High levels of miticides and agrochemicals in North American apiaries: implications for honey bee health

Assessing the impact of co-exposure to succinate dehydrogenase inhibitor (SDHI) fungicides and the intestinal parasite Nosema ceranae in the honey bee Apis mellifera

Over the past few decades, significant mortality rates have been reported in honey bee populations. The decline of these pollinators is thought to be linked to a combination of stressors, including both pathogens and pesticides. Here, we investigated the impact of chronic exposure of honey bees to a class of fungicides that inhibit succinate dehydrogenase (SDHI), in combination with the parasite Nosema ceranae. Bees were exposed under controlled laboratory conditions to N. ceranae and/or fed with two environmental concentrations of four different SDHIs (boscalid, bixafen, fluopyram, and fluxapyroxad). The bees were monitored for 21 days, during which several health parameters were evaluated, including survival, food consumption, parasitic load and lipid reserves. Additionally, a global RNA-Seq approach was used to analyze midgut transcriptional changes in non-infected and N. ceranae-infected bees treated with fluopyram. The results indicate complex and deleterious interactions of SDHI active substances, characterized by dose-response effects and non-monotonic reactions in uninfected bees. However, co-exposure to N. ceranae significantly modified these responses, with an antagonistic effect on survival and lipid reserves, which could be linked to mitochondrial disruption and activation of detoxification mechanisms. These results highlight the importance of considering bee co-exposure to multiple stressors over their lifespan.

A gut bacterial supplement for Asian honey bee (Apis cerana) enhances host tolerance to nitenpyram: Insight from microbiota-gut-brain axis

The widespread use of neonicotinoid pesticides has severely impacted honey bees, driving population declines. Gut microbiota are increasingly recognized for their role in mitigating pesticide toxicity. This study evaluated the ability of Gilliamella sp. G0441, a core microbiome member of the Asian honey bee (Apis cerana), to confer resistance to the toxicity of a neonicotinoid nitenpyram. Newly emerged Asian honey bees were first colonized with gut microbiota in the source colony, then divided into four treatments: SS (fed sucrose solution throughout), SN (fed sucrose solution, then exposed to nitenpyram), GS (fed Gilliamella, then sucrose solution), and GN (fed Gilliamella, then exposed to nitenpyram), and their responses-mortality, food consumption, body weight, and sucrose sensitivity-were assessed. The protective effects of Gilliamella administration on the host were further validated using a microbiota-free bee model. Gilliamella supplementation significantly mitigated nitenpyram-induced appetite suppression, weight loss, impaired learning, and gut microbiota disruption. Mechanistic analyses revealed that nitenpyram disrupted brain metabolism via the intestinal MAPK pathway, reducing ascorbate and aldarate metabolism. Prophylactic Gilliamella treatment reversed these effects, restored metabolic balance, and modulated esterase E4 expression, enhancing pesticide resistance. This study underscores Gilliamella's vital role in honey bee resilience to neonicotinoids, offering insights into the microbiota-gut-brain axis (MGBA) as a pathway for enhancing pesticide tolerance and ecological health.

Detoxification response in honey bee larvae exposed to agricultural intensification

Honey bee Apis mellifera colonies located in agroecosystems are exposed to pesticides and more fragmented habitats. The resources that bees obtain in these environments may be exposed to agrochemicals, which can accumulate in their colonies and be distributed among their nest mates. Hives placed in an agricultural setting located in the region of the Argentine Pampas were studied. Changes in the expression levels of insect cytochrome P450s, enzymes involved in the detoxification of xenobiotics, and the presence of pesticides in hive products at different times of crop management were evaluated. Our results showed that CYP6AS2 and CYP6AS4 expression in honey bee larvae increased significantly after crop flowering and pesticide application. Furthermore, residues of the herbicides atrazine and glyphosate, and the insecticide chlorantraniliprole were found in beeswax and honey samples collected from the same beehives, and their concentrations correlated with the expression profiles of CYP6AS2, CYP6AS3 and CYP9BD1. These results underscore the potential risks of pesticides exposure to larval development, highlighting the need to mitigate agrochemical use in agricultural landscapes to safeguard honey bee colonies.

Early life imidacloprid and copper exposure affects the gut microbiome, metabolism, and learning ability of honey bees (Apis mellifera)

The pesticide imidacloprid and the heavy metal copper provide some degree of protection to plants, while at the same time causing varying degrees of damage to bees. However, few studies have investigated the negative effects of imidacloprid and copper exposure on newly emerged bees (young bees), especially when both are present in a mix. In this study, young bees were exposed to sterile sucrose solutions containing imidacloprid (10 μg/L, 100 μg/L), copper (10 mg/L, 50 mg/L), or a mix of both (10 μg/L + 10 mg/L) for 5 days to assess their gut system and behavior, with survival and dietary consumption recorded over 21 days. We found that imidacloprid and copper reduced honeybee survival, dietary intake, and learning ability, decreased gut microbiota diversity, and caused metabolic disruptions. Notably, the mix of imidacloprid and copper had a synergistic negative effect. Correlation analyses revealed that the honeybee gut microbiota influences bee immunity and behavior by regulating metabolic pathways related to ascorbate, tryptophan, and carbohydrates. Our results demonstrate that imidacloprid and copper, either alone or in a mix, alter young bee health through a complex mechanism of toxicity. These findings highlight imidacloprid and copper's negative effects on young honeybees, offering insights for future pesticide and heavy metal impact research.

Time dynamics models for oxidative stress markers in honey bees (Apis mellifera) following paraquat-induced stress

Many agrochemicals disrupt redox homeostasis, yet the dynamics of oxidative stress responses in honey bees (Apis mellifera) remain insufficiently understood. This study established a controlled model to monitor ROS-related markers over time following paraquat injection, using Bayesian modeling to characterize time-dependent changes. We observed a transient rise in hydroperoxides and early fluctuation in adipokinetic hormone (AKH) levels, which declined and stabilized within 8hours. No significant differences were detected in secondary lipid peroxidation products (TBARS) among treatments. While injection does not represent natural exposure pathways, it enables precise dosing and timing, avoiding variability from oral intake. This experimental design provides a tractable system to investigate oxidative stress mechanisms under defined conditions. Our findings underscore the importance of time-resolved analysis in redox physiology and offer a mechanistic framework to complement field-relevant toxicological studies in bees and other beneficial insects.

Impact of a lambda-cyhalothrin formulation residues on larval Apis mellifera: examining midgut and fat body morphological response to insecticide chronic exposure

Pollination by honey bees (Apis mellifera) is crucial for maintaining biodiversity and crop yields. However, the widespread use of pesticides may threaten bees' survival by contaminating their resources. Lambda-cyhalothrin, a neurotoxic insecticide commonly used in agricultural pest control, poses particular risks. In insects, the midgut and fat body serve as primary barriers against xenobiotics, and exposure to these chemicals during larval development can impact adult bees. This study aimed to assess whether the residual concentration of lambda-cyhalothrin in pollen grains affects the midgut and fat body of larval A. mellifera workers after chronic exposure. The midgut epithelium of larvae exposed to a lambda-cyhalothrin-based insecticide (λ-CBI) exhibited autophagic vacuoles, apical cell protrusions, apocrine secretion, nuclear pyknosis, and high levels of polysaccharides and glycoconjugates in the cytoplasm, with smaller amounts in the brush border. Histochemical analysis revealed areas of vacuolation and damage to cell integrity in the midgut. In fat body cells, the insecticide increased polysaccharide storage and decreased lipid droplet diameter. Despite the histopathological damage, no effects were found in the larval development and adult emergence. These findings suggest the occurrence of apoptosis and autophagy in midgut cells and alterations in nutrient storage in the fat body of A. mellifera larvae exposed to the λ-CBI, potentially impacting the physiology and development of this pollinator with possible effects on adult workers.

