Imidacloprid activates ROS and causes mortality in honey bees (Apis mellifera) by inducing iron overload

Can Ahiflower® (Buglossoides arvensis) seed-oil supplementation help overcome the adverse effects of imidacloprid in honey bees?

In this study, we investigated the effects of nutritional supplementation as a strategy to mitigate the impacts of imidacloprid (neonicotinoid) on honey bees by using Ahiflower® (Buglossoides arvensis) seed-oil. This oil is rich in stearidonic-acid (SDA, 18:4n3), which is a precursor to eicosapentaenoic-acid (EPA) and docosahexaenoic-acid (DHA) that are known for their beneficial and protective effects. Specifically, we chronically fed newly emerged worker bees with sucrose syrup and pollen patties (control) that we supplemented with (i) imidacloprid (0.375 ng·μl-1), (ii) Ahiflower® oil (5 %) + imidacloprid (0.375 ng·μl-1), and (iii) Ahiflower® oil (5 %). Survival was recorded, and after 21 days, worker bees were sampled to measure mitochondrial respiration, ATP5A1 content, adenylate energy charge, lipid peroxidation in thorax as well as fatty acid composition and peroxidation index in whole bees. Our results indicate that (i) imidacloprid mostly hampers mitochondria, increases saturated fatty acids and decreases survival, (ii) oxidation of alternative substrates allows full recovery of mitochondrial respiration in the imidacloprid-treated group demonstrating mitochondrial flexibility, (iii) Ahiflower® oil in combination with imidacloprid partially restores mitochondrial respiration at the level of complexes I and II, restores fatty acid composition but fails to restore survival. These findings confirm the deleterious effects of imidacloprid on mitochondria while highlighting, for the first time, the potential benefits of Ahiflower® oil in mitochondrial function, though not on honey bee survival. In addition, this study highlights the importance of mitochondrial flexibility when organisms are exposed to toxicants at environmentally relevant levels.

Iron-binding transferrins regulate immunity and reproduction via tissue-specific iron redistribution in Spodoptera exigua

Transferrins are a multifunctional family of proteins that are essential for diverse physiological processes through their binding and transport of iron. Although previous studies have indicated that transferrins play crucial roles in insect antibacterial immunity and reproduction, the molecular mechanisms by which they regulate these essential processes remain poorly understood. Here, we identified and characterized transferrins in the beet armyworm, Spodoptera exigua (Hübner), an economically important agricultural pest, and elucidated their roles in innate immunity and reproduction. Four putative transferrin-coding genes were identified in the S. exigua genome, and structural analysis revealed that iron-binding domains were present exclusively in SeTsf1. Following infection with the entomopathogenic fungus Metarhizium anisopliae, SeTsf1 expression increased 3.2-fold, whereas iron levels decreased by 57.9 % in the hemolymph but increased by 51.6 % in the fat body. SeTsf1 knockdown significantly enhanced the susceptibility of S. exigua to M. anisopliae infection and abolished the hypoferremic response. Additionally, SeTsf1 silencing reduced egg production and hatching rates by 26 % and 28 %, respectively, and was accompanied by a 31 % decrease in ovarian iron content. Taken together, these findings demonstrate that SeTsf1 regulates immunity and reproduction through tissue-specific iron redistribution in S. exigua.

Landfill fire impact on bee health: beneficial effect of dietary supplementation with medicinal plants and probiotics in reducing oxidative stress and metal accumulation

The honey bee is an important pollinator insect susceptible to environmental contaminants. We investigated the effects of a waste fire event on elemental content, oxidative stress, and metabolic response in bees fed different nutrients (probiotics, Quassia amara, and placebo). The level of the elements was also investigated in honey and beeswax. Our data show a general increase in elemental concentrations in all bee groups after the event; however, the administration of probiotics and Quassia amara help fight oxidative stress in bees. Significantly lower concentrations of Ni, S, and U for honey in the probiotic group and a general and significant decrease in elemental concentrations for beeswax in the probiotic group and Li in the Quassia amara group were observed after the fire waste event. The comparison of the metabolic profiles through pre- and post-event PCA analyses showed that bees treated with different feeds react differently to the environmental event. The greatest differences in metabolic profiles are observed between the placebo-fed bees compared to the others. This study can help to understand how some stress factors can affect the health of bees and to take measures to protect these precious insects.

