR) are used to explore the fundamental XB interactions between strong XB-donor structures and NN compounds, with the latter found to possess multiple XB-acceptor binding sites. A fundamental understanding of these XB interactions allows for the functionalization of alkanethiolate-stabilized Au-NPs, known as monolayer-protected gold clusters (MPCs), with XB-donor capability (f-MPCs). In the presence of certain NN compounds such as imidacloprid, the f-MPCs subsequently exhibit visual XB-induced aggregation that is also measured with absorption (UV-vis) spectroscopy and verified with transmission electron microscopy (TEM) imaging. The demonstrated f-MPC-aggregation detection scheme has a number of favorable attributes, including quickly reporting the presence of the NN target, requiring only micrograms of suspect material, and being highly selective for imidacloprid, the most prevalent and most important NN insecticide compound. Requiring no instrumentation, the presented methodology can be envisioned as a simple screening test in which dipping a cotton swab of an unknown powder from a surface in a f-MPC solution causes f-MPCs to aggregate and yield a preliminary indication of imidacloprid presence.

Chronic larval exposure to thiacloprid impairs honeybee antennal selectivity, learning and memory performances

The use of agricultural neonicotinoid insecticides has sub-lethal chronic effects on bees that are more prevalent than acute toxicity. Among these insecticides, thiacloprid, a commonly used compound with low toxicity, has attracted significant attention due to its potential impact on the olfactory and learning abilities of honeybees. The effect of sub-lethal larval exposure to thiacloprid on the antennal activity of adult honeybees (Apis mellifera L.) is not yet fully understood. To address this knowledge gap, laboratory-based experiments were conducted in which honeybee larvae were administered thiacloprid (0.5 mg/L and 1.0 mg/L). Using electroantennography (EAG), the impacts of thiacloprid exposure on the antennal selectivity to common floral volatiles were evaluated. Additionally, the effects of sub-lethal exposure on odor-related learning and memory were also assessed. The results of this study reveal, for the first time, that sub-lethal larval exposure to thiacloprid decreased honeybee antenna EAG responses to floral scents, leading to increased olfactory selectivity in the high-dose (1.0 mg/L) group compared to the control group (0 mg/L vs. 1.0 mg/L: p = 0.042). The results also suggest that thiacloprid negatively affected odor-associated paired learning acquisition, as well as medium-term (1 h) (0 mg/L vs. 1.0 mg/L: p = 0.019) and long-term memory (24 h) (0 mg/L vs. 1.0 mg/L: p = 0.037) in adult honeybees. EAG amplitudes were dramatically reduced following R-linalool paired olfactory training (0 mg/L vs. 1.0 mg/L: p = 0.001; 0 mg/L vs. 0.5 mg/L: p = 0.027), while antennal activities only differed significantly in the control between paired and unpaired groups. Our results indicated that exposure to sub-lethal concentrations of thiacloprid may affect olfactory perception and learning and memory behaviors in honeybees. These findings have important implications for the safe use of agrochemicals in the environment.

The Synergistic Effect of Thiamethoxam and Synapsin dsRNA Targets Neurotransmission to Induce Mortality in Aphis gossypii

Sublethal doses of insecticides have many impacts on pest control and agroecosystems. Insects that survive a sublethal dose of insecticide could adapt their physiological and behavioral functions and resist this environmental stress, which contributes to the challenge of pest management. In this study, the sublethal effects of thiamethoxam on gene expression were measured through RNA sequencing in the melon aphid Aphis gossypii. Genes regulating energy production were downregulated, while genes related to neural function were upregulated. To further address the function of genes related to neurotransmission, RNA interference (RNAi) was implemented by transdermal delivery of dsRNA targeting synapsin (syn), a gene regulating presynaptic vesicle clustering. The gene expression of synapsin was knocked down and the mortality of aphids was increased significantly over the duration of the assay. Co-delivery of syn-dsRNA and thiamethoxam reversed the upregulation of synapsin caused by low-dose thiamethoxam and resulted in lethality to melon aphids, suggesting that the decreased presynaptic function may contribute to this synergistic lethal effect. In addition, the nanocarrier star polycation, which could bind both dsRNA and thiamethoxam, greatly improved the efficacy of lethality. These results increase our knowledge of the gene regulation induced by sublethal exposure to neonicotinoids and indicated that synapsin could be a potential RNAi target for resistance management of the melon aphid.

