A deficit of detoxification enzymes: pesticide sensitivity and environmental response in the honeybee

Unravelling the microplastic menace: Different polymers additively increase bee vulnerability

Microplastics (MPs) are growing and ubiquitous environmental pollutants and represent one of the greatest contemporary challenges caused by human activities. Current research has predominantly examined the singular toxicological effects of individual polymers, neglecting the prevailing reality of organisms confronted with complex contaminant mixtures and potential synergistic effects. To fill this research gap, we investigated the lethal and sublethal effects of two common MPs, polystyrene (PS - 4.8-5.8 μm) and poly(methyl methacrylate) (PMMA - 1-40 μm), and their combination (MIX), on the pollinating insect Apis mellifera. For each treatment, we evaluated the oral toxicity of two ecologically relevant and one higher concentration (0.5, 5 and 50 mg/L) and analysed their effects on the immune system and worker survival. As immune activation can alter the cuticular hydrocarbon profile of honey bees, we used gas chromatography-mass spectrometry (GC-MS) to investigate whether MPs lead to changes in the chemical profile of foragers and behavioural assay to test whether such changes affect behavioural patterns of social recognition, undermining overall colony integrity. The results indicate an additive negative effect of PS and PMMA on bee survival and immune response, even at ecologically relevant concentrations. Furthermore, alterations in cuticle profiles were observed with both MPs at the highest and intermediate concentrations, with PMMA being mainly responsible. Both MPs exposure resulted in a reduction in the abundance of several cuticular compounds. Hive entry guards did not show increased inspection or aggressive behaviour towards exposed foragers, allowing them to enter the colony without being treated differently from uncontaminated foragers. These findings raise concerns not only for the health of individual bees, but also for the entire colony, which could be at risk if contaminated nestmates enter the colony undetected, allowing MPs to spread throughout the hive.

Mechanisms of Pathogen and Pesticide Resistance in Honey Bees

Bees are the most important insect pollinators of the crops humans grow, and Apis mellifera, the Western honey bee, is the most commonly managed species for this purpose. In addition to providing agricultural services, the complex biology of honey bees has been the subject of scientific study since the 18th century, and the intricate behaviors of honey bees and ants, fellow hymenopterans, inspired much sociobiological inquest. Unfortunately, honey bees are constantly exposed to parasites, pathogens, and xenobiotics, all of which pose threats to their health. Despite our curiosity about and dependence on honey bees, defining the molecular mechanisms underlying their interactions with biotic and abiotic stressors has been challenging. The very aspects of their physiology and behavior that make them so important to agriculture also make them challenging to study, relative to canonical model organisms. However, because we rely on A. mellifera so much for pollination, we must continue our efforts to understand what ails them. Here, we review major advancements in our knowledge of honey bee physiology, focusing on immunity and detoxification, and highlight some challenges that remain.

Emerging trends to replace pesticides with nanomaterials: Recent experiences and future perspectives for ecofriendly environment

Despite the widespread usage to safeguard crops and manage pests, pesticides have detrimental effects on the environment and human health. The necessity to find sustainable agricultural techniques and meet the growing demand for food production has spurred the quest for pesticide substitutes other than traditional ones. The unique qualities of nanotechnology, including its high surface area-to-volume ratio, controlled release, and better stability, have made it a promising choice for pest management. Over the past ten years, there has been a noticeable growth in the usage of nanomaterials for pest management; however, concerns about their possible effects on the environment and human health have also surfaced. The purpose of this review paper is to give a broad overview of the worldwide trends and environmental effects of using nanomaterials in place of pesticides. The various types of nanomaterials, their characteristics, and their possible application in crop protection are covered. The limits of the current regulatory frameworks for nanomaterials in agriculture are further highlighted in this review. Additionally, it describes how standard testing procedures must be followed to assess the effects of nanomaterials on the environment and human health before their commercialization. In order to establish sustainable and secure nanotechnology-based pest control techniques, the review concludes by highlighting the significance of taking into account the possible hazards and benefits of nanomaterials for pest management and the necessity of an integrated approach. It also emphasizes the importance of more investigation into the behavior and environmental fate of nanomaterials to guarantee their safe and efficient application in agriculture.

Synergistic resistance of honeybee (Apis mellifera) and their gut microorganisms to fluvalinate stress

Fluvalinate is widely used in the control of Varroa destructor, but its residues in colonies threaten honeybees. The effect of fluvalinate-induced dysbiosis on honeybee-related gene expression and the gut microenvironment of honeybees has not yet been fully elucidated. In this study, two-day-old larvae to seven-day-old adult worker bees were continuously fed different amounts of fluvalinate-sucrose solutions (0, 0.5, 5, and 50 mg/kg), after which the expression levels of two immune-related genes (Hymenoptaecin and Defensin1) and three detoxication-related genes (GSTS3, CAT, and CYP450) in worker bees (1, 7, and 20 days old) were measured. The effect of fluvalinate on the gut microbes of worker bees at seven days old also was explored using 16S rRNA Illumina deep sequencing. The results showed that exposure of honeybees to the insecticide fluvalinate affected their gene expression and gut microbial composition. As the age of honeybees increased, the effect of fluvalinate on the expression of Hymenoptaecin, CYP450, and CAT decreased, and the abundance of honeybee gut bacteria was affected by increasing the fluvalinate concentration. These findings provide insights into the synergistic defense of honeybee hosts against exogenous stresses in conjunction with honeybee gut microbes.

Neonicotinoid exposure increases Varroa destructor (Mesostigmata: Varroidae) mite parasitism severity in honey bee colonies and is not mitigated by increased colony genetic diversity

Agrochemical exposure is a major contributor to ecological declines worldwide, including the loss of crucial pollinator species. In addition to direct toxicity, field-relevant doses of pesticides can increase species' vulnerabilities to other stressors, including parasites. Experimental field demonstrations of potential interactive effects of pesticides and additional stressors are rare, as are tests of mechanisms via which pollinators tolerate pesticides. Here, we controlled honey bee colony exposure to field-relevant concentrations of 2 neonicotinoid insecticides (clothianidin and thiamethoxam) in pollen and simultaneously manipulated intracolony genetic heterogeneity. We showed that exposure increased rates of Varroa destructor (Anderson and Trueman) parasitism and that while increased genetic heterogeneity overall improved survivability, it did not reduce the negative effect size of neonicotinoid exposure. This study is, to our knowledge, the first experimental field demonstration of how neonicotinoid exposure can increase V. destructor populations in honey bees and also demonstrates that colony genetic diversity cannot mitigate the effects of neonicotinoid pesticides.

Transcriptomic analysis of Anopheles gambiae from Benin reveals overexpression of salivary and cuticular proteins associated with cross-resistance to pyrethroids and organophosphates

BACKGROUND

Insecticide resistance (IR) is one of the major threats to malaria vector control programs in endemic countries. However, the mechanisms underlying IR are poorly understood. Thus, investigating gene expression patterns related to IR can offer important insights into the molecular basis of IR in mosquitoes. In this study, RNA-Seq was used to characterize gene expression in Anopheles gambiae surviving exposure to pyrethroids (deltamethrin, alphacypermethrin) and an organophosphate (pirimiphos-methyl).

RESULTS

Larvae of An. gambiae s.s. collected from Bassila and Djougou in Benin were reared to adulthood and phenotyped for IR using a modified CDC intensity bottle bioassay. The results showed that mosquitoes from Djougou were more resistant to pyrethroids (5X deltamethrin: 51.7% mortality; 2X alphacypermethrin: 47.4%) than Bassila (1X deltamethrin: 70.7%; 1X alphacypermethrin: 77.7%), while the latter were more resistant to pirimiphos-methyl (1.5X: 48.3% in Bassila and 1X: 21.5% in Djougou). RNA-seq was then conducted on resistant mosquitoes, non-exposed mosquitoes from the same locations and the laboratory-susceptible An. gambiae s.s. Kisumu strain. The results showed overexpression of detoxification genes, including cytochrome P450s (CYP12F2, CYP12F3, CYP4H15, CYP4H17, CYP6Z3, CYP9K1, CYP4G16, and CYP4D17), carboxylesterase genes (COEJHE5E, COE22933) and glutathione S-transferases (GSTE2 and GSTMS3) in all three resistant mosquito groups analyzed. Genes encoding cuticular proteins (CPR130, CPR10, CPR15, CPR16, CPR127, CPAP3-C, CPAP3-B, and CPR76) were also overexpressed in all the resistant groups, indicating their potential role in cross resistance in An. gambiae. Salivary gland protein genes related to 'salivary cysteine-rich peptide' and 'salivary secreted mucin 3' were also over-expressed and shared across all resistant groups.

