Influence of pollen feeding and physiological condition on pesticide sensitivity of the honey bee Apis mellifera carnica

Diverse pollen nutrition can improve the development of solitary bees but does not mitigate negative pesticide impacts

Floral resource loss and pesticide exposure are major threats to bees in intensively managed agroecosystems, but interactions among these drivers remain poorly understood. Altered composition and lowered diversity of pollen nutrition may reinforce negative pesticide impacts on bees. Here we investigated the development and survival of the solitary bee Osmia bicornis provisioned with three different pollen types, as well as a mixture of these types representing a higher pollen diversity. We exposed bees of each nutritional treatment to five pesticides at different concentrations in the laboratory. Two field-realistic concentrations of three nicotinic acetylcholine receptor (nAChR) modulating insecticides (thiacloprid, sulfoxaflor and flupyradifurone), as well as of two fungicides (azoxystrobin and tebuconazole) were examined. We further measured the expression of two detoxification genes (CYP9BU1, CYP9BU2) under exposure to thiacloprid across different nutrition treatments as a potential mechanistic pathway driving pesticide-nutrition interactions. We found that more diverse pollen nutrition reduced development time, enhanced pollen efficacy (cocoon weight divided by consumed pollen weight) and pollen consumption, and increased weight of O. bicornis after larval development (cocoon weight). Contrary to fungicides, high field-realistic concentrations of all three insecticides negatively affected O. bicornis by extending development times. Moreover, sulfoxaflor and flupyradifurone also reduced pollen efficacy and cocoon weight, and sulfoxaflor reduced pollen consumption and increased mortality. The expression of detoxification genes differed across pollen nutrition types, but was not enhanced after exposure to thiacloprid. Our findings highlight that lowered diversity of pollen nutrition and high field-realistic exposure to nAChR modulating insecticides negatively affected the development of O. bicornis, but we found no mitigation of negative pesticide impacts through increased pollen diversity. These results have important implications for risk assessment for bee pollinators, indicating that negative effects of nAChR modulating insecticides to developing solitary bees are currently underestimated.

Toxicity and sublethal effects of lead (Pb) intake on honey bees (Apis mellifera)

Heavy metal pollution is becoming a worldwide problem affecting pollinators. The massive use of lead (Pb), the most harmful metal for the biosphere, in industries has increased the risk for honey bees. Pb exerts toxicity on living organisms inducing mainly oxidative stress. We assessed the toxicity and sublethal effects of Pb ingestion on protein content, catalase (CAT) activity, fat content and fatty acid (FA) profile of honey bee workers (Apis mellifera L.) under different nutritional conditions during chronic exposure tests. The LD50 was 15.13 ± 6.11 μg Pb2+/bee, similar to other reports. A single oral sublethal dose of 15 μg of Pb2+ affected the survival of bees fed with sugary food for ten days after Pb ingestion while supplementing the diet with bee bread improved Pb tolerance. The highest protein content was found in bees fed with the sugar paste and bee bread diet without Pb. CAT activity tended to decrease in bees of Pb groups independently of diet. Fat content was not affected by the diet type received by bees or Pb ingestion, but the FAs profile varied according to the nutritional quality of the diet. The results highlight that a single sublethal dose of Pb negatively affected the body proteins of bees despite the nutritional condition but did not disturb the FAs profile of workers. Nutrition plays an important role in preventing Pb-induced toxicity in honey bees.

Individual and social defenses in Apis mellifera: a playground to fight against synergistic stressor interactions

The honeybee is an important species for the agri-food and pharmaceutical industries through bee products and crop pollination services. However, honeybee health is a major concern, because beekeepers in many countries are experiencing significant colony losses. This phenomenon has been linked to the exposure of bees to multiple stresses in their environment. Indeed, several biotic and abiotic stressors interact with bees in a synergistic or antagonistic way. Synergistic stressors often act through a disruption of their defense systems (immune response or detoxification). Antagonistic interactions are most often caused by interactions between biotic stressors or disruptive activation of bee defenses. Honeybees have developed behavioral defense strategies and produce antimicrobial compounds to prevent exposure to various pathogens and chemicals. Expanding our knowledge about these processes could be used to develop strategies to shield bees from exposure. This review aims to describe current knowledge about the exposure of honeybees to multiple stresses and the defense mechanisms they have developed to protect themselves. The effect of multi-stress exposure is mainly due to a disruption of the immune response, detoxification, or an excessive defense response by the bee itself. In addition, bees have developed defenses against stressors, some behavioral, others involving the production of antimicrobials, or exploiting beneficial external factors.

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.

Condition and Honey Productivity of Honeybee Colonies Depending on Type of Supplemental Feed for Overwintering

Harvested honey is usually replaced by an alternative sugar to overwinter honeybee colonies. Supplementation of winter stores with beet or cane sucrose is safe for colonies and does not cause winter mortality. Despite this, there are hypotheses that supplementation of inverted sugars has the potential to give better results in overwintering, spring growth, and honey production of the colonies, because bees are consuming already cleaved feed. Therefore, we compared the condition parameters and honey production in 70 colonies at four apiaries overwintered with stores from sucrose or inverted sugars. No statistically significant differences in dependence on the type of the supplemental feed were found. Inverted sugar was more expensive than sucrose for feeding colonies. Economic efficiency, physiological consequences, and other disadvantages of using invert syrups are discussed.

Binding and Detoxification of Insecticides by Potentially Probiotic Lactic Acid Bacteria Isolated from Honeybee (Apis mellifera L.) Environment-An In Vitro Study

Lactic acid bacteria (LAB) naturally inhabiting the digestive tract of honeybees are known for their ability to detoxify xenobiotics. The effect of chlorpyrifos, coumaphos, and imidacloprid on the growth of LAB strains was tested. All strains showed high resistance to these insecticides. Subsequently, the insecticide binding ability of LAB was investigated. Coumaphos and chlorpyrifos were bound to the greatest extent (up to approx. 64%), and imidacloprid to a much weaker extent (up to approx. 36%). The insecticides were detected in extra- and intracellular extracts of the bacterial cell wall. The ability of selected LAB to reduce the cyto- and genotoxicity of insecticides was tested on two normal (ovarian insect Sf-9 and rat intestinal IEC-6) cell lines and one cancer (human intestinal Caco-2) cell line. All strains exhibited various levels of reduction in the cyto- and genotoxicity of tested insecticides. It seems that coumaphos was detoxified most potently. The detoxification abilities depended on the insecticide, LAB strain, and cell line. The detoxification of insecticides in the organisms of honeybees may reduce the likelihood of the penetration of these toxins into honeybee products consumed by humans and may contribute to the improvement of the condition in apiaries and honeybee health.

Pollen diet mediates how pesticide exposure impacts brain gene expression in nest-founding bumble bee queens

A primary goal in biology is to understand the effects of multiple, interacting environmental stressors on organisms. Wild and domesticated bees are exposed to a wide variety of interacting biotic and abiotic stressors, with widespread declines in floral resources and agrochemical exposure being two of the most important. In this study, we used examinations of brain gene expression to explore the sublethal consequences of neonicotinoid pesticide exposure and pollen diet composition in nest-founding bumble bee queens. We demonstrate for the first time that pollen diet composition can influence the strength of bumble bee queen responses to pesticide exposure at the molecular level. Specifically, one pollen mixture in our study appeared to buffer bumble bee queens entirely against the effects of pesticide exposure, with respect to brain gene expression. Additionally, we detected unique effects of pollen diet and sustained (versus more temporary) pesticide exposure on queen gene expression. Our findings support the hypothesis that nutritional status can help buffer animals against the harmful effects of other stressors, including pesticides, and highlight the importance of using molecular approaches to explore sublethal consequences of stressors.