RNA metagenomics revealed insights into the viromes of honey bees (Apis mellifera) and Varroa mites (Varroa destructor) in Taiwan

The honey bee (Apis mellifera) is a vital pollinator for crops. However, they are infested by an ecto-parasite that has spread worldwide, Varroa mite (Varroa destructor). The Varroa mite is a vector of various western honey bee viruses. In this study, the prevalence of seven honey bee viruses (Deformed wing virus, Lake Sinai virus, Acute bee paralysis virus, Sacbrood virus, Kashmir bee virus, Black queen cell virus, Israeli acute paralysis virus), was screened with the honey bees, which were collected from fourteen apiaries from March 2023 to January 2024, and the Varroa mites, which were collected from two apiaries from July to October 2023 by using RT-PCR. Subsequently, metagenomic analyses were conducted on seven honey bee samples and two Varroa mite samples using next-generation sequencing with poly-A capture and rRNA depletion library construction methods. The results showed that 50% to 85.7% of honey bee viruses in each sample were detected by both methods, with up to three additional viruses identified when combining the two approaches. These findings underscore the importance of integrating both methods for comprehensive virome analysis. According to the virome analysis, 28 honey bee viruses were identified in honey bees and 11 in Varroa mites. Among these, 23 viruses were newly recorded in Taiwanese honey bee populations. Notably, three of the newly recorded viruses, Acute bee paralysis virus, Israeli acute paralysis virus, and Apis mellifera filamentous virus, are known to cause symptoms in honey bees, posing potential risks to their health. Six of these viruses were also detected in Varroa mites, highlighting their role in viral transmission. This study represents the first virome analysis of honey bees and Varroa mites in Taiwan, providing critical insights into honey bee health and establishing a foundation for future health assessment indices and mitigation strategies.

Pesticide residues in honey: Agricultural landscapes and commercial wax foundation sheets as potential routes of chronic exposure for honey bees

Pesticides pose significant threats to pollinators, and honey bees are frequently exposed through foraging and beekeeping practices. We assessed honey bee pesticide exposure by analyzing 92 pesticide residues in honey from 30 hobbyist apiaries across Massachusetts, along with store-bought honey and commercial wax foundation. For all samples, we calculated the risk of multiresidue toxicity to honey bees and assessed the role of landscape composition in predicting pesticides in local honey. Both honey and wax contained multiple pesticides, particularly neonicotinoids and piperonyl butoxide. Store-bought honey accumulated at least two times more residues than local, but did not differ significantly in toxicity. Overall, honey toxicity levels remained below thresholds of concern for bees and human consumption. Although our study had low agricultural land (∼6 %), croplands were positively correlated with pesticides in honey, while wetlands (∼ 15 %) were negatively correlated. Additionally, our study suggests that commercial wax exacerbates pesticide exposure.

Short-term persistence of foliar insecticides and fungicides in pumpkin plants and their pollinators

To minimize the risk to bees and other beneficial insects, plant protection chemicals are typically applied to pollinator-dependent crop plants when flowers are absent or unopened. However, this approach does not entirely remove the risk of pollinator exposure. Much research has focused on negative effects of systemic insecticides (e.g., seed treatments) on pollinators, but less is known about the level of hazard posed by translocation of non-systemic foliar-applied pesticides to pollen and nectar that bees consume. In this study we assess the frequency and persistence of six foliar-applied pesticides in pumpkin (Cucurbita pepo) tissues and in their bee visitors. We analyzed residues of three insecticides (carbaryl, lambda-cyhalothrin, permethrin) and three fungicides (chlorothalonil, quinoxyfen, triflumizole) in pumpkin leaves, pollen, and nectar collected from five farms in the north-central USA, one day before a spray event, and one, three, and seven days after. Bees foraging on pumpkin flowers were collected one day before and one day after spray and screened for the same pesticides. Overall, insecticides were present in 56% of leaf samples. Compared to leaves, fewer pollen (insecticide detected in 16%, fungicide in 16%) and nectar samples (14%, 0%) contained pesticides. We detected one insecticide (carbaryl) in two out of 69 samples of foraging bees, and only in male squash bees (not in bumble or honey bees), which have life history traits that bring them into prolonged close contact with the sprayed crop plants. The persistence of some agrochemicals in leaves, pollen, and nectar up to a week following application merits consideration when managing pollinator-dependent crops. Even pesticides that are traditionally considered contact-based and applied when flowers are unopened can reach pollen and nectar and produce measurable risk to bees.

Environmental pollution effect on honey bees and their derived products: a comprehensive analysis

Several factors, including environmental degradation, air pollution, intense urbanization, excessive agriculture, and climate change, endanger the well-being of animals and plants. One of the major issues with an increasingly negative impact is agricultural contamination with pesticides and antibiotics. Seed coatings with neonicotinoid insecticides used as a protective layer against pests are shown to exceed the permissible limits in most cases. Neonicotinoid compounds bind to nicotinic acetylcholine receptors, therefore affecting the honey bees' brain. Heavy metals in higher concentrations are lethal for honey bees, and the residue in bee products might pose a threat to human health. Highly effective acaricides used to treat Varroa destructor infestations in honey bee colonies have negative effects on honey bee reproduction, olfaction, and honey production. Furthermore, amitraz and fluvalinate are mostly found in the highest amounts and lead to decreased honey production and reduced colony reproduction, along with decreased learning ability and memory. However, scientific studies have shown that honey bees act as a reliable bio-indicator of environmental pollution. In response to the growing demand for bee products, the effects of adulteration and improper storage conditions have gotten worse and represent a new risk factor. In light of the shifting global economy, it is important to analyze consumer expectations and adjust manufacturing accordingly. By ensuring the manufacture of high-quality, traceable products devoid of drug residues, consumers will be better protected from subsequent health problems. This review's objectives are based on the necessity of identifying the risks associated with honey bees and bee products.

Exposure to a widely used mito-toxic fungicide negatively affects hemolymph protein and vitellogenin levels in honey bees (Apis mellifera)

Mito-toxic fungicides used in crop protection negatively affect pollinating insects. The fungicide formulation Pristine® (ai: 25.2 % boscalid, 12.8 % pyraclostrobin) induces precocious foraging, reduced lifespan, impaired homing abilities, and reduced body size at field-relevant concentrations. However, the underlying physiological mechanisms for these outcomes are poorly understood. To assess the hypothesis that Pristine® negatively affects the nutritional status of honey bees, we collected workers from colonies that were fed field-relevant concentrations of Pristine® fungicide. Workers were collected concurrently from two experiments in which colonies were subjected to long- or short-term fungicide exposure. Pristine® exposure significantly reduced hemolymph protein concentration in bees from the long-term but not short-term study, and reduced vitellogenin levels during the short-term summer exposure. These findings suggest that mito-toxic fungicides can negatively affect the nutritional status of honey bee workers inducing detrimental behavioral and health outcomes which ultimately impact colony health and growth patterns.

Honey bee immune response to trace concentrations of clothianidin goes beyond the macronutrients found in artificial diets

Honey bees (Apis mellifera) often encounter a variety of stressors in their environment, including poor nutrition and pesticides. These stressors interact and can be exacerbated in large-scale agroecosystems. We investigated how diets varying in macronutrient ratios can affect nurse bee susceptibility to pesticide stressors. Nurse bees were fed trace concentrations of clothianidin (CLO), a neonicotinoid insecticide known to have sublethal and lethal effects on honey bees, after newly emerged bees were given diets varying in proteins and lipids, a natural pollen diet, or sucrose solution diet. Bees given pollen had improved longevity, physiology, enzyme activity, and gene expression related to pesticide detoxification. The artificial diets helped improve bee health and physiology but did little to promote bee detoxification enzymes and genes. There was no effect of the trace CLO treatments on its own, but there was an interactive effect between our higher CLO treatment and poor nutrition on bee longevity and vitellogenin expression. Our results suggest that (1) exposure to even trace concentrations of CLO can interact with poor nutrition to undermine adult bee health and (2) macronutrients in artificial diets can help promote bee physiology, but other nutrients in pollen, such as potentially phytochemicals, are more directly linked honey bee tolerance to pesticide stress.

Weight of evidence assessment from field studies on effects of the insecticide sulfoxaflor on hymenopteran pollinators: sulfoxaflor environmental science review part V

Field studies involve combinations of exposure, natural dynamics, and effects in natural and agricultural environments. To be more realistic, field studies focussed on pollinating insects must consider the details of biology, life history, behavior, and pollination ecology of the test species. While expensive and time-consuming, these tests provide the most realistic information, especially for social insects, but are valuable for solitary bee species as well. They are more realistic than laboratory studies because they determine the combined effects of natural stressors including weather, food availability, parasites, and pathogens with anthropogenic stressors, such as the pesticide treatment itself, within agroecosystem landscapes. Twenty-four field studies conducted with bees to support the registration of sulfoxaflor and published work are included, and a standardized rating system for the quality and relevance of the studies was used. The studies included Apis mellifera L., Bombus terrestris L., and Osmia bicornis L. The results show that, when SFX products are applied at the highest labeled application rate with bees actively foraging or fed in syrup at equivalent rates, the effects are minor and temporary. Sublethal effects included lethargy, disorientation, and reduced body mass at emergence. No new modes of action and no treatment-related effects on brood rearing were found.

