Interactions between pesticides and pathogen susceptibility in honey bees

Evaluating the combined toxicity of broflanilide and myclobutanil on honeybees (Apis mellifera L.): Molecular mechanisms and protective effects of curcumin

Pesticide toxicity to honeybees has become a pressing ecological issue, yet the effects of pesticide co-exposure are still not fully understood. This research investigates the toxicological implications of concurrent exposure to broflanilide (BFL), a novel diamide insecticide, and myclobutanil (MYC), a commonly used triazole fungicide, on honeybees (Apis mellifera L.), while exploring potential preventive strategies. Acute toxicity tests revealed a significantly lower 96-hour lethal concentration 50 (LC50) for BFL (0.34 mg a.i. L-1) compared to MYC (82.3 mg a.i. L-1), and their co-exposure resulted in pronounced synergistic toxicity. Worker bees were exposed to environmentally relevant doses of BFL and MYC for 7 days, and midgut toxicity was assessed. The co-exposure caused severe midgut damage, including G-layer deterioration, loss of columnar epithelium integrity, and downregulation of the tight junction protein ZO-2. Additionally, oxidative stress-related genes (Sod1, Catalase, SelK, GstD1) were upregulated, accompanied by higher MDA levels and increased CAT and SOD activities. Furthermore, a greater number of TUNEL-positive cells were detected, along with elevated expression of apoptosis-related genes (Caspase-3-like, Caspase-8-like, Caspase-9-like) and higher caspase enzyme activities. Curcumin (Cur) was tested for its protective effects, and it significantly alleviated midgut damage, oxidative stress, and apoptosis. This study reveals the synergistic ecotoxicological effects of pesticide combinations and suggests Cur as a potential prevention strategy for mitigating their harmful impact on honeybees.

A nutritionally complete pollen-replacing diet protects honeybee colonies during stressful commercial pollination-requirement for isofucosterol

A steady supply of nutritionally adequate pollen from diverse flower sources is crucial for honeybee colonies. However, climate instability, large-scale agriculture and the loss of flower-rich landscapes have made this supply scarce and unpredictable, threatening both apiculture and sustainable crop pollination. We developed a nutritionally complete pollen-replacing diet that supports continuous brood production from May to October in colonies without access to pollen. Omitting isofucosterol, the third most abundant sterol in honeybees, causes significant reductions in brood production and neuromuscular dysfunction in adults, identifying isofucosterol as a critical micronutrient. In contrast, omitting 24-methylene cholesterol-the most abundant honeybee sterol-does not significantly affect brood production, and surprisingly, bees remain viable without it. Colonies fed a commercial diet severely declined in brood production after 36 days and died out. In a season-long experiment investigating the commercial pollination of blueberry and sunflower fields, a treatment group fed the complete diet overcame the detrimental effects of nutritional stress, unlike colonies in 'No Diet' and 'Commercial Diet' groups. This study suggests that feeding a complete, pollen-replacing diet to nutritionally stressed colonies can address the root causes of honeybees' growing nutritional deficiencies, supporting their health and their vital pollination services.

Imidacloprid and amitraz differentially alter antioxidant enzymes in honeybee (Apis mellifera) hemocytes when exposed to microbial pathogen-associated molecular patterns

Honeybees (Apis mellifera) are increasingly exposed to pesticides and microbial stressors, yet their combined effects on immune defenses remain unclear. Exposure to the neonicotinoid imidacloprid and the acaricide amitraz, alone and in combination, alters antioxidant enzyme activity in hemocytes when challenged with bacterial components such as lipopolysaccharide and peptidoglycan or the fungal-derived molecule zymosan A. The combination of pesticides with zymosan A synergistically suppresses superoxide dismutase and glutathione-S-transferase activity, while catalase activity remains unchanged. In contrast, lipopolysaccharide counteracts pesticide-induced oxidative stress, suggesting immune-pathway-specific modulation. The heightened vulnerability of honeybees to fungal-associated immune challenges in pesticide-contaminated environments compromises their ability to detoxify harmful substances and respond to infections. Such approaches that include comparison of different microbial interactions, pesticide cocktails, and immunity are needed. Understanding these interactions is essential for improving pesticide regulations and pollinator conservation efforts in the face of increasing environmental stressors.

Pesticide impacts on insect pollinators: Current knowledge and future research challenges

With the need to intensify agriculture to meet growing food demand, there has been significant rise in pesticide use to protect crops, but at different rates in different world regions. In 2016, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) global assessment on pollinators, pollination and food production identified pesticides as one of the major drivers of pollinator decline. This assessment highlighted that studies on the effects of pesticides on pollinating insects have been limited to only a few species, primarily from developed countries. Given the worldwide variation in the scale of intensive agricultural practices, pesticide application intensities are likely to vary regionally and consequently the associated risks for insect pollinators. We provide the first long-term, global analysis of inter-regional trends in the use of different classes of pesticide between 1995 and 2020 (FAOSTAT) and a review of literature since the IPBES pollination assessment (2016). All three pesticide classes use rates varied greatly with some countries seeing increased use by 3000 to 4000 % between 1995 and 2020, while for most countries, growth roughly doubled. We present forecast models to predict regional trends of different pesticides up to 2030. Use of all three pesticide classes is to increase in Africa and South America. Herbicide use is to increase in North America and Central Asia. Fungicide use is to increase across all Asian regions. In each of the respective regions, we also examined the number of studies since 2016 in relation to pesticide use trends over the past twenty-five years. Additionally, we present a comprehensive update on the status of knowledge on pesticide impacts on different pollinating insects from literature published during 2016-2022. Finally, we outline several research challenges and knowledge gaps with respect to pesticides and highlight some regional and international conservation efforts and initiatives that address pesticide reduction and/or elimination.

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.

Physiological effects of field concentrations and sublethal concentrations of sulfoxaflor on Apis mellifera

BACKGROUND

Bees (Apis mellifera), as important pollinators of agricultural crops, are at risk when pesticides are used. Sulfoxaflor is a new insecticide which acts on the nicotinic acetylcholine receptor (nAChR) in a similar way to neonicotinoids. The goal of this study is to evaluate the toxicity of sulfoxaflor and its effect on the A. mellifera exposure.

RESULTS

Initially, developmental indicators such as larval survival, pupation, and eclosion were inhibited by 5.0 mg/L (field concentration) sulfoxaflor. In the pupal stage, fat content was significantly increased, while the glycogen content decreased. In addition, A. mellifera heads were treated with 2.0 mg/L (sublethal concentration) of sulfoxaflor and analyzed by RNA sequencing. The transcriptome results indicated that 2.0 mg/L amounts of sulfoxaflor have adverse effects on the immune, digestive, and nervous systems. Sulfoxaflor down-regulated the expression of many genes involved in immunity, detoxification, the myosin cytoskeleton, sensory neurons, and odor-binding proteins.

CONCLUSION

Field concentration and sublethal concentration were used for the combined analysis of honeybees. The effect of sublethal concentration of sulfoxaflor on honeybees was studied for the first time from the perspective of transcriptome sequencing of honeybee head. A preliminary study was carried out on the stress of sulfoxaflor at sublethal concentration on honeybee workers, which has certain research significance and can provide theoretical basis for the use of sulfoxaflor in the field environment. © 2024 Society of Chemical Industry.

