Bees under interactive stressors: the novel insecticides flupyradifurone and sulfoxaflor along with the fungicide azoxystrobin disrupt the gut microbiota of honey bees and increase opportunistic bacterial pathogens

The larval gut of Spodoptera frugiperda harbours culturable bacteria with metabolic versatility after insecticide exposure

Spodoptera frugiperda (fall armyworm) poses a substantial risk to crops worldwide, resulting in considerable economic damage. The gut microbiota of insects plays crucial roles in digestion, nutrition, immunity, growth and, sometimes, the degradation of insecticides. The current study examines the effect of synthetic insecticides on the gut microbiome of third instar S. frugiperda larvae using both culture-dependent techniques and 16S rRNA gene sequencing for bacterial community profiling and diversity analysis. In untreated larvae, the sequencing approach revealed a diverse microbiome dominated by the phyla Firmicutes, Proteobacteria and Bacteroidota, with key genera including Bacteroides, Faecalibacterium and Pelomonas. In parallel, 323 bacterial strains were isolated and assigned to the orders Bacillales, Burkholderiales, Enterobacterales, Flavobacteriales, Lactobacillales, Micrococcales, Neisseriaies, Pseudomonadales, Sphingobacteriales and Xanthomonadales. The prevailing culturable species included Serratia marcescens, Klebsiella variicola and Enterobacter quasiroggenkampii. Treatment with sublethal concentrations of three insecticides (broflanilide, spinosad and indoxacarb) caused significant changes in gut microbiome diversity and composition. Treated larvae showed a shift towards increased Proteobacteria abundance and decreased Firmicutes. Specifically, Acinetobacter and Rhodococcus were dominant in treated samples. Functional predictions highlighted significant metabolic versatility involving nutrient processing, immune response, detoxification, xenobiotic metabolism, and stress response, suggesting microbial adaptation to insecticide exposure. Network correlation analysis highlighted disrupted microbial interactions and altered community structures under insecticide treatment. These findings enhance our understanding of how insecticides impact the gut microbiota in S. frugiperda and may inform future strategies for managing pest resistance through microbiome-based approaches.

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.

Neonicotinoid insecticide sulfoxaflor in the environment: a critical review of environmental fate, degradation mechanism, and toxic effects

In recent decades, neonicotinoids (NEOs) have become widely adopted in agriculture for the control of crop pests and plant pathogens, leading to improved crop yields and enhanced agricultural productivity. However, the prolonged and widespread use of NEOs has raised significant concerns regarding their environmental persistence, food safety, and public health risks. These pesticides have been shown to contaminate various environmental compartments, including soil, surface water, and groundwater, posing potential hazards to ecosystems and human health. Microbes play a crucial role in mitigating the environmental impact of toxic pesticides, with microbial degradation emerging as a promising, cost-effective strategy for degrading pesticide residues. Several sulfoxaflor (SUL)-degrading microbes have been isolated and characterized, yet the identification of microbes, genes, and enzymes responsible for the degradation of NEOs remains an area requiring further investigation. Despite some progress, few reviews have comprehensively addressed the underlying mechanisms of NEOs degradation. This paper provides a detailed review of research on the environmental distribution, exposure risks, and ecotoxicological effects of NEOs, with a particular focus on the environmental fate of SUL. It aims to offer a novel perspective on the fate of NEOs in the environment, their potential toxicological effects, and the role of microbes in mitigating their impact.

Insect immunity in the Anthropocene

Anthropogenic activities result in global change, including climate change, landscape degradation and pollution, that can alter insect physiology and immune defences. These changes may have contributed to global insect decline and the dynamics of insect-transmitted diseases. The ability of insects to mount immune responses upon infection is crucial for defence against pathogens and parasites. Suppressed immune defences reduce fitness by causing disease-driven mortality and elevated immune responses reduce energy available to invest in other fitness traits such as reproduction. Understanding the impact of anthropogenic factors on insect-pathogen interactions is therefore key to determining the contribution of anthropogenic global change to pathogen-driven global insect decline and the emergence and transmission of insect-borne diseases. Here, we synthesise evidence of the impact of anthropogenic factors on insect immunity. We found evidence that anthropogenic factors, such as insecticides and heavy metals, directly impacting insect immune responses by inhibiting immune activation pathways. Alternatively, factors such as global warming, heatwaves, elevated CO2 and landscape degradation can indirectly reduce insect immune responses via reducing the energy available for immune function. We further review how anthropogenic factors impact pathogen clearance and contribute to an increase in vector-borne diseases. We discuss the fitness cost of anthropogenic factors via pathogen-driven mortality and reduced reproductive output and how this can contribute to species extinction. We found that most research has determined the impact of a single anthropogenic factor on insect immune responses or pathogen resistance. We recommend studying the combined impact of multiple stressors on immune response and pathogen resistance to understand better how anthropogenic factors affect insect immunity. We conclude by highlighting the importance of initiatives to mitigate the impact of anthropogenic factors on insect immunity, to reduce the spread of vector-borne diseases, and to protect vulnerable ecosystems from emerging diseases.

Combined effects of microplastics and flupyradifurone on gut microbiota and oxidative status of honeybees (Apis mellifera L.)

The increasing accumulation of polystyrene microplastics (PS-MPs) and the widespread use of flupyradifurone (FPF) affect honeybee health adversely. However, the combined impact of PS-MPs and FPF toxicity on honeybees remains unknown. In this study, honeybee (Apis mellifera L.) was fed with sucrose solutions containing PS-MPs (0.5 or 5 μm, 50 mg/L), FPF (4 mg/L), or their combination for 21 days under laboratory conditions. The effects of PS-MPs and FPF on honeybee physiology, gut microbiota, and stress-related enzyme activities and genes were measured. The findings showed that concurrent exposure to PS-MPs and FPF significantly reduced honeybee survival, with additive effects, decreased sucrose consumption and body weight, and devastated midgut epithelial cells. FPF was the main stressor affecting survival, while PS-MPs exerted a greater influence on body weight. Co-exposure to PS-MPs (0.5 μm) and FPF disrupted gut microbiota, significantly decreasing Lactobacillus abundance. Supplementation with Lactobacillus helsingborgensis improved honeybee survival, highlighting the protective role of gut microbiota. PS-MPs exposure, alone or combined with FPF, increased oxidative stress and decreased detoxification and immune capabilities in honeybees. These findings suggested the combined toxicity of PS-MPs and FPF on honeybees, underscoring the potential ecology risk posed by multiple stressors.

Environmental pollution effect on honey bees and their derived products: a comprehensive analysis

Several factors, including environmental degradation, air pollution, intense urbanization, excessive agriculture, and climate change, endanger the well-being of animals and plants. One of the major issues with an increasingly negative impact is agricultural contamination with pesticides and antibiotics. Seed coatings with neonicotinoid insecticides used as a protective layer against pests are shown to exceed the permissible limits in most cases. Neonicotinoid compounds bind to nicotinic acetylcholine receptors, therefore affecting the honey bees' brain. Heavy metals in higher concentrations are lethal for honey bees, and the residue in bee products might pose a threat to human health. Highly effective acaricides used to treat Varroa destructor infestations in honey bee colonies have negative effects on honey bee reproduction, olfaction, and honey production. Furthermore, amitraz and fluvalinate are mostly found in the highest amounts and lead to decreased honey production and reduced colony reproduction, along with decreased learning ability and memory. However, scientific studies have shown that honey bees act as a reliable bio-indicator of environmental pollution. In response to the growing demand for bee products, the effects of adulteration and improper storage conditions have gotten worse and represent a new risk factor. In light of the shifting global economy, it is important to analyze consumer expectations and adjust manufacturing accordingly. By ensuring the manufacture of high-quality, traceable products devoid of drug residues, consumers will be better protected from subsequent health problems. This review's objectives are based on the necessity of identifying the risks associated with honey bees and bee products.

