Neonicotinoids interfere with specific components of navigation in honeybees

Detoxification response in honey bee larvae exposed to agricultural intensification

Honey bee Apis mellifera colonies located in agroecosystems are exposed to pesticides and more fragmented habitats. The resources that bees obtain in these environments may be exposed to agrochemicals, which can accumulate in their colonies and be distributed among their nest mates. Hives placed in an agricultural setting located in the region of the Argentine Pampas were studied. Changes in the expression levels of insect cytochrome P450s, enzymes involved in the detoxification of xenobiotics, and the presence of pesticides in hive products at different times of crop management were evaluated. Our results showed that CYP6AS2 and CYP6AS4 expression in honey bee larvae increased significantly after crop flowering and pesticide application. Furthermore, residues of the herbicides atrazine and glyphosate, and the insecticide chlorantraniliprole were found in beeswax and honey samples collected from the same beehives, and their concentrations correlated with the expression profiles of CYP6AS2, CYP6AS3 and CYP9BD1. These results underscore the potential risks of pesticides exposure to larval development, highlighting the need to mitigate agrochemical use in agricultural landscapes to safeguard honey bee colonies.

Flupyradifurone, imidacloprid and clothianidin disrupt the auditory processing in the locust CNS

Since the EU banned classic neonicotinoids like imidacloprid and clothianidin, they may be replaced by more recently marketed insecticides such as flupyradifurone. However, they all operate on the same neuropharmacological principle as selective agonists at the insect's nicotinic acetylcholine receptors. Here we investigated the impact of flupyradifurone, imidacloprid and clothianidin on the neuronal processing in the auditory pathway of the desert locust Schistocerca gregaria. While stepwise increasing the insecticide concentration in the haemolymph, we extracellularly recorded the spike responses of auditory afferents in the tympanal nerve and of auditory interneurons in the neck connectives. All three insecticides showed a very similar dose-dependent suppression of spike responses in the auditory interneurons ascending towards the brain, whereas the spike responses in the sensory neurons of the ears appeared unaffected. Furthermore, by systematic injection experiments we demonstrate that insecticide dosages which already supress the information transfer in the auditory pathway are by far too low to induce the typical poisoning symptoms like trembling, spasms, and paralysis. We discuss how sublethal intoxication with classical neonicotinoids or functionally related insecticides like flupyradifurone may disrupt the postsynaptic balance between excitation and inhibition in the auditory pathway of locusts and other orthopteran insects.

Romance in peril: A common pesticide impairs mating behaviours and male fertility of solitary bees (Osmiabicornis)

Mating behaviour and fertility are strong selective forces, driving the reproductive trends of animals. Mating disorders may therefore contribute to the recent decline in insect and pollinators health worldwide. While the impact of pesticides on pollinators is widely considered as a driving factor for reducing pollinators health, their effect on mating behaviour and male fertility remains widely overlooked. Here, we assessed the effects of field-realistic exposure to a common pesticide used as a neonicotinoid substitute worldwide, sulfoxaflor, on the behaviour and male physiology of the solitary bee, Osmia bicornis. We measured a variety of parameters focusing on behaviours occurring before, and during mating, as well as sperm quantity. For the first time, we demonstrate that short-term chronic, field-realistic exposure to a common pesticide reduced pre-copulatory display (-36 %) and sounds (-27 %), increased the number of copulations (+110 %) and the mating duration (+166 %), while finally reducing sperm quantity (-25 %) and mating success (-43 %). Our research raises considerable concern on the impact of field-realistic, low sublethal pesticide levels on the fertility and reproductive success of pollinators. Assessing the impact of pesticides on fitness parameters and implementing more sustainable agricultural solutions would allow mitigating the ongoing threat of pesticide pollution on wild insect populations and the broader environment.

Estimation and evaluation of usage, loss and ecological risk of neonicotinoid pesticides in a large catchment

Neonicotinoid pesticides (NNs) are increasingly used in agriculture, which may pose significant threats to aquatic organisms in receiving rivers. However, no studies have explored their entire process from application and transport to receptors within river basins. Here, we estimated the usage and loss of NNs in the Dongting Lake Basin in China using modeling approaches, and assessed NNs-associated aquatic ecological risks. Our research data showed that the annual usage of the nine NNs reached 1895 tonnes in the basin, with the peri-urban areas being the major users. We further calibrated and validated a SWAT model using various 13-years hydrological data and field measured NNs concentration data. The simulated total annual loss of NNs was 121 tonnes in the entire basin, 94 tonnes of which were discharged into the Dongting Lake. An obvious monthly variation was observed in the lake basin, with relatively higher NNs concentrations being found in summer. Results from the ecological risk assessment showed that NNs posed significant risks to aquatic organisms in approximately 11.2 % of river sections in the whole basin. The present study underscores the significant issue of NNs loss in the Dongting Lake Basin and warrants great attention to their potential risks to aquatic organisms.

Reduced Honeybee Pollen Foraging under Neonicotinoid Exposure: Exploring Reproducible Individual and Colony Level Effects in the Field Using AI and Simulation

Honeybees (Apis mellifera) are important pollinators. Their foraging behaviors are essential to colony sustainability. Sublethal exposure to pesticides such as neonicotinoids can significantly disrupt these behaviors, in particular pollen foraging. We investigated the effects of sublethal doses of the neonicotinoid imidacloprid on honeybee foraging, at both individual and colony levels, by integrating field experiments with artificial intelligence (AI)-based monitoring technology and mechanistic simulations using the BEEHAVE model. Our results replicated previous findings, which showed that imidacloprid selectively reduces pollen foraging at the colony level, with minimal impact on nectar foraging. Individually marked exposed honeybees exhibited prolonged pollen foraging trips, reduced pollen foraging frequency, and instances of drifting pollen foraging trips, likely due to impaired cognitive functions and altered metabolism. These behavioral changes at the individual level corroborated the previous model predictions derived from BEEHAVE, which highlights the value of combining experimental and simulation approaches to disentangle underlying mechanisms through which sublethal effects on individual foragers scale up to impact colony dynamics. Our findings have implications for future pesticide risk assessment, as we provide a robust feeding study design for evaluating pesticide effects on honeybee colonies and foraging in real landscapes, which could improve the realism of higher-tier ecological risk assessment.

Neonicotinoid pesticides in African agriculture: What do we know and what should be the focus for future research?

This review provides a comprehensive overview of the direct and indirect effects of neonicotinoid pesticides (NEO-P) within African agricultural ecosystems and identifies research gaps, particularly in the monitoring and regulation of pesticide use. We observed a decline in the numbers of NEO-P studies conducted in Africa since 2019 with 40.7% of the countries reporting at least one study to date. Imidacloprid (33.5%), acetamiprid (23.3%), and thiamethoxam (25.0%) are the most reported NEO-P across the continent with concentrations range from 9.0 × 10-5 to 7.2 × 107 mg kg-1, 1.7 × 10-5 to 2.1 × 103 mg kg-1, and 1.0 × 10-5 to 4.7 × 104 mg kg-1, respectively. NEO-P have been reported in honey, water, vegetables, fruits, and staple foods in most countries and in 92-100% of human urine samples collected in Ghana and Cameroon. This widespread presence indicates a potential food safety and public health concern, warranting further study. Studies on NEO-P interactions with bees have emanated mainly from North Africa (35.3% published studies) while Central/Middle, and Southern Africa accounted for 11.8% each of these studies, all of which were conducted in Cameroon and South Africa, respectively. It is important to have contextual evidence to understand neonicotinoids-pollinator interactions across specific African regions and countries; however, literature regarding the extent of NEO-P toxicities/effects on pollinators is required in 44 African countries. The environmental persistence of NEO-P and their broad-spectrum impact necessitate a re-evaluation of current regulatory practices and adoption of more sustainable pest management strategies across the continent. Furthermore, future studies should focus on investigating the long-term exposure to NEO-P, advanced computational methods in ecological risk assessments and eco-friendly alternatives to NEO-P.