CONCLUSION

Our results suggest that in addition to metabolic enzymes, cuticular and salivary gland proteins could play an important role in cross-resistance to multiple classes of insecticides in Benin. These genes warrant further investigation to validate their functional role in An. gambiae resistance to insecticides.

Exploring honey bee toxicological data as a proxy for assessing dimethoate sensitivity in stingless bees

The high diversity and distinctive characteristics of stingless bees pose challenges in utilizing toxicity test results for agrochemical registrations. Toxicity assessments were performed on 15 stingless bee species, along with the honey bee, using the insecticide dimethoate, following adapted OECD protocols. Median lethal doses over 24 h (24 h-LD50) were determined for exposure routes (acute oral or contact) and species. Species sensitivity distribution (SSD) curves were constructed and the 5% hazard doses (HD5) were estimated based on 24 h-LD50 values. The SSD curve was adjusted as the body weight and dimethoate response were correlated. Lighter bees (<10 mg) had lower 24 h-LD50 values. Contact exposure for adjusted HD5 suggested insufficient protection for Melipona mondury, whereas the oral exposure HD5 indicated no risks for the other 14 species. Comprehensive risk assessments are crucial for understanding the agrochemical impact on stingless bees, emphasizing the need for a broader species range in formulating conservation strategies.

Social life results in social stress protection: a novel concept to explain individual life-history patterns in social insects

Resistance to and avoidance of stress slow aging and confer increased longevity in numerous organisms. Honey bees and other superorganismal social insects have two main advantages over solitary species to avoid or resist stress: individuals can directly help each other by resource or information transfer, and they can cooperatively control their environment. These benefits have been recognised in the context of pathogen and parasite stress as the concept of social immunity, which has been extensively studied. However, we argue that social immunity is only a special case of a general concept that we define here as social stress protection to include group-level defences against all biotic and abiotic stressors. We reason that social stress protection may have allowed the evolution of reduced individual-level defences and individual life-history optimization, including the exceptional aging plasticity of many social insects. We describe major categories of stress and how a colonial lifestyle may protect social insects, particularly against temporary peaks of extreme stress. We use the honey bee (Apis mellifera L.) to illustrate how patterns of life expectancy may be explained by social stress protection and how modern beekeeping practices can disrupt social stress protection. We conclude that the broad concept of social stress protection requires rigorous empirical testing because it may have implications for our general understanding of social evolution and specifically for improving honey bee health.

Foraging Activity of Honey Bees (Apis mellifera L., 1758) and Exposure to Cadmium: a Review

Honey bees are commonly exposed to a broad spectrum of xenobiotics, including heavy metals. Heavy metal toxicity is of concern in the context of global pollinator declines, especially since honey bees seem to be particularly susceptible to xenobiotics in general. Here we summarize current knowledge on the interplay between cadmium, one of the most toxic and mobile elements in the environment, and honey bees, the primary managed pollinator species worldwide. Overall, cadmium pollution has been shown to be ubiquitous, affecting industrial, urban and rural areas alike. Uptake of this heavy metal by plants serves as the primary route of exposure for bees (through pollen and nectar). Reported cadmium toxicity consists of lethal and sublethal effects (reduced development and growth) in both adult and larval stages, as well as various molecular responses related to detoxification and cellular antioxidant defence systems. Other effects of cadmium in honey bees include the disruption of synaptic signalling, calcium metabolism and muscle function.

Route of exposure to veterinary products in bees: Unraveling pasture's impact on avermectin exposure and tolerance in stingless bees

Deforestation rapidly increases in tropical regions, primarily driven by converting natural habitats into pastures for extensive cattle ranching. This landscape transformation, coupled with pesticide use, are key drivers of bee population decline. Here, we investigate the impact of pasture-dominated landscapes on colony performance, pesticide exposure, and insecticide sensitivity of the stingless bee Tetragonisca angustula. We monitored 16 colonies located in landscapes with varying proportions of pasture. We collected bee bread for pesticide and palynological analysis. We found a positive correlation between pollen diversity and colony growth, with no effect of the proportion of pasture in the landscape. In contrast, we detected prevalent and hazardous concentrations of the insecticide abamectin (9.6-1,856 µg/kg) in bee bread, which significantly increased with a higher proportion of pasture. Despite the abamectin exposure, the bee colonies displayed no adverse effects on their growth, indicating a potential tolerance response. Further investigations revealed that bees from sites with higher proportions of pasture showed significantly reduced mortality when exposed to a lethal concentration of abamectin (0.021 µg/µL) after 48 h. Since abamectin is scarcely used in the study area, we designed an experiment to track ivermectin, a closely related antiparasitic drug used in cattle. Our findings uncovered a new exposure route of bees to pesticides, wherein ivermectin excreted by cattle is absorbed and biotransformed into abamectin within flowering plants in the pastures. These results highlight that unexplained exposure routes of bees to pesticides remain to be described while also revealing that bees adapt to changing landscapes.

Transcriptomic and biochemical insights into fall armyworm (Spodoptera frugiperda) responses on silicon-treated maize

Background

The fall armyworm, Spodoptera frugiperda, is an agricultural pest of significant economic concern globally, known for its adaptability, pesticide resistance, and damage to key crops such as maize. Conventional chemical pesticides pose challenges, including the development of resistance and environmental pollution. The study aims to investigate an alternative solution: the application of soluble silicon (Si) sources to enhance plant resistance against the fall armyworm.

Methods

Silicon dioxide (SiO2) and potassium silicate (K2SiO3) were applied to maize plants via foliar spray. Transcriptomic and biochemical analyses were performed to study the gene expression changes in the fall armyworm feeding on Si-treated maize.

Results

Results indicated a significant impact on gene expression, with a large number of differentially expressed genes (DEGs) identified in both SiO2 and K2SiO3 treatments. Furthermore, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis identified critical DEGs involved in specific pathways, including amino acid, carbohydrate, lipid, energy, xenobiotics metabolisms, signal transduction, and posttranslational modification, significantly altered at both Si sources. Biochemical analyses further revealed that Si treatments inhibited several enzyme activities (glutamate dehydrogenase, trehalase, glucose-6-phosphate dehydrogenase, chitinase, juvenile hormone esterase, and cyclooxygenase while simultaneously inducing others (total protein, lipopolysaccharide, fatty acid synthase, ATPase, and cytochrome P450), thus suggesting a toxic effect on the fall armyworm. In conclusion, Si applications on maize influence the gene expression and biochemical activities of the fall armyworm, potentially offering a sustainable pest management strategy.

Architecture and potential roles of a delta-class glutathione S-transferase in protecting honey bee from agrochemicals

The European honey bee, Apis mellifera, serves as the principle managed pollinator species globally. In recent decades, honey bee populations have been facing serious health threats from combined biotic and abiotic stressors, including diseases, limited nutrition, and agrochemical exposure. Understanding the molecular mechanisms underlying xenobiotic adaptation of A. mellifera is critical, considering its extensive exposure to phytochemicals and agrochemicals present in the environment. In this study, we conducted a comprehensive structural and functional characterization of AmGSTD1, a delta class glutathione S-transferase (GST), to unravel its roles in agrochemical detoxification and antioxidative stress responses. We determined the 3-dimensional (3D) structure of a honey bee GST using protein crystallography for the first time, providing new insights into its molecular structure. Our investigations revealed that AmGSTD1 metabolizes model substrates, including 1-chloro-2,4-dinitrobenzene (CDNB), p-nitrophenyl acetate (PNA), phenylethyl isothiocyanate (PEITC), propyl isothiocyanate (PITC), and the oxidation byproduct 4-hydroxynonenal (HNE). Moreover, we discovered that AmGSTD1 exhibits binding affinity with the fluorophore 8-Anilinonaphthalene-1-sulfonic acid (ANS), which can be inhibited with various herbicides, fungicides, insecticides, and their metabolites. These findings highlight the potential contribution of AmGSTD1 in safeguarding honey bee health against various agrochemicals, while also mitigating oxidative stress resulting from exposure to these substances.

