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

Toxic effects of acaricide fenazaquin on development, hemolymph metabolome, and gut microbiome of honeybee (Apis mellifera) larvae

Fenazaquin, a potent insecticide widely used to control phytophagous mites, has recently emerged as a potential solution for managing Varroa destructor mites in honeybees. However, the comprehensive impact of fenazaquin on honeybee health remains insufficiently understood. Our current study investigated the acute and chronic toxicity of fenazaquin to honeybee larvae, along with its influence on larval hemolymph metabolism and gut microbiota. Results showed that the acute median lethal dose (LD50) of fenazaquin for honeybee larvae was 1.786 μg/larva, and the chronic LD50 was 1.213 μg/larva. Although chronic exposure to low doses of fenazaquin exhibited no significant effect on larval development, increasing doses of fenazaquin resulted in significant increases in larval mortality, developmental time, and deformity rates. At the metabolic level, high doses of fenazaquin inhibited nucleotide, purine, and lipid metabolism pathways in the larval hemolymph, leading to energy metabolism disorders and physiological dysfunction. Furthermore, high doses of fenazaquin reduced gut microbial diversity and abundance, characterized by decreased relative abundance of functional gut bacterium Lactobacillus kunkeei and increased pathogenic bacterium Melissococcus plutonius. The disrupted gut microbiota, combined with the observed gut tissue damage, could potentially impair food digestion and nutrient absorption in the larvae. Our results provide valuable insights into the complex and diverse effects of fenazaquin on honeybee larvae, establishing an important theoretical basis for applying fenazaquin in beekeeping.

The Varroa paradox: infestation levels and hygienic behavior in feral scutellata-hybrid and managed Apis mellifera ligustica honey bees

The Varroa destructor mite is a parasitic threat to managed and feral honey bee colonies around the world. Beekeepers use miticides to eliminate Varroa in commercial hives, but these chemicals can diminish bee health and increase miticide resistance. In contrast, feral honey bees have developed multiple ways to counteract mites without chemical treatment. We compared mite levels, grooming habits, and mite-biting behavior between feral Africanized honey bees (genomically verified Apis mellifera scutellata hybrids) and managed Italian honey bees (A. mellifera ligustica). Surprisingly, there was no difference in mite infestation levels between scutellata-hybrids and managed bees over one year despite the regular use of miticides in managed colonies. We also found no differences in the social immunity responses of the two groups, as measured by their hygienic habits (through worker brood pin-kill assays), self-grooming, and mite-biting behavior. However, we provide the first report that both scutellata-hybrids and managed honey bees bite off mite chemosensory forelegs, which the mites use to locate brood cells for reproduction, to a significantly greater degree than other legs (a twofold greater reduction in foreleg length relative to the most anterior legs). Such biting may impair mite reproduction.

Comparison of APIStrip passive sampling with conventional sample techniques for the control of acaricide residues in honey bee hives

Western honey bees are very sensitive bioindicators for studying environmental conditions, hence frequently included in many investigations. However, it is very common in both research studies and health surveillance programs to sample different components of the colony, including adult bees, brood and their food reserves. These practices are undoubtedly aggressive for the colony as a whole, and may affect its normal functioning and even compromise its viability. APIStrip-based passive sampling allows long-term monitoring of residues without affecting the colony in any way. In this study, we compared the effectiveness in the control of acaricide residues by using passive and conventional sampling, where the residue levels of the acaricides coumaphos, tau-fluvalinate and amitraz were evaluated. Conventional and APIStrip-based sampling differ in methods for evaluating bee exposure to residues. APIStrip is less invasive than conventional sampling, offers more efficient measurement of environmental contaminants, and can be stored at room temperature, saving costs and minimizing operator error.

