Neonicotinoids target distinct nicotinic acetylcholine receptors and neurons, leading to differential risks to bumblebees

Combined Neurotoxic Effects of Commercial Formulations of Pyrethroid (Deltamethrin) and Neonicotinoid (Imidacloprid) Pesticides on Adult Zebrafish (Danio rerio): Behavioral, Molecular, and Histopathological Analysis

The use of different commercial products that involve one or multiple active substances with specific targeted-pests control has become a widespread practice. Because of this, a severe range of significant consequences has been often reported. Among the most used pesticides worldwide are deltamethrin (DM) and imidacloprid (IMI). With a significative effect on the insect's nervous system, DM acts on the voltage-gated sodium channels in nerve cell membranes, while IMI mimics the acetylcholine neurotransmitter by binding irreversibly to the nicotinic acetylcholine receptors. This study investigates the neurotoxic effects of sub-chronic exposure to commercial formulations of deltamethrin (DM) and imidacloprid (IMI) in adult zebrafish, both individually and in combination. The formulations used in this study contain additional ingredients commonly found in commercial pesticide products, which may contribute to overall toxicity. Fish were exposed to environmentally relevant concentrations of these pesticides for 21 days, individually or in combination. Behavioral, molecular, and histopathological analyses were conducted to assess the impact of these pesticides. Zebrafish exhibited dose-dependent behavioral alterations, particularly in the combined exposure groups, including increased erratic swimming and anxiety-like behavior. Gene expression analysis revealed significant changes in neurotrophic factors (BDNF, NGF, ntf-3, ntf-4/5, ntf-6/7) and their receptors (ntrk1, ntrk2a, ntrk2b, ntrk3a, ntrk3b, ngfra, ngfrb), indicating potential neurotoxic effects. Histopathological examination confirmed neuronal degeneration, gliosis, and vacuolization, with more severe impairments observed in pesticide mixture treatments. These findings highlight the neurotoxic potential of pesticide formulations in aquatic environments and emphasize the need for stricter regulations on pesticide mixtures and further research on pesticide interactions. Our findings emphasize that the combination of pesticides could trigger a synergistic effect by maximizing the toxicity of each compound. Thus, it is a well-known practice for pyrethroids and neonicotinoids to be used together in agriculture. Even so, its prevalence in agriculture and the need to investigate its actual impact on human health, biodiversity, and ecosystem mitigates the development of new strategies for assessing the risk and, at the same time, enhancing the effectiveness.

Sublethal pesticide exposure decreases mating and disrupts chemical signaling in a beneficial pollinator

Pesticides provide vital protection against insect pests and the diseases they vector but are simultaneously implicated in the drastic worldwide decline of beneficial insect populations. Convincing evidence suggests that even sublethal pesticide exposure has detrimental effects on both individual- and colony-level traits, but the mechanisms mediating these effects remained poorly understood. Here, we use bumble bees to examine how sublethal exposure to pesticides affects mating, a key life history event shared by nearly all insects, and whether these impacts are mediated via impaired sexual communication. In insects, mate location and copulation are primarily regulated through chemical signals and rely on both the production and perception of semiochemicals. We show through behavioral bioassays that mating success is reduced in bumble bee gynes after exposure to field-relevant sublethal doses of imidacloprid, and that this effect is likely mediated through a disruption of both the production and perception of semiochemicals. Semiochemical production was altered in gyne and male cuticular hydrocarbons (CHCs), but not in exocrine glands where sex pheromones are presumably produced (i.e., gyne mandibular glands and male labial glands). Male responsiveness to gyne mandibular gland secretion was reduced, but not the queen responsiveness to the male labial secretion. In addition, pesticide exposure reduced queen fat body lipid stores and male sperm quality. Overall, the exposure to imidacloprid affected the fitness and CHCs of both sexes and the antennal responses of males to gynes. Together, our findings identify disruption of chemical signaling as the mechanism through which sublethal pesticide exposure reduces mating success.

Four Neurotoxic Insecticides Impair Partner and Host Finding in the Parasitoid Leptopilina heterotoma and Bioactive Doses Can Be Taken up Via the Host

In modern agriculture, control of insect pests is achieved by using insecticides that can also have lethal and sublethal effects on beneficial non-target organisms. Here, we investigate acute toxicity and sublethal effects of four insecticides on the males' sex pheromone response and the female host finding ability of the Drosophila parasitoid Leptopilina heterotoma. The nicotinic acetylcholine receptor antagonists acetamiprid, flupyradifurone and sulfoxaflor, as well as the acetylcholinesterase inhibitor dimethoate were applied topically as acetone solutions. Males treated with all four insecticides no longer preferred the female sex pheromone in a T-olfactometer. Duration of wing fanning, an element of the pheromone-mediated male courtship behavior, was also reduced by all four insecticides. The ability of females to orientate towards host-infested feeding substrate was not affected by acetamiprid in the tested dose range. However, treatment with dimethoate, flupyradifurone and sulfoxaflor resulted in the loss of the females' preference for host odor. At the lowest doses interfering with olfactory abilities of L. heterotoma in this study (acetamiprid: 0.21 ng, dimethoate: 0.105 ng, flupyradifurone: 2.1 ng and sulfoxaflor: 0.21 ng), ≥ 90% of the wasps survive insecticide treatment. Male pheromone responses and female host finding were also disturbed in those L. heterotoma that had developed in D. melanogaster larvae reared on dimethoate-treated feeding medium at sublethal levels. Hence, doses of this insecticide sufficient to interfere with chemical orientation of L. heterotoma can be taken up by the parasitoid via the food chain.

Honeybee gut bacterial strain improved survival and gut microbiota homeostasis in Apis mellifera exposed in vivo to clothianidin

Pesticides are causing honeybee mortality worldwide. Research carried out on honeybees indicates that application of pesticides has a significant impact on the core gut community, which ultimately leads to an increase in the growth of harmful pathogens. Disturbances caused by pesticides also affect the way bacterial members interact, which results in gut microbial dysbiosis. Administration of beneficial microbes has been previously demonstrated to be effective in treating or preventing disease in honeybees. The objective of this study was to measure under in vivo conditions the ability of two bacterial strains (the Enterobacter sp. and Pantoea sp.) isolated from honeybee gut to improve survival and mitigate gut microbiota dysbiosis in honeybees exposed to a sublethal clothianidin dose (0.1 ppb). Both gut bacterial strains were selected for their ability to degrade clothianidin in vitro regardless of their host-microbe interaction characteristics (e.g., beneficial, neutral, or harmful). To this end, we conducted cage trials on 4- to 6-day-old newly emerging honeybees. During microbial administration, we jointly monitored the taxonomic distribution and activity level of bacterial symbionts quantifying 16S rRNA transcripts. First, curative administration of the Pantoea sp. strain significantly improved the survival of clothianidin-exposed honeybees compared to sugar control bees (i.e., supplemented with sugar [1:1]). Second, curative administration of the Enterobacter sp. strain significantly mitigated the clothianidin-induced dysbiosis observed in the midgut structural network, but without improving survival.

IMPORTANCE

The present work suggests that administration of bacterial strains isolated from honeybee gut may promote recovery of gut microbiota homeostasis after prolonged clothianidin exposure, while improving survival. This study highlights that gut bacterial strains hold promise for developing efficient microbial formulations to mitigate environmental pesticide exposure in honeybee colonies.

Pesticides and pollinator brain: How do neonicotinoids affect the central nervous system of bees?