Effects of the insecticide thiodicarb on non-target organs and behavior of the stingless bee Partamona helleri (Hymenoptera: Meliponini)

Stingless bees are vital pollinators in the Neotropics and can be exposed to pesticides used in agriculture during their foraging activities. Among these pesticides, the insecticide thiodicarb is commonly applied to bean and sunflower crops, posing a potential risk to the stingless bee Partamona helleri, which pollinates these plants. This study aimed to investigate the effects of thiodicarb on mortality, morphology, programmed cell death signaling pathways in the midgut and Malpighian tubules, and the locomotion behavior of P. helleri workers. The estimated lethal concentration (LC50) of thiodicarb for P. helleri was 87 μg a.i. mL-1. Bees fed this concentration exhibited morphological damage to the midgut epithelium and Malpighian tubules, including brush border degeneration, increased cytoplasm vacuolation, and the release of cell fragments into the intestinal lumen. In the midgut, regenerative cells showed cytoplasm disorganization and nuclear pyknosis. Immunofluorescence analysis revealed an increase in cell death via autophagy and apoptosis in the epithelial cells of the affected organs. Ingestion of thiodicarb also altered the bees' locomotion, resulting in increased meandering and decreased walking speed and total distance traveled. These findings demonstrate that the LC50 of thiodicarb causes damage to non-target organs as the midgut and Malpighian tubules, and impairs behavior, which may ultimately affect the pollination services provided by P. helleri. These results enhance our understanding of the vulnerability of stingless bees to insecticides and underscore the importance of strategies aimed at protecting these pollinators.

Co-exposure to a honeybee pathogen and an insecticide: synergistic effects in a new solitary bee host but not in Apis mellifera

Pesticides and pathogens are major drivers of bee declines. However, their potential interactions are poorly understood, especially for non-Apis bees. This study assessed the combined effects of infestation by the honeybee pathogen Vairimorpha ceranae and chronic exposure to the insecticide flupyradifurone on Osmia bicornis and Apis mellifera. We investigated whether V. ceranae could reproduce in a new solitary bee host (O. bicornis) and assessed sublethal and lethal effects of the pathogen and the pesticide, alone and in combination. We also analysed the interactive effects of the combined exposure on V. ceranae proliferation and bee survival in the two bee species. Newly emerged bees were orally infected with 100 000 spores of V. ceranae and then exposed ad libitum to flupyradifurone at field-realistic concentrations. We showed, for the first time to our knowledge, that V. ceranae can replicate in the midgut of O. bicornis, causing histological damage, impaired phototactic response, reduced food consumption and decreased longevity. The pathogen-pesticide combination caused a synergistic effect in O. bicornis, leading to an abrupt survival decline. In A. mellifera, V. ceranae and flupyradifurone showed antagonistic survival effects, but the pesticide promoted pathogen proliferation. Our results warn against the potential effects of pathogen spillover and multiple stressor exposure on non-Apis bees.

Impact of intensive agriculture and pathogens on honeybee (Apis mellifera) colony strength in northwestern Italy

Honeybee colony survival has significantly decreased in many countries over recent decades, which has been associated with multiple factors including pathogens, parasites, resource availability, and environmental stressors, with agricultural intensification playing a key role. This study assessed the effects of Varroa destructor mite infestation, viral prevalence and load, and agrochemical concentrations in the hive matrix on colony strength in two apiaries located in different agricultural contexts (intensive vs traditional) in Northwestern Italy from March to September 2021. The results revealed that colonies in the intensively managed area exhibited lower colony strength and higher mortality rates. Varroa destructor was found to interact with viruses, potentially increasing their effective virulence. Pesticide concentrations in hive matrices correlated with reduced colony strength, exacerbated by elevated pathogen loads. These findings highlighted the effects of agricultural chemicals together with pathogens on worsening bee health, raising urgent concerns for environmental management and regulatory policy.

Toxicity responses of different bee species to flupyradifurone and sulfoxaflor insecticides reveal species and sex-based variations

Mason bees (Osmia spp.) are solitary, tunnel-nesting bees. Several species, including the horn-faced bee (Osmia cornifrons) and the blue orchard bee (Osmia lignaria), are commercially managed, primarily for the pollination of fruit trees and tree nuts. They are efficient pollinators and have high pollen fidelity, and so can greatly benefit orchard yields compared to honey bees (Apis mellifera) alone. Apis mellifera are often used as surrogates for other pollinators during pesticide risk assessment. Non-Apis bee species, however, can be more sensitive to certain pesticides, so it is also important to research the impact of novel pesticides on other bee species. This study investigated the effect of two formulated pesticide products containing recently approved active ingredients, sulfoxaflor and flupyradifurone, on the survival of A. mellifera and three species of mason bees (O. lignaria, O. cornifrons, and Osmia californica). Bees were orally exposed to sulfoxaflor or flupyradifurone and their survival was measured over four days following exposure. Bee sensitivity to the insecticides varied by species and sex of bee. Apis mellifera was the least sensitive, followed by O. cornifrons, with O. lignaria and O. californica as the most sensitive. Male Osmia spp. bees were less sensitive than females. These insecticides may pose a higher risk to the health of Osmia spp. compared to A. mellifera.

Acetamiprid Exposure Disrupts Gut Microbiota in Adult and Larval Worker Honeybees (Apis mellifera L.)

Acetamiprid is a third-generation neonicotinoid insecticide that is now widely employed for the protection of crops grown in outdoor environments. This is because it is considerably less toxic to pollinating insects than other neonicotinoids. Previous studies have shown that acetamiprid has direct physiological effects on adult and larval bees. However, its effects on the potentially healthy gut microbiota of honeybees have not been fully elucidated. To further investigate the effects, adult and larval worker honeybees were exposed to sucrose solutions containing acetamiprid at concentrations of 0, 5, and 25 mg/L for a period of 7 days (adults) and 4 days (larvae). The results showed that acetamiprid exposure significantly disrupted the honeybees' intestinal microbiota. In adults, acetamiprid exposure led to a significant increase in the relative abundance of Commensalibacter, while the Bifidobacterium and Gilliamella levels decreased. In larvae, we observed significant changes in the microbial composition, notably a marked reduction in Bombella. Further analysis demonstrated that alterations in the gut microbiota of honeybee larvae were associated with disturbances in metabolic pathways that regulate energy metabolism and neurometabolism. These results suggest that acetamiprid affects bee health not only through direct physiological effects, but also through changes in the gut microbiota, which in turn affect the metabolic and immune function of bees. This study underscores the need to evaluate pesticides' risks from a microbiological standpoint and offers crucial insights into how acetamiprid impacts bee health by modifying the gut microbiota. These insights support the more comprehensive assessment of acetamiprid and similar pesticides regarding bee health.

Bumblebees under stress: Interacting effects of pesticides and heatwaves on colony development and longevity

Pollinator decline is linked to intensified agricultural practices, pathogens, climate change, and several other factors. We investigated the combined impact of heat and pesticide stress on food consumption, survival, and reproductive fitness of bumble bees. As climate change is expected to intensify heatwaves, we simulated a present-day and a future heatwave scenario (as expected in 50 years). In both scenarios, we exposed microcolonies to three widely used pesticides: azoxystrobin (fungicide), flupyradifurone, and sulfoxaflor (both insecticides)-mixed into pollen and nectar in field-realistic concentrations. We found that bees always consumed the least of sulfoxaflor-treated food, whereas consumption did not differ between other treatments or heatwave scenarios. Surprisingly, pesticide-stressed colonies performed slightly better in the future heatwave scenario in terms of reproductive fitness and survival. Sulfoxaflor consistently had the strongest negative effect, reducing survival rates, brood development, and food consumption, although effects were less severe in the future heatwave scenario.