Buffered fitness components: Antagonism between malnutrition and an insecticide in bumble bees

Global insect biodiversity declines due to reduced fitness are linked to interactions between environmental stressors. In social insects, inclusive fitness depends on successful mating of reproductives, i.e. males and queens, and efficient collaborative brood care by workers. Therefore, interactive effects between malnutrition and environmental pollution on sperm and feeding glands (hypopharyngeal glands (HPGs)) would provide mechanisms for population declines, unless buffered against due to their fitness relevance. However, while negative effects for bumble bee colony fitness are known, the effects of malnutrition and insecticide exposure singly and in combination on individuals are poorly understood. Here we show, in a fully-crossed laboratory experiment, that malnutrition and insecticide exposure result in neutral or antagonistic interactions for spermatozoa and HPGs of bumble bees, Bombus terrestris, suggesting strong selection to buffer key colony fitness components. No significant effects were observed for mortality and consumption, but significant negative effects were revealed for spermatozoa traits and HPGs. The combined effects on these parameters were not higher than the individual stressor effects, which indicates an antagonistic interaction between both. Despite the clear potential for additive effects, due to the individual stressors impairing muscle quality and neurological control, simultaneous malnutrition and insecticide exposure surprisingly did not reveal an increased impact compared to individual stressors, probably due to key fitness traits being resilient. Our data support that stressor interactions require empirical tests on a case-by-case basis and need to be regarded in context to understand underlying mechanisms and so adequately mitigate the ongoing decline of the entomofauna.

Butenolide Insecticide Flupyradifurone Affects Honey Bee Worker Antiviral Immunity and Survival

Honey bees face many environmental stressors, including exposure to pesticides and pathogens. A novel butenolide pesticide, flupyradifurone, was recently introduced to the US and shown to have a bee-friendly toxicity profile. Like the much-scrutinized neonicotinoids that preceded it, flupyradifurone targets the insect nervous system. Some neonicotinoids have been shown to interfere with antiviral immunity, which raised the concern that similar effects may be observed with flupyradifurone. In this study, we investigated how flupyradifurone and a neonicotinoid, clothianidin, affect the ability of honey bee workers to combat an infection of Israeli acute paralysis virus (IAPV). We exposed workers to field-realistic doses of the pesticides either with or without co-exposure with the virus, and then tracked survival and changes in viral titers. We repeated the experiment in the spring and fall to look for any seasonal effects. We found that flupyradifurone caused elevated mortality in the fall, but it did not lead to increased virus-induced mortality. Flupyradifurone also appeared to affect virus clearance, as bees co-exposed to the pesticide and virus tended to have higher viral titers after 48 hours than those exposed to the virus alone. Clothianidin had no effect on viral titers, and it actually appeared to increase resistance to viral infection in spring bees.

Flowering resources modulate the sensitivity of bumblebees to a common fungicide

Bees are exposed to various stressors, including pesticides and lack of flowering resources. Despite potential interactions between these stressors, the impacts of pesticides on bees are generally assumed to be consistent across bee-attractive crops, and regulatory risk assessments of pesticides neglect interactions with flowering resources. Furthermore, impacts of fungicides on bees are rarely examined in peer-reviewed studies, although these are often the pesticides that bees are most exposed to. In a full-factorial semi-field experiment with 39 large flight cages, we assessed the single and combined impacts of the globally used azoxystrobin-based fungicide Amistar® and three types of flowering resources (Phacelia, buckwheat, and a floral mix) on Bombus terrestris colonies. Although Amistar is classified as bee-safe, Amistar exposure through Phacelia monocultures reduced adult worker body mass and colony growth (including a 55% decline in workers and an 88% decline in males), while the fungicide had no impact on colonies in buckwheat or the floral mix cages. Furthermore, buckwheat monocultures hampered survival and fecundity irrespective of fungicide exposure. This shows that bumblebees require access to complementary flowering species to gain both fitness and fungicide tolerance and that Amistar impacts are flowering resource-dependent. Our findings call for further research on how different flowering plants affect bees and their pesticide tolerance to improve guidelines for regulatory pesticide risk assessments and inform the choice of plants that are cultivated to safeguard pollinators.

The Beneficial Effect of Pollen on Varroa Infested Bees Depends on Its Influence on Behavioral Maturation Genes

Honey bees collect nectar and pollen to fulfill their nutritional demands. In particular, pollen can influence longevity, the development of hypopharyngeal glands, and immune-competence of bees. Pollen can also mitigate the deleterious effects caused by the parasitic mite Varroa destructor and related deformed wing virus (DWV) infections. It has been shown that V. destructor accelerates the physiological and behavioral maturation of honey bees by influencing the interaction between two core physiological factors, Vitellogenin and juvenile hormone. In this study, we test the hypothesis that the beneficial effects of pollen on Varroa-infested bees are related to the hormonal control underpinning behavioral maturation. By analyzing the expression of genes associated to behavioral maturation in pollen-fed mite-infested bees, we show that treatment with pollen increases the lifespan of mite-infested bees by reversing the faster maturation induced by the parasite at the gene expression level. As expected, from the different immune-competence of nurse and forager bees, the lifespan extension triggered by pollen is also correlated with a positive influence of antimicrobial peptide gene expression and DWV load, further reinforcing the beneficial effect of pollen. This study lay the groundwork for future analyses of the underlying evolutionary processes and applications to improve bee health.

Acute Toxicity of Fungicide-Insecticide-Adjuvant Combinations Applied to Almonds During Bloom on Adult Honey Bees

Beekeepers report significant honey bee deaths during and after almond bloom. These losses pose a major problem for the California almond industry because of its dependence on honey bees as pollinators. The present study aimed to determine if combinations of pesticides applied during almond bloom during daylight hours were a possible explanation for these losses. In this study we aimed to mimic the spray application route of exposure to pesticides using a Potter Spray Tower to treat adult honey bees with commonly encountered pesticides and pesticide combinations at multiples of the maximum recommended field application rates. Tested insecticides included Altacor® and Intrepid®, and tested fungicides included Tilt®, Pristine®, Luna Sensation®, and Vangard®. Synergistic toxicity was observed when the fungicide Tilt (active ingredient propiconazole) was applied with the insecticide Altacor (chlorantraniliprole), though neither caused significant mortality when applied independently. The study also looked at the effect of adding a spray adjuvant, Dyne-Amic®, to pesticide mixtures. Dyne-Amic was toxic to honey bees at concentrations above the maximum recommended field application rate, and toxicity was increased when combined with the fungicide Pristine (pyraclostrobin and boscalid). Addition of Dyne-Amic also increased toxicity of the Tilt and Altacor combination. These results suggest that application of Altacor and Tilt in combination with an adjuvant at the recommended field application rates could cause mortality in adult honey bees. These findings highlight a potential explanation for honey bee losses around almond bloom, emphasize that the safety of spray adjuvants to bees should not be assumed, and provide support for recommendations to protect bees from pesticides through application at night when bees are not foraging. Environ Toxicol Chem 2022;41:1042-1053. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Unbalanced fatty acid diets impair discrimination ability of honey bee workers to damaged and healthy brood odors

Nutrition supports social insect colonies by regulating both individual performance and colony growth. In honey bee colonies, task-related behaviors such as nursing and foraging are partially mediated by nutrition. Young workers (nurses) consume almost all of the pollen in the hive, while foragers consume mostly nectar. Pollen provides vital proteins and lipids, consumed by nurse bees for approximately one week post eclosion. The role that lipids play in the physiology and behavior of adult bees is gaining significant attention. Recent research suggests that diets with balanced ratios of fatty acids increase olfactory learning in honey bees. Olfaction is crucial for young worker bees to perform brood care and cell cleaning behaviors, which is important for hive health and disease control. Thus, we targeted the early adult, pollen feeding stage to examine how fatty acids affect cognition to hive-relevant odors. We fed young workers (days 0-9) diets balanced or unbalanced in their ratio of essential fatty acids (ω-6:3) sourced from pollen or cooking oils. We then measured their ability to learn healthy and damaged brood odors, as well as their ability to discriminate between the two. Workers fed balanced diets could learn and discriminate between brood odors better than workers fed unbalanced diets. Consumption of both diet types decreased with age, but their cognitive effects remained. These results suggest that diet affects young worker cognitive development, which may affect task-related behaviors and colony hygiene.

