A nicotinic acetylcholine receptor agonist affects honey bee sucrose responsiveness and decreases waggle dancing

Evaluating the Potential Immunostimulatory Effects of Cryptomeria japonica Leaf Essential Oil on Honey Bees (Apis mellifera)

This study investigated the effects of Cryptomeria japonica leaf essential oil (CjLEO) on honey bee health, focusing on both toxicity and gene expression modulation. Initial toxicity assessments revealed that high concentrations of CjLEO (75 and 100 ppm) were lethal to honey bees, resulting in complete mortality within a short period. Conversely, a lower concentration of 10 ppm exhibited no significant toxic effects, prompting further investigation into its sublethal impacts. Transcriptome analysis via next-generation sequencing demonstrated that CjLEO at 10 ppm induced significant changes in honey bee gene expression compared to the control group. Principal component analysis (PCA) and differential gene expression (DEG) analysis identified more than 9,000 genes, with notable upregulation of immune-related genes, including hymenoptaecin, abaecin, and apidaecin1. Gene ontology (GO) enrichment analysis indicated that these differentially expressed genes were primarily associated with immune responses, such as defense and innate immune pathways. The chemical composition of CjLEO, characterized by GC-MS, identified 16 compounds, with major components including α-pinene, elemol, α-eudesmol, and kaur-16-ene. These compounds are known for their antimicrobial properties, which likely contribute to the observed immunomodulatory effects. CjLEO at a concentration of 10 ppm enhances honey bee immunity without exhibiting significant toxicity, positioning it a promising candidate for improving honey bee resilience against pathogens. Future research should investigate the mechanisms of immune activation and optimize application methods for practical beekeeping, aiming to improve colony health while reducing dependence on synthetic chemicals.

A non-adaptationist hypothesis of play behaviour

Play is a suite of apparently non-functional, pleasurable behaviours observed in human and non-human animals. Although the phenomenon has been studied extensively, no adaptationist behavioural theory of how play evolved can be supported by the available evidence. However, the advancement of the extended evolutionary synthesis and developments in systems biology offer alternative avenues for non-adaptationist physiological hypotheses. I therefore propose a hypothesis of play, based upon a complex ACh activity that is under agential control of the organism, whereby play initiates ACh-mediated feedforward and feedback processes which act to: (i) regulate metabolic processes; (ii) form new ACh receptors via ACh mRNA activity; (iii) mediate attention, memory consolidation and learning; and (iv) mediate social behaviours, reproduction and embryonic development. However, play occurs across taxa, but does not occur across all taxonomic groups or within all species of a taxonomic group. Thus, to support the validity of the proposed hypothesis, I further propose potential explanations for this anomaly, which include sampling and observer biases, altricial versus precocial juvenile development, and the influence of habitat niche and environmental conditions on behaviour. The proposed hypothesis thus offers new avenues for study in both the biological and social sciences, in addition to having potential applications in applied sciences, such as animal welfare and biomedical research. Crucially, it is hoped that this hypothesis will promote further study of a valid and behaviourally significant, yet currently enigmatic, biological phenomenon.

Field agrochemical exposure impacts locomotor activity in wild bumblebees

Agricultural intensification has been identified as one of the key causes of global insect biodiversity losses. These losses have been further linked to the widespread use of agrochemicals associated with modern agricultural practices. Many of these chemicals are known to have negative sublethal effects on commercial pollinators, such as managed honeybees and bumblebees, but less is known about the impacts on wild bees. Laboratory-based studies with commercial pollinators have consistently shown that pesticide exposure can impact bee behavior, with cascading effects on foraging performance, reproductive success, and pollination services. However, these studies typically assess only one chemical, neglecting the complexity of real-world exposure to multiple agrochemicals and other stressors. In the summer of 2020, we collected wild-foraging workers of the common eastern bumblebee, Bombus impatiens, from five squash (Cucurbita) agricultural sites (organic and conventional farms), selected to represent a range of agrochemical, including neonicotinoid insecticide, use. For each bee, we measured two behaviors relevant to foraging success and previously shown to be impacted by pesticide exposure: sucrose responsiveness and locomotor activity. Following behavioral testing, we used liquid chromatography-tandem mass spectrometry (LC-MS/MS) chemical analysis to detect and quantify the presence of 92 agrochemicals in each bumblebee. Bees collected from our sites did not vary in pesticide exposure as expected. While we found a limited occurrence of neonicotinoids, two fungicides (azoxystrobin and difenoconazole) were detected at all sites, and the pesticide synergist piperonyl butoxide (PBO) was present in all 123 bees. We found that bumblebees that contained higher levels of PBO were less active, and this effect was stronger for larger bumblebee workers. While PBO is unlikely to be the direct cause of the reduction in bee activity, it could be an indicator of exposure to pyrethroids and/or other insecticides that we were unable to directly quantify, but which PBO is frequently tank-mixed with during pesticide applications on crops. We did not find a relationship between agrochemical exposure and bumblebee sucrose responsiveness. To our knowledge, this is the first evidence of a sublethal behavioral impact of agrochemical exposure on wild-foraging bees.

A hypothesis of teleological evolution, via endogenous acetylcholine, nitric oxide, and calmodulin pathways

The Extended Evolutionary Synthesis (EES) addresses the issues in evolutionary biology which cannot be explained by neo-Darwinian theory. The EES paradigm recognises teleology and agency in living systems, and identifies that organisms can directly affect their evolutionary trajectory in a goal-directed manner, yet the physiological pathways via which this occurs remain unidentified. Here, I propose a physiological pathway via which organisms can alter their genotype and phenotype by making behavioural decisions with respect their activity levels, partitioning of resources either toward growth, defence against disease, or their behavioural response to stressors. Specifically, I hypothesize that agential, teleological decisions mediated by acetylcholine result in induced nitric oxide (NO) activity, which regulates metabolism, blood flow, and immune response. Nitric oxide, however, is also a key epigenetic molecule, being involved in DNA acetylation, methylation, and de-methylation. Further, NO alters the histone complexes which scaffold nuclear DNA strands, and is thus a good candidate in identifying a system which allows an organisms to make teleological genetic changes. The proposed mechanisms of inheritance of these genetic changes is via the paternal line, whereby epigenetic changes in the somatic Sertoli cells in animals are transcribed by mRNA and included in the germline cells - the male gametes. The microsporangium in plants, and the sporophore cells in fungi, meanwhile, are proposed to form similar systems in response to sensory detection of stressors. Whilst the hypothesis is presented as a simplified model for future testing, it opens new avenues for study in evolutionary biology.

A novel insecticide impairs bumblebee memory and sucrose responsiveness across high and low nutrition

Wild bees are important pollinators of crops and wildflowers but are exposed to a myriad of different anthropogenic stressors, such as pesticides and poor nutrition, as a consequence of intensive agriculture. These stressors do not act in isolation, but interact, and may exacerbate one another. Here, we assessed whether a field-realistic concentration of flupyradifurone, a novel pesticide that has been labelled as 'bee safe' by regulators, influenced bumblebee sucrose responsiveness and long-term memory. In a fully crossed experimental design, we exposed individual bumblebees (Bombus impatiens) to flupyradifurone at high (50% (w/w)) or low (15% (w/w)) sucrose concentrations, replicating diets that are either carbohydrate rich or poor, respectively. We found that flupyradifurone impaired sucrose responsiveness and long-term memory at both sucrose concentrations, indicating that better nutrition did not buffer the negative impact of flupyradifurone. We found no individual impact of sugar deficiency on bee behaviour and no significant interactions between pesticide exposure and poor nutrition. Our results add to a growing body of evidence demonstrating that flupyradifurone has significant negative impacts on pollinators, indicating that this pesticide is not 'bee safe'. This suggests that agrochemical risk assessments are not protecting pollinators from the unintended consequences of pesticide use.

