Development of biomarkers of exposure to xenobiotics in the honey bee Apis mellifera: application to the systemic insecticide thiamethoxam

Neonicotinoid insecticides in non-target organisms: Occurrence, exposure, toxicity, and human health risks

Pesticides have consistently portrayed a crucial role in the history of modern agricultural production. Neonicotinoid insecticides are classified as the fourth generation of pesticides, following organophosphorus, pyrethroids, and carbamates. Due to their broad-spectrum insecticidal activity, unique neurotoxic mode of action, and versatility of application methods, neonicotinoids have been widely used worldwide since their introduction. Recent studies have shown that neonicotinoids are frequently detected in a variety of food and environmental media around the world, posing considerable safety risks to human health and ecosystems, and therefore have become an emerging contaminant. However, the toxic effects and exposure risks of neonicotinoids to non-target organisms, including humans, have not received sufficient attention. Therefore, based on previous studies, this critical review concisely evaluates the occurrence and exposure levels of neonicotinoids in the environment and the associated risks to human health. The toxic effects of neonicotinoids on non-target organisms are systematically reviewed, including the aspects of acute toxicity, reproductive development, nervous system, immune function, genetics, and others. The potential toxic mechanism of these pesticides is discussed. The existing knowledge gaps are identified, and future prospects for neonicotinoids are proposed to provide scientific guidance for the safe and rational use of neonicotinoids and future research directions.

Acute toxicity and sublethal effects of thiamethoxam on the stingless bee Scaptotrigona postica: Survival, neural morphology, and enzymatic responses

Native and cultivated plants in the Neotropics benefit from the pollination services provided by stingless bees. The use of neonicotinoid insecticides negatively impacts bee health, even though bees are not their primary targets. This study determined the oral mean lethal concentration (LC50) of thiamethoxam (TMX) after 24 h of exposure for the stingless bee Scaptotrigona postica. Based on the LC₅₀ value (0.11 ng a.i./μL) obtained, two fractions of this value (1/10 and 1/100 LC₅₀) were selected to assess survival time (LT₅₀), as well as to conduct neural morphological and enzymatic analyses. The LC₅₀/100 group had a LT₅₀ of 15 days, compared to 17 days in the control group, while the LC₅₀/10 group survived for 8 days. Morphological analyses revealed increased Kenyon cell spacing and pyknosis in the mushroom bodies after 1, 3, and 6 days of exposure, suggesting that thiamethoxam adversely affects the brain of S. postica. Regarding enzymatic activity, comparisons between the control and the two sublethal concentrations revealed that Carboxylesterase and Glutathione S-transferase (GST) activity increased in the abdomens after six days of exposure. GST activity also increased in the bees' heads for the LC₅₀/10 concentration after six days of exposure (Control x TMX group). The enzymatic results suggests that thiamethoxam induces oxidative stress in S. postica. The results presented underscore the necessity of considering stingless bees in regulatory decisions regarding the use of insecticides, ensuring that the risks to this important group of pollinators are adequately assessed.

Effects of anthropogenic stress on stingless bees Melipona mandacaia inhabiting urban and natural environments

Bees play a crucial role as pollinators, significantly contributing to ecosystem health. However, they face growing threats from human activities. This study uses biomarkers to evaluate the health status of Melipona mandacaia, a stingless bee native to the Caatinga biome, as indicators of anthropogenic stress. Bees were collected from the unique Caatinga biome, which had no recorded human pressure, and from an urban area with high human pressure. These bees were then analyzed for various biomarkers to assess the different levels of anthropogenic stress. The biomarkers included cholinesterases (ChE) to assess neurotoxicity, catalase (CAT) to measure antioxidant responses, glutathione S-transferases (GST) for detoxification pathways, and lipid peroxidation (LPO) as an indicator of oxidative stress. The results reveal that ChE inhibition may be associated with stress levels due to human activities showing an inhibition pattern with increased stress levels (up to 54.4 % inhibition), while the remaining biomarkers showed mixed responses across the different stress-level areas. In addition, the use of a principal component analysis (PCA) allowed a separation between the different groups and the weigh of the measured variables to each anthropogenic stress group. The integrated biomarker response (IBR) index was applied showing a clear distinction among groups. The obtained results could be partly explained by the beekeeping practices in some locations, which may have mitigated the effects of anthropogenic stressors to a certain degree, especially in HS. These findings underscore the importance of monitoring wild bee health in the Caatinga and demonstrate the value of a multifaceted biomarker approach for understanding the impacts of anthropogenic stressors on bee populations in varied environments and the effects of beekeeping.

Semi-field studies on biochemical markers of honey bee workers (Apis mellifera) after exposure to pesticides and their mixtures

Due to the fact that many different pesticides are used in crop production and their residues can accumulate in the environment, bees are in contact with various pesticides at the same time. Most studies on their influence on honey bees focus on single substances in concentrations higher than those found in the environment. Our study assessed the chronic effects of commonly used pesticides and their mixtures on selected biochemical markers in worker bee hemolymph. Workers developed in the hive and were provisioned with to pesticides in concentrations corresponding to residues detected in pollen, honey, and/or nectar. Colonies were exposed daily to 0.5L for 7 days by feeding a sugar syrup containing a formulation of acetamiprid (250 ppb) (insecticide), glyphosate (7200 ppb) (herbicide), and tebuconazole (147 ppb) (fungicide) administered alone, in a binary or ternary mixture. Administered alone, acetamiprid significantly decreased the level of urea in the hemolymph of worker honey bees. Glyphosate did not affect significantly the level/activity of any of the biochemical markers. Tebuconazole caused changes in the levels of most of the studied biochemical markers. We found that tebuconazole, which as a fungicide is generally considered safe for bees, may be harmful and more research is required. The impact of fungicides is a crucial element of the assessment of threats to honey bees.

Apis mellifera as a Model Species to Evaluate Toxicological Effects of Fungicides Used in Vineyard Agroecosystems

Agroecosystems provide habitats, food, and water for many pollinators and insects, but they are also heavily exposed to threats from the widespread use of pesticides and fertilizers. Managed honeybees and wild bees encounter pesticides in vineyards by collecting morning dew from vine leaves and accessing sugars from grapes, particularly during dry periods. This study assessed the toxicological effects of the commercial fungicide formulations Fantic FNCWG® and Ramedit combi®, both individually and in combination, on honeybees. Using a multi-biomarker approach, we evaluated neurotoxicity, metabolic disturbances, phase II detoxification processes, and immune system function. Our findings revealed that commercial fungicide mixtures with multiple active ingredients affect bees differently than single active compounds. Biomarker responses highlighted how these complex mixtures disrupt various enzymatic pathways; including immune function; altering critical enzyme kinetics involved in detoxification and potentially impairing essential bee functions. This study emphasizes the need for more comprehensive research into the sublethal effects of commercial pesticides, particularly those used in vineyards, which are understudied compared to pesticides used in orchards.

A Field Trial to Demonstrate the Potential of a Vitamin B Diet Supplement in Reducing Oxidative Stress and Improving Hygienic and Grooming Behaviors in Honey Bees

The honey bee is an important insect pollinator that provides critical pollination services for natural and agricultural systems worldwide. However, inadequate food weakens honey bee colonies, making them vulnerable to various biotic and abiotic factors. In this study, we examined the impact of supplementary feeding on bees' genes for antioxidative enzymes and vitellogenin, oxidative stress parameters, and the hygienic and grooming behavior. The colonies were divided into two experimental groups (with ten hives each): a treatment group that received the plant-based supplement and a control group. The experiment was conducted in two seasons, spring and summer. After the treatment, in both seasons, all the monitored parameters in the treatment group differed from those in the control group. The expression levels of genes for antioxidative enzymes were significantly lower, but the vitellogenin gene transcript level was significantly higher. Values of oxidative stress parameters were significantly lower. The levels of hygienic and grooming behavior were significantly higher. Therefore, our field study indicates that the tested supplement exerted beneficial effects on bees, reflected in reduced oxidative stress and enhanced hygienic and grooming behavior.

