Pesticide Exposure Assessment Paradigm for Stingless Bees

Toxicological Assessments of Agrochemicals in Stingless Bees in Brazil: a Systematic Review

The growing concern with the decline of pollinators worldwide is centered on honey bees, due to their wide distribution, economic, and ecological importance. This type of concern remained less evident for stingless bees, which are widely distributed in the Neotropics, until recently. Since exposure to agrochemicals has been identified as one of the potential threats to bees, the present systematic review compiled information from toxicological evaluations in stingless bees in Brazil, home to a considerable portion of the existing species. This systematic review was performed considering species, research institutions, scientific journals, metrics, experimental set ups, and agrochemicals. The first article in this topic was published in 2010. Since then, 93 scientific papers were published, which showed that there are few species of stingless bees used for toxicological evaluations and Brazilian institutions lead these evaluations. Only 1.5% of the stingless bees' species that occur in Brazil were assessed through chronic exposure in the larval stage. The Universidade Federal de Viçosa (UFV) is responsible for 37% of the total publications. The main route of exposure was acute, using adults in laboratory conditions. The main group of agrochemicals studied were insecticides, in particular the neonicotinoids. The current results reveal the advances achieved and point out the gaps that still need to be filled considering toxicological evaluations in stingless bees.

Exposure of the stingless bee Melipona scutellaris to imidacloprid, pyraclostrobin, and glyphosate, alone and in combination, impair its walking activity and fat body morphology and physiology

The stingless bee Melipona scutellaris performs buzz pollination, effectively pollinating several wild plants and crops with economic relevance. However, most research has focused on honeybees, leaving a significant gap in studies concerning native species, particularly regarding the impacts of pesticide combinations on these pollinators. Thus, this study aimed to evaluate the sublethal effects of imidacloprid (IMD), pyraclostrobin (PYR), and glyphosate (GLY) on the behavior and fat body cell morphology and physiology of M. scutellaris. Foragers were orally exposed to the different pesticides alone and in combination for 48 h. Bees fed with contaminated solution walked less, moved slower, presented morphological changes in the fat body, including vacuolization, altered cell shape and nuclei morphology, and exhibited a higher count of altered oenocytes and trophocytes. In all exposed groups, alone and in combination, the number of cells expressing caspase-3 increased, but the TLR4 number of cells expressing decreased compared to the control groups. The intensity of HSP70 immunolabeling increased compared to the control groups. However, the intensity of the immunolabeling of HSP90 decreased in the IMD, GLY, and I + G (IMD + GLY) groups but increased in I + P-exposed bees (IMD + PYR). Alternatively, exposure to PYR and P + G (PYR + GLY) did not affect the immunolabeling intensity. Our findings demonstrate the hazardous effects and environmental consequences of isolated and combined pesticides on a vital neotropical pollinator. Understanding how pesticides impact the fat body can provide crucial insights into the overall health and survival of native bee populations, which can help develop more environmentally friendly approaches to agricultural practices.

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

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

Residual determination and acute toxicity of the neonicotinoid clothianidin in the neotropical stingless bee Tetragonisca angustula Latreille, 1811 (Apidae: Meliponini)

Bees play a crucial role as natural pollinators, ensuring the maintenance and stability of the world's biodiversity and agricultural crops. Native bees in neotropical regions belong to the Meliponini tribe, a larger group that differs significantly in behavior and biology from honeybees (e.g., Apis mellifera) and solitary bees (e.g., Osmia spp.). Hence, the exposure and effects of pesticides is also likely to vary among these different species. The aim of this study was to develop an analytical method to determine the presence of the neonicotinoid clothianidin in the Brazilian native stingless bee Tetragonisca angustula (local common name: Jataí). The method used for the chemical analysis involved a QuEChERS technique combined with UHPLC-MS/MS analysis. The developed method was subsequently used to analyze collected field samples. In addition, the acute toxicity of the pesticide to T. angustula was evaluated in a laboratory bioassay evaluating both lethal and sublethal endpoints. The analytical method was successfully developed with detection and quantification limits of 1.55 and 5 μg L-1, respectively, along with a linear range of 1-5 ng mL-1. Clothianidin was detected in environmental samples (9.2-32.9 ng g-1), and the exposure experiments demonstrated acute oral toxicity to adults of T. angustula, (24 h-LD50 of 0.16 ng a.i./bee), as well as no significative interference in acetylcholinesterase activity. Considering the obtained toxicity endpoints for T. angustula and those reported in the literature for other bee species, this study revealed that T. angustula is more (lethally) sensitive to clothianidin than other bee species, including those commonly used in environmental risk assessment studies. This thus also supports the call for using native test species in (regional) risk assessment evaluations.

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.