Studies on the novel effects of electron beam treated pollen on colony reproductive output in commercially-reared bumblebees (Bombus terrestris) for mass pollination applications

Commercially-reared bumblebees provide an important pollinator service that helps support food production and security. The deployment of an appropriate non-thermal disinfection technology for the bulk treatment of pollen collected from honeybees for the feeding of commercial bumblebees is important in order to mitigate against complex diseases and unwanted pathogen spillover to native bees. High level disinfection of pollen was achieved using an electron (e)-beam dose of 100 kGy that corresponded to 78 % loss of cellular viability of bee pathogens before feeding to bumblebees as measured by the novel in vitro use of flow cytometry (FCM). Novel findings showed that e-beam treated-pollen that was fed to bumblebees produced fewer females, gynes and exhibited an absence of males when compared to control bumblebee colonies that were fed untreated commercial pollen. A similar trend emerged in bumblebee colony reproductive outputs when using membrane filtered washed pollen. Proteomic analysis of bumblebees from individual colonies fed with treated-pollen revealed a differential abundance of proteins associated with stress, immunity and metabolism when compared to the untreated pollen control group. Microbiome analysis of the bumblebee gut content revealed differences in microbiota between treated and untreated pollen in bumblebee colony studies. This novel study evaluated the impact of industrial e-beam treated-pollen on complex bee disease mitigation where physically treated-pollen fed to bumblebees was shown to substantially affect colony reproductive outputs.

Mite non-reproduction, recapping behavior, and hygienic behavior (freeze-kill method) linked to Varroa destructor infestation levels in selected Apis mellifera colonies

The genetic selection of honey bees (Apis mellifera) possessing specific social hygienic behaviors offers the beekeeping industry the possibility of controlling the Varroa destructor parasite and thus reducing its dependence on acaricides. However, the links between these behavioral traits are not yet well defined, which limits genetic progress in breeding programs. We measured the following behavioral varroa resistance traits: freeze-kill brood (FKB) and pin-kill brood (PKB) assays, varroa-sensitive hygiene (VSH), pupae removal, mite non-reproduction (MNR), and recapping activity. We found 2 negative and significant relationships: 1) between the recapping of cells infested with varroa and the total number of recapped cells, and 2) between the recapping of cells infested with varroa and VSH. We also selected the best predictive model of varroa infestation levels using the "step-wise" approach based on the Akaike information criterion. Our model revealed that MNR and FKB were significantly related to the varroa population levels, with a negative relationship; recapping was significantly related to mite infestation levels, with a positive relationship. Thus, a higher MNR or FKB score was linked to lower levels of mite infestation in colonies on August 14 (prior to fall infestation treatments); a higher recapping activity was linked to a higher level of mite infestation. Recapping behavior could be a useful trait to aid the selection of varroa-resistant bee lineages.

Potassium ion channels as a molecular target to reduce virus infection and mortality of honey bee colonies

Declines in managed honey bee populations are multifactorial but closely associated with reduced virus immunocompetence and thus, mechanisms to enhance immune function are likely to reduce viral infection rates and increase colony viability. However, gaps in knowledge regarding physiological mechanisms or 'druggable' target sites to enhance bee immunocompetence has prevented therapeutics development to reduce virus infection. Our data bridge this knowledge gap by identifying ATP-sensitive inward rectifier potassium (KATP) channels as a pharmacologically tractable target for reducing virus-mediated mortality and viral replication in bees, as well as increasing an aspect of colony-level immunity. Bees infected with Israeli acute paralysis virus and provided KATP channel activators had similar mortality rates as uninfected bees. Furthermore, we show that generation of reactive oxygen species (ROS) and regulation of ROS concentrations through pharmacological activation of KATP channels can stimulate antiviral responses, highlighting a functional framework for physiological regulation of the bee immune system. Next, we tested the influence of pharmacological activation of KATP channels on infection of 6 viruses at the colony level in the field. Data strongly support that KATP channels are a field-relevant target site as colonies treated with pinacidil, a KATP channel activator, had reduced titers of seven bee-relevant viruses by up to 75-fold and reduced them to levels comparable to non-inoculated colonies. Together, these data indicate a functional linkage between KATP channels, ROS, and antiviral defense mechanisms in bees and define a toxicologically relevant pathway that can be used for novel therapeutics development to enhance bee health and colony sustainability in the field.