Phylogenomics of the Ecdysteroid Kinase-like (EcKL) Gene Family in Insects Highlights Roles in Both Steroid Hormone Metabolism and Detoxification

The evolutionary dynamics of large gene families can offer important insights into the functions of their individual members. While the ecdysteroid kinase-like (EcKL) gene family has previously been linked to the metabolism of both steroid molting hormones and xenobiotic toxins, the functions of nearly all EcKL genes are unknown, and there is little information on their evolution across all insects. Here, we perform comprehensive phylogenetic analyses on a manually annotated set of EcKL genes from 140 insect genomes, revealing the gene family is comprised of at least 13 subfamilies that differ in retention and stability. Our results show the only two genes known to encode ecdysteroid kinases belong to different subfamilies and therefore ecdysteroid metabolism functions must be spread throughout the EcKL family. We provide comparative phylogenomic evidence that EcKLs are involved in detoxification across insects, with positive associations between family size and dietary chemical complexity, and we also find similar evidence for the cytochrome P450 and glutathione S-transferase gene families. Unexpectedly, we find that the size of the clade containing a known ecdysteroid kinase is positively associated with host plant taxonomic diversity in Lepidoptera, possibly suggesting multiple functional shifts between hormone and xenobiotic metabolism. Our evolutionary analyses provide hypotheses of function and a robust framework for future experimental studies of the EcKL gene family. They also open promising new avenues for exploring the genomic basis of dietary adaptation in insects, including the classically studied coevolution of butterflies with their host plants.

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.

Trisiloxane Surfactants Negatively Affect Reproductive Behaviors and Enhance Viral Replication in Honey Bees

Trisiloxane surfactants are often applied in formulated adjuvant products to blooming crops, including almonds, exposing the managed honey bees (Apis mellifera) used for pollination of these crops and persisting in colony matrices, such as bee bread. Despite this, little is known regarding the effects of trisiloxane surfactants on important aspects of colony health, such as reproduction. In the present study, we use laboratory assays to examine how exposure to field-relevant concentrations of three trisiloxane surfactants found in commonly used adjuvant formulations affect queen oviposition rates, worker interactions with the queen, and worker susceptibility to endogenous viral pathogens. Trisiloxane surfactants were administered at 5 mg/kg in pollen supplement diet for 14 days. No effects on worker behavior or physiology could be detected, but our results demonstrate that hydroxy-capped trisiloxane surfactants can negatively affect queen oviposition and methyl-capped trisiloxane surfactants cause increased replication of Deformed Wing Virus in workers, suggesting that trisiloxane surfactant use while honey bees are foraging may negatively impact colony longevity and growth. Environ Toxicol Chem 2024;43:222-233. © 2023 SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Biomarker responses and lethal dietary doses of tau-fluvalinate and coumaphos in honey bees: Implications for chronic acaricide toxicity

Evidence suggests that acaricide residues, such as tau-fluvalinate and coumaphos, are very prevalent in honey bee colonies worldwide. However, the endpoints and effects of chronic oral exposure to these compounds remain poorly understood. In this study, we calculated LC50 and LDD50 endpoints for coumaphos and tau-fluvalinate, and then evaluated in vivo and in vitro effects on honey bees using different biomarkers. The LDD50 values for coumaphos were 0.539, and for tau-fluvalinate, they were 12.742 in the spring trial and 8.844 in the autumn trial. Chronic exposure to tau-fluvalinate and coumaphos resulted in significant changes in key biomarkers, indicating potential neurotoxicity, xenobiotic biotransformation, and oxidative stress. The Integrated Biomarker Response was stronger for coumaphos than for tau-fluvalinate, supporting their relative lethality. This study highlights the chronic toxicity of these acaricides and presents the first LDD50 values for tau-fluvalinate and coumaphos in honey bees, providing insights into the risks faced by colonies.

Impacts of the insecticide thiamethoxam on the native stingless bee Plebeia catamarcensis (Hymenoptera, Apidae, Meliponini)

Agricultural production and the indiscriminate use of insecticides such as thiamethoxam have put at risk the biodiversity and ecosystem services provided by bees, including native stingless species. Since most of the native species do not present economic importance, they may suffer "silent extinction", due to lack of monitoring of their colonies. Therefore, this study aimed to determine the lethal and sublethal concentrations of the insecticide thiamethoxam, with evaluation of its sublethal effects on mobility, in the stingless bee Plebeia catamarcensis (Holmberg, 1903). Foraging bees were collected and exposed to thiamethoxam to determine lethal (LC50) and sublethal concentrations. The 24 h LC50 was 0.408 ng a.i./μL, a value demonstrating that this species may be as sensitive as other stingless bees already studied. Sublethal concentrations influenced the locomotion abilities of the bees, making them hyperactive when exposed to LC50/10 and lethargic when exposed to LC50/100. The effects of sublethal concentrations on individuals may have collective consequences, especially in colonies with few individuals, as is the case of P. catamarcensis. The findings reinforce the hypothesis that thiamethoxam may contribute to the decline of native stingless bees, which can be significantly impacted when chronically exposed to agricultural production systems that use this insecticide, consequently affecting the ecosystem services provided by these bees.

Overexpression of cytochrome P450 and esterase genes involved in permethrin resistance in larvae and adults of Culex quinquefasciatus

Mosquitoes are important vectors of several arthropod-borne diseases, which remain a priority for epidemiological research. Mosquito vector control strategies have traditionally relied on chemical insecticides such as synthetic pyrethroids. However, the indiscriminate use of pesticides has resulted in the development of resistance in many mosquito species. In insects, resistance evolves primarily through the overexpression of one or more gene products from the cytochrome P450, carboxylesterase, and glutathione superfamilies. The current study examined the expression of cytochrome P450 CYP6M2, CYP6AA7, CYP6Z2, CYP9J34, α-Esterase, Esterase B1, and neuroactin genes in larvae and adults of a permethrin-resistant (PerRes) and susceptible (Sus) Culex quinquefasciatus strains. The results showed that the CYP6AA7 gene was overexpressed (10-fold) in larvae and adults with PerRes (p < 0.01) followed by CYPJ34 (9.0-fold) and CYP6Z2 (5.0-fold) compared to the Sus, whereas fewer changes in CYP6M gene expression were observed in PerRes adults (p < 0.05), and no expression was found in larvae. The esterase gene was overexpressed in PerRes larvae (9.0-fold) followed by adults (2.5-fold) compared to the susceptible strain. Based on data, the present study suggests that cytochrome P450, CYP6AA7, CYP6Z2, CYP9J34, α-Esterase, Esterase B1, and neuroactin genes were involved in permethrin resistance in larval and adult Cx. quinquefasciatus.

Structure-activity analysis suggests an olfactory function for the unique antennal delta glutathione transferase of Apis mellifera

Glutathione transferases (GST) are detoxification enzymes that conjugate glutathione to a wide array of molecules. In the honey bee Apis mellifera, AmGSTD1 is the sole member of the delta class of GSTs, with expression in antennae. Here, we structurally and biochemically characterized AmGSTD1 to elucidate its function. We showed that AmGSTD1 can efficiently catalyse the glutathione conjugation of classical GST substrates. Additionally, AmGSTD1 exhibits binding properties with a range of odorant compounds. AmGSTD1 has a peculiar interface with a structural motif we propose to call 'sulfur sandwich'. This motif consists of a cysteine disulfide bridge sandwiched between the sulfur atoms of two methionine residues and is stabilized by CH…S hydrogen bonds and S…S sigma-hole interactions. Thermal stability studies confirmed that this motif is important for AmGSTD1 stability and, thus, could facilitate its functions in olfaction.

Functional orthologs of honeybee CYP6AQ1 in stingless bees degrade the butenolide insecticide flupyradifurone

Flupyradifurone (FPF), a novel butenolide insecticide binding to nicotinic acetylcholine receptors (nAChRs), has been shown to be less acutely toxic to western honey bees (Apis mellifera) than other insecticides such as neonicotinoids sharing the same target-site. A previous study revealed that this is due to enhanced oxidative metabolism of FPF, mediated by three cytochrome P450 monooxygenases (P450s), including CYP6AQ1. Therefore, we followed a toxicogenomics approach and investigated the potential role of functional CYP6AQ1 orthologs in FPF metabolism from eight different bee species, including stingless bees (Tribe: Meliponini). We conducted a phylogenetic analysis on four stingless bee species, including Frieseomelitta varia, Heterotrigona itama, Melipona quadrifasciata and Tetragonula carbonaria to identify CYP6AQ1-like functional orthologs. Three non-Meliponini, but tropical bee species, i.e., Ammobates syriacus, Euglossa dilemma and Megalopta genalis were analyzed as well. We identified candidate P450s in all (neo)tropical species with greater than 61% and 67% predicted protein sequence identities when compared to A. mellifera CYP6AQ1 and Bombus terrestris CYP6AQ26, respectively. Heterologous expression in High Five insect cells of these functional orthologs revealed a common coumarin substrate profile and a preference for the O-debenzylation of bulkier substrates. Competition assays using the fluorescent probe substrate 7-benzyloxymethoxy-4-trifluoromethylcoumarin (BOMFC) with these enzymes indicated inhibition of BOMFC metabolism by increasing concentrations of FPF. Furthermore, UPLC-MS/MS analysis revealed the capacity of all CYP6AQ1-like orthologs to metabolize FPF by hydroxylation in vitro at various levels, indicating a conserved FPF detoxification potential in different (neo)tropical bee species including Meliponini. This research, employing a toxicogenomics approach, provides important insights into the potential of stingless and other tropical bee species to detoxify FPF, and highlights the significance of investigating the detoxification mechanisms of insecticides in non-Apis bee species by molecular tools to inform risk assessment and conservation efforts.