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.

Advancing ecotoxicity assessment: Leveraging pre-trained model for bee toxicity and compound degradability prediction

The prediction of ecological toxicity plays an increasingly important role in modern society. However, the existing models often suffer from poor performance and limited predictive capabilities. In this study, we propose a novel approach for ecological toxicity assessment based on pre-trained models. By leveraging pre-training techniques and graph neural network models, we establish a highperformance predictive model. Furthermore, we incorporate a variational autoencoder to optimize the model, enabling simultaneous discrimination of toxicity to bees and molecular degradability. Additionally, despite the low similarity between the endogenous hormones in bees and the compounds in our dataset, our model confidently predicts that these hormones are non-toxic to bees, which further strengthens the credibility and accuracy of our model. We also discovered the negative correlation between the degradation and bee toxicity of compounds. In summary, this study presents an ecological toxicity assessment model with outstanding performance. The proposed model accurately predicts the toxicity of chemicals to bees and their degradability capabilities, offering valuable technical support to relevant fields.

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

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

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.

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

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

Detrimental effects of amitraz exposure in honey bees (Apis mellifera) infected with Nosema ceranae

In recent years, there has been growing concern on the potential weakening of honey bees and their increased susceptibility to pathogens due to chronic exposure to xenobiotics. The present work aimed to study the effects on bees undergoing an infection by Nosema ceranae and being exposed to a frequently used in-hive acaricide, amitraz. To achieve this, newly emerged bees were individually infected with N. ceranae spores and/or received a sublethal concentration of amitraz in their diets under laboratory conditions. Mortality, food intake, total volume excrement, body appearance, and parasite development were registered. Bees exposed to both stressors jointly had higher mortality rates compared to bees exposed separately, with no difference in the parasite development. An increase in sugar syrup consumption was observed for all treated bees while infected bees fed with amitraz also showed a diminishment in pollen intake. These results coupled with an increase in the total number of excretion events, alterations in behavior and body surface on individuals that received amitraz could evidence the detrimental action of this molecule. To corroborate these findings under semi-field conditions, worker bees were artificially infected, marked, and released into colonies. Then, they were exposed to a commercial amitraz-based product by contact. The recovered bees showed no differences in the parasite development due to amitraz exposure. This study provides evidence to which extent a honey bee infected with N. ceranae could potentially be weakened by chronic exposure to amitraz treatment.

Biotic and abiotic stresses on honeybee health

Honeybees are the most critical pollinators providing key ecosystem services that underpin crop production and sustainable agriculture. Amidst a backdrop of rapid global change, this eusocial insect encounters a succession of stressors during nesting, foraging, and pollination. Ectoparasitic mites, together with vectored viruses, have been recognized as central biotic threats to honeybee health, while the spread of invasive giant hornets and small hive beetles also increasingly threatens colonies worldwide. Cocktails of agrochemicals, including acaricides used for mite treatment, and other pollutants of the environment have been widely documented to affect bee health in various ways. Additionally, expanding urbanization, climate change, and agricultural intensification often result in the destruction or fragmentation of flower-rich bee habitats. The anthropogenic pressures exerted by beekeeping management practices affect the natural selection and evolution of honeybees, and colony translocations facilitate alien species invasion and disease transmission. In this review, the multiple biotic and abiotic threats and their interactions that potentially undermine bee colony health are discussed, while taking into consideration the sensitivity, large foraging area, dense network among related nestmates, and social behaviors of honeybees.

Trisiloxane Surfactants Negatively Affect Reproductive Behaviors and Enhance Viral Replication in Honey Bees

Trisiloxane surfactants are often applied in formulated adjuvant products to blooming crops, including almonds, exposing the managed honey bees (Apis mellifera) used for pollination of these crops and persisting in colony matrices, such as bee bread. Despite this, little is known regarding the effects of trisiloxane surfactants on important aspects of colony health, such as reproduction. In the present study, we use laboratory assays to examine how exposure to field-relevant concentrations of three trisiloxane surfactants found in commonly used adjuvant formulations affect queen oviposition rates, worker interactions with the queen, and worker susceptibility to endogenous viral pathogens. Trisiloxane surfactants were administered at 5 mg/kg in pollen supplement diet for 14 days. No effects on worker behavior or physiology could be detected, but our results demonstrate that hydroxy-capped trisiloxane surfactants can negatively affect queen oviposition and methyl-capped trisiloxane surfactants cause increased replication of Deformed Wing Virus in workers, suggesting that trisiloxane surfactant use while honey bees are foraging may negatively impact colony longevity and growth. Environ Toxicol Chem 2024;43:222-233. © 2023 SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Imidacloprid increases the prevalence of the intestinal parasite Lotmaria passim in honey bee workers

A challenge in bee protection is to assess the risks of pesticide-pathogen interactions. Lotmaria passim, a ubiquitous unicellular parasite in honey bees, is considered harmful under specific conditions. Imidacloprid causes unpredictable side effects. Research indicates that both L. passim and imidacloprid may affect the physiology, behavior, immunity, microbiome and lifespan of honey bees. We designed cage experiments to test whether the infection of L. passim is affected by a sublethal dose of imidacloprid. Workers collected at the time of emergence were exposed to L. passim and 2.5 μg/L imidacloprid in the coexposure treatment group. First, samples of bees were taken from cages since they were 5 days old and 3 days postinfection, i.e., after finishing an artificial 24 h L. passim infection. Additional bees were collected every two additional days. In addition, bees frozen at the time of emergence and collected from the unexposed group were analyzed. Abdomens were analyzed using qPCR to determine parasite load, while corresponding selected heads were subjected to a label-free proteomic analysis. Our results show that bees are free of L. passim at the time of emergence. Furthermore, imidacloprid considerably increased the prevalence as well as parasite loads in individual bees. This means that imidacloprid facilitates infection, enabling faster parasite spread in a colony and potentially to surrounding colonies. The proteomic analysis of bee heads showed that imidacloprid neutralized the increased transferrin 1 expression by L. passim. Importantly, this promising marker has been previously observed to be upregulated by infections, including gut parasites. This study contributes to understanding the side effects of imidacloprid and demonstrates that a single xenobiotic/pesticide compound can interact with the gut parasite. Our methodology can be used to assess the effects of different compounds on L. passim.

Interaction of chlorothalonil and Varroa destructor on immature honey bees rearing in vitro

Under realistic environmental conditions, bees are often exposed to multiple stressors, especially Varroa destructor and pesticides. In this study, the effects of exposure to NOAEC of chlorothalonil during the larval stage, in the presence or absence of V. destructor, was examined in terms of survival, morphological and transcriptional changes. The interaction between chlorothalonil and V. destructor on the survival of honey bee was additive. V. destructor are the dominant factor in the interaction for survival and transcriptome alternation. The downregulation of the genes related to tissue growth and caste differentiation may directly link to the mortality of honey bees. Either chlorothalonil or V. destructor induces the irregular morphology of trophocytes and oenocytes in the fat body. In addition to irregular shapes, oenocytes in V. destructor alone and double-stressor treatment group showed altered nuclei and vacuoles in the cytoplasm. The interaction of V. destructor and chlorothalonil at the larval stage have potential adverse effects on the subsequent adult bees, with up-regulation of genes involved in lipid metabolism and detoxification/defense in fat body tissue. Our findings provide a comprehensive understanding of combinatorial effects between biotic and abiotic stressors on one of the most important pollinators, honey bees.