Lactic Acid Bacteria: A Probiotic to Mitigate Pesticide Stress in Honey Bee

Using probiotics, especially those containing lactic acid bacteria (LAB), to support honey bee health and alleviate the negative effects of pesticides represents a promising approach for sustainable beekeeping. Probiotics have shown their ability to boost honey bee immune systems, counteract pesticide impacts, and lower disease rates. Bacteria like Lactobacillus and Bifidobacterium have demonstrated their ability to degrade organophosphorus pesticides using phosphatase enzymes. Additionally, these bacteria are resistant to the harmful effects of pesticides and aid in detoxification. Furthermore, supplementing with LAB positively affects colony growth, resulting in increased honey production, improved pollen storage, and higher brood counts. Various methods of delivering probiotics, such as powdered supplements, sucrose syrup, and pollen patties, have been explored, each with its own set of challenges and considerations. Despite making significant progress, further study is still required to fully comprehend the precise interactions between probiotics and the physiology of honey bees, to improve delivery strategies, and to evaluate the wider ecological effects on hive microbiomes. By implementing probiotic strategies in beekeeping practices, we can create stronger and more resilient honey bee colonies that can thrive amidst environmental challenges, thus promoting the sustainability of pollination services.

Acute toxicity and sublethal effects of thiamethoxam on the stingless bee Scaptotrigona postica: Survival, neural morphology, and enzymatic responses

Native and cultivated plants in the Neotropics benefit from the pollination services provided by stingless bees. The use of neonicotinoid insecticides negatively impacts bee health, even though bees are not their primary targets. This study determined the oral mean lethal concentration (LC50) of thiamethoxam (TMX) after 24 h of exposure for the stingless bee Scaptotrigona postica. Based on the LC₅₀ value (0.11 ng a.i./μL) obtained, two fractions of this value (1/10 and 1/100 LC₅₀) were selected to assess survival time (LT₅₀), as well as to conduct neural morphological and enzymatic analyses. The LC₅₀/100 group had a LT₅₀ of 15 days, compared to 17 days in the control group, while the LC₅₀/10 group survived for 8 days. Morphological analyses revealed increased Kenyon cell spacing and pyknosis in the mushroom bodies after 1, 3, and 6 days of exposure, suggesting that thiamethoxam adversely affects the brain of S. postica. Regarding enzymatic activity, comparisons between the control and the two sublethal concentrations revealed that Carboxylesterase and Glutathione S-transferase (GST) activity increased in the abdomens after six days of exposure. GST activity also increased in the bees' heads for the LC₅₀/10 concentration after six days of exposure (Control x TMX group). The enzymatic results suggests that thiamethoxam induces oxidative stress in S. postica. The results presented underscore the necessity of considering stingless bees in regulatory decisions regarding the use of insecticides, ensuring that the risks to this important group of pollinators are adequately assessed.

Minimal toxicological impact of chlorothalonil on adult honey bees (Apis mellifera, L.)

Honey bees encounter a diverse array of pesticides in their foraging areas and inside their colonies. Beekeepers have expressed tremendous concern about the impacts of pesticides on honey bee colony health and their beekeeping business. The fungicide chlorothalonil is frequently detected at concentrations above 5 ppm within colonies. Exposure to chlorothalonil in lab studies have shown impacts on larval development and morphology of emerging adults while field studies have shown that colony losses are associated with chlorothalonil at 5 ppm. This research was conducted to test if chlorothalonil has effects on honey bee toxicity, insecticide synergism, detoxification activity, and expression of esterase and cytochrome P450 genes in order to assess if chlorothalonil may contribute to colony losses via direct or enhanced toxicity. Exposure to 10 μg topically applied doses or 5 ppm orally applied concentrations of technical or formulated chlorothalonil did not result in significant direct mortality, demonstrated <2-fold levels of synergism or antagonism with phenothrin, chlorpyrifos, and clothianidin, and did not impact activity or expression of detoxification enzymes. Therefore, the impacts of chlorothalonil on honey bee colony health is likely not due to toxicity or synergism but rather other physiological mechanisms.

Sensitivity and Resistance of Parasitic Mites (Varroa destructor, Tropilaelaps spp. and Acarapis woodi) Against Amitraz and Amitraz-Based Product Treatment: A Systematic Review

Resistance to amitraz in Varroa destructor mites poses a significant challenge to global beekeeping, leading to the declining efficacy of treatments and increased colony losses. This study aims to comprehensively map, characterize, and analyze the status of amitraz efficacy and resistance in Varroa and other parasitic mites such as Tropilaelaps spp. and Acarapis woodi. A systematic review, following PRISMA 2020 guidelines, examined 74 studies, revealing substantial variability in experimental protocols, mite origins, and environmental factors, all of which impacted toxicity assessments. These findings highlight the urgent need for standardized methodologies to ensure consistency and reliability. Resistance ratios (RR) and indices (RI) showed significant geographical variation, reflecting localized resistance development. Laboratory studies highlighted inconsistencies in detecting resistance, underscoring the importance of combining bioassays, molecular diagnostics, and field efficacy tests. Understanding the genetic and physiological mechanisms driving amitraz resistance, as well as their prevalence, is vital to devising sustainable management strategies. Establishing national monitoring programs and revising testing protocols are pivotal steps toward ensuring the continued effectiveness of acaricides. These measures, combined with coordinated efforts by researchers, beekeepers, and policymakers, are essential to safeguarding global honey bee populations and supporting the long-term sustainability of apiculture.

From larva to adult: In vitro rearing protocol for honey bee (Apis mellifera) drones

Development of a successful in vitro rearing protocol has been essential for pesticide safety assessment of immature honey bee workers under laboratory conditions. In contrast, pesticide safety testing of honey bee drones is limited, in part due to the lack of successful laboratory rearing protocols for this reproductive caste. Considering that healthy drones are essential for successful mating and reproduction of the honey bee queen, a standardized in vitro rearing protocol for honey bee drones is necessary to support reproductive safety studies, as well as to gain a deeper understanding of honey bee drone development. Using the established in vitro rearing protocol for honey bee workers, we modified the days of grafting and pupal transfer, as well as the diet volume, pupation plate orientation, and absorbent tissue in the pupal wells to successfully rear honey bee drones in vitro. In vitro-reared drones were evaluated for gross wing abnormalities, body weight, testes weight, and abdominal area, and compared with age-matched drones reared in field colonies. We found that honey bee drones reared in a vertically oriented pupation plate containing WypAll® absorbent tissue in each well had a mean survival to adulthood of 74 ± 3.5% (SEM) until adulthood. In contrast, drones reared in a horizontally oriented pupation plate containing Kimwipe® absorbent tissue in each well had significantly lower survival (5.5 ± 2.3%) and demonstrated gross wing abnormalities. All in vitro-reared drones had significantly lower body weight, testes weight and abdominal area relative to colony-reared control drones. Accordingly, we successfully developed an in vitro rearing protocol for honey bee drones which has the potential to improve future reproductive safety assessment of pesticides for honey bees.

Managed honey bees, Apis mellifera (Hymenoptera: Apidae), face greater risk from parasites and pathogens than mosquito control insecticide applications

As the primary pollinator for many crops, honey bees (Apis mellifera) are critically important to food production and the agricultural economy. Adult mosquito control is often suspected by the public and commercial beekeepers to harm honey bees, creating conflicts between industries. To investigate this matter, a two-year field study was conducted on vegetated wetlands in Salt Lake City, Utah, U.S.A. where honey bee colonies were placed in areas subjected to aerial adult mosquito control applications using the organophosphate naled. Comparison colonies were placed in areas not exposed to insecticides. Colony conditions were documented over the two-year period to capture both immediate and cumulative season-long effects of naled to honey bee health. A Before-After-Control-Impact (BACI) analysis of mortality data from treated and non-treated colonies using mixed effects models revealed no statistically significant differences, indicating that aerial applications of naled for mosquito control did not adversely affect these honey bee colonies. A Random Forest machine-learning model identified that Nosema infection, maximum temperatures, and seasonal progression were more significant contributors to bee mortality during the study period, whereas cumulative naled applications were among the least significant predictors. Non-parametric statistical tests (NMDS and PERMANOVA) indicated no differences in colony resources (pollen/honey/nectar; open/capped brood) and parasite (Varroa mites; Vairimorpha microsporidians) loads between exposed colonies and non-treatment colonies. These findings were consistent across different seasons and varying environmental conditions. Our results suggest that naled, when used as intended for mosquito control, does not pose a significant risk to managed honey bee populations in rural settings.