Neonicotinoids represent over a quarter of the global pesticide market. Research on their environmental impact has revealed their adverse effect on the cognitive functions of pollinators, in particular of bees. Cognitive impairments, mostly revealed by behavioural studies, are the phenotypic expression of an alteration in the underlying neural circuits, a matter deserving greater attention. Here, we reviewed studies on the impact of field-relevant doses of neonicotinoids on the neurophysiology and neurodevelopment of bees. In particular, we focus on their olfactory system as much knowledge has been gained on the different brain areas that participate in odour processing. Recent studies have revealed the detrimental effects of neonicotinoids at multiple levels of the olfactory system, including modulation of odorant-induced activity in olfactory sensory neurons, diminished neural responses in the antennal lobe (the first olfactory processing centre) and abnormal development of the neural connectivity within the mushroom bodies (central neuropils involved in multisensory integration, learning and memory storage, among others). Given the importance of olfactory perception for multiple aspects of bee biology, the reported disruption of the olfactory circuit, which can occur even upon exposure to sublethal doses of neonicotinoids, has severe consequences at both individual and colony levels. Moreover, the effects reported for a multimodal structure such as the mushroom bodies indicate that neonicotinoids' impact translates to other sensory domains. Assessing the impact of field-relevant doses of pesticides on bee neurophysiology is crucial for understanding how neonicotinoids influence their behaviour in ecological contexts and for defining effective and sustainable agricultural practices.

Potential acetylcholine-based communication in honeybee haemocytes and its modulation by a neonicotinoid insecticide

There is growing concern that some managed and wild insect pollinator populations are in decline, potentially threatening biodiversity and sustainable food production on a global scale. In recent years, there has been increasing evidence that sub-lethal exposure to neurotoxic, neonicotinoid pesticides can negatively affect pollinator immunocompetence and could amplify the effects of diseases, likely contributing to pollinator declines. However, a direct pathway connecting neonicotinoids and immune functions remains elusive. In this study we show that haemocytes and non-neural tissues of the honeybee Apis mellifera express the building blocks of the nicotinic acetylcholine receptors that are the target of neonicotinoids. In addition, we demonstrate that the haemocytes, which form the cellular arm of the innate immune system, actively express choline acetyltransferase, a key enzyme necessary to synthesize acetylcholine. In a last step, we show that the expression of this key enzyme is affected by field-realistic doses of clothianidin, a widely used neonicotinoid. These results support a potential mechanistic framework to explain the effects of sub-lethal doses of neonicotinoids on the immune function of pollinators.

Impact of environmental concentrations of fipronil on DNA integrity and brain structure of Bombus atratus bumblebees

Fipronil (FP) is an insecticide used in the treatment and control of pests, but it also adversely affects bees. Currently, there is no data on the genotoxic effects of FP in the brain of bumblebees. Thus, through the comet assay and routine morphological analysis, we analyzed the morphological effects and potential genotoxicity of environmentally relevant concentrations of FP on the brain of Bombus atratus. Bumblebees were exposed at concentrations of 2.5 μg/g and 3.5 μg/g for 96 hours. After the exposure, the brains were removed for morphological and morphometric analysis, and the comet assay procedure - used to detect DNA damage in individual cells using electrophoresis. Our data showed that both concentrations (2.5 μg/g and 3.5 μg/g) caused DNA damage in brain cells. These results corroborate the morphological data. We observed signs of synapse loss in the calyx structure, intercellular spaces between compact inner and non-compact inner cells, and cell swelling. This study provides unprecedented evidence of the effects of FP on DNA and cellular structures in the brain of B. atratus and reinforces the need to elucidate its toxic effects on other species to allow future risk assessments and conservation projects.

Exposure to an insecticide formulation alters chemosensory orientation, but not floral scent detection, in buff-tailed bumblebees (Bombus terrestris)

Although pesticide-free techniques have been developed in agriculture, pesticides are still routinely used against weeds, pests, and pathogens worldwide. These agrochemicals pollute the environment and can negatively impact human health, biodiversity and ecosystem services. Acetamiprid, an approved neonicotinoid pesticide in the EU, may exert sub-lethal effects on pollinators and other organisms. However, our knowledge on the scope and severity of such effects is still incomplete. Our experiments focused on the effects of the insecticide formulation Mospilan (active ingredient: 20% acetamiprid) on the peripheral olfactory detection of a synthetic floral blend and foraging behaviour of buff-tailed bumblebee (Bombus terrestris) workers. We found that the applied treatment did not affect the antennal detection of the floral blend; however, it induced alterations in their foraging behaviour. Pesticide-treated individuals started foraging later, and the probability of finding the floral blend was lower than that of the control bumblebees. However, exposed bumblebees found the scent source faster than the controls. These results suggest that acetamiprid-containing Mospilan may disrupt the activity and orientation of foraging bumblebees. We hypothesize that the observed effects of pesticide exposure on foraging behaviour could be mediated through neurophysiological and endocrine mechanisms. We propose that future investigations should clarify whether such sub-lethal effects can affect pollinators' population dynamics and their ecosystem services.

Impacts of neonicotinoid insecticides on bumble bee energy metabolism are revealed under nectar starvation

Bumble bees are an important group of insects that provide essential pollination services as a consequence of their foraging behaviors. These pollination services are driven, in part, by energetic exchanges between flowering plants and individual bees. Thus, it is important to examine bumble bee energy metabolism and explore how it might be influenced by external stressors contributing to declines in global pollinator populations. Two stressors that are commonly encountered by bees are insecticides, such as the neonicotinoids, and nutritional stress, resulting from deficits in pollen and nectar availability. Our study uses a metabolomic approach to examine the effects of neonicotinoid insecticide exposure on bumble bee metabolism, both alone and in combination with nutritional stress. We hypothesized that exposure to imidacloprid disrupts bumble bee energy metabolism, leading to changes in key metabolites involved in central carbon metabolism. We tested this by exposing Bombus impatiens workers to imidacloprid according to one of three exposure paradigms designed to explore how chronic versus more acute (early or late) imidacloprid exposure influences energy metabolite levels, then also subjecting them to artificial nectar starvation. The strongest effects of imidacloprid were observed when bees also experienced nectar starvation, suggesting a combinatorial effect of neonicotinoids and nutritional stress on bumble bee energy metabolism. Overall, this study provides important insights into the mechanisms underlying the impact of neonicotinoid insecticides on pollinators, and underscores the need for further investigation into the complex interactions between environmental stressors and energy metabolism.

Changes in soil microbial communities after exposure to neonicotinoids: A systematic review

Neonicotinoids are a group of nicotine-related chemicals widely used as insecticides in agriculture. Several studies have shown measurable quantities of neonicotinoids in the environment but little is known regarding their impact on soil microbial populations. The purpose of this systematic review was to clarify the effects of neonicotinoids on soil microbiology and to highlight any knowledge gaps. A formal systematic review was performed following PRISMA (Preferred Reporting Items for Systematic Review and Meta-Analyses) guidelines using keywords in PubMed, SCOPUS and Web of Science. This resulted in 29 peer-reviewed articles, whose findings diverged widely because of variable methodologies. Field-based studies were few (28%). Imidacloprid was the most widely used (66%) and soil microbial communities were most sensitive to it. Spray formulations were used in 83% of the studies and seed treatments in the rest. Diversity indices were the most frequently reported soil microbial parameter (62%). About 45% of the studies found that neonicotinoids had adverse impacts on soil microbial community structure, composition, diversity, functioning, enzymatic activity and nitrogen transformation. Interactions with soil physicochemical properties were poorly addressed in all studies. The need for more research, particularly field-based research on the effects of neonicotinoids on soil microorganisms was highlighted by this review.

