Unravelling the Molecular Determinants of Bee Sensitivity to Neonicotinoid Insecticides

Rational Design of Triazinone Derivatives with Low Bee Toxicity Based on the Binding Mechanism of Neonicotinoids to Apis mellifera

Bees, one of the most vital pollinators in the ecosystem and agriculture, are currently threatened by neonicotinoids. To explore the molecular mechanisms of neonicotinoid toxicity to bees, the different binding modes of imidacloprid, thiacloprid, and flupyradifurone with nicotinic acetylcholine receptor (nAChR) α1β1 and cytochrome P450 9Q3 (CYP9Q3) were studied using homology modeling and molecular dynamics simulations. These mechanisms provided a basis for the design of compounds with a potential low bee toxicity. Consequently, we designed and synthesized a series of triazinone derivatives and assessed their bioassays. Among them, compound 5a not only displayed substantially insecticidal activities against Aphis glycines (LC50 = 4.40 mg/L) and Myzus persicae (LC50 = 6.44 mg/L) but also had low toxicity to Apis mellifera. Two-electrode voltage clamp recordings further confirmed that compound 5a interacted with the M. persicae nAChR α1 subunit but not with the A. mellifera nAChR α1 subunit. This work provides a paradigm for applying molecular toxic mechanisms to the design of compounds with low bee toxicity, thereby aiding the future rational design of eco-friendly nicotinic insecticides.

Comparability of comparative toxicity: insect sensitivity to imidacloprid reveals huge variations across species but also within species

Pesticides have been identified as major drivers of insect biodiversity loss. Thus, the study of their effects on non-pest insect species has attracted a lot of attention in recent decades. In general toxicology, the 'gold standard' to assess the toxicity of a substance is to measure mass-specific LD50 (i.e. median lethal dose per unit body mass). In entomology, reviews attempting to compare these data across all available studies are lacking. To fill this gap in knowledge, we performed a systematic review of the lethality of imidacloprid for adult insects. Imidacloprid is possibly the most extensively studied insecticide in recent times, yet we found that little is comparable across studies, owing to both methodological divergence and missing estimates of body mass. By accounting for body mass whenever possible, we show how imidacloprid sensitivity spans across an apparent range of approximately six orders of magnitude across insect species. Very high variability within species can also be observed owing to differences in exposure methods and observation time. We suggest that a more comparable and comprehensive approach has both biological and economic relevance. Ultimately, this would help to identify differences that could direct research towards preventing non-target species from being negatively affected.

Assessment of toxic effects of imidacloprid on freshwater zooplankton: An experimental test for 27 species

The neonicotinoid pesticide imidacloprid has been used worldwide since 1992. As one of the most important chemicals used in pest control, there have been concerns that its run-off into rivers and lakes could adversely affect aquatic ecosystems, where zooplankton play a central role in the energy flow from primary to higher trophic levels. However, studies assessing the effects of pesticides at the species level have relied on a Daphnia-centric approach, and no studies have been conducted using species-level assessments on a broad range of zooplankton taxa. In the present study, we therefore investigated the acute toxicity of imidacloprid on 27 freshwater crustacean zooplankton (18 cladocerans, 3 calanoid copepods and 6 cyclopoid copepods). The experiment showed that a majority of calanoid copepods and cladocerans were not affected at all by imidacloprid, with the exception of one species each of Ceriodaphnia and Diaphasoma, while all six cyclopoid copepods showed high mortality rates, even at concentrations of imidacloprid typically found in nature. In addition, we found a remarkable intra-taxonomic variation in susceptibility to this chemical. As many cyclopoid copepods are omnivorous, they act as predators as well as competitors with other zooplankton. Accordingly, their susceptibility to imidacloprid is likely to cause different responses at the community level through changes in predation pressure as well as changes in competitive interactions. The present results demonstrate the need for species-level assessments of various zooplankton taxa to understand the complex responses of aquatic communities to pesticide disturbance.

Effect of chlorpyrifos-exposure on the expression levels of CYP genes in Daphnia magna and examination of a possibility that an up-regulated clan 3 CYP, CYP360A8, reacts with pesticides

Daphnia magna is a test organism used for ecological risk assessments of pesticides, but little is known about the expression levels of cytochrome P450s (CYP)s and their changes after pesticide exposure in the less than 24-h-olds used for ecotoxicity tests. In this study, D. magna juveniles were exposed to 0.2 μg/L of chlorpyrifos under the conditions for acute immobilization test as specified by the OECD test guideline for 24 h, and then the gene expression was compared between the control and chlorpyrifos-exposure groups by RNA-sequencing analysis, with a focus on CYP genes. Among 38 CYP genes expressed in the control group, seven were significantly up-regulated while two were significantly down-regulated in the chlorpyrifos-exposure group. Although the sublethal concentration of chlorpyrifos did not change their expression levels so drastically (0.8 < fold change < 2.6), CY360A8 of D. magna (DmCYP360A8), which had been proposed to be responsible for metabolism of xenobiotics, was abundantly expressed in controls yet up-regulated by chlorpyrifos. Therefore, homology modeling of DmCYP360A8 was performed based on the amino acid sequence, and then molecular docking simulations with the insecticides that were indicated to be metabolized by CYPs in D. magna were conducted. The results indicated that DmCYP360A8 could contribute to the metabolism of diazinon and chlorfenapyr but not chlorpyrifos. These findings suggest that chlorpyrifos is probably detoxified by other CYP(s) including up-regulated and/or constitutively expressed one(s).

Computational Modeling Oriented Substructure Splicing Application in the Identification of Thiazolidine Derivatives as Potential Low Honeybee Toxic Neonicotinoids

With the aim of identifying novel neonicotinoid insecticides with low bee toxicity, a series of compounds bearing thiazolidine moiety, which has been shown to be low bee toxic, were rationally designed through substructure splicing strategy and evaluated insecticidal activities. The optimal compounds A24 and A29 exhibited LC50 values of 30.01 and 17.08 mg/L against Aphis craccivora, respectively. Electrophysiological studies performed on Xenopus oocytes indicated that compound A29 acted on insect nAChR, with EC50 value of 50.11 μM. Docking binding mode analysis demonstrated that A29 bound to Lymnaea stagnalis acetylcholine binding protein through H-bonds with the residues of D_Arg55, D_Leu102, and D_Val114. Quantum mechanics calculation showed that A29 had a higher highest occupied molecular orbit (HOMO) energy and lower vertical ionization potential (IP) value compared to the high bee toxic imidacloprid, showing potentially low bee toxicity. Bee toxicity predictive model also indicated that A29 was nontoxic to honeybees. Our present work identified an innovative insecticidal scaffold and might facilitate the further exploration of low bee toxic neonicotinoid insecticides.