Effects of pollen patties with curcumin-steviol glycoside complex on Apis mellifera

The main objective of this study was to investigate the effects of pollen patty with supplementation of different concentrations of curcumin-steviol glycoside complex (CSG) in Apis mellifera (A. mellifera). Twelve colonies of A. mellifera were conducted from July 10th to August 21st for 42 days. A. mellifera were assigned to four dietary treatments with 3 replicates of equal size as follows: no supplementation of pollen patty (NC), supplementation of basal pollen patty (PC), supplementation of basal pollen diets + 0.04% of CSG (T1), supplementation of basal pollen diets + 0.08% of CSG (T2). The percentage of CSG was calculated based on the total weight of pollen patties. Thorax weight was significantly increased (p < 0.05) in the T2 diet compared with the NC and PC diet. There was no significant difference (p > 0.05) in pollen patties consumption among the PC, T1, and T2 diets. The T1 and T2 diets showed significantly higher (p < 0.05) honey production than the PC and NC diets. Also, the PC diet showed significantly higher (p < 0.05) honey production than the NC diet. The T2 showed significantly higher (p < 0.05) brood area than the PC and NC diets at 28 and 42 days. In addition, the PC and T1 diets showed significantly higher (p < 0.05) brood areas than the NC diet. The T1 and T2 diets showed significantly higher (p < 0.05) catalase and superoxide dismutase (SOD) 1 gene expression than the PC and NC diets. The expression of the thioredoxin reductase (Trxr) 1 gene was significantly higher (p < 0.05) in the T1 diet, and decreased in the order of the PC, T2, and NC diets. The expression of the SOD2 gene was significantly higher (p < 0.05) in the T1 diet than the PC and T2 diets and was significantly lower (p < 0.05) in the NC diet. Therefore, supplementation of CSG to pollen patty might be the ideal strategy to improve A. mellifera performances.

Interactions among Zinc, Iron, and Paraquat in the Physiological and Toxicological Responses of the Egyptian Cotton Leafworm Spodoptera littoralis

Agricultural pollutants co-interact and affect the vital functions, stress tolerance, resistance, immunity, and survival of insect pests. These metal-herbicide interactions have inevitable but remarkable effects on insects, which remain poorly understood. Here, we examined the effects of the interactions among zinc (Zn), iron (Fe), and paraquat (PQ) at a sublethal dose on the physiological response of the Egyptian cotton leafworm Spodoptera littoralis. Co-exposure to Zn and Fe improved leafworm survival (100% at 10-20 mg, 85% at 40 mg) compared to separate exposures. Low Zn/Fe/PQ toxicity likely stemmed from metal complexes having efficient chelating activity, enhancing resilience. Low exposure to Zn, Fe, and Zn/Fe increased food intake and larval weight and affected frass production. Interestingly, the combined application of Zn/Fe/PQ increased larval and pupal weight in surviving individuals. Zn/Fe was found to be crucial in the ecdysis of larvae into pupae, resulting in reduced larval mortality and a prolonged pupal ecdysis duration (% days). Providing important information regarding physiological responses and pest management, this study demonstrated the realistic conditions caused by the interactions of biological trace elements, such as Zn and Fe, with PQ. A disc diffusion susceptibility test in hemolymph bacteria revealed differences among Zn, Zn/Fe, and Zn/Fe/PQ, suggesting that their interaction might play an immunomodulatory role in S. littoralis.

The neonicotinoid acetamiprid reduces larval and adult survival in honeybees (Apis mellifera) and interacts with a fungicide mixture

