The adverse impact on lifespan, immunity, and forage behavior of worker bees (Apis mellifera Linnaeus 1758) after exposure to flumethrin

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.

Enhanced immune response and antimicrobial activity in honey bees (Apis mellifera) following application of oxalic acid-glycerine strips

Bee health is influenced by multiple factors, including nutrition, immunity, and parasitic pressures. Since the spread of Varroa destructor, overwintering survival has significantly declined, making it one of the most serious threats to honey bee (Apis mellifera L.) populations worldwide. Natural acaricides, such as oxalic acid (OA), are widely employed for managing Varroa mites; however, their pharmacodynamics, particularly their impacts on honey bee physiology and immunity, remain insufficiently understood. We studied effects of oxalic acid on honey bee workers. The study compared three treatments: flumethrin, OA-glycerine strips (OA-G), and OA trickling (OA-T). Twelve colonies were divided into four groups, with samples collected at five time points (0, 24, 48, 72, and 192 h). Physiological changes were assessed through markers of oxidative stress, longevity, and immune parameters. Exposure to oxalic acid via glycerine strips induced a humoral immune response in adult bees. The antimicrobial activity of hemolymph and levels of antimicrobial peptides (abaecin, apidaecin, defensin, and hymenoptaecin) were elevated between 48 and 192 h after OA-G treatment compared to the control group. In contrast, these parameters were not influenced by OA-T or flumethrin treatment. These findings suggest that OA-G strips activate the honey bee's immune system, providing insights into broader implications of OA use in beekeeping. It is crucial to determine whether the activation of humoral immune systems has positive or negative effects, as well as to develop standardized and reliable treatment protocols that ensure both - health of colonies and their effectiveness in controlling Varroa mite infestations.

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.

Sub-lethal exposure to 2,4-Dichlorophenoxyacetic acid disrupts nursing and foraging behaviors in honey bees

A popular herbicide from the chlorophenoxy group, 2,4-Dichlorophenoxyacetic acid (2,4-D) effectively controls broadleaf weeds in agricultural environments. However, its application threatens honey bee habitats and has been implicated in colony collapse disorder (CCD) due to its toxic effects. While the general hazards of 2,4-D to honey bees are recognized, its specific impact on nursing and foraging behaviors remains poorly understood. This study quantified the lethal dose (LD50) of 2,4-D for honey bees across developmental stages, finding LD50 values of 104.1 μg/bee for newly emerged bees, 456.6 μg/bee for nurse bees, and 221.6 μg/bee for foragers. We further investigated sub-lethal effects on nursing and foraging, observing that exposure led to significant reductions in hypopharyngeal gland (HG) acini size, essential for brood care, and decreased expression of AmGr10, an amino acid receptor gene linked to nursing behavior. For foragers, sub-lethal 2,4-D exposure impaired gustatory responsiveness to key feeding stimuli, such as sucrose and glucose. This impairment corresponded with a decrease in AmGr1 expression, a taste receptor gene critical for resource detection. Additionally, affected foragers showed reduced olfactory learning and memory, likely due to decreased expression of the octopamine receptor AmOA1, essential for associative learning processes. These findings provide compelling evidence that sub-lethal abdominal exposure to 2,4-D disrupts both nursing and foraging behaviors by impairing physiological and cognitive functions, ultimately jeopardizing colony health and resilience.

Impact of chlorantraniliprole on honey bees: Differential sensitivity and biological responses in Apis mellifera and Apis cerana

Chlorantraniliprole (CAP), a diamide insecticide, is extensively applied to combat pests in various crops. However, the widespread use of insecticides has raised concerns about their potential impact on pollinators. In the present study, we explored the toxic effects of CAP in two important honey bee species, Apis mellifera and Apis cerana. The 48 h LC50 values of CAP for A. mellifera and A. cerana was 256.052 mg/L and 109.709 mg/L, implying that A. cerana is more sensitive to CAP. Prolonged exposure to 40 mg/L CAP significantly impaired sucrose responsiveness and climbing activity in both bee species. Both species showed a decrease in GR activity and GSH content with increasing CAP concentration. By contrast, the activities of GST, CAT, P450 and NAD-MDH were increased in both A. mellifera and A. cerana, but the differences between the 10 mg/L and 40 mg/L treatments were less pronounced in A. mellifera. Moreover, the immune related genes exhibited differential responses to CAP when comparing the two species. Low CAP concentrations led to down-regulation in expression of toll but up-regulation in expression of apideacin and hymeopatecin in A. mellifera, whereas A. cerana exhibited minimal changes in these genes. Additionally, CAP significantly inhibited the expression of ER stress response genes gp-93 and P58 in A. mellifera, while 10 mg/L of CAP promoted P58 expression in A. cerana. Our results highlight species-specific effects with the possible, distinct detoxification mechanisms and immune responses between A. mellifera and A. cerana. These findings serve as a foundation for further evaluating the safety of CAP for honey bee species and offer insights into the scientific use of pesticides.

