Assessment of the Vulnerability to Pesticide Exposures Across Bee Species

Understanding and comparing relative pesticide risk among North American wild bees from their association with agriculture

In North America, approximately 21 % (739 species) of the total wild bee diversity is known to be associated with crops, with bee species varying in the extent of this association. While current evaluations of pesticide effects on bees primarily focus on a limited subset of species, a new focus is needed to ensure comprehensive protection of all wild bees in agricultural contexts. This study introduces a novel approach to characterize and compare the relative potential pesticide risk for wild bee species of their association with crops. Using intrinsic bee vulnerability traits and extrinsic factors like crop toxic loads and association strength, we calculated Bee-Crop Risk Scores for 594 wild bee species, identifying those experiencing the highest potential risk from pesticide exposure in North American agroecosystems. We discuss the influence of intrinsic and extrinsic factors on the relative potential risk calculated and outline avenues for refining our approach. As most species facing the highest potential risk from pesticide exposure across North America are ground-nesters, our study suggests that species (e.g., Osmia spp., Megachile spp.) commonly proposed as models for pesticide risk assessments may not accurately represent risk for those bee species facing the highest potential risk in agricultural contexts.

What can laboratory studies tell us about potential effects of pesticides on nontarget arthropods populations and communities in the field?

Over the past decades, concern has been increasing over reported declines in aboveground biodiversity on farmland. In many regions, data on the toxicity of pesticides to honeybees (Apis mellifera), but not wider nontarget arthropod (NTA) data, are required for pesticide registration. In Europe, the effects of pesticides on NTAs and honeybees have been the subject of regulatory risk assessment for more than 30 years, resulting in a large database. Although insecticides may be expected to affect NTA populations, solely identifying insecticidal modes of action for further NTA testing would result in redundancy among low-risk testing products and may also exclude other modes of action with potential effects in the field. This study assessed whether the honeybee acute risk assessment could provide any indication of the potential impact and recovery time of NTAs in cropped areas at the field scale and, if so, how it might be used in a tiered testing approach. The hazard quotients (HQs; foliar application rate/LR50) were derived for 151 active substances (32% insecticides, 28% fungicides, 38% herbicides, 2% plant growth regulators) for which toxicity data for established EU Tier 1 NTA indicator species (Typhlodromus pyri, Aphidius rhopalosiphi) and application rate data were available. These HQs were compared with published NTA HQ thresholds indicating the time to recovery of NTA populations and communities in field studies (>1 to >12 months). Using the same application rate data, honeybee acute risk quotient (RQ) and HQ were also determined and compared with NTA HQs and honeybee regulatory thresholds. These comparisons demonstrated that, where required, the current regulatory honeybee acute RQ of 0.4 or honeybee HQ of 50 can provide an efficient screening tier to target NTA testing at those products and uses with potential effects in the field where recovery may exceed 12 months. Integr Environ Assess Manag 2024;20:2326-2333. © 2024 SETAC.

No impact of cyantraniliprole on the hibernation success of bumble bees (Bombus terrestris audax) in a soil-mediated laboratory exposure study

Increasing evidence shows that wild bees, including bumble bees, are in decline due to a range of stressors, including pesticides. Our knowledge of pesticide impacts has consequently grown to enable the design of increasingly realistic risk assessment methods. However, one area where knowledge gaps may still hinder our ability to assess the full range of bee-pesticide interactions is the field of exposure. Exposure has historically been linked to either direct contact with pesticides or the ingestion of contaminated pollen and nectar by bees. However, bumble bees, and other wild bees, may also be exposed to pesticides while using contaminated soil as an overwintering substrate. Yet knowledge of how soil-mediated exposure affects bumble bee health is lacking. Here we take one of the first steps towards addressing this knowledge gap by designing a method for testing the effects of soil-mediated pesticide exposure on bumble bee queen hibernation success. We measured hibernation survival, body weight change and abdominal fat content and found that none of these responses were affected by a field realistic soil exposure to the novel insecticide cyantraniliprole. Our study may help in developing a standardised method to test the effects of the soil-mediated pesticide exposure route in bumble bee queens.