Plant protection products (PPPs), which are frequently used in agriculture, can be major stressors for honeybees. They have been found abundantly in the beehive, particularly in pollen. Few studies have analysed effects on honeybee larvae, and little is known about effects of insecticide-fungicide-mixtures, although this is a highly realistic exposure scenario. We asked whether the combination of a frequently used insecticide and fungicides would affect developing bees. Honeybee larvae (Apis mellifera carnica) were reared in vitro on larval diets containing different PPPs at two concentrations, derived from residues found in pollen. We used the neonicotinoid acetamiprid, the combined fungicides boscalid/dimoxystrobin and the mixture of all three substances. Mortality was assessed at larval, pupal, and adult stages, and the size and weight of newly emerged bees were measured. The insecticide treatment in higher concentrations significantly reduced larval and adult survival. Interestingly, survival was not affected by the high concentrated insecticide-fungicides-mixture. However, negative synergistic effects on adult survival were caused by the low concentrated insecticide-fungicides-mixture, which had no effect when applied alone. The lower concentrated combined fungicides led to significantly lighter adult bees, although the survival was unaffected. Our results suggest that environmental relevant concentrations can be harmful to honeybees. To fully understand the interaction of different PPPs, more combinations and concentrations should be studied in social and solitary bees with possibly different sensitivities.

From molecules to organisms: A multi-level approach shows negative effects of trace elements from sewage sludge used as soil improver on honeybees

The use of sewage sludge as a soil improver has been promoted in agroecosystems. However, sludges can contain toxic trace elements because of suboptimal wastewater treatment. Nonetheless, field studies investigating the negative effects of these practices on pollinators are lacking. We collected honeybees from an area where sewage sludge use is widespread, and one where it is precluded. Trace elements in soils and bees were quantified. Cadmium, chromium, lead, mercury, and nickel were investigated because they were the least correlated elements to each other and are known to be toxic. Their levels were related to oxidative stress and energy biomarkers, midgut epithelial health, body size and wing asymmetry of honeybees. We found increased carbohydrate content in sites with higher cadmium levels, increased histological damage to the midgut epithelium in the sewage sludge area, and the presence of dark spherites in the epithelium of bees collected from the sites with the highest lead levels. Finally, we found that honeybees with the highest lead content were smaller, and that wing fluctuating asymmetry increased in sites with increasing levels of mercury. To the best of our knowledge, this is the first comprehensive study of the concentration and effects on honeybees of trace elements potentially deriving from soil amendment practices.

In-depth transcriptome and physiological function analysis reveals the toxicology of sodium fluoride in the fall webworm Hyphantria cunea

Fluoride is an environmental pollutant that severely injures various organisms in ecosystems. Herein, the non-target organism, fall webworm (Hyphantria cunea), was used to determine the toxicological mechanism of NaF exposure. In this study, H. cunea exposed to NaF showed significant declines in growth and reproduction. The authors conducted RNA sequencing on adipose bodies and midgut tissues from NaF-exposed H. cunea larvae to uncover the toxicological mechanisms. The results showed that extracellular matrix-receptor interaction, pentose and glucuronate interconversions, fatty acid biosynthesis, and ferroptosis might contribute to NaF stress. NaF significantly decreased the antioxidant level, nitrous oxide synthase activity, and NO content, while significantly increasing lipid peroxidation. NaF induced significant changes in the expression of energy metabolism genes. However, the triglyceride content was significantly decreased and the lipase enzyme activity was significantly increased. Moreover, the expression levels of light and heavy chains of ferritin were inhibited in NaF-exposed H. cunea. NaF caused ferritin Fe2+overload in FerHCH1 and FerLCH knockdown H. cunea larvae, activated reactive oxygen species, and reduced the total iron content, eventually increasing the mortality H. cunea larvae. This study identified the toxicological mechanisms of NaF in lipid synthesis and energy metabolism in H. cunea, providing a basis for understanding the molecular mechanisms of NaF toxicity and developing pollution control strategies.

Changes in the proteome of Apis mellifera acutely exposed to sublethal dosage of glyphosate and imidacloprid

Uncontrolled use of pesticides has caused a dramatic reduction in the number of pollinators, including bees. Studies on the effects of pesticides on bees have reported effects on both metabolic and neurological levels under chronic exposure. In this study, variations in the differential expression of head and thorax-abdomen proteins in Africanized A. mellifera bees treated acutely with sublethal doses of glyphosate and imidacloprid were studied using a proteomic approach. A total of 92 proteins were detected, 49 of which were differentially expressed compared to those in the control group (47 downregulated and 2 upregulated). Protein interaction networks with differential protein expression ratios suggested that acute exposure of A. mellifera to sublethal doses of glyphosate could cause head damage, which is mainly associated with behavior and metabolism. Simultaneously, imidacloprid can cause damage associated with metabolism as well as, neuronal damage, cellular stress, and impairment of the detoxification system. Regarding the thorax-abdomen fractions, glyphosate could lead to cytoskeleton reorganization and a reduction in defense mechanisms, whereas imidacloprid could affect the coordination and impairment of the oxidative stress response.