Biotic and abiotic stresses on honeybee health

Honeybees are the most critical pollinators providing key ecosystem services that underpin crop production and sustainable agriculture. Amidst a backdrop of rapid global change, this eusocial insect encounters a succession of stressors during nesting, foraging, and pollination. Ectoparasitic mites, together with vectored viruses, have been recognized as central biotic threats to honeybee health, while the spread of invasive giant hornets and small hive beetles also increasingly threatens colonies worldwide. Cocktails of agrochemicals, including acaricides used for mite treatment, and other pollutants of the environment have been widely documented to affect bee health in various ways. Additionally, expanding urbanization, climate change, and agricultural intensification often result in the destruction or fragmentation of flower-rich bee habitats. The anthropogenic pressures exerted by beekeeping management practices affect the natural selection and evolution of honeybees, and colony translocations facilitate alien species invasion and disease transmission. In this review, the multiple biotic and abiotic threats and their interactions that potentially undermine bee colony health are discussed, while taking into consideration the sensitivity, large foraging area, dense network among related nestmates, and social behaviors of honeybees.

No-observed-adverse-effect-level (NOAEL) clothianidin, a neonicotinoid pesticide, impairs hippocampal memory and motor learning associated with alteration of gene expression in cerebellum

Neonicotinoid pesticides (NNs) have been associated with numerous neurobehavioral effects in rodents, raising concerns about their impact on cognitive function. Clothianidin (CLO), a type of NN, was orally administered to male mice (10 weeks old, C57BL/6N) at the no-observed-adverse-effect level (NOAEL) of 50 mg/kg/day as indicated in the pesticide risk assessment report. Behavioral tests (novel location recognition and rotarod tests) evaluated hippocampal memory and cerebellar motor learning. After each test, plasma monoamines (3-methoxytyramine, histamine, serotonin, tryptamine) were measured by LC-ESI/MS/MS (Liquid chromatography-electrospray ionization/tandem mass spectrometry), and cerebellar mRNA expression was quantified by microarray and qRT-PCR analyses. The NOAEL of CLO was found to impair hippocampal memory, leading to decreased spontaneous locomotor activity and motor function. We reported, for the first time, multiple alterations of gene expression in the cerebellum associated with motor dysfunction.

Sublethal effects of imidacloprid-contaminated honey stores on colony performance, queens, and worker activities in fall and early winter colonies

Neonicotinoid-contaminated sugar stores can have both near term and long term effects on honey bees due to their persistence in honey stores. Effects of imidacloprid food stores contaminants were examined in subtropical colonies that experience reduced brood rearing and foraging during overwintering. Colonies were given treatment sugar syrup containing 0 ppb (control), 20 ppb (field relevant), or 100 ppb (above field relevant) imidacloprid over six weeks to simulate contaminated fall nectar. Colonies were evaluated immediately (post-treatment) and 10 weeks (mid-winter) after treatment to compare proximal and latent effects. Post-treatment 0 ppb and 20 ppb colonies had more workers than 100 ppb colonies while 0 ppb colonies more brood than 20 ppb or 100 ppb colonies. Mid-winter 0 ppb and 20 ppb colonies had more workers than 100 ppb colonies and 0 ppb colonies more brood than 100 ppb colonies. Colonies experienced seasonal declines in stored pollen but no treatment effects. Lower 100 ppb colony performance was associated with reduced effort rather than lifespan. RFID (Radio Frequency Identification) tracking revealed that workers had similar adult lifespans across treatments; however, 100 ppb workers engaged in activities outside the colony for less time than 0 ppb workers. Imidacloprid exposure affected queen but not worker nutritional physiology. Nurses retained well-developed hypopharyngeal glands (as indicated by head protein) across treatments. Mid-winter queens from 0 ppb colonies had marginally higher ovary protein than queens from 100 ppb colonies and more ovary lipids than queens from 20 ppb colonies. However, queen nutrient stores in non-reproductive tissues (fat bodies) did not differ across treatments. Queens from different treatments were attended by comparable numbers of retinue workers and had similar gland contents of four QMP (Queen Mandibular Pheromone) components essential to queen care. High levels of imidacloprid in sugar stores can negatively affect colony performance months after initial storage.

Diverse communication strategies in bees as a window into adaptations to an unpredictable world

Communication is a fundamental feature of animal societies and helps their members to solve the challenges they encounter, from exploiting food sources to fighting enemies or finding a new home. Eusocial bees inhabit a wide range of environments and they have evolved a multitude of communication signals that help them exploit resources in their environment efficiently. We highlight recent advances in our understanding of bee communication strategies and discuss how variation in social biology, such as colony size or nesting habits, and ecological conditions are important drivers of variation in communication strategies. Anthropogenic factors, such as habitat conversion, climate change, or the use of agrochemicals, are changing the world bees inhabit, and it is becoming clear that this affects communication both directly and indirectly, for example by affecting food source availability, social interactions among nestmates, and cognitive functions. Whether and how bees adapt their foraging and communication strategies to these changes represents a new frontier in bee behavioral and conservation research.

Review on effects of some insecticides on honey bee health

Insecticides, one of the main agrochemicals, are useful for controlling pests; however, the indiscriminate use of insecticides has led to negative effects on nontarget insects, especially honey bees, which are essential for pollination services. Different classes of insecticides, such as neonicotinoids, pyrethroids, chlorantraniliprole, spinosad, flupyradifurone and sulfoxaflor, not only negatively affect honey bee growth and development but also decrease their foraging activity and pollination services by influencing their olfactory sensation, memory, navigation back to the nest, flight ability, and dance circuits. Honey bees resist the harmful effects of insecticides by coordinating the expression of genes related to immunity, metabolism, and detoxification pathways. To our knowledge, more research has been conducted on the effects of neonicotinoids on honey bee health than those of other insecticides. In this review, we summarize the current knowledge regarding the effects of some insecticides, especially neonicotinoids, on honey bee health. Possible strategies to increase the positive impacts of insecticides on agriculture and reduce their negative effects on honey bees are also discussed.

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.

Detection and Concentration of Neonicotinoids and Other Pesticides in Honey from Honey Bee Colonies Located in Regions That Differ in Agricultural Practices: Implications for Human and Bee Health

This is a preliminary study conducted to analyze the presence and concentration of pesticides in honey obtained from honey bee colonies located in two regions with managed ecosystems that differ in the intensity and technification of agricultural practices. Fourteen pesticides at variable concentrations were detected in 63% of the samples analyzed. The pesticides most frequently found at higher concentrations were insecticides (neonicotinoids, followed by organophosphates), herbicides, and fungicides. The number, frequency, and concentration of pesticides were higher in samples collected from hives located where intensive and highly-technified agriculture is practiced. Forty-three percent of the samples from that zone had residues of imidacloprid, compared with only 13% of the samples from the less-technified zone. Furthermore, 87.5% of those samples had imidacloprid concentrations that were above sublethal doses for honey bees (>0.25 ng/g) but that are not considered hazardous to human health by the European Commission. The results of this study suggest that honey can be used as a bioindicator of environmental contamination by pesticides, which highlights the need to continue monitoring contaminants in this product to determine the risks of pesticide impacts on pollinator health, on ecosystems, and on their potential implications to human health and other non-target organisms.