Environmental risk assessment of neonicotinoids in surface water

Neonicotinoids (NNIs) are active substances used as insecticides mainly in plant protection products (PPPs) but also in veterinary applications. The increasing evidence of affecting non-targeted organisms led the European Commission to severely restrict or even ban outdoor uses. To evaluate their current use and their influence in the ecological status of freshwater ecosystem, a total of 19 river water samples were collected to determine the presence of 5 NNIs (acetamiprid, clothianidin, imidacloprid, thiamethoxam and thiacloprid) in the Tagus basin. At least one target analyte was quantified by HPLC-MS/MS analysis in 17 of the 19 water samples, with ∑NNIs ranging from <MDL to 16.8 ng/L. Imidacloprid (2.75 ng/L; mean) and acetamiprid (0.47 ng/L) were quantified in most of the samples. Source identification evidences imidacloprid agricultural use. Risk assessment for different trophic levels was conducted with the data obtained calculating Risk Characterization Ratios (RCR) by two approaches, predicted non effect concentrations (PEC/PNEC) and Toxic Units (TU). RCRs were derived for each NNI and for the mixture of all (RCRmix). Results showed risk for imidacloprid in freshwater organism (RCRfw>1) and for the mix of NNIs (RCRmix (PEC/PNEC) > 1). RCRmix(PEC/PNEC) and the sum of toxic units (STU) showed a risky situation for some locations with different organisms related to agriculture practices. This data arouses concern about NNis (legal or forbidden) use in Tagus basin, and manifest the need of monitoring their presence and effect on the aquatic ecosystem.

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.

BDD electrochemical oxidation of neonicotinoid pesticides in natural surface waters. Operational, kinetic and energetic aspects

Neonicotinoids pesticides were introduced to the market in the 1990s to control various pests. Its accumulation in the environment supposes a severe problem that can affect human health. This study investigates the electrochemical degradation of four common neonicotinoid pesticides; thiamethoxam (TMX), imidacloprid (ICP), acetamiprid (ACP) and thiacloprid (TCP), in different natural surface waters by a boron-doped diamond anode (BDD). The most influencing variable was the current density (j), and to a lesser extent, the supporting electrolyte concentration (C_e). In optimal conditions (j = 34.14 mA cm^-2 and C_e = 10.00 mM, using Na₂SO₄ as electrolyte) pesticide removals for TMX, ICP, ACP and TCP were 97.2, 96.9, 87.8 and 98.2 %, respectively. The obtained results with different support electrolytes (Na₂SO₄, NaCl, NaNO₃ and HK₂PO₄) suggest that sulphate electrolyte was the optimum for TMX, ICP and ACP. However, for TCP, a total removal was achieved in less than 10 min using NaCl. It was also verified that the initial pH of the solution did not significantly influence the process in the range 3-9. All these results were rationalized in this paper. Finally, to evaluate the matrix influence, some experiments were carried out in different natural surface water matrices (river, reservoir and two different WWTP effluents). The factors influencing the process were the conductivity of the solution and the organic matter content. It was noticeable that the specific energy consumption (SEC) reduced by approximately 15 % for river water and WWTP effluent. High mineralization rates were obtained for all water matrices, with TOC removals ranging between 60 and 80 %.

Dynamically expressed single ELAV/Hu orthologue elavl2 of bees is required for learning and memory

Changes in gene expression are a hallmark of learning and memory consolidation. Little is known about how alternative mRNA processing, particularly abundant in neuron-specific genes, contributes to these processes. Prototype RNA binding proteins of the neuronally expressed ELAV/Hu family are candidates for roles in learning and memory, but their capacity to cross-regulate and take over each other's functions complicate substantiation of such links. Honey bees Apis mellifera have only one elav/Hu family gene elavl2, that has functionally diversified by increasing alternative splicing including an evolutionary conserved microexon. RNAi knockdown demonstrates that ELAVL2 is required for learning and memory in bees. ELAVL2 is dynamically expressed with altered alternative splicing and subcellular localization in mushroom bodies, but not in other brain regions. Expression and alternative splicing of elavl2 change during memory consolidation illustrating an alternative mRNA processing program as part of a local gene expression response underlying memory consolidation.

Effects of Insecticides and Microbiological Contaminants on Apis mellifera Health

Over the past two decades, there has been an alarming decline in the number of honey bee colonies. This phenomenon is called Colony Collapse Disorder (CCD). Bee products play a significant role in human life and have a huge impact on agriculture, therefore bees are an economically important species. Honey has found its healing application in various sectors of human life, as well as other bee products such as royal jelly, propolis, and bee pollen. There are many putative factors of CCD, such as air pollution, GMO, viruses, or predators (such as wasps and hornets). It is, however, believed that pesticides and microorganisms play a huge role in the mass extinction of bee colonies. Insecticides are chemicals that are dangerous to both humans and the environment. They can cause enormous damage to bees' nervous system and permanently weaken their immune system, making them vulnerable to other factors. Some of the insecticides that negatively affect bees are, for example, neonicotinoids, coumaphos, and chlorpyrifos. Microorganisms can cause various diseases in bees, weakening the health of the colony and often resulting in its extinction. Infection with microorganisms may result in the need to dispose of the entire hive to prevent the spread of pathogens to other hives. Many aspects of the impact of pesticides and microorganisms on bees are still unclear. The need to deepen knowledge in this matter is crucial, bearing in mind how important these animals are for human life.