The effect of lambda-cyhalothrin nanocapsules on the gut microbial communities and immune response of the bee elucidates the potential environmental impact of emerging nanopesticides

Emerging nanopesticides are gradually gaining widespread application in agriculture due to their excellent properties, but their potential risks to pollinating insects are not fully understood. In this study, lambda-cyhalothrin nanocapsules (LC-NCs) were constructed by electrostatic self-assembly method with iron mineralization optimization, and their effects on bee gut microbial communities and host immune-related factors were investigated. Microbiome sequencing revealed that LC-NCs increase the diversity of gut microbial communities and reduce the complexity of network features, disrupting the overall structure of the microbial communities. In addition, LC-NCs also had systemic effects on the immune response of bees, including increased activity of SOD and CAT enzymes and expression of their genes, as well as downregulation of Defensin1. Furthermore, we noticed that the immune system of the host was activated simultaneously with a rise in the abundance of beneficial bacteria in the gut. Our research emphasizes the importance of both the host and gut microbiota of holobiont in revealing the potential risks of LC-NCs to environmental indicators of honey bees, and provides references for exploring the interactions between host-microbiota systems under exogenous stress. At the same time, we hope that more research can focus on the potential impacts of nanopesticides on the ecological environment.

Pharmacology and molecular modeling studies of sulfoxaflor, flupyradifurone and neonicotinoids on the human neuronal α7 nicotinic acetylcholine receptor

We conducted electrophysiological and molecular docking studies using a heterologous expression system (Xenopus oocytes) to compare the effects of four neonicotinoids (acetamiprid, imidacloprid, clothianidin and thiamethoxam), one sulfoximine, (sulfoxaflor), and one butenolide (flupyradifurone), on human α7 neuronal nicotinic acetylcholine receptors (nAChRs). All neonicotinoids (except thiamethoxam), as well as the recently introduced nAChR competitive modulators, flupyradifurone and sulfoxaflor, appear to be weaker agonists than acetylcholine. Two mutations in loop C (E211N and E211P) and one mutation in loop D (Q79K), known to be involved in the binding properties of neonicotinoids were introduced to the α7 wild type. Interestingly, the acetylcholine and nicotine-evoked activation was not modified in human α7 mutated receptors, but the net charge was enhanced for clothianidin and imidacloprid, respectively. Flupyradifurone responses strongly increased under the Q79K mutation. The molecular docking investigations demonstrated that the orientations and interactions of the ligands considered were in accordance with those observed experimentally. Specifically, the charged fragments of acetylcholine and nicotine, used as reference ligands, and their neonicotinoid homologs were found to be surrounded by aromatic residues, with key interactions with Trp171 and Y210. Furthermore, the molecular docking investigations predicted the water-mediated interaction between the carbonyl oxygen of acetylcholine and the Nsp2 nitrogen of the pyridine ring for nicotine (as well as for the majority of the corresponding neonicotinoid fragments) and main chain NH of L141. The docking scores, extending over a significant range of 6 kcal/mol, showed that most neonicotinoids were poorly stabilized in the α7 nAChR compared to acetylcholine, except sulfoxaflor.

Modeling seasonal immune dynamics of honey bee (Apis mellifera L.) response to injection of heat-killed Serratia marcescens

The honey bee, Apis mellifera L., is one of the main pollinators worldwide. In a temperate climate, seasonality affects the life span, behavior, physiology, and immunity of honey bees. In consequence, it impacts their interaction with pathogens and parasites. In this study, we used Bayesian statistics and modeling to examine the immune response dynamics of summer and winter honey bee workers after injection with the heat-killed bacteria Serratia marcescens, an opportunistic honey bee pathogen. We investigated the humoral and cellular immune response at the transcriptional and functional levels using qPCR of selected immune genes, antimicrobial activity assay, and flow cytometric analysis of hemocyte concentration. Our data demonstrate increased antimicrobial activity at transcriptional and functional levels in summer and winter workers after injection, with a stronger immune response in winter bees. On the other hand, an increase in hemocyte concentration was observed only in the summer bee population. Our results indicate that the summer population mounts a cellular response when challenged with heat-killed S. marcescens, while winter honey bees predominantly rely on humoral immune reactions. We created a model describing the honey bee immune response dynamics to bacteria-derived components by applying Bayesian statistics to our data. This model can be employed in further research and facilitate the investigating of the honey bee immune system and its response to pathogens.

Acute exposure to fungicide fluazinam induces cell death in the midgut, oxidative stress and alters behavior of the stingless bee Partamona helleri (Hymenoptera: Apidae)

Stingless bees (Hymenoptera: Meliponini) are pollinators of both cultivated and wild crop plants in the Neotropical region. However, they are susceptible to pesticide exposure during foraging activities. The fungicide fluazinam is commonly applied in bean and sunflower cultivation during the flowering period, posing a potential risk to the stingless bee Partamona helleri, which serves as a pollinator for these crops. In this study, we investigated the impact of acute oral exposure (24 h) fluazinam on the survival, morphology and cell death signaling pathways in the midgut, oxidative stress and behavior of P. helleri worker bees. Worker bees were exposed for 24 h to fluazinam (field concentrations 0.5, 1.5 and 2.5 mg a.i. mL-1), diluted in 50 % honey aqueous solution. After oral exposure, fluazinam did not harm the survival of worker bees. However, sublethal effects were revealed using the highest concentration of fluazinam (2.5 mg a.i. mL-1), particularly a reduction in food consumption, damage in the midgut epithelium, characterized by degeneration of the brush border, an increase in the number and size of cytoplasm vacuoles, condensation of nuclear chromatin, and an increase in the release of cell fragments into the gut lumen. Bees exposed to fluazinam exhibited an increase in cells undergoing autophagy and apoptosis, indicating cell death in the midgut epithelium. Furthermore, the fungicide induced oxidative stress as evidenced by an increase in total antioxidant and catalase enzyme activities, along with a decrease in glutathione S-transferase activity. And finally, fluazinam altered the walking behavior of bees, which could potentially impede their foraging activities. In conclusion, our findings indicate that fluazinam at field concentrations is not lethal for workers P. helleri. Nevertheless, it has side effects on midgut integrity, oxidative stress and worker bee behavior, pointing to potential risks for this pollinator.

Temporospatial dynamics and host specificity of honeybee gut bacteria

Honeybees are important pollinators worldwide, with their gut microbiota playing a crucial role in maintaining their health. The gut bacteria of honeybees consist of primarily five core lineages that are spread through social interactions. Previous studies have provided a basic understanding of the composition and function of the honeybee gut microbiota, with recent advancements focusing on analyzing diversity at the strain level and changes in bacterial functional genes. Research on honeybee gut microbiota across different regions globally has provided insights into microbial ecology. Additionally, recent findings have shed light on the mechanisms of host specificity of honeybee gut bacteria. This review explores the temporospatial dynamics in honeybee gut microbiota, discussing the reasons and mechanisms behind these fluctuations. This synopsis provides insights into host-microbe interactions and is invaluable for honeybee health.

Uncovering hidden dangers: The combined toxicity of abamectin and lambda-cyhalothrin on honey bees

Studying the toxic effects of pesticides on bees has consistently been a prominent area of interest for researchers. Nonetheless, existing research has predominantly concentrated on individual toxicity assessments, leaving a gap in our understanding of mixed toxicity. This study delves into the individual and combined toxic effects of abamectin (ABA) and lambda-cyhalothrin (LCY) on honey bees (Apis mellifera) in laboratory settings. We discovered that ABA (96 h-LC50 value of 0.079 mg/L) exhibited greater acute toxicity to honey bees compared to LCY (96 h-LC50 value of 9.177 mg/L). Moreover, the mixture of ABA and LCY presented an acute antagonistic effect on honey bees. Additionally, our results indicated that exposure to LCY, at medium concentration, led to a reduction in the abundance of gut core bacterium Snodgrassella. However, an increase in the abundance of Bifidobacterium was noted when exposed to a medium concentration of LCY and its mixture with ABA. Transcriptomic analysis revealed significant regulation of certain genes in the medium concentration of all three treatments compared to the control group, primarily enriching in metabolism and immune-related pathways. Following chronic exposure to field-relevant concentrations of ABA, LCY, and their mixture, there were significant alterations in the activities of immunity-related enzyme polyphenol oxidase (PPO) and detoxification enzymes glutathione S-transferase (GST) and carboxylesterase (CarE). Additionally, the expression of four genes (abaecin, cyp9e2, cyp302a1, and GstD1) associated with immune and detoxification metabolism was significantly altered. These findings suggest a potential health risk posed by the insecticides ABA and LCY to honey bees. Despite exhibiting acute antagonistic effect, mixed exposure still induced damage to bees at all levels. This study advances our knowledge of the potential adverse effects of individual or combined exposure to these two pesticides on non-target pollinators and offers crucial guidance for the use of insecticides in agricultural production.