Evolution of five environmentally responsive gene families in a pine-feeding sawfly, Neodiprion lecontei (Hymenoptera: Diprionidae)

A central goal in evolutionary biology is to determine the predictability of adaptive genetic changes. Despite many documented cases of convergent evolution at individual loci, little is known about the repeatability of gene family expansions and contractions. To address this void, we examined gene family evolution in the redheaded pine sawfly Neodiprion lecontei, a noneusocial hymenopteran and exemplar of a pine-specialized lineage evolved from angiosperm-feeding ancestors. After assembling and annotating a draft genome, we manually annotated multiple gene families with chemosensory, detoxification, or immunity functions before characterizing their genomic distributions and molecular evolution. We find evidence of recent expansions of bitter gustatory receptor, clan 3 cytochrome P450, olfactory receptor, and antimicrobial peptide subfamilies, with strong evidence of positive selection among paralogs in a clade of gustatory receptors possibly involved in the detection of bitter compounds. In contrast, these gene families had little evidence of recent contraction via pseudogenization. Overall, our results are consistent with the hypothesis that in response to novel selection pressures, gene families that mediate ecological interactions may expand and contract predictably. Testing this hypothesis will require the comparative analysis of high-quality annotation data from phylogenetically and ecologically diverse insect species and functionally diverse gene families. To this end, increasing sampling in under-sampled hymenopteran lineages and environmentally responsive gene families and standardizing manual annotation methods should be prioritized.

Transcriptome analysis of Euwallacea interjectus reveals differentially expressed unigenes related to developmental stages and egg laying

Euwallacea interjectus (Curculionidae: Scolytinae) is an ambrosia beetle species in its early stages of research. Therefore, studying the related molecular mechanism associated with the development and egg laid is essential. Transcriptome sequencing was used in this study to compare the gene expression of the beetles at different developmental stages and female adults before and after oviposition. A total of 40,047 annotated unigenes were obtained. There were 4225 differentially expressed unigenes (DEUs) from larva to prepupa stage, 3651 DEUs between prepupa and pupa, 1675 DEUs generated from pupa to adult, and 4762 DEUs between females before and after oviposition. The most significant pathway differences between different development stages and before and after oviposition were selected through functional annotation of DEUs between different stages. Among them, there were many pathways related to protein metabolism including: neuroactive ligand-receptor interaction, endoplasmic reticulum and RNA transport. This study provides valuable information on the molecular regulation mechanism of development and the egg laid of E. interjectus.

Availability of Using Honeybees as Bioindicators of Pesticide Exposure in the Vicinity of Agricultural Environments in Taiwan

While pollinating, honeybees are subject to exposure to a variety of pesticides; with their characteristics of certain foraging distances, they could serve as bioindicators of pesticide exposure in a neighborhood. We conducted a study to assess availability by collecting and analyzing bee samples from 15 apiaries located in East Taiwan and dust samples from the adjacent environment, and by finding relations between both samples. Seventeen pesticides were selected for the analysis using gas or liquid chromatography coupled with mass spectrometry, and eight (three insecticides, two herbicides, and three fungicides) were more frequently detected from bee or dust samples; the levels of these pesticides were mostly under 1000 ng/g. Significant correlation results (r ≅ 0.8) between residue concentrations in bees and in dust suggest that honeybees could be a good bioindicator for exposure to herbicides and fungicides within certain ranges. The pesticide contents of sick/dead bees were much higher than those of healthy counterparts regarding any pesticide type, with the mean total concentrations of 635 ng/g and 176 ng/g, respectively. We conclude that honeybees could be used as bioindicators of pesticide exposure; sick/dead bees could serve as a warning sign of the severity of pesticide pollution.

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.

Molecular identification of carboxylesterase genes and their potential roles in the insecticides susceptibility of Grapholita molesta

Grapholita molesta is one of the most damaging pests worldwide in stone and pome fruits. Application of chemical pesticides is still the main method to control this pest, which results in resistance to several types of insecticides. Carboxylesterase (CarE) is one of the important enzymes involved in the detoxification metabolism and tolerance of xenobiotics and insecticides. However, the roles of CarEs in insecticides susceptibility of G. molesta are still unclear. In the present study, the enzyme activity of CarEs and the mRNA expression of six CarE genes were consistently elevated after treatment with three insecticides (emamectin benzoate, lambda-cyhalothrin, and chlorantraniliprole). According to spatio-temporal expression profiles, six CarE genes expressed differently in different developmental stages, and highly expressed in some detoxification metabolic organs. RNAi-mediated knockdown of these six CarE genes indicated that the susceptibility of G. molesta to all these three insecticides were obviously raised after GmCarE9, GmCarE14, GmCarE16, and GmCarE22 knockdown, respectively. Overall, these results demonstrated that GmCarE9, GmCarE14, GmCarE16, and GmCarE22 play a role in the susceptibility of G. molesta to emamectin benzoate, lambda-cyhalothrin, and chlorantraniliprole treatment. This study expands our understanding of CarEs in insects, that the same CarE gene could participate in the susceptibility to different insecticides.

Identification, expression profiles and involvement in insecticides tolerance and detoxification of carboxylesterase genes in Bactrocera dorsalis

Carboxylesterases (CarEs) are a multifunctional superfamily of enzymes and play an important role in detoxification of various insecticides in insects. The oriental fruit fly, Bactrocera dorsalis, is one of the most destructive agricultural pests and has developed different degrees of resistance to organophosphates in field. However, the involvement of BdCarEs in tolerance or resistance to other alternative insecticides are still unclear. In the present study, 33 BdCarEs genes were identified based on the genome database of B. dorsalis. Phylogenetic analysis demonstrated that they were classified into nine clades, with abundance of α-esterases. Meanwhile, the sequence characterization and the chromosome distribution were also analyzed. The spatiotemporal expression analysis of BdCarEs genes suggested that the diversity of potential function in different physiological processes. With the exception of BdCarE21, all BdCarEs genes responded to at least one insecticide exposure, and BdCarE20 was found to be up-regulated after exposure to all five tested insecticides individually. Eight BdCarEs genes were overexpressed in MR strain when compared to that in SS strain. Subsequently, knockdown the expression of representative BdCarEs genes significantly increased the susceptibility of the oriental fruit fly to corresponding insecticides, which indicated that the tested BdCarEs genes contributed to one or multiple insecticide detoxification. These findings provide valuable insights into the potential role in respond to tolerance or resistance to insecticides with different mode of action, and will facilitate development of efficiency management strategy for B. dorsalis.

Synergism and toxicity of iron nanoparticles derived from Trigonella foenum-graecum against pyrethriod treatment in S. litura and H. armigera (Lepidoptera: Noctuidae)

The tobacco cutworm, Spodoptera litura and cotton bollworm, Helicoverpa armigera (Lepidoptera: Noctuidae) are important pests of various agricultural crops that cause sevier economic loses throughout the world. Indiscriminate and frequent use of insecticide may lead to development of resistance in these pests. Nanotechnology has given an alternative to manage and overcome insecticide resistance for pest management strategies. In the present study the iron nanoparticles derived from Trigonella foenum-graecum leaf extract (FeNPs) was investigated for its ecofriendly management of pyrethroid resistance in two lepidopteron pest species at 24 h, 48 h and 72 h post treatment. The result showed high mortality (92.83% and 91.41%) of S. litura and H. armigera at 72 h treatment upon FeNPs and fenvalerate (Fen + FeNPs) teratment. Probit analysis revealed high LC₅₀ upon Fen + FeNPs treatment (130.31 and 89.32 mg/L) with a synergism ratio of 1.38 and 1.36. Antifeedant activity of six dofferent concentration of FeNPs revelaed increased antifeedant activity with respect to increasing concentration of nanoparticles ranging from 10 to 90% and 20-95% againt both insects (p<0.05). Detoxification activity of carboxylesterase was elevated at 630 μmol/mg protein/min (p<0.05) in fenvalerate treatment, whereas decreased activity was found (392umole/mg protein/min) in FeNPs and Fen + FeNPs treatment (P<0.001). GST and P450 activity was also increased in fenvalerate treatment, whereas decreased activity was observed in FeNPs and Fen + FeNPs. Esterase isoenzyme banding pattern revealed four bands in fenvalerate treatment and two bans (E3 and E4) in Fen + FeNPs combination. Hence the present study concludes that T. foenum-graecum synthesized iron nanoparticles could be an effective alternate for ecofriendly management of S. litura and H. armigera.

