Pesticide risk assessment at the molecular level using honey bee cytochrome P450 enzymes: A complementary approach

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.

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.

Sulfoxaflor effects depend on the interaction with other pesticides and Nosema ceranae infection in the honey bee (Apis mellifera)

Honey bees health is compromised by many factors such as the use of agrochemicals in agriculture and the various diseases that can affect them. Multiple studies have shown that these factors can interact, producing a synergistic effect that can compromise the viability of honey bees. This study analyses the interactions between different pesticides and the microsporidium Nosema ceranae and their effect on immune and detoxification gene expression, sugar consumption and mortality in the Iberian western honey bee (Apis mellifera iberiensis). For this purpose, workers were infected with N. ceranae and subjected to a sugar-water diet with field concentrations of the pesticides sulfoxaflor, azoxystrobin and glyphosate. Increased sugar intake and altered immune and cytochrome P450 gene expression were observed in workers exposed to sulfoxaflor and infected with N. ceranae. None of the pesticides affected Nosema spore production in honey bee gut. Of the three pesticides tested (alone or in combination) only sulfoxaflor increased mortality in honey bees. Taken together, our results suggest that the effects of sulfoxaflor were attenuated in contact with other pesticides, and that Nosema infection leads to increase sugar intake in sulfoxaflor-exposed bees. Overall, this underlines the importance of studying the interaction between different stressors to understand their overall impact not only on honey bee but also on wild bees health.

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.

Mixture toxic effects of thiacloprid and cyproconazole on honey bees (Apis mellifera L.)

Pesticide exposure remains one of the main factors in the population decline of insect pollinators. It is urgently necessary to assess the effects of mixtures on pollinator risk assessments because they are often exposed to numerous agrochemicals. In the present study, we explored the mixture toxic effects of thiacloprid (THI) and cyproconazole (CYP) on honey bees (Apis mellifera L.). Our findings revealed that THI possessed higher acute toxicity to A. mellifera (96-h LC₅₀ value of 216.3 mg a.i. L^-1) than CYP (96-h LC₅₀ value of 601.4 mg a.i. L^-1). It's worth noting that the mixture of THI and CYP exerted an acute synergistic effect on honey bees. At the same time, the activities of detoxification enzyme cytochrome P450s (CYP450s) and neuro target enzyme Acetylcholinesterase (AChE), as well as the expressions of seven genes (CRBXase, CYP306A1, CYP6AS14, apidaecin, defensing-2, vtg, and gp-93) associated with detoxification metabolism, immune response, development, and endoplasmic reticulum stress, were significantly altered in the combined treatment compared with the corresponding individual exposures of THI or CYP. These data indicated that a mixture of THI and CYP could disturb the physiological homeostasis of honey bees. Our study provides a theoretical basis for in-depth studies on the impacts of pesticide mixtures on the health of honey bees. Our study also provides important guidance for the rational application of pesticide mixtures to protect pollinators in agricultural production effectively.

A Modeling Approach for Assessing Ecological Risks of Neonicotinoid Insecticides from Emission to Nontarget Organisms: A Case Study of Cotton Plant

The use of neonicotinoid insecticides in agriculture has posed threats to ecological systems, and there is a need to assess the ecological risks of neonicotinoids from emission to nontarget organisms. We introduced a modeling approach to assess the ecological risks of neonicotinoids using honeybee and earthworm as model organisms, and the simulation was flexible under different environmental conditions. Using the cotton plant as an example, the simulation results demonstrated that under current recommended application rates, the use of common neonicotinoid insecticides posed no threat to earthworms, with the simulated risk quotients (RQs) much lower than 1. However, the simulation for some neonicotinoid insecticides (e.g., acetamiprid) indicated that using these insecticides on cotton plants could threaten honeybees, with simulated RQs higher than 1. The variability analysis showed that in high-latitude regions, the unacceptable risk to honeybees posed by insecticide application can be further elevated due to cold, wet weather that results in relatively high insecticide levels in pollen and nectar. The model evaluation showed large overlaps of simulated risk intervals between the proposed and existing (BeeREX) models. Because the proposed and existing models have different simulation mechanisms, we recommend that these two models be used together to complement each other in future studies. Environ Toxicol Chem 2023;42:928-938. © 2023 SETAC.

Over-expression of CP9 and CP83 increases whitefly cell cuticle thickness leading to imidacloprid resistance

Cuticular proteins (CPs) play an important role in protecting insects from adverse environmental conditions, like neonicotinoid insecticides, which are heavily used for numerous pests and caused environmental problems and public health concerns worldwide. However, the relationship between CPs and insecticides resistance in Bemisia tabaci, a serious and developed high insecticide resistance, is lacking. In this study, 125 CPs genes were identified in B. tabaci. Further phylogenetic tree showed the RR-2-type genes formed large gene groups in B. tabaci. Transcriptional expression levels of CPs genes at different developmental stages revealed that some CPs genes may play a specific role in insect development. The TEM results indicated that the cuticle thickness of susceptible strain was thinner than imidacloprid-resistance strain. Furthermore, 16 CPs genes (5 in RR-1 subfamily, 7 in RR-2 subfamily, 3 in CPAP3 subfamily and 1 in CPCFC subfamily) were activated in response to imidacloprid. And RNAi results indicated that CP9 and CP83 involved in imidacloprid resistance. In conclusion, this study was the first time to establish a basic information framework and evolutionary relationship between CPs and imidacloprid resistance in B. tabaci, which provides a basis for proposing integrated pest management strategies.