SolBeePopecotox: A Population Model for Pesticide Risk Assessments of Solitary Bees

In agricultural landscapes, solitary bees occur in a large diversity of species and are important for crop and wildflower pollination. They are distinguished from honey bees and bumble bees by their solitary lifestyle as well as different nesting strategies, phenologies, and floral preferences. Their ecological traits and presence in agricultural landscapes imply potential exposure to pesticides and suggest a need to conduct ecological risk assessments for solitary bees. However, assessing risks to the large diversity of managed and wild bees across landscapes and regions poses a formidable challenge. Population models provide tools to estimate potential population-level effects of pesticide exposures, can support field study design and interpretation, and can be applied to expand study data to untested conditions. We present a population model for solitary bees, SolBeePopecotox, developed for use in the context of ecological risk assessments. The trait-based model extends a previous version with the explicit representation of exposures to pesticides from relevant routes. Effects are implemented in the model using a simplified toxicokinetic-toxicodynamic model, BeeGUTS (GUTS = generalized unified threshold model for survival), adapted specifically for bees. We evaluated the model with data from semifield studies conducted with the red mason bee, Osmia bicornis, in which bees were foraging in tunnels over control and insecticide-treated oilseed rape fields. We extended the simulations to capture hypothetical semifield studies with two soil-nesting species, Nomia melanderi and Eucera pruinosa, which are difficult to test in empirical studies. The model provides a versatile tool for higher-tier risk assessments, for instance, to estimate effects of potential exposures, expanding available study data to untested species, environmental conditions, or exposure scenarios. Environ Toxicol Chem 2024;00:1-17. © 2024 SETAC.

Pesticide Contamination in Native North American Crops, Part II-Comparison of Flower, Honey Bee Workers, and Native Bee Residues in Lowbush Blueberry

In lowbush blueberry fields, we conducted residue analysis comparing flowers, trapped pollen (honey bee and Osmia spp.), and collected bees (honey bee workers, bumble bee queens, and non-Bombus spp. wild native bees). The study was conducted from 2012 to 2014. The number of pesticide residues, total concentrations, and risk to honey bees (Risk Quotient) on flowers were not significantly different from those determined for trapped honey bee pollen (except in one study year when residues detected in flower samples were significantly lower than residue numbers detected in trapped pollen). The compositions of residues were similar on flowers and trapped pollen. The number of residues detected in honey bee pollen was significantly greater than the number detected in Osmia spp. pollen, while the total concentration of residue was not different between the two types of pollen. The risk to honey bees was higher in trapped honey bee pollen than in trapped Osmia spp. pollen. The analysis of honey bee workers, native bumble bee queens, and native solitary bees showed that although more pesticide residues were detected on honey bee workers, there were no differences among the bee taxa in total residue concentrations or risk (as estimated in terms of risk to honey bees).

Combined effects of three insecticides with different modes of action on biochemical responses of the solitary bee Osmia bicornis

Bees are simultaneously exposed to a variety of pesticides, which are often applied in mixtures and can cause lethal and sublethal effects. The combined effects of pesticides, however, are not measured in the current risk assessment schemes. Additionally, the sublethal effects of pesticides on a variety of physiological processes are poorly recognized in bees, especially in non-Apis solitary bees. In this study, we used a full-factorial design to examine the main and interactive effects of three insecticide formulations with different modes of action (Mospilan 20 SP, Sherpa 100 EC, and Dursban 480 EC) on bee biochemical processes. We measured acetylcholinesterase (AChE), glutathione S-transferase (GST) and esterase (EST) activities, as well as a nonenzymatic biomarker associated with energy metabolism, i.e., ATP level. All studied endpoints were affected by Sherpa 100 EC, and the activities of AChE and EST as well as ATP levels were affected by Dursban 480 EC. Moreover, complex interactions between all three insecticides affected ATP levels, showing outcomes that cannot be predicted when testing each insecticide separately. The results indicate that even if interactive effects are sometimes difficult to interpret, there is a need to study such interactions if laboratory-generated toxicity data are to be extrapolated to field conditions.