Chronic exposure to field-realistic doses of imidacloprid resulted in biphasic negative effects on honey bee physiology

There have been many investigations on the negative effects of imidacloprid (IMD) on honey bees. IMD is known to disrupt honey bee physiology and colony health at a relatively low concentration compared to other pesticides. In this study, honey bee colonies were chronically exposed to field-realistic concentrations (5, 20, and 100 ppb) of IMD, and the body weight, flight performance, carbohydrate reserve, and lipid contents of forager bees analyzed. Transcriptome analyses followed by quantitative PCR were also conducted for both nurse and forager bees to elucidate any changes in energy metabolism related to phenotypic disorders. The body weights of newly emerged and nurse bees showed decreasing tendencies as the IMD concentration increased. In forager bees, however, IMD induced a biphasic change in body weight: body weight was decreased at the lower concentrations (5 and 20 ppb) but increased at the higher concentration (100 ppb). Nevertheless, the flight capability of forager bees significantly decreased in a concentration-dependent manner. The effects of IMD on target gene transcription in forager bees showed biphasic patterns between low (5 and 20 ppb) and high (100 ppb) concentrations. Nurse bees showed typical features of premature transition to foragers in a concentration-dependent manner. When exposed to low concentrations, forager bees exhibited downregulation of genes involved in carbohydrate and lipid metabolism and in the insulin/insulin-like growth factor signaling pathway, upregulation of transporter activity, and a dose-dependent body weight reduction, which were similar to insulin resistance and diabetic symptoms. However, increased lipid metabolism and decreased energy metabolism with body weight gain were observed at high IMD concentration. Considered together, these results suggest that field-realistic doses of IMD alter honey bee energy metabolism in distinctly different ways at low and high concentrations, both of which negatively affect honey bee colony health.

Non-additive gene interactions underpin molecular and phenotypic responses in honey bee larvae exposed to imidacloprid and thymol

Understanding the cumulative risk of chemical mixtures at environmentally realistic concentrations is a key challenge in honey bee ecotoxicology. Ecotoxicogenomics, including transcriptomics, measures responses in individual organisms at the molecular level which can provide insights into the mechanisms underlying phenotypic responses induced by one or more stressors and link impacts on individuals to populations. Here, fifth instar honey bee larvae were sampled from a previously reported field experiment exploring the phenotypic impacts of environmentally realistic chronic exposures of the pesticide imidacloprid (5 μg.kg^-1 for six weeks) and the acaricide thymol (250 g.kg^-1 applied via Apiguard gel in-hive for four weeks), both separately and in combination. RNA-seq was used to discover individual and interactive chemical effects on larval gene expression and to uncover molecular mechanisms linked to reported adult and colony phenotypes. The separate and combined treatments had distinct gene expression profiles which represented differentially affected signaling and metabolic pathways. The molecular signature of the mixture was characterised by additive interactions in canonical stress responses associated with oxidative stress and detoxification, and non-additive interactions in secondary responses including developmental, neurological, and immune pathways. Novel emergent impacts on eye development genes correlated with long-term defects in visual learning performance as adults. This is consistent with these chemicals working through independent modes of action that combine to impact common downstream pathways, and highlights the importance of establishing mechanistic links between molecular and phenotypic responses when predicting effects of chemical mixtures on ecologically relevant population outcomes.

Nuclear translocation of vitellogenin in the honey bee (Apis mellifera)

Vitellogenin (Vg) is a conserved protein used by nearly all oviparous animals to produce eggs. It is also pleiotropic and performs functions in oxidative stress resistance, immunity, and, in honey bees, behavioral development of the worker caste. It has remained enigmatic how Vg affects multiple traits. Here, we asked whether Vg enters the nucleus and acts via DNA-binding. We used cell fractionation, immunohistology, and cell culture to show that a structural subunit of honey bee Vg translocates into cell nuclei. We then demonstrated Vg-DNA binding theoretically and empirically with prediction software and chromatin immunoprecipitation with sequencing (ChIP-seq), finding binding sites at genes influencing immunity and behavior. Finally, we investigated the immunological and enzymatic conditions affecting Vg cleavage and nuclear translocation and constructed a 3D structural model. Our data are the first to show Vg in the nucleus and suggest a new fundamental regulatory role for this ubiquitous protein.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13592-022-00914-9.

Honey Bees (Hymenoptera: Apidae) Decrease Foraging But Not Recruitment After Neonicotinoid Exposure

Honey bees (Linnaeus, Hymenoptera: Apidae) are widely used as commercial pollinators and commonly forage in agricultural and urban landscapes containing neonicotinoid-treated plants. Previous research has demonstrated that honey bees display adverse behavioral and cognitive effects after treatment with sublethal doses of neonicotinoids. In laboratory studies, honey bees simultaneously increase their proportional intake of neonicotinoid-treated solutions and decrease their total solution consumption to some concentrations of certain neonicotinoids. These findings suggest that neonicotinoids might elicit a suboptimal response in honey bees, in which they forage preferentially on foods containing pesticides, effectively increasing their exposure, while also decreasing their total food intake; however, behavioral responses in semifield and field conditions are less understood. Here we conducted a feeder experiment with freely flying bees to determine the effects of a sublethal, field-realistic concentration of imidacloprid (IMD) on the foraging and recruitment behaviors of honey bees visiting either a control feeder containing a sucrose solution or a treatment feeder containing the same sucrose solution with IMD. We report that IMD-treated honey bees foraged less frequently (-28%) and persistently (-66%) than control foragers. Recruitment behaviors (dance frequency and dance propensity) also decreased with IMD, but nonsignificantly. Our results suggest that neonicotinoids inhibit honey bee foraging, which could potentially decrease food intake and adversely affect colony health.

Metabolomic analysis of honey bees (Apis mellifera) response to carbendazim based on UPLC-MS

Pesticides are one of the main causes of colony losses globally, posing a huge threat to the beekeeping industry. The fungicide carbendazim is commonly used on many crops worldwide, but the effects of fungicides on honey bees have received less attention than those of insecticides. Previous studies have shown that sublethal doses of carbendazim hinder growth and development and may destabilize and impede the development of honey bee colonies. The metabolome closely reflects brain activity at the functional level, allowing the effects of compounds such as fungicides to be investigated. Here, we established a model of carbendazim-treated honey bees, Apis mellifera, and used metabolomic approaches to better understand the effect of carbendazim on bee metabolic profiles. The results showed that 112 metabolites were significantly affected in carbendazim-treated bees compared to the control. Metabolites associated with energy and amino acid metabolism showed high abundance and were enriched for a wide range of pathways. In addition, the down-regulation of Aflatoxin B1exo-8,9-epoxide-GSH and glycerol diphosphate showed that carbenazim may affect the detoxification and immune system of honey bees. These results provide new insights into the interaction between fungicides and honey bees.

A common fungicide, Pristine®, impairs olfactory associative learning performance in honey bees (Apis mellifera)

Although fungicides were previously considered to be safe for important agricultural pollinators such as honey bees, recent evidence has shown that they can cause a number of behavioral and physiological sublethal effects. Here, we focus on the fungicide Pristine® (active ingredients: 25.2% boscalid, 12.8% pyraclostrobin), which is sprayed during the blooming period on a variety of crops and is known to affect honey bee mitochondria at field-relevant levels. To date, no study has tested the effects of a field-relevant concentration of a fungicide on associative learning ability in honey bees. We tested whether chronic, colony-level exposure at field-relevant and higher concentrations of Pristine® impairs performance on the proboscis extension reflex (PER) paradigm, an associative learning task. Learning performance was reduced at higher field-relevant concentrations of Pristine®. The reductions in learning performance could not be explained by effects on hunger or motivation, as sucrose responsiveness was not affected by Pristine® exposure. To determine whether Pristine®'s negative effects on learning performance were mediated at a specific life stage, we conducted a cross-fostering experiment that exposed bees to the fungicide either only as larvae, only as adults, or during both stages. We found that exposure across the entire life was necessary to significantly reduce learning performance, although non-significant reductions occurred when bees were exposed during just one stage. Our study provides strong evidence that Pristine® has significant sublethal effects on learning performance. As associative learning is a necessary ability for foraging, our results raise concerns that Pristine® could impair foraging abilities and substantially weaken colony health.