Variation in Pesticide Toxicity in the Western Honey Bee (Apis mellifera) Associated with Consuming Phytochemically Different Monofloral Honeys

Insecticide toxicity to insect herbivores has long been known to vary across different host plants; this phenomenon has been widely documented in both foliage-feeders and sap-feeders. Species-specific phytochemical content of hostplant tissues is assumed to determine the pattern of induction of insect enzymes that detoxify insecticides, but specific phytochemicals have rarely been linked to host plant-associated variation in pesticide toxicity. Moreover, no studies to date have examined the effects of nectar source identity and phytochemical composition on the toxicity of insecticides to pollinators. In this study, we compared LD50 values for the insecticide bifenthrin, a frequent contaminant of nectar and pollen in agroecosystems, in the western honey bee, Apis mellifera, consuming three phytochemically different monofloral honeys: Nyssa ogeche (tupelo), Robinia pseudoacacia (black locust), and Fagopyrum esculentum (buckwheat). We found that bifenthrin toxicity (LD50) values for honey bees across different honey diets is linked to their species-specific phytochemical content. The profiles of phenolic acids and flavonoids of buckwheat and locust honeys are richer than is the profile of tupelo honey, with buckwheat honey containing the highest total content of phytochemicals and associated with the highest bifenthrin LD50 in honey bees. The vector fitting in the ordination analysis revealed positive correlations between LD50 values and two honey phytochemical richness estimates, Chao1 and Abundance-based Coverage Estimator (ACE). These findings suggest unequal effects among different phytochemicals, consistent with the interpretation that certain compounds, including ones that are rare, may have a more pronounced effect in mitigating pesticide toxicity.

Sublethal acetamiprid exposure induces immunity, suppresses pathways linked to juvenile hormone synthesis in queens and affects cycle-related signaling in emerging bees

Acetamiprid is the only neonicotinoid registered in the European Union because the risks of neonicotinoids to honey bees and other pollinators are strictly regulated. Herein, we orally exposed honey bee colonies to sublethal concentrations of acetamiprid (20 μg/L) under isolated conditions. After one month of continuous exposure, the emerging bees and queens were collected and analyzed via high-throughput label-free quantitative proteomics using a data-independent acquisition strategy. Six and 34 significantly differentially expressed proteins (DEPs) were identified in the emerging bees and queens, respectively. Mrjp3 was the only DEP found in both sample types/castes, and its opposite regulation illustrated a differential response. The DEPs in the emerging bees (H/ACA RNP, Rap1GAP, Mrjp3, and JHE) suggested that sublethal exposure to acetamiprid affected cell cycle-related signaling, which may affect the life history of workers in the colony. The DEPs with increased levels in queens, such as Mrjps 1-4 and 6-7, hymenoptaecin, and apidaecin 22, indicated an activated immune response. Additionally, the level of farnesyl pyrophosphate synthase (FPPS), which is essential for the mevalonate pathway and juvenile hormone biosynthesis, was significantly decreased in queens. The impaired utilization of juvenile hormone in queens supported the identification of additional DEPs. Furthermore, the proteome changes suggested the existence of increased neonicotinoid detoxification by UDP-glucuronosyltransferase and increased amino acid metabolism. The results suggest that the continuous exposure of bee colonies to acetamiprid at low doses (nanograms per gram in feed) may pose a threat to the colonies. The different exposure routes and durations for the emerging bees and queens in our experiment must be considered, i.e., the emerging bees were exposed as larvae via feeding royal jelly and beebread provided by workers (nurse bees), whereas the queens were fed royal jelly throughout the experiment. The biological consequences of the proteomic changes resulting from sublethal/chronic exposure require future determination.

Potential of Ocotea indecora Essential Oil for Controlling Drosophila suzukii: Molecular Predictions for Toxicity and Selectivity to Beneficial Arthropods

The protection of soft-skinned fruits against Drosophila suzukii has relied primarily on the efficacy of a few synthetic molecules. Despite their short-term efficacy, these molecules can cause environmental pollution, unintendedly affect non-target organisms, and fail to provide sustainable control. The shortfalls of using synthetic pesticides warrant the search for alternatives, such as essential oils extracted from plants, with greater eco-friendlier properties. Here, we chemically characterized and evaluated the toxicity of the essential oil extracted from leaves of Ocotea indecora (Schott) Mez (Lauraceae) against D. suzukii via two exposure pathways (ingestion and contact). We also assessed the selectivity of the essential oil to two predatory natural enemies, Eriopis connexa and Chrysoperla externa and two pollinator bees, Apis mellifera and Partamona helleri. In addition, we conducted in silico predictions to investigate potential interactions between the major compound of the essential oil and the insects' transient receptor potential (TRP) channels. Our chromatographic analysis revealed sesquirosefuran (87%) as the major compound. Higher toxicity to adults of D. suzukii was observed in contact exposure (LC50 = 0.43 μL mL-1) compared to ingestion (LC50 = 0.72 μL mL-1). However, the essential oil did not cause mortality to the non-target organisms tested here, even when applied at 2.20 μL mL-1. Molecular predictions demonstrated that sesquirosefuran binds more stably to the TRP channels of D. suzukii than to those expressed in beneficial arthropods. Collectively, our findings provide the initial framework for the potential use of O. indecora essential oil as a sustainable alternative for managing D. suzukii infestations.

Insecticide resistance in social insects: assumptions, realities, and possibilities

Insecticide resistance is an evolved ability to survive insecticide exposure. Compared with nonsocial insects, eusocial insects have lower numbers of documented cases of resistance. Eusocial insects include beneficial and pest species that can be incidentally or purposely targeted with insecticides. The central goal of this review is to explore factors that either limit resistance or the ability to detect it in eusocial insects. We surveyed the literature and found that resistance has been documented in bees, but in other pest groups such as ants and termites, the evidence is more sparse. We suggest the path forward for better understanding eusocial resistance should include more tractable experimental models, comprehensive geographic sampling, and targeted testing of the impacts of social, symbiont, genetic, and ecological factors.

The molecular determinants of pesticide sensitivity in bee pollinators

Bees carry out vital ecosystem services by pollinating both wild and economically important crop plants. However, while performing this function, bee pollinators may encounter potentially harmful xenobiotics in the environment such as pesticides (fungicides, herbicides and insecticides). Understanding the key factors that influence the toxicological outcomes of bee exposure to these chemicals, in isolation or combination, is essential to safeguard their health and the ecosystem services they provide. In this regard, recent work using toxicogenomic and phylogenetic approaches has begun to identify, at the molecular level, key determinants of pesticide sensitivity in bee pollinators. These include detoxification systems that convert pesticides to less toxic forms and key residues in insecticide target-sites that underlie species-specific insecticide selectivity. Here we review this emerging body of research and summarise the state of knowledge of the molecular determinants of pesticide sensitivity in bee pollinators. We identify gaps in our knowledge for future research and examine how an understanding of the genetic basis of bee sensitivity to pesticides can be leveraged to, a) predict and avoid negative bee-pesticide interactions and facilitate the future development of pest-selective bee-safe insecticides, and b) inform traditional effect assessment approaches in bee pesticide risk assessment and address issues of ecotoxicological concern.

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.