Pollen contaminated with a triple-action fungicide induced oxidative stress and reduced longevity though with less impact on lifespan in honey bees from well fed colonies

Experiments were conducted to determine the effects of a triple-action fungicide on bees and whether improved nutrition can ameliorate eventual negative impacts. In cage tests, newly-emerged bees from well fed and from nutritionally-restricted honey bee colonies were fed for five days with pollen from sunflowers that had been sprayed or not with a commercial fungicide containing bixafen, prothioconazole and trifloxystrobin. Bees from well-fed colonies were significantly larger and consumed more uncontaminated pollen. They also exhibited increased glutathione peroxidase activity and higher concentrations of pyridine nucleotides, both of which are involved in antioxidase defense. However, pollen contaminated with fungicide led to an increase in lipoperoxidation, regardless of nutritional status. Bee longevity was reduced by both fungicide contamination of the pollen diet and poor nutritional condition. The fungicide adversely affected bees fed with contaminated pollen, though nutritional supplementation of the bee colonies that reared the bees partially compensated for these effects.

Assessment of oxidative status, detoxification capacity and immune responsiveness in honey bees with ageing

The honey bee (Apis mellifera L.), as an eusocial insect species, is an important model organism in research focusing on ageing and longevity, due to prominent seasonal lifespan plasticity within the worker caste (summer and winter worker bees). In this study, we employed a screening approach to evaluate several molecular parameters, providing comprehensive insights into the antioxidative (superoxide dismutase and catalase activity, reduced glutathione and sulfhydryl group content, total antioxidative capacity), detoxifying (glutathione S-transferase and acetylcholinesterase activity), and immune (phenol oxidase and glucose oxidase activity) status, as well as vitellogenin content, in the summer and winter generation of honey bees, across ageing stages and in two body compartments: the whole abdomen and the head. Summer worker bees were collected weekly for six weeks, while winter bees were collected monthly for five months. The results of our study clearly indicate a reduced overall antioxidative capacity of older groups of worker bees from both generations, while the parameters of immune responsiveness mostly contributed to the separation between the two generations based on season rather than age categories. Detoxification ability appeared to be more susceptible to environmental factors. An age-dependent increase in vitellogenin content was recorded in the abdomen, but without seasonal differences. These findings provide an excellent starting point for further investigations into age-related changes, particularly within the context of honey bee sociality.

Biological control of nosemosis in Apis mellifera L. with Acacia nilotica extract

Nosemosis is one of the most devastating diseases of Apis mellifera (Honey bees) caused by the single-celled spore-forming fungi Nosema apis, N. ceranae and N. neumanii, causing a severe loss on the colony vitality and productivity. Fumagillin, a MetAP2 inhibitor, was a certified treatment for controlling nosemosis, nevertheless, due to its deleterious effects on honey bees and humans, it is prohibited. So, searching for novel biological agents with affordable selectivity to target Nosema species infecting Apis mellifera, with nil toxicity to bees and humans is the main objective of this study. Nosema species were isolated from naturally infected honey bees. The methanolic extracts of Acacia nilotica, Elaeis guineensis, and Catharanthus roseus were tested to selectively control the growth of Nosema spp of honeybees. The spores of Nosema species were molecularly and morphologically identified. Among the tested plant extracts, the methanolic extracts (0.1%) of A. nilotica had the most activity towards Nosema spp causing about 37.8 and 32.5% reduction in the spores' load at 5- and 9-days post-infection, respectively, compared to the untreated control. At 0.1%, the A. nilotica methanolic extract exhibited the highest inhibitory effect for Nosema spores, without any obvious bee mortality. Catharanthus roseus displayed a reduction of spores by 27.02%, with bee mortality rate of 27.02%. At 1% for 5 dpi, the A. nilotica extracts led to 18.18% bee mortality, while the C. roseus extracts resulted in 100% mortality, as revealed from the toxicity and quantification bioassays. So, the extracts of A. nilotica and C. roseus had a significant effect in controlling the N. apis and N. ceranae titer compared to the infected untreated control at both time points. The titer of N. apis and N. ceranae was noticeably decreased by more than 80% and 90%, in response to A. nilotica, compared to the control. From the metabolic profiling by GC-MS analysis, the most frequent active compounds of A. nilotica were 2,4,6-trihy-droxybenzoic acid, 1,2-dihydroxybenzene, myristic acid, and linoleic acid. These compounds were analyzed in silico to assess their binding affinity to the ATP binding protein, methionine aminopeptidase and polar tube protein of Nosema species as target enzymes. The compound 2,4,6-trihydroxybenzoic acid had the lowest energy to bind with ATP binding protein, methionine aminopeptidase and polar tube protein of Nosema, followed by 1,2-dihydroxybenzene and myristic acid, compared to fumagilin. So, from the experimental and molecular docking analysis, the extracts of A. nilotica had the highest activity to attack the cellular growth machinery of Nosema species without an obvious effect to the honeybees, ensuring their prospective promising application.

Sublethal effects of nitenpyram on the development of silkworm

The utilization of nitenpyram for aphid and whitefly control may induce environmental contamination and negative repercussions on non-target organisms. Formerly, we found that nitenpyram would pollute the peripheral and sub-peripheral areas of the adjacent mulberry orchard. Under acute toxicity conditions, nitenpyram induced oxidative damage in silkworms, affected biological metabolism, synthesis, immunity, and signal transduction. Considering the impact of nitenpyram mist drift on mulberry leaves, we investigated the effects of low concentrations of nitenpyram on silkworms. The results showed that silkworms exposed to 0.17 mg/L, 0.35 mg/L and 0.70 mg/L of nitenpyram (1/40 LC50, 1/20 LC50 and 1/10 LC50) showed obvious poisoning symptoms. The cocoon weight and cocoon shell weight decreased gradually with increases in the concentration, and these decreases prolonged the growth and development time of silkworms and induced the detoxification enzymes carboxylesterase (CarE) and glutathione-S-transferase (GST) to cope with the stress damage caused by nitenpyram. Exposure to low concentrations of nitenpyram downregulates genes involved in the drug metabolism-other enzymes and peroxisome pathway in silkworms. Additionally, through injection of miRNA mimics and inhibitors, we discovered that detoxifying enzyme pathway genes are influenced by bmo-miR-3382-3P, bmo-miR-3213-5P and bmo-miR-133, regulating the immune response of silkworms. This study provides an overall view of the toxicity and detoxification metabolism of nitenpyram in silkworm, and provides a reference for environmental assessment.

Thiamethoxam toxicity on the stingless bee Friesiomelitta varia: LC50, survival time, and enzymatic biomarkers assessment

Bees play a crucial role as pollinating insects in both natural and cultivated areas. However, the use of pesticides, such as thiamethoxam, has been identified as a contributing factor compromising bee health. The current risk assessment primarily relies on the model species Apis mellifera, raising concerns about the applicability of these assessments to other bee groups, including stingless bees. In this study, we investigated the acute toxicity of thiamethoxam on the stingless bee Frieseomelitta varia by determining the average lethal concentration (LC50) and mean lethal time (LT50). Additionally, we evaluated the enzymatic profile of Acetylcholinesterase (AChE), Carboxylesterase-3 (CaE-3), and Glutathione S-Transferase (GST), in the heads and abdomens of F. varia after exposure to thiamethoxam (LC50/10). The LC50 of thiamethoxam was determined to be 0.68 ng ai/μL, and the LT50 values were 37 days for the control group, 25 days at LC50/10, and 27 days at LC50/100. The thiamethoxam significantly decreased the survival time of F. varia. Furthermore, the enzymatic profile exhibited differences in CaE3 activity within one day in the heads and ten days in the abdomen. GST activity showed differences in the abdomen after one and five days of thiamethoxam exposure. These findings suggests that the abdomen is more affected than the head after oral exposure to thiamethoxam. Our study provides evidence of the toxicity of thiamethoxam at both the cellular and organismal levels, reinforcing the need to include non-Apis species in pollinator risk assessments. and provide solid arguments for bee protection.

Spermidine supplementation influence on protective enzymes of Apis mellifera (Hymenoptera: Apidae)

Dietary supplementation has been proposed as a sustainable way to improve the health and resilience of honey bees (Apis mellifera, L.), as the decline in their numbers in recent decades has raised scientific, environmental, and economic concerns. Spermidine, a natural polyamine, has been shown to be a promising substance for honey bee supplementation, as its health-promoting effects have been demonstrated in numerous studies and in different organisms. As already shown, supplementation with spermidine at a certain concentration prolonged lifespan, reduced oxidative stress, and increased antioxidative capacity in honey bees. The aim of the present study was to investigate whether spermidine supplementation affects gene expression and/or enzyme activity of antioxidative and detoxification enzymes and immune response markers in honey bee workers. The different gene expression and enzyme activity patterns observed in abdominal and head tissues in response to spermidine supplementation suggest tissue-specific and concentration-dependent effects. In addition, the immune response markers suggest that spermidine has the ability to boost honey bee immunity. The observed changes make a valuable contribution to understanding the molecular mechanisms by which spermidine may exert its beneficial effects on the bee's health and lifespan. These results support the idea of the use of spermidine supplementation to promote bee health and resilience to environmental stressors, emphasizing that the dose must be carefully chosen to achieve a balance between the pro- and antioxidant effects of spermidine.