Exposure to sublethal concentrations of imidacloprid, pyraclostrobin, and glyphosate harm the behavior and fat body cells of the stingless bee Scaptotrigona postica

Pesticide use in agriculture threatens non-target insects such as bees. Considering the ecological and economic relevance of native bees, such as Scaptotrigona postica, and the insufficient studies on the effects of pesticides on their behavior and physiology, improving the current knowledge on this issue is essential. Therefore, this study investigated the sublethal effects of imidacloprid, pyraclostrobin, and glyphosate on the behavior and fat body cells of S. postica. Pesticide ingestion decreased the walking distance and mean velocity of bees compared to the control and solvent control groups. The oenocytes of the control groups were spherical, with central nuclei containing decondensed chromatin, and the trophocytes presented irregular morphology, with cells varying in shape and the cytoplasm filled with vacuoles and granules. However, bees exposed to pesticides showed extensive cytoarchitectural disruption in the fat body, such as vacuolization and shape changes in oenocytes and altered nuclei morphology in trophocytes. Moreover, pesticide exposure increased the number of atypical oenocytes and altered trophocytes, except for the PYR group, which showed a lower number of atypical oenocytes. Caspase-positive labeling significantly increased in all exposed bee groups. Alternatively, TLR4 labeling was significantly decreased in the exposed groups compared to the control groups. There was a significant increase in HSP90 immunolabeling in all exposed groups compared to the control. These findings reinforce the importance of research on the sublethal effects of low pesticide concentrations on key neotropical pollinators and prove that these toxic substances can impair their detoxification and immune defense.

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

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

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.

Breaking the cycle: Reforming pesticide regulation to protect pollinators

Over decades, pesticide regulations have cycled between approval and implementation, followed by the discovery of negative effects on nontarget organisms that result in new regulations, pesticides, and harmful effects. This relentless pattern undermines the capacity to protect the environment from pesticide hazards and frustrates end users that need pest management tools. Wild pollinating insects are in decline, and managed pollinators such as honey bees are experiencing excessive losses, which threatens sustainable food security and ecosystem function. An increasing number of studies demonstrate the negative effects of field-realistic exposure to pesticides on pollinator health and fitness, which contribute to pollinator declines. Current pesticide approval processes, although they are superior to past practices, clearly continue to fail to protect pollinator health. In the present article, we provide a conceptual framework to reform cyclical pesticide approval processes and better protect pollinators.

Honey bees and bumble bees may be exposed to pesticides differently when foraging on agricultural areas

In an agricultural environment, where crops are treated with pesticides, bees are likely to be exposed to a range of chemical compounds in a variety of ways. The extent to which different bee species are affected by these chemicals, largely depends on the concentrations and type of exposure. We quantified the presence of selected pesticide compounds in the pollen of two different entomophilous crops; oilseed rape (Brassica napus) and broad bean (Vicia faba). Sampling was performed in 12 sites in Ireland and our results were compared with the pollen loads of honey bees and bumble bees actively foraging on those crops in those same sites. Detections were compound specific, and the timing of pesticide application in relation to sampling likely influenced the final residue contamination levels. Most detections originated from compounds that were not recently applied on the fields, and samples from B. napus fields were more contaminated compared to those from V. faba fields. Crop pollen was contaminated only with fungicides, honey bee pollen loads contained mainly fungicides, while more insecticides were detected in bumble bee pollen loads. The highest number of compounds and most detections were observed in bumble bee pollen loads, where notably, all five neonicotinoids assessed (acetamiprid, clothianidin, imidacloprid, thiacloprid, and thiamethoxam) were detected despite the no recent application of these compounds on the fields where samples were collected. The concentrations of neonicotinoid insecticides were positively correlated with the number of wild plant species present in the bumble bee-collected pollen samples, but this relationship could not be verified for honey bees. The compounds azoxystrobin, boscalid and thiamethoxam formed the most common pesticide combination in pollen. Our results raise concerns about potential long-term bee exposure to multiple residues and question whether honey bees are suitable surrogates for pesticide risk assessments for all bee species.

Dust abraded from thiamethoxam-treated seed during sowing: Refining the risk assessment for native bees in Brazil

During sowing using pneumatic machinery, dust may be abraded from pesticide-treated seed and contaminate adjacent bee-attractive off-crop areas. This study quantified the risk to native bees of dust released during sowing of Brazilian crop seeds treated with a thiamethoxam formulation (Cruiser 350FS). To address toxicity to native bees, adult acute contact LD50 data for thiamethoxam were collated from the literature, a species sensitivity distribution generated, and the HD5 calculated. The LD50 HD5 was used to refine the default safety factor applied to the honeybee acute contact LD50 from 10 to 5.45 for thiamethoxam. Crop-specific abraded dust data (Heubach dust and Heubach AI) were generated for seeds treated with Cruiser 350FS sourced from on-farm and industrial facilities. The mean Heubach dust levels was ranked as cotton = maize > sunflower = soybean > drybean. There was no correlation between the measured residues of thiamethoxam (Heubach AI) and those estimated in dust based on the thiamethoxam content of Cruiser 350FS. A hazard quotient (HQ) for each crop (based on application rate, the default dust deposition factor, and the honeybee contact LD50/10) identified risks during sowing for all crops. Refinement of the application rate with the measured 90th percentile Heubach dust (assuming 100% thiamethoxam) resulted in sowing of industrially treated soybean and on-farm treated cotton being identified as risks. Further refinement using either the measured 90th percentile Heubach AI or the acute contact LD50 (HD5 ) resulted in sowing of all crops treated with Cruiser 350FS as being identified as low risk. Similar high quality seed treatment should be demonstrated for other formulations containing insecticides with high toxicity to bees. Data on dust drift from machinery and crops more representative of those in Brazil may allow further refinement of the default dust deposition value of 17% used in this study. Integr Environ Assess Manag 2023;19:1361-1373. © 2023 SETAC.