Neonicotinoid Exposures that Stimulate Predatory Stink Bug, Podisus maculiventris (Hemiptera: Pentatomidae), Reproduction Do Not Inhibit Its Behavior

Exposure to sublethal amounts of pesticide can compromise life-history traits and behavior of natural enemies thereby reducing their effectiveness as predators. However, sublethal exposures to pesticides and other stressors may also stimulate insects, a dose-response phenomenon known as hormesis. We previously reported stimulatory effects on reproduction in the beneficial insect predator Podisus maculiventris (Say) (Hemiptera: Pentatomidae) following exposure to sublethal concentrations of imidacloprid. Here we examined whether these same treatments stimulated behavior and/or predation of P. maculiventris. Stimulation of some behaviors occurred at a reproductively hormetic concentration and two additional sublethal concentrations, depending upon bioassay design and sex. We observed no substantial inhibition of behavior or predation at a reproductively hormetic concentration, demonstrating that reproductive fitness in P. maculiventris may be stimulated without compromising behaviors important in its effectiveness as a natural enemy.

Pesticide risk assessment in honeybees: Toward the use of behavioral and reproductive performances as assessment endpoints

The growing gap between new evidence of pesticide toxicity in honeybees and conventional toxicological assays recommended by regulatory test guidelines emphasizes the need to complement current lethal endpoints with sublethal endpoints. In this context, behavioral and reproductive performances have received growing interest since the 2000s, likely due to their ecological relevance and/or the emergence of new technologies. We review the biological interests and methodological measurements of these predominantly studied endpoints and discuss their possible use in the pesticide risk assessment procedure based on their standardization level, simplicity and ecological relevance. It appears that homing flights and reproduction have great potential for pesticide risk assessment, mainly due to their ecological relevance. If exploratory research studies in ecotoxicology have paved the way toward a better understanding of pesticide toxicity in honeybees, the next objective will then be to translate the most relevant behavioral and reproductive endpoints into regulatory test methods. This will require more comparative studies and improving their ecological relevance. This latter goal may be facilitated by the use of population dynamics models for scaling up the consequences of adverse behavioral and reproductive effects from individuals to colonies.

Low Concentration of Quercetin Reduces the Lethal and Sublethal Effects of Imidacloprid on Apis cerana (Hymenoptera: Apidae)

Large-scale use of systemic pesticides has been considered a potential factor for pollinator population decline. Phytochemicals, e.g., quercetin, have been demonstrated to increase the pesticide tolerance of Apis mellifera Linnaeus (Hymenoptera: Apidae), which is helpful to develop strategies to reduce the pesticides hazards to pollinators. In this study, we hypothesized phytochemicals could reduce the detrimental effects of imidacloprid on Apis cerana Fabricius. The lethal and sublethal effects of imidacloprid on A. cerana workers were investigated. The results showed that A. cerana workers chronically exposed to 100 μg/liter imidacloprid had a significantly shorter longevity by 10.81 d compared with control. Acute exposure to imidacloprid at 100 μg/liter impaired the sucrose responsiveness and memory retention of the workers, and 20 μg/liter reduced the sucrose responsiveness. The treatment with 37.8 mg/liter quercetin for 24 h could increase the longevity of A. cerana workers when chronically exposed to 100 μg/liter imidacloprid, and 75.6 mg/liter quercetin feeding treatment alleviated the impairment of sucrose responsiveness. However, workers treated with 151.2 mg/liter and 75.6 mg/liter quercetin had a significantly shorter longevity compared to that of bees chronically exposed to 100 μg/liter imidacloprid without quercetin treatment. Our results suggested that quercetin treatment could produce a biphasic influence on the lethal effects of imidacloprid on A. cerana. Quercetin at 37.8 mg/liter and 75.6 mg/liter in the diet before pesticide exposure was able to reduce the lethal and sublethal effects of imidacloprid, respectively, providing potential strategies to reduce the pesticides hazards to native honey bees (A. cerana).

EFSA Scientific Committee, More S, Bampidis V, Benford D, Bragard C, Halldorsson T, Hernández‐Jerez A, Bennekou SH, Koutsoumanis K, Machera K, Naegeli H, Nielsen SS, Schlatter J, Schrenk D, Silano V, Turck D, Younes M, Arnold G, Dorne J, Maggiore A, Pagani S, Szentes C, Terry S, Tosi S, Vrbos D, Zamariola G, Rortais A. A systems-based approach to the environmental risk assessment of multiple stressors in honey bees

The European Parliament requested EFSA to develop a holistic risk assessment of multiple stressors in honey bees. To this end, a systems-based approach that is composed of two core components: a monitoring system and a modelling system are put forward with honey bees taken as a showcase. Key developments in the current scientific opinion (including systematic data collection from sentinel beehives and an agent-based simulation) have the potential to substantially contribute to future development of environmental risk assessments of multiple stressors at larger spatial and temporal scales. For the monitoring, sentinel hives would be placed across representative climatic zones and landscapes in the EU and connected to a platform for data storage and analysis. Data on bee health status, chemical residues and the immediate or broader landscape around the hives would be collected in a harmonised and standardised manner, and would be used to inform stakeholders, and the modelling system, ApisRAM, which simulates as accurately as possible a honey bee colony. ApisRAM would be calibrated and continuously updated with incoming monitoring data and emerging scientific knowledge from research. It will be a supportive tool for beekeeping, farming, research, risk assessment and risk management, and it will benefit the wider society. A societal outlook on the proposed approach is included and this was conducted with targeted social science research with 64 beekeepers from eight EU Member States and with members of the EU Bee Partnership. Gaps and opportunities are identified to further implement the approach. Conclusions and recommendations are made on a way forward, both for the application of the approach and its use in a broader context.

The Electronic Bee Spy: Eavesdropping on Honeybee Communication via Electrostatic Field Recordings

As a canary in a coalmine warns of dwindling breathable air, the honeybee can indicate the health of an ecosystem. Honeybees are the most important pollinators of fruit-bearing flowers, and share similar ecological niches with many other pollinators; therefore, the health of a honeybee colony can reflect the conditions of a whole ecosystem. The health of a colony may be mirrored in social signals that bees exchange during their sophisticated body movements such as the waggle dance. To observe these changes, we developed an automatic system that records and quantifies social signals under normal beekeeping conditions. Here, we describe the system and report representative cases of normal social behavior in honeybees. Our approach utilizes the fact that honeybee bodies are electrically charged by friction during flight and inside the colony, and thus they emanate characteristic electrostatic fields when they move their bodies. These signals, together with physical measurements inside and outside the colony (temperature, humidity, weight of the hive, and activity at the hive entrance) will allow quantification of normal and detrimental conditions of the whole colony. The information provided instructs how to setup the recording device, how to install it in a normal bee colony, and how to interpret its data.