Pesticide residues in bee bread, propolis, beeswax and royal jelly - A review of the literature and dietary risk assessment

Due to pollinator decline observed worldwide, many studies have been conducted on the pesticide residue content of apicultural products including bee bread, propolis, beeswax and royal jelly. These products are consumed for their nutraceutical properties, although, little information is available on the human health risk posed by pesticides present in them. In our research, studies dealing with the pesticide contamination of the above-mentioned hive products are reviewed. Dietary exposures were calculated based on the recommended daily intake values and concentration data reported by scientific studies. Potential acute and chronic health risk of consumers were evaluated by comparing the exposure values with health-based guidance values. Available data indicate that a wide range of pesticide residues, especially acaricides may accumulate in bee bread, propolis and beeswax, up to concentration levels of more thousand μg/kg. Based on our observations, tau-fluvalinate, coumaphos, chlorfenvinphos, chlorpyrifos and amitraz are commonly detected pesticide active substances in beehive products. Our estimates suggest that coumaphos and chlorfenvinphos can accumulate in beeswax to an extent that pose a potential health risk to the consumers of comb honey. However, it appears that pesticide residues do not transfer to royal jelly, presumably due to the filtering activity of nurse bees during secretion.

The adverse effects of synthetic acaricide tau-fluvalinate (tech.) on winter adult honey bees

Currently several pyrethroids (e.g., flumethrin and tau-fluvalinate) are used in apiculture worldwide as acaricides/miticides. The long half-lives of pyrethroids in synthetic acaricides applied to hive matrices, may adversely affect the health of bee colony. The potentially adverse effects of synthetic acaricide/miticide tau-fluvalinate (tech.) on winter honeybees were assessed in this study (OECD 245 2017). No dose-dependent mortality in in vitro reared winter honeybees was observed after chronic oral 10-day exposure to syrup (50% w/v) spiked with a maximum concentration of 750 μg a.i./kg diet and its 1/10 concentration. The No Observed Effect Concentration is ≥ 750 μg a.i./kg diet. Tau-fluvalinate testing for the sublethal effects on bee immune system showed up-regulated gene expression encoding abaecin, lysozyme, and defensin in both tested groups, however the expression of hymenoptaecin gene was reduced. Moreover, tau-fluvalinate significantly induced levels of DNA damage in exposed bees, which can result in adverse genotoxic effect.

Classic Hoarding Cages Increase Gut Bacterial Abundance and Reduce the Individual Immune Response of Honey Bee (Apis mellifera) Workers

Laboratory experiments have advanced our understanding of honey bee (Apis mellifera) responses to environmental factors, but removal from the hive environment may also impact physiology. To examine whether the laboratory environment alters the honey bee gut bacterial community and immune responses, we compared bacterial community structure (based on amplicon sequence variant relative abundance), total bacterial abundance, and immune enzyme (phenoloxidase and glucose oxidase) activity of cohort honey bee workers kept under laboratory and hive conditions. Workers housed in the laboratory showed differences in the relative abundance of their core gut taxa, an increase in total gut bacterial abundance, and reduced phenoloxidase activity, compared to bees housed in hives.

Effects of Agaricus bisporus Mushroom Extract on Honey Bees Infected with Nosema ceranae

Simple Summary

Nosema ceranae affects honey bee (Apis mellifera L.) causing nosemosis disease that often induces serious problems in apiculture. Antibiotic fumagillin is the only licenced treatment against nosemosis, but its effectiveness is questioned and its usage associated with risk of bee mortality and appearance of residues in bee products. In search for alternative treatment for the control of nosemosis, water crude extract of Agaricus bisporus was tested on bees in laboratory (cage) experiments. Bee survival and food consumption were monitored together with Nosema infection level and expression of five genes (abaecin, hymenoptaecin, defensin, apidaecin, and vitellogenin) were evaluated in bees sampled on days 7 and 15. Apart from the gene for defensin, the expression of all tested genes was up-regulated in bees supplemented with A. bisporus extract. Both anti-Nosema and immune protective effects of A. bisporus extract were observed when supplementation started at the moment of N. ceranae infection or preventively (before or simultaneously with the Nosema infection).