High nutritional status promotes vitality of honey bees and mitigates negative effects of pesticides

Honey bee health is affected by multiple stressors, such as the exposure to plant protection products (PPPs), dietary limitation, monofloral diets and pressure of diseases and pathogens and their interactions. Here, we analysed the interacting effects of plant protection products and low nutritional pollen source on honey bee health under semi-field conditions. We established a healthy honey bee colony in each of 24 tents, planted either with monofloral maize, maize with a diverse flower strip or with monofloral Phacelia tanacetifolia. To evaluate the interaction between exposure to PPPs and nutritional status, a mixture of the insecticide thiacloprid and the fungicide prochloraz was applied. For each colony, we investigated brood capping rate as well as adult longevity, body and head weight, and enzyme activity of acetylcholinesterase and P450 reductase of newly hatched worker bees. We found a significant reduced capping rate in treated maize compared to flowering strips and Phacelia, but no interaction effect between pesticide treatment and nutritional status on capping rate. The response to treatment on the longevity of adults differed significantly between maize and Phacelia, with flower strips being intermediate, indicating interaction effects of PPP treatment and low pollen quality in maize compared to Phacelia and flowering strip treatments. Head weight of newly hatched worker bees showed significant interaction of nutritional status and treatment of PPPs. PPPs slightly increased body weight in all nutritional statuses, except for Phacelia. Enzyme activity of acetylcholinesterase and P450 reductase showed significant different responses between maize and Phacelia to PPP exposure, but not between maize and flowering strip. Our results support the hypothesis that higher pollen quality promotes development of larvae and pupae, longevity of adults and detoxification of PPPs.

Pollen nutrition fosters honeybee tolerance to pesticides

A reduction in floral resource abundance and diversity is generally observed in agro-ecosystems, along with widespread exposure to pesticides. Therefore, a better understanding on how the availability and quality of pollen diets can modulate honeybee sensitivity to pesticides is required. For that purpose, we evaluated the toxicity of acute exposure and chronic exposures to field realistic and higher concentrations of azoxystrobin (fungicide) and sulfoxaflor (insecticide) in honeybees provided with pollen diets of differing qualities (named S and BQ pollens). We found that pollen intake reduced the toxicity of the acute doses of pesticides. Contrary to azoxystrobin, chronic exposures to sulfoxaflor increased by 1.5- to 12-fold bee mortality, which was reduced by pollen intake. Most importantly, the risk of death upon exposure to a high concentration of sulfoxaflor was significantly lower for the S pollen diet when compared with the BQ pollen diet. This reduced pesticide toxicity was associated with a higher gene expression of vitellogenin, a glycoprotein that promotes bee longevity, a faster sulfoxaflor metabolization and a lower concentration of the phytochemical p-coumaric acid, known to upregulate detoxification enzymes. Thus, our study revealed that pollen quality can influence the ability of bees to metabolize pesticides and withstand their detrimental effects, providing another strong argument for the restoration of suitable foraging habitat.

Effects of Insecticides and Microbiological Contaminants on Apis mellifera Health

Over the past two decades, there has been an alarming decline in the number of honey bee colonies. This phenomenon is called Colony Collapse Disorder (CCD). Bee products play a significant role in human life and have a huge impact on agriculture, therefore bees are an economically important species. Honey has found its healing application in various sectors of human life, as well as other bee products such as royal jelly, propolis, and bee pollen. There are many putative factors of CCD, such as air pollution, GMO, viruses, or predators (such as wasps and hornets). It is, however, believed that pesticides and microorganisms play a huge role in the mass extinction of bee colonies. Insecticides are chemicals that are dangerous to both humans and the environment. They can cause enormous damage to bees' nervous system and permanently weaken their immune system, making them vulnerable to other factors. Some of the insecticides that negatively affect bees are, for example, neonicotinoids, coumaphos, and chlorpyrifos. Microorganisms can cause various diseases in bees, weakening the health of the colony and often resulting in its extinction. Infection with microorganisms may result in the need to dispose of the entire hive to prevent the spread of pathogens to other hives. Many aspects of the impact of pesticides and microorganisms on bees are still unclear. The need to deepen knowledge in this matter is crucial, bearing in mind how important these animals are for human life.

Supplemental forage ameliorates the negative impact of insecticides on bumblebees in a pollinator-dependent crop

Insecticide use and insufficient forage are two of the leading stressors to pollinators in agroecosystems. While these factors have been well studied individually, the experimental designs do not reflect real-world conditions where insecticide exposure and lack of forage occur simultaneously and could interactively suppress pollinator health. Using outdoor enclosures, we tested the effects of insecticides (imidacloprid + lambda-cyhalothrin) and non-crop forage (clover) in a factorial design, measuring the survival, behaviour and performance of bumblebees (Bombus impatiens), as well as pollination of the focal crop, watermelon. Colony survival was synergistically reduced to 17% in watermelon alone + insecticides (survival was 100% in all other treatments). However, behavioural shifts in foraging were mainly owing to insecticides (e.g. 95% reduced visitation rate to watermelon flowers), while impacts on hive performance were primarily driven by clover presence (e.g. 374% increase in the number of live eggs). Insecticide-mediated reductions in foraging decreased crop pollination (fruit set) by 32%. Altogether, these data indicate that both insecticides and non-crop forage play integral roles in shaping pollinator health in agricultural landscapes, but the relative importance and interaction of these two factors depend on which aspect of ‘health’ is being considered.

Polyphenols as Food Supplement Improved Food Consumption and Longevity of Honey Bees (Apis mellifera) Intoxicated by Pesticide Thiacloprid

Simple Summary

Worldwide, mass losses of honey bee colonies are being observed more frequently. Poor nutrition may cause honey bees to be more susceptible to pesticides and more vulnerable to diseases, and as a direct result of this, honey bee colonies can collapse. Another cause of mass bee colony collapse that is no less important is the use of pesticides. The level of toxicity of most pesticides is greatly affected by nutrient uptake. In addition, the honey bee genome is known to be specific for a significantly lower number of genes associated with detoxification compared with other insect species. Intake of phenolic and flavonoid substances in food can lead to increased expression of genes encoding detoxification enzymes in bees. Therefore, in this study, we evaluated in vitro the effect of phenolic and flavonoid substances on bee mortality and food consumption in the case of intoxication by pesticide thiacloprid. The results of this study showed a significant positive effect on honey bee survival rate as well as increased food intake. In addition, the expression level of genes encoding detoxification enzymes was determined.

Abstract

Malnutrition is one of the main problems related to the global mass collapse of honey bee colonies, because in honey bees, malnutrition is associated with deterioration of the immune system and increased pesticide susceptibility. Another important cause of mass bee colonies losses is the use of pesticides. Therefore, the goal of this study was to verify the influence of polyphenols on longevity, food consumption, and cytochrome P450 gene expression in worker bees intoxicated by thiacloprid. The tests were carried out in vitro under artificial conditions (caged bees). A conclusively lower mortality rate and, in parallel, a higher average food intake, were observed in intoxicated bees treated using a mixture of phenolic acids and flavonoids compared to untreated intoxicated bees. This was probably caused by increased detoxification capacity caused by increased expression level of genes encoding the cytochrome P450 enzyme in the bees. Therefore, the addition of polyphenols into bee nutrition is probably able to positively affect the detoxification capacity of bees, which is often reduced by the impact of malnutrition resulting from degradation of the environment and common beekeeping management.

Depletion kinetics and concentration- and time-dependent toxicity of a tertiary mixture of amitraz and its major hydrolysis products in honeybees

Although amitraz is one of the acaricides most commonly applied within beehives, to date, its time-dependent oral toxicity in honeybees has not been investigated, due to amitraz's instability in aqueous media. In aqueous media such as honey, amitraz rapidly forms a continuously changing tertiary mixture with two of its major hydrolysis products, DMF and DMPF. The contribution of each hydrolysis product to the overall oral toxicity of this acaricide is not known. Therefore, we aimed to characterize the depletion and formation kinetics of amitraz and its hydrolysis products in 50% sucrose solution provided to caged honeybees, including the calculation of the 50% lethal oral concentration (LC₅₀) of amitraz. We sought to determine the contribution of each component of the mixture to the overall observed toxicity. We also investigated the time- and concentration-dependent toxicity of the amitraz mixture and its hydrolysis products. A novel approach based on the analysis of the areas under the depletion and formation curves of amitraz and its hydrolysis products revealed that DMPF, amitraz and DMF accounted for 92%, 7% and 1% (respectively) of the overall toxicity of the mixture. The chronic oral LC₅₀ of amitraz was 3300 μmol/L, of similar magnitude as that of the non-toxic hydrolysis product DMF. The toxicity of DMPF and the mixture decreased over time; whereas the toxicity of DMF increased over time. Amitraz's instability in aqueous media and the highly toxic profile of DMPF, suggest that DMPF is the actual toxic entity responsible for amitraz's toxicity toward honeybees.