Characterization of near-field temporal and spatial variations of pesticide residues using honeybee specimens as bio-sensing matrices

This study was prompted by recent reports of the ubiquity of neonicotinoids (neonics) in environment and the likelihood of exposures and health hazards to non-target organisms. We aimed to quantify neonics levels in time- and location-match pollen and nectar samples foraged by honeybees (Apis mellifera) and characterized the temporal and spatial variations using a relative potency factor method to determine the total neonic levels, expressed as the imidacloprid-adjusted total neonics, IMIRPF (ng/g). Six pairs of pollen and nectar samples, a total of twelve samples, were collected from each of the thirty-two experimental hives during the active foraging months of March, April, and June and analyzed for eight neonics. We found 59% and 64% of pollen and nectar contained at least one neonic, respectively. Among those neonic-detected pollen and nectar samples, 45% and 77% of them contained more than one neonic, respectively. Imidacloprid and acetamiprid in pollen and clothianidin and thiamethoxam in nectar accounted for 60% and 83% detection, respectively. The highest 3-month average of IMIRPF in pollen (6.56 ng/g) and nectar (11.19 ng/g) were detected in a location with the predominant production of citrus fruit. The temporal and spatial variations of IMIRPF levels demonstrated the robustness of using paired pollen and nectar data as the bio-sensing matrices to facilitate the assessment of near-field exposure to total neonics and the delineation of risks.

Assessing the effects of a commercial fungicide and an herbicide, alone and in combination, on Apis mellifera: Insights from biomarkers and cognitive analysis

Agrochemicals play a vital role in protecting crops and enhancing agricultural production by reducing threats from pests, pathogens and weeds. The toxicological status of honey bees can be influenced by a number of factors, including pesticides. While extensive research has focused on the lethal and sublethal effects of insecticides on individual bees and colonies, it is important to recognise that fungicides and herbicides can also affect bees' health. Unfortunately, in the field, honey bees are exposed to mixtures of compounds rather than single substances. This study aimed to evaluate the effects of a commercial fungicide and a commercial herbicide, both individually and in combination, on honey bees. Mortality assays, biomarkers and learning and memory tests were performed, and the results were integrated to assess the toxicological status of honey bees. Neurotoxicity (acetylcholinesterase and carboxylesterase activities), detoxification and metabolic processes (glutathione S-transferase and alkaline phosphatase activities), immune system function (lysozyme activity and haemocytes count) and genotoxicity biomarkers (Nuclear Abnormalities assay) were assessed. The fungicide Sakura® was found to activate detoxification enzymes and affect alkaline phosphatase activity. The herbicide Elegant 2FD and the combination of both pesticides showed neurotoxic effects and induced detoxification processes. Exposure to the herbicide/fungicide mixture impaired learning and memory in honey bees. This study represents a significant advance in understanding the toxicological effects of commonly used commercial pesticides in agriculture and contributes to the development of effective strategies to mitigate their adverse effects on non-target insects.

Combined effects of three insecticides with different modes of action on biochemical responses of the solitary bee Osmia bicornis

Bees are simultaneously exposed to a variety of pesticides, which are often applied in mixtures and can cause lethal and sublethal effects. The combined effects of pesticides, however, are not measured in the current risk assessment schemes. Additionally, the sublethal effects of pesticides on a variety of physiological processes are poorly recognized in bees, especially in non-Apis solitary bees. In this study, we used a full-factorial design to examine the main and interactive effects of three insecticide formulations with different modes of action (Mospilan 20 SP, Sherpa 100 EC, and Dursban 480 EC) on bee biochemical processes. We measured acetylcholinesterase (AChE), glutathione S-transferase (GST) and esterase (EST) activities, as well as a nonenzymatic biomarker associated with energy metabolism, i.e., ATP level. All studied endpoints were affected by Sherpa 100 EC, and the activities of AChE and EST as well as ATP levels were affected by Dursban 480 EC. Moreover, complex interactions between all three insecticides affected ATP levels, showing outcomes that cannot be predicted when testing each insecticide separately. The results indicate that even if interactive effects are sometimes difficult to interpret, there is a need to study such interactions if laboratory-generated toxicity data are to be extrapolated to field conditions.

Interactive effects of dinotefuran and Nosema ceranae on the survival status and gut microbial community of honey bees

Growing evidences have shown that the decline in honey bee populations is mainly caused by the combination of multiple stressors. However, the impacts of parasitic Nosema ceranae to host fitness during long-term pesticide exposure-induced stress is largely unknown. In this study, the effects of chronic exposure to a sublethal dose of dinotefuran, in the presence or absence of N. ceranae, was examined in terms of survival, food consumption, detoxification enzyme activities and gut microbial community. The interaction between dinotefuran and Nosema ceranae on the survival of honey bee was synergistic. Co-exposure to dinotefuran and N. ceranae led to less food consumption and greater changes of enzyme activities involved in defenses against oxidative stress. Particularly, N. ceranae and dinotefuran-N. ceranae co-exposure significantly impacted the gut microbiota structure and richness in adult honey bees, while dinotefuran alone did not show significant alternation of core gut microbiota compared to the control group. We herein demonstrated that chronical exposure to dinotefuran decreases honey bee's survival but is not steadily associated with the gut microbiota dysbiosis; by contrast, N. ceranae parasitism plays a dominant role in the combination in influencing the gut microbial community of the host honey bee. Our findings provide a comprehensive understanding of combinatorial effects between biotic and abiotic stressors on one of the most important pollinators, honey bees.

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.

Elucidating the Role of Honey Bees as Biomonitors in Environmental Health Research

Recently, the One Health concept, which recognizes the interconnectedness of environmental, animal, and human health, has gained popularity. To collect data on environmental pollutants potentially harmful to human health over time, researchers often turn to natural organisms known as biomonitors. Honey bees, in particular, prove to be exceptionally valuable biomonitors due to their capacity to accumulate pollutants from the air, soil, and water within a specific radius during their foraging trips. This systematic literature review summarizes the previous application of the bee species Apis mellifera in pollutant monitoring in articles published during the period of 2010-2020. Nineteen studies were included in this systematic literature review. Of these studies, the majority (n = 15) focused on the detection of heavy metals in honey bees and beehive products, while 4 studies focused on air pollution by polycyclic aromatic hydrocarbons or particulate matter. The matrix most often applied was the whole honey bee. The included studies demonstrated that honey bees and hive products deliver quantitative and qualitative information about specific pollutants. In this regard, the whole honey bee was found to be the most reliable biomonitor. We found that the included studies differed in design and the methods used. Standardized studies could foster a more consistent interpretation of the levels detected in beehive matrices from an environmental health perspective.

Effects of thiamethoxam on brain structure of Bombus terrestris (Hymenoptera: Apidae) workers

Neonicotinoids are the most widely used pesticide compared to other major insecticide classes known worldwide and have the fastest growing market share. Many studies showed that neonicotinoid pesticides harm honeybee learning and farming activities, negatively affect colony adaptation and reduce pollination abilities. Bumblebees are heavily preferred species all over the world in order to ensure pollination in plant production. In this study, sublethal effects of the neonicotinoid insecticide thiamethoxam on the brain of Bombus terrestris workers were analyzed. Suspensions (1/1000, 1/100, 1/10) of the maximum recommended dose of thiamethoxam were applied to the workers. 48 h after spraying, morphological effects on the brains of workers were studied. According to area measurements of ICC's of Kenyon cells, there was a significant difference between 1/10 dose and all groups. On the other hand, areas of INC's of Kenyon cells showed a significant difference between the control group and all dose groups. Neuropil disorganization in the calyces increased gradually and differed significantly between the groups and was mostly detected at the highest dose (1/10). Apart from optic lobes, pycnotic nuclei were also observed in the middle region of calyces of mushroom bodies in the high dose group. Also, the width of the lamina, medulla and lobula parts of the optic lobes of each group and the areas of the antennal lobes were measured and significant differences were determined between the groups. The results of the study revealed that sublethal doses of thiamethoxam caused some negative impacts on brain morphology of B. terrestris workers.