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.

First Records of Heartbeats via ECG in a Stingless Bee, Melipona flavolineata (Apidae, Meliponini), during Contention Stress Using Isoflurane as an Anesthetic

The hemodynamic activity of Melipona flavolineata workers was evaluated during restraint stress for a period of 30 min. The observed parameters were power variation in the elapsed time, and subsequently, six periods of one second were divided and called A, B, C, D, E and F; in each period, the electrocardiographic parameters were evaluated: spike frequency, amplitude, spike intervals and spike duration. The experiment was carried out with eight worker bees of M. flavolineata, for which electrodes of a nickel-chromium alloy were made. The bees were previously anesthetized with isoflurane and properly contained and fixed in a base for stereotaxis in which the electrode was implanted. All these procedures were performed inside a Faraday cage. The results showed power oscillations during the recording, with the highest energy level being between 300 and 600 s. Spike frequency, spike amplitude, interval between spikes and spike duration parameters underwent changes during the restraint stress period. Thus, the cardiac activity of M. flavolineata can be used as a biomarker and can be used to clarify physiological issues or alterations caused by toxic agents and indicate risk factors for these animals.

Comparison of the Sensitivity of Tetragonisca angustula (Apidae-Meliponini) and Apis mellifera (Apidae-Apini) to Three Insecticides (Malathion, Imidacloprid, and Fipronil) Used in Costa Rica

The decline of insect pollinators is a significant concern within the current biodiversity crisis. The paradox between the benefits that these animals represent to humans and the evidence of human activities driving their extinction calls for the urgent protection of bees. To address the role of chemical pollution in this scenario, we assessed the acute toxicity as well as four biomarker responses (cholinesterase [ChE], glutathione S-transferase, catalase, and lipid peroxidation [LPO]) elicited by dietary 24-h exposure to three insecticides (malathion, imidacloprid, and fipronil) on the stingless neotropical bee Tetragonisca angustula and the honeybee Apis mellifera. Malathion was the most toxic substance to both species, with 48-h median lethal doses (LD50s) of 0.25 ng/bee to A. mellifera and 0.02 ng/bee to T. angustula. Fipronil was also highly toxic and presented a similar toxicity to both species, with 48-h LD50s of 0.5 ng/bee (A. mellifera) and 0.4 ng/bee (T. angustula). Imidacloprid had the lowest acute toxicity with a 48-h LD50 of 29 ng/bee for A. mellifera, whereas T. angustula tolerated exposure higher than 35 ng/bee. Apparent biomarker responses were observed in bees of both species that survived exposure to higher concentrations of malathion (ChE inhibition) and fipronil (increased LPO). Our results suggest that specific sensitivity to insecticides varies greatly among compounds and pollinator species, but the use of different representative species can facilitate the prioritization of substances regarding their risk to pollinators. Further research is necessary to better characterize the risk that pesticides represent in neotropical agricultural landscapes. Environ Toxicol Chem 2023;42:1022-1031. © 2023 SETAC.

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.

Stingless bee keeping: Biocultural conservation and agroecological education

Introduction

Stingless bee breeding, also called Meliponiculture, has existed for thousands of years in Mesoamerica among a variety of rural and indigenous cultures. Due to its biocultural importance, it represents a perfect device for agroecological education and scaling, as well as pollinator conservation. At the same time, promoting agroecological transitions are necessary for conserving the cultural heritage that meliponicultures represent.

Methods

We organized a series of activities based on this premise: documenting and dialoguing “saberes contemporáneos” (contemporary knowledges), design and implementation of community agroecological workshops, guided visits at the institutional Meliponary at ECOSUR Villahermosa and promotion of agroecological and biocultural school gardens, all in Tabasco, México. We used “diálogo de saberes” (knowledge dialogues) as a methodological approach, promoting respect for the contribution of the diversity of ontoepistemologies involved. We drew on the ideas of several pedagogues, mainly from popular education and critical pedagogy frameworks.