Different Sensitivity of Flower-Visiting Diptera to a Neonicotinoid Insecticide: Expanding the Base for a Multiple-Species Risk Assessment Approach

Insects play an essential role as pollinators of wild flowers and crops. At the same time, pollinators in agricultural environments are commonly exposed to pesticides, compromising their survival and the provision of pollination services. Although pollinators include a wide range of species from several insect orders, information on pesticide sensitivity is mostly restricted to bees. In addition, the disparity of methodological procedures used for different insect groups hinders the comparison of toxicity data between bees and other pollinators. Dipterans are a highly diverse insect order that includes some important pollinators. Therefore, in this study, we assessed the sensitivity of two hoverflies (Sphaerophoria rueppellii, Eristalinus aeneus) and one tachinid fly (Exorista larvarum) to a neonicotinoid insecticide (Confidor®, imidacloprid) following a comparative approach. We adapted the standardized methodology of acute contact exposure in honey bees to build dose-response curves and calculate median lethal doses (LD50) for the three species. The methodology consisted in applying 1 µL of the test solution on the thorax of each insect. Sphaerophoria rueppelli was the most sensitive species (LD50 = 10.23 ng/insect), and E. aeneus (LD50 = 18,176 ng/insect) the least. We then compared our results with those available in the literature for other pollinator species using species sensitivity distribution (SSD). Based on the SSD curve, the 95th percentile of pollinator species would be protected by a safety factor of 100 times the Apis mellifera endpoint. Overall, dipterans were less sensitive to imidacloprid than most bee species. As opposed to most bee species, oviposition and fecundity of many dipteran species can be reliably assessed in the laboratory. We measured the number of eggs laid following exposure to different insecticide doses and assessed the potential trade-off between oviposition and survival through the sublethal sensitivity index (SSI). Exposure to imidacloprid had a significant effect on fecundity, and SSI values indicated that oviposition is a sensitive endpoint for the three dipteran species tested. Future studies should integrate this information related to population dynamics in simulation models for environmental risk assessment.

High pesticide exposure and risk to bees in pollinator plantings adjacent to conventionally managed blueberry fields

Wildflower plantings adjacent to agricultural fields provide diverse floral resources and nesting sites for wild bees. However, their proximity to pest control activities in the crop may result in pesticide exposure if pesticides drift into pollinator plantings. To quantify pesticide residues in pollinator plantings, we sampled flowers and soil from pollinator plantings and compared them to samples from unenhanced field margins and crop row middles. At conventionally managed farms, flowers from pollinator plantings had similar exposure profiles to those from unenhanced field margins or crop row middles, with multiple pesticides and high and similar risk quotient (RQ) values (with pollinator planting RQ: 3.9; without pollinator planting RQ: 4.0). Whereas samples from unsprayed sites had significantly lower risk (RQ: 0.005). Soil samples had overall low risk to bees. Additionally, we placed bumble bee colonies (Bombus impatiens) in field margins of crop fields with and without pollinator plantings and measured residues in bee-collected pollen. Pesticide exposure was similar in pollen from sites with or without pollinator plantings, and risk was generally high (with pollinator planting RQ: 0.5; without pollinator planting RQ: 1.1) and not significant between the two field types. Risk was lower at sites where there was no pesticide activity (RQ: 0.3), but again there was no significant difference between management types. The insecticide phosmet, which is used on blueberry farms for control of Drosophila suzukii, accounted for the majority of elevated risk. Additionally, analysis of pollen collected by bumble bees found no significant difference in floral species richness between sites with or without pollinator plantings. Our results suggest that pollinator plantings do not reduce pesticide risk and do not increase pollen diversity collected by B. impatiens, further highlighting the need to reduce exposure through enhanced IPM adoption, drift mitigation, and removal of attractive flowering weeds prior to insecticide applications.

Prioritizing resource allocation to reduce adverse effects of pesticide risk for endangered species

The use of pesticides promotes food security because of the multiple benefits it brings to agriculture, such as reduction in crop losses. However, the use of pesticides can be potentially harmful to non-target species. In the U.S., the Environmental Protection Agency regulates the use of pesticides to manage the risks associated with these agents and to protect species under the Endangered Species Act. As part of these regulations, pesticides must be registered and then reviewed every 15 years to ensure the use conditions are updated with the best available data. The registration and review process can invoke corrective measures to ensure protection of endangered species. However, the registration review process is highly resource and time consuming. There is currently a backlog of unreviewed pesticides, leaving a large quantity of pesticides without updated use conditions to protect species. Identifying ways to streamline this process is urgently needed. We develop a sequencing approach to address the risk assessment bottleneck in the pesticide registration and review process and identify species that would benefit most from detailed assessments. We then demonstrate the magnitude of potential efficiencies using this sequencing process for 61 terrestrial listed species in the state of California. Our results show a consistent ranking of listed species according to their relative benefits from assessment, with 90 % of the species being robustly classified across scenarios in the sensitivity analysis. We found that prioritizing the assessment of a small group of species could potentially result in high conservation benefits, and identify species in need of more detailed data for a robust sequencing. We examine how a sequencing approach can guide decisions about what species might benefit most from different levels of assessment. Our results demonstrate the conservation benefits of employing a sequencing approach to prioritize the allocation of limited resources for endangered species.