Transcriptome analysis reveals the mechanism of antifungal peptide epinecidin-1 against Botrytis cinerea by mitochondrial dysfunction and oxidative stress

The marine antifungal peptide epinecidin-1 (EPI) have been shown to inhibit Botrytis cinerea growth, while the molecular mechanism have not been explored based on omics technology. This study aimed to investigate the molecular mechanism of EPI against B. cinerea by transcriptome technology. Our findings indicated that a total of 1671 differentially expressed genes (DEGs) were detected in the mycelium of B. cinerea treated with 12.5 μmol/L EPI for 3 h, including 773 up-regulated genes and 898 down-regulated genes. Cluster analysis showed that DEGs (including steroid biosynthesis, (unsaturated) fatty acid biosynthesis) related to cell membrane metabolism were significantly down-regulated, and almost all DEGs involved in DNA replication were significantly inhibited. In addition, it also induced the activation of stress-related pathways, such as the antioxidant system, ATP-binding cassette transporter (ABC) and MAPK signaling pathways, and interfered with the tricarboxylic acid (TCA) cycle and oxidative phosphorylation pathways related to mitochondrial function. The decrease of mitochondrial related enzyme activities (succinate dehydrogenase, malate dehydrogenase and adenosine triphosphatase), the decrease of mitochondrial membrane potential and the increase content of hydrogen peroxide further confirmed that EPI treatment may lead to mitochondrial dysfunction and oxidative stress. Based on this, we speculated that EPI may impede the growth of B. cinerea through its influence on gene expression, and may lead to mitochondrial dysfunction and oxidative stress.

Effects of the insecticide imidacloprid on the post-embryonic development of the honey bee Apis mellifera (Hymenoptera: Apidae)

The widespread use of pesticides in agriculture has been linked to declines in bee populations worldwide. Imidacloprid is a widely used systemic insecticide that can be found in the pollen and nectar of plants and has the potential to negatively impact the development of bee larvae. We investigated the effects of oral exposure to a realistic field concentration (20.5 ng g-1) of imidacloprid on the midgut and fat body of Apis mellifera worker larvae. Our results showed that larvae exposed to imidacloprid exhibited changes in the midgut epithelium, including disorganization of the brush border, nuclear chromatin condensation, cytoplasm vacuolization, and release of cell fragments indication cell death. Additionally, histochemical analysis revealed that the midgut brush border glycocalyx was disorganized in exposed larvae. The fat body cells of imidacloprid-exposed larvae had a decrease in the size of lipid droplets from 50 to 8 μm and increase of 100 % of protein content, suggesting possible responses to the stress caused by the insecticide. However, the expression of de cdc20 gene, which plays a role in cell proliferation, was not affected in the midgut and fat body of treated larvae. These results suggest that imidacloprid negatively affects non-target organs during the larval development of A. mellifera potentially impacting this important pollinator species.

Application of pesticide application measures to reduce residue based on the metabolic transfer law of imidacloprid in banana leaves and soil

An investigation of the metabolism and transfer of imidacloprid (IMI) in banana plants and soil was performed using high-resolution mass spectrometry. Results indicated the presence of eight IMI metabolites in soil and leaves that resulted from hydroxylation of the imidazolidine ring, the reduction and loss of nitro groups, and oxidative cleavage of methylene bridges. Six metabolites, including 4/5-hydroxy IMI (4/5-hydroxy), IMI olefin (olefin), and 6-chloronicotinic acid (6-CNA), were detected in the fruits following leaf treatment, while only three were detected after soil treatment. Quantitative analysis showed that the total amount of imidacloprid and its metabolites transferred from leaves to fruits was higher than that transferred from soil to fruits. Therefore, leaf transfer was considered the main means by which IMI and its metabolites transferred to banana fruits. We found that adjuvants tank-mixed with IMI could reduce the total concentration of pesticide transfer from leaves to fruits, especially reducing the amount of metabolites transformed from the reduction and loss of nitro groups and oxidative cleavage of methylene bridges, thus reducing the pesticide residue in fruits and achieving the purpose of reducing the safety risk.