Flumethrin exposure perturbs gut microbiota structure and intestinal metabolism in honeybees (Apis mellifera)

Flumethrin mitigates Varroa's harm to honeybee colonies; however, its residues in colonies threaten the fitness of honeybee hosts and gut microbiota. Our previous research has shown that flumethrin induces significant physiological effects on honeybee larvae; but the effects of flumethrin on the gut microbiota and metabolism of adult honeybees are still unknown. In this study, 1-day-old honeybees were exposed to 0, 0.01, 0.1, and 1 mg/L flumethrin for 14 days and the impacts of flumethrin on the intestinal system were evaluated. The results showed that exposure to 1 mg/L flumethrin significantly reduced honeybee survival and the activities of antioxidative enzymes (superoxide dismutase and catalase) and detoxification enzymes (glutathione S-transferase) in honeybee heads. Moreover, exposure to 0.01, 0.1, and 1 mg/L flumethrin significantly decreased the diversity of the honeybee gut microbiota. Results from untargeted metabolomics showed that long-term exposure to 0.01, 0.1, and 1 mg/L flumethrin caused changes in the metabolic pathways of honeybee gut microbes. Furthermore, increased metabolism of phenylalanine, tyrosine, and tryptophan derivatives was observed in honeybee gut microbes. These findings underscore the importance of careful consideration in using pesticides in apiculture and provide a basis for safeguarding honeybees from pollutants, considering the effects on gut microbes.

Comparative study of fenpropathrin and its main metabolite in soil-earthworm microcosms: Toxicity, degradation, transcriptome, and oxidative stress

This study comprehensively investigated the comparative acute toxicities, degradation, transcriptome, and oxidative stress induction of fenpropathrin (FEN) and its main metabolite 3-phenoxybenzoic acid (3-PBA)in soil-earthworm microcosms. FEN degradation half-life ranged from 19.09 to 28.52 days, and the peak-shaped trends of 3-PBA were also observed in different soil types. The LC50 values of FEN and 3-PBA were 12.75 and 7.49 μg/cm2, respectively, suggesting that 3-PBA was more toxic to earthworms. Furthermore, the sub-lethal toxicities indicated that 3-PBA exerted more prominent alterations in protein content, enzyme activity, lipid peroxidation, and oxidative stress in earthworms. Additionally, integrated biomarker response evaluations indicated that 3-PBA induced more prominent sub-lethal toxicity in earthworms than FEN. Finally, exposure to FEN and 3-PBA resulted in distinct differentially expressed genes (DEGs) in earthworms. Enrichment analysis revealed that these DEGs were predominantly enriched in purine metabolism and bile secretion pathways in earthworms. Moreover, the p53 signaling pathway, cell cycle, DNA replication, drug metabolism, and pyrimidine metabolism were also enriched in earthworms after exposure to FEN and 3-PBA. These results suggested that FEN and 3-PBA induced varying toxicities in earthworms. This study highlighted the systemic differences in the toxicities, degradation, transcriptome, and oxidative stress induction between FEN and 3-PBA in soil-earthworm microcosms. Our findings could be used for a comprehensive risk assessment of FEN and 3-PBA in the soil ecosystem.

Interactive effects of chlorothalonil and Varroa destructor on Apis mellifera during adult stage

The interaction between environmental factors affecting honey bees is of growing concern due to their potential synergistic effects on bee health. Our study investigated the interactive impact of Varroa destructor and chlorothalonil on workers' survival, fat body morphology, and the expression of gene associated with detoxification, immunity, and nutrition metabolism during their adult stage. We found that both chlorothalonil and V. destructor significantly decreased workers' survival rates, with a synergistic effect observed when bees were exposed to both stressors simultaneously. Morphological analysis of fat body revealed significant alterations in trophocytes, particularly a reduction in vacuoles and granules after Day 12, coinciding with the transition of the bees from nursing to other in-hive work tasks. Gene expression analysis showed significant changes in detoxification, immunity, and nutrition metabolism over time. Detoxification genes, such as CYP9Q2, CYP9Q3, and GST-D1, were downregulated in response to stressor exposure, indicating a potential impairment in detoxification processes. Immune-related genes, including defensin-1, Dorsal-1, and Kayak, exhibited an initially upregulation followed by varied expression patterns, suggesting a complex immune response to stressors. Nutrition metabolism genes, such as hex 70a, AmIlp2, VGMC, AmFABP, and AmPTL, displayed dynamic expression changes, reflecting alterations in nutrient utilization and energy metabolism in response to stressors. Overall, these findings highlight the interactive and dynamic effects of environmental stressor on honey bees, providing insights into the mechanisms underlying honey bee decline. These results emphasize the need to consider the interactions between multiple stressors in honey bee research and to develop management strategies to mitigate their adverse effects on bee populations.