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.

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.

Sensitivity of the Neotropical Solitary Bee Centris analis F. (Hymenoptera, Apidae) to the Reference Insecticide Dimethoate for Pesticide Risk Assessment

Currently, only Apis mellifera is used in environmental regulation to evaluate the hazard of pesticides to pollinators. The low representativeness of pollinators and bee diversity in this approach may result in insufficient protection for the wild species. This scenario is intensified in tropical environments, where little is known about the effects of pesticides on solitary bees. We aimed to calculate the medium lethal dose (LD50) and medium lethal concentration (LC50) of the insecticide dimethoate in the Neotropical solitary bee Centris analis, a cavity-nesting, oil-collecting bee distributed from Brazil to Mexico. Males and females of C. analis were exposed orally to dimethoate for 48 h under laboratory conditions. Lethality was assessed every 24 h until 144 h after the beginning of the test. After the LD50 calculation, we compared the value with available LD50 values in the literature of other bee species using the species sensitivity distribution curve. In 48 h of exposure, males showed an LD50 value 1.33 times lower than females (32.78 and 43.84 ng active ingredient/bee, respectively). Centris analis was more sensitive to dimethoate than the model species A. mellifera and the solitary bee from temperate zones, Osmia lignaria. However, on a body weight basis, C. analis and A. mellifera had similar LD50 values. Ours is the first study that calculated an LD50 for a Neotropical solitary bee. Besides, the results are of crucial importance for a better understanding of the effects of pesticides on the tropical bee fauna and will help to improve the risk assessment of pesticides to bees under tropical conditions, giving attention to wild species, which are commonly neglected. Environ Toxicol Chem 2023;42:2758-2767. © 2023 SETAC.

Description and validation of an improved method to feed solitary bees (Osmia spp.) known amounts of pesticides

Pesticide exposure is an important driver of bee declines. Laboratory toxicity tests provide baseline information on the potential effects of pesticides on bees, but current risk assessment schemes rely on one species, the highly social honey bee, Apis mellifera, and there is uncertainty regarding the extent to which this species is a suitable surrogate for other pollinators. For this reason, Osmia cornuta and Osmia bicornis have been proposed as model solitary bee species in the EU risk assessment scheme. The use of solitary bees in risk assessment requires the development of new methodologies adjusted to the biology of these species. For example, oral dosing methods used with honey bees cannot be readily applied to solitary bees due to differences in feeding behaviour and social interactions. In this study, we describe the "petal method", a laboratory feeding method, and validate its use in acute and chronic exposure oral tests with Osmia spp. We conducted five experiments in which we compared the performance of several artificial flowers combining visual and olfactory cues against the petal method, or in which variations of the petal method were confronted. We then use the results of these experiments to optimize the feeding arenas and propose standardized methods for both acute and chronic exposure tests. The petal method provides high levels of feeding success, thus reducing the number of bees needed. It works with a wide variety of petal species and with both female and male Osmia spp., thus ensuring reproducibility across studies. To validate the use of the petal method in ecotoxicology tests, we assess the toxicity of a standard reference insecticide, dimethoate, in O. cornuta adults and determine LD50 values for this species. The petal method should facilitate the inclusion of solitary bees in risk assessment schemes therefore increasing the protection coverage of pesticide regulation.

Effects of acephate and glyphosate-based agrochemicals on the survival and flight of Plebeia lucii Moure, 2004 (Apidae: Meliponini)

The conservation of terrestrial ecosystems depends largely on the preservation of pollinators, mainly bees. Stingless bees are among the main pollinators of native plants and crops in tropical regions, where they can be exposed to agrochemicals while foraging on contaminated flowers. In the present study, we investigated the effects on stingless bees of both a commonly used insecticide and herbicide in Brazil. Plebeia lucii Moure, 2004 (Apidae: Meliponini) foragers were orally chronically exposed to food contaminated with different concentrations of commercial formulations of the insecticide acephate or the herbicide glyphosate. Bee mortality increased with increasing agrochemical concentrations. Depending on its concentration, the acephate-based formulation reduced the lifespan and impaired the flight ability of bees. The glyphosate-based formulation was toxic only under unrealistic concentrations. Our results demonstrate that realistic concentrations of acephate-based insecticides harm the survival and alter the mobility of stingless bees. The ingestion of glyphosate-based herbicides was safe for forager bees under realistic concentrations.