Gut microbiota composition and gene expression changes induced in the Apis cerana exposed to acetamiprid and difenoconazole at environmentally realistic concentrations alone or combined

Apis cerana is an important pollinator of agricultural crops in China. In the agricultural environment, A. cerana may be exposed to acetamiprid (neonicotinoid insecticide) and difenoconazole (triazole fungicide), alone or in combination because they are commonly applied to various crops. At present, our understanding of the toxicological effects of acetamiprid and difenoconazole on honey bee gut microbiomes is limited. The primary objective of this study was to explore whether these two pesticides affect honey bees' gut microbiota and to analyze the transcriptional effects of these two pesticides on honey bees' head and gut. In this study, adults of A. cerana were exposed to acetamiprid and/or difenoconazole by contaminated syrup at field-realistic concentrations for 10 days. Results indicated that acetamiprid and/or difenoconazole chronic exposure did not affect honey bees' survival and food consumption, whereas difenoconazole decreased the weight of honey bees. 16S rRNA sequencing suggested that difenoconazole and the mixture of difenoconazole and acetamiprid decreased the diversity index and shaped the composition of gut bacteria microbiota, whereas acetamiprid did not impact the gut bacterial community. The ITS sequence data showed that neither of the two pesticides affected the fungal community structure. Meanwhile, we also observed that acetamiprid or difenoconazole significantly altered the expression of genes related to detoxification and immunity in honey bees' tissues. Furthermore, we observed that the adverse effect of the acetamiprid and difenoconazole mixture on honey bees' health was greater than that of a single mixture. Taken together, our study demonstrates that acetamiprid and/or difenoconazole exposure at field-realistic concentrations induced changes to the honey bee gut microbiome and gene expression.

Sensitivity to imidacloprid insecticide varies among some social and solitary bee species of agricultural value

Pollinator health risks from long-lasting neonicotinoid insecticides like imidacloprid has primarily focused on commercially managed, cavity-nesting bees in the genera Apis, Bombus, and Osmia. We expand these assessments to include 12 species of native and non-native crop pollinators of differing levels of body size, sociality, and floral specialization. Bees were collected throughout 2016 and 2017 from flowering blueberry, squash, pumpkin, sunflower and okra in south Mississippi, USA. Within 30-60 minutes of capture, bees were installed in bioassay cages made from transparent plastic cups and dark amber jars. Bees were fed via dental wicks saturated with 27% (1.25 M) sugar syrup containing a realistic range of sublethal concentrations of imidacloprid (0, 5, 20, or 100 ppb) that are often found in nectar. Bees displayed no visible tremors or convulsions except for a small sweat bee, Halictus ligatus, and only at 100ppb syrup. Imidacloprid shortened the captive longevities of the solitary bees. Tolerant bee species lived ~10 to 12 days in the bioassays and included two social and one solitary species: Halictus ligatus, Apis mellifera and Ptilothrix bombiformis (rose mallow bees), respectively. No other bee species tolerated imidacloprid as well as honey bees did, which exhibited no appreciable mortality and only modest paralysis across concentration. In contrast, native bees either lived shorter lives, experienced longer paralysis, or endured both. Overall, longevity decreased with concentration linearly for social bees and non-linearly for solitary species. The percentage of a bee's captive lifespan spent paralyzed increased logarithmically with concentration for all species, although bumble bees suffered longest. Of greatest concern was comparable debilitation of agriculturally valuable solitary bees at both low and high sublethal rates of imidacloprid.

Expression profile of the entire detoxification gene inventory of the western honeybee, Apis mellifera across life stages

The western honeybee, Apis mellifera, is a managed pollinator of many crops and potentially exposed to a wide range of foreign compounds, including pesticides throughout its life cycle. Honeybees as well as other insects recruit molecular defense mechanisms to facilitate the detoxification of xenobiotic compounds. The inventory of detoxification genes (DETOXome) is comprised of five protein superfamilies: cytochrome P450 monooxygenases (P450), carboxylesterases, glutathione S-transferases (GST), UDP-glycosyl transferases (UGT) and ATP-binding cassette (ABC) transporters. Here we characterized the gene expression profile of the entire honeybee DETOXome by analyzing 47 transcriptomes across the honeybee life cycle, including different larval instars, pupae, and adults. All life stages were well separated by principal component analysis, and K-means clustering revealed distinct temporal patterns of gene expression. Indeed, >50% of the honeybee detoxification gene inventory is found in one cluster and follows strikingly similar expression profiles, i.e., increased expression during larval development, followed by a sharp decline after pupation and a steep increase again in adults. This cluster includes 29 P450 genes dominated by CYP3 and CYP4 clan members, 15 ABC transporter genes mostly belonging to the ABCC subfamily and 13 carboxylesterase genes including almost all members involved in dietary/detox and hormone/semiochemical processing. RT-qPCR analysis of selected detoxification genes from all families revealed high expression levels in various tissues, especially Malpighian tubules, fatbody and midgut, supporting the view that these tissues are essential for metabolic clearance of environmental toxins and pollutants in honeybees. Our study is meant to spark further research on the molecular basis of detoxification in this critical pollinator to better understand and evaluate negative impacts from potentially toxic substances. Additionally, the entire gene set of 47 transcriptomes collected and analyzed provides a valuable resource for future honeybee research across different disciplines.

Genome-wide analyses of Glutathione S-transferase gene family and expression profiling under deltamethrin exposure in non-biting midge Propsilocerus akamusi

Glutathione S-transferases (GSTs) are major enzymes in detoxification phase II, and have been functioned in resistance to various insecticides or oxidative stress. Herein, we selected the non-biting midge, Propsilocerus akamusi, widespread in Asian aquatic ecosystems, to uncover the gene location, structure, and phylogenetics relationship of GSTs at genome scale first time. Thirty-three cytosolic and four microsomal GST genes were identified and located on the four chromosomes. The cytosolic GSTs involved in the eight subclasses and five GST genes were unclassified. The expansion of GST genes in P. akamusi experienced duplication events on the delta, theta, xi, iota, and unclassified subclasses. The RNA-Seq analyses and RT-qPCR validation showed that the expression of PaGSTt2 gene is significantly elevated, with deltamethrin concentration increasing. The tertiary structure of PaGSTt2 enzyme was reconstructed, which was different from the other theta gene in the active site. In addition, the GST genes of six chironomids were first described based on the assembled genomes to explore the difference of those in the adaptation to kinds of environments. The GST frame for P. akmusi and its expression profiles provide valuable resources to understand their role in insecticide resistance of this species, as well as those of other biting midges.

Positive selection in cytochrome P450 genes is associated with gonad phenotype and mating strategy in social bees

The honey bee, Apis mellifera differs from all other social bees in its gonad phenotype and mating strategy. Honey bee queens and drones have tremendously enlarged gonads, and virgin queens mate with several males. In contrast, in all the other bees, the male and female gonads are small, and the females mate with only one or very few males, thus, suggesting an evolutionary and developmental link between gonad phenotype and mating strategy. RNA-seq comparisons of A. mellifera larval gonads revealed 870 genes as differentially expressed in queens versus workers and drones. Based on Gene Ontology enrichment we selected 45 genes for comparing the expression levels of their orthologs in the larval gonads of the bumble bee Bombus terrestris and the stingless bee, Melipona quadrifasciata, which revealed 24 genes as differentially represented. An evolutionary analysis of their orthologs in 13 solitary and social bee genomes revealed four genes with evidence of positive selection. Two of these encode cytochrome P450 proteins, and their gene trees indicated a lineage-specific evolution in the genus Apis, indicating that cytochrome P450 genes may be involved in the evolutionary association of polyandry and the exaggerated gonad phenotype in social bees.