Antibacterial peptides from Monochamus alternatus induced oxidative stress and reproductive defects in pine wood nematode through the ERK/MAPK signaling pathway

Pine wilt disease is a devastating disease of pine caused by the pine wood nematode (PWN) Bursaphelenchus xylophilus. Long-term use of chemical nematicides leads to the development of resistance in nematodes and harms the environment. Evaluations for green environmental protection agents, identified the antibacterial peptide, MaltDef1, from Monochamus alternatus which had nematicidal effect. We studied its nematicidal activity and action against PWN. In this study, the antibacterial peptide S-defensin was synthesized from M. alternatus. The results showed that S-defensin caused mortality to the PWN, causing shrinkage, pore, cell membrane dissolution and muscle atrophy. In addition, PWN reproduction was also affected by S-defensin; it decreased in a concentration dependent manner with increasing treatment concentration. By contrast, reactive oxygen species (ROS) in vivo increased in a concentration-dependent manner. We applied transcriptome to analyze the changes in gene expressions in S-defensin treated PWN, and found that the most significantly enriched pathway was the ERK/MAPK signaling pathway. RNAi was used to validate the functions of four differential genes (Let-23, Let-60, Mek-2 and Lin-1) in this pathway. The results showed that knockdown of these genes significantly decreased the survival rate and reproductive yield of, and also increased ROS in PWN. The antibacterial peptide S-defensin had a significant inhibitory effect on the survival and reproduction of PWN, shown by cell membrane damage and intracellular biological oxidative stress via regulating the ERK/MAPK signaling pathway. This indicates that S-defensin has a target in B. xylophilus, against which new green target pesticides can be developed.

Proteomics and Immune Response Differences in Apis mellifera and Apis cerana Inoculated with Three Nosema ceranae Isolates

Nosema ceranae infects midgut epithelial cells of the Apis species and has jumped from its original host A. cerana to A. mellifera worldwide, raising questions about the response of the new host. We compared the responses of these two species to N. ceranae isolates from A. cerana, A. mellifera from Thailand and A. mellifera from France. Proteomics and transcriptomics results were combined to better understand the impact on the immunity of the two species. This is the first combination of omics analyses to evaluate the impact of N. ceranae spores from different origins and provides new insights into the differential immune responses in honeybees inoculated with N. ceranae from original A. cerana. No difference in the antimicrobial peptides (AMPs) was observed in A. mellifera, whereas these peptides were altered in A. cerana compared to controls. Inoculation of A. mellifera or A. cerana with N. ceranae upregulated AMP genes and cellular-mediated immune genes but did not significantly alter apoptosis-related gene expression. A. cerana showed a stronger immune response than A. mellifera after inoculation with different N. ceranae isolates. N. ceranae from A. cerana had a strong negative impact on the health of A. mellifera and A. cerana compared to other Nosema isolates.

Ferric citrate-induced colonic mucosal damage associated with oxidative stress, inflammation responses, apoptosis, and the changes of gut microbial composition

Ferric citrate (FC) has been used as an iron fortifier and nutritional supplement, which is reported to induce colitis in rats, however the underlying mechanism remains to be elucidated. We performed a 16-week study of FC in male healthy C57BL/6 mice (nine-month-old) with oral administration of Ctr (0.9 % NaCl), 1.25 % FC (71 mg/kg/bw), 2.5 % FC (143 mg/kg/bw) and 5 % FC (286 mg/kg/bw). FC-exposure resulted in colon iron accumulation, histological alteration and reduce antioxidant enzyme activities, such as glutathione (GSH), glutathione peroxidase (GSH-Px), superoxide dismutase (SOD) and total antioxidant capacity (T-AOC), together with enhanced lipid peroxidation level, including malondialdehyde (MDA) level and 4-Hydroxynonenal (4-HNE) protein expression. Exposure to FC was associated with upregulated levels of the interleukin (IL)- 6, IL-1β, IL-18, IL-8 and tumor necrosis factor α (TNF-α), while down-regulated levels of IL-4 and IL-10. Exposure to FC was positively associated with the mRNA and protein expressions of cysteine-aspartic proteases (Caspase)- 9, Caspase-3, Bcl-2-associated X protein (Bax), while negatively associated with B-cell lymphoma 2 (Bcl2) in mitochondrial apoptosis signaling pathway. FC-exposure changed the diversity and composition of gut microbes. Additionally, the serum lipopolysaccharide (LPS) contents increased in FC-exposed groups when compared with the control group, while the expression of colonic tight junction proteins (TJPs), such as Claudin-1 and Occludin were decreased. These findings indicate that the colonic mucosal injury induced by FC-exposure are associated with oxidative stress generation, inflammation response and cell apoptosis, as well as the changes in gut microbes diversity and composition.