Flupyradifurone reduces nectar consumption and foraging but does not alter honey bee recruitment dancing

Foraging is essential for honey bee colony fitness and is enhanced by the waggle dance, a recruitment behavior in which bees can communicate food location and quality. We tested if the consumption of nectar (sucrose solution) with a field-realistic concentration of 4 ppm flupyradifurone (FPF) could alter foraging behavior and recruitment dancing in Apis mellifera. Foragers were repelled by FPF. They visited the FPF feeder less often and spent less time imbibing sucrose solution (2.5 M, 65% w/w) with FPF. As a result, bees feeding on the FPF treatment consumed 16% less nectar. However, FPF did not affect dancing: there were no effects on unloading wait time, the number of dance bouts per nest visit, or the number of dance circuits performed per dance bout. FPF could therefore deter bees from foraging on contaminated nectar. However, the willingness of bees to recruit nestmates for nectar with FPF is concerning. Recruitment can rapidly amplify the number of foragers and could overcome the decrease in consumption of FPF-contaminated nectar, resulting in a net inflow of pesticide to the colony. FPF also significantly altered the expression of 116 genes, some of which may be relevant for the olfactory learning deficits induced by FPF and the toxicity of FPF.

Detrimental effects of clothianidin on foraging and dance communication in honey bees

Ongoing losses of pollinators are of significant international concern because of the essential role they have in our ecosystem, agriculture, and economy. Both chemical and non-chemical stressors have been implicated as possible contributors to their decline, but the increasing use of neonicotinoid insecticides has recently emerged as particularly concerning. In this study, honey bees were exposed orally to sublethal doses of the neonicotinoid clothianidin in the field in order to assess its effects on the foraging behavior, homing success, and dance communication. The foraging span and foraging activity at the contaminated feeder decreased significantly due to chronic exposure at field-realistic concentrations. Electrostatic field of dancing bees was measured and it was revealed that the number of waggle runs, the fanning time and the number of stop signals were significantly lower in the exposed colony. No difference was found in the homing success and the flight duration between control and treated bees released at a novel location within the explored area. However, a negative effect of the ambient temperature, and an influence of the location of the trained feeder was found. Finally, the residues of clothianidin accumulated in the abdomens of exposed foraging bees over time. These results show the adverse effects of a chronic exposure to sublethal doses of clothianidin on foraging and dance communication in honey bees.

Molecular Assessment of Genes Linked to Immune Response Traits of Honey Bees in Conventional and Organically Managed Apiaries

Simple Summary

Honey bees play a critical role in agriculture as they provide pollination services to many agricultural crops. However, honey bee populations continue to decline due to exposure to pesticides, habitat destruction, pests, diseases and beekeeping practices. In this study, we assessed selected biological parameters associated with honey bee health in two beekeeping practices (organic and conventional). We compared total protein content in young worker bees from organically and conventionally managed apiaries. We also assessed differential gene expression at two levels of Varroa mite infestations (0% and 5%) in selected genes involved in nutrition and cellular defense (vitellogenin (Vg), malvolio (Mvl), prophenoloxidase (PPO)-, genes involved in lifespan (superoxide dismutase (Sod 1), superoxide dismutase 2 (Sod2)) and immune function genes (immune deficiency (Imd), spaetzle (Spz). Total soluble protein in young adult worker bees was similar in both beekeeping practices. The genes PPO, Vg and Mvl were upregulated in young adult bees with no mite infestations from organically managed apiaries and could mount an immune response through Spz and Sod 1 when challenged by 5% Varroa mite infestation levels. Overall, these findings provide useful insights into the genetic response of honey bees under two beekeeping practices and could help improve honey bee health.

Abstract

Honey bees are of great economic importance, not only for honey production but also for crop pollination. However, honey bee populations continue to decline mainly due to exposure to pesticides, pathogens and beekeeping practices. In this study, total soluble protein was measured, total RNA was extracted and first-strand cDNAs were generated. Quantitative PCR was used to assess the relative expression (transcript abundances) of immune function-related genes in honey bees collected from organically and conventionally managed hives. Honey bees collected from conventionally managed hives with 0% Varroa mite infestation levels displayed an upregulated expression of the prophenoloxidase gene (cellular defense). Similarly, honey bees collected from organically managed hives had increased levels of the vitellogenin gene (immune function and longevity). The gene expression for malvolio (sucrose responsiveness) was highest in organically managed hives with 0% Varroa mite infestations. Young adult bees collected from organically managed hives with 5% Varroa mite infestation levels had upregulated expressions of the gene spaetzle, whereas bees from similarly infested, conventionally managed hives did not, suggesting that honey bees from organically managed hives could mount an immune response. In young adult bees collected from organically managed hives only, the expression of the immune deficiency gene (antimicrobial defense) was upregulated. The relative gene expression for superoxide dismutase 1 increased in young adult bees collected from hives with 5% Varroa mite infestation levels as expected. However, for superoxide dismutase 2, there was a high level of gene expression in adult bees from both conventionally managed hives with 0% Varroa mite infestation levels and organically managed hives with 5% Varroa mite infestations. The gene CYP9Q3 (pesticide detoxification) that metabolizes coumaphos and fluvalinate was upregulated in adult bees collected from organically managed bees. Overall, these findings provide useful insights into the genetic response of honey bees to some environmental stressors and could be an important component of best beekeeping practices that intend to enhance honey bee health.

Toxicogenomics provides insights to toxicity pathways of neonicotinoids to aquatic insect, Chironomus dilutus

Neonicotinoid insecticides have posed a great threat to non-target organisms, yet the mechanisms underlying their toxicity are not well characterized. Major modes of action (MoAs) of imidacloprid were analyzed in an aquatic insect Chironomus dilutus. Lethal and sublethal outcomes were assessed in the midges after 96-h exposure to imidacloprid. Global transcriptomic profiles were determined using de novo RNA-sequencing to more holistically identify toxicity pathways. Transcriptional 10% biological potency values derived from ranked KEGG pathways and GO terms were 0.02 (0.01-0.08) (mean (95% confidence interval) and 0.05 (0.04-0.06) μg L^-1, respectively, which were more sensitive than those from phenotypic traits (10% lethal concentration: 0.44 (0.23-0.79) μg L^-1; 10% burrowing behavior concentration: 0.30 (0.22-0.43) μg L^-1). Major MoAs of imidacloprid in aquatic species were identified as follows: the activation of nicotinic acetylcholine receptors (nAChRs) induced by imidacloprid impaired organisms' nerve system through calcium ion homeostasis imbalance and mitochondrial dysfunction, which posed oxidative stress and DNA damage and eventually caused death of organisms. The current investigation highlighted that imidacloprid affected C. dilutus at environmentally relevant concentrations, and elucidated toxicity pathways derived from gene alteration to individual outcomes, calling for more attention to toxicity of neonicotinoids to aquatic organisms.

The novel butenolide pesticide flupyradifurone does not alter responsiveness to sucrose at either acute or chronic short-term field-realistic doses in the honey bee, Apis mellifera

BACKGROUND

Sublethal exposure to neonicotinoids, a popular class of agricultural pesticides, can lead to behavioral effects that impact the health of pollinators. Therefore, new compounds, such as flupyradifurone (FPF), have recently been developed as 'safer' alternatives. FPF is an excitotoxic nicotinic acetylcholine receptor agonist, similar to neonicotinoids. Given the novelty of FPF, what data exist are focused mostly on assessing the effect of FPF on pollinator mortality. One important avenue for investigation is the potential effect of FPF on the sensitivity of nectar foragers, such as Apis mellifera, to sucrose concentrations. Neonicotinoids can alter this sucrose responsiveness and disrupt foraging. Compounding this effect, neonicotinoid-containing solutions are preferred by A. mellifera over pure sucrose solutions. We therefore conducted four studies, administering FPF under both acute and chronic conditions, and at field-realistic and higher than field-realistic doses, to assess the influence of FPF exposure on sucrose responsiveness and sucrose solutions with FPF in A. mellifera nectar foragers.

