Field recommended concentrations of pyraclostrobin exposure disturb the development and immune response of worker bees (Apis mellifera L.) larvae and pupae

Toxicity potential of a pyraclostrobin-based fungicide in plant and green microalgae models

Pyraclostrobin-based fungicides play an effective role in controlling fungal diseases and are extensively used in agriculture. However, there is concern regarding the potential adverse effects attributed to exposure to these fungicides on non-target organisms and consequent influence exerted on ecosystem functioning. Thus, it is essential to conduct studies with model organisms to determine the impacts of these fungicides on different groups of living organisms. The aim of this study was to examine the ecotoxicity associated with exposure to commercial fungicides containing pyraclostrobin. The focus of the analysis involved germination and initial development of seedlings of 4 plant models (Lactuca sativa, Raphanus sativus, Pennisetum glaucum and Triticum aestivum), in addition to determining the population growth rate and total carbohydrate content in microalga Raphidocelis subcapitata. The fungicide pyraclostrobin adversely influenced growth and development of the tested plants, indicating a toxic effect. The fungicide exerted a significant impact on the initial development of seedlings of all model species examined with T. aestivum plants displaying the greatest susceptibility to pyraclostrobin. Plants of this species exhibited inhibitory effects on both aerial parts and roots when treated with a concentration of 4.75 mg/L pyraclostrobin. In addition, the green microalga R. subcapitata was also significantly affected by the fungicide, especially at relatively high concentrations as evidenced by a reduction in total carbohydrate content. This commercial fungicide demonstrated potential phytotoxicity for the tested plant models and was also considered toxic to the selected microalgae, indicating an ecotoxic effect that might affect other organisms in aquatic environments.

Azoxystrobin Exposure Impacts on Development Status and Physiological Responses of Worker Bees (Apis mellifera L.) from Larval to Pupal Stages

Honeybee larvae and pupae form the cornerstone of colony survival, development, and reproduction. Azoxystrobin is an effective strobilurin fungicide that is applied during the flowering stage for controlling plant pathogens. The contaminated nectar and pollen resulting from its application are collected by forager bees and impact the health of honeybee larvae and pupae. The current study evaluated the survival, development, and physiological effects of azoxystrobin exposure on the larvae and pupae of Apis mellifera worker bees. The field-recommended concentrations of azoxystrobin were found to suppress the survival indices and lifespan in the larval as well as pupal stages; moreover, the rates of the survival and pupation of larvae as well as the body weights of the pupae and newly-emerged adult bees were significantly reduced upon long-term exposure to azoxystrobin. In addition, azoxystrobin ingestion induced changes in the expression of genes critical for the development, immunity, and nutrient metabolism of larvae and pupae, although the expression profile of these genes differed between the larval and pupal stages. Results indicated the chronic toxicity of azoxystrobin on the growth and development of honeybee larvae and pupae, which would affect their sensitivity to pathogens and other external stresses during the development stage and the study will provide vital information regarding the pollination safety and rational use of pesticides.

Novel fungicide and neonicotinoid insecticide impair flight behavior in pollen foraging honey bees, Apis mellifera

Bees are often exposed to pesticides affecting physiological functions and molecular mechanisms. Studies showed a potential link between altered expression of energy metabolism related transcripts and increased homing flight time of foragers exposed to pesticides. In this study, we investigated the effects of thiamethoxam and pyraclostrobin on longevity, flight behavior, and expression of transcripts involved in endocrine regulation (hbg-3, buffy, vitellogenin) and energy metabolism (cox5a, cox5b, cox17) using radio frequency identification (RFID) technology and quantitative polymerase chain reaction. Parallel, a laboratory study was conducted investigating whether pesticide exposure alone without the influence of flight activity caused similar expression patterns as in the RFID experiment. No significant effect on survival, homing flight duration, or return rate of exposed bees was detected. The overall time foragers spent outside the hive was significantly reduced post-exposure. Irrespective of the treatment group, a correlation was observed between cox5a, cox5b, cox17 and hbg-3 expression and prolonged homing flight duration. Our results suggest that flight behavior can impact gene expression and exposure to pesticides adversely affects the expression of genes that are important for maintaining optimal flight capacity. Our laboratory-based experiment showed significantly altered expression levels of cox5a, cox6c, and cox17. However, further work is needed to identify transcriptional profiles responsible for prolonged homing flight duration.