Host exposure to a common pollutant can influence diversity-disease relationships

Hosts and parasites are embedded in communities where species richness and composition can influence disease outcomes (diversity-disease relationships). The direction and magnitude of diversity-disease relationships are influenced by variation in competence (ability to support and transmit infections) of hosts in a community. However, host susceptibility to parasites, which mediates host competence, is not static and is influenced by environmental factors, including pollutants. Despite the role that pollutants can play in augmenting host susceptibility, how pollutants influence diversity-disease dynamics is not well understood. Using an amphibian-trematode model, we tested how NaCl influences diversity-disease dynamics. We predicted that NaCl exposure can alter relative susceptibility of host species to trematodes, leading to cascading effects on the diversity-disease relationship. To test these predictions, we exposed hosts to benign or NaCl environments and generated communities that differed in number and composition of host species. We exposed these communities to trematodes and measured disease outcomes at the community (total infections across all hosts within a community) and species levels (average number of infections per host species within a community). Host species differed in their relative susceptibility to trematodes when exposed to NaCl. Consequently, at the community level (total infections across all hosts within a community), we only detected diversity-disease relationships (dilution effects) in communities where hosts were exposed to NaCl. At the species level, disease outcomes (average number of infections/species) and whether multi-species communities supported lower number of infections relative to single-species communities depended on community composition. Notably, however, as with overall community infection, diversity-disease relationships only emerged when hosts were exposed to NaCl. Synthesis. Pollutants are ubiquitous in nature and can influence disease dynamics across a number of host-parasite systems. Here, we show that NaCl exposure can alter the relative susceptibility of host species to parasites, influencing the relationship between biodiversity and disease at both community and species levels. Collectively, our study contributes to the limited knowledge surrounding environmental mediators of host susceptibility and their influence on diversity-disease dynamics.

Re-using food resources from failed honey bee (Apis mellifera L.) colonies and their impact on colony queen rearing capacity

For over a decade, beekeepers have experienced high losses of honey bee (Apis mellifera L.) colonies due to a variety of stressors including pesticide exposure. Some of these chemical stressors may residually remain in the colony comb and food resources (pollen and nectar) of failed colonies and be later re-used by beekeepers when splitting and building back new colonies. The practice of re-using comb from previously perished colonies (termed "deadout") is common in beekeeping practice, but its role in affecting colony health is not well understood. Here, we evaluate the impact of reused, pesticide-contaminated "deadout" combs on colony function during the process of replacing a queen bee. Queenless microcolonies were established to monitor queen rearing capacity in two treatment groups: (1) colonies given frames containing food resources from deadout colonies in control "clean" apiaries and, (2) colonies given frames containing "contaminated" resources from deadout colonies originating from apiaries experiencing chronic pesticide exposure from widespread systemic pesticide pollution (including neonicotinoid insecticides: clothianidin and thiamethoxam). Results indicate that colonies given pesticide-contaminated resources produced fewer queen cells per colony and had a lower proportion of colonies successfully raising a functional, diploid egg-laying queen. This research highlights the deleterious effects of re-using deadout combs from colonies previously lost due to pesticide contamination.

Bee Products: The Challenges in Quality Control

In recent years, there has been a significant surge in demand for unprocessed natural foods due to the growing awareness of consumer health [...].

Exposure to pesticide residues in honey and its potential cancer risk assessment

Honey is the most recognized natural food by-product derived from flower nectar and the upper aero-digestive tract of the honeybees. Significance of honey for its medicinal importance are well-documented in the world's oldest medical literatures. However, the current urbanization, environmental contaminations and changes in agricultural, as well as apiculture practices has led to various types of contaminations in honey. Among all, pesticide contamination has become one of the major issues worldwide. This review focuses on the recent updates concerning pesticides occurrence in honey, as well as how the repeated use and long-term exposure to honey contaminated with pesticide residues could affect the human physiological functions, possibly leading to the development of various cancers. Our findings suggests that uncontrolled use of pesticides in farming and apiculture practices leads to the occurrence of pesticides residues in honey. Therefore, regular consumption of such honey will pose a serious threat to human health, since most of the pesticides has been reported as potential carcinogens. This review will draw the attention of honey consumers, scientific communities, apiculture farmers, as well as governing bodies to strictly monitor the pesticide usage in floriculture, agriculture as well as other related practices.

Low Levels of Hive Stress Are Associated with Decreased Honey Activity and Changes to the Gut Microbiome of Resident Honey Bees

Honey bees (Apis mellifera) face increasing threats to their health, particularly from the degradation of floral resources and chronic pesticide exposure. The properties of honey and the bee gut microbiome are known to both affect and be affected by bee health. Using samples from healthy hives and hives showing signs of stress from a single apiary with access to the same floral resources, we profiled the antimicrobial activity and chemical properties of honey and determined the bacterial and fungal microbiome of the bee gut and the hive environment. We found honey from healthy hives was significantly more active than honey from stressed hives, with increased phenolics and antioxidant content linked to higher antimicrobial activity. The bacterial microbiome was more diverse in stressed hives, suggesting they may have less capacity to exclude potential pathogens. Finally, bees from healthy and stressed hives had significant differences in core and opportunistically pathogenic taxa in gut samples. Our results emphasize the need for understanding and proactively managing bee health. IMPORTANCE Honey bees serve as pollinators for many plants and crops worldwide and produce valuable hive products such as honey and wax. Various sources of stress can disrupt honey bee colonies, affecting their health and productivity. Growing evidence suggests that honey is vitally important to hive functioning and overall health. In this study, we determined the antimicrobial activity and chemical properties of honey from healthy hives and hives showing signs of stress, finding that honey from healthy hives was significantly more antimicrobial, with increased phenolics and antioxidant content. We next profiled the bacterial and fungal microbiome of the bee gut and the hive environment, finding significant differences between healthy and stressed hives. Our results underscore the need for greater understanding in this area, as we found even apparently minor stress can have implications for overall hive fitness as well as the economic potential of hive products.