RESULTS

We found no evidence that FPF exposure under acute or chronic field-realistic conditions significantly altered sucrose responsiveness, and we did not find that bees exposed to FPF consumed more of the solution. However, at the much higher median lethal dose (48 h), among bees that survived, FPF-exposed foragers responded to significantly lower concentrations of sucrose than controls and responded at significantly higher rates to all concentrations of sucrose than controls.

CONCLUSION

We found no evidence that FPF alters the sucrose responsiveness of nectar foragers at field-realistic doses during winter or early spring, but caution and further investigation are warranted, particularly on the effects of FPF in conjunction with other stressors. © 2019 Society of Chemical Industry.

Evaluation of Residue Levels of Imidacloprid and Thiamethoxam After Foliar Application to the Citrus Varieties Lane Late, Valencia Late, Rohde Summer, and Nules

Neonicotinoids are used to protect citrus trees against pests. Dissipation and persistence of neonicotinoids in pollen and nectar of citrus trees after foliar applications and their potential exposure to pollinators have not been well characterized. Field studies were conducted using three orange and one mandarin varieties to compare the imidacloprid and thiamethoxam residue levels and their decline in pollen and nectar after treatments in pre-bloom close to flowering period and their persistence 1 yr after treatment. The possible risk to honeybees was assessed. In nectar, thiamethoxam and imidacloprid residues were between 61 and 99% lower than in pollen, depending on the citrus variety or/and the days after treatment when applied close to blooming. At the end of the flowering period, imidacloprid in pollen and nectar was not detected in the mandarin variety after treatment in pre-bloom, whereas for thiamethoxam, no residues were detected in nectar but 10 ng/g was detected in pollen. There were no quantifiable levels of residues for either neonicotinoids in pollen or nectar during the flowering period of the following year. Neonicotinoid residue levels and their decline in nectar and pollen in citrus depended on the timing of applications relative to flowering and on the citrus variety. The absence of neonicotinoid residues 1 yr out after foliar applications in all varieties assayed demonstrated that none of the neonicotinoids tested were persistent. The results could be different in other citrus varieties, and therefore, also the exposure assessment for managed pollinators.

Acute exposure to urban air pollution impairs olfactory learning and memory in honeybees

While the ecological effects of pesticides have been well studied in honeybees, it is unclear to what extent other anthropogenic contaminants such as air pollution may also negatively affect bee cognition and behaviour. To answer this question, we assessed the impacts of acute exposure to four ecologically relevant concentrations of a common urban air pollutant-diesel generated air pollution on honeybee odour learning and memory using a conditioned proboscis extension response assay. The proportion of bees that successfully learnt odours following direct air pollution exposure was significantly lower in bees exposed to low, medium and high air pollutant concentrations, than in bees exposed to current ambient levels. Furthermore, short- and long-term odour memory was significantly impaired in bees exposed to low medium and high air pollutant concentrations than in bees exposed to current ambient levels. These results demonstrate a clear and direct cognitive cost of air pollution. Given learning and memory play significant roles in foraging, we suggest air pollution will have increasing negative impacts on the ecosystem services bees provide and may add to the current threats such as pesticides, mites and disease affecting colony fitness.

Sub-Lethal Doses of Clothianidin Inhibit the Conditioning and Biosensory Abilities of the Western Honeybee Apis mellifera

Insects play an important role in the stability of ecosystems by fulfilling key functions such as pollination and nutrient cycling, as well as acting as prey for amphibians, reptiles, birds and mammals. The global decline of insects is therefore a cause for concern, and the role of chemical pesticides must be examined carefully. The lethal effects of insecticides are well understood, but sub-lethal concentrations have not been studied in sufficient detail. We therefore used the western honeybee Apis mellifera as a model to test the effect of the neonicotinoid insecticide clothianidin on the movement, biosensory abilities and odor-dependent conditioning of insects, titrating from lethal to sub-lethal doses. Bees treated with sub-lethal doses showed no significant movement impairment compared to untreated control bees, but their ability to react to an aversive stimulus was inhibited. These results show that clothianidin is not only highly toxic to honeybees, but can, at lower doses, also disrupt the biosensory capabilities of survivors, probably reducing fitness at the individual level. In our study, sub-lethal doses of clothianidin altered the biosensory abilities of the honeybee; possible consequences at the colony level are discussed.

The neonicotinoid clothianidin impairs memory processing in honey bees

Neonicotinoids act as agonists on the nicotinic Acetylcholine receptor (nAChR) in insect brains, an essential molecular component of central brain structures involved in learning and memory formation. Sublethal doses might, therefore, impair neural processes necessary for adaptive experience dependent behaviour and thus reduce the fitness of pollinating insects on the individual and community level. First, the question was addressed whether clothianidin has an aversive taste for honey bees and concluded with both a laboratory and a semi-field experiment that bees are unable to distinguish between control and contaminated sucrose solutions. In the laboratory, proboscis extension response conditioning was performed with forager bees exposed to different concentrations of clothianidin (0.1, 0.3 and 0.8 ng/bee) before learning, after learning during memory consolidation, and just before memory retention. These tests at different timings allowed uncovering an impairment of the consolidation and retrieval of memory due to the exposure to clothianidin. It was concluded that an acute exposure to clothianidin has an adverse effect on memory processing in honey bees.

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.

Immune related genes as markers for monitoring health status of honey bee colonies

Background

Honey bee population decline threatens the beekeeping sector, agriculture and global biodiversity. Early detection of colony mortality may facilitate rapid interventions to contain and prevent mortality spread. Among others, deformed wing virus (DWV) is capable of inducing colony losses, especially when combined with Varroa destructor mite. Since the bee immune system plays a crucial role in ensuring that bees are able to face these pathogens, we explored whether expression of immune genes could serve as biomarkers of colony health.

Results

Herein, we describe a preliminary immunological marker composed of two immune genes (relish and defensin), which provide insight on honey bee antiviral defense mechanism. Of the tested genes, relish expression correlated with the presence of DWV-Varroa complex, while decreased defensin expression correlated with poor resistance to this complex.

Conclusions

The monitoring of these genes may help us to better understand the complex physiology of honey bees’s immune system and to develop new approaches for managing the health impacts of DWV infection and varroa infestation in the field.

Chronic toxicity of clothianidin, imidacloprid, chlorpyrifos, and dimethoate to Apis mellifera L. larvae reared in vitro

BACKGROUND

The effects of chronic exposure to two neonicotinoids (clothianidin and imidacloprid) and two organophosphates (chlorpyrifos and dimethoate) on survival, developmental rate and larval weight of honey bee larvae reared in vitro were determined. Diets containing chemicals were fed to larvae with the range of concentrations for each compound based on published acute toxicity experiments and residues found in pollen and nectar, both components of the larval diet.

RESULTS

Four concentrations of each compound and controls were tested: chlorpyrifos: 0.5, 0.8, 1.2, 8 mg/L; clothianidin: 0.1, 0.4, 2, 10 mg L^-1 ; dimethoate: 0.02, 1, 6, 45 mg L^-1 ; imidacloprid: 0.4, 2, 4, 10 mg L^-1 ; positive control: dimethoate (45 mg L^-1 ); solvent control: acetone or methanol; and negative control. A significant decrease in survival, relative to the solvent control, occurred in the 0.8, 1.2 and 8 mg L^-1 chlorpyrifos, 0.4, 2 and 10 mg L^-1 clothianidin, and 45 mg L^-1 dimethoate diets, but not the imidacloprid diets.

CONCLUSION

The treatment of larval diets with clothianidin, dimethoate and imidacloprid did not affect survival, developmental rate, or weight of immature honey bees; however, treatment with chlorpyrifos did. Overall, our results are valuable for evaluating the chronic toxicity of these pesticides to developing honey bees. © 2018 Society of Chemical Industry.