Contrasting effects of fungicide and herbicide active ingredients and their formulations on bumblebee learning and behaviour

Fungicides and herbicides are two of the most heavily applied pesticide classes in the world, but receive little research attention with regards to their potential impacts on bees. As they are not designed to target insects, the mechanisms behind potential impacts of these pesticides are unclear. It is therefore important to understand their influence at a range of levels, including sublethal impacts on behaviours such as learning. We used the proboscis extension reflex (PER) paradigm to assess how the herbicide glyphosate and the fungicide prothioconazole affect bumblebee olfactory learning. We also assessed responsiveness, and compared the impacts of these active ingredients and their respective commercial formulations (Roundup Biactive and Proline). We found that learning was not impaired by either formulation but, of the bees that displayed evidence of learning, exposure to prothioconazole active ingredient increased learning level in some situations, while exposure to glyphosate active ingredient resulted in bumblebees being less likely to respond to antennal stimulation with sucrose. Our data suggest that fungicides and herbicides may not negatively impact olfactory learning ability when bumblebees are exposed orally to field-realistic doses in a lab setting, but that glyphosate has the potential to cause changes in responsiveness in bees. As we found impacts of active ingredients and not commercial formulations, this suggests that co-formulants may modify impacts of active ingredients in the products tested on olfactory learning without being toxic themselves. More research is needed to understand the mechanisms behind potential impacts of fungicides and herbicides on bees, and to evaluate the implications of behavioural changes caused by glyphosate and prothioconazole for bumblebee fitness.

Does pesticide use in agriculture present a risk to the terrestrial biota?

Inadequate pesticide application practices have many implications on human and environmental health. This research aimed at assessing pesticide risks on bees, non-target arthropods (NTAs) and earthworms, using PRIMET (Pesticide Risks in the Tropics to Man, Environment and Trade), a pesticide risk model, in the western highlands agro-ecological zone of Cameroon. For this purpose, information on pesticide usage stratagem (dosage, application interval and number of applications) and ecotoxicological properties (median lethal doses, persistence and no observable effect concentration) were gathered and entered into PRIMET to acquire the Predicted Exposure Concentration (PEC), No Effect Concentration (NEC) and Exposure Toxicity Ratio, ETR = PEC / NEC). The risk assessment revealed that the riskiest pesticides for earthworms were acetamiprid, glyphosate and imidacloprid with ETR values of 2963, 1667 and 419 respectively. For bees, acetamiprid, cypermethrin, emamectin benzoate, imidacloprid, and lambda-cyhalothrin were highly risky, with respective ETR values of 3252, 487, 278, 1383 and 295. The model predicted NTAs to be predominantly defenceless against cypermethrin and imidacloprid, as these compounds exhibited the topmost values of ETR of, 4.3 × 10⁸ and 4.4 × 10⁷, respectively. Other pesticides that were modelled to be highly risky to NTAs comprised chlorothalonil (ETR = 2076), cymoxanil (ETR = 1133), emamectin benzoate (ETR = 1700), lambda-cyhalothrin (ETR = 4900) and metalaxyl (ETR = 2303). Some compounds gave evidence of multi-level risks: imidacloprid exhibited high risk to all the organisms (earthworms, bees and NTAs); acetamiprid was risky to earthworms and bees, while cypermethrin, emamectin benzoate and lambda-cyhalothrin, were modelled to pose a risk to bees and NTAs. Regulating the use of these perilous pesticides should be encouraged in agroecosystems to protect environmental and human health.

The use of sewage sludge as remediation for imidacloprid toxicity in soils

This study investigated the influence of the sewage sludge (SS) soil amendment on the chronic toxicity of imidacloprid (through the seed dressing formulation MUCH 600 FS®-600 g active ingredient L^-1) to collembolans Folsomia candida. Individuals 10-12 days old were exposed to two contrasting tropical soils (Oxisol and Entisol) amended with SS doses (0, 20, 40, 80, 160, and 320 g SS kg^-1 soil; the SS doses have low intrinsic toxicity, which was checked before its application) in a full factorial combination with five imidacloprid concentrations (varying from 0.25 to 4 mg kg^-1 in Oxisol and 0.03-0.5 mg kg^-1 in Entisol) plus a control. None of the SS doses (without imidacloprid) in both soils reduced the number of generated juvenile collembolans. The imidacloprid concentrations reducing the collembolan reproduction in 50% (EC₅₀) in Oxisol and Entisol without SS were 0.49 and 0.08 mg kg^-1, respectively. However, the EC₅₀ values generally increased with increasing SS doses in soils, varying from 1.03 to 1.41 in Oxisol and 0.07 to 0.21 in Entisol. The SS-amended soils showed 2.1- to 2.9-fold lower imidacloprid toxicity (EC₅₀-based) in Oxisol and 1.8- to 2.7-fold lower toxicity in Entisol. Our results suggest the most effective SS doses alleviating the imidacloprid toxicity (EC₅₀-based) to collembolans are 20 g kg^-1 in Oxisol and 80 g kg^-1 in Entisol. These results indicate that the tested SS has the potential to be employed as a soil amendment agent by reducing the toxicity of imidacloprid to the reproduction of F. candida.