Potential Risk of Residues From Neonicotinoid-Treated Sugar Beet Flowering Weeds to Honey Bees (Apis mellifera L.)

In 2018 the European Union (EU) banned the three neonicotinoid insecticides imidacloprid, clothianidin (CLO), and thiamethoxam (TMX), but they can still be used if an EU Member State issues an emergency approval. Such an approval went into effect in 2021 for TMX-coated sugar beet seeds in Germany. Usually, this crop is harvested before flowering without exposing non-target organisms to the active ingredient or its metabolites. In addition to the approval, strict mitigation measures were imposed by the EU and the German federal states. One of the measures was to monitor the drilling of sugar beet and its impact on the environment. Hence we took residue samples from different bee and plant matrices and at different dates to fully map beet growth in the German states of Lower Saxony, Bavaria, and Baden-Württemberg. A total of four treated and three untreated plots were surveyed, resulting in 189 samples. Residue data were evaluated using the US Environmental Protection Agency BeeREX model to assess acute and chronic risk to honey bees from the samples, because oral toxicity data are widely available for both TMX and CLO. Within treated plots, we found no residues either in pools of nectar and honey crop samples (n = 24) or dead bee samples (n = 21). Although 13% of beebread and pollen samples and 88% of weed and sugar beet shoot samples were positive, the BeeREX model found no evidence of acute or chronic risk. We also detected neonicotinoid residues in the nesting material of the solitary bee Osmia bicornis, probably from contaminated soil of a treated plot. All control plots were free of residues. Currently, there are insufficient data on wild bee species to allow for an individual risk assessment. In terms of the future use of these highly potent insecticides, therefore, it must be ensured that all regulatory requirements are complied with to mitigate any unintentional exposure. Environ Toxicol Chem 2023;42:1167-1177. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Ecological traits interact with landscape context to determine bees' pesticide risk

Widespread contamination of ecosystems with pesticides threatens non-target organisms. However, the extent to which life-history traits affect pesticide exposure and resulting risk in different landscape contexts remains poorly understood. We address this for bees across an agricultural land-use gradient based on pesticide assays of pollen and nectar collected by Apis mellifera, Bombus terrestris and Osmia bicornis, representing extensive, intermediate and limited foraging traits. We found that extensive foragers (A. mellifera) experienced the highest pesticide risk-additive toxicity-weighted concentrations. However, only intermediate (B. terrestris) and limited foragers (O. bicornis) responded to landscape context-experiencing lower pesticide risk with less agricultural land. Pesticide risk correlated among bee species and between food sources and was greatest in A. mellifera-collected pollen-useful information for future postapproval pesticide monitoring. We provide foraging trait- and landscape-dependent information on the occurrence, concentration and identity of pesticides that bees encounter to estimate pesticide risk, which is necessary for more realistic risk assessment and essential information for tracking policy goals to reduce pesticide risk.

Are Botanical Biopesticides Safe for Bees (Hymenoptera, Apoidea)?

The recent global decline in insect populations is of particular concern for pollinators. Wild and managed bees (Hymenoptera, Apoidea) are of primary environmental and economic importance because of their role in pollinating cultivated and wild plants, and synthetic pesticides are among the major factors contributing to their decline. Botanical biopesticides may be a viable alternative to synthetic pesticides in plant defence due to their high selectivity and short environmental persistence. In recent years, scientific progress has been made to improve the development and effectiveness of these products. However, knowledge regarding their adverse effects on the environment and non-target species is still scarce, especially when compared to that of synthetic products. Here, we summarize the studies concerning the toxicity of botanical biopesticides on the different groups of social and solitary bees. We highlight the lethal and sublethal effects of these products on bees, the lack of a uniform protocol to assess the risks of biopesticides on pollinators, and the scarcity of studies on specific groups of bees, such as the large and diverse group of solitary bees. Results show that botanical biopesticides cause lethal effects and a large number of sublethal effects on bees. However, the toxicity is limited when comparing the effects of these compounds with those of synthetic compounds.