Pesticide Exposure and Effects on Non-Apis Bees

Bees are essential pollinators of many crops and wild plants, and pesticide exposure is one of the key environmental stressors affecting their health in anthropogenically modified landscapes. Until recently, almost all information on routes and impacts of pesticide exposure came from honey bees, at least partially because they were the only model species required for environmental risk assessments (ERAs) for insect pollinators. Recently, there has been a surge in research activity focusing on pesticide exposure and effects for non-Apis bees, including other social bees (bumble bees and stingless bees) and solitary bees. These taxa vary substantially from honey bees and one another in several important ecological traits, including spatial and temporal activity patterns, foraging and nesting requirements, and degree of sociality. In this article, we review the current evidence base about pesticide exposure pathways and the consequences of exposure for non-Apis bees. We find that the insights into non-Apis bee pesticide exposure and resulting impacts across biological organizations, landscapes, mixtures, and multiple stressors are still in their infancy. The good news is that there are many promising approaches that could be used to advance our understanding, with priority given to informing exposure pathways, extrapolating effects, and determining how well our current insights (limited to very few species and mostly neonicotinoid insecticides under unrealistic conditions) can be generalized to the diversity of species and lifestyles in the global bee community. We conclude that future research to expand our knowledge would also be beneficial for ERAs and wider policy decisions concerning pollinator conservation and pesticide regulation.

Effect of Acetamiprid, a Neonicotinoid Insecticide, on Locomotor Activity of the American Cockroach

Toxicological studies have shown that the American cockroach Periplaneta americana (Linnaeus) is a classical model for studying the mode of action of commonly used insecticides. In a previous study, we demonstrated that thiamethoxam and clothianidin decreased locomotor activity in an open-field-like apparatus. Here, we tested the effect of the neonicotinoid acetamiprid when applied orally, topically, or injected into the haemolymph. We found that acetamiprid was also able to impair locomotor activity in the open-field-like apparatus. When treated with acetamiprid, a strong alteration in locomotor activity was observed 1 h, 24 h, and 48 h after haemolymph and topical applications. Oral application induced an impairment of locomotor activity at 24 h and 48 h. A comparison of the present data with our previously published results showed that neonicotinoids were more active when injected into the haemolymph compared to oral and topical applications. These findings increased our understanding of the effect of neonicotinoid insecticides on insect locomotor activity, and demonstrated that the cyano-substituted neonicotinoid, acetamiprid, was able to alter cockroach locomotor activity.

Comprehensive analysis of the overexpressed cytochrome P450-based insecticide resistance mechanism in Spodoptera litura

Cytochrome P450s play critical roles in the metabolic resistance of insecticides in insects. Previous findings showed that enhanced P450 activity was an important mechanism mediating indoxacarb resistance, and multiple P450 genes were upregulated in indoxacarb resistant strains of Spodoptera litura. However, the functions of these P450 genes in insecticide resistance remain unknown. Here, the P450 inhibitor PBO effectively decreased the resistance of S. litura to indoxacarb. Ten upregulated P450 genes were characterized, all of which were overexpressed in response to indoxacarb induction. Knockdown of nine P450 genes decreased cell viability against indoxacarb, and further silencing of three genes (CYP339A1, CYP340G2, CYP321A19) in larvae enhanced the sensitivity to indoxacarb. Transgenic overexpression of these three genes increased resistance to indoxacarb in Drosophila melanogaster. Moreover, molecular modeling and docking predicted that these three P450 proteins could bind tightly to indoxacarb and N-decarbomethoxylated metabolite (DCJW). Interestingly, these three P450 genes may also mediate cross-resistance to chlorantraniliprole, λ-cyhalothrin and imidacloprid. Additionally, heterologous expression and metabolic assays confirmed that three recombinant P450s could effectively metabolize indoxacarb and DCJW. This study strongly demonstrates that multiple overexpressed mitochondrial and microsomal P450 genes were involved in insecticide resistance in S. litura.

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.

A cytochrome P450 insecticide detoxification mechanism is not conserved across the Megachilidae family of bees

Recent work has demonstrated that many bee species have specific cytochrome P450 enzymes (P450s) that can efficiently detoxify certain insecticides. The presence of these P450s, belonging or closely related to the CYP9Q subfamily (CYP9Q-related), is generally well conserved across the diversity of bees. However, the alfalfa leafcutter bee, Megachile rotundata, lacks CYP9Q-related P450s and is 170-2500 times more sensitive to certain insecticides than bee pollinators with these P450s. The extent to which these findings apply to other Megachilidae bee species remains uncertain. To address this knowledge gap, we sequenced the transcriptomes of four Megachile species and leveraged the data obtained, in combination with publicly available genomic data, to investigate the evolution and function of P450s in the Megachilidae. Our analyses reveal that several Megachilidae species, belonging to the Lithurgini, Megachilini and Anthidini tribes, including all species of the Megachile genus investigated, lack CYP9Q-related genes. In place of these genes Megachile species have evolved phylogenetically distinct CYP9 genes, the CYP9DM lineage. Functional expression of these P450s from M. rotundata reveal they lack the capacity to metabolize the neonicotinoid insecticides thiacloprid and imidacloprid. In contrast, species from the Osmiini and Dioxyini tribes of Megachilidae have CYP9Q-related P450s belonging to the CYP9BU subfamily that are able to detoxify thiacloprid. These findings provide new insight into the evolution of P450s that act as key determinants of insecticide sensitivity in bees and have important applied implications for pesticide risk assessment.

Early-Life Sublethal Thiacloprid Exposure to Honey Bee Larvae: Enduring Effects on Adult Bee Cognitive Abilities

Honey bees have significant ecological and economic value as important pollinators, but they are continuously exposed to various environmental stressors, including insecticides, which can impair their health and cause colony decline. (1) Background: Cognitive abilities are vital for the functional maintenance of honey bees; however, it remains unknown if chronic, low-dose exposure to thiacloprid during the larval stage impairs the cognitive abilities of emerged adult honey bees. (2) Methods: To explore this question, honey bee larvae were fed 0, 0.5, and 1.0 mg/L thiacloprid during their developmental phase. Then, the cognitive (i.e., olfactory learning and memory) abilities of adult honey bees were quantified to assess the delayed impacts of early-stage thiacloprid exposure on adult honey bee cognition. Neural apoptosis and transcriptomic level were also evaluated to explore the neurological mechanisms underlying these effects. (3) Results: Our results revealed that chronic larval exposure to sublethal thiacloprid impaired the learning and memory abilities of adult honey bees by inducing neuronal apoptosis and transcriptomic alterations. (4) Conclusions: We highlighted a previously unknown impairment caused by thiacloprid in honey bees.

Risk assessment requires several bee species to address species-specific sensitivity to insecticides at field-realistic concentrations

In the European registration process, pesticides are currently mainly tested on the honey bee. Since sensitivity data for other bee species are lacking for the majority of xenobiotics, it is unclear if and to which extent this model species can adequately serve as surrogate for all wild bees. Here, we investigated the effects of field-realistic contact exposure to a pyrethroid insecticide, containing lambda-cyhalothrin, on seven bee species (Andrena vaga, Bombus terrestris, Colletes cunicularius, Osmia bicornis, Osmia cornuta, Megachile rotundata, Apis mellifera) with different life history characteristics in a series of laboratory trials over two years. Our results on sensitivity showed significant species-specific responses to the pesticide at a field-realistic application rate (i.e., 7.5 g a.s./ha). Species did not group into distinct classes of high and low mortality. Bumble bee and mason bee survival was the least affected by the insecticide, and M. rotundata survival was the most affected with all individuals dead 48 h after application. Apis mellifera showed medium mortality compared to the other bee species. Most sublethal effects, i.e. behavioral abnormalities, were observed within the first hours after application. In some of the solitary species, for example O. bicornis and A. vaga, a higher percentage of individuals performed some abnormal behavior for longer until the end of the observation period. While individual bee weight explained some of the observed mortality patterns, differences are likely linked to additional ecological, phylogenetic or toxicogenomic parameters as well. Our results support the idea that honey bee data can be substitute for some bee species' sensitivity and may justify the usage of safety factors. To adequately cover more sensitive species, a larger set of bee species should be considered for risk assessment.