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.

Using the Honey Bee (Apis mellifera L.) Cell Line AmE-711 to Evaluate Insecticide Toxicity

One of the main contributors to poor productivity and elevated mortality of honey bee colonies globally is insecticide exposure. Whole-organism and colony-level studies have demonstrated the effects of insecticides on many aspects of honey bee biology and have also shown their interactions with pathogens. However, there is a need for in vitro studies using cell lines to provide greater illumination of the effects of insecticides on honey bee cellular and molecular processes. We used a continuous cell line established from honey bee embryonic tissues (AmE-711) in assays that enabled assessment of cell viability in response to insecticide exposure. We exposed AmE-711 cells to four formulations, each containing a different insecticide. Treatment of cells with the insecticides resulted in a concentration-dependent reduction in viability after a 24-h exposure, whereas long-term exposure (120 h) to sublethal concentrations had limited effects on viability. The 24-h exposure data allowed us to predict the half-maximal lethal concentration (LC50) for each insecticide using a four-parameter logistical model. We then exposed cells for 12 h to the predicted LC50 and observed changes in morphology that would indicate stress and death. Reverse transcription-quantitative polymerase chain reaction analysis corroborated changes in morphology: expression of a cellular stress response gene, 410087a, increased after an 18-h exposure to the predicted LC50. Demonstration of the effects of insecticides through use of AmE-711 provides a foundation for additional research addressing issues specific to honey bee toxicology and complements whole-organism and colony-level approaches. Moreover, advances in the use of AmE-711 in high-throughput screening and in-depth analysis of cell regulatory networks will promote the discovery of novel control agents with decreased negative impacts on honey bees. Environ Toxicol Chem 2023;42:88-99. Published 2022. This article is a U.S. Government work and is in the public domain in the USA. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Effects of chronic exposure to the new insecticide sulfoxaflor in combination with a SDHI fungicide in a solitary bee

The recent EU ban of the three most widely used neonicotinoids (imidacloprid, thiamethoxam and clothianidin) to all outdoors applications has stimulated the introduction of new insecticides into the market. Sulfoxaflor is a new systemic insecticide that, like neonicotinoids, acts as a modulator of nicotinic acetylcholine receptors. In agro-environments, bees can be exposed to this compound via contaminated pollen and nectar for long periods of time. Therefore, it is important to assess the potential effects of chronic exposure to sulfoxaflor, alone and in combination with fungicides, on pollinators. In this study, we tested the effects of chronic exposure to two field concentrations of sulfoxaflor (20 and 100 ppb) alone and in combination with four concentrations of the fungicide fluxapyroxad (7500, 15,000, 30,000 and 60,000 ppb) on syrup consumption and longevity in females of the solitary bee Osmia bicornis L. Exposure to 20 ppb of sulfoxaflor, alone and in combination with the fungicide, stimulated syrup consumption, but did not affect longevity. In contrast, syrup consumption decreased in bees exposed to 100 ppb, all of which died after 2-6 days of exposure. We found no evidence of synergism between the two compounds at any of the two sulfoxaflor concentrations tested. Comparison of our findings with the literature, confirms that O. bicornis is more sensitive to sulfoxaflor than honey bees. Our results highlight the need to include different bee species in risk assessment schemes.

The acute toxicity of pesticide mixtures to honeybees

Honeybees (Apis mellifera) frequently live in complex environments where exposure to mixtures of pesticides is possible. Although several studies have expressed concern regarding the combined effects of pesticide mixtures, other studies did not find increased toxicity. Thus, the primary objective of this study was to identify peer-reviewed literature measuring the toxicity of pesticide mixtures to honeybees and determine how frequently synergistic interactions occur. Many experiments (258) were identified that met the criteria for inclusion. When considering all experiments, 34% of experiments had model deviation ratios (MDR; expected toxicity/observed toxicity) greater than 2, suggesting greater-than-additive toxicity. Twelve percent of experiments had MDR values greater than 5, with several studies exceeding 100. However, most experiments that had higher MDRs included azole fungicides or acaricides as a component of the mixture. After removal of these groups, only 8% of experiments exceeded an MDR of 2, and no experiments exceeded 5. Moreover, the influence of the azole fungicides was dose dependent. If only experiments that used azole exposure at environmentally relevant concentrations were considered, azole fungicides had limited impact on neonicotinoid insecticides. However, pyrethroid insecticides still had greater than expected toxicity with 80% of experiments having MDR values greater than 2. Acaricides also had greater than expected incidence of synergy with approximately 30% of studies reporting MDR values greater than 2. It should be noted that even the azole studies considered environmentally relevant frequently used maximum exposure rates and worst-case exposure scenarios. The primary finding is that synergy is uncommon except for a few cases where known synergists (azole fungicides) and pesticides with variable metabolism potential, such as some pyrethroids, are in combination. Future work is still needed to refine the relevance of azole fungicides at commonly occurring environmental concentrations. Integr Environ Assess Manag 2022;18:1694-1704. © 2022 SETAC.