Field-realistic exposure to neonicotinoid and sulfoximine insecticides impairs visual and olfactory learning and memory in Polistes paper wasps

Exposure to insecticides may contribute to global insect declines due to sublethal insecticide effects on non-target species. Thus far, much research on non-target insecticide effects has focused on neonicotinoids in a few bee species. Much less is known about effects on other insect taxa or newer insecticides, such as sulfoxaflor. Here, we studied the effects of an acute insecticide exposure on both olfactory and visual learning in free-moving Polistes fuscatus paper wasps. Wasps were exposed to a single, field-realistic oral dose of low-dose imidacloprid, high-dose imidacloprid or sulfoxaflor. Then, visual and olfactory learning and short-term memory were assessed. We found that acute insecticide exposure influenced performance, as sulfoxaflor- and high-dose imidacloprid-exposed wasps made fewer correct choices than control wasps. Notably, both visual and olfactory performance were similarly impaired. Wasps treated with high-dose imidacloprid were also less likely to complete the learning assay than wasps from the other treatment groups. Instead, wasps remained stationary and unmoving in the testing area, consistent with imidacloprid interfering with motor control. Finally, wasps treated with sulfoxaflor were more likely to die in the week after treatment than wasps in the other treatment groups. Our findings demonstrate that sublethal, field-realistic dosages of both neonicotinoid- and sulfoximine-based insecticides impair wasp learning and short-term memory, which may have additional effects on survival and motor functioning. Insecticides have broadly detrimental effects on diverse non-target insects that may influence foraging effectiveness, pollination services and ecosystem function.

Effects of thiamethoxam on brain structure of Bombus terrestris (Hymenoptera: Apidae) workers

Neonicotinoids are the most widely used pesticide compared to other major insecticide classes known worldwide and have the fastest growing market share. Many studies showed that neonicotinoid pesticides harm honeybee learning and farming activities, negatively affect colony adaptation and reduce pollination abilities. Bumblebees are heavily preferred species all over the world in order to ensure pollination in plant production. In this study, sublethal effects of the neonicotinoid insecticide thiamethoxam on the brain of Bombus terrestris workers were analyzed. Suspensions (1/1000, 1/100, 1/10) of the maximum recommended dose of thiamethoxam were applied to the workers. 48 h after spraying, morphological effects on the brains of workers were studied. According to area measurements of ICC's of Kenyon cells, there was a significant difference between 1/10 dose and all groups. On the other hand, areas of INC's of Kenyon cells showed a significant difference between the control group and all dose groups. Neuropil disorganization in the calyces increased gradually and differed significantly between the groups and was mostly detected at the highest dose (1/10). Apart from optic lobes, pycnotic nuclei were also observed in the middle region of calyces of mushroom bodies in the high dose group. Also, the width of the lamina, medulla and lobula parts of the optic lobes of each group and the areas of the antennal lobes were measured and significant differences were determined between the groups. The results of the study revealed that sublethal doses of thiamethoxam caused some negative impacts on brain morphology of B. terrestris workers.

Do differentially charged nanoplastics affect imidacloprid uptake, translocation, and metabolism in Chinese flowering cabbage?

Micro(nano)plastics are ubiquitous in the environment. Among the microplastics, imidacloprid (IMI) concentration has been increasing in some intensive agricultural regions, thus receiving increased attention. However, only a few studies have investigated the interaction of nanoplastics (polystyrene (PS)) and IMI in vegetable crops. We studied the effects of positively (PS-NH₂) and negatively (PS-COOH) charged nanoplastics on the uptake, translocation, and degradation of IMI in Chinese flowering cabbage grown in Hoagland solution for 28 days. PS-NH₂ co-exposure with IMI inhibited plant growth, resulting in decreased plant weight, height, and root length. Translocation of IMI from the roots to the shoots was significantly lower in the presence of PS-NH₂, whereas PS-COOH accelerated the accumulation and translocation of IMI in plants, thus potentially affecting IMI metabolism in plants. Notably, IMI-NTG and 5-OH-IMI were the two dominant metabolites. PS-NH₂ co-exposure with IMI induced significant oxidation stress and considerably affected the activities of superoxide dismutase (SOD) and peroxidase (POD), indicating that the antioxidant defense system was the main mechanism for reducing oxidative damage. Notably, both positively and negatively charged nanoplastics can accumulate in Chinese flowering cabbage. Plants in the PS-COOH alone treatment group had the highest concentration of nanoplastics in both roots and shoots. The accumulation of nanoplastics, IMI, and its metabolites in plants raises concerns about their combined potential toxicity because it compromises food safety.

Neonicotinoid seed treatment on sugar beet in England: a qualitative analysis of the controversy, existing policy and viability of alternatives

In 2021, the United Kingdom Government granted the possibility of an emergency derogation for the use of the neonicotinoid seed treatment, thiamethoxam, on sugar beet in England. This was met with heavy criticism and controversy due to the body of evidence demonstrating toxicity of the insecticide to non-target species, particularly pollinators. However, many viewed this decision to be reasonable in this system, as sugar beet is a non-flowering crop, and derogations were only implemented if a set of conditions, including viral risk, were met. This research aims to understand the policy and the perspective of stakeholders in this debate, and identify key problems associated with thiamethoxam use on sugar beet. Semi-structured interviews combined with a modified policy analysis were used, incorporating framework analysis and comparative analysis. Political polarisation, whereby respondents felt that the debate had become anti-pesticide or pro-pesticide and lacked nuance, and the monopsony of British Sugar (a UK company that buys and processes sugar beet), were found to be the most prevalent issues currently impeding political progress and the enhancement of sustainable agriculture in this system. Virus forecasting was considered a successful strategy at the time of writing, although limitations to the model are also discussed. Non-chemical alternatives were found to be limited in this system due to the specificity of the pest system and the low threshold of virus yellows, while forecasting was considered to have the lowest net-environmental impact. Additional policy strategies to work alongside forecasting, such as public education and intergroup contact are also discussed. This study reflects a more general tug-of-war that often sets up a false dichotomy between food security and environmental sustainability. It highlights the importance of addressing the complexity of sustainable food production by opening up the discussion and taking a more nuanced and adaptive approach to policy.

Using the Honey Bee (Apis mellifera L.) Cell Line AmE-711 to Evaluate Insecticide Toxicity

One of the main contributors to poor productivity and elevated mortality of honey bee colonies globally is insecticide exposure. Whole-organism and colony-level studies have demonstrated the effects of insecticides on many aspects of honey bee biology and have also shown their interactions with pathogens. However, there is a need for in vitro studies using cell lines to provide greater illumination of the effects of insecticides on honey bee cellular and molecular processes. We used a continuous cell line established from honey bee embryonic tissues (AmE-711) in assays that enabled assessment of cell viability in response to insecticide exposure. We exposed AmE-711 cells to four formulations, each containing a different insecticide. Treatment of cells with the insecticides resulted in a concentration-dependent reduction in viability after a 24-h exposure, whereas long-term exposure (120 h) to sublethal concentrations had limited effects on viability. The 24-h exposure data allowed us to predict the half-maximal lethal concentration (LC50) for each insecticide using a four-parameter logistical model. We then exposed cells for 12 h to the predicted LC50 and observed changes in morphology that would indicate stress and death. Reverse transcription-quantitative polymerase chain reaction analysis corroborated changes in morphology: expression of a cellular stress response gene, 410087a, increased after an 18-h exposure to the predicted LC50. Demonstration of the effects of insecticides through use of AmE-711 provides a foundation for additional research addressing issues specific to honey bee toxicology and complements whole-organism and colony-level approaches. Moreover, advances in the use of AmE-711 in high-throughput screening and in-depth analysis of cell regulatory networks will promote the discovery of novel control agents with decreased negative impacts on honey bees. Environ Toxicol Chem 2023;42:88-99. Published 2022. This article is a U.S. Government work and is in the public domain in the USA. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Genomic architecture and sexually dimorphic expression underlying immunity in the red mason bee, Osmia bicornis

Insect pollinators provide crucial ecosystem services yet face increasing environmental pressures. The challenges posed by novel and reemerging pathogens on bee health means we need to improve our understanding of the immune system, an important barrier to infections and disease. Despite the importance of solitary bees, which are ecologically relevant, our understanding of the genomic basis and molecular mechanisms underlying their immune potential, and how intrinsic and extrinsic factors may influence it is limited. To improve our understanding of the genomic architecture underlying immunity of a key solitary bee pollinator, we characterized putative immune genes of the red mason bee, Osmia bicornis. In addition, we used publicly available RNA-seq datasets to determine how sexes differ in immune gene expression and splicing but also how pesticide exposure may affect immune gene expression in females. Through comparative genomics, we reveal an evolutionarily conserved set of more than 500 putative immune-related genes. We found genome-wide patterns of sex-biased gene expression, with greater enrichment of immune-related processes among genes with higher constitutive expression in males than females. Our results also suggest an up-regulation of immune-related genes in response to exposure to two common neonicotinoids, thiacloprid and imidacloprid. Collectively, our study provides important insights into the gene repertoire, regulation and expression differences in the sexes of O. bicornis, as well as providing additional support for how neonicotinoids can affect immune gene expression, which may affect the capacity of solitary bees to respond to pathogenic threats.