Exploring the risk of microplastics to pollinators: focusing on honey bees

The rapid increase in global plastic production and usage has led to global environmental contamination, with microplastics (MPs) emerging as a significant concern. Pollinators provide a crucial ecological service, while bee populations have been declining in recent years, and MPs have been recognized as a new risk factor contributing to their losses. Despite the pervasive distribution and persistence of MPs, understanding their risks to honey bees remains a critical knowledge gap. This review summarizes recent studies that investigate the toxicity of MPs on honey bee health from different perspectives. The findings revealed diverse and material-/size-/dosage-dependent outcomes, emphasizing the need for comprehensive assessments in the follow-up studies. MPs have been detected in honey and in bees' organs (e.g., gut and brain), posing potential threats to bee fitness, including altered behavior, cognitive abilities, compromised immunity, and dysfunction of the gut microbiota. It should be noticed that despite several laboratory studies suggesting the aforementioned adverse effects of MPs, field/semi-field experiments are still warranted. The synergistic toxicity of MPs with other environmental contaminants (pesticides, antibiotics, fungicides, heavy metals, etc.) still requires further investigation. Our review highlights the critical need to understand the relationships between MPs, pollinators, and the ecosystem to mitigate potential risks and ensure the sustainability of vital services provided by honey bees.

Unravelling the microplastic menace: Different polymers additively increase bee vulnerability

Microplastics (MPs) are growing and ubiquitous environmental pollutants and represent one of the greatest contemporary challenges caused by human activities. Current research has predominantly examined the singular toxicological effects of individual polymers, neglecting the prevailing reality of organisms confronted with complex contaminant mixtures and potential synergistic effects. To fill this research gap, we investigated the lethal and sublethal effects of two common MPs, polystyrene (PS - 4.8-5.8 μm) and poly(methyl methacrylate) (PMMA - 1-40 μm), and their combination (MIX), on the pollinating insect Apis mellifera. For each treatment, we evaluated the oral toxicity of two ecologically relevant and one higher concentration (0.5, 5 and 50 mg/L) and analysed their effects on the immune system and worker survival. As immune activation can alter the cuticular hydrocarbon profile of honey bees, we used gas chromatography-mass spectrometry (GC-MS) to investigate whether MPs lead to changes in the chemical profile of foragers and behavioural assay to test whether such changes affect behavioural patterns of social recognition, undermining overall colony integrity. The results indicate an additive negative effect of PS and PMMA on bee survival and immune response, even at ecologically relevant concentrations. Furthermore, alterations in cuticle profiles were observed with both MPs at the highest and intermediate concentrations, with PMMA being mainly responsible. Both MPs exposure resulted in a reduction in the abundance of several cuticular compounds. Hive entry guards did not show increased inspection or aggressive behaviour towards exposed foragers, allowing them to enter the colony without being treated differently from uncontaminated foragers. These findings raise concerns not only for the health of individual bees, but also for the entire colony, which could be at risk if contaminated nestmates enter the colony undetected, allowing MPs to spread throughout the hive.

Effects of Freshwater Acidification on the Gut Microbial Community of Trachemys scripta elegans

Freshwater acidification (FA) has become a global environmental problem, posing a potential threat to freshwater ecosystems. The gut microbiota plays a crucial role in the host's response and adaptation to new environments. In this study, we investigated the changes in microbial communities in Red-eared slider (Trachemys scripta elegans) under acidic conditions to reveal the ecological impacts of acidification on freshwater turtles. The results showed that there were significant differences in β-diversity (p = 0.03), while there were no significant differences in the α-diversity of gut microbiota in T. s. elegans between the different levels of acidification (pH of 5.5, 6.5, 7.5). Both the Gut Microbiome Health Index (GMHI) and the Microbial Dysbiosis Index (MDI) exhibited significant differences when comparing environments with a pH of 5.5 to those with a pH of 6.5 (p < 0.01). A comparative analysis between pH levels of 5.5 and 6.5 also revealed substantial differences (p < 0.01). Likewise, a comparative analysis between pH levels of 6.5 and 7.5 also revealed substantial differences (p < 0.01). At the phylum level, Firmicutes, Fusobacteria, and Bacteroidota formed a major part of the gut microbial community, Fusobacteria showed significant differences in different acidity environments (p = 0.03). At the genus level, Cetobacterium, Turicibacter, unclassified Eubacteriaceae, and Anaerorhabdus_furcosa_group showed significant differences in different acidity environments. The pH reduced interactivity in the gut microbiota of T. s. elegans. In addition, LEfSe analysis and functional prediction revealed that the potentially_pathogenic and stress_tolerant functional characteristics also showed significant differences in different acidity environments. The findings underscore the pivotal role of the gut microbiota in T. s. elegans in response to freshwater acidification and provide a foundation for further exploration into the impacts of acidification on freshwater ecosystems.

Effects of abamectin nanocapsules on bees through host physiology, immune function, and gut microbiome

Pesticide usage is a common practice to increase crop yields. Nevertheless, the existence of pesticide residues in the surrounding environment presents a significant hazard to pollinators, specifically the potential undisclosed dangers related to emerging nanopesticides. This study examines the impact of abamectin nanocapsules (AbaNCs), created through electrostatic self-assembly, as an insecticide on honey bees. It was determined that AbaNCs upregulated detoxification genes, including CYP450, as well as antioxidant and immune genes in honey bees. Furthermore, AbaNCs affected the activity of crucial enzymes such as superoxide dismutase (SOD). Although no apparent damage was observed in bee gut tissue, AbaNCs significantly decreased digestive enzyme activity. Microbiome sequencing revealed that AbaNCs disrupted gut microbiome, resulting in a reduction of beneficial bacteria such as Bifidobacterium and Lactobacillus. Additionally, these changes in the gut microbiome were associated with decreased activity of digestive enzymes, including lipase. This study enhances our understanding of the impact of nanopesticides on pollinating insects. Through the revelation of the consequences arising from the utilization of abamectin nanocapsules, we have identified potential stress factors faced by these pollinators, enabling the implementation of improved protective measures.

Toxic effects of acaricide fenazaquin on development, hemolymph metabolome, and gut microbiome of honeybee (Apis mellifera) larvae

Fenazaquin, a potent insecticide widely used to control phytophagous mites, has recently emerged as a potential solution for managing Varroa destructor mites in honeybees. However, the comprehensive impact of fenazaquin on honeybee health remains insufficiently understood. Our current study investigated the acute and chronic toxicity of fenazaquin to honeybee larvae, along with its influence on larval hemolymph metabolism and gut microbiota. Results showed that the acute median lethal dose (LD50) of fenazaquin for honeybee larvae was 1.786 μg/larva, and the chronic LD50 was 1.213 μg/larva. Although chronic exposure to low doses of fenazaquin exhibited no significant effect on larval development, increasing doses of fenazaquin resulted in significant increases in larval mortality, developmental time, and deformity rates. At the metabolic level, high doses of fenazaquin inhibited nucleotide, purine, and lipid metabolism pathways in the larval hemolymph, leading to energy metabolism disorders and physiological dysfunction. Furthermore, high doses of fenazaquin reduced gut microbial diversity and abundance, characterized by decreased relative abundance of functional gut bacterium Lactobacillus kunkeei and increased pathogenic bacterium Melissococcus plutonius. The disrupted gut microbiota, combined with the observed gut tissue damage, could potentially impair food digestion and nutrient absorption in the larvae. Our results provide valuable insights into the complex and diverse effects of fenazaquin on honeybee larvae, establishing an important theoretical basis for applying fenazaquin in beekeeping.