Intra-specific variation in sensitivity of Bombus terrestris and Osmia bicornis to three pesticides

There is growing evidence that pesticides may be among the causes of worldwide bee declines, which has resulted in repeated calls for their increased scrutiny in regulatory assessments. One recurring concern is that the current frameworks may be biased towards assessing risks to the honey bee. This paradigm requires extrapolating toxicity information across bee species. Most research effort has therefore focused on quantifying differences in sensitivity across species. However, our understanding of how responses to pesticides may vary within a species is still very poor. Here we take the first steps towards filling this knowledge gap by comparing acute, lethal hazards in sexes and castes of the eusocial bee Bombus terrestris and in sexes of the solitary bee Osmia bicornis after oral and contact exposure to the pesticides sulfoxaflor, Amistar (azoxystrobin) and glyphosate. We show that sensitivity towards pesticides varies significantly both within and across species. Bee weight was a meaningful predictor of pesticide susceptibility. However, weight could not fully explain the observed differences, which suggests the existence of unexplored mechanisms regulating pesticide sensitivity across bee sexes and castes. Our data show that intra-specific responses are an overlooked yet important aspect of the risk assessment of pesticides in bees.

Sequential phase I metabolism of pyrethroids by duplicated CYP6P9 variants results in the loss of the terminal benzene moiety and determines resistance in the malaria mosquito Anopheles funestus

Pyrethroid resistance in Anopheles funestus is threatening the eradication of malaria. One of the major drivers of pyrethroid resistance in An. funestus are cytochrome P450 monooxygenases CYP6P9a and CYP6P9b, which are found upregulated in resistant An. funestus populations from Sub-Saharan Africa and are known to metabolise pyrethroids. Here, we have functionally expressed CYP6P9a and CYP6P9b variants and investigated their interactions with azole-fungicides and pyrethroids. Some azole fungicides such as prochloraz inhibited CYP6P9a and CYP6P9b at nanomolar concentrations, whereas pyrethroids were weak inhibitors (>100 μM). Amino acid sequence comparisons suggested that a valine to isoleucine substitution at position 310 in the active site cavity of CYP6P9a and CYP6P9b, respectively, might affect substrate binding and metabolism. We therefore swapped the residues by site directed mutagenesis to produce CYP6P9a^I310V and CYP6P9b^V310I. CYP6P9b^V310I produced stronger metabolic activity towards coumarin substrates and pyrethroids, particularly permethrin. The V310I mutation was previously also detected in a pyrethroid resistant field population of An. funestus in Benin. Additionally, we found the first metabolite of permethrin and deltamethrin after hydroxylation, 4'OH permethrin and 4'OH deltamethrin, were also suitable substrates for CYP6P9-variants, and were depleted by both enzymes to a higher extent than as their respective parent compounds (approximately 20% more active). Further, we found that both metabolites were toxic against An. funestus FANG (pyrethroid susceptible) but not towards FUMOZ-R (pyrethroid resistant) mosquitoes, the latter suggesting detoxification by overexpressed CYP6P9a and CYP6P9b. We confirmed by mass-spectrometric analysis that CYP6P9a and CYP6P9b are capable of cleaving phenoxybenzyl-ethers in type I pyrethroid permethrin and type II pyrethroid deltamethrin and that both enzymes preferentially metabolise trans-permethrin. This provides new insight into the metabolism of pyrethroids and a greater understanding of the molecular mechanisms of pyrethroid resistance in An. funestus.

Phylogenomic and functional characterization of an evolutionary conserved cytochrome P450-based insecticide detoxification mechanism in bees

Bee pollinator pesticide risk assessment is a regulatory requirement for pesticide registration and is largely based on experimental data collected for surrogate species such as the western honeybee. Recently, CYP9Q3, a honeybee cytochrome P450 enzyme, has been shown to efficiently detoxify certain insecticides such as the butenolide flupyradifurone and the neonicotinoid thiacloprid. Here we analyzed genomic data for 75 bee species and demonstrated by the recombinant expression of 26 CYP9Q3 putative functional orthologs that this detoxification principle is an evolutionary conserved mechanism across bee families. Our toxicogenomics approach has the potential to inform pesticide risk assessment for nonmanaged bee species that are not accessible for acute toxicity testing.

The regulatory process for assessing the risks of pesticides to bees relies heavily on the use of the honeybee, Apis mellifera, as a model for other bee species. However, the validity of using A. mellifera as a surrogate for other Apis and non-Apis bees in pesticide risk assessment has been questioned. Related to this line of research, recent work on A. mellifera has shown that specific P450 enzymes belonging to the CYP9Q subfamily act as critically important determinants of insecticide sensitivity in this species by efficiently detoxifying certain insecticide chemotypes. However, the extent to which the presence of functional orthologs of these enzymes is conserved across the diversity of bees is unclear. Here we used a phylogenomic approach to identify > 100 putative CYP9Q functional orthologs across 75 bee species encompassing all major bee families. Functional analysis of 26 P450s from 20 representative bee species revealed that P450-mediated detoxification of certain systemic insecticides, including the neonicotinoid thiacloprid and the butenolide flupyradifurone, is conserved across all major bee pollinator families. However, our analyses also reveal that CYP9Q-related genes are not universal to all bee species, with some Megachilidae species lacking such genes. Thus, our results reveal an evolutionary conserved capacity to metabolize certain insecticides across all major bee families while identifying a small number of bee species where this function may have been lost. Furthermore, they illustrate the potential of a toxicogenomic approach to inform pesticide risk assessment for nonmanaged bee species by predicting the capability of bee pollinator species to break down synthetic insecticides.