Genome-Wide Identification of Neuropeptides and Their Receptors in an Aphid Endoparasitoid Wasp, Aphidius gifuensi

In insects, neuropeptides and their receptors not only play a critical role in insect physiology and behavior but also are the potential targets for novel pesticide discoveries. Aphidius gifuensis is one of the most important and widespread aphid parasitoids, and has been successfully used to control aphid. In the present work, we systematically identified neuropeptides and their receptors from the genome and head transcriptome of A. gifuensis. A total of 35 neuropeptide precursors and 49 corresponding receptors were identified. The phylogenetic analyses demonstrated that 35 of these receptors belong to family-A, four belong to family-B, two belong to leucine-rich repeat-containing GPCRs, four belong to receptor guanylyl cyclases, and four belong to receptor tyrosine kinases. Oral ingestion of imidacloprid significantly up-regulated five neuropeptide precursors and four receptors whereas three neuropeptide precursors and eight receptors were significantly down-regulated, which indicated that these neuropeptides and their receptors are potential targets of some commercial insecticides. The RT-qPCR results showed that dopamine receptor 1, dopamine receptor 2, octopamine receptor, allatostatin-A receptor, neuropeptides capa receptor, SIFamide receptor, FMRFamide receptor, tyramine receptor and short neuropeptide F predominantly were expressed in the head whilst the expression of ion transport peptide showed widespread distribution in various tissues. The high expression levels of these genes suggest their important roles in the central nervous system. Taken together, our study provides fundamental information that may further our understanding of neuropeptidergic signaling systems in the regulation of the physiology and behavior of solitary wasps. Furthermore, this information could also aid in the design and discovery of specific and environment-friendly insecticides.

Using radio frequency identification and locomotor activity monitoring to assess sleep, locomotor, and foraging rhythmicity in bumblebees

Bumblebees are a key pollinator. Understanding the factors that influence the timing of sleep and foraging trips is important for efficient foraging and pollination. Here, we illustrate how individual locomotor activity monitoring and colony-wide radio frequency identification tracking can be combined to analyze the effects of agrochemicals like neonicotinoids on locomotor and foraging rhythmicity and sleep quantity/quality in bumblebees. We also highlight aspects of the design that can be adapted for other invertebrates or agrochemicals, allowing broader application of these techniques.

For complete details on the use and execution of this protocol, please refer to Tasman et al. (2020).

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Easy and reliable way of testing circadian rhythmicity and sleep in invertebrates

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Covers colony care, equipment adaptation, and setup and experimental protocol

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This protocol can be used to study the effects of any water soluble/liquid insecticide

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The multiple ways to adapt the protocol for other organisms are highlighted

The Power of Drosophila melanogaster for Modeling Neonicotinoid Effects on Pollinators and Identifying Novel Mechanisms

Neonicotinoids are the most widely used insecticides in the world and are implicated in the widespread population declines of insects including pollinators. Neonicotinoids target nicotinic acetylcholine receptors which are expressed throughout the insect central nervous system, causing a wide range of sub-lethal effects on non-target insects. Here, we review the potential of the fruit fly Drosophila melanogaster to model the sub-lethal effects of neonicotinoids on pollinators, by utilizing its well-established assays that allow rapid identification and mechanistic characterization of these effects. We compare studies on the effects of neonicotinoids on lethality, reproduction, locomotion, immunity, learning, circadian rhythms and sleep in D. melanogaster and a range of pollinators. We also highlight how the genetic tools available in D. melanogaster, such as GAL4/UAS targeted transgene expression system combined with RNAi lines to any gene in the genome including the different nicotinic acetylcholine receptor subunit genes, are set to elucidate the mechanisms that underlie the sub-lethal effects of these common pesticides. We argue that studying pollinators and D. melanogaster in tandem allows rapid elucidation of mechanisms of action, which translate well from D. melanogaster to pollinators. We focus on the recent identification of novel and important sublethal effects of neonicotinoids on circadian rhythms and sleep. The comparison of effects between D. melanogaster and pollinators and the use of genetic tools to identify mechanisms make a powerful partnership for the future discovery and testing of more specific insecticides.