Results and discussion

We identified characteristics of stingless bees and meliponicultures that make them excellent mediators for biocultural conservation and agroecological education: the complex, deep and beautiful relation between humans and bees; meliponiculture's ecological and cultural importance; stingless bees as pollinators par excellence, landscape connectors, and charismatic species; the association of bees with values around work and community; meliponicultures' symbolic relevance and emotional significance; meliponicultures as promoters of intergenerational dialogue; bee keeping as an activity of caring for the continuity of life; sensory stimulation through contact with colonies; learning through doing in the practice of beekeeping; meliponicultures as an activity requiring skill but no special equipment; and meliponiculture's productive potential. This confluence of teaching-learning opportunities, cultural and moral values, care for the land and biocultural diversity, and economic potential makes meliponiculture a potent catalyst for agroecological learning and transitions.

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

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

Survival Rate of the Neotropical Stingless Bees Nannotrigona perilampoides and Frieseomelitta nigra after Exposure to Five Selected Insecticides, under Controlled Conditions

Insecticides used in agricultural pest management pose survival risks to the stingless bees that forage on crops in tropical and subtropical regions. In the present study, we evaluated, under laboratory conditions, the acute oral toxicity of five selected insecticides (dinotefuran, imidacloprid, flupyradifurone, spirotetramat, and cyantraniliprole) to two species of neotropical stingless bees: Nannotrigona perilampoides and Frieseomelitta nigra. At field recommended doses, dinotefuran, imidacloprid, and flupyradifurone caused the highest mortality in both bee species. These insecticides also caused the largest decrease in the survival rate when exposed to a 10-fold dilution of the field recommended doses. Notably, dinotefuran exerted a high effect even at 100-fold dilution (100% mortality). In contrast, cyantraniliprole had a low effect and spirotetramat was virtually nontoxic. These results suggest that some insecticides used to control sap-sucking insects may have a significant negative impact on the communities of stingless bees.

Laboratory Risk Assessment of Three Entomopathogenic Fungi Used for Pest Control toward Social Bee Pollinators

The use of fungal-based biopesticides to reduce pest damage and protect crop quality is often considered a low-risk control strategy. Nevertheless, risk assessment of mycopesticides is still needed since pests and beneficial insects, such as pollinators, co-exist in the same agroecosystem where mass use of this strategy occurs. In this context, we evaluated the effect of five concentrations of three commercial entomopathogenic fungi, Beauveria bassiana, Metarhizium anisopliae, and Cordyceps fumosorosea, by direct contact and ingestion, on the tropical stingless bees Scaptotrigona depilis and Tetragonisca angustula, temperate bee species, the honey bee Apis mellifera, and the bumble bee Bombus terrestris, at the individual level. Furthermore, we studied the potential of two infection routes, either by direct contact or ingestion. In general, all three fungi caused considerable mortalities in the four bee species, which differed in their response to the different fungal species. Scaptotrigona depilis and B. terrestris were more susceptible to B. bassiana than the other fungi when exposed topically, and B. terrestris and A. mellifera were more susceptible to M. anisopliae when exposed orally. Interestingly, increased positive concentration responses were not observed for all fungal species and application methods. For example, B. terrestris mortalities were similar at the lowest and highest fungal concentrations for both exposure methods. This study demonstrates that under laboratory conditions, the three fungal species can potentially reduce the survival of social bees at the individual level. However, further colony and field studies are needed to elucidate the susceptibility of these fungi towards social bees to fully assess the ecological risks.

Commonly used triazole fungicides accelerate the metamorphosis of digger wasps (Hymenoptera: Spheciformes)

Azole fungicides have been essential pillars of global food security since the commercialization of triadimefon. However, the potential for fungicides to induce sublethal effects on larval development and emergence from overwintering is underresearched. We hypothesized that contact exposure to field-realistic concentrations of a broad spectrum of triazole fungicides alters the pupation and metamorphosis of crabronid wasps. Therefore, triazole fungicides shape the hymenopteran communities in agrocenoses. We applied field-realistic concentrations of three triazole fungicides, difenoconazole, penconazole, and tebuconazole, to the defecated prepupae of Pemphredon fabricii (Hymenoptera: Crabronidae). We monitored their survival, pupation, and metamorphosis into adults, including the timing of these events. All three tested triazole fungicides altered the time to the metamorphosis into adults of P. fabricii prepupae compared to the vehicle-treated controls. This effect was concentration-independent within the recommended concentration ranges for foliar applications. However, the three triazole fungicides were not associated with any significant declines in overall survival. Thus, the commonly used triazole fungicides affect the synchronization of the metamorphosis into adults with the availability of food and nesting resources of the study species. The study compounds did not affect the survival, which agrees with previous studies of other azole fungicides, which revealed effects on survival only when used in combination with other compounds. Further research should address the multiplicative effects of the triazole fungicides with other agrochemicals on the timing of the metamorphosis of bees and wasps.