The Value of Hazard Quotients in Honey Bee (Apis mellifera) Ecotoxicology: A Review

Estimates of pesticide application hazards have grown to be one of the most common methodologies for evaluating the impact of pest management practices on honey bees. Typically, hazards are estimated by calculating a Hazard Quotient (HQ), which is based on acute toxicity data for different pesticides and the quantity of those pesticides applied to a field or detected on bees and matrices associated with their hive (honey, wax, pollen, and/or bee bread). Although use of HQ is widespread, there have been few reviews of this methodology, particularly with focus on how effective this method is at predicting effects of pesticides on hives. We evaluated 36 relevant papers, containing calculations of HQ to estimate hazards to honey bees. We observed that HQ was primarily calculated using two different approaches: (1) from the concentration of pesticides in the food, hive, or tissues of honey bees or (2) using the field application rate of the active ingredient as the estimation of pesticide hazard. Within and between HQ calculation methods, thresholds vary widely with some HQ thresholds set below 1 and others set at 10,000. Based on our review we identify key weakness with current HQ methodology and how studies relate HQ to honey bee health endpoints. First, HQ thresholds from studies of pesticides in hives are not based on the same pesticide consumption models from the EPA, potentially overestimating the risk of impacts to colonies. Conversely, HQ estimates calculated from field application rates are not based on eco-toxicological estimates of field exposure, resulting in an overestimation of pesticide reaching colonies. We suggest it is for these reasons that there is poor correspondence between HQ and field-level honey bee health endpoints. Considering these challenges, HQ calculations should be used cautiously in future studies and more research should be dedicated to field level exposure models.

Assessment of ecotoxicological effects of agrochemicals on bees using the PRIMET model, in the Tiko plain (South-West Cameroon)

Pesticide utilization in agriculture has many harmful effects of non-target organisms. This study assessed pesticide risk to bees using PRIMET (Pesticide Risks in the Tropics to Man, Environment and Trade), a pesticide risk model. Data was collected on pesticide application scheme (active ingredient, crop, dose, number of applications, application interval) and ecotoxicological properties (LD_50-Bee). These two groups of variables were introduced one after the other in PRIMET 2.0 to obtain the Predicted Exposure Concentration (PEC_bee), No Effect Concentration (NEC_bee) and Exposure Toxicity Ratio (ETR_bee = PEC_bee/NEC_bee). Eight insecticides (out of 15 assessed) and 1 nematicide (out of 1) posed a Definite Risk to bees with imidacloprid (PEC = 4412 g/ha; ETR = 1.09E+07) at the top position. Six insecticides (out of 16), and 1 nematicide (out of 1) posed a Possible Risk to bees. The insecticide oxamyl (PEC = 2044g/ha, ETR = 87) had the highest ETR in this category, followed by the nematicide ethoprophos (PEC = 5.4E+04 g/ha; ETR = 69). The results of this study revealed that 27 compounds, including 1 insecticide (out of 15), 10 herbicides (out of 10) and 16 fungicides (out of 16) posed No Risk to bees. Herbicides and fungicides appeared “safer” for bees as compared to other pesticide families. The fungicides, mancozeb (PEC = 1 g/ha, ETR = 0.006) and maneb (PEC = 1 g/ha, ETR = 0.006) had the lowest ETR out of all the 43 compounds assessed in the study. Regulation on the importation, distribution and use should be reinforced for very hazardous compounds such as imidacloprid, carbofuran, thiamethoxam and metaldehyde. Substituting the most toxic pesticides with less toxic ones such as novaluron (insecticide), oxadiazon (herbicide), mancozeb (fungicide) and maneb (fungicide) may help to reduce pesticide pressure on the environment.

Towards understanding transfluthrin efficacy in a pyrethroid-resistant strain of the malaria vector Anopheles funestus with special reference to cytochrome P450-mediated detoxification

Malaria vector control interventions rely heavily on the application of insecticides against anopheline mosquitoes, in particular the fast-acting pyrethroids that target insect voltage-gated sodium channels (VGSC). Frequent applications of pyrethroids have resulted in resistance development in the major malaria vectors including Anopheles funestus, where resistance is primarily metabolic and driven by the overexpression of microsomal cytochrome P450 monooxygenases (P450s). Here we examined the pattern of cross-resistance of the pyrethroid-resistant An. funestus strain FUMOZ-R towards transfluthrin and multi-halogenated benzyl derivatives, permethrin, cypermethrin and deltamethrin in comparison to the susceptible reference strain FANG. Transfluthrin and two multi-fluorinated derivatives exhibited micromolar potency - comparable to permethrin - to functionally expressed dipteran VGSC in a cell-based cation influx assay. The activity of transfluthrin and its derivatives on VGSC was strongly correlated with their contact efficacy against strain FUMOZ-R, although no such correlation was obtained for the other pyrethroids due to their rapid detoxification by the resistant strain. The low resistance levels for transfluthrin and derivatives in strain FUMOZ-R were only weakly synergized by known P450 inhibitors such as piperonyl butoxide (PBO), triflumizole and 1-aminobenzotriazole (1-ABT). In contrast, deltamethrin toxicity in FUMOZ-R was synergized > 100-fold by all three P450 inhibitors. The biochemical profiling of a range of fluorescent resorufin and coumarin compounds against FANG and FUMOZ-R microsomes identified 7-benzyloxymethoxy-4-trifluoromethylcoumarin (BOMFC) as a highly sensitive probe substrate for P450 activity. BOMFC was used to develop a fluorescence-based high-throughput screening assay to measure the P450 inhibitory action of potential synergists. Azole fungicides prochloraz and triflumizole were identified as extremely potent nanomolar inhibitors of microsomal P450s, strongly synergizing deltamethrin toxicity in An. funestus. Overall, the present study contributed to the understanding of transfluthrin efficacy at the molecular and organismal level and identified azole compounds with potential to synergize pyrethroid efficacy in malaria vectors.