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.

Biochemical responses, feeding and survival in the solitary bee Osmia bicornis following exposure to an insecticide and a fungicide alone and in combination

In agricultural ecosystems, bees are exposed to combinations of pesticides that may have been applied at different times. For example, bees visiting a flowering crop may be chronically exposed to low concentrations of systemic insecticides applied before bloom and then to a pulse of fungicide, considered safe for bees, applied during bloom. In this study, we simulate this scenario under laboratory conditions with females of the solitary bee, Osmia bicornis L. We studied the effects of chronic exposure to the neonicotinoid insecticide, Confidor® (imidacloprid) at a realistic concentration, and of a pulse (1 day) exposure of the fungicide Folicur® SE (tebuconazole) at field application rate. Syrup consumption, survival, and four biomarkers: acetylcholinesterase (AChE), carboxylesterase (CaE), glutathione S-transferase (GST), and alkaline phosphatase (ALP) were evaluated at two different time points. An integrated biological response (IBRv2) index was elaborated with the biomarker results. The fungicide pulse had no impact on survival but temporarily reduced syrup consumption and increased the IBRv2 index, indicating potential molecular alterations. The neonicotinoid significantly reduced syrup consumption, survival, and the neurological activity of the enzymes. The co-exposure neonicotinoid-fungicide did not increase toxicity at the tested concentrations. AChE proved to be an efficient biomarker for the detection of early effects for both the insecticide and the fungicide. Our results highlight the importance of assessing individual and sub-individual endpoints to better understand pesticide effects on bees.

Defining the Biologically Plausible Taxonomic Domain of Applicability of an Adverse Outcome Pathway: A Case Study Linking Nicotinic Acetylcholine Receptor Activation to Colony Death

For the majority of developed adverse outcome pathways (AOPs), the taxonomic domain of applicability (tDOA) is typically narrowly defined with a single or a handful of species. Defining the tDOA of an AOP is critical for use in regulatory decision-making, particularly when considering protection of untested species. Structural and functional conservation are two elements that can be considered when defining the tDOA. Publicly accessible bioinformatics approaches, such as the Sequence Alignment to Predict Across Species Susceptibility (SeqAPASS) tool, take advantage of existing and growing databases of protein sequence and structural information to provide lines of evidence toward structural conservation of key events (KEs) and KE relationships (KERs) of an AOP. It is anticipated that SeqAPASS results could readily be combined with data derived from empirical toxicity studies to provide evidence of both structural and functional conservation, to define the tDOA for KEs, KERs, and AOPs. Such data could be incorporated in the AOP-Wiki as lines of evidence toward biological plausibility for the tDOA. We present a case study describing the process of using bioinformatics to define the tDOA of an AOP using an AOP linking the activation of the nicotinic acetylcholine receptor to colony death/failure in Apis mellifera. Although the AOP was developed to gain a particular biological understanding relative to A. mellifera health, applicability to other Apis bees, as well as non-Apis bees, has yet to be defined. The present study demonstrates how bioinformatics can be utilized to rapidly take advantage of existing protein sequence and structural knowledge to enhance and inform the tDOA of KEs, KERs, and AOPs, focusing on providing evidence of structural conservation across species. Environ Toxicol Chem 2023;42:71-87. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Decreased efficiency of pollen collection due to Sulfoxaflor exposure leads to a reduction in the size of bumble bee workers in late European summer

Bumble bees (Bombus terrestris) are important pollinators of wild and crop plants. Despite their importance in the process of fruit and seed production on crop sites, their activity may be impaired due to exposure to pesticides. This species has a yearly life cycle and colony success may rely on effective foraging of workers on ruderal plants late in summer when most crops are no longer flowering. In the current study, we investigated the effect of chronic exposure to Sulfoxaflor on aspects of the foraging behavior of bumble bees and whether Sulfoxaflor influences the body size of workers of B. terrestris in a crop landscape. We found that 2 weeks of continuous exposure to Sulfoxaflor influenced workers’ foraging dynamics and collection of resources. However, there was no evidence that the 5 ppb dose of the pesticide impacted the ability of bees to handle flowers with different traits. Workers from colonies exposed to Sulfoxaflor were smaller. The effect on worker size may be explained as a consequence of the reduced pollen income per unit of worker foraging. Thus, if the effects of Sulfoxaflor applied directly to crops had the same effect as that observed on commercial bumble bees after our chronic exposure, it might negatively impact colony success due to the impact on pollen collection and the reduction in the size of workers.