Sub-lethal pesticide exposure interferes with honey bee memory of learnt colours

Neonicotinoid pesticide use has increased around the world despite accumulating evidence of their potential detrimental sub-lethal effects on the behaviour and physiology of bees, and its contribution to the global decline in bee health. Whilst flower colour is considered as one of the most important signals for foraging honey bees (Apis mellifera), the effects of pesticides on colour vision and memory retention in a natural setting remain unknown. We trained free flying honey bee foragers by presenting artificial yellow flower feeder, to an unscented artificial flower patch with 6 different flower colours to investigate if sub-lethal levels of imidacloprid would disrupt the acquired association made between the yellow flower colour from the feeder and food reward. We found that for doses higher than 4 % of LD50 value, the foraging honey bees no longer preferentially visited the yellow flowers within the flower patch and instead, we suspect, reverted back to baseline foraging preferences, with a complete loss of the yellow preference. Our honey bee colour vision modelling indicates that discriminating the yellow colour from the rest should have been easy cognitive task. Pesticide exposure also resulted in a significant increase in Lop1, UVop, and Blop, and a decrease in CaMKII and CREB gene expression. Our results suggest that memory loss is the most plausible mechanism to explain the alteration of bee foraging colour preference. Across bees, colour vision is highly conserved and is essential for efficient pollination services. Therefore, our findings have important implications for ecosystem health and agricultural services world-wide.

Pesticides in Honeybee Products-Determination of Pesticides in Bee Pollen, Propolis, and Royal Jelly from Polish Apiary

The bioaccumulation of pesticides in honeybee products (HBPs) should be studied for a number of reasons. The presence of pesticides in HBPs can provide new data on the risk related to the use of pesticides and their role in bee colony losses. Moreover, the degree of contamination of HBPs can lower their quality, weaken their beneficial properties, and, in consequence, may endanger human health. The aim of this study was to quantify a broad range of pesticide residues in three different HBPs-bee pollen, propolis, and royal jelly. Samples were collected in the years 2017-2019 from the apiary in west-central Poland. Bee products were analyzed for the presence of over 550 pesticides using the QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) method. Twenty-nine of the contaminants were quantified at least in one of the samples. Nine of them exceeded the maximum residue levels for honey. It should be noted that any dose of pesticides can cause a health hazard due to toxicity, since these substances may act synergistically. This current study revealed the high need for the pesticide monitoring of HBPs and proved that there is a need to expand the European Union Pesticides Database to include more HBPs.

Identifying and modeling the impact of neonicotinoid exposure on honey bee colony profit

Pollination by the European honey bee, Apis mellifera, is essential for the production of many crops, including highbush blueberries (Vaccinum corymbosum). To understand the impact of agrochemicals (specifically, neonicotinoids, a class of synthetic, neurotoxic insecticides) on these pollinators, we conducted a field study during the blueberry blooms of 2020 and 2021 in British Columbia (B.C.). Forty experimental honey bee colonies were placed in the Fraser Valley: half of the colonies were located within 1.5 km of highbush blueberry fields ("near" colonies) and half were located more than 1.5 km away ("far" colonies). We calculated risk quotients for these compounds using their chronic lethal dietary dose (LDD50) and median lethal concentration (LC50). Pesticide risk was similar between colonies located near and far from blueberry forage, suggesting that toxicity risks are regionally ubiquitous. Two systemic neonicotinoid insecticides, clothianidin and thiamethoxam, were found at quantities that exceeded chronic international levels of concern. We developed a profit model for a pollinating beekeeper in B.C. that was parameterized by: detected pesticide levels; lethal and sublethal bee health; and economic data. For colonies exposed to neonicotinoid pesticides in and out of the blueberry forage radii, there were economic consequences from colony mortality and sublethal effects such as a loss of honey production and compromised colony health. Further, replacing dead colonies with local bees was more profitable than replacing them with imported packages, illustrating that beekeeping management selection of local options can have a positive effect on overall profit.

Insecticide exposure alters flight-dependent gene-expression in honey bees, Apis mellifera

The increased reports of wild bee declines and annual losses of managed bees pose a significant threat to biodiversity and agricultural productivity. While these losses and declines are likely driven by various factors, the exposure of bees to agrochemicals has raised significant concern due to their ubiquitous use and potential adverse effects. Despite numerous studies suggesting neonicotinoids can negatively affect bees at the behavioral and molecular level, data linking these two factors remains sparse. Here we provide data on the impact of an acute dose of the neonicotinoid thiamethoxam on the flight performance and molecular transcription profiles of foraging honey bees (Apis mellifera). Using a controlled experimental design with tethered flight mills, we measured flight distance, duration, and speed, alongside the expression of genes involved in energy metabolism, hormone regulation, and biosynthesis. Acute thiamethoxam exposure resulted in hyperactive flight behavior but led to significant dysregulation of genes associated with oxidative phosphorylation, indicating potential disruptions in cellular energy production. These molecular changes were particularly evident when bees engaged in flight activities, suggesting that the combined stress of pesticide exposure and physical exertion exacerbates negative outcomes. Our study provides new insights into the molecular mechanisms underlying neonicotinoid-induced impairments in bee physiology that can help understand the potential long-term consequences of xenobiotic exposure on the foraging abilities of bees and ultimately fitness.

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.

Ornamental plants as vectors of pesticide exposure and potential threat to biodiversity and human health

The production of conventional ornamental plants is pesticide-intensive. We investigated whether pesticide active ingredients (AIs) are still present in ornamentals at the time of purchase and assessed their potential ecotoxicity to non-target organisms. We purchased 1000 pot plants and 237 cut flowers of different species from garden centers in Austria and Germany between 2011 and 2021 and analyzed them for up to 646 AIs. Ecotoxicological risks of AIs were assessed by calculating toxic loads for honeybees (Apis mellifera), earthworms (Eisenia fetida), birds (Passer domesticus), and mammals (Rattus norvegicus) based on the LD50 values of the detected AIs. Human health risks of AIs were assessed on the basis of the hazard statements of the Globally Harmonized System. Over the years, a total of 202 AIs were detected in pot plants and 128 AIs in cut flowers. Pesticide residues were found in 94% of pot plants and 97% of cut flowers, with cut flowers containing about twice as many AIs (11.0 ± 6.2 AIs) as pot plants (5.8 ± 4.0 AIs). Fungicides and insecticides were found most frequently. The ecotoxicity assessment showed that 47% of the AIs in pot plants and 63% of the AIs in cut flowers were moderately toxic to the considered non-target organisms. AIs found were mainly toxic to honeybees; their toxicity to earthworms, birds, and mammals was about 105 times lower. Remarkably, 39% of the plants labeled as "bee-friendly" contained AIs that were toxic to bees. More than 40% of pot plants and 72% of cut flowers contained AIs classified as harmful to human health. These results suggest that ornamental plants are vectors for potential pesticide exposure of consumers and non-target organisms in home gardens.