Low concentration of indoxacarb interferes with the growth and development of silkworm by damaging the structure of midgut cells

As an important economic insect, Bombyx mori plays an essential role in the development of the agricultural economy. Indoxacarb, a novel sodium channel blocker insecticide, has been widely used for the control of various pests in agriculture and forestry, and its environmental pollution caused by flight control operations has seriously affected the safe production of sericulture in recent years. However, the lethal toxicity and adverse effects of indoxacarb on silkworm remain largely unknown. In this study, the toxicity of indoxacarb on the 5th instar larvae of silkworm was determined, with an LC50 (72 h) of 2.07 mg/L. Short-term exposure (24 h) to a low concentration of indoxacarb (1/2 LC50) showed significantly reduced body weight and survival rate of silkworm larvae. In addition, indoxacarb also led to decreased cocoon weight and cocoon shell weight, but had no significant effects on pupation, adult eclosion, and oviposition. Histopathological and ultrastructural analysis indicated that indoxacarb could severely damage the structure of the midgut epithelial cells, and lead to physiological impairment of the midgut. A total of 3883 differentially expressed genes (DEGs) were identified by midgut transcriptome sequencing and functionally annotated using GO and KEGG. Furthermore, the transcription level and enzyme activity of the detoxification related genes were determined, and our results suggested that esterases (ESTs) might play a major role in metabolism of indoxacarb in the midgut of B. mori. Future studies to examine the detoxification or biotransformation function of candidate genes will greatly enhance our understanding of indoxacarb metabolism in B. mori. The results of this study provide a theoretical basis for elucidating the mechanism of toxic effects of indoxacarb on silkworm by interfering with the normal physiological functions of the midgut.

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

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

Applying Artificial Neural Networks to Oxidative Stress Biomarkers in Forager Honey Bees (Apis mellifera) for Ecological Assessment

Insect pollinators provide an important ecosystem service that supports global biodiversity and environmental health. The study investigates the effects of the environmental matrix on six oxidative stress biomarkers in the honey bee Apis mellifera. Thirty-five apiaries located in urban, forested, and agricultural areas in Central Italy were sampled during the summer season. Enzyme activities in forager bees were analyzed using an artificial neural network, allowing the identification and representation of the apiary patterns in a Self-Organizing Map. The SOM nodes were correlated with the environmental parameters and tissue levels of eight heavy metals. The results indicated that the apiaries were not clustered according to their spatial distribution. Superoxide dismutase expressed a positive correlation with Cr and Mn concentrations; catalase with Zn, Mn, Fe, and daily maximum air temperature; glutathione S-transferase with Cr, Fe, and daily maximal air temperature; and glutathione reductase showed a negative correlation to Ni and Fe exposure. This study highlights the importance of exploring how environmental stressors affect these insects and the role of oxidative stress biomarkers. Artificial neural networks proved to be a powerful approach to untangle the complex relationships between the environment and oxidative stress biomarkers in honey bees. The application of SOM modeling offers a valuable means of assessing the potential effects of environmental pressures on honey bee populations.

Comparison of the Sensitivity of Tetragonisca angustula (Apidae-Meliponini) and Apis mellifera (Apidae-Apini) to Three Insecticides (Malathion, Imidacloprid, and Fipronil) Used in Costa Rica

The decline of insect pollinators is a significant concern within the current biodiversity crisis. The paradox between the benefits that these animals represent to humans and the evidence of human activities driving their extinction calls for the urgent protection of bees. To address the role of chemical pollution in this scenario, we assessed the acute toxicity as well as four biomarker responses (cholinesterase [ChE], glutathione S-transferase, catalase, and lipid peroxidation [LPO]) elicited by dietary 24-h exposure to three insecticides (malathion, imidacloprid, and fipronil) on the stingless neotropical bee Tetragonisca angustula and the honeybee Apis mellifera. Malathion was the most toxic substance to both species, with 48-h median lethal doses (LD50s) of 0.25 ng/bee to A. mellifera and 0.02 ng/bee to T. angustula. Fipronil was also highly toxic and presented a similar toxicity to both species, with 48-h LD50s of 0.5 ng/bee (A. mellifera) and 0.4 ng/bee (T. angustula). Imidacloprid had the lowest acute toxicity with a 48-h LD50 of 29 ng/bee for A. mellifera, whereas T. angustula tolerated exposure higher than 35 ng/bee. Apparent biomarker responses were observed in bees of both species that survived exposure to higher concentrations of malathion (ChE inhibition) and fipronil (increased LPO). Our results suggest that specific sensitivity to insecticides varies greatly among compounds and pollinator species, but the use of different representative species can facilitate the prioritization of substances regarding their risk to pollinators. Further research is necessary to better characterize the risk that pesticides represent in neotropical agricultural landscapes. Environ Toxicol Chem 2023;42:1022-1031. © 2023 SETAC.

Investigating the effects of glyphosate on the bumblebee proteome and microbiota

Glyphosate is one of the most widely used herbicides globally. It acts by inhibiting an enzyme in an aromatic amino acid synthesis pathway specific to plants and microbes, leading to the view that it poses no risk to other organisms. However, there is growing concern that glyphosate is associated with health effects in humans and an ever-increasing body of evidence that suggests potential deleterious effects on other animals including pollinating insects such as bees. Although pesticides have long been considered a factor in the decline of wild bee populations, most research on bees has focussed on demonstrating and understanding the effects of insecticides. To assess whether glyphosate poses a risk to bees, we characterised changes in survival, behaviour, sucrose solution consumption, the digestive tract proteome, and the microbiota in the bumblebee Bombus terrestris after chronic exposure to field relevant doses of technical grade glyphosate or the glyphosate-based formulation, RoundUp Optima+®. Regardless of source, there were changes in response to glyphosate exposure in important cellular and physiological processes in the digestive tract of B. terrestris, with proteins associated with oxidative stress regulation, metabolism, cellular adhesion, the extracellular matrix, and various signalling pathways altered. Interestingly, proteins associated with endocytosis, oxidative phosphorylation, the TCA cycle, and carbohydrate, lipid, and amino acid metabolism were differentially altered depending on whether the exposure source was glyphosate alone or RoundUp Optima+®. In addition, there were alterations to the digestive tract microbiota of bees depending on the glyphosate source No impacts on survival, behaviour, or food consumption were observed. Our research provides insights into the potential mode of action and consequences of glyphosate exposure at the molecular, cellular and organismal level in bumblebees and highlights issues with the current honeybee-centric risk assessment of pesticides and their formulations, where the impact of co-formulants on non-target organisms are generally overlooked.

Non-optimal ambient temperatures aggravate insecticide toxicity and affect honey bees Apis mellifera L. gene regulation

In this study, we conducted a transcriptional analysis of five honey bee genes to examine their functional involvement vis-à-vis ambient temperatures and exposure to imidacloprid. In a 15-day cage experiment, three cohorts of one-day-old sister bees emerged in incubators, were distributed into cages, and maintained at three different temperatures (26 °C, 32 °C, 38 °C). Each cohort was fed a protein patty and three concentrations of imidacloprid-tainted sugar (0 ppb, 5 ppb and 20 ppb) ad libitum. Honey bee mortality, syrup and patty consumption were monitored daily over 15 days. Bees were sampled every three days for a total of five time points. RT-qPCR was used to longitudinally assess gene regulation of Vg, mrjp1, Rsod, AChE-2 and Trx-1 using RNA extracted from whole bee bodies. Kaplan-Meier models show that bees kept at both non-optimal temperatures (26 °C and 38 °C) were more susceptible to imidacloprid, with significantly higher mortality (P < 0.001 and P < 0.01, respectively) compared to the control. At 32 °C, no differences in mortality (P = 0.3) were recorded among treatments. In both imidacloprid treatment groups and the control, the expression of Vg and mrjp1 was significantly downregulated at 26 °C and 38 °C compared to the optimal temperature of 32 °C, indicating major influence of ambient temperature on the regulation of these genes. Within the ambient temperature groups, both imidacloprid treatments exclusively downregulated Vg and mrjp1 at 26 °C. AChE-2 and the poorly characterized Rsod gene were both consistently upregulated at the highest temperature (38 °C) compared to the ideal temperature (32 °C) in all treatment groups. Trx-1 showed no effect to both temperature and imidacloprid treatments and was regulated in an age-related manner. Overall, our results indicate that ambient temperatures amplify imidacloprid toxicity and affect honey bee gene regulation.