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.

Function of Cytochrome P450s and Gut Microbiome in Biopesticide Adaptation of Grapholita molesta on Different Host Diets

Insects that feed on various host plants possess diverse xenobiotic adaptations; however, the underlying mechanisms are poorly understood. In the present study, we used Grapholita molesta, which shifts feeding sites from peach shoots to apple fruits, as a model to explore the effects of shifts in host plant diet on the profiles of cytochrome P450s and the gut bacteria microbiome, as well as their effects on biopesticide adaptation. We found that the sensitivity of the fruit-feeding G. molesta to emamectin benzoate biopesticide was significantly lower than that of the shoot-feeding larvae. We also found that the P450 enzyme activity and the expression of nine cytochrome P450s were enhanced in G. molesta fed on Fuji apples compared to those fed on peach shoots. The survival rates of G. molesta exposed to emamectin benzoate significantly decreased as each of three of four emamectin benzoate-inducted cytochrome P450 genes were silenced. Furthermore, we discovered the gut bacteria dynamics of G. molesta changed with the host shift and the structure of the gut bacteria microbiome was determined by the final diet ingested; additionally, the dysbiosis of the gut microbiota induced by antibiotics could significantly increase the sensitivity to emamectin benzoate. Taken together, our results suggest that the expression of P450s and the composition of the gut bacteria microbiome promote adaptation to emamectin benzoate in G. molesta, providing new insights into the molecular mechanisms underlying xenobiotic adaptation in this notorious pest.

Exposure to sublethal concentrations of thiacloprid insecticide modulated the expression of microRNAs in honeybees (Apis mellifera L.)

This study aimed to investigate the sublethal effects of thiacloprid on microRNA (miRNA) expression in honeybees (Apis mellifera L.) and the role of a specific miRNA, ame-miR-283-5p, in thiacloprid resistance. The high-throughput small RNA-sequencing was used to analyze global miRNA expression profile changes in honeybees orally exposed to sublethal concentrations of thiacloprid (20 mg/L and 4 mg/L) for 72 h. Thiacloprid at 20 mg/L had no observed adverse effects. In addition, bees were fed with miRNA mimics or inhibitors to increase or decrease ame-miR-283-5p expression, and its effects on P450 gene expression (CYP9Q2 and CYP9Q3) were examined. Thiacloprid susceptibility was also detected. The results showed that treatment with thiacloprid at 20 mg/L and 4 mg/L induced 11 and five differentially expressed miRNAs (DEMs), respectively. Bioinformatic analysis suggested that the DEMs are mainly involved in the regulation of growth and development, metabolism, nerve conduction, and behavior. ame-miR-283-5p was downregulated by both concentrations, which was validated using quantitative real-time reverse transcription PCR analysis. Enhancing ame-miR-283-5p expression significantly inhibited CYP9Q2 mRNA and protein expression, and increased thiacloprid toxicity, while reducing ame-miR-283-5p expression significantly promoted CYP9Q2 expression, and decreased thiacloprid susceptibility. Our study revealed a novel role of miRNAs in insecticide resistance in honeybees.

Divergent amplifications of CYP9A cytochrome P450 genes provide two noctuid pests with differential protection against xenobiotics

Here, we provide mechanistic support for the involvement of the CYP9A subfamily of cytochrome P450 monooxygenases in the detoxification of host plant defense compounds and chemical insecticides in Spodoptera exigua and Spodoptera frugiperda. Our comparative genomics shows that a large cluster of CYP9A genes occurs in the two species but with significant differences in its contents, including several species-specific duplicates and substantial sequence divergence, both between orthologs and between duplicates. Bioassays of CRISPR-Cas9 knockouts of the clusters show that, collectively, the CYP9As can detoxify two furanocoumarin plant defense compounds (imperatorin and xanthotoxin) and insecticides representing three different chemotypes (pyrethroids, avermectins, and oxadiazines). However, in vitro metabolic assays of heterologously expressed products of individual genes show several differences between the species in the particular CYP9As with activities against these compounds. We also find that the clusters show tight genetic linkage with high levels of pyrethroid resistance in field strains of the two species. We propose that their divergent amplifications of the CYP9A subfamily have not only contributed to the development of the broad host ranges of these species over long evolutionary timeframes but also supplied them with diverse genetic options for evolving resistance to chemical insecticides in the very recent past.

Validation of biomarkers for neonicotinoid exposure in Folsomia candida under mutual exposure to diethyl maleate

Neonicotinoid insecticides are harmful to non-target soil invertebrates, which are crucial for sustainable agriculture. Gene expression biomarkers could provide economic and high-throughput metrics of neonicotinoid exposure and toxicity to non-target invertebrates. Thereby, biomarkers can help guide remediation efforts or policy enforcement. Gene expression of Glutathione S-Transferase 3 (GST3) has previously been proposed as a biomarker for the neonicotinoid imidacloprid in the soil ecotoxicological model species Folsomia candida (Collembola). However, it remains unclear how reliably gene expression of neonicotinoid biomarkers, such as GST3, can indicate the exposure to the broader neonicotinoid family under putative GST enzymatic inhibition. In this work, we exposed springtails to two neonicotinoids, thiacloprid and imidacloprid, alongside diethyl maleate (DEM), a known GST metabolic inhibitor that imposes oxidative stress. First, we determined the influence of DEM on neonicotinoid toxicity to springtail fecundity. Second, we surveyed the gene expression of four biomarkers, including GST3, under mutual exposure to neonicotinoids and DEM. We observed no effect of DEM on springtail fecundity. Moreover, the expression of GST3 was only influenced by DEM under mutual exposure with thiacloprid but not with imidacloprid. The results indicate that GST3 is not a robust indicator of neonicotinoid exposure and that probable GST enzymatic inhibition mediates the toxicity of imidacloprid and thiacloprid differentially. Future research should investigate biomarker reliability under shifting metabolic conditions such as provided by DEM exposure.

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.

Gene expression in bumble bee larvae differs qualitatively between high and low concentration imidacloprid exposure levels

Neonicotinoid pesticides negatively impact bumble bee health, even at sublethal concentrations. Responses to the neonicotinoid imidacloprid have been studied largely at individual adult and colony levels, focusing mostly on behavioral and physiological effects. Data from developing larvae, whose health is critical for colony success, are deficient, particularly at the molecular level where transcriptomes can reveal disruption of fundamental biological pathways. We investigated gene expression of Bombus impatiens larvae exposed through food provisions to two field-realistic imidacloprid concentrations (0.7 and 7.0 ppb). We hypothesized both concentrations would alter gene expression, but the higher concentration would have greater qualitative and quantitative effects. We found 678 genes differentially expressed under both imidacloprid exposures relative to controls, including mitochondrial activity, development, and DNA replication genes. However, more genes were differentially expressed with higher imidacloprid exposure; uniquely differentially expressed genes included starvation response and cuticle genes. The former may partially result from reduced pollen use, monitored to verify food provision use and provide additional context to results. A smaller differentially expressed set only in lower concentration larvae, included neural development and cell growth genes. Our findings show varying molecular consequences under different field-realistic neonicotinoid concentrations, and that even low concentrations may affect fundamental biological processes.