Environmental pharmacology-Dosing the environment: IUPHAR review 36

Pesticide action is predominantly measured as a toxicological outcome, with pharmacological impact of sublethal doses on bystander species left largely undocumented. Likewise, chronic exposure, which often results in responses different from acute administration, has also been understudied. In this article, we propose the application of standard pharmacological principles, already used to establish safe clinical dosing regimens in humans, to the 'dosing of the environment'. These principles include relating the steady state dose of an agent to its beneficial effects (e.g. pest control), while minimising harmful impacts (e.g. off-target bioactivity in beneficial insects). We propose the term 'environmental therapeutic window', analogous to that used in mammalian pharmacology, to guide risk assessment. To make pharmacological terms practically useful to environmental protection, quantitative data on pesticide action need to be made available in a freely accessible database, which should include toxicological and pharmacological impacts on both target and off-target species.

Mechanism of the distinct toxicity level of imidacloprid and thiacloprid against honey bees: An in silico study based on cytochrome P450 9Q3

The honey bee, Apis mellifera, shows variation in sensitivity to imidacloprid and thiacloprid, which does not reside at the target site but rather in the rapidly oxidative metabolism mediated by P450s (such as a single P450, CYP9Q3). An in silico study was conducted to investigate the various metabolism of imidacloprid and thiacloprid. The binding potency of thiacloprid was stronger and a stable π-π interaction with Phe121 and the N-H⋯N hydrogen bond with Asn214 are found in the CYP9Q3-thiacloprid system but absent in imidacloprid, which might affect the potential metabolic activity. Moreover, the values of highest occupied molecular orbit (HOMO) energy and the vertical ionization potential (IP) of two compounds demonstrated that thiacloprid is more likely to oxidation. The findings revealed the probable binding modes of imidacloprid and thiacloprid with CYP9Q3 and might facilitate future design of the low bee toxicity neonicotinoid insecticides.

The Insecticide Imidacloprid Decreases Nannotrigona Stingless Bee Survival and Food Consumption and Modulates the Expression of Detoxification and Immune-Related Genes

Stingless bees are ecologically and economically important species in the tropics and subtropics, but there has been little research on the characterization of detoxification systems and immune responses within them. This is critical for understanding their responses to, and defenses against, a variety of environmental stresses, including agrochemicals. Therefore, we studied the detoxification and immune responses of a stingless bee, Nanotrigona perilampoides, which is an important stingless bee that is widely distributed throughout Mexico, including urban areas, and has the potential to be used in commercial pollination. We first determined the LC50 of the neonicotinoid insecticide imidacloprid for foragers of N. perilampoides, then chronically exposed bees for 10 days to imidacloprid at two field-realistic concentrations, LC10 (0.45 ng/µL) or LC20 (0.74 ng/µL), which are respectively 2.7 and 1.3-fold lower than the residues of imidacloprid that have been found in honey (6 ng/g) in central Mexico. We found that exposing N. perilampoides stingless bees to imidacloprid at these concentrations markedly reduced bee survival and food consumption, revealing the great sensitivity of this stingless bee to the insecticide in comparison to honey bees. The expression of detoxification (GSTD1) and immune-related genes (abaecin, defensin1, and hymenopteacin) in N. perilampoides also changed over time in response to imidacloprid. Gene expression was always lower in bees after 8 days of exposure to imidacloprid (LC10 or LC20) than it was after 4 days. Our results demonstrate that N. perilampoides stingless bees are extremely sensitive to imidacloprid, even at low concentrations, and provide greater insight into how stingless bees respond to pesticide toxicity. This is the first study of its kind to look at detoxification systems and immune responses in Mexican stingless bees, an ecologically and economically important taxon.

The flavonoid rutin protects against cognitive impairments by imidacloprid and fipronil

The ongoing decline of bee populations and its impact on food security demands integrating multiple strategies. Sublethal impairments associated with exposure to insecticides, affecting the individual and the colony levels, have led to insecticide moratoria and bans. However, legislation alone is not sufficient and remains a temporary solution to an evolving market of insecticides. Here, we asked whether bees can be prophylactically protected against sublethal cognitive effects of two major neurotoxic insecticides, imidacloprid and fipronil, with different mechanisms of action. We evaluated the protective effect of the prophylactic administration of the flavonoid rutin, a secondary plant metabolite, present in nectar and pollen, and known for its neuroprotective properties. Following controlled or ad libitum administration of rutin, foragers of the North American bumble bee Bombus impatiens received oral administration of the insecticides at sublethal realistic dosages. Learning acquisition, memory retention and decision speed were evaluated using olfactory absolute conditioning of the proboscis extension response. We show that the insecticides primarily impair acquisition but not retention or speed of the conditioned proboscis extension response. We further show that the administration of the flavonoid rutin successfully protects the bees against impairments produced by acute and chronic administration of insecticides. Our results suggest a new avenue for the protection of bees against sublethal cognitive effects of insecticides.

Highlighted Article: Prophylactically feeding bumble bees with rutin protects their learning and memory performance against oral exposure to insecticides with different mechanisms of action.

Exposure to the novel insecticide flupyradifurone impairs bumblebee feeding motivation, learning, and memory retention

Bees are vital pollinators of crops and wildflowers and as such, wild bee declines threaten food security and functioning ecosystems. One driver of bee declines is the use of systemic insecticides, such as commonly used neonicotinoids. However, rising pest resistance to neonicotinoids, and restrictions on their use in the EU, has increased the demand for replacement insecticides to control crop pests. Flupyradifurone is a novel systemic insecticide that is thought to be relatively 'bee safe' although it can be present in the nectar and pollen of bee-attractive crops. Bumblebees rely on learning to forage efficiently, and thus detriments to learning performance may have downstream consequences on their ability to forage. While neonicotinoids negatively influence bumblebee learning and memory, whether this is also the case for their replacements is unclear. Here, we exposed bumblebees (Bombus impatiens) to an acute, field-realistic dose of flupyradifurone before training them to learn either an olfactory or colour association. We found that flupyradifurone impaired bumblebees' learning and memory performance in both olfactory and visual modalities. Flupyradifurone-treated bees were also less motivated to feed. Given the similarity between the detriments to cognition found here and those previously reported for neonicotinoids, this implies that these insecticides may have similar sub-lethal effects on bees. Restrictions on neonicotinoid use are therefore unlikely to benefit bees if novel insecticides like flupyradifurone are used as an alternative, highlighting that current agrochemical risk assessments are not protecting bees from the unwanted consequences of pesticide use. Sub-lethal assessments on non-Apis bees should be made mandatory in agrochemical regulation to ensure that novel insecticides are indeed 'bee safe'.