Current Insights into Sublethal Effects of Pesticides on Insects

The effect of pesticides on insects is often discussed in terms of acute and chronic toxicity, but an important and often overlooked aspect is the impact of sublethal doses on insect physiology and behavior. Pesticides can influence various physiological parameters of insects, including the innate immune system, development, and reproduction, through a combination of direct effects on specific exposed tissues and the modification of behaviors that contribute to health and reproductive success. Such behaviors include mobility, feeding, oviposition, navigation, and the ability to detect pheromones. Pesticides also have a profound effect on insect learning and memory. The precise effects depend on many different factors, including the insect species, age, sex, caste, physiological condition, as well as the type and concentration of the active ingredients and the exposure route. More studies are needed to assess the effects of different active ingredients (and combinations thereof) on a wider range of species to understand how sublethal doses of pesticides can contribute to insect decline. This review reflects our current knowledge about sublethal effects of pesticides on insects and advancements in the development of innovative methods to detect them.

Mapping seasonal migration in a songbird hybrid zone -- heritability, genetic correlations, and genomic patterns linked to speciation

Seasonal migration is a widespread behavior relevant for adaptation and speciation, yet knowledge of its genetic basis is limited. We leveraged advances in tracking and sequencing technologies to bridge this gap in a well-characterized hybrid zone between songbirds that differ in migratory behavior. Migration requires the coordinated action of many traits, including orientation, timing, and wing morphology. We used genetic mapping to show these traits are highly heritable and genetically correlated, explaining how migration has evolved so rapidly in the past and suggesting future responses to climate change may be possible. Many of these traits mapped to the same genomic regions and small structural variants indicating the same, or tightly linked, genes underlie them. Analyses integrating transcriptomic data indicate cholinergic receptors could control multiple traits. Furthermore, analyses integrating genomic differentiation further suggested genes underlying migratory traits help maintain reproductive isolation in this hybrid zone.

Synergistic negative effects between a fungicide and high temperatures on homing behaviours in honeybees

Interactions between environmental stressors may contribute to ongoing pollinator declines, but have not been extensively studied. Here, we examined the interaction between the agricultural fungicide Pristine (active ingredients: 25.2% boscalid, 12.8% pyraclostrobin) and high temperatures on critical honeybee behaviours. We have previously shown that consumption of field-realistic levels of this fungicide shortens worker lifespan in the field and impairs associative learning performance in a laboratory-based assay. We hypothesized that Pristine would also impair homing and foraging behaviours in the field, and that an interaction with hot weather would exacerbate this effect. Both field-relevant Pristine exposure and higher air temperatures reduced the probability of successful return on their own. Together, the two factors synergistically reduced the probability of return and increased the time required for bees to return to the hive. Pristine did not affect the masses of pollen or volumes of nectar or water brought back to the hive by foragers, and it did not affect the ratio of forager types in a colony. However, Pristine-fed bees brought more concentrated nectar back to the hive. As both agrochemical usage and heat waves increase, additive and synergistic negative effects may pose major threats to pollinators and sustainable agriculture.

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

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

Divergent impacts of the neonicotinoid insecticide, clothianidin, on flight performance metrics in two species of migratory butterflies

Long-distance flight is crucial for the survival of migratory insects, and disruptions to their flight capacity can have significant consequences for conservation. In this study, we examined how a widely used insecticide, clothianidin (class: neonicotinoid), impacted the flight performance of two species of migratory butterflies, monarchs (Danaus plexippus) and painted ladies (Vanessa cardui). To do this, we quantified the free-flight energetics and tethered-flight velocity and distance of the two species using flow-through respirometry and flight mill assays. Our findings show differential effects of the pesticide on the two species. For painted ladies, we found that clothianidin exposure reduced average free-flight metabolic rates, but did not affect either average velocity or total distance during tethered flight. Other studies have linked low flight metabolic rates with reduced dispersal capacity, indicating that clothianidin exposure may hinder painted lady flight performance in the wild. Conversely, for monarchs, we saw no significant effect of clothianidin exposure on average free-flight metabolic rates but did observe increases in the average velocity, and for large individuals, total distance achieved by clothianidin-exposed monarchs in tethered flight. This suggests a potential stimulatory response of monarchs to low-dose exposures to clothianidin. These findings indicate that clothianidin exposure has the potential to influence the flight performance of butterflies, but that not all species are impacted in the same way. This highlights the need to be thoughtful when selecting performance assays, as different assays can evaluate fundamentally distinct aspects of physiology, and as such may yield divergent results.

Pesticide Exposure and Effects on Non-Apis Bees

Bees are essential pollinators of many crops and wild plants, and pesticide exposure is one of the key environmental stressors affecting their health in anthropogenically modified landscapes. Until recently, almost all information on routes and impacts of pesticide exposure came from honey bees, at least partially because they were the only model species required for environmental risk assessments (ERAs) for insect pollinators. Recently, there has been a surge in research activity focusing on pesticide exposure and effects for non-Apis bees, including other social bees (bumble bees and stingless bees) and solitary bees. These taxa vary substantially from honey bees and one another in several important ecological traits, including spatial and temporal activity patterns, foraging and nesting requirements, and degree of sociality. In this article, we review the current evidence base about pesticide exposure pathways and the consequences of exposure for non-Apis bees. We find that the insights into non-Apis bee pesticide exposure and resulting impacts across biological organizations, landscapes, mixtures, and multiple stressors are still in their infancy. The good news is that there are many promising approaches that could be used to advance our understanding, with priority given to informing exposure pathways, extrapolating effects, and determining how well our current insights (limited to very few species and mostly neonicotinoid insecticides under unrealistic conditions) can be generalized to the diversity of species and lifestyles in the global bee community. We conclude that future research to expand our knowledge would also be beneficial for ERAs and wider policy decisions concerning pollinator conservation and pesticide regulation.

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.

S-dinotefuran affects the social behavior of honeybees (Apis mellifera)and increases their risk in the colony

The toxic effects of neonicotinoid pesticides on honeybees is a global concern, whereas little is known about the effect of stereoisomeric pesticides among honeybee social behavior. In this study, we investigated the effects of stereoisomeric dinotefuran on honeybee social behavior. We found that honeybees exhibit a preference for consuming food containing S-dinotefuran, actively engage in trophallaxis with S-dinotefuran-consuming peers, and consequently acquire higher levels of S-dinotefuran compared with R-dinotefuran. In comparison to R-dinotefuran, S-dinotefuran stimulates honeybees to elevate their body temperature, thereby attracting more peers for trophallaxis. Transcriptome analysis revealed a significant enrichment of thermogenesis pathways due to S-dinotefuran exposure. Additionally, metabolome data indicated that S-dinotefuran may enhance body temperature by promoting lipid synthesis in the lysine degradation pathway. Consequently, body temperature emerges as a key factor influencing honeybee social behavior. Our study is the first to highlight the propensity of S-dinotefuran to raise honeybee body temperature, which prompts honeybee to preferentially engage in trophallaxis with peers exhibiting higher body temperatures. This preference may lead honeybees to collect more dinotefuran-contaminated food in the wild, significantly accelerating dinotefuran transmission within a population. Proactive trophallaxis further amplifies the risk of neonicotinoid pesticide transmission within a population, making honeybees that have consumed S-dinotefuran particularly favored within their colonies. These findings may contribute to our understanding of the higher risk associated with neonicotinoid use compared with other pesticides.

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.