Vairimorpha (Nosema) ceranae can promote Serratia development in honeybee gut: an underrated threat for bees?

The genus Serratia harbors opportunistic pathogenic species, among which Serratia marcescens is pathogenic for honeybees although little studied. Recently, virulent strains of S. marcescens colonizing the Varroa destructor mite's mouth were found vectored into the honeybee body, leading to septicemia and death. Serratia also occurs as an opportunistic pathogen in the honeybee's gut with a low absolute abundance. The Serratia population seems controlled by the host immune system, but its presence may represent a hidden threat, ready to arise when honeybees are weakened by biotic and abiotic stressors. To shed light on the Serratia pathogen, this research aims at studying Serratia's development dynamics in the honeybee body and its interactions with the co-occurring fungal pathogen Vairimorpha ceranae. Firstly, the degree of pathogenicity and the ability to permeate the gut epithelial barrier of three Serratia strains, isolated from honeybees and belonging to different species (S. marcescens, Serratia liquefaciens, and Serratia nematodiphila), were assessed by artificial inoculation of newborn honeybees with different Serratia doses (104, 106, and 108 cells/mL). The absolute abundance of Serratia in the gut and in the hemocoel was assessed in qPCR with primers targeting the luxS gene. Moreover, the absolute abundance of Serratia was assessed in the gut of honeybees infected with V. ceranae at different development stages and supplied with beneficial microorganisms and fumagillin. Our results showed that all tested Serratia strains could pass through the gut epithelial barrier and proliferate in the hemocoel, with S. marcescens being the most pathogenic. Moreover, under cage conditions, Serratia better proliferates when a V. ceranae infection is co-occurring, with a positive and significant correlation. Finally, fumagillin and some of the tested beneficial microorganisms could control both Serratia and Vairimorpha development. Our findings suggest a correlation between the two pathogens under laboratory conditions, a co-occurring infection that should be taken into consideration by researches when testing antimicrobial compounds active against V. ceranae, and the related honeybees survival rate. Moreover, our findings suggest a positive control of Serratia by the environmental microorganism Apilactobacillus kunkeei in a in vivo model, confirming the potential of this specie as beneficial bacteria for honeybees.

A systemic study of cyenopyrafen in strawberry cultivation system: Efficacy, residue behavior, and impact on honeybees (Apis mellifera L.)

The pesticide application method is one of the important factors affecting its effectiveness and residues, and the risk of pesticides to non-target organisms. To elucidate the effect of application methods on the efficacy and residue of cyenopyrafen, and the toxic effects on pollinators honeybees in strawberry cultivation, the efficacy and residual behavior of cyenopyrafen were investigated using foliar spray and backward leaf spray in field trials. The results showed that the initial deposition of cyenopyrafen using backward leaf spray on target leaves reached 5.06-9.81 mg/kg at the dose of 67.5-101.25 g a.i./ha, which was higher than that using foliar spray (2.62-3.71 mg/kg). The half-lives of cyenopyrafen in leaves for foliar and backward leaf spray was 2.3-3.3 and 5.3-5.9 d, respectively. The residues (10 d) of cyenopyrafen in leaves after backward leaf spray was 1.41-3.02 mg/kg, which was higher than that after foliar spraying (0.25-0.37 mg/kg). It is the main reason for the better efficacy after backward leaf spray. However, the residues (10 d) in strawberry after backward leaf spray and foliar spray was 0.04-0.10 and < 0.01 mg/kg, which were well below the established maximum residue levels of cyenopyrafen in Japan and South Korea for food safety. To further investigate the effects of cyenopyrafen residues after backward leaf spray application on pollinator honeybees, sublethal effects of cyenopyrafen on honeybees were studied. The results indicated a significant inhibition in the detoxification metabolic enzymes of honeybees under continuous exposure of cyenopyrafen (0.54 and 5.4 mg/L) over 8 d. The cyenopyrafen exposure also alters the composition of honeybee gut microbiota, such as increasing the relative abundance of Rhizobiales and decreasing the relative abundance of Acetobacterales. The comprehensive data on cyenopyrafen provide basic theoretical for environmental and ecological risk assessment, while backward leaf spray proved to be effective and safe for strawberry cultivation.

Systemic pesticides in a solitary bee pollen food store affect larval development and increase pupal mortality

Solitary bees are often exposed to various pesticides applied for pest control on farmland while providing pollination services to food crops. Increasing evidence suggests that sublethal toxicity of agricultural pesticides affects solitary bees differently than the social bees used to determine regulatory thresholds, such as honey bees and bumblebees. Studies on solitary bees are challenging because of the difficulties in obtaining large numbers of eggs or young larvae for bioassays. Here we show the toxic and sublethal developmental effects of four widely used plant systemic pesticides on the Japanese orchard bee (Osmia cornifrons). Pollen food stores of this solitary bee were treated with different concentrations of three insecticides (acetamiprid, flonicamid, and sulfoxaflor) and a fungicide (dodine). Eggs were transplanted to the treated pollen and larvae were allowed to feed on the pollen stores after egg hatch. The effects of chronic ingestion of contaminated pollen were measured until adult eclosion. This year-long study revealed that chronic exposure to all tested pesticides delayed larval development and lowered larval and adult body weights. Additionally, exposure to the systemic fungicide resulted in abnormal larval defecation and increased mortality at the pupal stage, indicating potential risk to bees from fungicide exposure. These findings demonstrate potential threats to solitary bees from systemic insecticides and fungicides and will help in making policy decisions to mitigate these effects.

The honeybee microbiota and its impact on health and disease

Honeybees (Apis mellifera) are key pollinators that support global agriculture and are long-established models for developmental and behavioural research. Recently, they have emerged as models for studying gut microbial communities. Earlier research established that hindguts of adult worker bees harbour a conserved set of host-restricted bacterial species, each showing extensive strain variation. These bacteria can be cultured axenically and introduced to gnotobiotic hosts, and some have basic genetic tools available. In this Review, we explore the most recent research showing how the microbiota establishes itself in the gut and impacts bee biology and health. Microbiota members occupy specific niches within the gut where they interact with each other and the host. They engage in cross-feeding and antagonistic interactions, which likely contribute to the stability of the community and prevent pathogen invasion. An intact gut microbiota provides protection against diverse pathogens and parasites and contributes to the processing of refractory components of the pollen coat and dietary toxins. Absence or disruption of the microbiota results in altered expression of genes that underlie immunity, metabolism, behaviour and development. In the field, such disruption by agrochemicals may negatively impact bees. These findings demonstrate a key developmental and protective role of the microbiota, with broad implications for bee health.

Exposure to a fungicide for a field-realistic duration does not alter bumble bee fecal microbiota structure

Social bees are frequently exposed to pesticides when foraging on nectar and pollen. Recent research has shown that pesticide exposure not only impacts social bee host health but can also alter the community structure of social bee gut microbiotas. However, most research on pesticide-bee gut microbiota interactions has been conducted in honey bees; bumble bees, native North American pollinators, have received less attention and, due to differences in their ecology, may be exposed to certain pesticides for shorter durations than honey bees. Here, we examine how exposure to the fungicide chlorothalonil for a short, field-realistic duration alters bumble bee fecal microbiotas (used as a proxy for gut microbiotas) and host performance. We expose small groups of Bombus impatiens workers (microcolonies) to field-realistic chlorothalonil concentrations for 5 days, track changes in fecal microbiotas during the exposure period and a recovery period, and compare microcolony offspring production between treatments at the end of the experiment. We also assess the use of fecal microbiotas as a gut microbiota proxy by comparing community structures of fecal and gut microbiotas. We find that chlorothalonil exposure for a short duration does not alter bumble bee fecal microbiota structure or affect microcolony production at any concentration but that fecal and gut microbiotas differ significantly in community structure. Our results show that, at least when exposure durations are brief and unaccompanied by other stressors, bumble bee microbiotas are resilient to fungicide exposure. Additionally, our work highlights the importance of sampling gut microbiotas directly, when possible.IMPORTANCEWith global pesticide use expected to increase in the coming decades, studies on how pesticides affect the health and performance of animals, including and perhaps especially pollinators, will be crucial to minimize negative environmental impacts of pesticides in agriculture. Here, we find no effect of exposure to chlorothalonil for a short, field-realistic period on bumble bee fecal microbiota community structure or microcolony production regardless of pesticide concentration. Our results can help inform pesticide use practices to minimize negative environmental impacts on the health and fitness of bumble bees, which are key native, commercial pollinators in North America. We also find that concurrently sampled bumble bee fecal and gut microbiotas contain similar microbes but differ from one another in community structure and consequently suggest that using fecal microbiotas as a proxy for gut microbiotas be done cautiously; this result contributes to our understanding of proxy use in gut microbiota research.