Real-time monitoring of honeybee colony daily activity and bee loss rates can highlight the risk posed by a pesticide

Information on honeybee foraging performance and especially bee loss rates at the colony level are crucial for evaluating the magnitude of effects due to pesticide exposure, thereby ensuring that protection goals for honeybee colonies are met (i.e. threshold of acceptable effects). However, current methods for monitoring honeybee foraging activity and mortality are very approximate (visual records) or are time-limited and mostly based on single cohort analysis. We therefore assess the potential of bee counters, that enable a colony-level and continuous monitoring of bee flight activity and mortality, in pesticide risk assessment. After assessing the background activity and bee loss rates, we exposed colonies to two concentrations of sulfoxaflor (a neurotoxic insecticide) in sugar syrup: a concentration that was considered to be field realistic (0.59 μg/ml) and a higher concentration (2.36 μg/ml) representing a worst-case exposure scenario. We did not find any effect of the field-realistic concentration on flight activity and bee loss rates. However, a two-fold decrease in daily flight activity and a 10-fold increase in daily bee losses were detected in colonies exposed to the highest sulfoxaflor concentration as compared to before exposure. When compared to the theoretical trigger values associated with the specific protection goal of 7 % colony-size reduction, the observed fold changes in daily bee losses were often found to be at risk for colonies. In conclusion, the real-time and colony-level monitoring of bee loss rates, combined with threshold values indicating at which levels bee loss rates threaten the colony, have great potential for improving regulatory pesticide risk assessments for honeybees under field conditions.

Pesticide exposure and forage shortage in rice cropping system prevents honey bee colony establishment

As one of the key stable crops to feed half of the world's population, how rice cropping system affects honey bee health regarding pesticide exposure and forage availability is under investigated. We predicted honey bees were stressed by high pesticide exposure and forage dearth in monoculture rice systems. Providing access to natural habitats is a typical approach to mitigate the negative impact of intensive agriculture on honey bees. We aimed to determine if bee colonies located in landscapes with more cover of forest habitat would collect more forage and be exposed to less pesticides. We selected beekeeping locations in rice dominated landscapes (as control), mosaic landscapes of rice and medium woodland (MW) cover, and landscapes of high woodland (HW) cover, respectively, in July when rice starts bloom and pesticides are commonly used. Colonies were inspected at a biweekly frequency from July to October with population growth and forage (nectar and pollen) availability estimated. Pollen and bees were collected in middle August for pesticide exposure analysis. We did not observe enhancement in forage availability and reduction in pesticide exposure in landscapes with increased forest habitat (i.e., MW or HW cover), and all colonies failed in the end. Other natural habitats that can supplement flower shortage periods in forest can be considered for supporting bee health. Our results suggest that forest should be carefully assessed for being incorporated into beekeeping management or pollinator conservation when forest phenology can be a factor to affect its impact as a natural habitat.

Molecular Detection and Phylogenetic Analysis of Deformed Wing Virus and Sacbrood Virus Isolated from Pollen

Among many pathogens and pests, honey bee viruses are known as one of the most common cause of diseases in honey bee colonies. In this study, we demonstrate that pollen grains and bee bread are potential sources of viral DNA. We extracted DNA from 3 types of pollen samples: directly provided by beekeepers (n = 12), purchased from trade markets (n = 5), and obtained from honeycombs (bee bread, n = 10). The extracted DNA was used for molecular detection (RT-PCR analysis) of six of the most widely distributed honey bee viruses: deformed wing virus, sacbrood virus, acute bee paralysis virus, black queen cell virus, Kashmir bee virus, Israeli acute paralysis virus, and chronic bee paralysis virus. We successfully managed to establish only the deformed wing virus (DWV) and the sacbrood virus (SBV), with different distribution frequencies depending on the territory of the country. The phylogenetic analyses of Bulgarian isolates were performed with the most similar sequences available in molecular databases from other countries. Phylogenies of Bulgarian viral strains demonstrated genetically heterogeneous populations of DWV and relatively homogenous populations of SBV. In conclusion, the results obtained from the current study have shown that pollen is a valuable source for molecular detection of honey bee pathogens. This allows epidemiological monitoring of honey bee diseases at a regional and a national level.

Imidacloprid Pesticide Causes Unexpectedly Severe Bioelement Deficiencies and Imbalance in Honey Bees Even at Sublethal Doses

Pesticides impair honeybee health in many ways. Imidacloprid (IMD) is a pesticide used worldwide. No information exists on how IMD impact the bees' body bioelement balance, which is essential for bee health. We hypothesized that IMD disturbs this balance and fed the bees (in field conditions) with diets containing 0 ppb (control), 5 ppb (sublethal considered field-relevant), and 200 ppb (adverse) doses of IMD. IMD severely reduced the levels of K, Na, Ca, and Mg (electrolytic) and of Fe, Mo, Mn, Co, Cu, Ni, Se, and Zn, while those of Sn, V, and Cr (enzymatic) were increased. Levels of P, S, Ti, Al, Li, and Sr were also decreased, while only the B content (physiologically essential) was increased. The increase in Tl, Pb, and As levels (toxic) was alarming. Generally, IMD, even in sublethal doses, unexpectedly led to severe bioelement malnutrition in 69% of bioelements and to a stoichiometric mismatch in the remaining ones. This points to the IMD-dependent bioelement disturbance as another, yet unaccounted for, essential metabolic element which can interfere with apian health. Consequently, there is a need for developing methods of bioelement supplementation of the honey bee diet for better preventing bee colony decline and protecting apian health status when faced with pesticides.

Mixture toxicities of tetrachlorantraniliprole and tebuconazole to honey bees (Apis mellifera L.) and the potential mechanism

The extensive use of pesticides has negative effects on the health of insect pollinators. Although pollinators in the field are seldom exposed to individual pesticides, few reports have assessed the toxic impacts of pesticide combinations on them. In this work, we purposed to reveal the combined impacts of tetrachlorantraniliprole (TET) and tebuconazole (TEB) on honey bees (Apis mellifera L.). Our data exhibited that TET had greater toxicity to A. mellifera (96-h LC₅₀ value of 298.2 mg a.i. L^-1) than TEB (96-h LC₅₀ value of 1,841 mg a.i. L^-1). The mixture of TET and TEB displayed acute synergistic toxicity to the pollinators. Meanwhile, the activities of CarE, CYP450, trypsin, and sucrase, as well as the expressions of five genes (ppo, abaecin, cat, CYP4G11, and CYP6AS14) associated with immune response, oxidative stress, and detoxification metabolism, were conspicuously altered when exposed to the mixture relative to the individual exposures. These results provided an overall comprehension of honey bees upon the challenge of sublethal toxicity between neonicotinoid insecticides and triazole fungicides and could be used to assess the intricate toxic mechanisms in honey bees when exposed to pesticide mixtures. Additionally, these results might guide pesticide regulation strategies to enhance the honey bee populations.

Strategies and techniques to mitigate the negative impacts of pesticide exposure to honey bees

In order to support food, fiber, and fuel production around the world, billions of kilograms of pesticides are applied to crop fields every year to suppress pests, plant diseases and weeds. These fields are often home to the most important commercial pollinators, honey bees (Apis spp.), which improve yield and quality of many agricultural products. The pesticides applied to support crop health can be detrimental to honey bee health. The conflict of pesticide use and reliance on honey bees contributes to significant honey bee colony losses across the world. Recommendations for reducing impact on honey bees are generally suggested in literature, pesticide regulations, and by crop consultants, but without a considerable discussion of the realistic limitations of protecting honey bees. New techniques in farming and beekeeping can reduce pesticide exposure through reduction in bee exposure, reduced toxicity of pesticides, and remedies that can be in response to exposure. However, lack of assessment of those new techniques under a systematical, comprehensive framework may overestimate or underestimate these techniques' potential to protect honey bees from pesticide damage. In this review, we summarize the current and arising strategies and techniques with the goal to inspire the development and adoption of pesticide mitigation practices for both agriculture and apiculture.

