Neural conduction, visual motion detection, and insect flight behaviour are disrupted by low doses of imidacloprid and its metabolites

Imidacloprid affects the visual behavior of adult zebrafish (Danio rerio) by mediating the expression of opsin and phototransduction genes and altering the metabolism of neurotransmitters

Imidacloprid poses a significant threat to aquatic ecosystems. In this study, we investigated the visual toxicity of imidacloprid and the underlying molecular mechanisms in adult zebrafish. After exposure to imidacloprid at environmental relevant concentrations (10 and 100μg/L) for 21 days, the detectable contents of imidacloprid were 23.0 ± 0.80 and 121 ± 1.56 ng/mg in eyes of adult zebrafish, respectively. The visual behavior of adult zebrafish was impaired including a reduced ability to track smoothly visual stimuli and visually guided self-motion. The immunofluorescence experiment showed that the content of Rhodopsin (Rho) in the retina of zebrafish was changed significantly. The expression rhythm of genes played key roles in capturing photons in dim (rho) and bright (opn1mw3, opn1lw2 and opn1sw2) light, and in phototransduction (gnb3b, arr3a and rpe65a), was disrupted significantly throughout a 24-h period in adult zebrafish. Targeted metabolomics analysis showed that the content of 16 metabolites associated with neurotransmitter function changed significantly, and were enriched in top three metabolism pathways including Arginine biosynthesis, Alanine, aspartate and glutamate metabolism, and Tryptophan metabolism. These results indicated that imidacloprid exposure at environmentally relevant concentrations could cause optical toxicity through disturbing the expression of opsins and affecting the phototransduction in the retina of zebrafish adults.

Simulating immunosuppressive mechanism of Microplitis bicoloratus bracovirus coordinately fights Spodoptera frugiperda

Parasitoid wasps control pests via a precise attack leading to the death of the pest. However, parasitoid larvae exhibit self-protection strategies against bracovirus-induced reactive oxygen species impairment. This has a detrimental effect on pest control. Here, we report a strategy for simulating Microplitis bicoloratus bracovirus using Mix-T dsRNA targeting 14 genes associated with transcription, translation, cell-cell communication, and humoral signaling pathways in the host, and from wasp extracellular superoxide dismutases. We implemented either one-time feeding to the younger instar larvae or spraying once on the corn leaves, to effectively control the invading pest Spodoptera frugiperda. This highlights the conserved principle of "biological pest control," as elucidated by the triple interaction of parasitoid-bracovirus-host in a cooperation strategy of bracovirus against its pest host.

Imidacloprid-induced stress affects the growth of pepper plants by disrupting rhizosphere-plant microbial and metabolite composition

Overusing imidacloprid (IMI) has been found to impede secondary metabolism and hinder plant growth. The impact of IMI stress on the interaction between metabolites, rhizosphere, and plant-microbe dispersion through various pathways in pepper plants has not been extensively studied. This study investigated the effects of IMI on plant signaling components, secondary metabolic pathways, and microbial communities in the rhizosphere and phyllosphere. Here, the distribution of IMI and its metabolites (6-chloronicotinic acid, IMI-desnitro, 5-hydroxy-IMI, IMI-urea, and IMI-olefin) was primarily observed in the pepper plant leaves. A rise in IMI concentration had a more significant inhibitive effect on the metabolism of pepper leaves than on pepper roots. The findings of non-target metabolomics indicated that IMI exposure primarily suppresses secondary metabolism in pepper plants, encompassing flavones, phenolic acids, and phytohormones. Notably, the IMI treatment disrupted the equilibrium between plants and microbes by decreasing the population of microorganisms such as Vicinamibacteria, Verrucomicrobiae, Gemmatimonadetes, and Gammaproteobacteria in the phyllosphere, as well as Vicinamibacteria, Gemmatimonadetes, Gammaproteobacteria, and Alphaproteobacteria in the rhizosphere of pepper plants. The study demonstrates that overexposure to IMI harms microbial composition and metabolite distribution in the rhizosphere soil and pepper seedlings, inhibiting plant growth.

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.

Acute and chronic toxicity of imidacloprid in the pollinator fly, Eristalis tenax L., assessed using a novel oral bioassay