The survival and flight capacity of commercial honeybees and endangered stingless bees are impaired by common agrochemicals

The impact of agrochemicals on native Brazilian bees may be underestimated, since studies of non-target effects on bees have, by and large, concerned mostly the Apis mellifera L. Furthermore, bees may be exposed in the field to multiple agrochemicals through different routes, thus suggesting the necessity for more comprehensive toxicological experiments. Here, we assessed the lethal and sublethal toxicity of multiple agrochemicals (herbicide [glyphosate - Roundup®], fungicide [mancozeb], insecticide [thiamethoxam]) through distinct routes of exposure (contact or ingestion) to an endangered native Brazilian bee Melipona (Michmelia) capixaba Moure & Camargo, 1994 and to A. mellifera. Results indicate that none of the agrochemicals caused feeding repellency on the bees. Thiamethoxam caused high mortality of both species, regardless of the route of exposure or the dose used. In addition, thiametoxam altered the flight capacity of M. capixaba when exposed to the lowest dose via contact exposure. The field dose of glyphosate caused high mortality of both bee species after oral exposure as well as impaired the flight capacity of A. mellifera (ingestion exposure) and M. capixaba (contact exposure). The lower dose of glyphosate also impaired the flight of M. capixaba through either routes of exposure. Exposure of A. mellifera through contact and ingestion to both doses of mancozeb caused high mortality and significantly impaired flight capacity. Taken altogether, the results highlight the importance of testing the impact of multiple agrochemicals (i.e. not just insecticides) through different routes of exposure in order to understand more comprehensively the potential risks for Apis and non-Apis bees.

Acute and chronic effects of sublethal neonicotinoid thiacloprid to Asian honey bee (Apis cerana cerana)

Pesticide pollution is one of the most important factors for global bee declines. Despite many studies have revealed that the most important Chinese indigenous species，Apis cerana, is presenting a high risk on exposure to neonicotinoids, the toxicology information on Apis cerana remain limited. This study was aimed to determine the acute and chronic toxic effects of thiacloprid (IUPAC name: {(2Z)-3-[(6-Chloro-3-pyridinyl)methyl]-1,3-thiazolidin-2-ylidene}cyanamide) on behavioral and physiological performance as well as genome-wide transcriptome in A. cerana. We found the 1/5 LC50 of thiacloprid significantly impaired learning and memory abilities after both acute and chronic exposure, nevertheless, has no effects on the sucrose responsiveness and phototaxis climbing ability of A. cerana. Moreover, activities of detoxification enzyme P450 monooxygenases and CarE were increased by short-term exposure to thiacloprid, while prolonged exposure caused suppression of CarE activity. Neither acute nor chronic exposure to thiacloprid altered honey bee AChE activities. To further study the potential defense molecular mechanisms in Asian honey bee under pesticide stress, we analyzed the transcriptomes of honeybees in response to thiacloprid stress. The transcriptomic profiles revealed consistent upregulation of immune- and stress-related genes by both acute or chronic treatments. Our results suggest that the chronic exposure to thiacloprid produced greater toxic effects than a single administration to A. cerana. Altogether, our study deepens the understanding of the toxicological characteristic of A. cerana against thiacloprid, and could be used to further investigate the complex molecular mechanisms in Asian honey bee under pesticide stress.

Navigation and dance communication in honeybees: a cognitive perspective

Flying insects like the honeybee experience the world as a metric layout embedded in a compass, the time-compensated sun compass. The focus of the review lies on the properties of the landscape memory as accessible by data from radar tracking and analyses of waggle dance following. The memory formed during exploration and foraging is thought to be composed of multiple elements, the aerial pictures that associate the multitude of sensory inputs with compass directions. Arguments are presented that support retrieval and use of landscape memory not only during navigation but also during waggle dance communication. I argue that bees expect landscape features that they have learned and that are retrieved during dance communication. An intuitive model of the bee's navigation memory is presented that assumes the picture memories form a network of geographically defined locations, nodes. The intrinsic components of the nodes, particularly their generalization process leads to binding structures, the edges. In my view, the cognitive faculties of landscape memory uncovered by these experiments are best captured by the term cognitive map.

Atrazine exposure can dysregulate the immune system and increase the susceptibility against pathogens in honeybees in a dose-dependent manner

Recently, concerns regarding the impact of agrochemical pesticides on non-target organisms have increased. The effect of atrazine, the second-most widely used herbicide in commercial farming globally, on honeybees remains poorly understood. Here, we evaluated how atrazine impacts the survival of honeybees and pollen and sucrose consumption, investigating the morphology and mRNA expression levels of midgut tissue, along with bacterial composition (relative abundance) and load (absolute abundance) in the whole gut. Atrazine did not affect mortality, but high exposure (37.3 mg/L) reduced pollen and sucrose consumption, resulting in peritrophic membrane dysplasia. Sodium channels and chitin synthesis were considered potential atrazine targets, with the expression of various genes related to lipid metabolism, detoxification, immunity, and chemosensory activity being inhibited after atrazine exposure. Importantly, 37.3 mg/L atrazine exposure substantially altered the composition and size of the gut microbial community, clearly reducing both the absolute and relative abundance of three core gram-positive taxa, Lactobacillus Firm-5, Lactobacillus Firm-4, and Bifidobacterium asteroides. With altered microbiome composition and a weakened immune system following atrazine exposure, honeybees became more susceptible to infection by the opportunistic pathogen Serratia marcescens. Thus, considering its scale of use, atrazine could negatively impact honeybee populations worldwide, which may adversely affect global food security.

Pesticide residues in nectar and pollen of melon crops: Risk to pollinators and effects of a specific pesticide mixture on Bombus terrestris (Hymenoptera: Apidae) micro-colonies

Residues detected in pollen collected by honey bees are often used to estimate pesticide exposure in ecotoxicological studies. However, for a more accurate assessment of pesticides effect on foraging pollinators, residues found directly on flowers are a more realistic exposure approximation. We conducted a multi-residue analysis of pesticides on pollen and nectar of melon flowers collected from five fields. The cumulative chronic oral exposure Risk Index (RI) was calculated for Apis mellifera, Bombus terrestris and Osmia bicornis to multiple pesticides. However, this index could underestimate the risk since sublethal or synergistic effects are not considered. Therefore, a mixture containing three of the most frequently detected pesticides in our study was tested for synergistic impact on B. terrestris micro-colonies through a chronic oral toxicity test. According to the result, pollen and nectar samples contained numerous pesticide residues, including nine insecticides, nine fungicides, and one herbicide. Eleven of those were not applied by farmers during the crop season, revealing that melon agroecosystems may be pesticide contaminated environments. The primary contributor to the chronic RI was imidacloprid and O. bircornis is at greatest risk for lethality resulting from chronic oral exposure at these sites. In the bumblebee micro-colony bioassay, dietary exposure to acetamiprid, chlorpyrifos and oxamyl at residue level concentration, showed no effects on worker mortality, drone production or drone size and no synergies were detected when pesticide mixtures were evaluated. In conclusion, our findings have significant implications for improving pesticide risk assessment schemes to guarantee pollinator conservation. In particular, bee pesticide risk assessment should not be limited to acute exposure effects to isolated active ingredients in honey bees. Instead, risk assessments should consider the long-term pesticide exposure effects in both pollen and nectar on a range of bees that reflect the diversity of natural ecosystems and the synergistic potential among pesticide formulations.