Impact of landscape composition on honey bee pollen contamination by pesticides: A multi-residue analysis

The honey bee is the most common and important managed pollinator of crops. In recent years, honey bee colonies faced high mortality for multiple causes, including land-use change and the use of plant protection products (hereafter pesticides). This work aimed to explore how contamination by pesticides of pollen collected by honey bees was modulated by landscape composition and seasonality. We placed two honey bee colonies in 13 locations in Northern Italy in contrasting landscapes, from which we collected pollen samples monthly during the whole flowering season in 2019 and 2020. We searched for almost 400 compounds, including fungicides, herbicides, insecticides, and acaricides. We then calculated for each pollen sample the Pollen Hazard Quotient (PHQ), an index that provides a measure of multi-residue toxicity of contaminated pollen. Almost all pollen samples were contaminated by at least one compound. We detected 97 compounds, mainly fungicides, but insecticides and acaricides showed the highest toxicity. Fifteen % of the pollen samples had medium-high or high levels of PHQ, which could pose serious threats to honey bees. Fungicides showed a nearly constant PHQ throughout the season, while herbicides and insecticides and acaricides showed higher PHQ values in spring and early summer. Also, PHQ increased with increasing cover of agricultural and urban areas from April to July, while it was low and independent of landscape composition at the end of the season. The cover of perennial crops, i.e., fruit trees and vineyards, but not of annual crops, increased PHQ of pollen samples. Our work highlighted that the potential toxicity of pollen collected by honey bees was modulated by complex interactions among pesticide category, seasonality, and landscape composition. Due to the large number of compounds detected, our study should be complemented with additional experimental research on the potential interactive effects of multiple compounds on honey bee health.

Cladosporium-Insect Relationships

The range of interactions between Cladosporium, a ubiquitous fungal genus, and insects, a class including about 60% of the animal species, is extremely diverse. The broad case history of antagonism and mutualism connecting Cladosporium and insects is reviewed in this paper based on the examination of the available literature. Certain strains establish direct interactions with pests or beneficial insects or indirectly influence them through their endophytic development in plants. Entomopathogenicity is often connected to the production of toxic secondary metabolites, although there is a case where these compounds have been reported to favor pollinator attraction, suggesting an important role in angiosperm reproduction. Other relationships include mycophagy, which, on the other hand, may reflect an ecological advantage for these extremely adaptable fungi using insects as carriers for spreading in the environment. Several Cladosporium species colonize insect structures, such as galleries of ambrosia beetles, leaf rolls of attelabid weevils and galls formed by cecidomyid midges, playing a still uncertain symbiotic role. Finally, the occurrence of Cladosporium in the gut of several insect species has intriguing implications for pest management, also considering that some strains have proven to be able to degrade insecticides. These interactions especially deserve further investigation to understand the impact of these fungi on pest control measures and strategies to preserve beneficial insects.

The Response of the Honey Bee Gut Microbiota to Nosema ceranae Is Modulated by the Probiotic Pediococcus acidilactici and the Neonicotinoid Thiamethoxam

The honey bee Apis mellifera is exposed to a variety of biotic and abiotic stressors, such as the highly prevalent microsporidian parasite Nosema (Vairimorpha) ceranae and neonicotinoid insecticides. Both can affect honey bee physiology and microbial gut communities, eventually reducing its lifespan. They can also have a combined effect on the insect's survival. The use of bacterial probiotics has been proposed to improve honey bee health, but their beneficial effect remains an open question. In the present study, western honey bees were experimentally infected with N. ceranae spores, chronically exposed to the neonicotinoid thiamethoxam, and/or supplied daily with the homofermentative bacterium Pediococcus acidilactici MA18/5M thought to improve the honey bees' tolerance to the parasite. Deep shotgun metagenomic sequencing allowed the response of the gut microbiota to be investigated with a taxonomic resolution at the species level. All treatments induced significant changes in honey bee gut bacterial communities. Nosema ceranae infection increased the abundance of Proteus mirabilis, Frischella perrara, and Gilliamella apicola and reduced the abundance of Bifidobacterium asteroides, Fructobacillus fructosus, and Lactobacillus spp. Supplementation with P. acidilactici overturned some of these alterations, bringing back the abundance of some altered species close to the relative abundance found in the controls. Surprisingly, the exposure to thiamethoxam also restored the relative abundance of some species modulated by N. ceranae. This study shows that stressors and probiotics may have an antagonistic impact on honey bee gut bacterial communities and that P. acidilactici may have a protective effect against the dysbiosis induced by an infection with N. ceranae.

Chronic exposure to pesticides disrupts the bacterial and fungal co-existence and the cross-kingdom network characteristics of honey bee gut microbiome

Gut microbiome communities have a significant impact on bee health and disease and have been shown to be shaped by a variety of factors, including exposure to pesticides and inhive chemicals. However, it is unknown whether pesticide exposure affects the coexistence and cross-kingdom network parameters of bee gut microbiome communities because microbes may compete in the gut environment under different stressors. Therefore, we conducted additional analysis of the microbiome data from our previous study in which we discovered that exposure to two novel insecticides flupyradifurone (FPF) and sulfoxaflor (Sulf) or/and a fungicide, azoxystrobin (Azoxy) caused dysbiosis of bee gut microbiota that was associated with an increase in the relative abundance of opportunistic pathogens such as Serratia marcescens. We investigated for the first time the potential cross-kingdom fungal-bacterial interactions using co-occurrence pattern correlation and network analysis. We discovered that exposure to FPF or Sulf alone or in combination with Azoxy fungicide influenced the co-existence patterns of fungal and bacterial communities. Significant differences in degree centrality, closeness centrality, and eigenvector centrality distribution indices were also found in single and double-treatment groups compared to controls. The effects of FPF and Sulf alone on cross-kingdom parameters (bacterial to fungal node ratio, degree of centrality, closeness centrality, and eigenvector centrality) were distinct, but this was reversed when they were combined with Azoxy fungicide. The fungal and bacterial hub taxa identified differed, with only a few shared hubs across treatments, suggesting microbial cross-kingdom networks may be disrupted differently under different stressors. Our findings add to our understanding of pesticide effects on the bee gut microbiome and bee health in general, while also emphasizing the importance of cross-kingdom network analysis in future microbiome research.

Trace metals with heavy consequences on bees: A comprehensive review

The pervasiveness of human imprint on Earth is alarming and most animal species, including bees (Hymenoptera: Apoidea: Anthophila), must cope with several stressors. Recently, exposure to trace metals and metalloids (TMM) has drawn attention and has been suggested as a threat for bee populations. In this review, we aimed at bringing together all the studies (n = 59), both in laboratories and in natura, that assessed the effects of TMM on bees. After a brief comment on semantics, we listed the potential routes of exposure to soluble and insoluble (i.e. nanoparticle) TMM, and the threat posed by metallophyte plants. Then, we reviewed the studies that addressed whether bees could detect and avoid TMM in their environment, as well as the ways bee detoxify these xenobiotics. Afterwards, we listed the impacts TMM have on bees at the community, individual, physiological, histological and microbial levels. We discussed around the interspecific variations among bees, as well as around the simultaneous exposure to TMM. Finally, we highlighted that bees are likely exposed to TMM in combination or with other stressors, such as pesticides and parasites. Overall, we showed that most studies focussed on the domesticated western honey bee and mainly addressed lethal effects. Because TMM are widespread in the environment and have been shown to result in detrimental consequences, evaluating their lethal and sublethal effects on bees, including non-Apis species, warrants further investigations.