Hormesis and insects: Effects and interactions in agroecosystems

Insects in agroecosystems contend with many stressors - e.g., chemicals, heat, nutrient deprivation - that are often encountered at low levels. Exposure to mild stress is now well known to induce hormetic (stimulatory) effects in insects, with implications for insect management, and ecological structure and function in agroecosystems. In this review, we examine the major ecological niches insects occupy or guilds to which they belong in agroecosystems and how hormesis can manifest within and across these groups. The mechanistic underpinnings of hormesis in insects are starting to become established, explaining the many phenotypic hormetic responses observed in insect reproduction, development, and behavior. Whereas potential effects on insect populations are well supported in laboratory experiments, field-based hypothesis-driven research on hormesis is greatly lacking. Furthermore, because most ecological paradigms are founded within the context of communities, entomological agroecologists interested in hormesis need to 'level up' and test hypotheses that explore effects on species interactions, and community structure and functioning. Embedded in this charge is to continue experimentation on herbivorous pest species while shifting more focus towards insect natural enemies, pollinators, and detritivores - guilds that play crucial roles in highly functioning agroecosystems that have been understudied in hormesis research. Important areas for future insect agroecology research on hormesis are discussed.

A Combined LD50 for Agrochemicals and Pathogens in Bumblebees (Bombus terrestris [Hymenoptera: Apidae])

Neonicotinoid insecticides are the most commonly used insecticide in the world and can have significant sub-lethal impacts on beneficial insects, including bumblebees, which are important pollinators of agricultural crops and wild-flowers. This has led to bans on neonicotinoid use in the EU and has resulted in repeated calls for the agrochemical regulatory process to be modified. For example, there is increasing concern about 1) the underrepresentation of wild bees, such as bumblebees, in the regulatory process, and 2) the failure to determine how agrochemicals, such as neonicotinoids, interact with other commonly occurring environmental stressors, such as parasites. Here, we modify an OECD approved lethal dose (LD50) experimental design and coexpose bumblebees (Bombus terrestris) to the neonicotinoid thiamethoxam and the highly prevalent trypanosome parasite Crithidia bombi, in a fully crossed design. We found no difference in the LD50 of thiamethoxam on bumblebees that had or had not been inoculated with the parasite (Crithidia bombi). Furthermore, thiamethoxam dosage did not appear to influence the parasite intensity of surviving bumblebees, and there was no effect of either parasite or insecticide on sucrose consumption. The methodology used demonstrates how existing ring-tested experimental designs can be effectively modified to include other environmental stressors such as parasites. Moving forward, the regulatory process should implement methodologies that assess the interactions between agrochemicals and parasites on non-Apis bees and, in cases when this is not practical, should implement post-regulatory monitoring to better understand the real-world consequences of agrochemical use.

Detection of imidacloprid and metabolites in Northern Leopard frog (Rana pipiens) brains

Neonicotinoids are a new type of highly water-soluble insecticide used in agricultural practices to eliminate pests. Neonicotinoids bind almost irreversibly to postsynaptic nicotinic acetylcholine receptors in the central nervous system of invertebrates, resulting in overstimulation, paralysis, and death. Imidacloprid, the most commonly used neonicotinoid, is often transported to nearby wetlands through subsurface tile drains and has been identified as a neurotoxin in several aquatic non-target organisms. The aim of the present study was to determine if imidacloprid could cross the blood-brain barrier in adult Northern Leopard frogs (Rana pipiens) following exposure to 0, 0.1, 1, 5, or 10 μg/L for 21 days. Additionally, we quantified the breakdown product of imidacloprid, imidacloprid-olefin, and conducted feeding trials to better understand how imidacloprid affects foraging behavior over time. Exposure groups had 12 to 313 times more imidacloprid in the brain relative to the control and breakdown products showed a dose-response relationship. Moreover, imidacloprid brain concentrations were approximately 14 times higher in the 10 μg/L treatment compared to the water exposure concentration, indicating imidacloprid can bioaccumulate in the amphibian brain. Reaction times to a food stimulus were 1.5 to 3.2 times slower among treatment groups compared to the control. Furthermore, there was a positive relationship between mean response time and log-transformed imidacloprid brain concentration. These results indicate imidacloprid can successfully cross the blood-brain barrier and bioaccumulate in adult amphibians. Our results also provide insights into the relationship between imidacloprid brain concentration and subsequent altered foraging behavior.

Application of Molecular Docking, Homology Modeling, and Chemometric Approaches to Neonicotinoid Toxicity against Aphis craccivora

Neonicotinoids are known as effective pesticides against various insect species. They can harm useful insects including honeybees, with a relatively low threat to nontarget organisms and the environment. This paper presents combined methods to explore the insecticidal activity of neonicotinoids with diverse scaffolds, active against Aphis craccivora. Pharmacophore, molecular docking into the active site of nicotinic acetylcholine receptor homology model, and linear and non-linear regression approaches were used to find new insecticide candidates. The potential toxic effects against honeybees were evaluated using the molecular docking in the active site of the new Aphis mellifera homology model. Four new untested compounds were assigned as insecticide candidates, active against Aphis craccivora with less potential toxic effects for honeybees. This approach may be an effective strategy to design environmentally friendly insecticides against the cowpea aphid.

Improved mitochondrial function corrects immunodeficiency and impaired respiration in neonicotinoid exposed bumblebees

Neonicotinoid pesticides undermine pollinating insects including bumblebees. However, we have previously shown that mitochondrial damage induced by neonicotinoids can be corrected by 670nm light exposure. But we do not know if this protection extends to immunity or what the minimum effective level of 670nm light exposure is necessary for protection. We use whole body bee respiration in vivo as a metric of neonicotinoid damage and assess the amount of light exposure needed to correct it. We reveal that only 1 min of 670nm exposure is sufficient to correct respiratory deficits induced by pesticide and that this also completely repairs damaged immunocompetence measured by haemocyte counts and the antibacterial action of hemolymph. Further, this single 1 min exposure remains effective for 3–6 days. Longer exposures were not more effective. Such data are key for development of protective light strategies that can be delivered by relatively small economic devices placed in hives.

Neonicotinoid residues in honey from urban and rural environments

Pesticide residues in honey can negatively affect bee health. Although recent studies have detected neonicotinoid residues in honeys from around the world, little is known about how residues relate to land use and vegetation composition. To investigate potential relationships, we sampled multi-floral honey from 30 Apis mellifera hives from urban, agricultural and semi-natural habitats (SNH), identified and quantified three neonicotinoids present (clothianidin, imidacloprid and thiacloprid) using UHPLC-MS, and classified surrounding land use up to 5 km around hive sites. Neonicotinoids were most frequently detected in honeys from hives in agricultural habitats, and 70% of all samples contained at least one of the three neonicotinoid compounds. Imidacloprid was the most frequently detected neonicotinoid (found in 43% of honey samples) followed by clothianidin (40%) and thiacloprid (37%). Almost half (48%) of samples contained at least two neonicotinoids, and two of the 30 samples contained all three. Clothianidin and thiacloprid were more frequently detected in honeys from urban habitats, highlighting that exposure to pesticides does not just occur in agricultural settings. This suggests that pesticide use in urban domestic, sport and amenity contexts, given potential exposure of bees and other pollinators, needs urgent consideration.

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.