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Transfluthrin and derivatives lack cross-resistance in resistant Anopheles funestus.

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Pyrethroid resistance in An. funestus is strongly synergized by azole fungicides.

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BOMFC is a highly active fluorescent probe substrate for microsomal cytochrome P450 monooxygenases in An. funestus.

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Azole fungicides are nanomolar inhibitors of microsomal cytochrome P450 monooxygenases in An. funestus.

A mechanism-based approach unveils metabolic routes potentially mediating chlorantraniliprole synergism in honey bees, Apis mellifera L., by azole fungicides

BACKGROUND

Almond production in California is an intensively managed agroecosystem dependent on managed pollination by honey bees, Apis mellifera L. A recent laboratory study reported synergism in honey bees between chlorantraniliprole, a common diamide insecticide used in almond orchards, and the fungicide propiconazole. Indeed, there is an emerging body of evidence that honey bee cytochrome P450 monooxygenases of the CYP9Q subfamily are involved in the detoxification of insecticides across a diverse range of chemical classes. The objective of the present study was to unveil the molecular background of the described synergism and to explore the potential role of CYP9Q enzymes in diamide detoxification.

RESULTS

Our study confirmed the previously reported synergistic potential of propiconazole on chlorantraniliprole in acute contact toxicity bioassays, whereas no synergism was observed for flubendiamide. Fluorescence-based biochemical assays revealed an interaction of chlorantraniliprole, but not flubendiamide, with functionally expressed CYP9Q2 and CYP9Q3. These findings were validated by an increased chlorantraniliprole tolerance of transgenic Drosophila lines expressing CYP9Q2/3, and an analytically confirmed oxidative metabolism of chlorantraniliprole by recombinantly expressed enzymes. Furthermore, we showed that several triazole fungicides used in almond orchards, including propiconazole, were strong nanomolar inhibitors of functionally expressed honey bee CYP9Q2 and CYP9Q3, whereas other fungicides such as iprodione and cyprodinil did not inhibit these enzymes.

CONCLUSION

Honey bee CYP9Q enzymes are involved in chlorantraniliprole metabolism and inhibited by triazole fungicides possibly leading to synergism in acute contact toxicity bioassays. Our mechanistic approach has the potential to inform tier I honey bee pesticide risk assessment.

Biochemical profiling of functionally expressed CYP6P9 variants of the malaria vector Anopheles funestus with special reference to cytochrome b5 and its role in pyrethroid and coumarin substrate metabolism

Cytochrome P450 monooxygenases (P450s) are well studied enzymes catalyzing the oxidative metabolism of xenobiotics in insects including mosquitoes. Their duplication and upregulation in agricultural and public health pests such as anopheline mosquitoes often leads to an enhanced metabolism of insecticides which confers resistance. In the laboratory strain Anopheles funestus FUMOZ-R the duplicated P450s CYP6P9a and CYP6P9b are highly upregulated and proven to confer pyrethroid resistance. Microsomal P450 activity is regulated by NADPH cytochrome P450 oxidoreductase (CPR) required for electron transfer, whereas the modulatory role of cytochrome b₅ (CYB5) on insect P450 activity is less clear. In previous studies CYP6P9a and CYP6P9b were recombinantly expressed in tandem with An. gambiae CPR using E. coli-expression systems and CYB5 added to the reaction mix to enhance activity. However, the precise role of CYB5 on substrate turn-over when combined with CYP6P9a and CYP6P9b remains poorly investigated, thus one objective of our study was to address this knowledge gap. In contrast to the CYP6P9 variants, the expression levels of both CYB5 and CPR were not upregulated in the pyrethroid resistant FUMOZ-R strain when compared to the susceptible FANG strain, suggesting no immediate regulatory role of these genes in pyrethroid resistance in FUMOZ-R. Here, for the first time we recombinantly expressed CYP6P9a and CYP6P9b from An. funestus in a baculovirus expression system using High-5 insect cells. Co-expression of each enzyme with CPR from either An. gambiae or An. funestus did not reveal noteworthy differences in catalytic capacity. Whereas the co-expression of An. funestus CYB5 - tested at different multiplicity of infection (MOI) ratios - resulted in a significantly higher metabolization of coumarin substrates as measured by fluorescence assays. This was confirmed by Michaelis-Menten kinetics using the most active substrate, 7-benzyloxymethoxy-4-trifluoromethylcoumarin (BOMFC). We observed a similar increase in coumarin substrate turnover by adding human CYB5 to the reaction mix. Finally, we compared by UPLC-MS/MS analysis the depletion rate of deltamethrin and the formation of 4'OH-deltamethrin by recombinantly expressed CYP6P9a and CYP6P9b with and without CYB5 and detected no difference in the extent of deltamethrin metabolism. Our results suggest that co-expression (or addition) of CYB5 with CYP6P9 variants, recombinantly expressed in insect cells, can significantly enhance their metabolic capacity to oxidize coumarins, but not deltamethrin.