A systematic review of research conducted by pioneer groups in ecotoxicological studies with bees in Brazil: advances and perspectives

Brazil presents the most threatened endemic or rare species among neotropical regions, with the Hymenoptera order, to which bees belong, classified as a high-risk category. In Brazil, the main cause of bee death is the indiscriminate use of pesticides. In this context, groups such as Bee Ecotoxicology and Conservation Laboratory (LECA in Portuguese) and Bees and Environmental Services (ASAs in Portuguese) have become a reference in studies evaluating the impacts of pesticides on bees since 1976. Thus, the objective of this review was to conduct a quantitative and qualitative review of the studies conducted by these groups to evaluate and compile the advances made over the years, identify potential knowledge gaps for future studies, and support the sensitivities of stingless bees when compared to the species Apis mellifera. The quantitative analyses showed that most studies were carried out in the genus Apis, under laboratory conditions. However, more recently (since 2003), studies have also focused on stingless bees and the neonicotinoid class of insecticides. The most relevant gaps identified were the lack of studies under field conditions and on bee biology. The qualitative analyses indicated that Brazilian stingless bees are more susceptible to pesticides than A. mellifera and require a much lower average dose, concentration, or lethal time to display morphological and behavioral damage or decreased lifespan. Thus, future studies should work towards establishing more representative protocols for stingless bees. Furthermore, public policies must be created for the protection and conservation of bees native to Brazil.

Are native bees in Brazil at risk from the exposure to the neonicotinoid imidacloprid?

All across the world, different countries use Ecological risk assessments (ERA) of pesticides to pollinators as a regulatory tool to understand the safety of pesticide use in agriculture. However, pesticide application is still recognized as one of the main stress factors causing a decline in the global population of bees. In all ERA procedures, the effects of pesticides on the honey bee species Apis mellifera are used as a reference for the effects on all different bee species. To evaluate if tropical native bees are protected by the current risk assessment procedures and to propose improvements to the methods, we assessed the ecological risk of the neonicotinoid imidacloprid posed to native and exotic bee species. The risk was assessed through a low (TIER I) and an intermediate (TIER II) level of analysis. For TIER I the USEPA BeeREX model was used and for TIER II the Species Sensitivity Distribution (SSD) approach was adopted. For the imidacloprid exposure conditions, four different crops were taken into consideration; bean, passion fruit, sunflower and tomato. The imidacloprid risk on native species was assessed both by extrapolating the effects obtained to Apis species, and by using ecotoxicological data from tests performed with native species. In TIER I, the risks calculated through empirical data showed that more than 50% of the non-Apis species presented risk levels of 28-180% higher than those obtained with the extrapolation factor used in the Brazilian pesticide regulation. In TIER II, the SSDs showed that most of the native bees are more sensitive to imidacloprid than the Africanized A. mellifera. This is the first study in which an ERA of a pesticide was conducted on tropical bee species. Here we also present some gaps and perspectives for future studies aiming to improve the risk assessment of pesticides in terrestrial environments.

The threat of pesticide and disease co-exposure to managed and wild bee larvae

Brood diseases and pesticides can reduce the survival of bee larvae, reduce bee populations, and negatively influence ecosystem biodiversity. However, major gaps persist in our knowledge regarding the routes and implications of co-exposure to these stressors in managed and wild bee brood. In this review, we evaluate the likelihood for co-exposure to brood pathogen and pesticide stressors by examining the routes of potential co-exposure and the possibility for pollen and nectar contaminated with pathogens and pesticides to become integrated into brood food. Furthermore, we highlight ways in which pesticides may increase brood disease morbidity directly, through manipulating host immunity, and indirectly through disrupting microbial communities in the guts of larvae, or compromising brood care provided by adult bees. Lastly, we quantify the brood research bias towards Apis species and discuss the implications the bias has on brood disease and pesticide risk assessment in wild bee communities. We advise that future studies should place a higher emphasis on evaluating bee brood afflictions and their interactions with commonly encountered stressors, especially in wild bee species.

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Brood exposure to pathogens and pesticides may occur frequently and in combination during the consumption of pollen and nectar.

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Brood pathogen virulence can be directly increased due to pesticide-mediated manipulation of larvae immune responses.

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Pesticides may indirectly increase brood disease morbidity by affecting larval gut microbial compositionand adult bee health.

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Research bias towards Apis species skews our understanding and management of brood disease and pesticide risks in wild bees.

Chronic exposure to a common biopesticide is detrimental to individuals and colonies of the paper wasp Polistes versicolor

Risk assessments of agrochemicals on non-target insects are biased in studies with surrogate groups, such as pollinators. In social insects, such investigations are generally restricted to lethal tests with adults maintained individually, simulating a non-realistic scenario. Here, we performed a holistic approach to resemble a chronic field exposure of Polistes versicolor (Hymenoptera: Vespidae) to a common biopesticide. These wasps are predators that perform biological control in the agroecosystems. Wasps were chronically subjected to the ingestion of different concentrations of azadirachtin. The neonicotinoid imidacloprid was used as a positive control. For the first time, we demonstrated that the biopesticide azadirachtin is detrimental for individual and colony survival and impairs colony reproduction of a social wasp maintained in the laboratory. Our data also indicated that neonicotinoid imidacloprid is harmful to wasps and their colonies. Therefore, the concomitant use of azadirachtin and paper wasps in integrated pest management strategies should be carefully evaluated, because the constant use of this pesticide can be detrimental for social wasps, possibly reducing biological control.