The sublethal effects of neonicotinoids on spiders are independent of their nutritional status

Spiders were recently shown to be adversely affected by field-realistic concentrations of a broad scale of neonicotinoid insecticides. Among the reported effects of neonicotinoids on invertebrates were declines in lipid biosynthesis and upregulation of β-oxidation, while vertebrate models suggest increased adipogenesis following treatment with neonicotinoids. Therefore, we hypothesized that there exists synergy between the effects of diet and concurrent exposure to field-realistic concentrations of neonicotinoid insecticides. To address this hypothesis, we fed first instars of the large wolf spider Hogna antelucana with two types of diets and exposed them to field-realistic concentrations of three formulations of neonicotinoids (thiamethoxam, thiacloprid and acetamiprid). We then measured the growth of the tested spiders; the lipid and protein content of their bodies; and their behavior, including ballooning, rappelling, and locomotor parameters. The two tested diets consisted of casein-treated and sucrose-treated Drosophila melanogaster. The dietary treatments affected the lipid and protein content of the spiders, their body weight and carapace length but did not affect any of the measured behavioral parameters. Surprisingly, we did not find any effects of acute exposure to neonicotinoid insecticides on the lipid or protein reserves of spiders. Exposure to neonicotinoids altered the behavior of the spiders as reported previously in other spider species; however, these effects were not affected by dietary treatments. Overall, the dietary treatments did not have any major synergy with acute exposure to field-realistic concentrations of neonicotinoid insecticides.

Concentration- and time-dependent toxicity of commonly encountered pesticides and pesticide mixtures to honeybees (Apis mellifera L.)

Honeybees are exposed to a wide range of pesticides for long periods via contaminated water, pollen and nectar. Some of those pesticides might constitute health hazards in a time- and dose-dependent manner. Time-dependent toxicity profiles for many applied pesticides are lacking, despite the fact that such profiles are crucial for toxicological evaluations. Therefore, we sought to determine the time-dependent toxicities of pesticides/pesticide metabolites frequently found in Israeli beehives, namely, amitraz metabolites, N'-(2,4-dimethylphenyl)-N-methylformamidine (DMPF) and N-(2,4-dimethylphenyl)-formamide (DMF), coumaphos, imidacloprid, thiacloprid, acetamiprid and dimethoate (toxic reference). By applying accepted methodological approaches such as the modified Haber's rule (product of concentration and exposure duration leads to a constant effect) and comparisons between cumulative doses at different time points, we determined the time-dependent toxicities of these pesticides. We also studied the mixture toxicities of frequently occurring pesticide combinations and estimated their potential contributions to the overall toxicities of neonicotinoids. Thiacloprid was the only pesticide that complied with Haber's rule. DMPF, dimethoate and imidacloprid exhibited time-diminished -toxicities. In contrast, DMF and acetamiprid exhibited time-reinforced toxicities. Neither the binary mixtures nor the tertiary mixtures of DMF, DMPF and coumaphos at 10 times their environmentally relevant concentrations potentiated the neonicotinoids' toxicities. DMPF and imidacloprid were found to present the greatest hazard to honeybees, based on their 50% lethal cumulative dose and 50% lethal time. Amitraz's instability, its low detection frequency and high toxicity profile of its metabolite, DMPF, lead us to the conclusion that DMPF constitutes the actual toxic entity responsible for amitraz's toxic effect.

Sugar content of diet does not buffer against chronic oral imidacloprid exposure in the alfalfa leafcutting bee (Hymenoptera: Megachilidae)

Bees are economically critical pollinators, but are declining broadly due to several stressors, including nontarget exposure to insecticides and deficiencies in nutrition. Understanding the simultaneous impact of stressors, particularly interactions between them, is critical to effectively conserving bees. Although behavioral effects of pesticides like neonicotinoids have received some attention in solitary bees, our understanding of how they are modulated by diet quality is limited. Furthermore, scarce data exist on what concentrations of orally ingested neonicotinoids elicit mortality in solitary bees. In a controlled exposure laboratory experiment, we investigated how diet quality, as sugar concentration, and chronic oral exposure to imidacloprid affect adult alfalfa leafcutting bees, Megachile rotundata (Fabricius). We provided individuals ad libitum with either 20 or 50% (m/m) sucrose syrups containing either 0, 30, or 300 ppb imidacloprid (measuring 0, 27, and 209 ppb via an ELISA assay). Over 5 wk, we tracked behavior and survivorship of individuals. Imidacloprid decreased survivorship in a dose-dependent fashion, but sucrose content did not affect survivorship, even in bees not fed imidacloprid. In the high imidacloprid treatment, 45% of bees were observed in a motionless supine position while still alive, with this effect appearing to be buffered against by the higher sucrose diet. Our results suggest that diets higher in sugar concentration may prevent an intermediate stage of poisoning, but do not ultimately extend longevity. In devising risk assessments for bees, it is important to consider that interactions between stressors may occur in the stages leading up to death even if survivorship is unaffected.

Molecular Assessment of Genes Linked to Immune Response Traits of Honey Bees in Conventional and Organically Managed Apiaries

Simple Summary

Honey bees play a critical role in agriculture as they provide pollination services to many agricultural crops. However, honey bee populations continue to decline due to exposure to pesticides, habitat destruction, pests, diseases and beekeeping practices. In this study, we assessed selected biological parameters associated with honey bee health in two beekeeping practices (organic and conventional). We compared total protein content in young worker bees from organically and conventionally managed apiaries. We also assessed differential gene expression at two levels of Varroa mite infestations (0% and 5%) in selected genes involved in nutrition and cellular defense (vitellogenin (Vg), malvolio (Mvl), prophenoloxidase (PPO)-, genes involved in lifespan (superoxide dismutase (Sod 1), superoxide dismutase 2 (Sod2)) and immune function genes (immune deficiency (Imd), spaetzle (Spz). Total soluble protein in young adult worker bees was similar in both beekeeping practices. The genes PPO, Vg and Mvl were upregulated in young adult bees with no mite infestations from organically managed apiaries and could mount an immune response through Spz and Sod 1 when challenged by 5% Varroa mite infestation levels. Overall, these findings provide useful insights into the genetic response of honey bees under two beekeeping practices and could help improve honey bee health.

Abstract

Honey bees are of great economic importance, not only for honey production but also for crop pollination. However, honey bee populations continue to decline mainly due to exposure to pesticides, pathogens and beekeeping practices. In this study, total soluble protein was measured, total RNA was extracted and first-strand cDNAs were generated. Quantitative PCR was used to assess the relative expression (transcript abundances) of immune function-related genes in honey bees collected from organically and conventionally managed hives. Honey bees collected from conventionally managed hives with 0% Varroa mite infestation levels displayed an upregulated expression of the prophenoloxidase gene (cellular defense). Similarly, honey bees collected from organically managed hives had increased levels of the vitellogenin gene (immune function and longevity). The gene expression for malvolio (sucrose responsiveness) was highest in organically managed hives with 0% Varroa mite infestations. Young adult bees collected from organically managed hives with 5% Varroa mite infestation levels had upregulated expressions of the gene spaetzle, whereas bees from similarly infested, conventionally managed hives did not, suggesting that honey bees from organically managed hives could mount an immune response. In young adult bees collected from organically managed hives only, the expression of the immune deficiency gene (antimicrobial defense) was upregulated. The relative gene expression for superoxide dismutase 1 increased in young adult bees collected from hives with 5% Varroa mite infestation levels as expected. However, for superoxide dismutase 2, there was a high level of gene expression in adult bees from both conventionally managed hives with 0% Varroa mite infestation levels and organically managed hives with 5% Varroa mite infestations. The gene CYP9Q3 (pesticide detoxification) that metabolizes coumaphos and fluvalinate was upregulated in adult bees collected from organically managed bees. Overall, these findings provide useful insights into the genetic response of honey bees to some environmental stressors and could be an important component of best beekeeping practices that intend to enhance honey bee health.