The Role of Pathogens in Bumblebee Decline: A Review

Bumblebees, the most important wild pollinators in both agricultural and natural ecosystems, are declining worldwide. The global decline of bumblebees may threaten biodiversity, pollination services, and, ultimately, agricultural productivity. Several factors, including pesticide usage, climate change, habitat loss, and species invasion, have been documented in the decline of bumblebee species, but recent studies have revealed the dominating role of pathogens and parasites over any of these causes. Unfortunately, there is a lack of a full understanding of the role of pathogens and parasites in the decline of bumblebee species. The current study provides a comprehensive review of how pathogens and parasites contribute to the decline of bumblebee species. The study also explores the prevalence of each pathogen and parasite within bumblebee populations. Furthermore, we address the synergistic effects of pathogens and other stressors, such as pesticides, climatic effects, and habitat loss, on bumblebee populations. To summarize, we propose possible conservation and management strategies to preserve the critical role of bumblebees in pollination services and thus to support ecosystem and agricultural health.

Discovery of multiple bee-hazardous pesticides in ornamental plants via the Bee-Plex multi-target microsphere screening method

Exposure to pesticides is one of the main drivers of global bee decline. However, the occurrence of pesticides in bee-attracting crops remains underexposed due to the lack of efficient on-site screening approaches for multi-analyte monitoring. Utilizing color-encoded superparamagnetic microspheres, we constructed a portable 8-plex indirect competitive microsphere-based immunoassay for the simultaneous determination of multiple bee-hazardous residues (Bee-Plex). Through a single measurement within 40 min, Bee-Plex exhibited high sensitivities with IC50values of 0.04, 0.08, 0.14, 0.15, 0.78, 0.86, 7.72, and 8.79 ng/mL for imidacloprid, parathion, fipronil, emamectin, carbofuran, chlorpyrifos, fenpropathrin and carbaryl, respectively. Moreover, the implementation of multiple broad-specific antibodies enables a wide-range screening profile for 30 pesticides and pesticide metabolites, detecting 6 neonicotinoids, 6 N-methyl carbamates 6 organophosphates, 5 avermectins, 5 pyrethroids and 2 phenylpyrazoles. The combination of Bee-Plex screening (93 % accuracy) and LC-MS/MS confirmatory analysis revealed contaminations of neonicotinoids (100 %) and avermectins (70 %) in roses, with occurrence frequencies of 79 %, 79 %, 21 %, 21 %, 7 %, and 7 % for imidacloprid, acetamiprid, clothianidin, thiacloprid, imidaclothiz, and nitenpyram, respectively. Above all, this study offers a powerful analytical tool for rapid screening of multiple bee-hazardous pesticides, offering new insights in the occurrence of multi-pesticide contamination in ornamental plants.

Arising amitraz and pyrethroids resistance mutations in the ectoparasitic Varroa destructor mite in Canada

The ectoparasitic mite Varroa destructor remains a great threat for the beekeeping industry, for example contributing to excessive winter colony loss in Canada. For decades, beekeepers have sequentially used the registered synthetic varroacides tau-fluvalinate, coumaphos, amitraz, and flumethrin, leading to the risk of resistance evolution in the mites. In addition to the widespread resistance to coumaphos and pyrethroids, a decline in amitraz efficacy has recently been reported in numerous beekeeping regions in Canada. The goals of this study were to assess the evolution of resistance to amitraz in Canadian mite populations and to evaluate the presence and incidence of mutations previously associated with resistance to amitraz and pyrethroids in V. destructor. Our bioassay results confirmed the presence of amitraz-resistant mites in the population of Alberta. These phenotypic results were complemented by targeted genotyping of the octopamine receptor gene Octβ2R which revealed the presence of the mutation Y215H in 90% of tested apiaries with local allele frequencies ranging from 5 to 95%. The phenotypic resistance showed a significant correlation with the presence of this mutation across apiaries. In parallel, the L925I and L925M mutations in the voltage-gated sodium channel were identified in 100% of the tested apiaries with frequencies ranging from 33 to 97%, suggesting that resistance to pyrethroids remains widespread. These results support the notion that the practice of relying on a single treatment for a prolonged period can increase rates of resistance to current varroacides. Our findings suggest the need for large-scale resistance monitoring via genotyping to provide timely information to beekeepers and regulators. This will enable them to make an effective management plan, including rotation of available treatments to suppress or at least delay the evolution of resistance in V. destructor populations.

Identifying and modeling the impact of neonicotinoid exposure on honey bee colony profit

Pollination by the European honey bee, Apis mellifera, is essential for the production of many crops, including highbush blueberries (Vaccinum corymbosum). To understand the impact of agrochemicals (specifically, neonicotinoids, a class of synthetic, neurotoxic insecticides) on these pollinators, we conducted a field study during the blueberry blooms of 2020 and 2021 in British Columbia (B.C.). Forty experimental honey bee colonies were placed in the Fraser Valley: half of the colonies were located within 1.5 km of highbush blueberry fields ("near" colonies) and half were located more than 1.5 km away ("far" colonies). We calculated risk quotients for these compounds using their chronic lethal dietary dose (LDD50) and median lethal concentration (LC50). Pesticide risk was similar between colonies located near and far from blueberry forage, suggesting that toxicity risks are regionally ubiquitous. Two systemic neonicotinoid insecticides, clothianidin and thiamethoxam, were found at quantities that exceeded chronic international levels of concern. We developed a profit model for a pollinating beekeeper in B.C. that was parameterized by: detected pesticide levels; lethal and sublethal bee health; and economic data. For colonies exposed to neonicotinoid pesticides in and out of the blueberry forage radii, there were economic consequences from colony mortality and sublethal effects such as a loss of honey production and compromised colony health. Further, replacing dead colonies with local bees was more profitable than replacing them with imported packages, illustrating that beekeeping management selection of local options can have a positive effect on overall profit.

Sublethal fungicide-insecticide co-exposure affects nest recognition and parental investment in a solitary bee

Fungicides may interact synergistically with insecticides. However, our understanding of the impacts of sublethal insecticide-fungicide combinations on solitary bees is mostly restricted to laboratory studies, providing no information about potential consequences on behavior and reproductive success. We analyzed the effects of a fungicide application, alone and in combination with sublethal levels of an insecticide, on the nesting behavior and reproductive output of the solitary bee Osmia cornuta. We released individually-marked females into oilseed rape field cages, and subsequently sprayed the plants with four treatments: control (water), fungicide (tebuconazole), insecticide (acetamiprid at a sublethal concentration), and mixture (fungicide + insecticide). We recorded nesting activity before and after the sprays and assessed post-spray individual reproductive success. Bees of the single pesticide treatments were unaffected by the sprays and did not differ from control bees in any of the parameters measured. The longevity of bees of the mixture treatment was unaffected. However, these bees showed reduced foraging activity, shorter in-nest pollen-nectar deposition times, and increased difficulty recognizing their nesting cavity, leading to a decrease in provisioning rate, parental investment, and offspring production. Our study demonstrates that co-exposure to a fungicide with otherwise harmless levels of an insecticide caused behavioral effects with consequences on reproductive success. Because longevity was unaffected, these effects would not have been easily detected in a chronic laboratory test. Our results have important implications for bee risk assessment, which should account for exposure to multiple compounds and address behavioral effects and reproductive output under semi-field and/or field conditions.

Pesticide exposure patterns in honey bees during migratory pollination

Monitoring pesticide exposures in honey bees provides fundamental risk information that informs efforts to improve regulatory policy, pesticide use, and beekeeping management so pollinators are protected in realistic field conditions. We investigated pesticide exposures to bee colonies while colonies moved along commercial migratory routes in 2022 and 2023 to pollinate multiple pollinator-dependent, high-value U.S. specialty crops (e.g., almonds in California and apples and cherries in Washington). We found evident pesticide exposure patterns, including increasing exposures (both levels and number of pesticides) to fungicides during almond pollination, higher exposures to insecticides and persistent exposures to fungicides during springtime fruit pollination, and declining exposures in summer. Exposure risk assessment by risk quotient (RQ) model based on residues in bee bread indicates no concern of acute toxicity to adult honey bees during pollination, however, during colony inspections we found severe brood mortality in fields associated with high exposure to buprofezin, an insect growth regulator (IGR) thought to be safe for adult bees, which is permitted for use any time across the season. Our results suggest a need to improve compliance with insecticide label requirements during tree fruit pollination and a need for further research into the negative impacts of IGR on colony health especially on immature bees to inform potential policy changes.