Are fungicides a driver of European foulbrood disease in honey bee colonies pollinating blueberries?

Introduction

Blueberry producers in Canada depend heavily on pollination services provided by honey bees (Apis mellifera L.). Anecdotal reports indicate an increased incidence of European foulbrood (EFB), a bacterial disease caused by Melissococcus plutonius, is compromising pollination services and colony health. Fungicidal products are commonly used in blueberry production to prevent fungal diseases such as anthracnose and botrytis fruit rot. Pesticide exposure has been implicated in honey bee immunosuppression; however, the effects of commercial fungicidal products, commonly used during blueberry pollination, on honey bee larval susceptibility to EFB have not been investigated.

Methods

Using an in vitro infection model of EFB, we infected first instar honey bee larvae with M. plutonius 2019 BC1, a strain isolated from an EFB outbreak in British Columbia, Canada, and chronically exposed larvae to environmentally relevant concentrations of fungicide products over 6 days. Survival was monitored until pupation or eclosion.

Results

We found that larvae chronically exposed to one, two, or three fungicidal products [Supra® Captan 80WDG (Captan), low concentration of Kenja™ 400SC (Kenja), Luna® Tranquility (Luna), and/or Switch® 62.5 WG (Switch)], did not significantly reduce survival from EFB relative to infected controls. When larvae were exposed to four fungicide products concurrently, we observed a significant 24.2% decrease in survival from M. plutonius infection (p = 0.0038). Similarly, higher concentrations of Kenja significantly reduced larval survival by 24.7–33.0% from EFB (p < 0.0001).

Discussion

These in vitro results suggest that fungicides may contribute to larval susceptibility and response to M. plutonius infections. Further testing of other pesticide combinations is warranted as well as continued surveillance of pesticide residues in blueberry-pollinating colonies.

Honey bee foraging and pesticide exposure in a desert urban agroecosystem

The negative impacts of industrial farming on honey bee health have been widely recognized regarding pesticide use and natural foraging habitat loss. An assessment of suitability of urban farms regarding honey bee health is necessary for sustainable development of agriculture and apiculture in urban settings. Urban farms that adopt organic farming practices with restrictions on synthetic pesticide use and conservation of natural habitat can potentially create an environment to mitigate these environmental stressors on honey bees. In this experiment, bee-collected pollen was taken from honey bee colonies that were located on five organically managed urban farms located in Albuquerque, New Mexico, to evaluate pesticide exposure and forage use. We also explored the influence of hive equipment on honey bee health in a high desert climate. We found that honey bees on organic urban farms were not stressed by pesticides with limited pesticide types detected (2 out of 187), low residue levels (< 20 µg/kg) and low toxicity (either no, or low toxicity with LD50 at 1,450,300 µg/kg). Honey bees had access to diverse forage resources based on pollen barcoding data. When comparing hive equipment between 10-frame, 8-frame Langstroth and top bar hives, it was determined that 8-frame hives could significantly enhance honey bee health including colony survival and weight growth, comb construction and brood production. Our results suggest that organic urban farms are appropriate locations for securing honey bee health and food safety in a desert climate; while, the selection of hive equipment should be considered when mitigating environmental stress to colonies.

Squash bees host high diversity and prevalence of parasites in the northeastern United States

The squash bee Eucera (Peponapis) pruinosa is emerging as a model species to study how stressors impact solitary wild bees in North America. Here, we describe the prevalence of trypanosomes, microsporidians and mollicute bacteria in E. pruinosa and two other species, Bombus impatiens and Apis mellifera, that together comprise over 97% of the pollinator visitors of Cucurbita agroecosystems in Pennsylvania (United States). Our results indicate that all three parasite groups are commonly detected in these bee species, but E. pruinosa often exhibit higher prevalences. We further describe novel trypanosome parasites detected in E. pruinosa, however it is unknown how these parasites impact these bees. We suggest future work investigates parasite replication and infection outcomes.

Infectious disease and cognition in wild populations

Infectious disease is linked to impaired cognition across a breadth of host taxa and cognitive abilities, potentially contributing to variation in cognitive performance within and among populations. Impaired cognitive performance can stem from direct damage by the parasite, the host immune response, or lost opportunities for learning. Moreover, cognitive impairment could be compounded by factors that simultaneously increase infection risk and impair cognition directly, such as stress and malnutrition. As highlighted in this review, however, answers to fundamental questions remain unresolved, including the frequency, duration, and fitness consequences of infection-linked cognitive impairment in wild animal populations, the cognitive abilities most likely to be affected, and the potential for adaptive evolution of cognition in response to accelerating emergence of infectious disease.

Occurrence of Honey Bee (Apis mellifera L.) Pathogens in Wild Pollinators in Northern Italy

Diseases contribute to the decline of pollinator populations, which may be aggravated by the interspecific transmission of honey bee pests and pathogens. Flowers increase the risk of transmission, as they expose the pollinators to infections during the foraging activity. In this study, both the prevalence and abundance of 21 honey bee pathogens (11 viruses, 4 bacteria, 3 fungi, and 3 trypanosomatids) were assessed in the flower-visiting entomofauna sampled from March to September 2021 in seven sites in the two North-Italian regions, Emilia-Romagna and Piedmont. A total of 1,028 specimens were collected, identified, and analysed. Of the twenty-one pathogens that were searched for, only thirteen were detected. Altogether, the prevalence of the positive individuals reached 63.9%, with Nosema ceranae, deformed wing virus (DWV), and chronic bee paralysis virus (CBPV) as the most prevalent pathogens. In general, the pathogen abundance averaged 5.15 * 106 copies, with CBPV, N. ceranae, and black queen cell virus (BQCV) as the most abundant pathogens, with 8.63, 1.58, and 0.48 * 107 copies, respectively. All the detected viruses were found to be replicative. The sequence analysis indicated that the same genetic variant was circulating in a specific site or region, suggesting that interspecific transmission events among honey bees and wild pollinators are possible. Frequently, N. ceranae and DWV were found to co-infect the same individual. The circulation of honey bee pathogens in wild pollinators was never investigated before in Italy. Our study resulted in the unprecedented detection of 72 wild pollinator species as potential hosts of honey bee pathogens. Those results encourage the implementation of monitoring actions aiming to improve our understanding of the environmental implications of such interspecific transmission events, which is pivotal to embracing a One Health approach to pollinators' welfare.