Temperature related toxicity features of acute acetamiprid and thiacloprid exposure in Daphnia magna and implications on reproductive performance

This study investigated the potential for elevated temperature to alter the toxicity of acetamiprid (ACE) and thiacloprid (Thia) in the ecotoxicity model Daphnia magna. The modulation of CYP450 monooxygenases (ECOD), ABC transporter activity (MXR) and incident cellular reactive oxygen species (ROS) overproduction was screened in premature daphnids following acute (48 h) exposure to sublethal concentrations of ACE and Thia (0.1-, 1.0 μM) at standard 21 °C and elevated 26 °C temperatures. Delayed outcomes of acute exposures were further evaluated based on the reproduction performance of daphnids monitored over 14 days of recovery. Exposures to ACE and Thia at 21^o C elicited moderate induction of ECOD activity, pronounced inhibition of MXR activity and severe ROS overproduction in daphnids. In the high thermal regime, treatments resulted in significantly lower induction of ECOD activity and inhibition of MXR activity, suggesting a suppressed metabolism of neonicotinoids and less impaired membrane transport activity in daphnids. Elevated temperature on its own, caused a three-fold rise in ROS levels in control daphnids, while ROS overproduction upon neonicotinoid exposure was less accentuated. Acute exposures to ACE and Thia caused significant decreases also in the reproduction of daphnids, indicating delayed outcomes even at environmentally relevant concentrations. Both the cellular alterations in exposed daphnids and decreases in their reproductive output post exposures evidenced closely similar toxicity patterns and potentials for the two neonicotinoids. While elevated temperature elicited only a shift in baseline cellular alterations evoked by neonicotinoids, it significantly worsened the reproductive performance of daphnids following neonicotinoid exposures.

Relationship closeness of tolerance to two neonicotinoids with their internal body burden in two estuarine resident marine crustaceans

The estuarine resident crustacean sand shrimp, Crangon uritai, has a higher tolerance to neonicotinoid insecticides than that of the kuruma prawns, Penaeus japonicus. However, the reason for the differential sensitivities between the two marine crustaceans remains to be understood. This study explored the mechanism underlying differential sensitivities based on insecticide body residues after exposing both said crustaceans to two insecticides (acetamiprid and clothianidin) with or without oxygenase inhibitor piperonyl butoxide (PBO) for 96 h. Two graded-concentration groups were formed; group H (1/15-1 times the 96-h LC₅₀ values) and L (one-tenth the concentration of group H). Results showed that the internal concentration in survived specimens tended to be lower in sand shrimp than in kuruma prawns. Co-treatment of PBO with two neonicotinoids not only increased sand shrimp mortality in the H group, but also altered metabolism of acetamiprid into its metabolite, N-desmethyl acetamiprid. Furthermore, molting during the exposure period enhanced bioconcentration of insecticides, but not affects survival. Collectively, the higher tolerance of sand shrimp than that of kuruma prawns to the two neonicotinoids can be explained by lower bioconcentration potential and more involvement of oxygenase in their alleviating lethal toxicity.

Pesticide residues in nectar and pollen of melon crops: Risk to pollinators and effects of a specific pesticide mixture on Bombus terrestris (Hymenoptera: Apidae) micro-colonies

Residues detected in pollen collected by honey bees are often used to estimate pesticide exposure in ecotoxicological studies. However, for a more accurate assessment of pesticides effect on foraging pollinators, residues found directly on flowers are a more realistic exposure approximation. We conducted a multi-residue analysis of pesticides on pollen and nectar of melon flowers collected from five fields. The cumulative chronic oral exposure Risk Index (RI) was calculated for Apis mellifera, Bombus terrestris and Osmia bicornis to multiple pesticides. However, this index could underestimate the risk since sublethal or synergistic effects are not considered. Therefore, a mixture containing three of the most frequently detected pesticides in our study was tested for synergistic impact on B. terrestris micro-colonies through a chronic oral toxicity test. According to the result, pollen and nectar samples contained numerous pesticide residues, including nine insecticides, nine fungicides, and one herbicide. Eleven of those were not applied by farmers during the crop season, revealing that melon agroecosystems may be pesticide contaminated environments. The primary contributor to the chronic RI was imidacloprid and O. bircornis is at greatest risk for lethality resulting from chronic oral exposure at these sites. In the bumblebee micro-colony bioassay, dietary exposure to acetamiprid, chlorpyrifos and oxamyl at residue level concentration, showed no effects on worker mortality, drone production or drone size and no synergies were detected when pesticide mixtures were evaluated. In conclusion, our findings have significant implications for improving pesticide risk assessment schemes to guarantee pollinator conservation. In particular, bee pesticide risk assessment should not be limited to acute exposure effects to isolated active ingredients in honey bees. Instead, risk assessments should consider the long-term pesticide exposure effects in both pollen and nectar on a range of bees that reflect the diversity of natural ecosystems and the synergistic potential among pesticide formulations.

Development of an efficient insecticide substrate and inhibitor screening system of insect P450s using fission yeast

Metabolic resistance is one of the most frequent mechanisms of insecticide resistance, characterized by an increased expression of several important enzymes and transporters, especially cytochrome P450s (CYPs). Due to the large number of P450s in pests, determining the precise relationship between these enzymes and the insecticide substrates is a challenge. Herein, we developed a luminescence-based screening system for efficient identification of insecticide substrates and insect P450 inhibitors. We recombinantly expressed Bemisia tabaci CYP6CM1vQ (Bt CYP6CM1vQ) in the fission yeast Schizosaccharomyces pombe and subsequently permeabilized the yeast cells to convert them into "enzyme bags". We exploited these enzyme bags to screen the activity of twelve luciferin substrates and identified Luciferin-FEE as the optimal competing probe that was further used to characterize the metabolism of eight candidate commercial insecticides. Among them, Bt CYP6CM1vQ exhibited notable activity against pymetrozine and imidacloprid. Their binding modes were predicted by homology modeling and molecular docking, revealing the mechanisms of the metabolism. We also tested the inhibitory effect of eight known P450 inhibitors using our system and identified letrozole and 1-benzylimidazole as showing significant activity against Bt CYP6CM1vQ, with IC₅₀ values of 23.74 μM and 1.30 μM, respectively. Their potential to be developed as an insecticide synergist was further proven by an in vitro toxicity assay using imidacloprid-resistant Bemisia tabaci. Overall, our luciferin-based enzyme bag method is capable of providing a robust and efficient screening of insect P450 substrates and, more importantly, inhibitors to overcome the resistance.

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.