Toxicological assessment of agrochemicals on bees using machine learning tools

Machine learning (ML) is a branch of artificial intelligence (AI) that enables the analysis of complex multivariate data. ML has significant potential in risk assessments of non-target insects for modeling the multiple factors affecting insect health, including the adverse effects of agrochemicals. Here, the potential of ML for risk assessments of glyphosate (herbicide; formulation) and imidacloprid (insecticide, neonicotinoid; formulation) on the stingless bee Melipona quadrifasciata was explored. The collective behavior of forager bees was analyzed after in vitro exposure to agrochemicals. ML algorithms were applied to identify the agrochemicals that the bees have been exposed to based on multivariate behavioral features. Changes in the in situ detection of different proteins in the midgut were also studied. Imidacloprid exposure leads to the greatest changes in behavior. The ML algorithms achieved a higher accuracy (up to 91%) in identifying agrochemical contamination. The two agrochemicals altered the detection of cells positive for different proteins, which can be detrimental to midgut physiology. This study provides a holistic assessment of the sublethal effects of glyphosate and imidacloprid on a key pollinator. The procedures used here can be applied in future studies to monitor and predict multiple environmental factors affecting insect health in the field.

Harmful effects of fipronil exposure on the behavior and brain of the stingless bee Partamona helleri Friese (Hymenoptera: Meliponini)

Fipronil is a pesticide widely used to control agricultural and household insect pests. However, fipronil is highly toxic to non-target insects, including pollinators. In this study, we investigated the acute effects of fipronil on the behavior, brain morphology, antioxidant activity, and proteins related to signaling pathways on the brain of workers of the stingless bee Partamona helleri. The ingestion of fipronil increases both the walking distance and velocity and causes enlarged intercellular spaces in the Kenyon cells and intense vacuolization in the neuropils of the brain. Moreover, fipronil decreases the activity of catalase (CAT) and increases the activity of glutathione S-transferase (GST). However, there is no difference in superoxide dismutase (SOD) activity between the control and fipronil. Regarding immunofluorescence analysis, bees exposed to fipronil showed an increase in the number of cells positive for cleaved caspase-3 and peroxidase, but a reduction in the number of cells positive for ERK 1/2, JNK and Notch, suggesting neuron death and impaired brain function. Our results demonstrate that fipronil has harmful effects on the behavior and brain of a stingless bee, which may threaten the individuals and colonies of this pollinator.

Acute toxicity of the insecticide abamectin and the fungicide difenoconazole (individually and in mixture) to the tropical stingless bee Melipona scutellaris

Stingless bees have been recognized as essential plant pollinators and producers of various natural products in neotropical areas. Research into the potential risks of pesticides they may be exposed to in agricultural fields, however, remains meagre. Especially the toxicity of pesticide mixtures likely to occur under real-world conditions and that are likely to exert synergetic effects has been poorly studied. The aim of the present study was therefore to evaluate the single and mixture acute contact and oral toxicity of commercial products containing the insecticide abamectin and the fungicide difenoconazole in laboratory bioassays with the Brazilian native stingless bee Melipona scutellaris. In addition, a comparison of the insecticide sensitivity of stingless bees relative to the honeybee Apis mellifera was made based on previously published toxicity data. Except for oral exposure to abamectin, M. scutellaris appeared to be more sensitive that A. mellifera in the single compound toxicity tests. A difenoconazole concentration at the NOEC (no observed effect concentration) level indicated a synergetic toxic interaction with abamectin. A sensitivity comparison based on published toxicity data for A. mellifera and stingless bees indicated several insecticidal modes of action having a high relative sensitivity to stingless bees that need especial consideration in future studies. The research findings highlight the need for testing native bee species and environmentally relevant pesticide mixtures in risk assessments to avoid underestimation of potential risks to bee populations and the subsequent loss of pollination ecosystem services.

Assessment of the Vulnerability to Pesticide Exposures Across Bee Species

In many countries, the western honey bee is used as surrogate in pesticide risk assessments for bees. However, uncertainty remains in the estimation of pesticide risk to non-Apis bees because their potential routes of exposure to pesticides, life histories, and ecologies differ from those of honey bees. We applied the vulnerability concept in pesticide risk assessment to 10 bee species including the honey bee, 2 bumble bee species, and 7 solitary bee species with different nesting strategies. Trait-based vulnerability considers the evaluation of a species at the level of both the organism (exposure and effect) and the population (recovery), which goes beyond the sensitivity of individuals to a toxicant assessed in standard laboratory toxicity studies by including effects on populations in the field. Based on expert judgment, each trait was classified by its relationship to the vulnerability to pesticide exposure, effects (intrinsic sensitivity), and population recovery. The results suggested that the non-Apis bees included in our approach are potentially more vulnerable to pesticides than the honey bee due to traits governing exposure and population recovery potential. Our analysis highlights many uncertainties related to the interaction between bee ecology and the potential exposures and population-level effects of pesticides, emphasizing the need for more research to identify suitable surrogate species for higher tier bee risk assessments. Environ Toxicol Chem 2021;40:2640-2651. © 2021 SETAC.