Pesticide-Virus Interactions in Honey Bees: Challenges and Opportunities for Understanding Drivers of Bee Declines

Honey bees are key agricultural pollinators, but beekeepers continually suffer high annual colony losses owing to a number of environmental stressors, including inadequate nutrition, pressures from parasites and pathogens, and exposure to a wide variety of pesticides. In this review, we examine how two such stressors, pesticides and viruses, may interact in additive or synergistic ways to affect honey bee health. Despite what appears to be a straightforward comparison, there is a dearth of studies examining this issue likely owing to the complexity of such interactions. Such complexities include the wide array of pesticide chemical classes with different modes of actions, the coupling of many bee viruses with ectoparasitic Varroa mites, and the intricate social structure of honey bee colonies. Together, these issues pose a challenge to researchers examining the effects pesticide-virus interactions at both the individual and colony level.

Influence of land use on chlorpyrifos and persistent organic pollutant levels in honey bees, bee bread and honey: Beehive exposure assessment

This work reports the spatial and temporal variations on the dynamics of OCPs, PCBs, PBDEs and chlorpyrifos in honey bee, bee bread and honey samples, as well as soil and flowers from the surrounding areas, considering, different land uses. Honey bee samples showed the highest pollutant levels, with a predominance of the industrial contaminants over pesticides. Chlorpyrifos showed the highest concentration during the application period in almost all samples from the soybean field (S2), in concordance with its current use. By other hand, the recalcitrant compounds such as, DDTs, BDE #47 and also light PCBs exhibited the highest levels in beehive samples from the field adjacent to urban disposal waste (S3). In both soils and flower samples a prevalence of obsolete compounds over chlorpyrifos was observed, and the 6-CB predominated among the homologous groups of PCBs These results highlights the importance of soils as sink of these persistent contaminants, which became available depending on environmental conditions. Results revealed that the land uses and seasonal variations have directly impacted on the levels of agrochemicals, PCBs and PBDEs found in the beehive matrixes. This survey provides novel evidence about the current situation of pollution on honey bee colonies under temperate climates and contributes to the knowledge of this poor studied topic in Argentina.

Pollen defenses negatively impact foraging and fitness in a generalist bee (Bombus impatiens: Apidae)

Plants may benefit from limiting the community of generalist floral visitors if the species that remain are more effective pollinators and less effective pollenivores. Plants can reduce access to pollen through altered floral cues or morphological structures, but can also reduce consumption through direct pollen defenses. We observed that Eucera (Peponapis) pruinosa, a specialist bee on Cucurbita plants, collected pure loads of pollen while generalist honey bees and bumble bees collected negligible amounts of cucurbit pollen, even though all groups of bees visited these flowers. Cucurbit flowers have no morphological adaptations to limit pollen collection by bees, thus we assessed their potential for physical, nutritional, and chemical pollen traits that might act as defenses to limit pollen loss to generalist pollinators. Bumble bee (Bombus impatiens) microcolonies experienced reduced pollen consumption, mortality, and reproduction as well as increased stress responses when exposed to nutritional and mechanical pollen defenses. These bees also experienced physiological effects of these defenses in the form of hindgut expansion and gut melanization. Chemical defenses alone increased the area of gut melanization in larger bees and induced possible compensatory feeding. Together, these results suggest that generalist bumble bees avoid collecting cucurbit pollen due to the physiological costs of physical and chemical pollen defenses.

The effect of carbohydrate sources: Sucrose, invert sugar and components of mānuka honey, on core bacteria in the digestive tract of adult honey bees (Apis mellifera)

Bacteria within the digestive tract of adult honey bees are likely to play a key role in the digestion of sugar-rich foods. However, the influence of diet on honey bee gut bacteria is not well understood. During periods of low floral abundance, beekeepers often supplement the natural sources of carbohydrate that honey bees collect, such as nectar, with various forms of carbohydrates such as sucrose (a disaccharide) and invert sugar (a mixture of the monosaccharides glucose and fructose). We compared the effect of these sugar supplements on the relative abundance of bacteria in the gut of bees by feeding bees from a single colony, two natural diets: mānuka honey, a monofloral honey with known antibacterial properties, and a hive diet; and artificial diets of invert sugar, sucrose solution, and sucrose solutions containing synthesised compounds associated with the antibacterial properties of mānuka honey. 16S ribosomal RNA (rRNA)-based sequencing showed that dietary regimes containing mānuka honey, sucrose and invert sugar did not alter the relative abundance of dominant core bacteria after 6 days of being fed these diets. However, sucrose-rich diets increased the relative abundances of three sub-dominant core bacteria, Rhizobiaceae, Acetobacteraceae, and Lactobacillus kunkeei, and decreased the relative abundance of Frischella perrara, all which significantly altered the bacterial composition. Acetogenic bacteria from the Rhizobiaceae and Acetobacteraceae families increased two- to five-fold when bees were fed sucrose. These results suggest that sucrose fuels the proliferation of specific low abundance primary sucrose-feeders, which metabolise sugars into monosaccharides, and then to acetate.

Assessment of Pollen Diversity Available to Honey Bees (Hymenoptera: Apidae) in Major Cropping Systems During Pollination in the Western United States

Global western honey bee, Apis mellifera (L.) (Hymenoptera: Apidae), colony declines pose a significant threat to food production worldwide. Poor nutrition resulting from habitat loss, extensive monocultures, and agricultural intensification is among the several suggested drivers for colony declines. Pollen is the primary source of protein for honey bees; therefore, both pollen abundance and diversity are critical for colony growth and survival. Many cropping systems that employ honey bee colonies for pollination may lack sufficient pollen diversity and abundance to provide optimal bee nutrition. In this observational study, we documented the diversity and relative abundance of pollen collected by honey bees in five major pollinator-dependent crops in the western United States. We sampled pollen from pollen traps installed on honey bee colonies in the following cropping systems-almond, cherry, highbush blueberry, hybrid carrot, and meadowfoam. The pollen diversity was estimated by documenting the number of different pollen pellet colors and plant taxa found in each pollen sample. The lowest pollen diversity was found in almond crop. Relatively higher quantities of pollen collection were collected in almond, cherry, and meadowfoam cropping systems. The information gleaned from this study regarding pollen diversity and abundance may help growers, land managers, and beekeepers improve pollen forage available to bees in these cropping systems.

Influence of chronic exposure to thiamethoxam and chronic bee paralysis virus on winter honey bees

Co-exposure to pesticides and viruses is likely to occur in honey bee colonies. Pesticides can be present in pollen, nectar, and persist in stored food (honey and bee bread), and viruses can be highly prevalent in honey bee colonies. Therefore, the present study describes the influence of chronic co-exposure to thiamethoxam and Chronic bee paralysis virus (CBPV) on bee survival, virus loads, expression level of immune and detoxication genes, and pesticide metabolism Experiments were performed on honey bees collected from a winter apiary with reduced viral contaminations. No synergistic effect of co-exposure was observed on bee survival, nor on the ability of bees to metabolise the pesticide into clothianidin. However, we found that co-exposure caused an increase in CBPV loads that reached the viral levels usually found in overt infections. The effect of co-exposure on CBPV replication was associated with down-regulation of vitellogenin and dorsal-1a gene transcription. Nevertheless, the observed effects might be different to those occurring in spring or summer bees, which are more likelyco-exposed to thiamethoxam and CBPV and exhibit a different physiology.