Nurse honey bees filter fungicide residues to maintain larval health

Residues of plant protection products (PPPs) are frequently detected in bee matrices1,2,3,4,5,6 due to foraging bees collecting contaminated nectar and pollen, which they bring back to their hive. The collected material is further used by nurse bees to produce glandular secretions for feeding their larvae.7 Potential exposure to PPPs occurs through direct oral ingestion, contact during foraging, or interaction with contaminated hive material.8,9 Contaminants can pose health risks to adult worker bees,10,11 queens,12,13 drones (males),14 or larvae,15,16 potentially impacting colony health and productivity. However, residue concentrations can vary significantly between analyzed matrices, and potential accumulation or dilution steps have not been widely investigated. Although research has provided valuable insights into contamination risks, there remain gaps in our understanding of the entire pathway from field, via foragers, stored products, nurse bees, and finally to food jelly, i.e., royal, worker, and drone jelly, and the larvae, including all possible processing steps.17 We collected samples of bee-relevant matrices following the in-field spray application of the product Pictor Active, containing the fungicides boscalid and pyraclostrobin. The samples were analyzed for residues along this entire pathway. Fungicide residues were reduced by a factor of 8-80 from stored product to nurse bees' heads, suggesting a filtering function of nurse bees. Furthermore, detected residues in larval food jelly resulted from added pollen and not from nurse bee secretions. Calculated risk quotients were at least twice as low as the threshold values, suggesting a low risk to honey bee colonies from these fungicides at the tested application rate.

Bumblebees under stress: Interacting effects of pesticides and heatwaves on colony development and longevity

Pollinator decline is linked to intensified agricultural practices, pathogens, climate change, and several other factors. We investigated the combined impact of heat and pesticide stress on food consumption, survival, and reproductive fitness of bumble bees. As climate change is expected to intensify heatwaves, we simulated a present-day and a future heatwave scenario (as expected in 50 years). In both scenarios, we exposed microcolonies to three widely used pesticides: azoxystrobin (fungicide), flupyradifurone, and sulfoxaflor (both insecticides)-mixed into pollen and nectar in field-realistic concentrations. We found that bees always consumed the least of sulfoxaflor-treated food, whereas consumption did not differ between other treatments or heatwave scenarios. Surprisingly, pesticide-stressed colonies performed slightly better in the future heatwave scenario in terms of reproductive fitness and survival. Sulfoxaflor consistently had the strongest negative effect, reducing survival rates, brood development, and food consumption, although effects were less severe in the future heatwave scenario.

Temporal entry of pesticides through pollen into the bee hive and their fate in beeswax

Honey bees are often exposed to a variety of contaminants, including pesticides from agricultural use. The aim of this study was to investigate the temporal entry of pesticides into the hive by examining the seasonal timing of honey bees bringing pesticide-contaminated pollen into their colonies and the subsequent accumulation of these pesticides in beeswax. Pollen and beeswax samples were collected biweekly from five colonies situated in an agricultural environment in Switzerland. In pollen, 23 pesticides (out of 50) were quantified, including 4 insecticides, 4 herbicides, 12 fungicides, a transformation product, an acaricide, and a synergist. The maximal insecticide concentration levels measured in individual pollen samples were 69.4 μg/kg (thiacloprid), 48.3 μg/kg (acetamiprid), 13.8 μg/kg (spinosad), and 11.1 μg/kg (indoxacarb), while fungicide levels ranged up to 2212.7 μg/kg (cyprodinil), and herbicides were up to 71.9 μg/kg (prosulfocarb). Eighteen of the pesticides found in pollen were also quantifiable in beeswax. Among these were 17 lipophilic pesticides with logarithmic octanol water coefficients (log Kow) equal or above 2.5, which showed similar temporal profiles and order of accumulation magnitude as in pollen. For example, maximal concentrations measured in individual beeswax samples were 12.4 μg/kg for indoxacarb (insecticide), 986.4 μg/kg for cyprodinil (fungicide), and 21.6 μg/kg for prosulfocarb (herbicide). Furthermore, pesticides with log Kow between 2.5 and 7.0 remained in the beeswax during wax purification. Our study shows that a large variety of pesticides brought into the hive through pollen potentially stay in the beeswax during recycling, thus constantly exposing honey bees to pesticides.

Sublethal Effects Induced by a Cyflumetofen Formulation on Honeybee Apis mellifera L. Workers: Assessment of Midgut, Hypopharyngeal Glands, and Fat Body Integrity

Worldwide, both cultivated and wild plants are pollinated by the honey bee, Apis mellifera. Bee numbers are declining as a result of a variety of factors, including increased pesticide use. Cyflumetofen controls pest mites in some plantations pollinated by bees, which may be contaminated with residual sublethal concentrations of this pesticide, in nectar and pollen. We evaluated the effects of a sublethal concentration of a cyflumetofen formulation on the midgut, hypopharyngeal gland, and fat body of A. mellifera workers orally exposed for 72 h or 10 days. The midgut epithelium of treated bees presented digestive cells with cytoplasm vacuoles and some cell fragmentation, indicating autophagy and cell death. After being exposed to the cyflumetofen formulation for 72 h, the midgut showed a higher injury rate than the control bees, but after 10 days, the organs had recovered. In the hypopharyngeal gland of treated bees, the end apparatus was filled with secretion, suggesting that the acaricide interferes with the secretory regulation of this gland. Histochemical tests revealed differences in the treated bees in both exposure periods in the midgut and hypopharyngeal glands. The acaricide caused cytotoxic effects on the midgut digestive cells, with apical protrusions, plasma membrane rupture, and several vacuoles in the cytoplasm, features of cell degeneration. In the hypopharyngeal glands of the treated bees, the secretory cells presented small electron-dense and large electron-lucent secretory granules. The fat body cells had no changes in comparison with the control bees. In conclusion, the cyflumetofen formulation at sublethal concentrations causes damage to the midgut and the hypopharyngeal glands of honey bee, which may compromise the functions of these organs and colony fitness. Environ Toxicol Chem 2024;43:2455-2465. © 2024 SETAC.

Early exposure to glyphosate during larval development induces late behavioural effects on adult honey bees

As the most abundant pollinator insect in crops, Apis mellifera is a sentinel species of the pollinator communities. In these ecosystems, honey bees of different ages and developmental stages are exposed to diverse agrochemicals. However, most toxicological studies analyse the immediate effects during exposure. Late effects during adulthood after early exposure to pollutants during larval development are poorly studied in bees. The herbicide glyphosate (GLY) is the most applied pesticide worldwide. GLY has been detected in honey and beebread from hives near treated crops. Alterations in growth, morphogenesis or organogenesis during pre-imaginal development could induce late adverse effects after the emergence. Previous studies have demonstrated that GLY alters honey bee development, immediately affecting survival, growth and metabolism, followed by late teratogenic effects. The present study aims to determine the late impact on the behaviour and physiology of adult bees after pre-imaginal exposure to GLY. For that, we reared brood in vitro or in the hive with sub-chronic exposure to the herbicide with the average detected concentration in hives. Then, all newly emerged bees were reared in an incubator until maturity and tested when they became nurse-aged bees. Three behavioural responses were assessed as markers of cognitive and physiological impairment. Our results show i) decreased sensitivity to sucrose regardless of the rearing procedure, ii) increased choice latency and locomotor alterations during chemotaxis and iii) impaired associative learning. These late toxicity signs could indicate adverse effects on task performance and colony efficiency.

Contamination profile and hazards of neonicotinoid insecticides in honey from apiaries in Beijing, China

The residues of neonicotinoid insecticides in honey have raised global concern for their adverse effects on non-target organisms. However, information on the presence of neonicotinoids in raw honey in China is limited. Our study investigated the distribution profiles of neonicotinoids in raw honey samples collected from apiaries in plain and mountainous areas surrounding Beijing City. At least one of four neonicotinoids, imidacloprid, thiamethoxam, acetamiprid, or clothianidin, was found in 46.9% of samples. Neonicotinoids in multi-floral honey in plain areas exhibited higher concentrations and prevalence than in uni-floral honey collected from mountainous areas. These results indicated that neonicotinoid residues in honey were linked to the agricultural ecosystems influenced by geographies, particularly the intensity of agriculture and nectariferous plant types. The dietary risks to adult and children health from neonicotinoid exposure were deemed de minimis, while risks to honeybees at the maximum concentration level require much attention through refined, higher-tier assessments and possible mitigation measures for the use of these products.

