Formetanate toxicity and changes in antioxidant enzyme system of Apis mellifera larvae

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.

The role of the veterinary diagnostic toxicologist in apiary health

Susceptibility of individuals and groups to toxicants depends on complex interactions involving the host, environment, and other exposures. Apiary diagnostic investigation and honey bee health are truly population medicine: the colony is the patient. Here we provide basic information on the application of toxicology to the testing of domestic honey bees, and, in light of recent research, expand on some of the challenges of interpreting analytical chemistry findings as they pertain to hive health. The hive is an efficiently organized system of wax cells used to store brood, honey, and bee bread, and is protected by the bee-procured antimicrobial compound propolis. Toxicants can affect individual workers outside or inside the hive, with disease processes that range from acute to chronic and subclinical to lethal. Toxicants can impact brood and contaminate honey, bee bread, and structural wax. We provide an overview of important natural and synthetic toxicants to which honey bees are exposed; behavioral, husbandry, and external environmental factors influencing exposure; short- and long-term impacts of toxicant exposure on individual bee and colony health; and the convergent impacts of stress, nutrition, infectious disease, and toxicant exposures on colony health. Current and potential future toxicology testing options are included. Common contaminants in apiary products consumed or used by humans (honey, wax, pollen), their sources, and the potential need for product testing are also noted.

Acute oral toxicity, apoptosis, and immune response in nurse bees (Apis mellifera) induced by flupyradifurone

The potential toxicity of flupyradifurone (FPF) to honey bees has been a subject of controversy in recent years. Understanding the effect of pesticides on nurse bees is important because the fitness of nurse bees is critical for in-hive activities, such as larval survival and performing hive maintenance. In order to evaluate the acute oral toxicity of flupyradifurone on nurse bees, flupyradifurone at five different concentrations was selected to feed both larvae and nurse bees. Our results showed that nurse bees were more sensitive to flupyradifurone than larvae (LD50 of the acute oral toxicity of flupyradifurone was 17.72 μg a.i./larva and 3.368 μg a.i./nurse bee). In addition, the apoptotic rates of neurons in mushroom bodies of nurse bees were significantly induced by flupyradifurone at sublethal concentrations (8 mg/L, 20 mg/L, and 50 mg/L) and the median lethal concentration LC50 (125 mg/L). The expression of immune-related genes (Hsp90, Toll-8/Tollo, and defensin) was significantly changed in exposed nurse bees at the field-realistic concentration of flupyradifurone. However, three detoxifying enzyme genes (CYP9Q1, -2, and -3) were not affected by pesticide exposure. Our data suggest that although flupyradifurone had a relatively lower acute oral toxicity than many other common pesticides, exposures to the field-realistic and other sublethal concentrations of flupyradifurone still have cytotoxicity and immune-responsive effects on nurse bees. Therefore, flupyradifurone should be considered for its application in crops.

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.

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

BACKGROUND

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

RESULTS

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

CONCLUSION

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

The effects of beta-cypermethrin, chlorbenzuron, chlorothalonil, and pendimethalin on Apis mellifera ligustica and Apis cerana cerana larvae reared in vitro

BACKGROUND

Declines in bee populations and diversity have drawn international attention. The long-term use of chemical pesticides has affected bee behavior and physiology. This study aimed to investigate the effects of chronic exposure to four commonly used chemical pesticides (beta-cypermethrin, chlorbenzuron, chlorothalonil and pendimethalin) on the growth of Apis mellifera ligustica and Apis cerana cerana larvae reared in vitro.

RESULTS

Pesticide type and concentration were the main factors affecting honeybee fitness. Beta-cypermethrin and chlorbenzuron had chronic toxic effects on bee larvae. They reduced the fitness of A. m. ligustica and A. c. cerana even at low doses of 323.5 ng g^-1 for beta-cypermethrin and 62.6 ng g^-1 for chlorbenzuron in bee bread. The effects were positively associated with the dietary amounts of pesticides. By contrast, chlorothalonil and pendimethalin exposure did not affect bee larvae despite changes in enzyme activities. Caution is still needed with chlorothalonil, which led to a decrease in harvest adult bee numbers at a high dose (6937.2 ng g^-1 ). Furthermore, a difference in pesticide resistance was observed, suggesting that A. m. ligustica may tolerate toxic effects better than A. c. cerana.

CONCLUSION

This study sheds new light on chronic toxicity in bee larvae exposed to residues in bee bread. The results could guide the scientific and rational use of chemical pesticides to reduce the potential risks to A. m. ligustica and A. c. cerana. © 2021 Society of Chemical Industry.