Variation in the physiological response of adult worker bees of different ages (Apis mellifera L.) to pyraclostrobin stress

The social division of labor within the honeybee colony is closely related to the age of the bees, and the age structure is essential to the development and survival of the colony. Differences in tolerance to pesticides and other external stresses among worker bees of different ages may be related to their social division of labor and corresponding physiological states. Pyraclostrobin was widely used to control the fungal diseases of nectar and pollen plants, though it was not friend to honey bees and other pollinators. This work aimed to determine the effects of field recommended concentrations of pyraclostrobin on the activities of protective and detoxifying enzymes, on the expression of genes involved in nutrient metabolism, and immune response in worker bees of different ages determined to investigate the physiological and biochemical differences in sensitivity to pyraclostrobin among different age of worker bees. The result demonstrates that the tolerance of adult worker bees to pyraclostrobin was negatively correlated with their age, and the significantly reduced survival rate of forager bees (21 day-old) with continued fungicide exposure. The activities of protective enzymes (CAT and SOD) and detoxifying enzymes (CarE, GSTs and CYP450) in different ages of adult worker bees were significantly altered, indicating the physiological response and the regulatory capacity of worker bees of different ages to fungicide stress was variation. Compared with 1 and 8 day-old worker bees, the expression of nutrient-related genes (ilp1 and ilp2) and immunity-related genes (apidaecin and defensin1) in forager bees (21 day-old) was gradually downregulated with increasing pyraclostrobin concentrations. Moreover, the expression of vitellogenin and hymenoptaecin in forager bees (21 day-old) was also decreased in high concentration treatment groups (250 and 313 mg/L). The present study confirmed the findings of the chronic toxicity of pyraclostrobin on the physiology and biochemistry of worker bees of different ages, especially to forager bees (21 day-old). These results would provide important physiological and biochemical insight for better understanding the potential risks of pyraclostrobin on honeybees and other non-target pollinators.

Effect of fungicidal contamination on survival, morphology, and cellular immunity of Apis mellifera (Hymenoptera: Apidae)

Pesticide residues have been reported in hive-stored products for long periods. Larvae of honey bees experience oral or contact exposure to these products during their normal growth and development inside the cells. We analyzed various toxicological, morphogenic, and immunological effects of residue-based concentrations of two fungicides, captan and difenoconazole, on the larvae of worker honey bees, Apis mellifera. Selected concentrations (0.08, 0.4, 2, 10, and 50 ppm) of both fungicides were applied topically at a volume of 1 µL/larva/cell as single and multiple exposures. Our results revealed a continuous, concentration-dependent decrease in brood survival after 24 h of treatment to the capping and emergence stages. Compared to larvae with a single exposure, the multiply exposed youngest larvae were most sensitive to fungicidal toxicity. The larvae that survived higher concentrations, especially multiple exposures, showed several morphological defects at the adult stage. Moreover, difenoconazole-treated larvae showed a significantly decreased number of granulocytes after 1 h of treatment followed by an increase after 24 h of treatment. Thus, fungicidal contamination poses a great risk as the tested concentrations showed adverse effects on the survival, morphology, and immunity of larval honey bees.

Ternary Mixture of Azoxystrobin, Boscalid and Pyraclostrobin Disrupts the Gut Microbiota and Metabolic Balance of Honeybees (Apis cerana cerana)

There is a growing risk of pollinators being exposed to multiple fungicides due to the widespread use of fungicides for plant protection. A safety assessment of honeybees exposed to multiple commonly used fungicides is urgently required. Therefore, the acute oral toxicity of the ternary mixed fungicide of ABP (azoxystrobin: boscalid: pyraclostrobin = 1:1:1, m/m/m) was tested on honeybees (Apis cerana cerana), and its sublethal effect on foragers’ guts was evaluated. The results showed that the acute oral median lethal concentration (LD50) of ABP for foragers was 12.6 μg a.i./bee. ABP caused disorder of the morphological structure of midgut tissue and affected the intestinal metabolism; the composition and structure of the intestinal microbial community was perturbed, which altered its function. Moreover, the transcripts of genes involved in detoxification and immunity were strongly upregulated with ABP treatment. The study implies that exposure to a fungicide mixture of ABP can cause a series of negative effects on the health of foragers. This work provides a comprehensive understanding of the comprehensive effects of common fungicides on non-target pollinators in the context of ecological risk assessment and the future use of fungicides in agriculture.