The effects of short-term glyphosate-based herbicide exposure on insect gene expression profiles

Glyphosate-based herbicides (GBHs) are the most frequently used herbicides worldwide. The use of GBHs is intended to tackle weeds, but GBHs have been shown to affect the life-history traits and antioxidant defense system of invertebrates found in agroecosystems. Thus far, the effects of GBHs on detoxification pathways among invertebrates have not been sufficiently investigated. We performed two different experiments-1) the direct pure glyphosate and GBH treatment, and 2) the indirect GBH experiment via food-to examine the possible effects of environmentally relevant GBH levels on the survival of the Colorado potato beetle (Leptinotarsa decemlineata) and the expression profiles of their detoxification genes. As candidate genes, we selected four cytochrome P450 (CYP), three glutathione-S-transferase (GST), and two acetylcholinesterase (AChE) genes that are known to be related to metabolic or target-site resistances in insects. We showed that environmentally relevant levels of pure glyphosate and GBH increased the probability for higher mortality in the Colorado potato beetle larvae in the direct experiment, but not in the indirect experiment. The GBHs or glyphosate did not affect the expression profiles of the studied CYP, GST, or AChE genes; however, we found a large family-level variation in expression profiles in both the direct and indirect treatment experiments. These results suggest that the genes selected for this study may not be the ones expressed in response to glyphosate or GBHs. It is also possible that the relatively short exposure time did not affect gene expression profiles, or the response may have already occurred at a shorter exposure time. Our results show that glyphosate products may affect the survival of the herbivorous insect already at lower levels, depending on their sensitivity to pesticides.

Genome-wide identification, classification, and expression profiling of serine esterases and other esterase-related proteins in the tobacco hornworm, Manduca sexta

Serine esterases (SEs) are hydrolases that catalyze the conversion of carboxylic esters into acids and alcohols. Lipases and carboxylesterases constitute two major groups of SEs. Although over a hundred of insect genomes are known, systematic identification and classification of SEs are rarely performed, likely due to large size and complex composition of the gene family in each species. Considering their key roles in lipid metabolism and other physiological processes, we have categorized 144 M. sexta SEs and SE homologs (SEHs), 114 of which contain a motif of GXSXG. Multiple sequence alignment and phylogenetic tree analysis have revealed 39 neutral lipases (NLs), 3 neutral lipase homologs (NLHs), 11 acidic lipases (ALs), 3 acidic lipase homologs (ALHs), a lipase-3, a triglyceride lipase, a monoglyceride lipase, a hormone-sensitive lipase, and a GDSL lipase. Eighty-three carboxylesterase genes encode 29 α-esterases (AEs), 12 AEHs (e.g., SEH4-1-3), 20 feruloyl esterases (FEs), 2 FEHs, 2 β-esterases (BEs), 2 integument esterases (IEs), 1 IEH, 4 juvenile hormone esterases, 2 acetylcholinesterases, gliotactin, 6 neuroligins, neurotactin, and an uncharacteristic esterase homolog. In addition to these GXSXG proteins, we have identified 26 phospholipases and 13 thioesterases. Expression profiling of these genes in specific tissues and stages has provided insights into their functions including digestion, detoxification, hormone processing, neurotransmission, reproduction, and developmental regulation. In summary, we have established a framework of information on SEs and related proteins in M. sexta to stimulate their research in the model species and comparative investigations in agricultural pests or disease vectors.

Metabolic profiling of Apis mellifera larvae treated with sublethal acetamiprid doses

Acetamiprid is a neonicotinoid insecticide used in crop protection worldwide. Such widespread application can pose risks to pollinator insects, particularly to honeybees (Apis mellifera); therefore, the evaluation of the harmful effects of acetamiprid is necessary. Recent studies report behavior and gene expression dysfunction in honeybees, related to acetamiprid contamination. However, most studies do not consider potential metabolism disorders. To examine the effects of sublethal acetamiprid doses on the hemolymph metabolism of honeybees, worker bee larvae(2 days old) were fed with sucrose water containing different concentrations of acetamiprid (0, 5, and 25 mg/L) until capped (6 days old). The hemolymph (200 μL) of freshly capped larvae was collected for liquid chromatography-mass spectrometry (LC-MS). Overall, increasing acetamiprid exposure induced greater metabolic variations in worker bee larvae(treated groups compared to untreated). In the positive ion mode, 36 common differential metabolites in the acetamiprid-treated groups were screened from the identified differential metabolites. Of these, 19 metabolites were upregulated, and 17 were downregulated. 10 common differential metabolites were screened in the negative ion mode. 3 metabolites were upregulated, and 7 metabolites were downregulated. These common metabolites included traumatic acid, indole etc. These commonly differentiated metabolites were classified as compounds with biological roles, lipids, and phytochemical compounds, and others. The metabolic pathways of common differentiated metabolites with significant differences (P < 0.05) included the metabolism of tryptophan, purines, phenylalanine, etc. As the concentration of acetamiprid increased, the content of traumatic acid increased, the content of tryptophan metabolite l-kynurenine and indole decreased, and the content of lipids also decreased. Our results revealed that the damage to honeybee larvae increased when the acetamiprid solution formulations residue in their food had a concentration higher than 5 mg/L, causing metabolic disorders in various substances in larvae. Analysis of these metabolic processes can provide a theoretical basis for further research on the metabolism of acetamiprid-treated honeybees and elucidate the detoxification mechanisms.

Differential bumble bee gene expression associated with pathogen infection and pollen diet

BACKGROUND

Diet and parasitism can have powerful effects on host gene expression. However, how specific dietary components affect host gene expression that could feed back to affect parasitism is relatively unexplored in many wild species. Recently, it was discovered that consumption of sunflower (Helianthus annuus) pollen reduced severity of gut protozoan pathogen Crithidia bombi infection in Bombus impatiens bumble bees. Despite the dramatic and consistent medicinal effect of sunflower pollen, very little is known about the mechanism(s) underlying this effect. However, sunflower pollen extract increases rather than suppresses C. bombi growth in vitro, suggesting that sunflower pollen reduces C. bombi infection indirectly via changes in the host. Here, we analyzed whole transcriptomes of B. impatiens workers to characterize the physiological response to sunflower pollen consumption and C. bombi infection to isolate the mechanisms underlying the medicinal effect. B. impatiens workers were inoculated with either C. bombi cells (infected) or a sham control (un-infected) and fed either sunflower or wildflower pollen ad libitum. Whole abdominal gene expression profiles were then sequenced with Illumina NextSeq 500 technology.

RESULTS

Among infected bees, sunflower pollen upregulated immune transcripts, including the anti-microbial peptide hymenoptaecin, Toll receptors and serine proteases. In both infected and un-infected bees, sunflower pollen upregulated putative detoxification transcripts and transcripts associated with the repair and maintenance of gut epithelial cells. Among wildflower-fed bees, infected bees downregulated immune transcripts associated with phagocytosis and the phenoloxidase cascade.

CONCLUSIONS

Taken together, these results indicate dissimilar immune responses between sunflower- and wildflower-fed bumble bees infected with C. bombi, a response to physical damage to gut epithelial cells caused by sunflower pollen, and a strong detoxification response to sunflower pollen consumption. Identifying host responses that drive the medicinal effect of sunflower pollen in infected bumble bees may broaden our understanding of plant-pollinator interactions and provide opportunities for effective management of bee pathogens.

Genome-Wide Identification and Expression Pattern of Cytochrome P450 Genes in the Social Aphid Pseudoregma bambucicola

Cytochrome P450 monooxygenases (P450s) have a variety of functions, including involvement in the metabolism of exogenous substances and the synthesis and degradation of endogenous substances, which are important for the growth and development of insects. Pseudoregma bambucicola is a social aphid that produces genetically identical but morphologically and behaviorally distinct first-instar soldiers and normal nymphs within colonies. In this study, we identified 43 P450 genes based on P. bambucicola genome data. Phylogenetic analysis showed that these genes were classified into 4 clans, 13 families, and 23 subfamilies. The CYP3 and CYP4 clans had a somewhat decreased number of genes. In addition, differential gene expression analysis based on transcriptome data showed that several P450 genes, including CYP18A1, CYP4G332, and CYP4G333, showed higher expression levels in soldiers compared to normal nymphs and adult aphids. These genes may be candidates for causing epidermal hardening and developmental arrest in soldiers. This study provides valuable data and lays the foundation for the study of functions of P450 genes in the social aphid P. bambucicola.