A single point mutation in the Bemisia tabaci cytochrome-P450 CYP6CM1 causes enhanced resistance to neonicotinoids

The tobacco whitefly, Bemisia tabaci, is a polyphagous crop pest which causes high levels of economic damage across the globe. Insecticides are often required for the effective control of this species, among which the neonicotinoid class have been particularly widely used. Deciphering the mechanisms responsible for resistance to these chemicals is therefore critical to maintain control of B. tabaci and limit the damage it causes. An important mechanism of resistance to neonicotinoids in B. tabaci is the overexpression of the cytochrome P450 gene CYP6CM1 which leads to the enhanced detoxification of several neonicotinoids. In this study we show that qualitative changes in this P450 dramatically alter its metabolic capacity to detoxify neonicotinoids. CYP6CM1 was significantly over-expressed in two strains of B. tabaci which displayed differing levels of resistance to the neonicotinoids imidacloprid and thiamethoxam. Sequencing of the CYP6CM1 coding sequence from these strains revealed four different alleles encoding isoforms carrying several amino acid changes. Expression of these alleles in vitro and in vivo provided compelling evidence that a mutation (A387G), present in two of the CYP6CM1 alleles, results in enhanced resistance to several neonicotinoids. These data demonstrate the importance of both qualitative and quantitative changes in genes encoding detoxification enzymes in the evolution of insecticide resistance and have applied implications for resistance monitoring programs.

Potential risk to pollinators from neonicotinoid applications to host trees for management of spotted lanternfly, Lycorma delicatula (Hemiptera: Fulgoridae)

Neonicotinoid insecticides are used to manage spotted lanternfly (Lycorma delicatula (White); hereafter SLF), a recently introduced pest in the United States. Neonicotinoids can harm nontargets, such as pollinators potentially exposed via floral resources of treated plants. We quantified neonicotinoid residues in whole flowers of two SLF host plant species, red maple (Acer rubrum L. [Sapindales: Sapindaceae]) and tree-of-heaven (Ailanthus altissima (Mill.) [Sapindales: Simaroubaceae]), treated with post-bloom imidacloprid or dinotefuran applications that differed in timing and method of application. In red maple flowers, dinotefuran residues from fall applications were significantly higher than summer applications, while imidacloprid residues from fall applications were significantly lower than summer applications. Residues did not differ between application methods or sites. In tree-of-heaven flowers, dinotefuran residues were only detected in one of 28 samples at a very low concentration. To assess acute mortality risk to bees from oral exposure to residues in these flowers, we calculated risk quotients (RQ) using mean and 95% prediction interval residue concentrations from treatments in this study and lethal concentrations obtained from acute oral bioassays for Apis mellifera (L. (Hymenoptera: Apidae)) and Osmia cornifrons (Radoszkowski (Hymenoptera: Megachilidae)), then compared these RQs to a level of concern. For A. mellifera, only one treatment group, applied at 2X maximum label rate, had an RQ that exceeded this level. However, several RQs for O. cornifrons exceeded the level of concern, suggesting potential acute risk to solitary bees. Further studies are recommended for more comprehensive risk assessments to nontargets from neonicotinoid use for SLF management.

A conserved hymenopteran-specific family of cytochrome P450s protects bee pollinators from toxic nectar alkaloids

Many plants produce chemical defense compounds as protection against antagonistic herbivores. However, how beneficial insects such as pollinators deal with the presence of these potentially toxic chemicals in nectar and pollen is poorly understood. Here, we characterize a conserved mechanism of plant secondary metabolite detoxification in the Hymenoptera, an order that contains numerous highly beneficial insects. Using phylogenetic and functional approaches, we show that the CYP336 family of cytochrome P450 enzymes detoxifies alkaloids, a group of potent natural insecticides, in honeybees and other hymenopteran species that diverged over 281 million years. We linked this function to an aspartic acid residue within the main access channel of CYP336 enzymes that is highly conserved within this P450 family. Together, these results provide detailed insights into the evolution of P450s as a key component of detoxification systems in hymenopteran species and reveal the molecular basis of adaptations arising from interactions between plants and beneficial insects.

RNAi-mediated silencing of AccCYP6k1 revealed its role in the metabolic detoxification of Apis cerana cerana

Insect cytochrome P450 monooxygenases (P450s or CYPs) perform important functions in the metabolic detoxification of both endogenous and exogenous substrates. However, the mechanism of action of the P450 genes in bees is unclear. In this study, we investigated the effects of AccCYP6k1 on the metabolism and detoxification of Apis cerana cerana. Spatiotemporal expression profiling revealed that the expression of AccCYP6k1 was the highest in foragers (A15) and was mainly expressed in the leg, midgut and head. RT-qPCR results showed that AccCYP6k1 exhibited different expression patterns following exposure to xenobiotics. In addition, silencing AccCYP6k1 increased the pesticides sensitivity and affected the detoxification system and antioxidant process of A. cerana cerana. In brief, the induced expression of AccCYP6k1 is related to the resistance of A. cerana cerana, while knockdown AccCYP6k1 affect the pesticides resistance and metabolic detoxification system of A. cerana cerana. These findings not only support the theoretical basis of metabolic detoxification in bees but also provide a better understanding of P450-mediated resistance to pesticides in insects.

The complete genome assemblies of 19 insect pests of worldwide importance to agriculture

There are many insect pests worldwide that damage agricultural crop and reduce yield either by direct feeding or by the transmission of plant diseases. To date, control of pest insects has been achieved largely by applying synthetic insecticides. However, insecticide use can be seriously impacted by legislation that limits their use or by the evolution of resistance in the target pest. Thus, there is a move towards less use of insecticides and increased adoption of integrated pest management strategies using a wide range of non-chemical and chemical control methods. For good pest control there is a need to understand the mode of action and selectivity of insecticides, the life cycles of the pests and their biology and behaviours, all of which can benefit from good quality genome data. Here we present the complete assembled (chromosome level) genomes (incl. mtDNA) of 19 insect pests, Agriotes lineatus (click beetle/wireworm), Aphis gossypii (melon/cotton aphid), Bemisia tabaci (cotton whitefly), Brassicogethes aeneus (pollen beetle), Ceutorhynchus obstrictus (seedpod weevil), Chilo suppressalis (striped rice stem borer), Chrysodeixis includens (soybean looper), Diabrotica balteata (cucumber beetle), Diatraea saccharalis (sugar cane borer), Nezara viridula (green stink bug), Nilaparvata lugens (brown plant hopper), Phaedon cochleariae (mustard beetle), Phyllotreta striolata (striped flea beetle), Psylliodes chrysocephala (cabbage stem flea beetle), Spodoptera exigua (beet army worm), Spodoptera littoralis (cotton leaf worm), Diabrotica virgifera (western corn root worm), Euschistus heros (brown stink bug) and Phyllotreta cruciferae (crucifer flea beetle). For the first 15 of these we also present the annotation of genes encoding potential xenobiotic detoxification enzymes. This public resource will aid in the elucidation and monitoring of resistance mechanisms, the development of highly selective chemistry and potential techniques to disrupt behaviour in a way that limits the effect of the pests.