No effect of dual exposure to sulfoxaflor and a trypanosome parasite on bumblebee olfactory learning

Bees are important pollinators in wild and agricultural ecosystems, and understanding the factors driving their global declines is key to maintaining these pollination services. Learning, which has been a focus of previous ecotoxicological studies in bees, may play a key role in driving colony fitness. Here we move beyond the standard single-stressor approach to ask how multiple stressors, an agrochemical (sulfoxaflor, a relatively new insecticide) and a parasite (Crithidia bombi, a prevalent gut parasite of bumblebees), impact learning in the bumblebee Bombus terrestris. We developed a modified version of the classic proboscis extension reflex assay to assess the combined effects of acute oral sulfoxaflor exposure and infection by C. bombi on olfactory learning of bumblebee workers. We found no evidence that either sulfoxaflor, C. bombi, or their combination had any significant effect on bumblebee olfactory learning, despite their known negative impacts on other aspects of bumblebee health. This suggests that losses in cognitive ability, as measured here, are unlikely to explain the impacts of sulfoxaflor and its interactions with other stressors on bumblebees. Our novel methodology provides a model system within which to test interactive effects of other key stressors on bee health.

Bee Stressors from an Immunological Perspective and Strategies to Improve Bee Health

Honeybees are the most prevalent insect pollinator species; they pollinate a wide range of crops. Colony collapse disorder (CCD), which is caused by a variety of biotic and abiotic factors, incurs high economic/ecological loss. Despite extensive research to identify and study the various ecological stressors such as microbial infections, exposure to pesticides, loss of habitat, and improper beekeeping practices that are claimed to cause these declines, the deep understanding of the observed losses of these important insects is still missing. Honeybees have an innate immune system, which includes physical barriers and cellular and humeral responses to defend against pathogens and parasites. Exposure to various stressors may affect this system and the health of individual bees and colonies. This review summarizes and discusses the composition of the honeybee immune system and the consequences of exposure to stressors, individually or in combinations, on honeybee immune competence. In addition, we discuss the relationship between bee nutrition and immunity. Nutrition and phytochemicals were highlighted as the factors with a high impact on honeybee immunity.

Evaluation of queen cell acceptance and royal jelly production between hygienic and non-hygienic honey bee (Apis mellifera) colonies

Honey bees are crucial for pollination services globally and produce important hive products including honey, royal jelly, pollen, and propolis that are being used commercially in food, cosmetics, and alternative medicinal purposes. Among the bee products, royal jelly (RJ) has long attracted scientists' interest because of its importance in honey caste differentiation. The present research was carried out to determine the acceptance rate of queen cells, and RJ production between the hygienic and non-hygienic lines. Further, this study unveils the effect of pollen substitute diets on the queen cell acceptance rate and RJ yields between both bee stocks. Results showed that the uncapped brood cells and dead brood's removal percentage was significantly more in hygienic bee colonies in comparison to non-hygienic bee colonies (p < 0.05). The average percentage of larval acceptance was statistically higher in hygienic lines (64.33 ± 2.91%) compared to non-hygienic lines (29.67 ± 1.20%). Similarly, the RJ mean weight per colony differed statistically between both bee stocks (p<0.001), which were 12.23 ± 0.52 g and 6.72 ± 0.33 g, respectively. Moreover, our results demonstrated that a significant difference was observed in larval acceptance rate, RJ yields (per colony and per cup) between both bee stocks those fed on various diets. However, no significant difference was recorded in RJ yields (per colony and per cup) between both bee stock that feeds on either commercially available pollen or pollen substitute. This study may provide future applications in helping bee breeders to choose the bees that carry a higher level of hygienic behavior with high RJ production traits.

Molecular histoproteomy by MALDI mass spectrometry imaging to uncover markers of the impact of Nosema on Apis mellifera

Matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI IMS) is a powerful technology used to investigate the spatio-temporal distribution of a huge number of molecules throughout a body/tissue section. In this paper, we report the use of MALDI IMS to follow the molecular impact of an experimental infection of Apis mellifera with the microsporidia Nosema ceranae. We performed representative molecular mass fingerprints of selected tissues obtained by dissection. This was followed by MALDI IMS workflows optimization including specimen embedding and positioning as well as washing and matrix application. We recorded the local distribution of peptides/proteins within different tissues from experimentally infected versus non infected honeybees. As expected, a distinction in these molecular profiles between the two conditions was recorded from different anatomical sections of the gut tissue. More importantly, we observed differences in the molecular profiles in the brain, thoracic ganglia, hypopharyngeal glands, and hemolymph. We introduced MALDI IMS as an effective approach to monitor the impact of N. ceranae infection on A. mellifera. This opens perspectives for the discovery of molecular changes in peptides/proteins markers that could contribute to a better understanding of the impact of stressors and toxicity on different tissues of a bee in a single experiment.

Chemical Stimulants and Stressors Impact the Outcome of Virus Infection and Immune Gene Expression in Honey Bees (Apis mellifera)

Western honey bees (Apis mellifera) are ecologically, agriculturally, and economically important plant pollinators. High average annual losses of honey bee colonies in the US have been partially attributed to agrochemical exposure and virus infections. To examine the potential negative synergistic impacts of agrochemical exposure and virus infection, as well as the potential promise of phytochemicals to ameliorate the impact of pathogenic infections on honey bees, we infected bees with a panel of viruses (i.e., Flock House virus, deformed wing virus, or Sindbis virus) and exposed to one of three chemical compounds. Specifically, honey bees were fed sucrose syrup containing: (1) thyme oil, a phytochemical and putative immune stimulant, (2) fumagillin, a beekeeper applied fungicide, or (3) clothianidin, a grower-applied insecticide. We determined that virus abundance was lower in honey bees fed 0.16 ppb thyme oil augmented sucrose syrup, compared to bees fed sucrose syrup alone. Parallel analysis of honey bee gene expression revealed that honey bees fed thyme oil augmented sucrose syrup had higher expression of key RNAi genes (argonaute-2 and dicer-like), antimicrobial peptide expressing genes (abaecin and hymenoptaecin), and vitellogenin, a putative honey bee health and age indicator, compared to bees fed only sucrose syrup. Virus abundance was higher in bees fed fumagillin (25 ppm or 75 ppm) or 1 ppb clothianidin containing sucrose syrup relative to levels in bees fed only sucrose syrup. Whereas, honey bees fed 10 ppb clothianidin had lower virus levels, likely because consuming a near lethal dose of insecticide made them poor hosts for virus infection. The negative impact of fumagillin and clothianidin on honey bee health was indicated by the lower expression of argonaute-2, dicer-like, abaecin, and hymenoptaecin, and vitellogenin. Together, these results indicate that chemical stimulants and stressors impact the outcome of virus infection and immune gene expression in honey bees.

Varying impact of neonicotinoid insecticide and acute bee paralysis virus across castes and colonies of black garden ants, Lasius niger (Hymenoptera: Formicidae)

Pesticides and pathogens are known drivers of declines in global entomofauna. However, interactions between pesticides and viruses, which could range from antagonistic, over additive to synergistic, are poorly understood in ants. Here, we show that in ants the impact of single and combined pesticide and virus stressors can vary across castes and at the colony level. A fully-crossed laboratory assay was used to evaluate interactions between a sublethal dose of the neonicotinoid thiamethoxam and Acute bee paralysis virus (ABPV) in black garden ants, Lasius niger. After monitoring colonies over 64 weeks, body mass, neonicotinoid residues and virus titres of workers and queens, as well as worker behavioural activity were measured. ABPV, but not thiamethoxam, reduced activity of workers. Neonicotinoid exposure resulted in reduced body mass of workers, but not of queens. Further, thiamethoxam facilitated ABPV infections in queens, but not in workers. Overall, virus exposure did not compromise detoxification and body mass, but one colony showed high virus titres and worker mortality. Although the data suggest additive effects at the level of individuals and castes, co-exposure with both stressors elicited antagonistic effects on colony size. Our results create demand for long-term holistic risk assessment of individual stressors and their interactions to protect biodiversity.