Imidacloprid is a neonicotinoid neurotoxin that remains widely used worldwide and persists in the environment, resulting in chronic exposure to non-target insects. To accurately map dose-dependent effects of such exposure across taxa, toxicological assays need to assess relevant modes of exposure across indicator species. However, due to the difficulty of these experiments, contact bioassays are most frequently used to quantify dose. Here, we developed a novel naturalistic feeding bioassay to precisely measure imidacloprid ingestion and its toxicity for acute and chronic exposure in a dipteran, Eristalis tenax L., an important member of an under-represented pollinator group. Flies which ingested imidacloprid dosages lower than 12.1 ng/mg all showed consistent intake volumes and learned improved feeding efficiency over successive feeding sessions. In contrast, at doses of 12.1 ng/mg and higher flies showed a rapid onset of severe locomotive impairment which prevented them from completing the feeding task. Neither probability of survival nor severe locomotive impairment were significantly higher than the control group until doses of 1.43 ng/mg or higher were reached. We were unable to measure a median lethal dose for acute exposure (72 h) due to flies possessing a relatively high tolerance for imidacloprid. However, with chronic exposure (18 days), mortality went up and an LD50 of 0.41 ng/mg was estimated. Severe locomotive impairment (immobilisation) tended to occur earlier and at lower dosages than lethality, with ED50s of 7.82 ng/mg and 0.17 ng/mg for acute and chronic exposure, respectively. We conclude that adult Eristalis possess a much higher tolerance to this toxin than the honeybees that they mimic. The similarity of the LD50 to other dipterans such as the fruitfly and the housefly suggests that there may be a phylogenetic component to pesticide tolerance that merits further investigation. The absence of obvious adverse effects at sublethal dosages also underscores a need to develop better tools for quantifying animal behaviour to evaluate the impact of insecticides on foraging efficiency in economically important species.

Imidacloprid-based commercial pesticide causes behavioral, biochemical, and hematological impairments in Wistar rats

Imidacloprid (IMI) is a neonicotinoid insecticide employed worldwide for crop protection. IMI's mode of action occurs through the agonism of postsynaptic nicotinic acetylcholine receptors (nAChRs), with high specificity for insect nAChRs although there are reports of mammals' toxicity. Studies on IMI's neurotoxicity are not conclusive; therefore, the aim of this study was to evaluate the subchronic toxic effects of an IMI based commercial pesticide on rats. Adult male Wistar rats received an IMI suspension via the oral route at doses of 1.5, 5, and 15 mg/kg for 45 consecutive days. IMI caused an increase in rearing and time spent at the periphery in the locomotor activity test and a decrease in time spent to finish the OX maze task (p < 0.05; ANOVA/Bonferroni). In blood, there was a decrease in mean corpuscular hemoglobin and mean corpuscular hemoglobin concentration (p < 0.05; ANOVA/Bonferroni) and an increase in serum butyrylcholinesterase activity (p < 0.001; ANOVA/Bonferroni). Therefore, subchronic administration of an IMI-based-pesticide caused behavioral and systemic impairments in rats.

Acute Application of Imidacloprid Alters the Sensitivity of Direction Selective Motion Detecting Neurons in an Insect Pollinator

Cholinergic pesticides, such as the neonicotinoid imidacloprid, are the most important insecticides used for plant protection worldwide. In recent decades, concerns have been raised about side effects on non-target insect species, including altered foraging behavior and navigation. Although pollinators rely on visual cues to forage and navigate their environment, the effects of neonicotinoids on visual processing have been largely overlooked. To test the effect of acute treatment with imidacloprid at known concentrations in the brain, we developed a modified electrophysiological setup that allows recordings of visually evoked responses while perfusing the brain in vivo. We obtained long-lasting recordings from direction selective wide-field, motion sensitive neurons of the hoverfly pollinator, Eristalis tenax. Neurons were treated with imidacloprid (3.9 μM, 0.39 μM or a sham control treatment using the solvent (dimethylsulfoxide) only. Exposure to a high, yet sub-lethal concentration of imidacloprid significantly alters their physiological response to motion stimuli. We observed a general effect of imidacloprid (3.9 μM) increasing spontaneous activity, reducing contrast sensitivity and giving weaker directional tuning to wide-field moving stimuli, with likely implications for errors in flight control, hovering and routing. Our electrophysiological approach reveals the robustness of the fly visual pathway against cholinergic perturbance (i.e., at 0.39 μM) but also potential threatening effects of cholinergic pesticides (i.e., evident at 3.9 μM) for the visual motion detecting system of an important pollinator.

The toxicity and toxicokinetics of imidacloprid and a bioactive metabolite to two aquatic arthropod species

Previous studies have explored effects of imidacloprid and its metabolites on terrestrial species, such as bees, and indicated the importance of some active metabolites. However, the biotransformation of IMI and the toxicity of its metabolites to aquatic arthropods are largely unknown, especially the mechanisms driving species sensitivity differences and time-cumulative toxicity effects. To assess the potential effects of the metabolization of IMI and the toxicokinetics and toxicity of the metabolite(s) on aquatic arthropods, we first studied the acute toxicity of IMI and relevant metabolites to the mayfly species Cloen dipterum (sensitive to IMI) and the amphipod species Gammarus pulex (less sensitive to IMI). Secondly, toxicokinetic experiments were conducted using both the parent compound and imidacloprid-olefin (IMI-ole), a metabolite assessed as toxic in the acute tests and defined as bioactive. Of the four tested metabolites, only IMI-ole was readily biotransformed from the parent IMI and showed similar toxicity to C. dipterum as IMI. However, C. dipterum was hardly able to eliminate IMI-ole from its body. For G. pulex, IMI-ole was also the only detected metabolite causing toxicity, but the biotransformation of IMI to IMI-ole was slower and lower in G. pulex compared to C. dipterum, and G. pulex eliminated IMI-ole quicker than C. dipterum. Our results on internal kinetics of IMI and IMI-ole, and on biotransformation of IMI indicated that the metabolite IMI-ole was toxic and was rather persistent inside the body tissue of both invertebrate species, especially for C. dipterum. In conclusion, as IMI and IMI-ole have similar toxicity and IMI was replaced rapidly by IMI-ole which in turn was poorly eliminated by C. dipterum, the overall toxicity is a function of dose and time. As a result, no long-term threshold of effects of IMI may exist for C. dipterum as the poor elimination results in an ongoing increase of toxicity over time for mayflies as also found experimentally in previous published papers.