Resilience of transfluthrin to oxidative attack by duplicated CYP6P9 variants known to confer pyrethroid resistance in the major malaria mosquito Anopheles funestus

Resistance to common pyrethroids, such as deltamethrin and permethrin is widespread in the malaria mosquito Anopheles funestus and mainly conferred by upregulated cytochrome P450 monooxygenases (P450s). In the pyrethroid resistant laboratory strain An. funestus FUMOZ-R the duplicated genes CYP6P9a and CYP6P9b are highly upregulated and have been shown to metabolize various pyrethroids, including deltamethrin and permethrin. Here, we recombinantly expressed CYP6P9a and CYP6P9b from An. funestus using a baculovirus expression system and evaluated the interaction of the multifluorinated benzyl pyrethroid transfluthrin with these enzymes by different approaches. First, by Michaelis-Menten kinetics in a fluorescent probe assay with the model substrate 7-benzyloxymethoxy-4-trifluoromethylcoumarin (BOMFC), we showed the inhibition of BOMFC metabolism by increasing concentrations of transfluthrin. Second, we tested the metabolic capacity of recombinantly expressed CYP6P9 variants to degrade transfluthrin utilizing UPLC-MS/MS analysis and detected low depletion rates, explaining the virtual lack of resistance of strain FUMOZ-R to transfluthrin observed in previous studies. However, as both approaches suggested an interaction of CYP6P9 variants with transfluthrin, we analyzed the oxidative metabolic fate and failed to detect hydroxylated transfluthrin, but low amounts of an M-2 transfluthrin metabolite. Based on the detected metabolite we hypothesize oxidative attack of the gem-dimethyl substituted cyclopropyl moiety, resulting in the formation of an allyl cation upon ring opening. In conclusion, these findings support the resilience of transfluthrin to P450-mediated pyrethroid resistance, and thus, reinforces its employment as an important resistance-breaking pyrethroid in resistance management strategies to control the major malaria vector An. funestus.

Genome-Wide Identification and Expression Analysis of the Cytochrome P450 Gene Family in Bemisia tabaci MED and Their Roles in the Insecticide Resistance

The whitefly, Bemisia tabaci MED (Hemiptera: Aleyrodidae), is an omnivorous agricultural pest, which causes huge economic losses to agriculture and is highly resistant to many pesticides. The overexpression of cytochrome P450 may play an important role in host adaptation and insecticide resistance in B. tabaci MED. Therefore, the present study systematically analyzed the cytochrome P450 gene family at the genome-wide level to understand its function in B. tabaci MED. Our analysis identified 58 cytochrome P450 genes in B. tabaci MED, among which 24 were novel. Phylogenetic analysis revealed broad functional and species-specific diversification in B. tabaci MED P450, suggesting the role of multiple P450 genes in detoxifying. Reverse transcription-real time quantitative PCR (RT-qPCR) showed that CYP4CS2, CYP4CS5, CYP4CS6, CYP4CS8, CYP6DW4, CYP6DW5, CYP6DW6, CYP6DZ8, and CYP6EN1 genes increased significantly after two days of exposure to imidacloprid. Interestingly, all nine genes belonged to the CYP4 and CYP6 families. A decrease in the expression of five genes (CYP6DW4, CYP6DW5, CYP6DW6, CYP6DZ8, and CYP4CS6) via RNA interference (RNAi) resulted in a significant increase in the mortalities of whiteflies when exposed to imidacloprid. These results indicate that the overexpression of the P450 genes may play an essential role in imidacloprid tolerance of B. tabaci MED. Thus, the present study provides basic information on P450 genes in B. tabaci MED, which will further help elucidate the insecticide resistance mechanism in the agricultural pest whitefly.

Investigating the effects of glyphosate on the bumblebee proteome and microbiota

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

Expression of subunits of an insecticide target receptor varies across tissues, life stages, castes, and species of social bees

Global losses of insects jeopardize ecosystem stability and crop pollination. Robust evidence indicates that insecticides have contributed to these losses. Notably, insecticides targeting nicotinic acetylcholine receptors (nAChRs) have neurotoxic effects on beneficial insects. Because each nAChR consists of five subunits, the alternative arrangements of subunits could create a multitude of receptors differing in structure and function. Therefore, understanding whether the use of subunits varies is essential for evaluating and predicting the effects of insecticides targeting such receptors. To better understand how the use and composition of nAChRs differ within and between insect pollinators, we analysed RNA-seq gene expression data from tissues and castes of Apis mellifera honey bees and life stages and castes of the Bombus terrestris bumble bees. We reveal that all analysed tissues express nAChRs and that relative expression levels of nAChR subunits vary widely across almost all comparisons. Our work thus shows fine-tuned spatial and temporal expression of nAChRs. Given that coexpression of subunits underpins the compositional diversity of functional receptors and that the affinities of insecticides depend on nAChR composition, our findings provide a likely mechanism for the various damaging effects of nAChR-targeting insecticides on insects. Furthermore, our results indicate that the appraisal of insecticide risks should carefully consider variation in molecular targets.

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.

Nutritional resources modulate the responses of three bee species to pesticide exposure

The response of bee species to various stressors is assumed to depend on the availability of sufficient nutrients in their environment. We compare the response of three bee species (Apis mellifera, Bombus terrestris, Osmia bicornis) under laboratory conditions. Survival, physiology, and sensitivity, after exposure to the fungicide prochloraz, the insecticide chlorantraniliprole, and their mixture with different nutritional resources (sugar only, sugar with amino acids or pollen) were observed. Prochloraz reduced the bee survival of A. mellifera and O. bicornis fed with pollen, but not with other diets. Chlorantraniliprole impaired the survival of A. mellifera fed with sugar or pollen diet, but not with amino acid diet. The mixture impaired survival of A. mellifera and O. bicornis in association with every diet. B. terrestris was only affected by chlorantraniliprole and its mixture with prochloraz fed with sugar diet. The activity of P450 reductase was higher in A. mellifera fed with amino acids in all treatments, whereas no effect emerged in O. bicornis and B. terrestris. Our results indicate that the sensitivity of bee species after exposure to agrochemicals is affected by diet. Thus, balanced and species-dependent nutrition ameliorated the effects. Further field studies are necessary to evaluate the potential effects of such mixtures on bee populations.

Genetics of tolerance in honeybees to the neonicotinoid clothianidin

The effects of neonicotinoid insecticides (NNIs) on honeybee health are intensely debated, with numerous studies showing negative effects of exposure, while others report no such effects. We carried out experiments to study the genetic and molecular basis of NNI tolerance in honeybees, which may underlie the discrepancies observed in the literature. We discovered that worker survival post-exposure to an acute oral dose of clothianidin is heritable (H ² = 37.8%). Tolerance to clothianidin was not associated with differences in the expression of detoxification enzymes in our experiments. Instead, mutations in the primary neonicotinoid detoxification genes CYP9Q1 and CYP9Q3 were strongly associated with worker survival post-clothianidin exposure. In some instances, the strong association between CYP9Q haplotypes and worker survival was associated with the protein's predicted binding affinity for clothianidin. Our findings have implications regarding future toxicological studies utilizing honeybees as a model pollinator.