Biological comparative study between Wolbachia-infected Aedes aegypti mosquito and Wolbachia-uninfected strain, Jeddah city, Saudi Arabia

In this study, samples of Wolbachia-infected Aedes aegypti mosquitoes were collected from Al-Safa district in Jeddah city, Saudi Arabia. The presence of Wolbachia bacteria in mosquitoes was confirmed by PCR technique and they were reared and propagated in the laboratory. Comparative studies were conducted between Wolbachia-infected A. Aegypti and the Wolbachia-uninfected laboratory strain in terms of their ability to withstand drought, resist two types of insecticides and the activities of pesticide detoxification enzymes. The Wolbachia-infected A. aegypti strain proved less able to withstand the drought period, as the egg-hatching rate of the Wolbachia-uninfected strain was greater than that of the Wolbachia-infected strain after one, two and three months of dry periods. Compared to the Wolbachia-uninfected strain, the Wolbachia-infected strain demonstrated a relatively greater resistance to tested pesticides, namely Baton 100EC and Fendure 25EC which may be attributed to the higher levels of the detoxification enzymes glutathione-S-transferase and catalase and the lower levels of esterase and acetylcholine esterase.

Increased survival of honey bees consuming pollen and beebread is associated with elevated biomarkers of oxidative stress

Introduction

Significant losses of honey bee colonies have been observed worldwide in recent decades. Inadequate nutrition is considered to be one of the factors that can reduce honey bee resistance to abiotic and biotic environmental stresses. Accordingly, we assessed the impact of food composition on worker bee survival.

Methods

Bees in cages were fed six different diets, and then their survival, levels of thiobarbituric acid reactive substances and protein carbonyl groups, catalase and lysozyme activities were evaluated.

Results and Discussion

After 17 days of feeding, the lowest mortality was observed in the group of bees that received sucrose solution with the addition of willow pollen or artificial rapeseed beebread or artificial willow beebread (diets 4–6). The highest mortality was found in bees that consumed only sucrose solution (diet 1) or the sucrose solution supplemented with a mixture of amino acids (diet 2), which can be explained by the lack of vitamins and microelements in these diets. In the group of bees that received the sucrose solution with rapeseed pollen (diet 3), mortality was intermediate. To check whether the decrease in insect survival could be related to oxidative damage, we evaluated biomarkers of oxidative stress. Consumption of pollen (diets 3 and 5) and artificial beebread (diets 4 and 6) enhances protein carbonylation in worker bees. Feeding bees artificial beebread also resulted in increase in lipid peroxidation and catalase activity, which is probably due to the presence of hydrogen peroxide in the honey contained in beebread. Remarkably, the increase in biomarkers of oxidative stress was not accompanied by adverse but positive effects on insect survival. A lack of amino acids and proteins in the diet 1 did not cause oxidative stress, but led to an increase in lysozyme activity in hemolymph, a biomarker of immune system status. In conclusion, we believe that the increase in oxidative stress biomarkers we found do not indicate oxidative damage, but rather reflect the changes in redox balance due to consumption of certain dietary options.

Biochemical responses, feeding and survival in the solitary bee Osmia bicornis following exposure to an insecticide and a fungicide alone and in combination

In agricultural ecosystems, bees are exposed to combinations of pesticides that may have been applied at different times. For example, bees visiting a flowering crop may be chronically exposed to low concentrations of systemic insecticides applied before bloom and then to a pulse of fungicide, considered safe for bees, applied during bloom. In this study, we simulate this scenario under laboratory conditions with females of the solitary bee, Osmia bicornis L. We studied the effects of chronic exposure to the neonicotinoid insecticide, Confidor® (imidacloprid) at a realistic concentration, and of a pulse (1 day) exposure of the fungicide Folicur® SE (tebuconazole) at field application rate. Syrup consumption, survival, and four biomarkers: acetylcholinesterase (AChE), carboxylesterase (CaE), glutathione S-transferase (GST), and alkaline phosphatase (ALP) were evaluated at two different time points. An integrated biological response (IBRv2) index was elaborated with the biomarker results. The fungicide pulse had no impact on survival but temporarily reduced syrup consumption and increased the IBRv2 index, indicating potential molecular alterations. The neonicotinoid significantly reduced syrup consumption, survival, and the neurological activity of the enzymes. The co-exposure neonicotinoid-fungicide did not increase toxicity at the tested concentrations. AChE proved to be an efficient biomarker for the detection of early effects for both the insecticide and the fungicide. Our results highlight the importance of assessing individual and sub-individual endpoints to better understand pesticide effects on bees.

Ixodicidal effect of extracts from Cordia boissieri, Artemisia ludoviciana and Litchi chinensis on Rhipicephalus (Boophilus) microplus (Acari: Ixodidae)

The ixodicidal activity of the methanolic extracts of Artemisia ludoviciana (Astereceae), Cordia boissieri (Boraginaceae) and Litchi chinensis (Sapindaceae) against two field populations of Rhipicephalus (Boophilus) microplus from the state of Nuevo Leon (NL) and Veracruz (VER) was evaluated. The extract of L. chinensis in the concentration of 150 mg/ml showed efficacies of 100% and 99% against engorged females and mortalities of 98% and 99% against larvae. C. boissieri in the same concentration showed efficacies of 71% and 37% against engorged adults and mortalities of 33.04% and 10.33% against larvae and A. ludoviciana had efficacies of 94% and 83% in adults and mortalities of 89.39% and 89.21% against larvae in both populations respectively. The enzymatic activity of Acetylcholinesterase (AChE), Carboxylesterase (CaE), Glutathione-S-Transferase (GST) and Alkaline Phosphatase (ALP) was measured in both populations of ticks. As a result, a significant difference between both populations was shown, being the VER population the one that exhibited a higher enzymatic activity (p ≤ 0.05). It can be concluded that the methanolic extract of the seed of L. chinensis shows potential ixodicidal activity and can be used as an alternative source of tick control, however, prior characterization, toxicity and formulation studies are necessary.

Joint toxic effects of thiamethoxam and flusilazole on the adult worker honey bees (Apis mellifera L.)

Insect pollinators are routinely exposed to a complex mixture of many pesticides. However, traditional environmental risk assessment is only carried out based on ecotoxicological data of single substances. In this context, we aimed to explore the potential effects when worker honey bees (Apis mellifera L.) were simultaneously challenged by thiamethoxam (TMX) and flusilazole (FSZ). Results displayed that TMX possessed higher toxicity to A. mellifera (96-h LC₅₀ value of 0.11 mg a. i. L^-1) than FSZ (96-h LC₅₀ value of 738 mg a. i. L^-1). Furthermore, the mixture of TMX and FSZ exhibited an acute synergistic impact on the pollinators. Meanwhile, the activities of SOD, caspase 3, caspase 9, and PPO, as well as the expressions of six genes (abaecin, dorsal-2, defensin-2, vtg, caspase-1, and CYP6AS14) associated with oxidative stress, immune response, lifespan, cell apoptosis, and detoxification metabolism were noteworthily varied in the individual and mixture challenges than at the baseline level. These data revealed that it is imminently essential to investigate the combined toxicity of pesticides since the toxicity evaluation from individual compounds toward honey bees may underestimate the toxicity in realistic conditions. Overall, the present results could help understand the potential contribution of pesticide mixtures to the decline of bee populations.

Using physiology to better support wild bee conservation

There is accumulating evidence that wild bees are experiencing a decline in terms of species diversity, abundance or distribution, which leads to major concerns about the sustainability of both pollination services and intrinsic biodiversity. There is therefore an urgent need to better understand the drivers of their decline, as well as design conservation strategies. In this context, the current approach consists of linking observed occurrence and distribution data of species to environmental features. While useful, a highly complementary approach would be the use of new biological metrics that can link individual bee responses to environmental alteration with population-level responses, which could communicate the actual bee sensitivity to environmental changes and act as early warning signals of bee population decline or sustainability. We discuss here through several examples how the measurement of bee physiological traits or performance can play this role not only in better assessing the impact of anthropogenic pressures on bees, but also in guiding conservation practices with the help of the documentation of species' physiological needs. Last but not least, because physiological changes generally occur well in advance of demographic changes, we argue that physiological traits can help in predicting and anticipating future population trends, which would represent a more proactive approach to conservation. In conclusion, we believe that future efforts to combine physiological, ecological and population-level knowledge will provide meaningful contributions to wild bee conservation-based research.