Regioselective hydroxylation of carbendazim by mammalian cytochrome P450: A combined experimental and computational study

Carbendazim (CBZ), a broad-spectrum pesticide frequently detected in fruits and vegetables, could trigger potential toxic risks to mammals. To facilitate the assessment of health risks, this study aimed to characterize the cytochrome P450 (CYPs)-mediated metabolism profiles of CBZ by a combined experimental and computational study. Our results demonstrated that CYPs-mediated region-selective hydroxylation was a major metabolism pathway for CBZ in liver microsomes from various species including rat, mouse, minipig, dog, rabbit, guinea pig, monkey, cow and human, and the metabolite was biosynthesized and well-characterized as 6-OH-CBZ. CYP1A displayed a predominant role in the region-selective hydroxylation of CBZ that could attenuate its toxicity through converting it into a less toxic metabolite. Meanwhile, five other common pesticides including chlorpyrifos-methyl, prochloraz, chlorfenapyr, chlorpyrifos, and chlorothalonil could significantly inhibit the region-selective hydroxylation of CBZ, and consequently remarkably increased CBZ exposure in vivo. Furthermore, computational study clarified the important contribution of the key amino acid residues Ser122, and Asp313 in CYP1A1, as well as Asp320 in CYP1A2 to the hydroxylation of CBZ through hydrogen bonds. These results would provide some useful information for the metabolic profiles of CBZ by mammalian CYPs, and shed new insights into CYP1A-mediated metabolic detoxification of CBZ and its health risk assessment.

The Role of Cytochrome P450s in Insect Toxicology and Resistance

Insect cytochrome P450 monooxygenases (P450s) perform a variety of important physiological functions, but it is their role in the detoxification of xenobiotics, such as natural and synthetic insecticides, that is the topic of this review. Recent advances in insect genomics and postgenomic functional approaches have provided an unprecedented opportunity to understand the evolution of insect P450s and their role in insect toxicology. These approaches have also been harnessed to provide new insights into the genomic alterations that lead to insecticide resistance, the mechanisms by which P450s are regulated, and the functional determinants of P450-mediated insecticide resistance. In parallel, an emerging body of work on the role of P450s in defining the sensitivity of beneficial insects to insecticides has been developed. The knowledge gained from these studies has applications for the management of P450-mediated resistance in insect pests and can be leveraged to safeguard the health of important beneficial insects.

Spodoptera frugiperda Sf9 cells as a model system to investigate the role of detoxification gene expression in response to xenobiotics

Spodoptera frugiperda (fall armyworm) is a highly destructive invasive pest that feeds on numerous crops including maize and rice. It has developed sophisticated mechanisms to detoxify xenobiotics such as secondary plant metabolites as well as manmade insecticides. The aim of the study was to explore the detoxification response to plant secondary metabolites and insecticides employing a S. frugiperda Sf9 cell model exposed to indole 3-carbinol (I3C) and methoprene. The cell Inhibitory Concentration 50 (IC₅₀) for these molecules was determined and IC₁₀, IC₂₀ and IC₃₀ doses were used to monitor the induction profiles of detoxification genes. Cytochrome P450 monooxygenases (P450s) of the CYP9A subfamily were the most inducible genes of the seven examined. Our results also showed the induction of the transcription factor Cap'n'collar isoform C (CncC). Transient transformation of Sf9 cells overexpressing CncC and its partner muscle aponeurosis fibromatosis (Maf) induces overexpression of CYP4M14, CYP4M15, CYP321A9 and GSTE1 while CYP9As were not induced. Next, we determined the capacity of recombinantly expressed CYP9A30, CYP9A31 and CYP9A32 to interact with methoprene and I3C. Fluorescence-based biochemical assays revealed an interaction of methoprene with functionally expressed CYP9A30, CYP9A31 and CYP9A32 whereas almost no interaction was detected for I3C, suggesting the ability of CYP9As to metabolize methoprene. Our results showed that Sf9 cells could be a useful model to decipher detoxification pathways of S. frugiperda.