Lethal and sublethal synergistic effects of a new systemic pesticide, flupyradifurone (Sivanto®), on honeybees

The honeybee ( Apis mellifera L.) is an important pollinator and a model for pesticide effects on insect pollinators. The effects of agricultural pesticides on honeybee health have therefore raised concern. Bees can be exposed to multiple pesticides that may interact synergistically, amplifying their side effects. Attention has focused on neonicotinoid pesticides, but flupyradifurone (FPF) is a novel butenolide insecticide that is also systemic and a nicotinic acetylcholine receptor (nAChR) agonist. We therefore tested the lethal and sublethal toxic effects of FPF over different seasons and worker types, and the interaction of FPF with a common SBI fungicide, propiconazole. We provide the first demonstration of adverse synergistic effects on bee survival and behaviour (poor coordination, hyperactivity, apathy) even at FPF field-realistic doses (worst-case scenarios). Pesticide effects were significantly influenced by worker type and season. Foragers were consistently more susceptible to the pesticides (4-fold greater effect) than in-hive bees, and both worker types were more strongly affected by FPF in summer as compared with spring. Because risk assessment (RA) requires relatively limited tests that only marginally address bee behaviour and do not consider the influence of bee age and season, our results raise concerns about the safety of approved pesticides, including FPF. We suggest that pesticide RA also test for common chemical mixture synergies on behaviour and survival.

Varroa destructor feeds primarily on honey bee fat body tissue and not hemolymph

The parasitic mite Varroa destructor is the greatest single driver of the global honey bee health decline. Better understanding of the association of this parasite and its host is critical to developing sustainable management practices. Our work shows that this parasite is not consuming hemolymph, as has been the accepted view, but damages host bees by consuming fat body, a tissue roughly analogous to the mammalian liver. Both hemolymph and fat body in honey bees were marked with fluorescent biostains. The fluorescence profile in the guts of mites allowed to feed on these bees was very different from that of the hemolymph of the host bee but consistently matched the fluorescence profile unique to the fat body. Via transmission electron microscopy, we observed externally digested fat body tissue in the wounds of parasitized bees. Mites in their reproductive phase were then fed a diet composed of one or both tissues. Mites fed hemolymph showed fitness metrics no different from the starved control. Mites fed fat body survived longer and produced more eggs than those fed hemolymph, suggesting that fat body is integral to their diet when feeding on brood as well. Collectively, these findings strongly suggest that Varroa are exploiting the fat body as their primary source of sustenance: a tissue integral to proper immune function, pesticide detoxification, overwinter survival, and several other essential processes in healthy bees. These findings underscore a need to revisit our understanding of this parasite and its impacts, both direct and indirect, on honey bee health.

Larval Pollen Stress Increases Adult Susceptibility to Clothianidin in Honey Bees

Neonicotinoid insecticides have come under scrutiny for their potential role in honey bee declines. Additionally, reduced access to forage in agricultural areas creates the potential for risk interactions with these pesticides in regions critical for honey production. In this study, we sought to determine whether sufficient access to pollen during larval development could mitigate stress associated with oral clothianidin exposure in honey bee adults. An apiary was established where pollen traps deprived half of the colonies of pollen, which was then supplemented to the others. Adults were fed 0, 10, 40, 200, or 400 µg/L clothianidin in the laboratory, and larval and adult lipids and superoxide dismutase (SOD) activities were compared between feeding treatments. Survival at sublethal concentrations of clothianidin was significantly reduced for adult bees reared in pollen deprived colonies. Adult SOD activity was affected by clothianidin dose but not larval feeding treatment, though within the pollen-deprived cohort, SOD was greater in controls than those fed clothianidin. Larval SOD differed between field replicates, with supplemented colonies having slightly higher activity levels during a period of pollen dearth, indicating that supplementation during these periods is particularly important for mitigating oxidative stress within the hive. Larval lipids were significantly higher in supplemented colonies during a substantial pollen flow, though adult lipids were unaffected by feeding treatment. These results suggest that during periods of pollen dearth, oxidative stress and adult worker longevity will be improved by supplementing colonies with locally collected pollen.

Multidimensional relationships of herbicides with insect-crop food webs

Controlling weeds is critical for improving the yield and quality of crops. Herbicides are the most commonly applied pesticides in agro-ecosystems. Herbicides affect insects directly as contact damage and indirectly by influencing food supplies. The innate susceptibility, life stages, and mode of feeding of insects can affect the herbicide-insect interaction. Interaction of herbicides with insect pest and beneficial insects is mainly indirect and absence of weeds either can reduce the insect population or causes switching of host plant and hence can also increase the population. The direct effect of herbicides depends on carrier or surfactant used. Presence of herbicides also provides surfactant to insecticides and increases impact of insecticides. At present, most reports on impact of herbicides indicate alterations in insect survival or egg production due to increase or decrease in host plant population as an indirect affect, only a handful studies reported a direct topical effect of these herbicides on egg, larvae/nymphs and adults of various insects. Further exploration of this interaction seems intriguing. Use of bio-herbicides, cultural control methods, and judicious use of herbicides could offer ecologically sustainable approaches to reduce impact of herbicides on insects.

Chronic exposure to imidacloprid or thiamethoxam neonicotinoid causes oxidative damages and alters carotenoid-retinoid levels in caged honey bees (Apis mellifera)

Over the last decade, the persistent dwindling of the populations of honey bees has become a growing concern. While this phenomenon is partly attributed to neonicotinoids (NEOCs), chronic exposures to these insecticides at environmentally-relevant concentrations are needed to fully estimate their implications. In this study, honey bees were orally exposed for 10 days to low field-realistic concentrations of NEOCs known for their effects on the cholinergic system (imidacloprid – IMI or thiamethoxam – THM). Selected biomarkers were measured such as acetylcholinesterase (AChE) activity, lipid peroxidation (LPO), α-tocopherol as well as several forms of vitamin A (retinoids) and carotenoids. Bees exposed to IMI showed lower levels of two carotenoids (α-carotene and α-cryptoxanthin) and α-tocopherol. The THM exposure increased the oxidized vitamin A metabolites in bees conjointly with the LPO. These results could be the consequence of a pro-oxidant effect of NEOCs and were observed at levels where no effects were recorded for AChE activity. This study reveals that exposure to low levels of NEOCs alters the carotenoid-retinoid system in honey bees. This would merit further investigation as these compounds are important in various aspects of bees’ health. Overall, this study contributes to the development of biomonitoring tools for the health of bees and other pollinators.

In-Hive Acaricides Alter Biochemical and Morphological Indicators of Honey Bee Nutrition, Immunity, and Development

The honey bee is a widely managed crop pollinator that provides the agricultural industry with the sustainability and economic viability needed to satisfy the food and fiber needs of our society. Excessive exposure to apicultural pesticides is one of many factors that has been implicated in the reduced number of managed bee colonies available for crop pollination services. The goal of this study was to assess the impact of exposure to commonly used, beekeeper-applied apicultural acaricides on established biochemical indicators of bee nutrition and immunity, as well as morphological indicators of growth and development. The results described here demonstrate that exposure to tau-fluvalinate and coumaphos has an impact on 1) macronutrient indicators of bee nutrition by reducing protein and carbohydrate levels, 2) a marker of social immunity, by increasing glucose oxidase activity, and 3) morphological indicators of growth and development, by altering body weight, head width, and wing length. While more work is necessary to fully understand the broader implications of these findings, the results suggest that reduced parasite stress due to chemical interventions may be offset by nutritional and immune stress.

Interactions between pesticides and pathogen susceptibility in honey bees

There exist a variety of factors that negatively impact the health and survival of managed honey bee colonies, including the spread of parasites and pathogens, loss of habitat, reduced availability or quality of food resources, climate change, poor queen quality, changing cultural and commercial beekeeping practices, as well as exposure to agricultural and apicultural pesticides both in the field and in the hive. These factors are often closely intertwined, and it is unlikely that a single stressor is driving colony losses. There is a growing consensus, however, that increasing prevalence of parasites and pathogens are among the most significant threats to managed bee colonies. Unfortunately, improper management of hives by beekeepers may exacerbate parasite populations and disease transmission. Furthermore, research continues to accumulate that describes the complex and largely harmful interactions that exist between pesticide exposure and bee immunity. This brief review summarizes our progress in understanding the impact of pesticide exposure on bees at the individual, colony, and community level.

Stress decreases pollen foraging performance in honeybees

Foraging in honeybees is energetically demanding. Here, we examined whether stressors, which generally increase metabolic demands, can impair foraging performance. A controlled non-pathogenic stressor (immune challenge) resulted in a change in the foraging preferences of bees. It reduced pollen foraging and increased the duration of trips in pollen foragers. Stress also reduced the amount of octopamine in the brain of pollen foragers (a biogenic amine involved in the regulation of foraging and flight behaviour in insects). According to the literature, flight metabolic rate is higher during pollen foraging than during nectar foraging, and nectar gives a higher energetic return relative to the foraging effort when compared with pollen. We thus propose that stress might be particularly detrimental to the performance of pollen foragers, and stressed bees prefer the energy-rich resource of nectar. In conclusion, stress, even at low levels, could have consequences for bee foraging behaviour and thereby the nutritional balance of the colony.