Acute thiamethoxam exposure induces hepatotoxicity and neurotoxicity in juvenile Chinese mitten crab (Eriocheir sinensis)

The similar nervous system structure between crustaceans and insects and the high-water solubility of thiamethoxam can lead to the more severe toxicity of thiamethoxam to crustaceans. However, the effects of thiamethoxam on crustaceans are unclear. Therefore, a 96-h acute toxicity test was performed to explore the hepatotoxicity and neurotoxicity effects of thiamethoxam on Chinese mitten crab (Eriocheir sinensis) at concentrations 0 µg/L, 150 µg/L and 300 µg/L. The antioxidant and detoxification systems (including phases I and II) were significantly activated after exposure of juvenile crabs to thiamethoxam for 24 h in 300 µg/L group, whereas the toxic activation effect in 150 μg/L group was delayed. Moreover, a similar pattern was observed for the transcription levels of immune-related genes. Further analysis of inflammatory signaling pathway-related genes showed that thiamethoxam exposure with 300 µg/L for 24 h may induce a pro-inflammatory response through the NF-κB pathway. In contrast, the gene expression levels in 150 µg/L group were significantly upregulated compared with 0 µg/L group after 96 h. In addition, although the acute exposure of 150 μg/L thiamethoxam did not seem to induce significant neurotoxicity, the acetylcholinesterase activity was significantly decreased in 300 μg/L group after thiamethoxam exposure for 96 h. Correspondingly, thiamethoxam exposure with 300 µg/L for 24 h resulted in significantly downregulated transcriptional levels of synaptic transmission-related genes (e.g. dopamine-, gamma-aminobutyric acid- and serotonin-related receptors). Therefore, thiamethoxam may be harmful and cause potential toxic threats such as neurotoxicity and metabolic damage to crustaceans.

Modified QuEChERS Method for Extracting Thiamethoxam and Imidacloprid from Stingless Bees: Development, Application, and Green Metrics

In the present study, a method for the determination of residues of the neonicotinoid insecticides thiamethoxam and imidacloprid in the stingless bee Melipona scutellaris Latreille (1811) was optimized through a factorial design, tested using green metrics, and then applied to exposed bees. It combines the extraction with a modified quick, easy, cheap, effective, rugged, and safe method and the determination by liquid chromatography-tandem mass spectrometry analysis. Different parameters such as the mass of the sample, dispersive sorbents, and elution solvents were assessed. Method validation parameters were checked and include sensitivity, specificity, and linearity. The limit of quantification of 0.0025 μg g^-1 was obtained for both insecticides, where accuracy was 94%-100% with satisfactory intraday and interday precisions (relative standard deviation <10%). The qualified method was applied to orally and topically exposed bee samples, and the results indicated that it is suitable for the determination and quantification of neonicotinoid pesticide residues in this species. Moreover, green analytical metrics like the National Environmental Methods Index, Eco Scale score, high-performance liquid chromatography with an environmental assessment tool (HPLC-EAT), waste generation, and amount of sample were compared with methods described in the literature involving neonicotinoid analysis in honeybees. As a result, the present study displayed the highest Eco Scale score and HPLC-EAT score and the second smallest amount of sample and waste generated. Thus, the method meets green analytical metrics more than other methods. In this sense, besides the application, the multicriteria decision analysis tool employed suggests that this is a good option as a green analytical method. Environ Toxicol Chem 2022;41:2365-2374. © 2022 SETAC.

Multibiomarker responses after exposure to a sublethal concentration of thiamethoxam in the African honeybee (Apis mellifera intermissa)

Thiamethoxam is an insecticide mainly used in agriculture to control insect pests. However, non-target insect species, such as honeybees, may also be impacted. In this study, adults of Apis mellifera intermissa were orally exposed under laboratory conditions to a sublethal concentration of thiamethoxam (CL₂₅₌ 0.17 ng/μl) for 9 days and the effects were evaluated at the biochemical level, by monitoring specific oxidative stress and neuronal biomarkers. Results showed an increase in the antioxidant enzymes, glutatione-S-transferase (GST), catalase (CAT) and glutathione peroxidase (GPx) and in content of malondialdehyde (MDA). The activity of acetylcholinesterase (AChE) was downregulated as evidence of a neurotoxic action and no significant change was observed in glutathione (GSH). Exposure to the insecticide thiamethoxam induced oxidative stress and defense mechanisms affecting honeybee physiology.

Melatonin enhances the antioxidant capacity to rescue the honey bee Apis mellifera from the ecotoxicological effects caused by environmental imidacloprid

Imidacloprid severely poisons the nontarget insect honey bee Apis mellifera. Few treatments are available to mitigate the adverse effects of imidacloprid. The primary concern is that the molecular understanding of imidacloprid toxicity is not comprehensive enough. Oxidative stress is the primary pathophysiological mechanism by which pesticides cause high mortality. Our pilot study found for the first time that imidacloprid stimulates bee brains to secrete melatonin, a free radical scavenger. However, the molecular basis for imidacloprid toxicity and the role of melatonin in coping with imidacloprid have not been systematically investigated in bees. This study administered an environmental dose of imidacloprid (36 ng/bee) orally to A. mellifera. The detoxification gene cytochrome P450 CYP4G11 was significantly induced. However, potent cytotoxicity of imidacloprid suppressed the expression of the antioxidants catalase (CAT) and thioredoxin reductase (TrxR), and the activity of guaiacol peroxidase (GPX), superoxide dismutase (SOD), and reduced glutathione (GSH) was not induced. The levels of reactive oxygen species (ROS) and the lipid peroxidation marker malondialdehyde (MDA) were increased. The expression of the apoptotic genes cysteinyl aspartate specific proteinase (Caspase-3) and apoptosis inducing factor (AIF) increased, and the apoptotic features of midgut cells were prominently apparent. These results suggest that imidacloprid disrupts the bee antioxidant system, causing severe oxidative stress and tissue damage and ultimately leading to apoptosis. Significantly, however, imidacloprid exposure also stimulated bee brains to continuously secrete melatonin. Further preadministration of exogenous melatonin (200 ng/bee) orally to bees significantly reversed and enhanced the activity of the imidacloprid-suppressed antioxidants CAT, SOD, and GSH, which allowed imidacloprid-induced ROS accumulation to be effectively alleviated. The MDA content, apoptotic genes Caspase-3 and AIF, and detoxification gene CYPG411 expression were restored to normalization; midgut cell damage, apoptosis, and mortality were significantly reduced. These findings strongly suggest that melatonin enhanced bee antioxidant capacity, thus attenuating oxidative stress and apoptosis to confer imidacloprid tolerance to honey bees. Melatonin secretion may be a defense mechanism to mitigate imidacloprid toxicity.

Interaction between Thiamethoxam and Deformed Wing Virus Type A on Wing Characteristics and Expression of Immune and Apoptosis Genes in Apis mellifera

Simple Summary

Honey bees are key pollinators in agricultural crops. Today, honey bee colonies in decline are a global concern as a result of various stressors, including pesticides, pathogens, honey bee health, and parasites. A healthy honey bee colony refers to colonies that are not exposed to biotic and abiotic stressors. In this study, we examine how thiamethoxam (pesticide) and deformed wing virus type A (DWV-A) interact in effects on honey bee health. The results revealed that the honey bees were infected with DWV-A and were additionally exposed to thiamethoxam, showing effects that increased the mortality rate, and crippled wings in newly emerged adult honey bees. Moreover, the exposure to thiamethoxam and DWV-A injection resulted in induced expression of immune genes (hymenoptaecin gene) while downregulation of two apoptosis genes (caspase8-like, caspase9-like genes). The impact interaction of pesticide and DWV-A have on the expression of apoptosis genes can directly affect viral susceptibility in the honey bee host.