Dynamic Roles of Insect Carboxyl/Cholinesterases in Chemical Adaptation

Insects have evolved several intricate defense mechanisms to adapt to their chemical environment. Due to their versatile capabilities in hydrolytic biotransformation, insect carboxyl/cholinesterases (CCEs) play vital roles in the development of pesticide resistance, facilitating the adaptation of insects to their host plants, and manipulating insect behaviors through the olfaction system. CCEs confer insecticide resistance through the mechanisms of qualitative or quantitative changes of CCE-mediated enhanced metabolism or target-site insensitivity, and may contribute to the host plant adaptation. CCEs represent the first odorant-degrading enzymes (ODEs) discovered to degrade insect pheromones and plant odors and remain the most promising ODE candidates. Here, we summarize insect CCE classification, currently characterized insect CCE protein structure characteristics, and the dynamic roles of insect CCEs in chemical adaptation.

Mixture effects of thiamethoxam and seven pesticides with different modes of action on honey bees (Aplis mellifera)

Even though honey bees in the field are routinely exposed to a complex mixture of many different agrochemicals, few studies have surveyed toxic effects of pesticide mixtures on bees. To elucidate the interactive actions of pesticides on crop pollinators, we determined the individual and joint toxicities of thiamethoxam (THI) and other seven pesticides [dimethoate (DIM), methomyl (MET), zeta-cypermethrin (ZCY), cyfluthrin (CYF), permethrin (PER), esfenvalerate (ESF) and tetraconazole (TET)] to honey bees (Aplis mellifera) with feeding toxicity test. Results from the 7-days toxicity test implied that THI elicited the highest toxicity with a LC₅₀ data of 0.25 (0.20-0.29) μg mL^-1, followed by MET and DIM with LC₅₀ data of 4.19 (3.58-4.88) and 5.30 (4.65-6.03) μg mL^-1, respectively. By comparison, pyrethroids and TET possessed relatively low toxicities with their LC₅₀ data from the range of 33.78 (29.12-38.39) to 1125 (922.4-1,442) μg mL^-1. Among 98 evaluated THI-containing binary to octonary mixtures, 29.59% of combinations exhibited synergistic effects. In contrast, 18.37% of combinations exhibited antagonistic effects on A. mellifera. Moreover, 54.8% pesticide combinations incorporating THI and TET displayed synergistic toxicities to the insects. Our findings emphasized that the coexistence of several pesticides might induce enhanced toxicity to honey bees. Overall, our results afforded worthful toxicological information on the combined actions of neonicotinoids and current-use pesticides on honey bees, which could accelerate farther comprehend on the possible detriments of other pesticide mixtures in agro-environment.

Exposure of chlorothalonil and acetamiprid reduce the survival and cause multiple internal disturbances in Apis mellifera larvae reared in vitro

Background: Chlorothalonil and acetamiprid are chemical pesticides commonly used in agricultural production and have been shown to have negative effects on bee's fitness. Despite many studies have revealed that honey bee (Apis mellifera L.) larvae are posting a high risk on exposure to pesticides, but the toxicology information of chlorothalonil and acetamiprid on bee larvae remain limited. Results: The no observed adverse effect concentration (NOAEC) of chlorothalonil and acetamiprid for honey bee larvae were 4 μg/mL and 2 μg/mL, respectively. Except for CarE, the enzymic activities of GST and P450 were not influenced by chlorothalonil at NOAEC, while chronic exposure to acetamiprid slightly increased the activities of the three tested enzymes at NOAEC. Further, the exposed larvae showed significantly higher expression of genes involved in a series of different toxicologically relevant process following, including caste development (Tor (GB44905), InR-2 (GB55425), Hr4 (GB47037), Ac3 (GB11637) and ILP-2 (GB10174)), immune system response (abaecin (GB18323), defensin-1 (GB19392), toll-X4 (GB50418)), and oxidative stress response (P450, GSH, GST, CarE). Conclusion: Our results suggest that the exposure to chlorothalonil and acetamiprid, even at concentrations below the NOAEC, showed potentially effects on bee larvae's fitness, and more important synergistic and behavioral effects that can affect larvae fitness should be explored in the further.

Surrogate species in pesticide risk assessments: Toxicological data of three stingless bees species

Discussions about environmental risk reassessment of pesticides have grown in the last decades, especially in tropical and subtropical regions since the diversity of bee species in these places is quite different. Stingless bees are highly affected by pesticides, and toxicity information is necessary to include them in the regulatory process of countries that hosts a diversity of these species. Therefore, the present study aimed to evaluate the Median Lethal Concentration (LC₅₀), estimate the Median Lethal Dose (LD₅₀) and compared the sensitivity of three species of stingless bees exposed to the commercial formulation of the neonicotinoid thiamethoxam (TMX). The LD₅₀ was estimated based on the LC₅₀ determined in the present study (LC₅₀ = 0.329 ng a.i./μL for Tetragonisca angustula; 0.624 ng a.i./μL for Scaptotrigona postica, and 0.215 ng a.i./μL for Melipona scutellaris). Considering these data, toxicity endpoints were used to fit species sensitive distribution curves (SSD) and determine the sensitivity ratio. The results showed that all the stingless bees tested are more sensitive to TMX than the Apis mellifera, the model organism used in ecotoxicological tests. Regarding the oral LC₅₀, the most susceptible and most tolerant species were M. scutellaris > T. angustula > S. postica > A. mellifera. Following the same evaluated pattern, for the LD₅₀ (considering the weight of the bees - ng a.i./g bee), we have: M. scutellaris > S. postica > T. angustula > A. mellifera, and without the weight considered (ng a.i./bee): T. angustula > M. scutellaris > S. postica > A. mellifera. The different sensitivities among stingless bee species highlight the importance of inserting more than one surrogate species with a variety of sizes in research and protocol development. Additionally, the research suggests the need to investigate patterns regarding the influence of body mass on pesticide sensitivity among stingless bee species.

Strategies and techniques to mitigate the negative impacts of pesticide exposure to honey bees

In order to support food, fiber, and fuel production around the world, billions of kilograms of pesticides are applied to crop fields every year to suppress pests, plant diseases and weeds. These fields are often home to the most important commercial pollinators, honey bees (Apis spp.), which improve yield and quality of many agricultural products. The pesticides applied to support crop health can be detrimental to honey bee health. The conflict of pesticide use and reliance on honey bees contributes to significant honey bee colony losses across the world. Recommendations for reducing impact on honey bees are generally suggested in literature, pesticide regulations, and by crop consultants, but without a considerable discussion of the realistic limitations of protecting honey bees. New techniques in farming and beekeeping can reduce pesticide exposure through reduction in bee exposure, reduced toxicity of pesticides, and remedies that can be in response to exposure. However, lack of assessment of those new techniques under a systematical, comprehensive framework may overestimate or underestimate these techniques' potential to protect honey bees from pesticide damage. In this review, we summarize the current and arising strategies and techniques with the goal to inspire the development and adoption of pesticide mitigation practices for both agriculture and apiculture.

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

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

Toxicological evaluation of different pesticides in Tetragonisca angustula Latreille (Hymenoptera, Apidae)

The stingless bee Tetragonisca angustula is an important pollinator of different agricultural and native crops. This study evaluated changes in the relative activity of esterases and critical electrolyte concentration in brain cells after exposure to pesticides malathion and thiamethoxam. Lethal concentration 50% showed greater toxicity of thiamethoxam in relation to malathion. Esterases EST-3 and EST-4 (carboxylesterase) were partially inhibited after contamination by contact and ingestion of malathion and contamination by contact with thiamethoxam, suggesting participation of these esterases in the metabolization of these compounds. The lowest critical electrolyte concentration (CEC) was found after contamination by malathion ingestion (0.15 M), indicating changes in gene expression. The alterations observed in the intensity of EST-3 and EST-4 and the chromatin structure indicate that pesticides can act in gene expression and be used as biomarkers of contaminant residues. Furthermore, knowing the susceptibility of T. angustula bees to pesticides, it would be possible to use this species for biomonitoring environmental quality in preserved areas and agroecosystems.