Impacts of Neonicotinoids on the Bumble Bees Bombus terrestris and Bombus impatiens Examined through the Lens of an Adverse Outcome Pathway Framework

Bumble bees (Bombus sp.) are important pollinators for agricultural systems and natural landscapes and have faced population declines globally in recent decades. Neonicotinoid pesticides have been implicated as one of the reasons for the population reductions in bumble bees and other pollinators due to their widespread use, specificity to the invertebrate nervous system, and toxicity to bees. Adverse outcome pathways (AOPs) are used to describe the mechanism of action of a toxicant through sequential levels of biological organization to understand the key events that occur for a given adverse outcome. We used the AOP framework to organize and present the current literature available on the impacts of neonicotinoids on bumble bees. The present review focuses on Bombus terrestris and B. impatiens, the 2 most commonly studied bumble bees due to their commercial availability. Our review does not seek to describe an AOP for the molecular initiating event shared by neonicotinoids, but rather aims to summarize the current literature and determine data gaps for the Bombus research community to address. Overall, we highlight a great need for additional studies, especially those examining cellular and organ responses in bumble bees exposed to neonicotinoids. Environ Toxicol Chem 2021;40:309-322. © 2020 SETAC. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Neonicotinoids disrupt memory, circadian behaviour and sleep

Globally, neonicotinoids are the most used insecticides, despite their well-documented sub-lethal effects on beneficial insects. Neonicotinoids are nicotinic acetylcholine receptor agonists. Memory, circadian rhythmicity and sleep are essential for efficient foraging and pollination and require nicotinic acetylcholine receptor signalling. The effect of field-relevant concentrations of the European Union-banned neonicotinoids: imidacloprid, clothianidin, thiamethoxam and thiacloprid were tested on Drosophila memory, circadian rhythms and sleep. Field-relevant concentrations of imidacloprid, clothianidin and thiamethoxam disrupted learning, behavioural rhythmicity and sleep whilst thiacloprid exposure only affected sleep. Exposure to imidacloprid and clothianidin prevented the day/night remodelling and accumulation of pigment dispersing factor (PDF) neuropeptide in the dorsal terminals of clock neurons. Knockdown of the neonicotinoid susceptible Dα1 and Dβ2 nicotinic acetylcholine receptor subunits in the mushroom bodies or clock neurons recapitulated the neonicotinoid like deficits in memory or sleep/circadian behaviour respectively. Disruption of learning, circadian rhythmicity and sleep are likely to have far-reaching detrimental effects on beneficial insects in the field.

The Neonicotinoid Insecticide Imidacloprid Disrupts Bumblebee Foraging Rhythms and Sleep

Neonicotinoids have been implicated in the large declines observed in insects such as bumblebees, an important group of pollinators. Neonicotinoids are agonists of nicotinic acetylcholine receptors that are found throughout the insect central nervous system and are the main mediators of synaptic neurotransmission. These receptors are important for the function of the insect central clock and circadian rhythms. The clock allows pollinators to coincide their activity with the availability of floral resources and favorable flight temperatures, as well as impact learning, navigation, and communication. Here we show that exposure to the field-relevant concentration of 10 μg/L imidacloprid caused a reduction in bumblebee foraging activity, locomotion, and foraging rhythmicity. Foragers showed an increase in daytime sleep and an increase in the proportion of activity occurring at night. This could reduce foraging and pollination opportunities, reducing the ability of the colony to grow and reproduce, endangering bee populations and crop yields.

Effects of Nosema ceranae (Dissociodihaplophasida: Nosematidae) and Flupyradifurone on Olfactory Learning in Honey Bees, Apis mellifera (Hymenoptera: Apidae)

The health of insect pollinators, particularly the honey bee, Apis mellifera (Linnaeus, 1758), is a major concern for agriculture and ecosystem health. In response to mounting evidence supporting the detrimental effects of neonicotinoid pesticides on pollinators, a novel 'bee safe' butenolide compound, flupyradifurone (FPF) has been registered for use in agricultural use. Although FPF is not a neonicotinoid, like neonicotinoids, it is an excitotoxic nicotinic acetylcholine receptor agonist. In addition, A. mellifera faces threats from pathogens, such as the microsporidian endoparasite, Nosema ceranae (Fries et al. 1996). We therefore sought 1) to increase our understanding of the potential effects of FPF on honey bees by focusing on a crucial behavior, the ability to learn and remember an odor associated with a food reward, and 2) to test for a potential synergistic effect on such learning by exposure to FPF and infection with N. ceranae. We found little evidence that FPF significantly alters learning and memory at short-term field-realistic doses. However, at high doses and at chronic, field-realistic exposure, FPF did reduce learning and memory in an olfactory conditioning task. Infection with N. ceranae also reduced learning, but there was no synergy (no significant interaction) between N. ceranae and exposure to FPF. These results suggest the importance of continued studies on the chronic effects of FPF.

The neonicotinoid thiacloprid causes transcriptional alteration of genes associated with mitochondria at environmental concentrations in honey bees

Thiacloprid is widely used in agriculture and may affect pollinators. However, its molecular effects are poorly known. Here, we report the global gene expression profile in the brain of honey bee foragers assessed by RNA-sequencing. Bees were exposed for 72 h to nominal concentrations of 25 and 250 ng/bee via sucrose solution. Determined residue concentrations by LC-MS/MS were 0.59 and 5.49 ng/bee, respectively. Thiacloprid exposure led to 5 and 71 differentially expressed genes (DEGs), respectively. Nuclear genes encoding mitochondrial ribosomal proteins and enzymes involved in oxidative phosphorylation, as well as metabolism enzymes and transporters were altered at 5.49 ng/bee. Kyoto Encylopedia of Genes and Genomes (KEGG) analysis revealed that mitochondrial ribosome proteins, mitochondrial oxidative phosphorylation, pyrimidine, nicotinate and nicotinamide metabolism and additional metabolic pathways were altered. Among 21 genes assessed by RT-qPCR, the transcript of farnesol dehydrogenase involved in juvenile hormone III synthesis was significantly down-regulated. Transcripts of cyp6a14-like and apolipophorin-II like protein, cytochrome oxidase (cox17) and the non-coding RNA (LOC102654625) were significantly up-regulated at 5.49 ng/bee. Our findings indicate that thiacloprid causes transcriptional changes of genes prominently associated with mitochondria, particularly oxidative phosphorylation. This highlight potential effects of this neonicotinoid on energy metabolism, which may compromise bee foraging and thriving populations at environmentally relevant concentrations.

Assessments on the molecular toxic mechanisms of fipronil and neonicotinoids with glutathione transferase Phi8

As the most widely used pesticides, fipronils and neonicotinoids exhibit harmful effects to many species including crops mainly via the oxidative damages. However, the potential toxic mechanisms of these pesticides to plants remain unclear. In this work, glutathione S-transferase Phi8 was employed as the biomarker to assess the adverse oxidative effects of these two kinds of pesticides. The structural changes and binding characteristics of AtGSTF8 with the pesticides were investigated by multispectral techniques and the latest generation neonicotinoid dinotefuran exhibited the most evident effects on the structure of AtGSTF8. Then dinotefuran displayed weak binding ability to AtGSTF8 comparing with fipronil and clothianidin based on the bio-layer interferometry technique. Besides, the glutathione S-transferase activities of AtGSTF8 were decreased upon binding with these two kinds of pesticides but dinotefuran displayed minor effect on the enzyme activity. At last, dinotefuran and clothianidin were presumed to locate on the molecular surface of AtGSTF8, while fipronil was predicted to insert into the cavity of AtGSTF8 which was adjacent to the active G-site based on the molecular docking results. The molecular investigations on the toxic mechanisms would help to evaluate the harmful effects of these two kinds of prevalent pesticides to plants.