Overview of the testing and assessment of effects of microbial pesticides on bees: strengths, challenges and perspectives

Currently, there is a growing interest in developing biopesticides and increasing their share in the plant protection market as sustainable tools in integrated pest management (IPM). Therefore, it is important that regulatory requirements are consistent and thorough in consideration of biopesticides' unique properties. While microbial pesticides generally have a lower risk profile, they present special challenges in non-target organism testing and risk assessment since, in contrast to chemical pesticides, their modes of action include infectivity and pathogenicity rather than toxicity alone. For this reason, non-target organism testing guidelines designed for conventional chemical pesticides are not necessarily directly applicable to microbial pesticides. Many stakeholders have recognised the need for improvements in the guidance available for testing microbial pesticides with honey bees, particularly given the increasing interest in development and registration of microbial pesticides and concerns over risks to pollinators. This paper provides an overview of the challenges with testing and assessment of the effects of microbial pesticides on honey bees (Apis mellifera), which have served as a surrogate for both Apis and non-Apis bees, and provides a foundation toward developing improved testing methods.

Fungicide pyraclostrobin affects midgut morphophysiology and reduces survival of Brazilian native stingless bee Melipona scutellaris

Native stingless bees are key pollinators of native flora and important for many crops. However, the loss of natural fragments and exposure to pesticides can hinder the development of colonies and represent a high risk for them. Nevertheless, most studies are conducted with honeybees and there are not many studies on native species, especially in relation to the effects of fungicides on them. Therefore, the objective of this paper is to evaluate the effects of sublethal concentrations of pyraclostrobin, on Melipona scutellaris forager workers. These Brazilian native stingless bees were submitted to continuous oral exposure to three concentrations of pyraclostrobin in sirup: 0.125 ng a.i./µL (P1), 0.025 ng a.i./µL (P2), and 0.005 ng a.i./µL (P3). Histopathological and histochemical parameters of midgut, as well as survival rate were evaluated. All concentrations of fungicide showed an increase in the midgut lesion index and morphological signs of cell death, such as cytoplasmic vacuolizations, presence of atypical nuclei or pyknotic nuclei. Histochemical analyzes revealed a decreased marking of polysaccharides and neutral glycoconjugates both in the villi and in peritrophic membrane in all exposed-groups in relation to control-groups. P1 and P2 groups presented a reduction in total protein marking in digestive cells in relation to control groups. As a consequence of alteration in the midgut, all groups exposed to fungicide showed a reduced survival rate. These findings demonstrate that sublethal concentrations of pyraclostrobin can lead to significant adverse effects in stingless bees. These effects on social native bees indicate the need for reassessment of the safety of fungicides to bees.

Lethal and Sublethal Effects of Pyriproxyfen on Apis and Non-Apis Bees

Pyriproxyfen is a juvenile hormone mimic used extensively worldwide to fight pests in agriculture and horticulture. It also has numerous applications as larvicide in vector control. The molecule disrupts metamorphosis and adult emergence in the target insects. The same types of adverse effects are expected on non-target insects. In this context, the objective of this study was to evaluate the existing information on the toxicity of pyriproxyfen on the honey bee (Apis mellifera) and non-Apis bees (bumble bees, solitary bees, and stingless bees). The goal was also to identify the gaps necessary to fill. Thus, whereas the acute and sublethal toxicity of pyriproxyfen against A. mellifera is well-documented, the information is almost lacking for the non-Apis bees. The direct and indirect routes of exposure of the non-Apis bees to pyriproxyfen also need to be identified and quantified. More generally, the impacts of pyriproxyfen on the reproductive success of the different bee species have to be evaluated as well as the potential adverse effects of its metabolites.

Is the Water Supply a Key Factor in Stingless Bees' Intoxication?

Water is an important resource for stingless bees, serving for both honey dilution and the composition of larval food inside nests, yet can be an important route of exposure to pesticides. Assuming bees can forage naturally on pesticide-contaminated or noncontaminated areas, we investigated whether water supply influences the choice between neonicotinoid-dosed or nondosed feeders and on mortality of the stingless bee, Melipona scutellaris (Latreille, Hymenoptera, Apidae). At the field concentration, there was no significant mortality; however, the bees were not able to distinguish the feeders. In the cages containing high-concentration feeders, with water supply, the bees preferred nondosed food, and with no water, the mortality increased. Considering that in the field it is common to find extrapolated concentrations, our work suggested that water may allow avoidance of high dosed food and minimize mortality.

What is the most suitable native bee species from the Neotropical region to be proposed as model-organism for toxicity tests during the larval phase?