Apis cerana Is Less Sensitive to Most Neonicotinoids, Despite of Their Smaller Body Mass

Multiple stressors and interaction between them may be responsible for the decline of global pollinators. Among them, exposure to neonicotinoids has been getting more attention and has been considered as a main stressor. The Western honey bee (Apis mellifera L.) (Hymenoptera: Apidae) and Chinese indigenous honey bee (Apis cerana F.) (Hymenoptera: Apidae) are two managed honey bee species in China. These two species are widely used in beekeeping, and many wild A. cerana is widely spread in forests and contributes to the ecosystem. It is predicated that A. cerana is more sensitive to insecticides than A. mellifera due to their smaller mass. Here, we found that although the body mass of A. cerana is significantly lower than A. mellifera, the sensitivity of the two species to neonicotinoids are not associated with their body mass but depended on the chemical structure of neonicotinoids. To dinotefuran, the two species showed the similar sensitivity. To acetamiprid, A. mellifera was less sensitive than A. cerana. However, to imidacloprid and thiamethoxam, A. mellifera was more sensitive than A. cerana. These results suggested that the sensitivity of honey bees to neonicotinoids is closely associated with the structure of pesticides, but not with body mass of bees. It is also indicated that the hazards of pesticides to the different pollinators could not be inferred from one species to another.

Honey bee (Apis mellifera) nurses do not consume pollens based on their nutritional quality

Honey bee workers (Apis mellifera) consume a variety of pollens to meet the majority of their requirements for protein and lipids. Recent work indicates that honey bees prefer diets that reflect the proper ratio of nutrients necessary for optimal survival and homeostasis. This idea relies on the precept that honey bees evaluate the nutritional composition of the foods provided to them. While this has been shown in bumble bees, the data for honey bees are mixed. Further, there is controversy as to whether foragers can evaluate the nutritional value of pollens, especially if they do not consume it. Here, we focused on nurse workers, who eat most of the pollen coming into the hive. We tested the hypothesis that nurses prefer diets with higher nutritional value. We first determined the nutritional profile, number of plant taxa (richness), and degree of hypopharyngeal gland (HG) growth conferred by three honey bee collected pollens. We then presented nurses with these same three pollens in paired choice assays and measured consumption. To further test whether nutrition influenced preference, we also presented bees with natural pollens supplemented with protein or lipids and liquid diets with protein and lipid ratios equal to the natural pollens. Different pollens conferred different degrees of HG growth, but despite these differences, nurse bees did not always prefer the most nutritious pollens. Adding protein and/or lipids to less desirable pollens minimally increased pollen attractiveness, and nurses did not exhibit a strong preference for any of the three liquid diets. We conclude that different pollens provide different nutritional benefits, but that nurses either cannot or do not assess pollen nutritional value. This implies that the nurses may not be able to communicate information about pollen quality to the foragers, who regulate the pollens coming into the hive.

Neonicotinoid pesticides and nutritional stress synergistically reduce survival in honey bees

The honey bee is a major pollinator whose health is of global concern. Declines in bee health are related to multiple factors, including resource quality and pesticide contamination. Intensive agricultural areas with crop monocultures potentially reduce the quality and quantity of available nutrients and expose bee foragers to pesticides. However, there is, to date, no evidence for synergistic effects between pesticides and nutritional stress in animals. The neonicotinoids clothianidin (CLO) and thiamethoxam (TMX) are common systemic pesticides that are used worldwide and found in nectar and pollen. We therefore tested if nutritional stress (limited access to nectar and access to nectar with low-sugar concentrations) and sublethal, field-realistic acute exposures to two neonicotinoids (CLO and TMX at 1/5 and 1/25 of LD50) could alter bee survival, food consumption and haemolymph sugar levels. Bee survival was synergistically reduced by the combination of poor nutrition and pesticide exposure (-50%). Nutritional and pesticide stressors reduced also food consumption (-48%) and haemolymph levels of glucose (-60%) and trehalose (-27%). Our results provide the first demonstration that field-realistic nutritional stress and pesticide exposure can synergistically interact and cause significant harm to animal survival. These findings have implications for current pesticide risk assessment and pollinator protection.

Honey bee-collected pollen in agro-ecosystems reveals diet diversity, diet quality, and pesticide exposure

European honey bees Apis mellifera are important commercial pollinators that have suffered greater than normal overwintering losses since 2007 in North America and Europe. Contributing factors likely include a combination of parasites, pesticides, and poor nutrition. We examined diet diversity, diet nutritional quality, and pesticides in honey bee-collected pollen from commercial colonies in the Canadian Maritime Provinces in spring and summer 2011. We sampled pollen collected by honey bees at colonies in four site types: apple orchards, blueberry fields, cranberry bogs, and fallow fields. Proportion of honey bee-collected pollen from crop versus noncrop flowers was high in apple, very low in blueberry, and low in cranberry sites. Pollen nutritional value tended to be relatively good from apple and cranberry sites and poor from blueberry and fallow sites. Floral surveys ranked, from highest to lowest in diversity, fallow, cranberry, apple, and blueberry sites. Pesticide diversity in honey bee-collected pollen was high from apple and blueberry sites and low from cranberry and fallow sites. Four different neonicotinoid pesticides were detected, but neither these nor any other pesticides were at or above LD₅₀ levels. Pollen hazard quotients were highest in apple and blueberry sites and lowest in fallow sites. Pollen hazard quotients were also negatively correlated with the number of flower taxa detected in surveys. Results reveal differences among site types in diet diversity, diet quality, and pesticide exposure that are informative for improving honey bee and land agro-ecosystem management.

Impacts of Dietary Phytochemicals in the Presence and Absence of Pesticides on Longevity of Honey Bees (Apis mellifera)

Because certain flavonols and phenolic acids are found in pollen and nectar of most angiosperms, they are routinely ingested by Apis mellifera, the western honey bee. The flavonol quercetin and the phenolic acid p-coumaric acid are known to upregulate detoxification enzymes in adult bees; their presence or absence in the diet may thus affect the toxicity of ingested pesticides. We conducted a series of longevity assays with one-day-old adult workers to test if dietary phytochemicals enhance longevity and pesticide tolerance. One-day-old bees were maintained on sugar syrup with or without casein (a phytochemical-free protein source) in the presence or absence of quercetin and p-coumaric acid as well as in the presence or absence of two pyrethroid insecticides, bifenthrin and β-cyfluthrin. Dietary quercetin (hazard ratio, HR = 0.82), p-coumaric acid (HR = 0.91) and casein (HR = 0.74) were associated with extended lifespan and the two pyrethroid insecticides, 4 ppm bifenthrin (HR = 9.17) and 0.5 ppm β-cyfluthrin (HR = 1.34), reduced lifespan. Dietary quercetin enhanced tolerance of both pyrethroids; p-coumaric acid had a similar effect trend, although of reduced magnitude. Casein in the diet appears to eliminate the life-prolonging effect of p-coumaric acid in the absence of quercetin. Collectively, these assays demonstrate that dietary phytochemicals influence honey bee longevity and pesticide stress; substituting sugar syrups for honey or yeast/soy flour patties may thus have hitherto unrecognized impacts on adult bee health.