Pesticide risk assessment: honeybee workers are not all equal regarding the risk posed by exposure to pesticides

Toxicological studies in honeybees have long shown that a single pesticide dose or concentration does not necessarily induce a single response. Inter-individual differences in pesticide sensitivity and/or the level of exposure (e.g., ingestion of pesticide-contaminated matrices) may explain this variability in risk posed by a pesticide. Therefore, to better inform pesticide risk assessment for honeybees, we studied the risk posed by pesticides to two behavioral castes, nurse, and forager bees, which are largely represented within colonies and which exhibit large differences in their physiological backgrounds. For that purpose, we determined the sensitivity of nurses and foragers to azoxystrobin (fungicide) and sulfoxaflor (insecticide) upon acute or chronic exposure. Azoxystrobin was found to be weakly toxic to both types of bees. However, foragers were more sensitive to sulfoxaflor than nurses upon acute and chronic exposure. This phenomenon was not explained by better sulfoxaflor metabolization in nurses, but rather by differences in body weight (nurses being 1.6 times heavier than foragers). Foragers consistently consumed more sugar syrup than nurses, and this increased consumption was even more pronounced with pesticide-contaminated syrup (at specific concentrations). Altogether, the stronger susceptibility and exposure of foragers to sulfoxaflor contributed to increases of 2 and tenfold for the acute and chronic risk quotients, respectively, compared to nurses. In conclusion, to increase the safety margin and avoid an under-estimation of the risk posed by insecticides to honeybees, we recommend systematically including forager bees in regulatory tests.

Binding and Detoxification of Insecticides by Potentially Probiotic Lactic Acid Bacteria Isolated from Honeybee (Apis mellifera L.) Environment-An In Vitro Study

Lactic acid bacteria (LAB) naturally inhabiting the digestive tract of honeybees are known for their ability to detoxify xenobiotics. The effect of chlorpyrifos, coumaphos, and imidacloprid on the growth of LAB strains was tested. All strains showed high resistance to these insecticides. Subsequently, the insecticide binding ability of LAB was investigated. Coumaphos and chlorpyrifos were bound to the greatest extent (up to approx. 64%), and imidacloprid to a much weaker extent (up to approx. 36%). The insecticides were detected in extra- and intracellular extracts of the bacterial cell wall. The ability of selected LAB to reduce the cyto- and genotoxicity of insecticides was tested on two normal (ovarian insect Sf-9 and rat intestinal IEC-6) cell lines and one cancer (human intestinal Caco-2) cell line. All strains exhibited various levels of reduction in the cyto- and genotoxicity of tested insecticides. It seems that coumaphos was detoxified most potently. The detoxification abilities depended on the insecticide, LAB strain, and cell line. The detoxification of insecticides in the organisms of honeybees may reduce the likelihood of the penetration of these toxins into honeybee products consumed by humans and may contribute to the improvement of the condition in apiaries and honeybee health.

Comparative analysis of detoxification-related gene superfamilies across five hemipteran species

Background

Hemiptera is one of the most speciose orders of insects, and the most speciose considering Hemimetabola. Through their evolutive history, hemipterans with different feeding habits have adapted to deal with different chemical challenges. Three major gene families are involved in xenobiotic detoxification in insects: the cytochromes P450 (CYPs), carboxyl/cholinesterases (CCEs), and glutathione transferases (GSTs). Here we perform a comparative analysis on the complement of these gene superfamilies across five hemipteran species; four heteropterans (the pentatomid plant feeders Nezara viridula and Halyomorpha halys; the hematophagous Cimex lectularius, Cimicidae, and Rhodnius prolixus, Reduviidae), and one Auchenorrhyncha plant feeder (Nilaparvata lugens).

Results

Our results point to an expansion of several enzyme families associated with xenobiotic detoxification in heteropterans with respect to other species and the existence of a dynamic evolution pattern including CYP3 clan, hormone and pheromone processing class in the CCE superfamily, and sigma class in GST superfamily. Other detoxification-related families are reduced in the hemipteran species analyzed here: reduction or even absence of epsilon class and reduced delta class in GST superfamily; absence of mitochondrial CYP12 family; absence of CYP9 family in CYP3 clan; and reduction or even absence of some dietary/detoxification groups of CCEs. Interestingly, the most polyphagous species analyzed here (H. halys) is also the one that presents the largest repertoire of detoxification enzymes. Gene cluster analysis suggests that this could be due to gene duplication events.

Conclusions

The evolutionary analysis performed here reveals characteristics that are both common and particular for heteropterans. The composition and organization of detoxification-related gene families could shed light on evolutionary forces that shaped their divergence. These families are important for both the detoxification of diet products and for conferring tolerance or resistance to synthetic insecticides. Furthermore, we present the first comprehensive analysis of detoxification gene superfamilies in N. viridula, an understudied species in spite of its economic relevance as a crop pest. The information obtained is of interest for basic insect science as well as for the control of harmful species and the management of insecticide resistance.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08974-y.

Genome-wide and expression-profiling analyses of the cytochrome P450 genes in Tenebrionidea

Cytochrome P450 monooxygenases (CYPs) are present in almost all areas of the tree of life. As one of the largest and most diverse superfamilies of multifunctional enzymes, they play important roles in the metabolism of xenobiotics and biosynthesis of endogenous compounds, shaping the success of insects. In this study, the CYPome (an omics term for all the CYP genes in a genome) diversification was examined in the four Tenebrionidea species through genome-wide analysis. A total of 483 CYP genes were identified, of which 103, 157, 122, and 101 were respectively deciphered from the genomes of Tebebrio molitor, Asbolus verucosus, Hycleus cichorii and Hycleus phaleratus. These CYPs were classified into four major clans (mitochondrial, CYP2, CYP3, and CYP4), and clans CYP3 and CYP4 are most diverse. Phylogenetic analysis showed that most CYPs of these Tenebrionidea beetles from each clan had a very close 1:1 orthology to each other, suggesting that they originate closely and have evolutionally conserved function. Expression analysis at different developmental stages and in various tissues showed the life stage-, gut-, salivary gland-, fat body-, Malpighian tubule-, antennae-, ovary- and testis-specific expression patterns of T. molitor CYP genes, implying their various potential roles in development, detoxification, immune response, digestion, olfaction, and reproduction. Our studies provide a platform to understand the evolution of Tenebrionidea CYP gene superfamily, and a basis for further functional investigation of the T. molitor CYPs involved in various biological processes.

Biomarker development for neonicotinoid exposure in soil under interaction with the synergist piperonyl butoxide in Folsomia candida

Pesticide toxicity is typically assessed by exposing model organisms to individual compounds and measuring effects on survival and reproduction. These tests are time-consuming, labor-intensive, and do not accurately capture the effect of pesticide mixtures. Moreover, it is unfeasible to screen the nearly infinite combinations of mixtures for synergistic effects on model organisms. Therefore, reliable molecular indicators of pesticide exposure have to be identified, i.e., biomarkers. These biomarkers can form the basis of rapid and economical screening procedures to assess the toxicity of pesticides even under synergistic interaction with other pollutants. In this study, we screened the expression patterns of eight genes for suitability as a biomarker for neonicotinoid exposure in the soil ecotoxicological model Folsomia candida (springtails). Springtails were exposed to the neonicotinoids imidacloprid and thiacloprid either alone or with various levels of piperonyl butoxide (PBO), which inhibits cytochrome P450 enzymes (CYPs): a common point of synergistic interaction between neonicotinoid and other pesticides. First, we confirmed PBO as a potency enhancer for neonicotinoid toxicity to springtail fecundity, and then used it as a tool to confirm biomarker robustness. We identified two genes that are reliably indicative for neonicotinoid exposure even under metabolic inhibition of CYPs by PBO, nicotinic acetylcholine receptor-subunit alpha 1 (nAchR) and sodium-coupled monocarboxylate transporter (SMCT). These results can form the basis for developing high-throughput screening procedures for neonicotinoid exposure in varying mixture compositions.

Comparative genomic analysis of carboxylesterase genes in Tenebrio molitor and other four tenebrionids

Carboxylesterases (COEs) have various functions in wide taxons of organisms. In insects, COEs are important enzymes involved in the hydrolysis of a variety of ester-containing xenobiotics, neural signal transmission, pheromone degradation, and reproductive development. Understanding the diversity of COEs is basic to illustrate their functions. In this study, we identified 53, 105, 37, and 39 COEs from the genomes of Tenebrio molitor, Asbolus verucosus, Hycleus cichorii, and H. phaleratus in the superfamily of Tenebrionidea, respectively. Phylogenetic analysis showed that 234 COEs from these four species and those reported in Tribolium castaneum (63) could be divided into 12 clades and three major classes. The α-esterases significantly expanded in T. molitor, A. verucosus, and T. castaneum compared to dipteran and hymenopteran insects. In T. molitor, most COEs showed tissue and stage-specific but not a sex-biased expression. Our results provide insights into the diversity and evolutionary characteristics of COEs in tenebrionids, and lay a foundation for the functional characterization of COEs in the yellow mealworm.