Potential risk to pollinators from neonicotinoid applications to host trees for management of spotted lanternfly, Lycorma delicatula (Hemiptera: Fulgoridae)

Neonicotinoid insecticides are used to manage spotted lanternfly (Lycorma delicatula (White); hereafter SLF), a recently introduced pest in the United States. Neonicotinoids can harm nontargets, such as pollinators potentially exposed via floral resources of treated plants. We quantified neonicotinoid residues in whole flowers of two SLF host plant species, red maple (Acer rubrum L. [Sapindales: Sapindaceae]) and tree-of-heaven (Ailanthus altissima (Mill.) [Sapindales: Simaroubaceae]), treated with post-bloom imidacloprid or dinotefuran applications that differed in timing and method of application. In red maple flowers, dinotefuran residues from fall applications were significantly higher than summer applications, while imidacloprid residues from fall applications were significantly lower than summer applications. Residues did not differ between application methods or sites. In tree-of-heaven flowers, dinotefuran residues were only detected in one of 28 samples at a very low concentration. To assess acute mortality risk to bees from oral exposure to residues in these flowers, we calculated risk quotients (RQ) using mean and 95% prediction interval residue concentrations from treatments in this study and lethal concentrations obtained from acute oral bioassays for Apis mellifera (L. (Hymenoptera: Apidae)) and Osmia cornifrons (Radoszkowski (Hymenoptera: Megachilidae)), then compared these RQs to a level of concern. For A. mellifera, only one treatment group, applied at 2X maximum label rate, had an RQ that exceeded this level. However, several RQs for O. cornifrons exceeded the level of concern, suggesting potential acute risk to solitary bees. Further studies are recommended for more comprehensive risk assessments to nontargets from neonicotinoid use for SLF management.

A Sublethal Concentration of Sulfoxaflor Has Minimal Impact on Buff-Tailed Bumblebee (Bombus terrestris) Locomotor Behaviour under Aversive Conditioning

Pesticide exposure has been cited as a key threat to insect pollinators. Notably, a diverse range of potential sublethal effects have been reported in bee species, with a particular focus on effects due to exposure to neonicotinoid insecticides. Here, a purpose-built thermal-visual arena was used in a series of pilot experiments to assess the potential impact of approximate sublethal concentrations of the next generation sulfoximine insecticide sulfoxaflor (5 and 50 ppb) and the neonicotinoid insecticides thiacloprid (500 ppb) and thiamethoxam (10 ppb), on the walking trajectory, navigation and learning abilities of the buff-tailed bumblebee (Bombus terrestris audax) when subjected to an aversive conditioning task. The results suggest that only thiamethoxam prevents forager bees from improving in key training parameters (speed and distanced travelled) within the thermal visual arena. Power law analyses further revealed that a speed-curvature power law, previously reported as being present in the walking trajectories of bumblebees, is potentially disrupted under thiamethoxam (10 ppb) exposure, but not under sulfoxaflor or thiacloprid exposure. The pilot assay described provides a novel tool with which to identify subtle sublethal pesticide impacts, and their potential causes, on forager bees, that current ecotoxicological tests are not designed to assess.

Modeling disruption of Apis mellifera (honey bee) odorant-binding protein function with high-affinity binders

Chemical toxins pose a great threat to honey bee health because they affect memory and cognition, diminish immunity, and increase susceptibility to infection, resulting in decreased colony performance, reproduction, and survival. Although the behavioral effects of sub-lethal chemical exposure on honey bees have been intensively studied, how xenobiotics affect olfaction, at the molecular level, still needs to be elucidated. In the present work, in silico tools, such as molecular docking, binding free energy calculations, and molecular dynamics simulations are used to predict if environmental chemicals have stronger binding affinities to honey bee antennal odorant-binding protein 14 (OBP14) than the representative floral odors citralva, eugenol, and the fluorescent probe 1-N-phenylnaphthylamine. Based on structural analysis, 21 chemicals from crop pesticides, household appliances, cosmetics, food, public health-related products, and other sources, many of which are pervasive in the hive environment, have higher binding affinities than the floral odors. These results suggest that chemical exposures are likely to interfere with the honey bee's sense of smell and this disruptive mechanism may be responsible for the lower associative learning and memory based on olfaction found in bees exposed to pesticides. Moreover, bees mainly rely on olfactory cues to perceive their environment and orient themselves as well as to discriminate and identify their food, predators, nestmates, and diseased individuals that need to be removed with hygienic behavior. In summary, sub-lethal exposure to environmental toxins can contribute to colony collapse in several ways from the disruption of proper olfaction functioning.

Imidacloprid Pesticide Causes Unexpectedly Severe Bioelement Deficiencies and Imbalance in Honey Bees Even at Sublethal Doses

Pesticides impair honeybee health in many ways. Imidacloprid (IMD) is a pesticide used worldwide. No information exists on how IMD impact the bees' body bioelement balance, which is essential for bee health. We hypothesized that IMD disturbs this balance and fed the bees (in field conditions) with diets containing 0 ppb (control), 5 ppb (sublethal considered field-relevant), and 200 ppb (adverse) doses of IMD. IMD severely reduced the levels of K, Na, Ca, and Mg (electrolytic) and of Fe, Mo, Mn, Co, Cu, Ni, Se, and Zn, while those of Sn, V, and Cr (enzymatic) were increased. Levels of P, S, Ti, Al, Li, and Sr were also decreased, while only the B content (physiologically essential) was increased. The increase in Tl, Pb, and As levels (toxic) was alarming. Generally, IMD, even in sublethal doses, unexpectedly led to severe bioelement malnutrition in 69% of bioelements and to a stoichiometric mismatch in the remaining ones. This points to the IMD-dependent bioelement disturbance as another, yet unaccounted for, essential metabolic element which can interfere with apian health. Consequently, there is a need for developing methods of bioelement supplementation of the honey bee diet for better preventing bee colony decline and protecting apian health status when faced with pesticides.

Geographical and Seasonal Analysis of the Honeybee Microbiome

We previously showed that colonies of thriving and non-thriving honeybees co-located in a single geographically isolated apiary harboured strikingly different microbiomes when sampled at a single time point in the honey season. Here, we profiled the microbiome in returning forager bees from 10 to 12 hives in each of 6 apiaries across the southern half of Ireland, at early, middle, and late time points in the 2019 honey production season. Despite the wide range of geographical locations and forage available, apiary site was not the strongest determinant of the honeybee microbiome. However, there was clear clustering of the honeybee microbiome by time point across all apiaries, independent of which apiary was sampled. The clustering of microbiome by time was weaker although still significant in three of the apiaries, which may be connected to their geographic location and other external factors. The potential forage effect was strongest at the second timepoint (June-July) when the apiaries also displayed greatest difference in microbiome diversity. We identified bacteria in the forager bee microbiome that correlated with hive health as measured by counts of larvae, bees, and honey production. These findings support the hypothesis that the global honeybee microbiome and its constituent species support thriving hives.