Pollution status, influencing factors and environmental risks of neonicotinoids, fipronil and its metabolites in a typical semi-closed bay in China

The occurrence, spatiotemporal variations, influence factors and environmental risks of eight common neonicotinoids (NEOs), fipronil, and three fipronil metabolites (fipronil and its metabolites are collectively referred to as FIPs) in different seasons from the estuary to the inner area of Jiaozhou Bay, China were comprehensively investigated. First- and second-generation NEOs were found to be the predominant pesticides in this area. The average contents of ∑NEOs and ∑FIPs from the estuary to the inner bay decreased from 12.99 ng/L to 0.82 ng/L and from 1.10 ng/L to 0.17 ng/L, respectively. NEO and FIP concentrations were higher in summer and autumn. High ∑NEO content is distributed in main inflow rivers, such as Dagu River and Licun River, which are influenced by pesticide application. NEO concentrations in all rivers were high upstream and low downstream because of the influence of heavy rainfall and seawater dilution in summer. NEO concentrations were high along the coast and low at the mouth and center of Jiaozhou Bay in summer and autumn and evenly distributed in winter and spring. Temperature has a great influence on most NEOs and FIPs owing to its effect on their degradation. Nitrogen-containing nutrients have an important influence on the distribution of fipronil and acetamiprid, which may be due to the activity of nitrogen-containing functional groups in their structure. Only Licun River, Dagu River and Haibo river sewage treatment plant in summer posed a certain risk of chronic toxicity for NEOs using the new threshold established by the species sensitive distribution (SSD) method for Chinese native aquatic lives. These findings should arouse people's attention.

Binary and ternary toxicological interactions of clothianidin and eight commonly used pesticides on honey bees (Apis mellifera)

Although many toxicological evaluations have been conducted for honey bees (Apis mellifera), most of these studies have only focused on the effects of individual chemicals. However, honey bees are usually exposed to pesticide mixtures under field conditions. In this study, we examined the effects of individual pesticides and mixtures of clothianidin (CLO) with eight other pesticides [carbaryl (CAR), thiodicarb (THI), chlorpyrifos (CHL), beta-cyfluthrin (BCY), gamma-cyhalothrin (GCY), tetraconazole (TET), spinosad (SPI) and indoxacarb (IND)] on honey bees using a feeding method. Toxicity tests of a 4-day exposure to individual pesticides revealed that CLO had the highest toxicity to A. mellifera, with an LC₅₀ value of 0.24 μg a.i. mL^-1, followed by IND and CHL with LC₅₀ values of 3.40 and 3.56 μg a.i. mL^-1, respectively. SPI and CAR had relatively low toxicities, with LC₅₀ values of 7.19 and 8.42 μg a.i. mL^-1, respectively. In contrast, TET exhibited the least toxicity, with an LC₅₀ value of 258.7 μg a.i. mL^-1. Most binary mixtures of CLO with other pesticides exerted additive and antagonistic effects. However, all the ternary mixtures containing CLO and TET (except for CLO+TET+THD) elicited synergistic responses to bees. Either increased numbers of components in the mixture or/and a unique mode of action appeared to be responsible for the higher toxicity of mixtures. Our findings emphasized the need for risk assessment of pesticide mixtures rather than the individual chemicals. Our data also provided information that might help growers avoid increased toxicity and unnecessary injury to pollinators.

A toxicogenomics approach reveals characteristics supporting the honey bee (Apis mellifera L.) safety profile of the butenolide insecticide flupyradifurone

Flupyradifurone, a novel butenolide insecticide, selectively targets insect nicotinic acetylcholine receptors (nAChRs), comparable to structurally different insecticidal chemotypes such as neonicotinoids and sulfoximines. However, flupyradifurone was shown in acute toxicity tests to be several orders of magnitude less toxic to western honey bee (Apis mellifera L.) than many other insecticides targeting insect nAChRs. The underlying reasons for this difference in toxicity remains unknown and were investigated here. Pharmacokinetic studies after contact application of [¹⁴C]flupyradifurone to honey bees revealed slow uptake, with internalized compound degraded into a few metabolites that are all practically non-toxic to honey bees in both oral and contact bioassays. Furthermore, receptor binding studies revealed a lack of high-affinity binding of these metabolites to honey bee nAChRs. Screening of a library of 27 heterologously expressed honey bee cytochrome P450 enzymes (P450s) identified three P450s involved in the detoxification of flupyradifurone: CYP6AQ1, CYP9Q2 and CYP9Q3. Transgenic Drosophila lines ectopically expressing CYP9Q2 and CYP9Q3 were significantly less susceptible to flupyradifurone when compared to control flies, confirming the importance of these P450s for flupyradifurone metabolism in honey bees. Biochemical assays using the fluorescent probe substrate 7-benzyloxymethoxy-4-(trifluoromethyl)-coumarin (BOMFC) indicated a weak, non-competitive inhibition of BOMFC metabolism by flupyradifurone. In contrast, the azole fungicides prochloraz and propiconazole were strong nanomolar inhibitors of these flupyradifurone metabolizing P450s, explaining their highly synergistic effects in combination with flupyradifurone as demonstrated in acute laboratory contact toxicity tests of adult bees. Interestingly, the azole fungicide prothioconazole is only slightly synergistic in combination with flupyradifurone - an observation supported by molecular P450 inhibition assays. Such molecular assays have value in the prediction of potential risks posed to bees by flupyradifurone mixture partners under applied conditions. Quantitative PCR confirmed the expression of the identified P450 genes in all honey bee life-stages, with highest expression levels observed in late larvae and adults, suggesting honey bees have the capacity to metabolize flupyradifurone across all life-stages. These findings provide a biochemical explanation for the low intrinsic toxicity of flupyradifurone to honey bees and offer a new, more holistic approach to support bee pollinator risk assessment by molecular means.

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

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