Harmful effects of fipronil exposure on the behavior and brain of the stingless bee Partamona helleri Friese (Hymenoptera: Meliponini)

Fipronil is a pesticide widely used to control agricultural and household insect pests. However, fipronil is highly toxic to non-target insects, including pollinators. In this study, we investigated the acute effects of fipronil on the behavior, brain morphology, antioxidant activity, and proteins related to signaling pathways on the brain of workers of the stingless bee Partamona helleri. The ingestion of fipronil increases both the walking distance and velocity and causes enlarged intercellular spaces in the Kenyon cells and intense vacuolization in the neuropils of the brain. Moreover, fipronil decreases the activity of catalase (CAT) and increases the activity of glutathione S-transferase (GST). However, there is no difference in superoxide dismutase (SOD) activity between the control and fipronil. Regarding immunofluorescence analysis, bees exposed to fipronil showed an increase in the number of cells positive for cleaved caspase-3 and peroxidase, but a reduction in the number of cells positive for ERK 1/2, JNK and Notch, suggesting neuron death and impaired brain function. Our results demonstrate that fipronil has harmful effects on the behavior and brain of a stingless bee, which may threaten the individuals and colonies of this pollinator.

Sublethal effects of Isoclast™ Active (50% sulfoxaflor water dispersible granules) on larval and adult worker honey bees (Apis mellifera L.)

Sulfoxaflor is a novel sulfoximine insecticide which is widely used to control crop pests. Risk assessments have reported its high toxicity to pollinators. However, sulfoxaflor is not persistent in the environment and few studies have addressed its negative effects on larval and newly emerged honeybees at environmentally relevant concentrations. In the present study, the sublethal effects of a sulfoxaflor commercial product, Isoclast™ Active, were evaluated in the laboratory using larvae and newly emerged worker honeybees. The results of 96-h acute toxicity showed that Isoclast is moderately toxic to adult bees, and it could induce significant death and growth failure of larvae after continuous dietary intake. In addition, Isoclast induced significant changes in antioxidative (SOD, CAT), lipid peroxidation (POD, LPO, MDA), detoxification (GST, GR, GSH) and signal transduction-related (AChE, ACh) enzymes or products both in larvae and adult honey bees under residue levels. Here we firstly reported the lethal and sublethal effects of commercial sulfoxaflor to honeybees' larvae and young workers. All these findings revealed the potential risks of sulfoxaflor residue in environment to honey bees, and may also to other pollinators. This is a laboratory mimic studies, and further studies are still needed to investigate the risks and in-depth mechanisms of sulfoxaflor to bees in field.

Identification of glutathione-S-transferase genes by transcriptome analysis in Meteorus pulchricornis (Hymenoptera: Braconidae) and their expression patterns under stress of phoxim and cypermethrin

Meteorus pulchricornis (Wesmael) (Hymenoptera: Braconidae) is a preponderant endoparasitoid wasp, attacking the larvae of many lepidopteran pests. We present the first body transcriptome dataset for M. pulchricornis. In total, 50,781,796 clean reads were obtained and 33,144 unigenes were assembled; 15,458 unigenes showed a significant similarity (E value < 10^-5) to known proteins in the NCBI non-redundant protein database. Gene ontology and cluster of orthologous group analyses were performed to classify the functions of genes. To better understand the role of glutathione-S-transferases (GSTs) in detoxification mechanism in M. pulchricornis, we identified seventeen GST genes (MpulGSTs) from the body transcriptome. Among these, fifteen MpulGSTs belonged to cytosolic GSTs and the other two belonged to microsomal classes. The cytosolic GSTs were classified into four different clades: four in delta, three in omega, seven in sigma, and one in zeta. The expression levels of these MpulGSTs after exposure to sub-lethal concentrations of phoxim and cypermethrin were determined using real-time quantitative polymerase chain reaction: seven MpulGSTs (MpulGSTD3, MpulGSTS1, MpulGSTS2, MpulGSTS4, MpulGSTS6 MpulGSTO3, and MpulGSTmic1) and 11 MpulGSTs (MpulGSTD1, MpulGSTD2, MpulGSTD3, MpulGSTO2, MpulGSTS1, MpulGSTS2, MpulGSTS3, MpulGSTS4, MpulGSTS5, MpulGSTS7, and MpulGSTmic1) were highly expressed, respectively. These results suggested that GST genes may play a pivotal role in detoxification process in M. pulchricornis. Our findings would provide a theoretical base for elucidating insecticide susceptibility and should promote functional research on specific GST genes in parasitoid wasps.