Effect of repeated intakes of a neonicotinoid insecticide on the foraging behaviours of Apis mellifera in field trials

Evaluating the effects of neonicotinoids on forager bees in conditions as near as possible to those in nature presents a considerable challenge. Tackling this challenge is, however, necessary to establish their negative side effects on these pollinators. For instance, it is still under debate the mechanism by which bees seem to recognize low-level contaminations of neonicotinoid insecticides in nectar and pollen of the flowers they visit and limit collection to protect themselves and their hive from a possible intoxication. In this study, we propose an experimental system that involves the use of foragers in free flight foraging repeatedly on artificial feeders containing a sucrose solution contaminated with clothianidin, as well as foragers feeding at adjacent control feeders, allowing us to observe changes in their foraging activity. The progressive disappearance of foragers from the contaminated feeders became increasingly clear and rapid with the increase in clothianidin concentration. The lowest concentration at which we observed an effect was around 10 µg/L, which corresponds to the maximum residual concentration (10 ng/g) observed in pollen and nectar of flowers close to open fields sown with seeds coated with insecticides. At the highest concentrations tested (80 µg/L), there was an almost total abandonment of the feeders. The estimated quantity of contaminated sucrose solution collected by foragers showed an almost linear relationship inversely proportional to clothianidin concentration, whilst the estimated quantity of insecticide collected by a forager increased and then stabilised at the highest concentrations tested of 40 and 80 µg/L. Irregular mortality was not observed in front of the hives, furthermore, foragers did not show evident memory of the position of the treated units in the trials on the 2 consecutive days. The decrease in foraging activity in the presence of a few µg/L of insecticide in the sucrose solution appears to limit the introduction of elevated amounts of toxic substances into the hives, which would have serious consequences for the young bees and the brood. At the same time, in the absence of an alternative energy source, even reduced feeding of the hive can compromise colony health.

Assessment of acute and chronic toxicity of cyantraniliprole and sulfoxaflor on honey bee (Apis mellifera) larvae

BACKGROUND

Recently, cyantraniliprole (CYA) and sulfoxaflor (SUL) have been considered as alternatives to neonicotinoid insecticides. In this study, we evaluated the acute and chronic toxicities of CYA and SUL on honey bee (Apis mellifera L.) larvae reared in vitro.

RESULTS

In the acute toxicity test, the following test doses were used to determine the median lethal dose (LD₅₀ ): CYA 0.007, 0.014, 0.028, 0.056 and 0.112 μg larva^-1 ; SUL 2.5, 5, 10, 20 and 40 μg larva^-1 . In the chronic toxicity test, the following test doses were used to determine the LD₅₀ : CYA 0.00512, 0.0128, 0.032, 0.08 and 0.2 μg larva^-1 ; SUL 0.0625, 0.125, 0.25, 0.5 and 1.0 μg larva^-1 . The acute LD₅₀ values of CYA and SUL were 0.047 and 11.404 μg larva^-1 , respectively. Larvae acutely exposed to SUL had significantly lower body weight than controls, but those exposed to CYA showed no difference. The no observed adverse effect level (NOAEL) and LD₅₀ values of the chronic toxicity tests for each insecticide were 0.00512 and 0.064 μg larva^-1 for CYA, and 0.0625 μg larva^-1 and 0.212 μg larva^-1 for SUL, respectively. Larvae chronically exposed to SUL emerged as bees with deformed wings, reaching adult deformation rates of over 50%; however, CYA had no effect on adult deformation.

CONCLUSION

Exposure to CYA increased larval mortality but did not cause any adult deformation, whereas SUL exposure increased pupal mortality and caused wing deformation in newly emerged bees. Our study may be useful for the assessment of pesticide toxicity by providing valuable findings on the effects of these insecticides on honey bee larvae. © 2022 Society of Chemical Industry.

Field-realistic concentrations of a neonicotinoid insecticide influence socially regulated brood development in a bumblebee

The systemic neonicotinoid insecticides are considered as one of the key culprits contributing to ongoing declines in pollinator health and abundance. Bumblebees are among the most important pollinators of temperate zone plants, making their susceptibility to neonicotinoid exposure of great concern. We report that bumblebee (Bombus terrestris) colonies exposed to field-realistic concentrations of the commonly used neonicotinoid Imidacloprid grew slower, consumed less food, and produced fewer workers, males and gynes, but unexpectedly produced larger workers compared to control colonies. Behavioural observations show that queens in pesticide-treated colonies spend more time inactive and less time caring for the brood. We suggest that the observed effects on brood body size are driven by a decreased queen ability to manipulate the larva developmental programme. These findings reveal an intricate and previously unknown effect of insecticides on the social interactions controlling brood development in social insect colonies. Insecticide influences on the social mechanisms regulating larval development are potentially detrimental for bumblebees, in which body size strongly influences both caste differentiation and the division of labour among workers, two organization principles of insect societies.

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.

Lethal, sublethal, and combined effects of pesticides on bees: A meta-analysis and new risk assessment tools

Multiple stressors threaten bee health, a major one being pesticides. Bees are simultaneously exposed to multiple pesticides that can cause both lethal and sublethal effects. Risk assessment and most research on bee health, however, focus on lethal individual effects. Here, we performed a systematic literature review and meta-analysis that summarizes and re-interprets the available qualitative and quantitative information on the lethal, sublethal, and combined toxicity of a comprehensive range of pesticides on bees. We provide results (1970-2019) for multiple bee species (Bombus, Osmia, Megachile, Melipona, Partamona, Scaptotrigona), although most works focused on Apis mellifera L. (78 %). Our harmonised results document the lethal toxicity of pesticides in bees (n = 377 pesticides) and the types of sublethal testing methods and related effects that cause a sublethal effect (n = 375 sublethal experiments). We identified the most common combinations of pesticides and mode of actions tested, and summarize the experimental methods, magnitude of the interactions, and robustness of available data (n = 361 experiments). We provide open access searchable, comprehensive, and integrated list of pesticides and their levels causing lethal, sublethal, and combined effects. We report major data gaps related to pesticide's sublethal (71 %) and combined (e.g., ~99 %) toxicity. We identified pesticides and mode of actions of greatest concern in terms of sublethal (chlorothalonil, pymetrozine, glyphosate; neonicotinoids) and combined (tau-fluvalinate combinations; acetylcholinesterase inhibitors and neonicotinoids) effects. Although certain pesticides have faced regulatory restrictions in specific countries (chlorothalonil, pymetrozine, neonicotinoids), most are still widely used worldwide (e.g., glyphosate). This work aims at facilitating the implementation of more comprehensive and harmonised research and risk assessments, considering sublethal and combined effects. To ensure safeguarding pollinators and the environment, we advocate for a more refined and holistic assessment that do not only focus on lethality but uses harmonised methods to test sublethal and relevant combinations.

Decreased efficiency of pollen collection due to Sulfoxaflor exposure leads to a reduction in the size of bumble bee workers in late European summer

Bumble bees (Bombus terrestris) are important pollinators of wild and crop plants. Despite their importance in the process of fruit and seed production on crop sites, their activity may be impaired due to exposure to pesticides. This species has a yearly life cycle and colony success may rely on effective foraging of workers on ruderal plants late in summer when most crops are no longer flowering. In the current study, we investigated the effect of chronic exposure to Sulfoxaflor on aspects of the foraging behavior of bumble bees and whether Sulfoxaflor influences the body size of workers of B. terrestris in a crop landscape. We found that 2 weeks of continuous exposure to Sulfoxaflor influenced workers’ foraging dynamics and collection of resources. However, there was no evidence that the 5 ppb dose of the pesticide impacted the ability of bees to handle flowers with different traits. Workers from colonies exposed to Sulfoxaflor were smaller. The effect on worker size may be explained as a consequence of the reduced pollen income per unit of worker foraging. Thus, if the effects of Sulfoxaflor applied directly to crops had the same effect as that observed on commercial bumble bees after our chronic exposure, it might negatively impact colony success due to the impact on pollen collection and the reduction in the size of workers.