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.

Effects of Artificial Sugar Supplementation on the Composition and Nutritional Potency of Honey from Apis cerana

In the global apiculture industry, reward feeding and supplementary feeding are essential for maintaining bee colonies. Beekeepers provide artificial supplements to their colonies, typically in the form of either a honey-water solution or sugar syrup. Owing to cost considerations associated with beekeeping, most beekeepers opt for sugar syrup. However, the effects of different types of artificial sugar supplements on bee colonies and their subsequent impact on honey composition remain unclear. To address this gap, this study compared the chemical composition, antioxidant capacity, and nutritional potency of three types of honey: honey derived from colonies fed sugar syrup (sugar-based product, SP) or a honey-water solution (honey-sourced honey, HH) and naturally sourced honey (flower-sourced honey, FH), which served as the control. The results revealed that FH outperformed HH and SP in terms of total acidity, sugar content, total protein content, and antioxidant capacity, and HH outperformed SP. Regarding nutritional efficacy, including the lifespan and learning and memory capabilities of worker bees, FH exhibited the best outcomes, with no significant differences observed between HH and SP. This study underscores the importance of sugar source selection in influencing honey quality and emphasizes the potential consequences of substituting honey with sugar syrup in traditional apiculture practices.

Early larval exposure to flumethrin induces long-term impacts on survival and memory behaviors of adult worker bees Apis mellifera

Flumethrin has been supplied as an acaricide for Varroa mite control in world-wide apiculture due to its low lethal effects on honey bees. However, little is known about the effects of short-term flumethrin exposure in the larval stage on adult life stage of bees involving survival status, foraging and memory-related behaviors. Here, we found that exposure to flumethrin at 1 mg/L during larval stage reduced survival and altered foraging activities including induced precocious foraging activity, decreased foraging trips and time, and altered rotating day-off status of adult worker bees using the radio frequency identification system. Furthermore, larval exposure at 1 mg/L flumethrin influenced the correct proboscis extension responses of 7-day-old worker bees and decreased homing rates of 20-day-old worker bees, suggesting that 1 mg/L flumethrin exposure at larval stage could affect memory-related behaviors of adult bees; meanwhile, three genes related to memory (GluRA, Nmdar1 and Tyr1) were certainly down-regulated varying different flumethrin concentrations (0.01, 0.1, and 1 mg/L). Combined with transcriptomic sequencing, differentially expressed genes involved in olfactory memory of adult bees were completely down-regulated under flumethrin exposure. Our findings highlight the unprecedented impact of short-term exposure of insecticides on honey bees in long-term health monitoring under field conditions.

Effects of larval exposure to the insecticide flumethrin on the development of honeybee (Apis mellifera) workers

Flumethrin is a widely used acaricide, but its improper use often leads to residue accumulation in honeybee colonies, thus threatening the health of honeybees, especially at the larval stage. Therefore, this study aimed to describe the direct toxicity of flumethrin on honeybee (Apis mellifera) larvae by conducting bioassays for immune and detoxification-related enzymes and transcriptome sequencing to determine the potential effects on newly emerged adults who were exposed to flumethrin during the larval stage. Results showed that the higher the concentration of flumethrin the honeybee larvae were exposed to, the greater the damage to the physiology of honeybee larvae and the newly emerged worker bees. When honeybee larvae were exposed to flumethrin concentrations higher than 0.01 mg/L, the activities of glutathione sulfur transferase and carboxylesterase were affected, and the metabolism-related genes in the head of newly emerged honeybees exposed to flumethrin during the larval stage were down-regulated. Flumethrin concentration higher than 0.1 mg/L significantly increased mixed-functional oxidase content in honeybee larvae, reduced the larval survival rate, and down-regulated the expression levels of olfactory-related and antioxidant-related genes in newly emerged honeybees. Furthermore, a flumethrin concentration of 1 mg/L significantly down-regulated the expression levels of immune and detoxification-related genes in newly emerged honeybees. These findings provide a comprehensive understanding of the response of honeybee larvae to sublethal flumethrin toxicity and could be used to further investigate the complex molecular mechanisms in honeybees under pesticide stress.