Toxicity of oxalic acid and impact on some antioxidant enzymes on in vitro-reared honeybee larvae

Nowadays, Varroa destructor is considered as a serious pest of honeybees (Apis mellifera) and its resistance to acaricides has been reported in Europe since the early 1990s. That is why new methods of treatment for Varroa mites are still in focus of many scientists. In our study, we determined the lethal concentration LC₅₀ (72 h) of 2.425% oxalic acid solution following single spray exposure of honeybee larvae under laboratory conditions (Guideline OECD 237 2013). Potential sublethal effects of oxalic acid were monitored through the determination of the activity of antioxidant enzymes. Activation of primary antioxidant enzymes was observed at 1.75% of oxalic acid; 3.5% of oxalic acid brought on a statistically significant increase of glutathione S-transferase activity. This change was accompanied by an increase in thiobarbituric acid reactive substances, products of lipid peroxidation. Our results indicate that oxalic acid may be harmful to bee brood when present during application.

Chronic toxicity of clothianidin, imidacloprid, chlorpyrifos, and dimethoate to Apis mellifera L. larvae reared in vitro

BACKGROUND

The effects of chronic exposure to two neonicotinoids (clothianidin and imidacloprid) and two organophosphates (chlorpyrifos and dimethoate) on survival, developmental rate and larval weight of honey bee larvae reared in vitro were determined. Diets containing chemicals were fed to larvae with the range of concentrations for each compound based on published acute toxicity experiments and residues found in pollen and nectar, both components of the larval diet.

RESULTS

Four concentrations of each compound and controls were tested: chlorpyrifos: 0.5, 0.8, 1.2, 8 mg/L; clothianidin: 0.1, 0.4, 2, 10 mg L^-1 ; dimethoate: 0.02, 1, 6, 45 mg L^-1 ; imidacloprid: 0.4, 2, 4, 10 mg L^-1 ; positive control: dimethoate (45 mg L^-1 ); solvent control: acetone or methanol; and negative control. A significant decrease in survival, relative to the solvent control, occurred in the 0.8, 1.2 and 8 mg L^-1 chlorpyrifos, 0.4, 2 and 10 mg L^-1 clothianidin, and 45 mg L^-1 dimethoate diets, but not the imidacloprid diets.

CONCLUSION

The treatment of larval diets with clothianidin, dimethoate and imidacloprid did not affect survival, developmental rate, or weight of immature honey bees; however, treatment with chlorpyrifos did. Overall, our results are valuable for evaluating the chronic toxicity of these pesticides to developing honey bees. © 2018 Society of Chemical Industry.

Effect of Sublethal Doses of Imidacloprid on the Biological Performance of Aphid Endoparasitoid Aphidius gifuensis (Hymenoptera: Aphidiidae) and Influence on Its Related Gene Expression

The integrated pest management (IPM) strategy was developed and used in combination with pesticides and beneficial biological control agents. To further develop IPM efficiency, it is important to evaluate the side effects of pesticides on biological control agents. Aphidius gifuensis is one of the most important aphid natural enemies and has been successfully used to control Myzys persicae and other aphid species. Imidacloprid (IMD) is a popular pesticide used worldwide and is highly toxic to non-target arthropods. Here, we investigated the short-term sublethal toxicity of IMD in Aphidius gifuensis and its impact on the biological performance and gene expression of this parasitoid. We found that sublethal IMD doses had a significant negative effect on the life history traits of female A. gifuensis, including shortening the lifespan and lowering parasitic capacity. Moreover, exposure to sublethal IMD also adversely affected the response of A. gifuensis to aphid-infested plant volatiles. Based on the transcriptome analysis, we found that the exposure to sublethal IMD doses significantly affected expression of genes involved in the central nervous system, energy metabolism, olfactory, and detoxification system of A. gifuensis. RT-qPCR also revealed that short term expose to sublethal IMD doses significantly induced the gene expression of genes related to the central nervous system (nAChRa7, nAChRa9, TbH, OAR1, NFR, TYR, and DAR1), olfactory system (OR28 and IR8a1), and detoxification system (CYP49p3, CYP6a2, and POD), while it suppressed the expression of genes involved in the central nervous system (nAChRa4 and nAChRb1), olfactory system (Orco1, IR8a2, and GR1), and detoxification system (GST2). Furthermore, exposure to sublethal doses of IMD also significantly increased the activities of CarEs and POD, whereas we observed no influence on the activities of CAT, GST, and SOD. Our results indicate that sublethal IMD doses might adversely affect the biological performance of A. gifuensis by altering gene expression related to the function of olfactory, nervous, energy metabolism, and detoxification systems. Thus, how the use of pesticides directly affect insect population should be considered when used in conjunction with natural pest parasitoids in IPM strategies.