Neonicotinoid and sulfoximine pesticides differentially impair insect escape behavior and motion detection

Novel insecticides are developed and implemented in agriculture without a broad understanding of their sublethal effects. Although all act via nicotinic acetylcholine receptors, neonicotinoids and the novel sulfoxaflor insecticide exhibit differences in relative toxicity. In this study comparing the effects of these insecticides on visual motion detection and escape behavior, we show that sulfoxaflor displays decreased sublethal toxicity despite similar lethal endpoints of these insecticides. Imidacloprid reduces putative neural population code variability when responding to approaching objects, suggesting that neonics may constrain the tuning of visual sensory circuits. We suggest that neuroethologic methods are powerful tools to link toxic effects across levels of biological organization and further our understanding of how neural populations operate in complex sensory environments.

Insect nervous systems offer unique advantages for studying interactions between sensory systems and behavior, given their complexity with high tractability. By examining the neural coding of salient environmental stimuli and resulting behavioral output in the context of environmental stressors, we gain an understanding of the effects of these stressors on brain and behavior and provide insight into normal function. The implication of neonicotinoid (neonic) pesticides in contributing to declines of nontarget species, such as bees, has motivated the development of new compounds that can potentially mitigate putative resistance in target species and declines of nontarget species. We used a neuroethologic approach, including behavioral assays and multineuronal recording techniques, to investigate effects of imidacloprid (IMD) and the novel insecticide sulfoxaflor (SFX) on visual motion-detection circuits and related escape behavior in the tractable locust system. Despite similar LD₅₀ values, IMD and SFX evoked different behavioral and physiological effects. IMD significantly attenuated collision avoidance behaviors and impaired responses of neural populations, including decreases in spontaneous firing and neural habituation. In contrast, SFX displayed no effect at a comparable sublethal dose. These results show that neonics affect population responses and habituation of a visual motion detection system. We propose that differences in the sublethal effects of SFX reflect a different mode of action than that of IMD. More broadly, we suggest that neuroethologic assays for comparative neurotoxicology are valuable tools for fully addressing current issues regarding the proximal effects of environmental toxicity in nontarget species.

The Neurophysiological Bases of the Impact of Neonicotinoid Pesticides on the Behaviour of Honeybees

Acetylcholine is the main excitatory neurotransmitter in the honeybee brain and controls a wide range of behaviours that ensure the survival of the individuals and of the entire colony. Neonicotinoid pesticides target this neurotransmission pathway and can thereby affect the behaviours under its control, even at doses far below the toxicity limit. These sublethal effects of neonicotinoids on honeybee behaviours were suggested to be partly responsible for the decline in honeybee populations. However, the neural mechanisms by which neonicotinoids influence single behaviours are still unclear. This is mainly due to the heterogeneity of the exposure pathways, doses and durations between studies. Here, we provide a review of the state of the science in this field and highlight knowledge gaps that need to be closed. We describe the agonistic effects of neonicotinoids on neurons expressing the different nicotinic acetylcholine receptors and the resulting brain structural and functional changes, which are likely responsible for the behavioural alterations reported in bees exposed to neonicotinoids.

A Neonicotinoid Insecticide at a Rate Found in Nectar Reduces Longevity but Not Oogenesis in Monarch Butterflies, Danaus plexippus (L.). (Lepidoptera: Nymphalidae)

The monarch butterfly in North America has suffered a serious population decline since the mid-1990s. The introduction and widespread use of neonicotinoid insecticides during the same time period has been suggested as a potential driver of this decline but no studies have looked at the impact of these insecticides on adult monarchs. A brief laboratory study assessed the impact of Imidacloprid, the most commonly used neonicotinoid, on western monarch butterfly longevity and oogenesis. Imidacloprid at 23.5 ppb, a field-realistic rate reported from wild nectar and pollen, was fed ad libitum to newly-eclosed monarchs in a sugar-based diet for 22 days. Treated monarchs showed reduced longevity, suffering 78.8% mortality by day 22, compared to 20% in untreated monarchs. Prior to death, butterflies exhibited signs of poisoning including uncoordinated flapping of wings and uncontrolled vibrating of wings and body. Imidacloprid did not reduce egg production. Shortened adult longevity has serious consequences for monarch population development, migration and overwintering. The potential widespread impact of imidacloprid-contaminated crop and wild flower nectar, may be a significant driver of monarch population decline. More research on the impact of neonicotinoid insecticides on the monarch and other butterflies should be viewed as a serious priority.