Optimization of in vitro culture of honeybee nervous tissue for pesticide risk assessment

The most used pesticides have neurotoxic action on the neurotransmitter system of target and non-targeted insects, such as honeybees. However, honeybees have foremost importance worldwide, which has encouraged the development of tools to evaluate the action of specific pesticide molecules on their nervous system, providing accurate data on damage to their brain. In this sense, our study aimed to optimize in vitro honeybee nervous tissue culture to assess pesticide risks. To this end, six forager honeybee brains were dissected and transferred to different combinations of Leibovitz-15 (L-15) culture medium supplemented with Fetal Bovine Serum (FBS), Hank's Balanced Salt Solution (HBSS), and Insect Medium Supplement (IMS). Nervous tissues were collected after different incubation times (1, 6, 12, and 24 h) for morphology and Kenyon cell analyses. Our results showed that L-15 medium supplemented with HBSS and with HBSS plus FBS were the best media for culturing honey nervous tissue, as they resulted in less tissue spacing and cell disarrangement. Therefore, they may be assessed in future ecotoxicological tests.

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.

Effects of agricultural landscape structure, insecticide residues, and pollen diversity on the life-history traits of the red mason bee Osmia bicornis

Agricultural landscapes have changed substantially in recent decades, shifting from the dominance of small fields (S) with diverse cropping systems toward large-scale monoculture (L), where landscape heterogeneity disappears. In this study, artificial nests of the red mason bee, Osmia bicornis, were placed in S and L landscape types on the perimeter of oilseed rape fields representing different oilseed rape coverages (ORC, % land cover). The local landscape structure around each nest was characterised within a 100, 200, 500, and 1000 m radius using ORC and 14 landscape characteristics, which were then reduced by non-metric multidimensional scaling (nMDS) to two axes: nMDS1 characterised the dataset primarily according to land fragmentation and the main crop, whereas nMDS2 captured the prevalence of more natural areas in the landscape. Pollen diversity and insecticide risk levels in the pollen provisions collected by the bees were analysed, and their dependence on the landscape structure was tested. Thereafter, the effects of pollen diversity, insecticide risk, and landscape structure on the life-history traits of bees and their sensitivity to topically applied Dursban 480 EC were determined. Pollen taxa richness in a single nest ranged from 3 to 12, and 34 pesticides were detected in the pollen at concentrations of up to 320 ng/g for desmedipham. The O. bicornis foraging range was relatively large, indicating that the landscape structure within a radius of ~1000 m around the nest is important for this species. Pollen diversity in the studied areas was of minor importance for bee performance, but the ORC or landscape structure significantly affected the life-history traits of the bees. Contamination of pollen with insecticides affected the bees by decreasing the mass of newly emerged adults but their sensitivity to Dursban 480 EC was not related to environmental variables.

Effects of Provision Type and Pesticide Exposure on the Larval Development of Osmia lignaria (Hymenoptera: Megachilidae)

Wild and managed bee populations are in decline, and one of many environmental causes is the impact of pesticides on developing bees. For solitary bees, delayed larval development could lead to asynchronous adult emergence, unhealthy and inefficient adult pollinators, and decreased brood production and survival. We examined a methodology for testing Osmia lignaria Say (Hymenoptera: Megachilidae) larval responses to pesticide exposure using a laboratory bioassay. We created two provision types: a homogenized blend of O. lignaria provisions from an apple orchard and homogenized almond pollen pellets collected by honey bees plus sugar water. Pesticides were administered to the provisions to compare toxic effects. We recorded larval developmental durations for second-fifth instar and for fifth instar to cocoon initiation for larvae fed provisions treated with water (control) or doses of three pesticides and a representative spray-tank mixture (acetamiprid, boscalid/pyraclostrobin, dimethoate, and acetamiprid plus boscalid/pyraclostrobin). All larvae survived to cocoon initiation when only water was added to provisions. Impacts of pesticide treatments significantly differed between the apple and almond homogenates. The greatest treatment effects occurred when the homogenized almond provision was mixed with acetamiprid alone and when combined with boscalid/pyraclostrobin. Optimizing bioassays through the use of appropriate larval food for exposing solitary bee larvae to agrochemicals is crucial for assessing risks for pollinators.