The Behavioral Toxicity of Insect Growth Disruptors on Apis mellifera Queen Care

As social insects, honey bees (Apis mellifera) rely on the coordinated performance of various behaviors to ensure that the needs of the colony are met. One of the most critical of these behaviors is the feeding and care of egg laying honey bee queens by non-fecund female worker attendants. These behaviors are crucial to honey bee reproduction and are known to be elicited by the queen’s pheromone blend. The degree to which workers respond to this blend can vary depending on their physiological status, but little is known regarding the impacts of developmental exposure to agrochemicals on this behavior. This work investigated how exposing workers during larval development to chronic sublethal doses of insect growth disruptors affected their development time, weight, longevity, and queen pheromone responsiveness as adult worker honey bees. Exposure to the juvenile hormone analog pyriproxyfen consistently shortened the duration of pupation, and pyriproxyfen and diflubenzuron inconsistently reduced the survivorship of adult bees. Finally, pyriproxyfen and methoxyfenozide treated bees were found to be less responsive to queen pheromone relative to other treatment groups. Here, we describe these results and discuss their possible physiological underpinnings as well as their potential impacts on honey bee reproduction and colony performance.

Methylene blue can act as an antidote to pesticide poisoning of bumble bee mitochondria

The population of bumble bees and other pollinators has considerably declined worldwide, probably, due to the toxic effect of pesticides used in agriculture. Inexpensive and available antidotes can be one of the solutions for the problem of pesticide toxicity for pollinators. We studied the properties of the thiazine dye Methylene blue (MB) as an antidote against the toxic action of pesticides in the bumble bee mitochondria and found that MB stimulated mitochondrial respiration mediated by Complex I of the electron transport chain (ETC) and increased respiration of the mitochondria treated with mitochondria-targeted (chlorfenapyr, hydramethylnon, pyridaben, tolfenpyrad, and fenazaquin) and non-mitochondrial (deltamethrin, metribuzin, and penconazole) pesticides. MB also restored the mitochondrial membrane potential dissipated by the pesticides affecting the ETC. The mechanism of MB action is most probably related to its ability to shunt electron flow in the mitochondrial ETC.

Conservation genomics reveals pesticide and pathogen exposure in the declining bumble bee Bombus terricola

In recent years, many pollinators have experienced large population declines, which threaten food security and the stability of natural ecosystems. Bumble bees are particularly important because their ability to “buzz” pollinate and tolerate cooler conditions make them critical pollinators for certain plants and regions. Here, we apply a conservation genomics approach to study the vulnerable Bombus terricola. We sequenced RNA from 30 worker abdomens, 18 of which were collected from agricultural sites and 12 of which were collected from nonagricultural sites. We found transcriptional signatures associated with exposure to insecticides, with gene expression patterns suggesting that bumble bees were exposed to neonicotinoids and/or fipronil—two compounds known to negatively impact bees. We also found transcriptional signatures associated with pathogen infections. In addition to the transcriptomic analysis, we carried out a metatranscriptomic analysis and detected five pathogens in the abdomens of workers, three of which are common in managed honey bee and bumble bee colonies. Our conservation genomics study provides functional support for the role of pesticides and pathogen spillover in the decline of B. terricola. We demonstrate that conservation genomics is an invaluable tool which allows researchers to quantify the effects of multiple stressors that impact pollinator populations in the wild.

Pesticides in honey bee colonies: Establishing a baseline for real world exposure over seven years in the USA

Honey bees Apis mellifera forage in a wide radius around their colony, bringing back contaminated food resources that can function as terrestrial bioindicators of environmental pesticide exposure. Evaluating pesticide exposure risk to pollinators is an ongoing problem. Here we apply five metrics for pesticide exposure risk (prevalence, diversity, concentration, significant pesticide prevalence, and hazard quotient (HQ)) to a nation-wide field study of honey bees, Apis mellifera in the United States. We examined samples from 1055 apiaries over seven years for 218 different pesticide residues and metabolites, determining that bees were exposed to 120 different pesticide products with a mean of 2.78 per sample. Pesticides in pollen were highly prevalent and variable across states. While pesticide diversity increased over time, most detections occurred at levels predicted to be of low risk to colonies. Varroacides contributed most to concentration, followed by fungicides, while insecticides contributed most to diversity above a toxicity threshold. High risk samples contained one of 12 different insecticides or varroacides. Exposures predicted to be low-risk were nevertheless associated with colony morbidity, and low-level fungicide exposures were tied to queen loss, Nosema infection, and brood diseases.

Pesticides residues and metabolites in honeybees: A Greek overview exploring Varroa and Nosema potential synergies

The aim of this study was to investigate reported cases of honeybee mortality incidents and the potential association to pesticide exposure and to their metabolites. The same honeybee samples were also assessed for Varroa mites, and Nosema microsporidia provoked infections to provide an integrated picture of all observable stressors that may impact bees' survival. Thus, honeybee samples from different areas of Greece (2014-2018) were analyzed for the presence of pesticide residues and metabolites. In this context, an existing LC-ESI-QqQ-MS multiresidue method of analytes of different chemical classes such as neonicotinoids, organophosphates, triazoles, carbamates, was enriched with additional active substances, developed and validated. A complementary GC-EI-QqQ-MS method was also exploited for the same scope covering pyrethroid compounds. Both methods monitored more than 150 active substances and metabolites and presented acceptable linearity over the ranges assayed. The calculated recoveries ranged from 65 to 120% for the three concentration levels, while the precision (RSD%) values ranged between 4 and 15%. Therefore, this approach proved sufficient to act as a monitoring tool for the determination of pesticide residues in cases of suspected honeybee poisoning incidents. From the analysis of 320 samples, the presence of 70 active substances and metabolites was confirmed with concentrations varying from 1.4 ng/g to 166 μg/g. Predominant detections were the acaricide coumaphos, several neonicotinoids exemplified by clothianidin, organophosporous compounds dimethoate and chlorpyrifos, and some pyrethroids. Metabolites of imidacloprid, chlorpyrifos, coumaphos, acetamiprid, fenthion and amitraz were also identified. Concerning Nosema and Varroa they were identified in 27 and 22% of samples examined, respectively, verifying their prevalence and coexistence with pesticides and their metabolites in honeybees.