Imidacloprid degrading efficiency of Pseudomonas plecoglossicida MBSB-12 isolated from pesticide contaminated tea garden soil of Assam

Long-term use of toxic pesticides in agricultural grounds has led to adverse effects on the environment and human health. Microbe-mediated biodegradation of pollutants is considered an effective strategy for the removal of contaminants in agricultural and environmental sustainability. Imidacloprid, a neonicotinoid class of pesticides, was widely applied insecticide in the control of pests in agricultural fields including the tea gardens of Assam. Here, native bacteria from imidacloprid contaminating tea garden soils were isolated and screened for imidacloprid degradation efficiency under laboratory conditions. Out of the 30 bacterial isolates, 4 were found to tolerate high concentrations of imidacloprid (25,000 ppm), one of which isolate MBSB-12 showed the highest efficiency for imidacloprid tolerance and utilization as the sole carbon source. Morphological, biochemical, and 16 S ribosomal RNA gene sequencing-based characterization revealed the isolate as Pseudomonas plecoglossicida MBSB-12. The isolate reduced 87% of extractable imidacloprid from the treated soil in 90 days compared to the control soil (without bacterial treatment). High-Resolution Mass Spectrometry (HRMS) analysis indicated imidacloprid breakdown to comparatively less harmful products viz., imidacloprid guanidine olefin [m/z = 209.0510 (M + H)⁺], imidacloprid urea [m/z = 212.0502 (M + H)⁺] and a dechlorinated degraded product of imidacloprid with m/z value 175.0900 (M + H)⁺. Further investigation on the molecular machinery of P. plecoglossicida MBSB-12 involved in the degradation of imidacloprid is expected to provide a better understanding of the degradation pathway.

Characterisation of the heat shock protein Tid and its involvement in stress response regulation in Apis cerana

Objective: The impact of various environmental stresses on native Apis cerana cerana fitness has attracted intense attention in China. However, the defence responses of A. cerana cerana to different stressors are poorly understood. Here, we aimed to elucidate the regulatory mechanism mediated by the tumorous imaginal discs (Tid) protein of A. cerana cerana (AccTid) in response to stressors. Methods: We used some bioinformatics softwares to analyse the characterisation of Tid. Then, qRT-PCR, RNA interference and heat resistance detection assays were used to explore the function of Tid in stress response in A. cerana cerana. Results: AccTid is a homologous gene of human Tid1 and Drosophila Tid56, contains a conserved J domain and belongs to the heat shock protein DnaJA subfamily. The level of AccTid induced expression was increased under temperature increases from 40°C to 43°C and 46°C, and AccTid knockdown decreased the heat resistance of A. cerana cerana, indicating that the upregulation of AccTid plays an important role when A. cerana cerana is exposed to heat stress. Interestingly, contrary to the results of heat stress treatment, the transcriptional level of AccTid was inhibited by cold, H₂O₂ and some agrochemical stresses and showed no significant change under ultraviolet ray and sodium arsenite stress. These results suggested that the requirement of A. cerana cerana for Tid differs markedly under different stress conditions. In addition, knockdown of AccTid increased the mRNA levels of some Hsps and antioxidant genes. The upregulation of these Hsps and antioxidant genes may be a functional complement of AccTid knockdown. Conclusion: AccTid plays a crucial role in A. cerana cerana stress responses and may mediate oxidative damage caused by various stresses. Our findings will offer fundamental knowledge for further investigations of the defence mechanism of A. cerana cerana against environmental stresses.