Synergistic adverse effects of microfibers and freshwater acidification on host-microbiota interactions in the water flea Daphnia magna

Microfibers are the most common type of microplastics in freshwater environments. Anthropogenic climate stressors, such as freshwater acidification (FA), can interact with plastic pollution to disrupt freshwater ecosystems. However, the underlying mechanisms responsible for the interactive effects of microfibers and FA on aquatic organisms remain poorly understood. In this study, we investigated individual Daphnia magna-microbiota interactions affected by interactions between microfibers and FA (MFA). We found that the accumulated amount of microfibers in pH-treatment groups was significantly higher than in the control groups, resulting in negative consequences on reproduction, growth, and sex ratio. We also observed that MFA interactions induced immunity- and reproduction-related biological processes. In particular, the abundance of pathogenic bacteria increased only in MFA groups, indicating that MFA interactions can cause intestinal damage. Our integrated analysis of microbiomes and host transcriptomes revealed that synergistic adverse effects of MFAs are closely related to changes in microbial communities, suggesting that D. magna fitness and the microbial community are causally linked. These finding may help elucidate the toxicity mechanisms governing the responses of D. magna to microfibers and acidification interactions, and to host-microbiome-environment interactions.

Composition and diversity of bacterial communities associated with honey bee foragers from two contrasting environments

The honey bee is associated with a diverse community of microbes (viruses, bacteria, fungi, and protists), commonly known as the microbiome. Here, we present data on honey bee microbiota from two localities having different surrounding landscapes - mountain (the Rhodope Mountains) and lowland (the Danube plain). The bacterial communities of abdomen of adult bees were studied using amplicon sequencing of the 16S rRNA gene. The composition and dominance structure and their variability within and between localities, alpha and beta diversity, and core and differential taxa were compared at different hierarchical levels (operational taxonomic units to phylum). Seven genera (Lactobacillus, Gilliamella, Bifidobacterium, Commensalibacter, Bartonella, Snodgrassella, and Frischella), known to include core gut-associated phylotypes or species clusters, dominated (92-100%) the bacterial assemblages. Significant variations were found in taxa distribution across both geographical regions and within each apiary. Lactobacillus (Firmicutes) prevailed significantly in the mountain locality followed by Gilliamella and Bartonella (Proteobacteria). Bacteria of four genera, core (Bartonella and Lactobacillus) and non-core (Pseudomonas and Morganella), dominated the bee-associated assemblages of the Danube plain locality. Several ubiquitous bacterial genera (e.g., Klebsiella, Serratia, and Providencia), some species known also as potential and opportunistic bee pathogens, had been found in the lowland locality. Beta diversity analyses confirmed the observed differences in the bacterial communities from both localities. The occurrence of non-core taxa contributes substantially to higher microbial richness and diversity in bees from the Danube plain locality. We assume that the observed differences in the microbiota of honey bees from both apiaries are due to a combination of factors specific for each region. The surrounding landscape features of both localities and related vegetation, anthropogenic impact and land use intensity, the beekeeping management practices, and bee health status might all contribute to observed differences in bee microbiota traits.

Gut microbiome helps honeybee (Apis mellifera) resist the stress of toxic nectar plant (Bidens pilosa) exposure: Evidence for survival and immunity

Honeybee (Apis mellifera) ingestion of toxic nectar plants can threaten their health and survival. However, little is known about how to help honeybees mitigate the effects of toxic nectar plant poisoning. We exposed honeybees to different concentrations of Bidens pilosa flower extracts and found that B. pilosa exposure significantly reduced honeybee survival in a dose-dependent manner. By measuring changes in detoxification and antioxidant enzymes and the gut microbiome, we found that superoxide dismutase, glutathione-S-transferase and carboxylesterase activities were significantly activated with increasing concentrations of B. pilosa and that different concentrations of B. pilosa exposure changed the structure of the honeybee gut microbiome, causing a significant reduction in the abundance of Bartonella (p < 0.001) and an increase in Lactobacillus. Importantly, by using Germ-Free bees, we found that colonization by the gut microbes Bartonella apis and Apilactobacillus kunkeei (original classification as Lactobacillus kunkeei) significantly increased the resistance of honeybees to B. pilosa and significantly upregulated bee-associated immune genes. These results suggest that honeybee detoxification systems possess a level of resistance to the toxic nectar plant B. pilosa and that the gut microbes B. apis and A. kunkeei may augment resistance to B. pilosa stress by improving host immunity.

Bees just wanna have fungi: a review of bee associations with nonpathogenic fungi

Bee-fungus associations are common, and while most studies focus on entomopathogens, emerging evidence suggests that bees associate with a variety of symbiotic fungi that can influence bee behavior and health. Here, we review nonpathogenic fungal taxa associated with different bee species and bee-related habitats. We synthesize results of studies examining fungal effects on bee behavior, development, survival, and fitness. We find that fungal communities differ across habitats, with some groups restricted mostly to flowers (Metschnikowia), while others are present almost exclusively in stored provisions (Zygosaccharomyces). Starmerella yeasts are found in multiple habitats in association with many bee species. Bee species differ widely in the abundance and identity of fungi hosted. Functional studies suggest that yeasts affect bee foraging, development, and pathogen interactions, though few bee and fungal taxa have been examined in this context. Rarely, fungi are obligately beneficial symbionts of bees, whereas most are facultative bee associates with unknown or ecologically contextual effects. Fungicides can reduce fungal abundance and alter fungal communities associated with bees, potentially disrupting bee-fungi associations. We recommend that future study focus on fungi associated with non-honeybee species and examine multiple bee life stages to document fungal composition, abundance, and mechanistic effects on bees.

Pesticide exposure and the microbiota-gut-brain axis

The gut microbiota exist within a dynamic ecosystem shaped by various factors that includes exposure to xenobiotics such as pesticides. It is widely regarded that the gut microbiota plays an essential role in maintaining host health, including a major influence on the brain and behaviour. Given the widespread use of pesticides in modern agriculture practices, it is important to assess the long-term collateral effects these xenobiotic exposures have on gut microbiota composition and function. Indeed, exposure studies using animal models have shown that pesticides can induce negative impacts on the host gut microbiota, physiology and health. In tandem, there is a growing body of literature showing that the effects of pesticide exposure can be extended to the manifestation of behavioural impairments in the host. With the increasing appreciation of the microbiota-gut-brain axis, in this review we assess whether pesticide-induced changes in gut microbiota composition profiles and functions could be driving these behavioural alterations. Currently, the diversity of pesticide type, exposure dose and variation in experimental designs hinders direct comparisons of studies presented. Although many insights presented, the mechanistic connection between the gut microbiota and behavioural changes remains insufficiently explored. Future experiments should therefore focus on causal mechanisms to examine the gut microbiota as the mediator of the behavioural impairments observed in the host following pesticide exposure.

Transcriptomic Responses Underlying the High Virulence of Black Queen Cell Virus and Sacbrood Virus following a Change in Their Mode of Transmission in Honey Bees (Apis mellifera)

BACKGROUND

Over the last two decades, honey bees (Apis mellifera) have suffered high rates of colony losses that have been attributed to a variety of factors, chief among which are viral pathogens, such as deformed wing virus (DWV), whose virulence has increased because of vector-based transmission by the invasive, ectoparasitic varroa mite (Varroa destructor). A shift in the experimental mode of transmission of the black queen cell virus (BQCV) and sacbrood virus (SBV) from fecal/food-oral (direct horizontal) to vector-mediated (indirect horizontal) transmission also results in high virulence and viral titers in pupal and adult honey bees. Agricultural pesticides represent another factor that acts independently or in interaction with pathogens, and they are also thought to cause colony loss. Understanding the molecular mechanisms underlying the higher virulence following a vector-based mode of transmission provides deeper insight into honey bee colony losses, as does determining whether or not host-pathogen interactions are modulated by exposure to pesticides.