Abstract

Agaricus bisporus water crude extract was tested on honey bees for the first time. The first part of the cage experiment was set for selecting one concentration of the A. bisporus extract. Concentration of 200 µg/g was further tested in the second part of the experiment where bee survival and food consumption were monitored together with Nosema infection level and expression of five genes (abaecin, hymenoptaecin, defensin, apidaecin, and vitellogenin) that were evaluated in bees sampled on days 7 and 15. Survival rate of Nosema-infected bees was significantly greater in groups fed with A. bisporus-enriched syrup compared to those fed with a pure sucrose syrup. Besides, the anti-Nosema effect of A. bisporus extract was greatest when applied from the third day which coincides with the time of infection with N. ceranae. Daily food consumption did not differ between the groups indicating good acceptability and palatability of the extract. A. bisporus extract showed a stimulative effect on four out of five monitored genes. Both anti-Nosema and nutrigenomic effects of A. bisporus extract were observed when supplementation started at the moment of N. ceranae infection or preventively (before or simultaneously with the infection).

Residual Tau-Fluvalinate in Honey Bee Colonies Is Coupled with Evidence for Selection for Varroa destructor Resistance to Pyrethroids

Varroa destructor is considered one of the most devastating parasites of the honey bee, Apis mellifera, and a major problem for the beekeeping industry. Currently, the main method to control Varroa mites is the application of drugs that contain different acaricides as active ingredients. The pyrethroid tau-fluvalinate is one of the acaricides most widely used in beekeeping due to its efficacy and low toxicity to bees. However, the intensive and repetitive application of this compound produces a selective pressure that, when maintained over time, contributes to the emergence of resistant mites in the honey bee colonies, compromising the acaricidal treatments efficacy. Here we studied the presence of tau-fluvalinate residues in hives and the evolution of genetic resistance to this acaricide in Varroa mites from honey bee colonies that received no pyrethroid treatment in the previous four years. Our data revealed the widespread and persistent tau-fluvalinate contamination of beeswax and beebread in hives, an overall increase of the pyrethroid resistance allele frequency and a generalized excess of resistant mites relative to Hardy-Weinberg equilibrium expectations. These results suggest that tau-fluvalinate contamination in the hives may seriously compromise the efficacy of pyrethroid-based mite control methods.

Application of the Natural Products NOZEMAT HERB and NOZEMAT HERB PLUS Can Decrease Honey Bee Colonies Losses during the Winter

Honey bees (Apis mellifera L.) are crucial pollinators for many crops and natural ecosystems. However, honey bee colonies have been experiencing heavy overwinter mortality in almost all parts of the world. In the present study we have investigatеd, for the first time, the effects from the application of the herbal supplements NOZEMAT HERB® (NH) and NOZEMAT HERB PLUS® (NHP) on overwintering honey bee colony survival and on total protein and lysozyme content. To achieve this, in early autumn 2019, 45 colonies were selected and treated with these herbal supplements. The total protein and lysozyme content were evaluated after administration of NH and NHP twice the following year (June and September 2020). The obtained results have shown that both supplements have a positive effect on overwintering colony survival. Considerable enhancement in longevity of “winter bees” has been observed after the application of NHP, possibly due to the increased functionality of the immune system and antioxidant detoxification capacity. Although the mechanisms of action of NH and NHP are yet to be completely elucidated, our results suggest a new holistic approach on overwintering honey bee colony survival and welfare.