Antioxidation Defenses of Apis mellifera Queens and Workers Respond to Imidacloprid in Different Age-Dependent Ways: Old Queens Are Resistant, Foragers Are Not

Simple Summary

Honey bees are unique for studies on aging because queens live 40-fold longer than workers. An efficient antioxidant defense (ADS) is thought to be pivotal for longevity, but not always. How were different ADSs shaped by evolution in young and old queens and workers? Honey bees, the essential pollinators, are facing depopulation due, at least in part, to pesticides, such as imidacloprid, an oxidative stressor. Is an evolutionarily shaped ADS still useful for contemporary young and old queens/workers? Answering these questions is important for emerging oxidative-stress ecology and protecting contemporary honey bees. The ADS activity was determined in 1-day-old, 20-day-old, and 2-year-old queens and in 1-day-old and 20-day-old workers (foragers) fed without (control) or with low or high imidacloprid (in bee food). ADS was upregulated in workers with age but downregulated in queens. However, imidacloprid oxidative stress suppressed the active ADS in workers, particularly 20-day-old foragers, but not in 1-day-old queens. Unexpectedly, poor ADS activity in 2-year-old queens was highly upregulated by imidacloprid. Thus, queen and worker ADSs respond to imidacloprid in opposite ways, and old queens were still resistant, but foragers were not. This may be unfavorable for foragers dwelling in ecosystems that expose them to pesticides.

Abstract

We investigated how different antioxidant defenses (ADSs) were shaped by evolution in young/old Apis mellifera workers and queens to broaden the limited knowledge on whether ADSs are effective in contemporary pesticide environments and to complete bee oxidative-aging theory. We acquired 1-day-old, 20-day-old, and 2-year-old queens and 1-day-old and 20-day-old workers (foragers) fed 0, 5, or 200 ppb imidacloprid, a pesticide oxidative stressor. The activities of catalase, glutathione peroxidase, glutathione S-transferase, and superoxide dismutase and the level of total antioxidant potential were determined in hemolymph. The ADS was upregulated in workers with age but downregulated in queens. Imidacloprid suppressed the ADS in all workers, particularly in foragers with an upregulated ADS, but it did not affect the ADS in 1-day-old queens. In contrast to foragers, the downregulated ADS of 2-year-old queens was unexpectedly highly upregulated by imidacloprid, which has not been previously shown in such old queens. The principal component analysis confirmed that queen and worker ADSs responded to imidacloprid in opposite ways, and ADS of 2-year-queens was markedly different from those of others. Thus, evolutionary shaped ADSs of older queens and workers may be of the limited use for foragers dwelling in pesticide ecosystems, but not for old queens.

Current Status of Loop-Mediated Isothermal Amplification Technologies for the Detection of Honey Bee Pathogens

Approximately one-third of the typical human Western diet depends upon pollination for production, and honey bees (Apis mellifera) are the primary pollinators of numerous food crops, including fruits, nuts, vegetables, and oilseeds. Regional large scale losses of managed honey bee populations have increased significantly during the last decade. In particular, asymptomatic infection of honey bees with viruses and bacterial pathogens are quite common, and co-pathogenic interaction with other pathogens have led to more severe and frequent colony losses. Other multiple environmental stress factors, including agrochemical exposure, lack of quality forage, and reduced habitat, have all contributed to the considerable negative impact upon bee health. The ability to accurately diagnose diseases early could likely lead to better management and treatment strategies. While many molecular diagnostic tests such as real-time PCR and MALDI-TOF mass spectrometry have been developed to detect honey bee pathogens, they are not field-deployable and thus cannot support local apiary husbandry decision-making for disease control. Here we review the field-deployable technology termed loop-mediated isothermal amplification (LAMP) and its application to diagnose honey bee infections.

Heterocyclic Amine-Induced Feeding Deterrence and Antennal Response of Honey Bees

The productivity and survival of managed honey bee colonies is negatively impacted by a diverse array of interacting factors, including exposure to agrochemicals, such as pesticides. This study investigated the use of volatile heterocyclic amine (HCA) compounds as potential short-term repellents that could be employed as feeding deterrents to reduce the exposure of bees to pesticide-treated plants. Parent and substituted HCAs were screened for efficacy relative to the repellent N,N-diethyl-meta-toluamide (DEET) in laboratory and field experiments. Additionally, electroantennogram (EAG) recordings were conducted to determine the level of antennal response in bees. In video-tracking recordings, bees were observed to spend significantly less time with an HCA-treated food source than an untreated source. In a high-tunnel experiment, the HCA piperidine was incorporated in a feeding station and found to significantly reduce bee visitations relative to an untreated feeder. In field experiments, bee visitations were significantly reduced on melon flowers (Cucumis melo L.) and flowering knapweed (Centaurea stoebe L.) that were sprayed with a piperidine solution, relative to untreated plants. In EAG recordings, the HCAs elicited antennal responses that were significantly different from control or vehicle responses. Overall, this study provides evidence that HCAs can deter individual bees from food sources and suggests that this deterrence is the result of antennal olfactory detection. These findings warrant further study into structure-activity relationships that could lead to the development of short-term repellent compounds that are effective deterrents to reduce the contact of bees to pesticide-treated plants.

Effects of developmental exposure to pesticides in wax and pollen on honey bee (Apis mellifera) queen reproductive phenotypes

Stressful conditions during development can have sub-lethal consequences on organisms aside from mortality. Using previously reported in-hive residues from commercial colonies, we examined how multi-pesticide exposure can influence honey bee (Apis mellifera) queen health. We reared queens in beeswax cups with or without a pesticide treatment within colonies exposed to treated or untreated pollen supplement. Following rearing, queens were open-mated and then placed into standard hive equipment in an "artificial swarm" to measure subsequent colony growth. Our treated wax had a pesticide Hazard Quotient comparable to the average in beeswax from commercial colonies, and it had no measurable effects on queen phenotype. Conversely, colonies exposed to pesticide-treated pollen had a reduced capacity for viable queen production, and among surviving queens from these colonies we observed lower sperm viability. We found no difference in queen mating number across treatments. Moreover, we measured lower brood viability in colonies later established by queens reared in treated-pollen colonies. Interestingly, royal jelly from colonies exposed to treated pollen contained negligible pesticide residues, suggesting the indirect social consequences of colony-level pesticide exposure on queen quality. These findings highlight how conditions during developmental can impact queens long into adulthood, and that colony-level pesticide exposure may do so indirectly.

Viral impacts on honey bee populations: A review

Honey bee is vital for pollination and ecological services, boosting crops productivity in terms of quality and quantity and production of colony products: wax, royal jelly, bee venom, honey, pollen and propolis. Honey bees are most important plant pollinators and almost one third of diet depends on bee's pollination, worth billions of dollars. Hence the role that honey bees have in environment and their economic importance in food production, their health is of dominant significance. Honey bees can be infected by various pathogens like: viruses, bacteria, fungi, or infested by parasitic mites. At least more than 20 viruses have been identified to infect honey bees worldwide, generally from Dicistroviridae as well as Iflaviridae families, like ABPV (Acute Bee Paralysis Virus), BQCV (Black Queen Cell Virus), KBV (Kashmir Bee Virus), SBV (Sacbrood Virus), CBPV (Chronic bee paralysis virus), SBPV (Slow Bee Paralysis Virus) along with IAPV (Israeli acute paralysis virus), and DWV (Deformed Wing Virus) are prominent and cause infections harmful for honey bee colonies health. This issue about honey bee viruses demonstrates remarkably how diverse this field is, and considerable work has to be done to get a comprehensive interpretation of the bee virology.