Acute and chronic toxicity of imidacloprid in the pollinator fly, Eristalis tenax L., assessed using a novel oral bioassay

Imidacloprid is a neonicotinoid neurotoxin that remains widely used worldwide and persists in the environment, resulting in chronic exposure to non-target insects. To accurately map dose-dependent effects of such exposure across taxa, toxicological assays need to assess relevant modes of exposure across indicator species. However, due to the difficulty of these experiments, contact bioassays are most frequently used to quantify dose. Here, we developed a novel naturalistic feeding bioassay to precisely measure imidacloprid ingestion and its toxicity for acute and chronic exposure in a dipteran, Eristalis tenax L., an important member of an under-represented pollinator group. Flies which ingested imidacloprid dosages lower than 12.1 ng/mg all showed consistent intake volumes and learned improved feeding efficiency over successive feeding sessions. In contrast, at doses of 12.1 ng/mg and higher flies showed a rapid onset of severe locomotive impairment which prevented them from completing the feeding task. Neither probability of survival nor severe locomotive impairment were significantly higher than the control group until doses of 1.43 ng/mg or higher were reached. We were unable to measure a median lethal dose for acute exposure (72 h) due to flies possessing a relatively high tolerance for imidacloprid. However, with chronic exposure (18 days), mortality went up and an LD50 of 0.41 ng/mg was estimated. Severe locomotive impairment (immobilisation) tended to occur earlier and at lower dosages than lethality, with ED50s of 7.82 ng/mg and 0.17 ng/mg for acute and chronic exposure, respectively. We conclude that adult Eristalis possess a much higher tolerance to this toxin than the honeybees that they mimic. The similarity of the LD50 to other dipterans such as the fruitfly and the housefly suggests that there may be a phylogenetic component to pesticide tolerance that merits further investigation. The absence of obvious adverse effects at sublethal dosages also underscores a need to develop better tools for quantifying animal behaviour to evaluate the impact of insecticides on foraging efficiency in economically important species.

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.

Large-scale study investigating the effects of a tank mixture containing thiacloprid-prochloraz on honey bees (Apis mellifera)

Risk assessment of plant protection products (PPPs) will be conducted before authorization for their possible effects on non-target organisms, including honey bees. Tank mixtures are often common practice by farmers, and mostly their effects on honey bees are not routinely assessed. To enable a realistic assessment of laboratory-reported effects of a combination of the insecticide thiacloprid and fungicide prochloraz on honey bees, a large-scale field study with spray application in winter oilseed rape was conducted in four regions in Germany. Several parameters were investigated, including mortality, flight activity, and colony development. Residue analysis of various materials (e.g., dead bees, nectar, and pollen) was conducted to assess exposure level. We observed several intoxication symptoms 2 h after application, including a high number of moribund bees and dead bees on the first day after application (DAA +1) compared to the control. Adverse effects were observed on the number of open brood cells, with a significant reduction of approximately 22% compared to control over the experimental period. High residue concentrations were detected on flowers and dead bees on the day of application, which decreased rapidly within six days. The residue concentrations detected were higher in bee-collected materials than in materials stored in the hive. In conclusion, exposure to a combination containing thiacloprid-prochloraz poses a high risk to honey bees. Thus, the application of such a mixture on flowering crops is restricted in Germany.

Acute toxicity of pesticide mixtures to honey bees is generally additive, and well predicted by Concentration Addition

Understanding the frequency of non-additive effects of pesticides (synergism and antagonism) is important in the context of risk assessment. The goal of this study was to investigate the prevalence of non-additive effects of pesticides to honey bees (Apis mellifera). We investigated a large set of mixtures including insecticides and fungicides of different chemical modes of action and classes. The mixtures included represent a relevant sample of pesticides that are currently used globally. We investigated whether the experimental toxicity of the mixtures could be predicted based on the Concentration Addition (CA) model for acute contact and oral adult bee toxicity tests. We measured the degree of deviation from the additivity predictions of the experimental toxicity based on the well-known Mixture Deviation Ratio (MDR). Further, we investigated the appropriate MDR thresholds that should be used for the identification of non-additive effects based on acceptable rates for false positive (alpha) and true positive (beta) findings. We found that a deviation factor of MDR = 5 is a sound reference for labeling potential non-additive effects in acute adult bee experimental designs when assuming a typical Coefficient of Variation (CV%) = 100 in the determination of the LD₅₀ of a pesticide (a factor of 2× deviation in the LD ₅₀ resulting from inter-experimental variability). We found that only 2.4 % and 9 % of the mixtures evaluated had an MDR > 5 and MDR < 0.2, respectively. The frequency and magnitude of deviation from additivity found for bees in this study are consistent with those of other terrestrial and aquatic taxa. Our findings suggest that additivity is a good baseline for predicting the toxicity of pesticide mixtures to bees, and that the rare cases of synergy of pesticide mixtures to bees are not random but have a mechanistic basis.

Chronic larval exposure to thiacloprid impairs honeybee antennal selectivity, learning and memory performances

The use of agricultural neonicotinoid insecticides has sub-lethal chronic effects on bees that are more prevalent than acute toxicity. Among these insecticides, thiacloprid, a commonly used compound with low toxicity, has attracted significant attention due to its potential impact on the olfactory and learning abilities of honeybees. The effect of sub-lethal larval exposure to thiacloprid on the antennal activity of adult honeybees (Apis mellifera L.) is not yet fully understood. To address this knowledge gap, laboratory-based experiments were conducted in which honeybee larvae were administered thiacloprid (0.5 mg/L and 1.0 mg/L). Using electroantennography (EAG), the impacts of thiacloprid exposure on the antennal selectivity to common floral volatiles were evaluated. Additionally, the effects of sub-lethal exposure on odor-related learning and memory were also assessed. The results of this study reveal, for the first time, that sub-lethal larval exposure to thiacloprid decreased honeybee antenna EAG responses to floral scents, leading to increased olfactory selectivity in the high-dose (1.0 mg/L) group compared to the control group (0 mg/L vs. 1.0 mg/L: p = 0.042). The results also suggest that thiacloprid negatively affected odor-associated paired learning acquisition, as well as medium-term (1 h) (0 mg/L vs. 1.0 mg/L: p = 0.019) and long-term memory (24 h) (0 mg/L vs. 1.0 mg/L: p = 0.037) in adult honeybees. EAG amplitudes were dramatically reduced following R-linalool paired olfactory training (0 mg/L vs. 1.0 mg/L: p = 0.001; 0 mg/L vs. 0.5 mg/L: p = 0.027), while antennal activities only differed significantly in the control between paired and unpaired groups. Our results indicated that exposure to sub-lethal concentrations of thiacloprid may affect olfactory perception and learning and memory behaviors in honeybees. These findings have important implications for the safe use of agrochemicals in the environment.

Genomic architecture and sexually dimorphic expression underlying immunity in the red mason bee, Osmia bicornis

Insect pollinators provide crucial ecosystem services yet face increasing environmental pressures. The challenges posed by novel and reemerging pathogens on bee health means we need to improve our understanding of the immune system, an important barrier to infections and disease. Despite the importance of solitary bees, which are ecologically relevant, our understanding of the genomic basis and molecular mechanisms underlying their immune potential, and how intrinsic and extrinsic factors may influence it is limited. To improve our understanding of the genomic architecture underlying immunity of a key solitary bee pollinator, we characterized putative immune genes of the red mason bee, Osmia bicornis. In addition, we used publicly available RNA-seq datasets to determine how sexes differ in immune gene expression and splicing but also how pesticide exposure may affect immune gene expression in females. Through comparative genomics, we reveal an evolutionarily conserved set of more than 500 putative immune-related genes. We found genome-wide patterns of sex-biased gene expression, with greater enrichment of immune-related processes among genes with higher constitutive expression in males than females. Our results also suggest an up-regulation of immune-related genes in response to exposure to two common neonicotinoids, thiacloprid and imidacloprid. Collectively, our study provides important insights into the gene repertoire, regulation and expression differences in the sexes of O. bicornis, as well as providing additional support for how neonicotinoids can affect immune gene expression, which may affect the capacity of solitary bees to respond to pathogenic threats.