Neonicotinoids suppress contact chemoreception in a common farmland spider

Neonicotinoid insecticides are increasingly recognized for their role as information disruptors by modifying the chemical communication system of insects and therefore decreasing the chances of reproduction in target insects. However, data from spiders are lacking. In the present study, we tested the responses of males of a common agrobiont spider, Pardosa agrestis, to the application of field-realistic concentration of acetamiprid, which was formulated as Mospilan, and trace amounts of thiacloprid, which was formulated as Biscaya. We applied fresh or 24-h-old residues of Mospilan or Biscaya to the males just prior to the experiment or treated only the surface of a tunnel containing female draglines. We evaluated the ability of the males to recognize female cues from female dragline silk in a Y-maze. The field-realistic, sublethal doses of Mospilan altered pheromone-guided behavior. The choice of the tunnel with female draglines by males was hampered by tarsal treatment of the males with 24 h-old residues of Mospilan. The mating dance display was commonly initiated in control males that came into contact with female draglines and was suppressed by the Mospilan treatments in all three experimental settings. Some males only initiated the mating dance but did not manage to complete it; this was particularly true for males that were treated tarsally with fresh Mospilan residues, as none of these males managed to complete the mating dance. All three experimental settings with Mospilan decreased the frequency of males that managed to both select the tunnel with female draglines and complete the mating dance. The responses to the low-dose Biscaya were much milder and the study was not sufficiently powered to confirm the effects of Biscaya; however, the surprisingly observed trends in responses to very low Biscaya concentrations call for further analyses of long-term effects of trace amounts of neonicotinoids on the pheromone-guided behavior of spiders. These are the first conclusive data regarding the effects of commercially available formulations of neonicotinoid insecticides on the intraspecific chemical communication of spiders.

Imidacloprid impairs performance on a model flower handling task in bumblebees (Bombus impatiens)

Bumblebees exposed to neonicotinoid pesticides collect less pollen on foraging trips. Exposed bumblebees are also slower to learn to handle flowers, which may account for reduced pollen collection. It is unclear, however, why neonicotinoid exposure slows learning to handle flowers. We investigated the effect of imidacloprid, a neonicotinoid pesticide, on bumblebee motor learning using a lab model of flower handling. Bumblebees learned to invert inside a narrow tube and lift a petal-shaped barrier to reach a reward chamber. Imidacloprid-exposed bumblebees showed a dose-dependent delay to solve the task, which resulted from reduced switching between behavioural strategies and a subsequent delay in use of the successful strategy. This effect was consistent in colonies exposed at 10 but not 2.6 ppb, suggesting a variable effect on individuals at lower doses. These results help to explain why exposed bumblebees are slow to learn to handle flowers and collect less pollen on foraging trips.

Honeybees fail to discriminate floral scents in a complex learning task after consuming a neonicotinoid pesticide

Neonicotinoids are pesticides used to protect crops but with known secondary influences at sublethal doses on bees. Honeybees use their sense of smell to identify the queen and nestmates, to signal danger and to distinguish flowers during foraging. Few behavioural studies to date have examined how neonicotinoid pesticides affect the ability of bees to distinguish odours. Here, we used a differential learning task to test how neonicotinoid exposure affects learning, memory and olfactory perception in foraging-age honeybees. Bees fed with thiamethoxam could not perform differential learning and could not distinguish odours during short- and long-term memory tests. Our data indicate that thiamethoxam directly impacts the cognitive processes involved in working memory required during differential olfactory learning. Using a combination of behavioural assays, we also identified that thiamethoxam has a direct impact on the olfactory perception of similar odours. Honeybees fed with other neonicotinoids (clothianidin, imidacloprid, dinotefuran) performed the differential learning task, but at a slower rate than the control. These bees could also distinguish the odours. Our data are the first to show that neonicotinoids have compound specific effects on the ability of bees to perform a complex olfactory learning task. Deficits in decision making caused by thiamethoxam exposure could mean that this is more harmful than other neonicotinoids, leading to inefficient foraging and a reduced ability to identify nestmates.

Global Trends in Bumble Bee Health

Bumble bees (Bombus) are unusually important pollinators, with approximately 260 wild species native to all biogeographic regions except sub-Saharan Africa, Australia, and New Zealand. As they are vitally important in natural ecosystems and to agricultural food production globally, the increase in reports of declining distribution and abundance over the past decade has led to an explosion of interest in bumble bee population decline. We summarize data on the threat status of wild bumble bee species across biogeographic regions, underscoring regions lacking assessment data. Focusing on data-rich studies, we also synthesize recent research on potential causes of population declines. There is evidence that habitat loss, changing climate, pathogen transmission, invasion of nonnative species, and pesticides, operating individually and in combination, negatively impact bumble bee health, and that effects may depend on species and locality. We distinguish between correlational and causal results, underscoring the importance of expanding experimental research beyond the study of two commercially available species to identify causal factors affecting the diversity of wild species.

A holistic study of neonicotinoids neuroactive insecticides-properties, applications, occurrence, and analysis

Among pesticides and foliar sprays involved in the treatment of seed, soil, and grass, also to crops, an important group is neonicotinoids. Neonicotinoid pesticides present similar properties with nicotine, but the mentioned compounds are less harmful for humans. Nevertheless, neonicotinoids are poisonous to insects and some invertebrates, which can act against insects' central nervous system, leading to their death. Moreover, neonicotinoids can affect the reproduction, foraging, and flying ability of honeybee and other insects including pollinators. In the present study, some neonicotinoids, such as imidacloprid, acetamiprid, clothianidin, thiacloprid, and thiamethoxam together with their toxic effects, have been presented. The Environmental Protection Agency (EPA) classifies these neonicotinoids as II and III class toxicity agents. Due to accumulation of these pesticides into the pollen of treated plants, especially due to their toxic effects against pollinators, the consequences of the occurrence of these insecticides have been discussed. Analytical aspects and methods involved in the isolation and determination of this class of pesticides have been presented in this contribution.

The Impact of Pesticides on Flower-Visiting Insects: A Review with Regard to European Risk Assessment

Flower-visiting insects (FVIs) are an ecologically diverse group of mobile, flying species that should be protected from pesticide effects according to European policy. However, there is an ongoing decline of FVI species, partly caused by agricultural pesticide applications. Therefore, the risk assessment framework needs to be improved. We synthesized the peer-reviewed literature on FVI groups and their ecology, habitat, exposure to pesticides, and subsequent effects. The results show that FVIs are far more diverse than previously thought. Their habitat, the entire agricultural landscape, is potentially contaminated with pesticides through multiple pathways. Pesticide exposure of FVIs at environmentally realistic levels can cause population-relevant adverse effects. This knowledge was used to critically evaluate the European regulatory framework of exposure and effect assessment. The current risk assessment should be amended to incorporate specific ecological properties of FVIs, that is, traits. We present data-driven tools to improve future risk assessments by making use of trait information. There are major knowledge gaps concerning the general investigation of groups other than bees, the collection of comprehensive data on FVI groups and their ecology, linking habitat to FVI exposure, and study of previously neglected complex population effects. This is necessary to improve our understanding of FVIs and facilitate the development of a more protective FVI risk assessment. Environ Toxicol Chem 2019;38:2355-2370. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

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.

An assessment of acute insecticide toxicity loading (AITL) of chemical pesticides used on agricultural land in the United States

We present a method for calculating the Acute Insecticide Toxicity Loading (AITL) on US agricultural lands and surrounding areas and an assessment of the changes in AITL from 1992 through 2014. The AITL method accounts for the total mass of insecticides used in the US, acute toxicity to insects using honey bee contact and oral LD₅₀ as reference values for arthropod toxicity, and the environmental persistence of the pesticides. This screening analysis shows that the types of synthetic insecticides applied to agricultural lands have fundamentally shifted over the last two decades from predominantly organophosphorus and N-methyl carbamate pesticides to a mix dominated by neonicotinoids and pyrethroids. The neonicotinoids are generally applied to US agricultural land at lower application rates per acre; however, they are considerably more toxic to insects and generally persist longer in the environment. We found a 48- and 4-fold increase in AITL from 1992 to 2014 for oral and contact toxicity, respectively. Neonicotinoids are primarily responsible for this increase, representing between 61 to nearly 99 percent of the total toxicity loading in 2014. The crops most responsible for the increase in AITL are corn and soybeans, with particularly large increases in relative soybean contributions to AITL between 2010 and 2014. Oral exposures are of potentially greater concern because of the relatively higher toxicity (low LD₅₀s) and greater likelihood of exposure from residues in pollen, nectar, guttation water, and other environmental media. Using AITL to assess oral toxicity by class of pesticide, the neonicotinoids accounted for nearly 92 percent of total AITL from 1992 to 2014. Chlorpyrifos, the fifth most widely used insecticide during this time contributed just 1.4 percent of total AITL based on oral LD₅₀s. Although we use some simplifying assumptions, our screening analysis demonstrates an increase in pesticide toxicity loading over the past 26 years, which potentially threatens the health of honey bees and other pollinators and may contribute to declines in beneficial insect populations as well as insectivorous birds and other insect consumers.