Abstract

Honey bees are economically important insects for crop pollination. They play a significant role as pollinators of wild plants and agricultural crops and produce economical products, such as honey, royal jelly, wax, pollen, propolis, and venom. Despite their ecological and economical importance, the global honey bee population is in decline due to factors including pathogens, parasites, intensive agriculture, and pesticides. Moreover, these factors may be interlinked and exacerbate the loss of honey bees. This study aimed to investigate the interaction between a pesticide, thiamethoxam, and deformed wing virus type A (DWV-A) to honey bees and the effects on survival rate, wing characteristics, and expression of immune and apoptosis genes in Apis mellifera. We described the potential interaction between thiamethoxam and DWV-A on honey bee wing characteristics, DWV-A loads, and the expressions of immune (defensin, abaecin, and hymenoptaecin) and apoptosis genes (buffy, apaf1, caspase3-like, caspase8-like, and caspase9-like). Honey bee larvae were fed with three different thiamethoxam doses (0.001, 1.4, and 14.3 ng/µL of the diet). Then, thiamethoxam-treated white-eyed pupae were injected with 10⁷ copy numbers/honey bee of the DWV-A genome. The interaction between thiamethoxam and DWV-A caused a high mortality rate, crippled wings in newly emerged adult honey bees (100%), and resulted in induced expression of hymenoptaecin gene compared to the control group, while downregulation of caspase8-like, caspase9-like genes compared to the DWV injection group. Therefore, the potential interaction between thiamethoxam and DWV-A might have a deleterious effect on honey bee lifespan. The results from this study could be used as a tool to combat DWV-A infection and mitigate pesticide usage to alleviate the decrease in the honey bee population.

Toxicity of the Pesticides Imidacloprid, Difenoconazole and Glyphosate Alone and in Binary and Ternary Mixtures to Winter Honey Bees: Effects on Survival and Antioxidative Defenses

To explain losses of bees that could occur after the winter season, we studied the effects of the insecticide imidacloprid, the herbicide glyphosate and the fungicide difenoconazole, alone and in binary and ternary mixtures, on winter honey bees orally exposed to food containing these pesticides at concentrations of 0, 0.01, 0.1, 1 and 10 µg/L. Attention was focused on bee survival, food consumption and oxidative stress. The effects on oxidative stress were assessed by determining the activity of enzymes involved in antioxidant defenses (superoxide dismutase, catalase, glutathione-S-transferase, glutathione reductase, glutathione peroxidase and glucose-6-phosphate dehydrogenase) in the head, abdomen and midgut; oxidative damage reflected by both lipid peroxidation and protein carbonylation was also evaluated. In general, no significant effect on food consumption was observed. Pesticide mixtures were more toxic than individual substances, and the highest mortalities were induced at intermediate doses of 0.1 and 1 µg/L. The toxicity was not always linked to the exposure level and the number of substances in the mixtures. Mixtures did not systematically induce synergistic effects, as antagonism, subadditivity and additivity were also observed. The tested pesticides, alone and in mixtures, triggered important, systemic oxidative stress that could largely explain pesticide toxicity to honey bees.

Detection of insecticide detoxification enzymes activities in Aedes aegypti mosquito, the vector of dengue fever in Saudi Arabia

In this study, the sensitivity of Aedes aegypti mosquitoe larvae to four types of pesticides two phosphorous-based and two pyrethroid insecticides was investigated. The larvae revealed approximately 1.126-fold more susceptibility to Safrotin (LC50 = 0.127 ppm) than Fendure (LC50 = 0.143) in the case of phosphorous-based pesticides and approximately 1.265-fold more susceptibility to AlphaQuest (LC50 = 0.0347 ppm) than Klash (LC50 = 0.0439) in the case of pyrothroid insecticides. Comparison between groups revealed that AlphaQuest was more effective than Klash, Safrotin and Fendure by approximately 1.3, 3.6 and 4.1-fold, respectively. The presence of enzyme activities relevant to insecticide resistance was often evaluated using enzyme assays to detect the underlying resistance mechanisms that may not be detected using bioassays. In this study, the results revealed significant decrease in the activity of esterase, glutathione- S- transferase and acetylcholine esterase enzymes to varying degrees. There were significant increases in catalase and total glutathione activity in all treatments compared to the control. The study concluded that this variation in enzyme activities is due to the type and purity of the additive compound and the source and purity of the active ingredient. The study recommends using the catalase enzyme and total glutathione as a biomarker indication for pesticide synergistic intoxication in aquatic animals.

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

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

Environmental exposures associated with honey bee health

Bee health is declining on a global scale, yet the exact causes and their interactions responsible for the decline remain unknown. To more objectively study bee health, recently biomarkers have been proposed as an essential tool, because they can be rapidly quantified and standardized, serving as a comparable measure across bee species and varying environments. Here, we used a systems biology approach to draw associations between endogenous and exogenous chemical profiles, with pesticide exposure, or the abundance of the 21 most common honey bee diseases. From the analysis we identified chemical biomarkers for both pesticide exposure and bee diseases along with the mechanistic biological pathways that may influence disease onset and progression. We found a total of 2352 chemical features, from 30 different hives, sampled from seven different locations. Of these, a total of 1088 significant associations were found that could serve as chemical biomarker profiles for predicting both pesticide exposure and the presence of diseases in a bee colony. In almost all cases we found novel external environmental exposures within the top seven associations with bee diseases and pesticide exposures, with the majority having previously unknown connections to bee health. We highlight the exposure-outcome paradigm and its ability to identify previously uncategorized interactions from different environmental exposures associated with bee diseases, pesticides, mechanisms, and potential synergistic interactions of these that are responsible for honey bee health decline.

Enzymatic responses in the head and midgut of Africanized Apis mellifera contaminated with a sublethal concentration of thiamethoxam

The increasing use of insecticides, promoted by the intensification of agriculture, has raised concerns about their influence on the decline of bee colonies, which play a fundamental role in pollination. Thus, it is fundamental to elucidate the effects of insecticides on bees. This study investigated the damage caused by a sublethal concentration of thiamethoxam - TMX (0.0227 ng/μL of feed) in the head and midgut of Africanized Apis mellifera, by analyzing the enzymatic biomarkers, oxidative stress, and occurrence of lipid peroxidation. The data showed that the insecticide increased acetylcholinesterase activity (AChE) and glutathione-S-transferase (GST), whereas carboxylesterase (CaE3) activity decreased in the heads. Our results indicate that the antioxidant enzymes were less active in the head because only glutathione peroxidase (GPX) showed alterations. In the midgut, there were no alkaline phosphatase (ALP) or superoxide dismutase (SOD) responses and a decrease in the activity of CaE was observed. Otherwise, there was an increase in GPX, and the TBARS (thiobarbituric acid reactive substances) assay also showed differences in the midgut. The TBARS (thiobarbituric acid reactive substances) assay also showed differences in the midgut. The results showed enzymes such as CaE3, GST, AChE, ALP, SOD, and GPX, as well as the TBARS assay, are useful biomarkers on bees. They may be used in combination as a promising tool for characterizing bee exposure to insecticides.

First application of an Integrated Biological Response index to assess the ecotoxicological status of honeybees from rural and urban areas

Understanding the effects of environmental contaminants on honeybees is essential to minimize their impacts on these important pollinating insects. The aim of this study was to assess the ecotoxicological status of honeybees in environments undergoing different anthropic pressure: a wood (reference site), an orchard, an agricultural area, and an urban site, using a multi-biomarker approach. To synthetically represent the ecotoxicological status of the honeybees, the responses of the single biomarkers were integrated by the Integrated Biological Response (IBRv2) index. Overall, the strongest alteration of the ecotoxicological status (IBRv2 = 7.52) was detected in the bees from the orchard due to the alteration of metabolic and genotoxicity biomarkers indicating the presence of pesticides, metals, and lipophilic compounds. Honeybees from the cultivated area (IBRv2 = 7.18) revealed an alteration especially in neurotoxicity, metabolic, and genotoxicity biomarkers probably related to the presence of pesticides, especially fungicides. Finally, in the urban area (IBRv2 = 6.60), the biomarker results (GST, lysozyme, and hemocytes) indicated immunosuppression in the honeybees and the effects of the presence of lipophilic compounds and metals in the environment.