Imidacloprid alters ant sociobehavioral traits at environmentally relevant concentrations

Much research has focused on the effects of neonicotinoids on honey bees, however, relatively few studies have investigated their effects on ants, a taxonomically-related eusocial insect of high ecological importance. This study quantified how dietary exposures to environmentally-relevant levels of a neonicotinoid insecticide (imidacloprid) affected foraging and nest building of the western harvester ant over 14 days. Using a replicated design, statistically-significant reductions in ant foraging success (50% or greater) occurred at concentrations as low as 50 ppb compared to controls. Both the number of ants entering the maze and the percentage of foraging ants able to locate food were impacted by imidacloprid exposure. Ants exposed to 50 ppb also took three times longer than controls to find food in a test maze. This concentration is among the lowest levels of imidacloprid reported to affect ants and is well within the range of concentrations found in pollen and nectar of imidacloprid-treated plants. Ant foraging success was also impaired at comparable levels as those reported for the honey bee. Although more refinement and research are needed, results from this study suggest that the western harvester ant may be useful for screening the effects of neurotoxic chemicals on their navigation and foraging, two behaviors which are critical to maintaining colony health of ants and the ecological services they provide.

Enhancement of chronic bee paralysis virus levels in honeybees acute exposed to imidacloprid: A Chinese case study

Though honeybee populations have not yet been reported to be largely lost in China, many stressors that affect the health of honeybees have been confirmed. Honeybees inevitably come into contact with environmental stressors that are not intended to target honeybees, such as pesticides. Although large-scale losses of honeybee colonies are thought to be associated with viruses, these viruses usually lead to covert infections and to not cause acute damage if the bees do not encounter outside stressors. To reveal the potential relationship between acute pesticides and viruses, we applied different doses of imidacloprid to adult bees that were primarily infected with low levels (4.3×10⁵ genome copies) of chronic bee paralysis virus (CBPV) to observe whether the acute oral toxicity of imidacloprid was able to elevate the level of CBPV. Here, we found that the titer of CBPV was significantly elevated in adult bees after 96h of acute treatment with imidacloprid at the highest dose 66.9ng/bee compared with other treatments and controls. Our study provides clear evidence that exposure to acute high doses of imidacloprid in honeybees persistently infected by CBPV can exert a remarkably negative effect on honeybee survival. These results imply that acute environmental stressors might be one of the major accelerators causing rapid viral replication, which may progress to cause mass proliferation and dissemination and lead to colony decline. The present study will be useful for better understanding the harm caused by this pesticide, especially regarding how honeybee tolerance to the viral infection might be altered by acute pesticide exposure.

Neonicotinoids decrease sucrose responsiveness of honey bees at first contact

For two decades, neonicotinoid insecticides have been extensively used worldwide. Targeting neuronal receptors, they have deleterious effects on the behaviour and physiology of many insects. Bees are exposed to these insecticides in pollen and nectar while providing pollination services to agricultural crops, and neonicotinoids have been shown to impair navigation and decrease their foraging activity. We have previously reported the effect of dietary thiamethoxam on sucrose responsiveness of young worker bees. Here, we exposed caged foragers to sublethal acute doses of clothianidin, imidacloprid, and thiamethoxam, then tested them individually for sucrose responsiveness using standard methods. In addition, we tested the response to a range of sucrose solutions laced with neonicotinoids on bees previously unexposed to neonicotinoids. This paradigm mimics the situation where foragers would first encounter poisoned nectars varying in sugar concentration. Bees were exposed to the insecticides in the feeding solution for 24 h before testing, or in the test solutions, or both. The three compounds had a detrimental effect on responses to mid-to-high sucrose concentrations under all experimental conditions, and unexposed bees tested with laced sucrose displayed unexpected low responses to the higher sucrose concentrations tested. This attenuation of sucrose response is further evidence that neonicotinoids are multisensory disruptors, with potent actions against pollinators and other beneficial insects at first contact.

Harnessing model organisms to study insecticide resistance

The vinegar fly, Drosophila melanogaster, has made an enormous contribution to our understanding of insecticide targets, metabolism and transport. This contribution has been enabled by the unmatched capacity to manipulate genes in D. melanogaster and the fact that lessons learn in this system have been applicable to pests, because of the evolutionary conservation of key genes, particularly those encoding targets. With the advent of the CRISPR-Cas9 gene editing technology, genes can now be manipulated in pest species, but this review points to advantages that are likely to keep D. melanogaster at the forefront of insecticide research.

Impaired associative learning after chronic exposure to pesticides in young adult honey bees

Neonicotinoids are the most widespread insecticides in agriculture, preferred for their low toxicity to mammals and their systemic nature. Nevertheless, there have been increasing concerns regarding their impact on non-target organisms. Glyphosate is also widely used in crops and, therefore, traces of this pesticide are likely to be found together with neonicotinoids. Although glyphosate is considered a herbicide, adverse effects have been found on animal species, including honey bees. Apis mellifera is one of the most important pollinators in agroecosystems and is exposed to both these pesticides. Traces can be found in nectar and pollen of flowers that honey bees visit, but also in honey stores inside the hive. Young workers, which perform in-hive tasks that are crucial for colony maintenance, are potentially exposed to both these contaminated resources. These workers present high plasticity and are susceptible to stimuli that can modulate their behaviour and impact on colony state. Therefore, by performing standardised assays to study sublethal effects of these pesticides, these bees can be used as bioindicators. We studied the effect of chronic joint exposure to field-realistic concentrations of the neonicotinoid imidacloprid and glyphosate on gustatory perception and olfactory learning. Both pesticides reduced sucrose responsiveness and had a negative effect on olfactory learning. Glyphosate also reduced food uptake during rearing. The results indicate differential susceptibility according to honey bee age. The two agrochemicals had adverse effects on different aspects of honey bee appetitive behaviour, which could have repercussions for food distribution, propagation of olfactory information and task coordination within the nest.

Interactions between pesticides and pathogen susceptibility in honey bees

There exist a variety of factors that negatively impact the health and survival of managed honey bee colonies, including the spread of parasites and pathogens, loss of habitat, reduced availability or quality of food resources, climate change, poor queen quality, changing cultural and commercial beekeeping practices, as well as exposure to agricultural and apicultural pesticides both in the field and in the hive. These factors are often closely intertwined, and it is unlikely that a single stressor is driving colony losses. There is a growing consensus, however, that increasing prevalence of parasites and pathogens are among the most significant threats to managed bee colonies. Unfortunately, improper management of hives by beekeepers may exacerbate parasite populations and disease transmission. Furthermore, research continues to accumulate that describes the complex and largely harmful interactions that exist between pesticide exposure and bee immunity. This brief review summarizes our progress in understanding the impact of pesticide exposure on bees at the individual, colony, and community level.

Assessment of acute sublethal effects of clothianidin on motor function of honeybee workers using video-tracking analysis

Sublethal impacts of pesticides on the locomotor activity might occur to different degrees and could escape visual observation. Therefore, our objective is the utilization of video-tracking to quantify how the acute oral exposure to different doses (0.1-2ng/bee) of the neonicotinoid "clothianidin" influences the locomotor activity of honeybees in a time course experiment. The total distance moved, resting time as well as the duration and frequency of bouts of laying upside down are measured. Our results show that bees exposed to acute sublethal doses of clothianidin exhibit a significant increase in the total distance moved after 30 and 60min of the treatment at the highest dose (2ng/bee). Nevertheless, a reduction of the total distance is observed at this dose 90min post-treatment compared to the distance of the same group after 30min, where the treated bees show an arched abdomen and start to lose their postural control. The treated bees with 1ng clothianidin show a significant increase in total distance moved over the experimental period. Moreover, a reduction in the resting time and increase of the duration and frequency of bouts of laying upside down at these doses are found. Furthermore, significant effects on the tested parameters are observed at the dose (0.5ng/bee) first at 60min post-treatment compared to untreated bees. The lowest dose (0.1ng/bee) has non-significant effects on the motor activity of honeybees compared to untreated bees over the experimental period.