METHODS

Through an experimental design with controlled laboratory, we investigated the effects of the modes of transmission of BQCV and SBV (feeding vs. vector-mediated via injection) alone or in combination with chronic exposure to sublethal and field-realistic concentrations of flupyradifurone (FPF), a novel agricultural insecticide, on honey bee survival and transcription responses by using high-throughput RNA sequencing (RNA-seq) analysis.

RESULTS

Co-exposure to viruses via feeding (VF) or injection (VI) and FPF insecticide had no statistically significant interactive effect on their survival compared to, respectively, VF or VI treatments alone. Transcriptomic analysis revealed a distinct difference in the gene expression profiles of bees inoculated with viruses via injection (VI) and exposed to FPF insecticide (VI+FPF). The number of differentially expressed genes (DEGs) at log2 (fold-change) > 2.0 in VI bees (136 genes) or/and VI+FPF insecticide (282 genes) was very high compared to that of VF bees (8 genes) or the VF+FPF insecticide treatment (15 genes). Of these DEGs, the expression in VI and VI+FPF bees of some immune-related genes, such as those for antimicrobial peptides, Ago2, and Dicer, was induced. In short, several genes encoding odorant binding proteins, chemosensory proteins, odor receptors, honey bee venom peptides, and vitellogenin were downregulated in VI and VI+FPF bees.

CONCLUSIONS

Given the importance of these suppressed genes in honey bees' innate immunity, eicosanoid biosynthesis, and olfactory associative function, their inhibition because of the change in the mode of infection with BQCV and SBV to vector-mediated transmission (injection into haemocoel) could explain the high virulence observed in these viruses when they were experimentally injected into hosts. These changes may help explain why other viruses, such as DWV, represent such a threat to colony survival when transmitted by varroa mites.

The effects of glyphosate, pure or in herbicide formulation, on bumble bees and their gut microbial communities

The widespread use of glyphosate-based formulations to eliminate unwanted vegetation has increased concerns regarding their effects on non-target organisms, such as honey bees and their gut microbial communities. These effects have been associated with both glyphosate and co-formulants, but it is still unknown whether they translate to other bee species. In this study, we tested whether glyphosate, pure or in herbicide formulation, can affect the gut microbiota and survival rates of the eastern bumble bee, Bombus impatiens. We performed mark-recapture experiments with bumble bee workers from four different commercial colonies, which were exposed to field relevant concentrations of glyphosate or a glyphosate-based formulation (0.01 mM to 1 mM). After a 5-day period of exposure, we returned the bees to their original colonies, and they were sampled at days 0, 3 and 7 post-exposure to investigate changes in microbial community and microbiota resilience by 16S rRNA amplicon sequencing and quantitative PCR. We found that exposure to glyphosate, pure or in herbicide formulation, reduced the relative abundance of a beneficial bee gut bacterium, Snodgrassella, in bees from two of four colonies when compared to control bees at day 0 post-exposure, but this reduction became non-significant at days 3 and 7 post-exposure, suggesting microbiota resilience. We did not find significant changes in total bacteria between control and exposed bees. Moreover, we observed an overall trend in decreased survival rates in bumble bees exposed to 1 mM herbicide formulation during the 7-day post-exposure period, suggesting a potential negative effect of this formulation on bumble bees.

Nationwide Screening for Bee Viruses in Apis mellifera Colonies in Egypt

Honey bees are essential for crop and wild plant pollination. However, many countries have reported high annual colony losses caused by multiple possible stressors. Diseases, particularly those caused by viruses, are a major cause of colony losses. However, little is known about the prevalence of honey bee pathogens, particularly virus prevalence, in Egyptian honey bees. To address this shortfall, we determined the prevalence of widespread bee viruses in honey bee colonies in Egypt-whether it is affected by geography, the season, or infestation with Varroa destructor (varroa) mites. Honey bee worker samples were collected from 18 geographical regions across Egypt during two seasons: winter and summer of 2021. Three apiaries were chosen in each region, and a pooled sample of 150 worker bees was collected from five colonies in each apiary then screened by qPCR for 10 viral targets: acute bee paralysis virus (ABPV), black queen cell virus (BQCV), chronic bee paralysis virus (CBPV), deformed wing virus (DWV) genotypes A (DWV-A), B (DWV-B) and D (Egyptian bee virus), Israeli acute paralysis virus (IAPV), Kashmir bee virus (KBV), sacbrood virus (SBV), and slow bee paralysis virus (SBPV). Our results revealed that DWV-A was the most prevalent virus, followed by BQCV and ABPV; the DWV genotype now spreading across the world, DWV-B, was not detected. There was no difference in varroa infestation rates as well as virus prevalence between winter and summer. However, colonies infected with BQCV had a significantly higher varroa count (adjusted p < 0.05) in the winter season, indicating that there is a seasonal association between the intensity of infestation by varroa and the presence of this virus. We provide data on the current virus prevalence in Egypt, which could assist in the protection of Egypt's beekeeping industry. Moreover, our study aids in the systematic assessment of the global honey bee virome by filling a knowledge gap about the prevalence of honey bee viruses in Egypt.

Surrogate species in pesticide risk assessments: Toxicological data of three stingless bees species

Discussions about environmental risk reassessment of pesticides have grown in the last decades, especially in tropical and subtropical regions since the diversity of bee species in these places is quite different. Stingless bees are highly affected by pesticides, and toxicity information is necessary to include them in the regulatory process of countries that hosts a diversity of these species. Therefore, the present study aimed to evaluate the Median Lethal Concentration (LC₅₀), estimate the Median Lethal Dose (LD₅₀) and compared the sensitivity of three species of stingless bees exposed to the commercial formulation of the neonicotinoid thiamethoxam (TMX). The LD₅₀ was estimated based on the LC₅₀ determined in the present study (LC₅₀ = 0.329 ng a.i./μL for Tetragonisca angustula; 0.624 ng a.i./μL for Scaptotrigona postica, and 0.215 ng a.i./μL for Melipona scutellaris). Considering these data, toxicity endpoints were used to fit species sensitive distribution curves (SSD) and determine the sensitivity ratio. The results showed that all the stingless bees tested are more sensitive to TMX than the Apis mellifera, the model organism used in ecotoxicological tests. Regarding the oral LC₅₀, the most susceptible and most tolerant species were M. scutellaris > T. angustula > S. postica > A. mellifera. Following the same evaluated pattern, for the LD₅₀ (considering the weight of the bees - ng a.i./g bee), we have: M. scutellaris > S. postica > T. angustula > A. mellifera, and without the weight considered (ng a.i./bee): T. angustula > M. scutellaris > S. postica > A. mellifera. The different sensitivities among stingless bee species highlight the importance of inserting more than one surrogate species with a variety of sizes in research and protocol development. Additionally, the research suggests the need to investigate patterns regarding the influence of body mass on pesticide sensitivity among stingless bee species.

Chronic Exposure to Polystyrene Microplastic Fragments Has No Effect on Honey Bee Survival, but Reduces Feeding Rate and Body Weight

Microplastics (MPs), in the form of fragments and fibers, were recently found in honey samples collected in Ecuador as well as in honey bees collected from Denmark and China. However, little is known about how MPs impact bee health. To fill this knowledge gap, we investigated the potential toxicity of irregularly shaped polystyrene (PS)-MP fragments on honey bee health. In the first experiment of its kind with honey bees, we chronically exposed bees with a well-established gut microbiome to small (27 ± 17 µm) or large (93 ± 25 µm) PS-MP fragments at varying concentrations (1, 10, 100 µg mL^-1) for 14 days. Bee mortality, food consumption, and body weight were all studied. We found that chronic exposure to PS-MP fragments has no effect on honey bee survival, but reduced the feeding rate and body weight, particularly at 10 µg PS-MP fragments per mL, which may have long-term consequences for honey bee health. The findings of this study could assist in the risk assessment of MPs on pollinator health.

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

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