Combined Effects of Pesticides and Electromagnetic-Fields on Honeybees: Multi-Stress Exposure

Honeybee and general pollinator decline is extensively reported in many countries, adding new concern to the general biodiversity loss. Many studies were addressed to assess the causes of pollinator decline, concluding that in most cases multi-stress effects were the most probable ones. In this research, the combined effects of two possible stress sources for bees, pesticides and electromagnetic fields (multi-stress conditions), were analyzed in the field. Three experimental sites were chosen: a control one far from direct anthropogenic stress sources, a pesticide-stress site and multi-stress one, adding to the same exposure to pesticides the presence of an electromagnetic field, coming from a high-voltage electric line. Experimental apiaries were monitored weekly for one year (from April 2017 to April 2018) by means of colony survival, queen activity, storage and brood amount, parasites and pathogens, and several biomarkers in young workers and pupae. Both exposure and effect biomarkers were analysed: among the first, acetylcholinesterase (AChE), catalase (CAT), glutathione S-transferase (GST) and alkaline phosphatase (ALP) and Reactive Oxygen Species (ROS); and among the last, DNA fragmentation (DNAFRAGM) and lipid peroxidation (LPO). Results showed that bee health conditions were the worst in the multi-stress site with only one colony alive out of the four ones present at the beginning. In this site, a complex picture of adverse effects was observed, such as disease appearance (American foulbrood), higher mortality in the underbaskets (common to pesticide-stress site), behavioral alterations (queen changes, excess of honey storage) and biochemical anomalies (higher ALP activity at the end of the season). The overall results clearly indicate that the multi-stress conditions were able to induce biochemical, physiological and behavioral alterations which severely threatened bee colony survival.

Toxicological status changes the susceptibility of the honey bee Apis mellifera to a single fungicidal spray application

During all their life stages, bees are exposed to residual concentrations of pesticides, such as insecticides, herbicides, and fungicides, stored in beehive matrices. Fungicides are authorized for use during crop blooms because of their low acute toxicity to honey bees. Thus, a bee that might have been previously exposed to pesticides through contaminated food may be subjected to fungicide spraying when it initiates its first flight outside the hive. In this study, we assessed the effects of acute exposure to the fungicide in bees with different toxicological statuses. Three days after emergence, bees were subjected to chronic exposure to the insecticide imidacloprid and the herbicide glyphosate, either individually or in a binary mixture, at environmental concentrations of 0.01 and 0.1 μg/L in food (0.0083 and 0.083 μg/kg) for 30 days. Seven days after the beginning of chronic exposure to the pesticides (10 days after emergence), the bees were subjected to spraying with the fungicide difenoconazole at the registered field dosage. The results showed a delayed significant decrease in survival when honey bees were treated with the fungicide. Fungicide toxicity increased when honey bees were chronically exposed to glyphosate at the lowest concentration, decreased when they were exposed to imidacloprid, and did not significantly change when they were exposed to the binary mixture regardless of the concentration. Bees exposed to all of these pesticide combinations showed physiological disruptions, revealed by the modulation of several life history traits related mainly to metabolism, even when no effect of the other pesticides on fungicide toxicity was observed. These results show that the toxicity of active substances may be misestimated in the pesticide registration procedure, especially for fungicides.

Physiological effects of the interaction between Nosema ceranae and sequential and overlapping exposure to glyphosate and difenoconazole in the honey bee Apis mellifera

Pathogens and pollutants, such as pesticides, are potential stressors to all living organisms, including honey bees. Herbicides and fungicides are among the most prevalent pesticides in beehive matrices, and their interaction with Nosema ceranae is not well understood. In this study, the interactions between N. ceranae, the herbicide glyphosate and the fungicide difenoconazole were studied under combined sequential and overlapping exposure to the pesticides at a concentration of 0.1 µg/L in food. In the sequential exposure experiment, newly emerged bees were exposed to the herbicide from day 3 to day 13 after emerging and to the fungicide from day 13 to day 23. In the overlapping exposure experiment, bees were exposed to the herbicide from day 3 to day 13 and to the fungicide from day 7 to day 17. Infection by Nosema in early adult life stages (a few hours post emergence) greatly affected the survival of honey bees and elicited much higher mortality than was induced by pesticides either alone or in combination. Overlapping exposure to both pesticides induced higher mortality than was caused by sequential or individual exposure. Overlapping, but not sequential, exposure to pesticides synergistically increased the adverse effect of N. ceranae on honey bee longevity. The combination of Nosema and pesticides had a strong impact on physiological markers of the nervous system, detoxification, antioxidant defenses and social immunity of honey bees.

Acute toxicity of Siltac EC to the honey bee (Apis mellifera)

<b>Different types of pesticides are commonly used in modern agriculture. Honey bees (Apis mellifera) are sensitive indicators of environmental contamination with these substances. Exposure of honey bees to pesticides can lead to changes in their behaviour and increase mortality, so it is important to develop formulations that provide alternatives to common (‘chemical’) pesticides. The preparation Siltac EC, that has recently been developed (patent no. WO 2016/061259), shows promise as an effective substitute. This preparation is based on a physical interaction with the pest. It does not contain chemicals classified as pesticides. The aim of the current study was to evaluate the toxicity of Siltac EC to adult honeybee workers. The experiments showed that both contact and oral acute toxicity were very low and the preparation can be initially considered safe for honey bees.

The Power of Drosophila melanogaster for Modeling Neonicotinoid Effects on Pollinators and Identifying Novel Mechanisms

Neonicotinoids are the most widely used insecticides in the world and are implicated in the widespread population declines of insects including pollinators. Neonicotinoids target nicotinic acetylcholine receptors which are expressed throughout the insect central nervous system, causing a wide range of sub-lethal effects on non-target insects. Here, we review the potential of the fruit fly Drosophila melanogaster to model the sub-lethal effects of neonicotinoids on pollinators, by utilizing its well-established assays that allow rapid identification and mechanistic characterization of these effects. We compare studies on the effects of neonicotinoids on lethality, reproduction, locomotion, immunity, learning, circadian rhythms and sleep in D. melanogaster and a range of pollinators. We also highlight how the genetic tools available in D. melanogaster, such as GAL4/UAS targeted transgene expression system combined with RNAi lines to any gene in the genome including the different nicotinic acetylcholine receptor subunit genes, are set to elucidate the mechanisms that underlie the sub-lethal effects of these common pesticides. We argue that studying pollinators and D. melanogaster in tandem allows rapid elucidation of mechanisms of action, which translate well from D. melanogaster to pollinators. We focus on the recent identification of novel and important sublethal effects of neonicotinoids on circadian rhythms and sleep. The comparison of effects between D. melanogaster and pollinators and the use of genetic tools to identify mechanisms make a powerful partnership for the future discovery and testing of more specific insecticides.

Lipolytic Activity of a Carboxylesterase from Bumblebee (Bombus ignitus) Venom

Bee venom is a complex mixture composed of peptides, proteins with enzymatic properties, and low-molecular-weight compounds. Although the carboxylesterase in bee venom has been identified as an allergen, the enzyme's role as a venom component has not been previously elucidated. Here, we show the lipolytic activity of a bumblebee (Bombus ignitus) venom carboxylesterase (BivCaE). The presence of BivCaE in the venom secreted by B. ignitus worker bees was confirmed using an anti-BivCaE antibody raised against a recombinant BivCaE protein produced in baculovirus-infected insect cells. The enzymatic activity of the recombinant BivCaE protein was optimal at 40 °C and pH 8.5. Recombinant BivCaE protein degrades triglycerides and exhibits high lipolytic activity toward long-chain triglycerides, defining the role of BivCaE as a lipolytic agent. Bee venom phospholipase A₂ binds to mammalian cells and induces apoptosis, whereas BivCaE does not affect mammalian cells. Collectively, our data demonstrate that BivCaE functions as a lipolytic agent in bee venom, suggesting that BivCaE will be involved in distributing the venom via degradation of blood triglycerides.

Review on Sublethal Effects of Environmental Contaminants in Honey Bees (Apis mellifera), Knowledge Gaps and Future Perspectives

Honey bees and the pollination services they provide are fundamental for agriculture and biodiversity. Agrochemical products and other classes of contaminants, such as trace elements and polycyclic aromatic hydrocarbons, contribute to the general decline of bees' populations. For this reason, effects, and particularly sublethal effects of contaminants need to be investigated. We conducted a review of the existing literature regarding the type of effects evaluated in Apis mellifera, collecting information about regions, methodological approaches, the type of contaminants, and honey bees' life stages. Europe and North America are the regions in which A. mellifera biological responses were mostly studied and the most investigated compounds are insecticides. A. mellifera was studied more in the laboratory than in field conditions. Through the observation of the different responses examined, we found that there were several knowledge gaps that should be addressed, particularly within enzymatic and molecular responses, such as those regarding the immune system and genotoxicity. The importance of developing an integrated approach that combines responses at different levels, from molecular to organism and population, needs to be highlighted in order to evaluate the impact of anthropogenic contamination on this pollinator species.