Seed-coating of rapeseed (Brassica napus) with the neonicotinoid clothianidin affects behaviour of red mason bees (Osmia bicornis) and pollination of strawberry flowers (Fragaria × ananassa)

Neonicotinoid insecticides applied to flowering crops can have negative impacts on bees, with implications for crop pollination. To assess if exposure to the neonicotinoid clothianidin via a treated crop (rapeseed) affected bee behaviour, pollination performance (to strawberry), and bee reproduction, we provided each of 12 outdoor cages with rapeseed (autumn-sown plants complemented with a few spring-sown plants to extend the flowering period) grown from either clothianidin-treated or untreated (control) seeds, together with strawberry plants and a small population of red mason bees (Osmia bicornis). We expected clothianidin to reduce bee foraging activity, resulting in impaired strawberry pollination and bee reproduction. During the early stage of the experiment, we observed no difference between treatments in the length of entire foraging trips, or the combined number of rapeseed and strawberry flowers that the bees visited during these trips. During the later stage of the experiment, we instead determined the time a female took to visit 10 rapeseed flowers, as a proxy for foraging performance. We found that they were 10% slower in clothianidin cages. Strawberries weighed less in clothianidin cages, suggesting reduced pollination performance, but we were unable to relate this to reduced foraging activity, because the strawberry flowers received equally many visits in the two treatments. Clothianidin-exposed females sealed their nests less often, but offspring number, sex ratio and weight were similar between treatments. Observed effects on bee behaviour appeared by the end of the experiment, possibly because of accumulated effects of exposure, reduced bee longevity, or higher sensitivity of the protocols we used during the later phase of the experiment. Although the lack of a mechanistic explanation calls for interpreting the results with cautiousness, the lower strawberry weight in clothianidin cages highlights the importance of understanding complex effects of plant protection products, which could have wider consequences than those on directly exposed organisms.

Chronic exposure to insecticides impairs honeybee optomotor behaviour

Honeybees use wide-field visual motion information to calculate the distance they have flown from the hive, and this information is communicated to conspecifics during the waggle dance. Seed treatment insecticides, including neonicotinoids and novel insecticides like sulfoxaflor, display detrimental effects on wild and managed bees, even when present at sublethal quantities. These effects include deficits in flight navigation and homing ability, and decreased survival of exposed worker bees. Neonicotinoid insecticides disrupt visual motion detection in the locust, resulting in impaired escape behaviors, but it had not previously been shown whether seed treatment insecticides disrupt wide-field motion detection in the honeybee. Here, we show that sublethal exposure to two commonly used insecticides, imidacloprid (a neonicotinoid) and sulfoxaflor, results in impaired optomotor behavior in the honeybee. This behavioral effect correlates with altered stress and detoxification gene expression in the brain. Exposure to sulfoxaflor led to sparse increases in neuronal apoptosis, localized primarily in the optic lobes, however there was no effect of imidacloprid. We propose that exposure to cholinergic insecticides disrupts the honeybee's ability to accurately encode wide-field visual motion, resulting in impaired optomotor behaviors. These findings provide a novel explanation for previously described effects of neonicotinoid insecticides on navigation and link these effects to sulfoxaflor for which there is a gap in scientific knowledge.

Impact of Chronic Exposure to Two Neonicotinoids on Honey Bee Antennal Responses to Flower Volatiles and Pheromonal Compounds

Volatile compounds provide important olfactory cues for honey bees (Apis mellifera L.), which are essential for their ecology, behavior, and social communication. In the external environment bees locate food sources by the use of floral scents, while inside the hive, pheromones such as the queen mandibular pheromone (QMP) and alarm pheromones serve important functions in regulating colony life and inducing aggressive responses against intruders and parasites. Widely reported alterations of various behaviors in- and outside the hive following exposure to pesticides could therefore be associated with a disturbance of odor sensitivity. In the present study, we tested the effects of neonicotinoid pesticides at field concentrations on the ability of honey bees to perceive volatiles at the very periphery of the olfactory system. Bee colonies were subjected to treatments during the summer with either Imidacloprid or Thiacloprid at sublethal concentrations. Antennal responses to apple (Malus domestica L.) flower volatiles were studied by GC-coupled electro-antennographic detection (GC-EAD), and a range of volatiles, a substitute of the QMP, and the alarm pheromone 2-heptanone were tested by electroantennography (EAG). Short-term and long-term effects of the neonicotinoid treatments were investigated on bees collected in the autumn and again in the following spring. Treatment with Thiacloprid induced changes in antennal responses to specific flower VOCs, with differing short- and long-term effects. In the short term, increased antennal responses were observed for benzyl-alcohol and 1-hexanol, which are common flower volatiles but also constituents of the honey bee sting gland secretions. The treatment with Thiacloprid also affected antennal responses to the QMP and the mandibular alarm pheromone 2-heptanone. In the short term, a faster signal degeneration of the response signal to the positive control citral was recorded in the antennae of bees exposed to Thiacloprid or Imidacloprid. Finally, we observed season-related differences in the antennal responses to multiple VOCs. Altogether, our results suggest that volatile-specific alterations of antennal responses may contribute to explaining several behavioral changes previously observed in neonicotinoid-exposed bees. Treatment effects were generally more prominent in the short term, suggesting that adverse effects of neonicotinoid exposure may not persist across generations.

Exposure of Larvae to Sublethal Thiacloprid Delays Bee Development and Affects Transcriptional Responses of Newly Emerged Honey Bees

Understanding the cause of honey bee (Apis mellifera) population decline has attracted immense attention worldwide in recent years. Exposure to neonicotinoid pesticides is considered one of the most probable factors due to the physiological and behavioral damage they cause to honey bees. However, the influence of thiacloprid, a relatively less toxic cyanogen-substituted form of neonicotinoid, on honey bee (Apis mellifera L.) development is not well studied. The toxicity of sublethal thiacloprid to larvae, pupae, and emerging honey bees was assessed under laboratory conditions. We found that thiacloprid reduced the survival rate of larvae and pupae, and delayed the development of bees which led to lower bodyweight and size. Furthermore, we identified differentially expressed genes involved in metabolism and immunity though RNA-sequencing of newly-emerged adult bees. GO enrichment analysis identified genes involved in metabolism, catalytic activity, and transporter activity. KEGG pathway analysis indicated that thiacloprid induced up-regulation of genes related to glutathione metabolism and Toll-like receptor signaling pathway. Overall, our results suggest that chronic sublethal thiacloprid can affect honey bee colonies by reducing survival and delaying bee development.

A food-ingested sublethal concentration of thiamethoxam has harmful effects on the stingless bee Melipona scutellaris

In recent years, the importance of bee's biodiversity in the Neotropical region has been evidencing the relevance of including native bees in risk assessments. Therefore, the sublethal effects of the insecticide thiamethoxam on the survival and morphological parameters of the stingless bee Melipona scutellaris were investigated in the present study. Cells from both non-target organs (Malpighian tubules and midgut) and target organs (brain) were analyzed for morphological alterations using light microscopy and transmission electron microscopy. The findings showed that when M. scutellaris foragers were exposed to a sublethal concentration of thiamethoxam (LC_50/100 = 0.000543 ng a. i./μL), longevity was not reduced but brain function was affected, even with the non-target organs attempting to detoxify. The cellular damage in all the organs was mostly reflected in irregular nuclei shape and condensed chromatin, indicating cell death. The most frequent impairments in the Malpighian tubules were loss of microvilli, disorganization of the basal labyrinth, and cytoplasmic loss. These characteristics are related to an attempt by the cells to increase the excretion process, probably because of the high number of toxic molecules that reach the Malpighian tubules and need to be secreted. In general, damages that compromise the absorption of nutrients, excretion, memory, and learning processes, which are essential for the survival of M. scutellaris, were found. The present results also fill in gaps on how these bees respond to thiamethoxam exposure and will be useful in future risk assessments for the conservation of bee biodiversity.