The impact of landscape structure on pesticide exposure to honey bees

Pesticides may have serious negative impacts on bee populations. The pesticide exposure of bees could depend on the surrounding landscapes in which they forage. In this study, we assess pesticide exposure across various land-use categories, while targeting the Japanese honey bee, Apis cerana japonica, a native subspecies of the eastern honey bee. In a project involving public participation, we measured the concentrations of major pesticides in honey and beeswax collected from 175 Japanese honey bee colonies across Japan and quantitatively analyzed the relationships between pesticide presence/absence or pesticide concentration and land-use categories around the colonies. Our findings revealed that the surrounding environment in which bees live strongly influences pesticide residues in beehive materials, whether the pesticides are systemic or not, with a clear trend for each land-use category. Agricultural lands, particularly paddy fields and orchards, and urban areas resulted in higher pesticide exposure, whereas forests presented a lower risk of exposure. To effectively control pesticide exposure levels in bees, it is essential to understand pesticide usage patterns and to develop appropriate regulatory systems in non-agricultural lands, similar to those in agricultural lands.

Pesticides and pollinator brain: How do neonicotinoids affect the central nervous system of bees?

Neonicotinoids represent over a quarter of the global pesticide market. Research on their environmental impact has revealed their adverse effect on the cognitive functions of pollinators, in particular of bees. Cognitive impairments, mostly revealed by behavioural studies, are the phenotypic expression of an alteration in the underlying neural circuits, a matter deserving greater attention. Here, we reviewed studies on the impact of field-relevant doses of neonicotinoids on the neurophysiology and neurodevelopment of bees. In particular, we focus on their olfactory system as much knowledge has been gained on the different brain areas that participate in odour processing. Recent studies have revealed the detrimental effects of neonicotinoids at multiple levels of the olfactory system, including modulation of odorant-induced activity in olfactory sensory neurons, diminished neural responses in the antennal lobe (the first olfactory processing centre) and abnormal development of the neural connectivity within the mushroom bodies (central neuropils involved in multisensory integration, learning and memory storage, among others). Given the importance of olfactory perception for multiple aspects of bee biology, the reported disruption of the olfactory circuit, which can occur even upon exposure to sublethal doses of neonicotinoids, has severe consequences at both individual and colony levels. Moreover, the effects reported for a multimodal structure such as the mushroom bodies indicate that neonicotinoids' impact translates to other sensory domains. Assessing the impact of field-relevant doses of pesticides on bee neurophysiology is crucial for understanding how neonicotinoids influence their behaviour in ecological contexts and for defining effective and sustainable agricultural practices.

Synergistic effects between microplastics and glyphosate on honey bee larvae

Microplastic (MPs) pollution has emerged as a global ecological concern, however, the impact of MPs exposure, particularly in conjunction with other pollutants such as glyphosate (GLY) on honey bee remains unknown. This study investigated the effects of exposure to different concentrations of MPs and their combination with GLY on honey bee larvae development, or during the larvae period, regulation of major detoxification, antioxidant and immune genes, and oxidative stress biomarkers. Results revealed that combined exposure to MPs and GLY decreased larvae survivorship and weight, while exposure to MPs alone showed no significant differences. Both MPs and GLY alone downregulated the defensin-1 gene, but only combined exposure with GLY downregulated the hymenoptaecin gene and increased catalase enzyme activity. The data suggest a synergistic effect of MPs and GLY, leading to immunosuppression and reduced larvae survival and weight. These findings highlight potential risks of two prevalent environmental pollutants on honey bee health.

The power to (detect) change: Can honey bee collected pollen be used to monitor pesticide residues in the landscape?

Analysis of trapped honey bee pollen for pesticide residues is the most widely used method of monitoring the amount of pesticide entering colonies and its change over time. In this study, we collected and analyzed pollen from 70 sites across four bee-pollinated crops over two years to characterize the variation in pesticide detection across sites, crops and at different periods during bloom. Hazard Quotient, HQ, is the most common way that pesticide residues are aggregated into a single pesticide hazard value in the current literature. Therefore, change in pesticide hazard (HQ) was quantified in composite pollen samples collected from pollen traps and in pollen color subsamples separated into pollen from the target crop being pollinated and pollen from other plant species. We used our estimates of the variation in HQ to calculate the number of sample location sites needed to detect a 5% annual change in HQ across all crops or within specific crops over a 5-year period. The number of sites required to be sampled varied by crop and year and ranged between 139 and 7194 sites, costing an estimated $129,548 and $3.35 million, respectively. The HQ values detectable for this cost would be 575 and 154. We identified additional factors that complicate the interpretation of the results as a way to evaluate changes in pest management practices at a state level. First, in all but one crop (meadowfoam), the pollen collected from outside the crop honey bee colonies were pollinating comprised a major percentage of the total pollen catch. Moreover, we found that when the overall quantity of pollen from different pollen sources was taken into account, differences in HQ among crops widened. We also found that while HQ estimates remain consistent across the bloom period for some crops, such as cherry, we observed large differences in other crops, notably meadowfoam. Overall, our results suggest the current practice of interpreting pesticides levels in pollen may come with limitations for agencies charged with improving pesticide stewardship due to the high variation associated with HQ values over time and across crops. Despite the limitations of HQ for detecting change in pesticide hazard, there remains a potential for HQ to provide feedback to regulators and scientists on field-realistic pesticide hazard within a landscape.

Phytochemical profiles of honey bees (Apis mellifera) and their larvae differ from the composition of their pollen diet

Pollen and nectar consumed by honey bees contain plant secondary metabolites (PSMs) with vital roles in plant-insect interactions. While PSMs can be toxic to bees, they can also be health-promoting, e.g. by improving pesticide and pathogen tolerances. As xenobiotics, PSMs undergo post-ingestion chemical modifications that can affect their bioactivity and transmission to the brood. Despite the importance of understanding honey bee PSM metabolism and distribution for elucidating bioactivity mechanisms, these aspects remain largely unexplored. In this study, we used HPLC-MS/MS to profile 47 pollen PSMs in honey bees and larvae. Both adult bees and larvae had distinct PSM profiles that differed from their diet. This is likely due to post-ingestion metabolism and compound-dependent variations in PSM transmission to the brood via nurse bee jelly. Phenolic acids and flavonoid aglycones were most abundant in bees and larvae, whereas alkaloids, cyanogenic glycosides and diterpenoids had the lowest abundance despite being consumed in higher concentrations. This study documents larval exposure to a variety of PSMs for the first time, with concentrations increasing from early to late larval instars. Our findings provide novel insights into the post-ingestion fate of PSMs in honey bees, providing a foundation for further exploration of biotransformation pathways and PSM effects on honey bee health.

Honey bees for pesticide monitoring in the landscape: Which bee matrices should be used?

Among bee species, the western honey bee (Apis mellifera) is preferred in monitoring studies performed in the agricultural landscape, while bee matrices, pollen, and honey are mostly a subject of these studies due to their unique composition. A justified question about the relevance of other bee matrices, like larvae, foragers, beebread, and/or wax, has been raised. The ability of different bee matrices (wax, pollen grains, bee bread, foragers, larvae, nectar, and honey) to absorb pesticide residues is subjected in this study. All samples were collected during a crop flowering season (oilseed rape) on intensively managed agricultural land in Slovakia and Germany. The observed high variability in residue levels, profile, and number of detections among studied matrices from Germany, west, and east Slovakia gave us an assumption of the use of different agricultural practices between these two countries. Fungicides clearly dominated across all samples in all sampling regions. The increased pesticide profile positively correlated with the oilseed rape pollen grains in pollen pellets and/or bee bread. Bee wax, pollen, and bee bread showed a high number of detected active substances and total residue concentrations among matrices, indicating their high ability to absorb pesticide residues in the surrounding hive environment.