Modality-specific impairment of learning by a neonicotinoid pesticide

Neonicotinoid pesticides can impair bees' ability to learn and remember information about flowers, critical for effective foraging. Although these effects on cognition may contribute to broader effects on health and performance, to date they have largely been assayed in simplified protocols that consider learning in a single sensory modality, usually olfaction. Given that real flowers display a variety of potentially useful signals, we assessed the effects of acute neonicotinoid exposure on multimodal learning in free-flying bumblebees. We found that neonicotinoid consumption differentially impacted learning of floral stimuli, impairing scent, but not colour, learning. These findings raise questions about the mechanisms by which pesticides might differentially impair sensory systems, with implications for how neonicotinoids affect multiple aspects of bee ecology.

A Neonicotinoid Affects the Mating Behavior of Spalangia endius (Hymenoptera: Pteromalidae), a Biological Control Agent of Filth Flies

Spalangia endius Walker is a parasitoid wasp that is commercially available as a biological control agent for filth fly pests in livestock-rearing operations. Imidacloprid is often used to control these flies. The present study examined the sublethal effect of field-realistic concentrations of imidacloprid on mating behavior, offspring sex ratios, and male preference for virgin females. After exposure to imidacloprid, S. endius females that survived were less likely to mate than control females, which will result in male-biased sex ratios because only mated females can produce daughters. Males did not avoid exposed females, but exposed females were almost always unreceptive. Males that survived exposure to imidacloprid exhibited reduced mating competitiveness against unexposed males. However, if an exposed male mated, his mate's sex ratio and ability to control flies was unaffected. Exposed males were also still able to discriminate against mated, and thus usually unreceptive, females. Together with previous studies, these results suggest that not only does imidacloprid reduce the ability of S. endius females to survive and parasitize hosts, but when an exposed female does survive and parasitize hosts, she is likely to produce just sons, because of her lack of receptivity. More-male-biased populations of S. endius will decrease their efficacy for fly control. Thus, the use of imidacloprid along with this parasitoid may be financially inefficient for pest management.

Pesticide exposure affects flight dynamics and reduces flight endurance in bumblebees

The emergence of agricultural land use change creates a number of challenges that insect pollinators, such as eusocial bees, must overcome. Resultant fragmentation and loss of suitable foraging habitats, combined with pesticide exposure, may increase demands on foraging, specifically the ability to collect or reach sufficient resources under such stress. Understanding effects that pesticides have on flight performance is therefore vital if we are to assess colony success in these changing landscapes. Neonicotinoids are one of the most widely used classes of pesticide across the globe, and exposure to bees has been associated with reduced foraging efficiency and homing ability. One explanation for these effects could be that elements of flight are being affected, but apart from a couple of studies on the honeybee (Apis mellifera), this has scarcely been tested. Here, we used flight mills to investigate how exposure to a field realistic (10 ppb) acute dose of imidacloprid affected flight performance of a wild insect pollinator-the bumblebee, Bombus terrestris audax. Intriguingly, observations showed exposed workers flew at a significantly higher velocity over the first ¾ km of flight. This apparent hyperactivity, however, may have a cost because exposed workers showed reduced flight distance and duration to around a third of what control workers were capable of achieving. Given that bumblebees are central place foragers, impairment to flight endurance could translate to a decline in potential forage area, decreasing the abundance, diversity, and nutritional quality of available food, while potentially diminishing pollination service capabilities.

Temporal pattern in levels of the neonicotinoid insecticide, imidacloprid, in an urban stream

Imidacloprid is a widely used insecticide with high runoff potential posing a significant threat to aquatic ecosystems. In order to determine the spatial and temporal concentrations of imidacloprid in Forester Creek, a tributary to the San Diego River, surface water samples were collected from two sites under wet-weather and dry-weather conditions. Solid phase extraction and liquid chromatography tandem mass spectrometry were utilized to quantify imidacloprid levels in all samples. Imidacloprid was detected with 100% frequency in surface water samples from Forester Creek with a median concentration of 16.9 ng/L (range: 3.8-96.8 ng/L). Over 60% of samples exceeded U.S. EPA's chronic exposure benchmark (10 ng/L). Temporal analysis displayed significantly higher levels in wet-weather than dry-weather (median 45.6 ng/L vs. 8.2 ng/L (p < 0.05)), demonstrating the influence of wet-weather runoff on stream quality. Imidacloprid generally followed a first flush pattern with the highest levels observed on the rising portion of the hydrograph as compared to the remainder of the storm, further indicating that the build-up and wash off from land surfaces during storms is a major source of imidacloprid into urban surface waters. To our knowledge, the present study is the first to document this first flush pattern for imidacloprid in an urban stream in southern California. Such data on the occurrence and levels of imidacloprid in this urban stream contribute to the limited knowledge on imidacloprid in urban environments and will promote a better understanding of sources and effects of the neonicotinoid pesticide within the southern California region.

A neonicotinoid pesticide impairs foraging, but not learning, in free-flying bumblebees

Neonicotinoids are widely-used pesticides implicated in the decline of bees, known to have sub-lethal effects on bees’ foraging and colony performance. One proposed mechanism for these negative effects is impairment to bees’ ability to learn floral associations. However, the effects of neonicotinoids on learning performance have largely been addressed using a single protocol, where immobilized bees learn an association based on a single sensory modality. We thus have an incomplete understanding of how these pesticides affect bee learning in more naturalistic foraging scenarios. We carried out the first free-foraging study into the effects of acute exposure of a neonicotinoid (imidacloprid) on bumblebees’ (Bombus impatiens) ability to learn associations with visual stimuli. We uncovered dose-dependent detrimental effects on motivation to initiate foraging, amount of nectar collected, and initiation of subsequent foraging bouts. However, we did not find any impairment to bees’ ability to learn visual associations. While not precluding the possibility that other forms of learning are impaired, our findings suggest that some of the major effects of acute neonicotinoid exposure on foraging performance may be due to motivational and/or sensory impairments. In light of these findings, we discuss more broadly how pesticide effects on pollinator cognition might be studied.

Caste- and pesticide-specific effects of neonicotinoid pesticide exposure on gene expression in bumblebees

Social bees are important insect pollinators of wildflowers and agricultural crops, making their reported declines a global concern. A major factor implicated in these declines is the widespread use of neonicotinoid pesticides. Indeed, recent research has demonstrated that exposure to low doses of these neurotoxic pesticides impairs bee behaviours important for colony function and survival. However, our understanding of the molecular-genetic pathways that lead to such effects is limited, as is our knowledge of how effects may differ between colony members. To understand what genes and pathways are affected by exposure of bumblebee workers and queens to neonicotinoid pesticides, we implemented a transcriptome-wide gene expression study. We chronically exposed Bombus terrestriscolonies to either clothianidin or imidacloprid at field-realistic concentrations while controlling for factors including colony social environment and worker age. We reveal that genes involved in important biological processes including mitochondrial function are differentially expressed in response to neonicotinoid exposure. Additionally, clothianidin exposure had stronger effects on gene expression amplitude and alternative splicing than imidacloprid. Finally, exposure affected workers more strongly than queens. Our work demonstrates how RNA-Seq transcriptome profiling can provide detailed novel insight on the mechanisms mediating pesticide toxicity to a key insect pollinator.