Current knowledge of detoxification mechanisms of xenobiotic in honey bees

The western honey bee Apis mellifera is the most important managed pollinator species in the world. Multiple factors have been implicated as potential causes or factors contributing to colony collapse disorder, including honey bee pathogens and nutritional deficiencies as well as exposure to pesticides. Honey bees' genome is characterized by a paucity of genes associated with detoxification, which makes them vulnerable to specific pesticides, especially to combinations of pesticides in real field environments. Many studies have investigated the mechanisms involved in detoxification of xenobiotics/pesticides in honey bees, from primal enzyme assays or toxicity bioassays to characterization of transcript gene expression and protein expression in response to xenobiotics/insecticides by using a global transcriptomic or proteomic approach, and even to functional characterizations. The global transcriptomic and proteomic approach allowed us to learn that detoxification mechanisms in honey bees involve multiple genes and pathways along with changes in energy metabolism and cellular stress response. P450 genes, is highly implicated in the direct detoxification of xenobiotics/insecticides in honey bees and their expression can be regulated by honey/pollen constitutes, resulting in the tolerance of honey bees to other xenobiotics or insecticides. P450s is also a key detoxification enzyme that mediate synergism interaction between acaricides/insecticides and fungicides through inhibition P450 activity by fungicides or competition for detoxification enzymes between acaricides. With the wide use of insecticides in agriculture, understanding the detoxification mechanism of insecticides in honey bees and how honeybees fight with the xenobiotis or insecticides to survive in the changing environment will finally benefit honeybees' management.

Variations in the Availability of Pollen Resources Affect Honey Bee Health

Intensive agricultural systems often expose honey bees (Apis mellifera L.) to large temporal variations in the availability (quantity, quality and diversity) of nutritional resources. Such nutritional irregularity is expected to affect honey bee health. We therefore tested under laboratory conditions the effect of such variation in pollen availability on honey bee health (survival and nursing physiology—hypopharyngeal gland development and vitellogenin expression). We fed honey bees with different diets composed of pollen pellets collected by honey bees in an agricultural landscape of western France. Slight drops (5–10%) in the availability of oilseed rape (Brassica napus L.) pollen resulted in significant reductions of all tested variables. Despite some variations in taxonomic diversity and nutritional quality, the pollen mixes harvested over the season had a similar positive influence on honey bee health, except for the one collected in late July that induced poor survival and nursing physiology. This period coincided with the mass-flowering of maize (Zea mays L.), an anemophilous crop which produces poor-quality pollen. Therefore, changes in bee health were not connected to variations in pollen diversity but rather to variations in pollen depletion and quality, such as can be encountered in an intensive agricultural system of western France. Finally, even though pollen can be available ad libitum during the mass-flowering of some crops (e.g. maize), it can fail to provide bees with diet adequate for their development.

Fatty acid profiles of monofloral clover beebread and pollen and proteomics of red clover (Trifolium pratense) pollen

Fatty acids were identified in monofloral beebread (BB) and bee pollen (BP) loads collected from Trifolium pratense L. A gas chromatography method was used to identify and quantify fatty acids: Thirty-five fatty acids were identified in BB and 42 in BP. A high amount of the healthy n-3 fatty acids was found. The ratio of polyunsaturated fatty acids n-3 to n-6 reached a value of 8.42 and 3.35 in the latter products. The proteomic analysis also was performed on the manually collected T. pratense pollen, and the most abundant protein groups were subjected to mass spectrometry analysis. Proteins identified in T. pratense pollen are involved in the main cellular functions (cell membrane formation, organelles traffic, and mainly metabolic processes). Because of the composition of fatty acids in BB and BP and a variety of proteins present in pollen, these products are considered to be favorable for human nutrition and health.

Rising atmospheric CO2 is reducing the protein concentration of a floral pollen source essential for North American bees

At present, there is substantive evidence that the nutritional content of agriculturally important food crops will decrease in response to rising levels of atmospheric carbon dioxide, Ca However, whether Ca-induced declines in nutritional quality are also occurring for pollinator food sources is unknown. Flowering late in the season, goldenrod (Solidago spp.) pollen is a widely available autumnal food source commonly acknowledged by apiarists to be essential to native bee (e.g. Bombus spp.) and honeybee (Apis mellifera) health and winter survival. Using floral collections obtained from the Smithsonian Natural History Museum, we quantified Ca-induced temporal changes in pollen protein concentration of Canada goldenrod (Solidago canadensis), the most wide spread Solidago taxon, from hundreds of samples collected throughout the USA and southern Canada over the period 1842-2014 (i.e. a Ca from approx. 280 to 398 ppm). In addition, we conducted a 2 year in situtrial of S. Canadensis populations grown along a continuous Ca gradient from approximately 280 to 500 ppm. The historical data indicated a strong significant correlation between recent increases in Ca and reductions in pollen protein concentration (r(2)= 0.81). Experimental data confirmed this decrease in pollen protein concentration, and indicated that it would be ongoing as Ca continues to rise in the near term, i.e. to 500 ppm (r(2)= 0.88). While additional data are needed to quantify the subsequent effects of reduced protein concentration for Canada goldenrod on bee health and population stability, these results are the first to indicate that increasing Ca can reduce protein content of a floral pollen source widely used by North American bees.

Effects of Pesticide Treatments on Nutrient Levels in Worker Honey Bees (Apis mellifera)

Honey bee colony loss continues to be an issue and no factor has been singled out as to the cause. In this study, we sought to determine whether two beekeeper-applied pesticide products, tau-fluvalinate and Fumagilin-B^®, and one agrochemical, chlorothalonil, impact the nutrient levels in honey bee workers in a natural colony environment. Treatments were performed in-hive and at three different periods (fall, spring, and summer) over the course of one year. Bees were sampled both at pre-treatment and two and four weeks post-treatment, weighed, and their protein and carbohydrate levels were determined using BCA and anthrone based biochemical assays, respectively. We report that, based on the pesticide concentrations tested, no significant negative impact of the pesticide products was observed on wet weight, protein levels, or carbohydrate levels of bees from treated colonies compared with bees from untreated control colonies.

Omega-3 deficiency impairs honey bee learning

Deficiency in essential omega-3 polyunsaturated fatty acids (PUFAs), particularly the long-chain form of docosahexaenoic acid (DHA), has been linked to health problems in mammals, including many mental disorders and reduced cognitive performance. Insects have very low long-chain PUFA concentrations, and the effect of omega-3 deficiency on cognition in insects has not been studied. We show a low omega-6:3 ratio of pollen collected by honey bee colonies in heterogenous landscapes and in many hand-collected pollens that we analyzed. We identified Eucalyptus as an important bee-forage plant particularly poor in omega-3 and high in the omega-6:3 ratio. We tested the effect of dietary omega-3 deficiency on olfactory and tactile associative learning of the economically highly valued honey bee. Bees fed either of two omega-3-poor diets, or Eucalyptus pollen, showed greatly reduced learning abilities in conditioned proboscis-extension assays compared with those fed omega-3-rich diets, or omega-3-rich pollen mixture. The effect on performance was not due to reduced sucrose sensitivity. Omega-3 deficiency also led to smaller hypopharyngeal glands. Bee brains contained high omega-3 concentrations, which were only slightly affected by diet, suggesting additional peripheral effects on learning. The shift from a low to high omega-6:3 ratio in the Western human diet is deemed a primary cause of many diseases and reduced mental health. A similar shift seems to be occurring in bee forage, possibly an important factor in colony declines. Our study shows the detrimental effect on cognitive performance of omega-3 deficiency in a nonmammal.

Evaluating sub-lethal effects of orchard-applied pyrethroids using video-tracking software to quantify honey bee behaviors

Managed honey bee, Apis mellifera L., colonies are contracted to pollinate fruit and nut orchards improving crop quality and yield. Colonies placed in orchards are potentially exposed to pyrethroid insecticides used for broad-spectrum pest control. Pyrethroids have been reported to pose minimal risk to bees due to their low application rates in the field and putative repellent properties. This repellency is believed to alter foraging behavior with the benefit of preventing bees from encountering a lethal dose in the field. However, sub-lethal exposure to pyrethroids may adversely impact bee behavior potentially resulting in social dysfunction or disruption of foraging. This study quantified behaviors associated with sub-lethal exposure to orchard-applied pyrethroids including, lambda-cyhalothrin, esfenvalerate, and permethrin, using video tracking software, Ethovision XT (Noldus Information Technologies). Bee locomotion, social interaction, and time spent near a food source were measured over a 24-h period. Bees treated with a pyrethroid traveled 30-71% less than control bees. Social interaction time decreased by 43% for bees treated with a high sub-lethal dose of esfenvalerate. Bees exposed to a high sub-lethal dose of permethrin spent 67% less time in social interaction and spent more than 5 times as long in the food zone compared to control bees.