Currently, Brazil has a full framework for pesticide risk assessment established for Apis mellifera, based on the North American approach. However, the use of Apis mellifera as model-organism as a surrogate for Brazilian native species of stingless bees has been questioned. Assessments on other stages of development than adult individual are essential. Our study aimed to standardize in vitro larval rearing method for the stingless bee species Scaptotrigona postica and Tetragonisca angustula, comparing the results to those obtained for M. scutellaris (previously described), for proposing the most suitable one for using in toxicological larval tests. We used the most efficient method for determining the toxicity of dimethoate on S. postica larvae. We presented the first comparative approach of responses to in vitro larval rearing methods among native bee species from Neotropical region, for use in risk assessment. Our results showed that S. postica was the most suitable native species to be proposed as model-organism. In addition, our results are also very useful for a ring test to validate the method, in accordance to OECD.

Plant protection product residues in plant pollen and nectar: A review of current knowledge

Exposure to Plant Protection Products, PPPs, (fungicides, herbicides and insecticides) is a significant stressor for bees and other pollinators, and has recently been the focus of intensive debate and research. Specifically, exposure through contaminated pollen and nectar is considered pivotal, as it presents the highest risk of PPP exposure across all bee species. However, the actual risk that multiple PPP residues might pose to non-target species is difficult to assess due to the lack of clear evidence of their actual concentrations. To consolidate the existing knowledge of field-realistic residues detected in pollen and nectar directly collected from plants, we performed a systematic literature review of studies over the past 50 years (1968-2018). We found that pollen was the matrix most frequently evaluated and, of the compounds investigated, the majority were detected in pollen samples. Although the overall most studied category of PPPs were the neonicotinoid insecticides, the compounds with the highest median concentrations of residues in pollen were: the broad spectrum carbamate carbofuran (1400 ng/g), the fungicide and nematicide iprodione (524 ng/g), and the organophosphate insecticide dimethoate (500 ng/g). In nectar, the highest median concentration of PPP residues detected were dimethoate (1595 ng/g), chlorothalonil (76 ng/g), and the insecticide phorate (53.5 ng/g). Strong positive correlation was observed between neonicotinoid residues in pollen and nectar of cultivated plant species. The maximum concentrations of several compounds detected in nectar and pollen were estimated to exceed the LD_50s for honey bees, bumble bees and four solitary bee species, by several orders of magnitude. However, there is a paucity of information for the biggest part of the world and there is an urgent need to expand the range of compounds evaluated in PPP studies.

Immunosuppression response to the neonicotinoid insecticide thiacloprid in females and males of the red mason bee Osmia bicornis L

Solitary bees are frequently exposed to pesticides, which are considered as one of the main stress factors that may lead to population declines. A strong immune defence is vital for the fitness of bees. However, the immune system can be weakened by environmental factors that may render bees more vulnerable to parasites and pathogens. Here we demonstrate for the first time that field-realistic concentrations of the commonly used neonicotinoid insecticide thiacloprid can severely affect the immunocompetence of Osmia bicornis. In detail, males exposed to thiacloprid solutions of 200 and 555 µg/kg showed a reduction in hemocyte density. Moreover, functional aspects of the immune defence - the antimicrobial activity of the hemolymph - were impaired in males. In females, however, only a concentration of 555 µg/kg elicited similar immunosuppressive effects. Although males are smaller than females, they consumed more food solution. This leads to a 2.77 times higher exposure in males, probably explaining the different concentration thresholds observed between the sexes. In contrast to honeybees, dietary exposure to thiacloprid did not affect melanisation or wound healing in O. bicornis. Our results demonstrate that neonicotinoid insecticides can negatively affect the immunocompetence of O. bicornis, possibly leading to an impaired disease resistance capacity.

Impact of Biotic and Abiotic Stressors on Managed and Feral Bees

Large-scale declines in bee abundance and species richness over the last decade have sounded an alarm, given the crucial pollination services that bees provide. Population dips have specifically been noted for both managed and feral bee species. The simultaneous increased cultivation of bee-dependent agricultural crops has given rise to additional concern. As a result, there has been a surge in scientific research investigating the potential stressors impacting bees. A group of environmental and anthropogenic stressors negatively impacting bees has been isolated. Habitat destruction has diminished the availability of bee floral resources and nest habitats, while massive monoculture plantings have limited bee access to a variety of pollens and nectars. The rapid spread and increased resistance buildup of various bee parasites, pathogens, and pests to current control methods are implicated in deteriorating bee health. Similarly, many pesticides that are widely applied on agricultural crops and within beehives are toxic to bees. The global distribution of honey bee colonies (including queens with attendant bees) and bumble bee colonies from crop to crop for pollination events has been linked with increased pathogen stress and increased competition with native bee species for limited resources. Climatic alterations have disrupted synchronous bee emergence with flower blooming and reduced the availability of diverse floral resources, leading to bee physiological adaptations. Interactions amongst multiple stressors have created colossal maladies hitting bees at one time, and in some cases delivering additive impacts. Initiatives including the development of wild flower plantings and assessment of pesticide toxicity to bees have been undertaken in efforts to ameliorate current bee declines. In this review, recent findings regarding the impact of these stressors on bees and strategies for mitigating them are discussed.