Effects of glyphosate exposure on honeybees

Honeybees show an important pollination ability and play vital roles in improving crop yields and increasing plant genetic diversity, thereby generating tremendous economic benefits for humans. However, honeybee survival is affected by a number of biological and abiotic stresses, including the effects of fungi, bacteria, viruses, parasites, and especially agrochemicals. Glyphosate, a broad-spectrum herbicide that is primarily used for weed control in agriculture, has been reported to have lethal and sublethal effects on honeybees. Here, we summarize recent advances in research on the effects of glyphosate on honeybees, including effects on their behaviors, growth and development, metabolic processes, and immune defense, providing a detailed reference for studying the mechanism of action of pesticides. Furthermore, we provide possible directions for future research on glyphosate toxicity to honeybees.

Toxicological Effect and Molecular Mechanism of the Chiral Neonicotinoid Dinotefuran in Honeybees

With the increasing demand for pollinating services, the wellness of honeybees has received widespread attention. Recent evidence indicated honeybee health might be posed a potential threat by widely used neonicotinoids worldwide. However, little is known about the molecular mechanism of these insecticides in honeybees especially at an enantiomeric level. In this study, we selected two species of bees, Apis mellifera (A. mellifera) and Apis cerana (A. cerana), to assess the toxicity and molecular mechanism of neonicotinoid dinotefuran and its enantiomers. The results showed that S-dinotefuran was more toxic than rac-dinotefuran and R-dinotefuran to honeybees by oral and contact exposures as much as 114 times. A. cerana was more susceptible to highly toxic enantiomer S-dinotefuran. S-dinotefuran induced the immune system response in A. cerana after 48 h exposure and significant changes were observed in the neuronal signaling of A. mellifera under three forms of dinotefuran exposure. Moreover, molecular docking also revealed that S-dinotefuran formed more hydrogen bonds than R-dinotefuran with nicotinic acetylcholine receptor, indicating the higher toxicity of S-dinotefuran. Data provided here show that R-dinotefuran may be a safer alternative to control pests and protect pollinators than rac-dinotefuran.

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.

Correlation Between Increased Homing Flight Duration and Altered Gene Expression in the Brain of Honey Bee Foragers After Acute Oral Exposure to Thiacloprid and Thiamethoxam

Neonicotinoids as thiamethoxam and thiacloprid are suspected to be implicated in the decline of honey bee populations. As nicotinic acetylcholine receptor agonists, they disturb acetylcholine receptor signaling in insects, leading to neurotoxicity and are therefore globally used as insecticides. Several behavioral studies have shown links between neonicotinoid exposure of bees and adverse effects on foraging activity, homing flight performance and reproduction, but the molecular aspects underlying these effects are not well-understood. In the last years, several studies through us and others showed the effects of exposure to neonicotinoids on gene expression in the brain of honey bees. Transcripts of acetylcholine receptors, hormonal regulation, stress markers, detoxification enzymes, immune system related genes and transcripts of the energy metabolism were altered after neonicotinoid exposure. To elucidate the link between homing flight performance and shifts in gene expression in the brain of honey bees after neonicotinoid exposure, we combined homing flight activity experiments applying RFID technology and gene expression analysis. We analyzed the expression of endocrine factors, stress genes, detoxification enzymes and genes linked to energy metabolism in forager bees after homing flight experiments. Three different experiments (experiment I: pilot study; experiment II: "worst-case" study and experiment III: laboratory study) were performed. In a pilot study, we wanted to investigate if we could see differences in gene expression between controls and exposed bees (experiment I). This first study was followed by a so-called "worst-case" study (experiment II), where we investigated mainly differences in the expression of transcripts linked to energy metabolism between fast and slow returning foragers. We found a correlation between homing flight duration and the expression of cytochrome c oxidase subunit 5A, one transcript linked to oxidative phosphorylation. In the third experiment (experiment III), foragers were exposed in the laboratory to 1 ng/bee thiamethoxam and 8 ng/bee thiacloprid followed by gene expression analysis without a subsequent flight experiment. We could partially confirm the induction of cytochrome c oxidase subunit 5A, which we detected in experiment II. In addition, we analyzed the effect of the feeding mode (group feeding vs. single bee feeding) on data scattering and demonstrated that single bee feeding is superior to group feeding as it significantly reduces variability in gene expression. Based on the data, we thus hypothesize that the disruption of energy metabolism may be one reason for a prolongation of homing flight duration in neonicotinoid treated bees.

Using Citronella to Protect Bees (honeybee Apis mellifera L.) from certain Insecticides and Their Nano Formulations

Abstract Experiments were performed investigating citronella (Cymbopogon winterianus Jowitt) as a repellent to honeybee Apis mellifera (L.) (Hymenoptera: Apidae) in Egypt, it was conducted in laboratory in the Department of Entomology and Pesticides Science, Faculty of Agriculture, Cairo University, to check long-term survival of honeybee when exposed to different nano insecticides alone or combined with citronella at the same examination box for each. In this study, we used a modeling approach regarding survival data of caged worker bees under chronic exposure to four insecticides (Chloropyrophos, Nano-chloropyrophos Imidacloprid, Nano-Imidacloprid) each of them was supplemented in a box alone and in combination with citronella. Having three replicates and five concentrations (100, 200, 300, 400 and 500 ppm). Laboratory bioassay of these insecticides showed that chloropyrophos and nano chloropyrophos were the most toxic at their high dose (500 ppm) with LT50 of 120.98 and 122.02 followed by 132.14 and 136.5 minutes for Imidacloprid and Nano-Imidacloprid, respectively. No consumption occurred by bees to mixed sugar syrup with insecticides in all treatments when citronella was added. These data highly recommended that adding citronella is very effective when nicotinoid pesticides are used to longevity honeybee life and keep bee safe.

Searching beyond the streetlight: Neonicotinoid exposure alters the neurogenomic state of worker honey bees

Neonicotinoid insecticides have been implicated in honey bee declines, with many studies showing that sublethal exposure impacts bee behaviors such as foraging, learning, and memory. Despite the large number of ecotoxicological studies carried out to date, most focus on a handful of worker phenotypes leading to a "streetlight effect" where the a priori choice of phenotypes to measure may influence the results and conclusions arising from the studies. This bias can be overcome with the use of toxicological transcriptomics, where changes in gene expression can provide a more objective view of how pesticides alter animal traits. Here, we used RNA sequencing to examine the changes in neurogenomic states of nurse and forager honey bees that were naturally exposed to neonicotinoids in the field and artificially exposed to neonicotinoids in a controlled experiment. We found that neonicotinoid exposure influenced the neurogenomic state of foragers and nurses in different ways; foragers experienced shifts in expression of genes involved in cognition and development, while nurses experienced shifts in expression of genes involved in metabolism. Our study suggests that neonicotinoids influence nurse and forager bees in a different manner. We also found no to minimal overlap in the differentially expressed genes in our study and in previously published studies, which might help reconcile the seemingly contradictory results often reported in the neonicotinoid literature.