Thiamethoxam toxicity on the stingless bee Friesiomelitta varia: LC50, survival time, and enzymatic biomarkers assessment

Bees play a crucial role as pollinating insects in both natural and cultivated areas. However, the use of pesticides, such as thiamethoxam, has been identified as a contributing factor compromising bee health. The current risk assessment primarily relies on the model species Apis mellifera, raising concerns about the applicability of these assessments to other bee groups, including stingless bees. In this study, we investigated the acute toxicity of thiamethoxam on the stingless bee Frieseomelitta varia by determining the average lethal concentration (LC50) and mean lethal time (LT50). Additionally, we evaluated the enzymatic profile of Acetylcholinesterase (AChE), Carboxylesterase-3 (CaE-3), and Glutathione S-Transferase (GST), in the heads and abdomens of F. varia after exposure to thiamethoxam (LC50/10). The LC50 of thiamethoxam was determined to be 0.68 ng ai/μL, and the LT50 values were 37 days for the control group, 25 days at LC50/10, and 27 days at LC50/100. The thiamethoxam significantly decreased the survival time of F. varia. Furthermore, the enzymatic profile exhibited differences in CaE3 activity within one day in the heads and ten days in the abdomen. GST activity showed differences in the abdomen after one and five days of thiamethoxam exposure. These findings suggests that the abdomen is more affected than the head after oral exposure to thiamethoxam. Our study provides evidence of the toxicity of thiamethoxam at both the cellular and organismal levels, reinforcing the need to include non-Apis species in pollinator risk assessments. and provide solid arguments for bee protection.

Interactive effects of chlorothalonil and Varroa destructor on Apis mellifera during adult stage

The interaction between environmental factors affecting honey bees is of growing concern due to their potential synergistic effects on bee health. Our study investigated the interactive impact of Varroa destructor and chlorothalonil on workers' survival, fat body morphology, and the expression of gene associated with detoxification, immunity, and nutrition metabolism during their adult stage. We found that both chlorothalonil and V. destructor significantly decreased workers' survival rates, with a synergistic effect observed when bees were exposed to both stressors simultaneously. Morphological analysis of fat body revealed significant alterations in trophocytes, particularly a reduction in vacuoles and granules after Day 12, coinciding with the transition of the bees from nursing to other in-hive work tasks. Gene expression analysis showed significant changes in detoxification, immunity, and nutrition metabolism over time. Detoxification genes, such as CYP9Q2, CYP9Q3, and GST-D1, were downregulated in response to stressor exposure, indicating a potential impairment in detoxification processes. Immune-related genes, including defensin-1, Dorsal-1, and Kayak, exhibited an initially upregulation followed by varied expression patterns, suggesting a complex immune response to stressors. Nutrition metabolism genes, such as hex 70a, AmIlp2, VGMC, AmFABP, and AmPTL, displayed dynamic expression changes, reflecting alterations in nutrient utilization and energy metabolism in response to stressors. Overall, these findings highlight the interactive and dynamic effects of environmental stressor on honey bees, providing insights into the mechanisms underlying honey bee decline. These results emphasize the need to consider the interactions between multiple stressors in honey bee research and to develop management strategies to mitigate their adverse effects on bee populations.

Assessment of Lambda-Cyhalothrin and Spinetoram Toxicity and Their Effects on the Activities of Antioxidant Enzymes and Acetylcholinesterase in Honey Bee (Apis mellifera) Larvae

Honeybees play a crucial role as agricultural pollinators and are frequently exposed to various pollutants, including pesticides. In this study, we aimed to evaluate the toxicity of lambda-cyhalothrin (LCY) and spinetoram (SPI) in honey bee larvae reared in vitro through single (acute) and repeated (chronic) exposure. The acute LD50 values for LCY and SPI were 0.058 (0.051-0.066) and 0.026 (0.01-0.045) μg a.i./larva, respectively. In chronic exposure, the LD50 values of LCY and SPI were 0.040 (0.033-0.046) and 0.017 (0.014-0.019) μg a.i./larva, respectively. The chronic no-observed-effect dose of LCY and SPI was 0.0125 μg a.i./larva. Adult deformation rates exceeded 30% in all LCY treatment groups, showing statistically significant differences compared to the solvent control group (SCG). Similarly, SPI-treated bees exhibited significantly more deformities than SCG. Furthermore, we examined the activities of several enzymes, namely, acetylcholinesterase (AChE), glutathione-S-transferase (GST), catalase (CAT), and superoxide dismutase (SOD), in larvae, pupae, and newly emerged bees after chronic exposure at the larval stage (honey bee larval chronic LD50, LD50/10 (1/10th of LD50), and LD50/20 (1/20th of LD50)). LCY and SPI induced significant changes in detoxification (GST), antioxidative (SOD and CAT), and signaling enzymes (AChE) during the developmental stages (larvae, pupae, and adults) of honey bees at sublethal and residue levels. Our results indicate that LCY and SPI may affect the development of honey bees and alter the activity of enzymes associated with oxidative stress, detoxification, and neurotransmission. These results highlight the potential risks that LCY and SPI may pose to the health and normal development of honey bees.

Exposure to sublethal levels of insecticide-fungicide mixtures affect reproductive success and population growth rates in the solitary bee Osmia cornuta

In agricultural environments, bees are routinely exposed to combinations of pesticides. For the most part, exposure to these pesticide mixtures does not result in acute lethal effects, but we know very little about potential sublethal effects and their consequences on reproductive success and population dynamics. In this study, we orally exposed newly emerged females of the solitary bee Osmia cornuta to environmentally-relevant levels of acetamiprid (a cyano-substituted neonicotinoid insecticide) singly and in combination with tebuconazole (a sterol-biosynthesis inhibitor (SBI) fungicide). The amount of feeding solution consumed during the exposure phase was lowest in bees exposed to the pesticide mixture. Following exposure, females were individually marked and released into oilseed rape field cages to monitor their nesting performance and assess their reproductive success. The nesting performance and reproductive success of bees exposed to the fungicide or the insecticide alone were similar to those of control bees and resulted in a 1.3-1.7 net population increases. By contrast, bees exposed to the pesticide mixture showed lower establishment, shortened nesting period, and reduced fecundity. Together, these effects led to a 0.5-0.6 population decrease. Female establishment and shortened nesting period were the main population bottlenecks. We found no effects of the pesticide mixture on nest provisioning rate, offspring body weight or sex ratio. Our study shows how sublethal pesticide exposure may affect several components of bee reproductive success and, ultimately, population growth. Our results calls for a rethinking of pollinator risk assessment schemes, which should target not only single compounds but also combinations of compounds likely to co-occur in agricultural environments.

Identifying pesticides of high concern for ecosystem, plant, animal, and human health: A comprehensive field study across Europe and Argentina

The widespread and excessive use of pesticides in modern agricultural practices has caused pesticide contamination of the environment, animals, and humans, with confirmed serious health consequences. This study aimed to identify the 20 most critical substances based on an analysis of detection frequency (DF) and median concentrations (MC) across environmental and biological matrices. A sampling campaign was conducted across 10 case study sites in Europe and 1 in Argentina, each encompassing conventional and organic farming systems. We analysed 209 active substances in a total of 4609 samples. All substances ranked among the 20 most critical were detected in silicon wristbands worn by humans and animals and indoor dust from both farming systems. Five of them were detected in all environmental matrices. Overall, higher values of DF and MC, including in the blood plasma of animals and humans, were recorded in samples of conventional compared to organic farms. The differences between farming systems were greater in the environmental samples and less in animal and human samples. Ten substances were detected in animal blood plasma from conventional farms and eight in animal blood plasma from organic farms. Two of those, detected in both farming systems, are classified as hazardous for mammals (acute). Five substances detected in animal blood plasma from organic farms and seven detected in animal blood plasma from conventional farms are classified as hazardous for mammals (dietary). Three substances detected in human blood plasma are classified as carcinogens. Seven of the substances detected in human blood plasma are classified as endocrine disruptors. Six substances, of which five were detected in human blood plasma, are hazardous for reproduction/development. Efforts are needed to elucidate the unknown effects of mixtures, and it is crucial that such research also considers biocides and banned substances, which constitute a baseline of contamination that adds to the effect of substances used in agriculture.

Acute toxicity of the fungicide captan to honey bees and mixed evidence for synergism with the insecticide thiamethoxam

Honey bees are commonly co-exposed to pesticides during crop pollination, including the fungicide captan and neonicotinoid insecticide thiamethoxam. We assessed the impact of exposure to these two pesticides individually and in combination, at a range of field-realistic doses. In laboratory assays, mortality of larvae treated with captan was 80-90% greater than controls, dose-independent, and similar to mortality from the lowest dose of thiamethoxam. There was evidence of synergism (i.e., a non-additive response) from captan-thiamethoxam co-exposure at the highest dose of thiamethoxam, but not at lower doses. In the field, we exposed whole colonies to the lowest doses used in the laboratory. Exposure to captan and thiamethoxam individually and in combination resulted in minimal impacts on population growth or colony mortality, and there was no evidence of synergism or antagonism. These results suggest captan and thiamethoxam are each acutely toxic to immature honey bees, but whole colonies can potentially compensate for detrimental effects, at least at the low doses used in our field trial, or that methodological differences of the field experiment impacted results (e.g., dilution of treatments with natural pollen). If compensation occurred, further work is needed to assess how it occurred, potentially via increased queen egg laying, and whether short-term compensation leads to long-term costs. Further work is also needed for other crop pollinators that lack the social detoxification capabilities of honey bee colonies and may be less resilient to pesticides.