SwarmSight: Real-time Tracking of Insect Antenna Movements and Proboscis Extension Reflex Using a Common Preparation and Conventional Hardware

Many scientifically and agriculturally important insects use antennae to detect the presence of volatile chemical compounds and extend their proboscis during feeding. The ability to rapidly obtain high-resolution measurements of natural antenna and proboscis movements and assess how they change in response to chemical, developmental, and genetic manipulations can aid the understanding of insect behavior. By extending our previous work on assessing aggregate insect swarm or animal group movements from natural and laboratory videos using the video analysis software SwarmSight, we developed a novel, free, and open-source software module, SwarmSight Appendage Tracking (SwarmSight.org) for frame-by-frame tracking of insect antenna and proboscis positions from conventional web camera videos using conventional computers. The software processes frames about 120 times faster than humans, performs at better than human accuracy, and, using 30 frames per second (fps) videos, can capture antennal dynamics up to 15 Hz. The software was used to track the antennal response of honey bees to two odors and found significant mean antennal retractions away from the odor source about 1 s after odor presentation. We observed antenna position density heat map cluster formation and cluster and mean angle dependence on odor concentration.

Effects of sublethal doses of thiacloprid and its formulation Calypso® on the learning and memory performance of honey bees

Learning and memory play a central role in the behavior and communication of foraging bees. We have previously shown that chronic uptake of the neonicotinoid thiacloprid affects the behavior of honey bees in the field. Foraging behavior, homing success, navigation performance and social communication were impaired. Thiacloprid collected at a feeding site at low doses accumulates in foragers over time. Here, we applied a laboratory standard procedure (the proboscis-extension response conditioning) in order to assess which processes, acquisition, memory consolidation and/or memory retrieval were compromised after bees were fed either with thiacloprid or the formulation of thiacloprid named Calypso^® at different sublethal doses. Extinction and generalization tests allowed us to investigate whether bees respond to a learned stimulus, and how selectively. We showed that thiacloprid, as active substance and as formulation, poses a substantial risk to honey bees by disrupting learning and memory functions. These data support and specify the data collected in the field.

Honey bee-collected pollen in agro-ecosystems reveals diet diversity, diet quality, and pesticide exposure

European honey bees Apis mellifera are important commercial pollinators that have suffered greater than normal overwintering losses since 2007 in North America and Europe. Contributing factors likely include a combination of parasites, pesticides, and poor nutrition. We examined diet diversity, diet nutritional quality, and pesticides in honey bee-collected pollen from commercial colonies in the Canadian Maritime Provinces in spring and summer 2011. We sampled pollen collected by honey bees at colonies in four site types: apple orchards, blueberry fields, cranberry bogs, and fallow fields. Proportion of honey bee-collected pollen from crop versus noncrop flowers was high in apple, very low in blueberry, and low in cranberry sites. Pollen nutritional value tended to be relatively good from apple and cranberry sites and poor from blueberry and fallow sites. Floral surveys ranked, from highest to lowest in diversity, fallow, cranberry, apple, and blueberry sites. Pesticide diversity in honey bee-collected pollen was high from apple and blueberry sites and low from cranberry and fallow sites. Four different neonicotinoid pesticides were detected, but neither these nor any other pesticides were at or above LD₅₀ levels. Pollen hazard quotients were highest in apple and blueberry sites and lowest in fallow sites. Pollen hazard quotients were also negatively correlated with the number of flower taxa detected in surveys. Results reveal differences among site types in diet diversity, diet quality, and pesticide exposure that are informative for improving honey bee and land agro-ecosystem management.

Weight of evidence evaluation of a network of adverse outcome pathways linking activation of the nicotinic acetylcholine receptor in honey bees to colony death

Ongoing honey bee (Apis mellifera) colony losses are of significant international concern because of the essential role these insects play in pollinating crops. Both chemical and non-chemical stressors have been implicated as possible contributors to colony failure; however, the potential role(s) of commonly-used neonicotinoid insecticides has emerged as particularly concerning. Neonicotinoids act on the nicotinic acetylcholine receptors (nAChRs) in the central nervous system to eliminate pest insects. However, mounting evidence indicates that neonicotinoids also may adversely affect beneficial pollinators, such as the honey bee, via impairments on learning and memory, and ultimately foraging success. The specific mechanisms linking activation of the nAChR to adverse effects on learning and memory are uncertain. Additionally, clear connections between observed impacts on individual bees and colony level effects are lacking. The objective of this review was to develop adverse outcome pathways (AOPs) as a means to evaluate the biological plausibility and empirical evidence supporting (or refuting) the linkage between activation of the physiological target site, the nAChR, and colony level consequences. Potential for exposure was not a consideration in AOP development and therefore this effort should not be considered a risk assessment. Nonetheless, development of the AOPs described herein has led to the identification of research gaps which, for example, may be of high priority in understanding how perturbation of pathways involved in neurotransmission can adversely affect normal colony functions, causing colony instability and subsequent bee population failure. A putative AOP network was developed, laying the foundation for further insights as to the role of combined chemical and non-chemical stressors in impacting bee populations. Insights gained from the AOP network assembly, which more realistically represents multi-stressor impacts on honey bee colonies, are promising toward understanding common sensitive nodes in key biological pathways and identifying where mitigation strategies may be focused to reduce colony losses.

Sublethal doses of imidacloprid disrupt sexual communication and host finding in a parasitoid wasp

Neonicotinoids are widely used insecticides, but their use is subject of debate because of their detrimental effects on pollinators. Little is known about the effect of neonicotinoids on other beneficial insects such as parasitoid wasps, which serve as natural enemies and are crucial for ecosystem functioning. Here we show that sublethal doses of the neonicotinoid imidacloprid impair sexual communication and host finding in the parasitoid wasp Nasonia vitripennis. Depending on the dose, treated females were less responsive to the male sex pheromone or unable to use it as a cue at all. Courtship behaviour of treated couples was also impeded resulting in a reduction of mating rates by up to 80%. Moreover, treated females were no longer able to locate hosts by using olfactory cues. Olfaction is crucial for the reproductive success of parasitoid wasps. Hence, sublethal doses of neonicotinoids might compromise the function of parasitoid wasps as natural enemies with potentially dire consequences for ecosystem services.

Neonicotinoid-induced impairment of odour coding in the honeybee

Exposure to neonicotinoid pesticides is considered one of the possible causes of honeybee (Apis mellifera) population decline. At sublethal doses, these chemicals have been shown to negatively affect a number of behaviours, including performance of olfactory learning and memory, due to their interference with acetylcholine signalling in the mushroom bodies. Here we provide evidence that neonicotinoids can affect odour coding upstream of the mushroom bodies, in the first odour processing centres of the honeybee brain, i.e. the antennal lobes (ALs). In particular, we investigated the effects of imidacloprid, the most common neonicotinoid, in the AL glomeruli via in vivo two-photon calcium imaging combined with pulsed odour stimulation. Following acute imidacloprid treatment, odour-evoked calcium response amplitude in single glomeruli decreases, and at the network level the representations of different odours are no longer separated. This demonstrates that, under neonicotinoid influence, olfactory information might reach the mushroom bodies in a form that is already incorrect. Thus, some of the impairments in olfactory learning and memory caused by neonicotinoids could, in fact, arise from the disruption in odor coding and olfactory discrimination ability of the honey bees.