The impacts of chlorothalonil and diflubenzuron on Apis mellifera L. larvae reared in vitro

Chlorothalonil is a broad-spectrum fungicide and diflubenzuron is an insect growth regulator used to control many insect larvae feeding on agricultural, forest and ornamental plants. Honey bee larvae may be exposed to both via contaminated pollen, in the form of beebread, added to their diet by their adult nurse sisters. In this study, we determined how single (acute: 72 h mortality) and repeated (chronic: mortality until emergence as adults) exposure to chlorothalonil and diflubenzuron in their diet affected honey bee larvae reared in vitro. The tested doses of chlorothalonil (20, 100, or 200 mg/L) did not impact 72 h larval mortality acutely relative to that of the solvent control. The 72 h mortality of larvae exposed to 1.6 mg/L and higher doses of diflubenzuron acutely in their diet (47.2-63.9% mortality) was significantly higher than that of larvae fed the solvent control, with no predictable dose dependent pattern observed. In the chronic toxicity tests, consuming an artificial diet with 30 or 100 mg/L chlorothalonil and 0.8, 1.3 or 2 mg/L diflubenzuron significantly lowered the survival of honey bee larvae over that of larvae feeding on the solvent control diet. We calculated risk quotients (RQs) for both compounds using the data we generated in our experiments. Collectively, the RQs suggest that neither compound is likely to affect larval mortality directly at field relevant doses given that pollen composes only a fraction of the total larval diet. Nevertheless, our data do not preclude any sublethal effects that chronic exposure to either compound may cause.

The Herbicide Glyphosate Negatively Affects Midgut Bacterial Communities and Survival of Honey Bee during Larvae Reared in Vitro

Effects of glyphosate on survival, developmental rate, larval weight, and midgut bacterial diversity of Apis mellifera were tested in the laboratory. Larvae were reared in vitro and fed diet containing glyphosate 0.8, 4, and 20 mg/L. The dependent variables were compared with negative control and positive control (dimethoate 45 mg/L). Brood survival decreased in 4 or 20 mg/L glyphosate treatments but not in 0.8 mg/L, and larval weight decreased in 0.8 or 4 mg/L glyphosate treatments. Exposure to three concentrations did not affect the developmental rate. Furthermore, the intestinal bacterial communities were determined using high-throughput sequencing targeting the V3-V4 regions of the 16S rDNA. All core honey bee intestinal bacterial phyla such as Proteobacteria (30.86%), Firmicutes (13.82%), and Actinobacteria (11.88%) were detected, and significant changes were found in the species diversity and richness in 20 mg/L glyphosate group. Our results suggest that high concentrations of glyphosate are deleterious to immature bees.

Acute toxicity of five pesticides to Apis mellifera larvae reared in vitro

BACKGROUND

The reported high loss rates of managed honey bee colonies have been attributed to diverse stressors including pesticides. Honey bee larvae can be exposed to pesticides in contaminated nectar, pollen and wax. Due to the difficulties of rearing larvae in vitro, research focusing on adult bee exposure to pesticides is more common than that on larva exposure to pesticides. Herein, we aimed to assess the acute toxicity of five insecticides to honey bee larvae using an improved in vitro rearing method.

RESULTS

LC₅₀ and LD₅₀ were calculated for larvae at 72 h following a single diet exposure administered when the larvae were 84 ± 12 h old. Solvent control larval mortalities were less than 15% at 72 h. The LC₅₀ values (mg L^-1 ) for each tested pesticide were as follows: amitraz, 494.27; chlorpyrifos, 15.39; coumaphos, 90.01; fluvalinate, 27.69; and imidacloprid, 138.84. The LD₅₀ values in µg per larva were 14.83 (amitraz), 0.46 (chlorpyrifos), 2.70 (coumaphos), 0.83 (fluvalinate) and 4.17 (imidacloprid).

CONCLUSION

The toxicity of the test pesticides to honey bee larvae from most to least toxic was chlorpyrifos > fluvalinate > coumaphos = imidacloprid > amitraz. © 2017 Society of Chemical Industry.