Forever Pesticides: A Growing Source of PFAS Contamination in the Environment

BACKGROUND

Environmental contamination by fluorinated chemicals, in particular chemicals from the per- and polyfluoroalkyl substances (PFAS) class, has raised concerns around the globe because of documented adverse impacts on human health, wildlife, and ecosystem quality. Recent studies have indicated that pesticide products may contain a variety of chemicals that meet the PFAS definition, including the active pesticide ingredients themselves. Given that pesticides are some of the most widely distributed pollutants across the world, the legacy impacts of PFAS addition into pesticide products could be widespread and have wide-ranging implications on agriculture and food and water contamination, as well as the presence of PFAS in rural environments.

OBJECTIVES

The purpose of this commentary is to explore different ways that PFAS can be introduced into pesticide products, the extent of PFAS contamination of pesticide products, and the implications this could have for human and environmental health.

METHODS

We submitted multiple public records requests to state and federal agencies in the United States and Canada and extracted relevant data from those records. We also compiled data from publicly accessible databases for our analyses.

DISCUSSION

We found that the biggest contributor to PFAS in pesticide products was active ingredients and their degradates. Nearly a quarter of all US conventional pesticide active ingredients were organofluorines and 14% were PFAS, and for active ingredients approved in the last 10 y, this had increased to 61% organofluorines and 30% PFAS. Another major contributing source was through PFAS leaching from fluorinated containers into pesticide products. Fluorination of adjuvant products and "inert" ingredients appeared to be limited, although this represents a major knowledge gap. We explored aspects of immunotoxicity, persistence, water contamination, and total fluorine load in the environment and conclude that the recent trend of using fluorinated active ingredients in pesticides may be having effects on chemical toxicity and persistence that are not given adequate oversight in the United States. We recommend a more stringent risk assessment approach for fluorinated pesticides, transparent disclosure of "inert" ingredients on pesticide labels, a complete phase-out of post-mold fluorination of plastic containers, and greater monitoring in the United States. https://doi.org/10.1289/EHP13954.

Mechanisms of Pathogen and Pesticide Resistance in Honey Bees

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

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.

Pesticide Contamination in Native North American Crops, Part I-Development of a Baseline and Comparison of Honey Bee Exposure to Residues in Lowbush Blueberry and Cranberry

A pesticide exposure baseline for honey bees was compiled for two New England cropping systems, the native North American plant species consisting of lowbush blueberry (Vaccinium angustifolium Aiton) and cranberry (Vaccinium macrocarpon Aiton). More unique pesticide compounds were applied in blueberry than cranberry, but the numbers of pesticides discovered in trapped honey bee pollen were similar between the two crop systems. Not all pesticides found in pollen were the result of the applications reported by growers of either crop. When comparing residues, number of pesticides detected, total concentration, and risk quotient varied between the two crops. Also, blueberry was dominated by fungicides and miticides (varroacides) and cranberry was dominated by insecticides and herbicides. When comparing reported grower applications that were matched with detection in residues, the proportion of pesticide numbers, concentrations, and risk quotients varied by crop system and pesticide class. In most cases, pesticide residue concentrations were of low risk (low risk quotient) to honey bees in these crops. Estimation of decay rates of some of the most common pesticide residues under field conditions could aid growers in selection of less persistent compounds, together with safe application dates, prior to bringing in honey bees for pollination.

A field realistic model to assess the effects of pesticides residues and adulterants on honey bee gene expression

While studies on the sublethal effects of chemical residues in beeswax on adult honey bees are increasing, the study protocols assessing the impacts on honey bee brood in realistic conditions still need to be investigated. Moreover, little is known about the residue's effect on gene expression in honey bee brood. This study reports the effects of chlorpyriphos-ethyl, acrinathrin and stearin worker pupae exposure through contaminated or adulterated beeswax on the gene expression of some key health indicators, using a novel in vivo realistic model. Larvae were reared in acrinathrin (12.5, 25, 10 and 100 ppb) and chlorpyriphos-ethyl (5, 10, 500 and 5000 ppb) contaminated or stearin adulterated beeswax (3, 4, 5, 6 and 9%) in newly formed colonies to reduce the influence of external factors. On day 11, mortality rates were assessed. Honey bee pupae were extracted from the comb after 19 days of rearing and were analysed for the gene expression profile of four genes involved in the immune response to pathogens and environmental stress factors (Imd, dorsal, domeless and defensin), and two genes involved in detoxifications mechanisms (CYP6AS14 and CYP9Q3). We found no linear relation between the increase in the pesticide concentrations and the brood mortality rates, unlike stearin where an increase in stearin percentage led to an exponential increase in brood mortality. The immune system of pupae raised in acrinathrin contaminated wax was triggered and the expression of CYP6AS14 was significantly upregulated (exposure to 12.5 and 25 ppb). Almost all expression levels of the tested immune and detoxification genes were down-regulated when pupae were exposed to chlorpyrifos-contaminated wax. The exposure to stearin triggered the immune system and detoxification system of the pupae. The identification of substance-specific response factors might ultimately serve to identify molecules that are safer for bees and the ecosystem's health.

Interaction of acetamiprid, Varroa destructor, and Nosema ceranae in honey bees

Health of honey bees is threatened by a variety of stressors, including pesticides and parasites. Here, we investigated effects of acetamiprid, Varroa destructor, and Nosema ceranae, which act either alone or in combination. Our results suggested that interaction between the three factors was additive, with survival risk increasing as the number of stressors increased. Although exposure to 150 μg/L acetamiprid alone did not negatively impact honey bee survival, it caused severe damage to midgut tissue. Among the three stressors, V. destructor posed the greatest threat to honey bee survival, and N. ceranae exacerbated intestinal damage and increased thickness of the midgut wall. Transcriptomic analysis indicated that different combinations of stressors elicited specific gene expression responses in honey bees, and genes involved in energy metabolism, immunity, and detoxification were altered in response to multiple stressor combinations. Additionally, genes associated with Toll and Imd signalling, tyrosine metabolism, and phototransduction pathway were significantly suppressed in response to different combinations of multiple stressors. This study enhances our understanding of the adaptation mechanisms to multiple stressors and aids in development of suitable protective measures for honey bees. ENVIRONMENTAL IMPLICATION: We believe our study is environmentally relevant for the following reasons: This study investigates combined effects of pesticide, Varroa destructor, and Nosema ceranae. These stressors are known to pose a threat to long-term survival of honey bees (Apis mellifera) and stability of the ecosystems. The research provides valuable insights into the adaptive mechanisms of honey bees in response to multiple stressors and developing effective conservation strategies. Further research can identify traits that promote honey bee survival in the face of future challenges from multiple stressors to maintain the overall stability of environment.

Microbial Symbiont-Based Detoxification of Different Phytotoxins and Synthetic Toxic Chemicals in Insect Pests and Pollinators

Insects are the most diverse form of life, and as such, they interact closely with humans, impacting our health, economy, and agriculture. Beneficial insect species contribute to pollination, biological control of pests, decomposition, and nutrient cycling. Pest species can cause damage to agricultural crops and vector diseases to humans and livestock. Insects are often exposed to toxic xenobiotics in the environment, both naturally occurring toxins like plant secondary metabolites and synthetic chemicals like herbicides, fungicides, and insecticides. Because of this, insects have evolved several mechanisms of resistance to toxic xenobiotics, including sequestration, behavioral avoidance, and enzymatic degradation, and in many cases had developed symbiotic relationships with microbes that can aid in this detoxification. As research progresses, the important roles of these microbes in insect health and function have become more apparent. Bacterial symbionts that degrade plant phytotoxins allow host insects to feed on otherwise chemically defended plants. They can also confer pesticide resistance to their hosts, especially in frequently treated agricultural fields. It is important to study these interactions between insects and the toxic chemicals they are exposed to in order to further the understanding of pest insect resistance and to mitigate the negative effect of pesticides on nontarget insect species like Hymenopteran pollinators.