Sublethal concentrations of clothianidin affect honey bee colony growth and hive CO2 concentration

The effects of agricultural pesticide exposure upon honey bee colonies is of increasing interest to beekeepers and researchers, and the impact of neonicotinoid pesticides in particular has come under intense scrutiny. To explore potential colony-level effects of a neonicotinoid pesticide at field-relevant concentrations, honey bee colonies were fed 5- and 20-ppb concentrations of clothianidin in sugar syrup while control colonies were fed unadulterated syrup. Two experiments were conducted in successive years at the same site in southern Arizona, and one in the high rainfall environment of Mississippi. Across all three experiments, adult bee masses were about 21% lower among colonies fed 20-ppb clothianidin than the untreated control group, but no effects of treatment on brood production were observed. Average daily hive weight losses per day in the 5-ppb clothianidin colonies were about 39% lower post-treatment than in the 20-ppb clothianidin colonies, indicating lower consumption and/or better foraging, but the dry weights of newly-emerged adult bees were on average 6–7% lower in the 5-ppb group compared to the other groups, suggesting a nutritional problem in the 5-ppb group. Internal hive CO₂ concentration was higher on average in colonies fed 20-ppb clothianidin, which could have resulted from greater CO₂ production and/or reduced ventilating activity. Hive temperature average and daily variability were not affected by clothianidin exposure but did differ significantly among trials. Clothianidin was found to be, like imidacloprid, highly stable in honey in the hive environment over several months.

Carbon nanofibers are bioaccumulated in Aphylla williamsoni (Odonata) larvae and cause REDOX imbalance and changes of acetylcholinesterase activity

Carbon-based materials have been considered very promising for the technological industry due to their unique physical and chemical properties, namely: ability to reduce production costs and to improve the efficiency of several products. However, there is little information on what is the level of exposure that leads to adverse effects and what kind of effects is expected in aquatic biota. Thus, the aim of the present study was to evaluate the toxicity of carbon nanofibers (CNFs) in dragonfly larvae (Aphylla williamsoni) based on predictive oxidative-stress biomarkers, antioxidant activity reduction and neurotoxicity. After ephemeral models' exposure to CNFs (48 h; at 500 μg/L), data have shown that these pollutants did not change larvae's nutritional status given the concentration of total soluble carbohydrates, total proteins and triglycerides in them. However, the levels of both nitric oxide and substances reactive to thiobarbituric acid (lipid peroxidation indicators) have increased and the antioxidant activity based on total thiol levels and on 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity (%) has reduced, and it suggests REDOX imbalance induction by CNFs. In addition, larvae exposed to these pollutants showed significant acetylcholinesterase activity reduction in comparison to the control group. Thus, the present study has brought further knowledge about how carbon-based materials can affect benthic macroinvertebrates and emphasized their ecotoxicological potential in freshwater environments.

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.

Comparative effects of technical-grade and formulated chlorantraniliprole to the survivorship and locomotor activity of the honey bee, Apis mellifera (L.)

BACKGROUND

The loss of honey bee colonies is a nationally recognized problem that demands attention from both the scientific community and the beekeeping industry. One outstanding threat is the unintended exposure of these pollinators to agricultural pesticides. Anthranilic diamides, such as chlorantraniliprole, are registered for use in stone and pome fruits, vegetables, turf, and grains. There are few publicly available studies that provide an analysis of chlorantraniliprole effects on the survivorship and locomotion activity of beneficial, pollinating insects such as honey bees. The data gathered in this study provide the acute toxicity, 30-day survivorship, and locomotor activity of honey bees exposed to technical-grade chlorantraniliprole and three formulated products with chlorantraniliprole as the active ingredient.

RESULTS

Neither the technical-grade nor the formulated products of chlorantraniliprole were acutely toxic to honey bees following 4 or 72h treatments at the tested concentrations. A 4 h treatment of technical-grade and formulated chlorantraniliprole did not significantly affect the 30-day survivorship, although significantly higher mortality was observed after 30 days for bees receiving a 72 h treatment of technical-grade chlorantraniliprole and two formulated products. The locomotion activity, or total walking distance, of bees receiving a 4 h treatment of one chlorantraniliprole formulation was significantly reduced, with these individuals recovering their normal locomotion activity at 48 h post exposure. Conversely, there was observed lethargic behavior and significantly reduced walking distances for bees provided with a 72 h treatment of technical-grade chlorantraniliprole and each formulated product.

CONCLUSION

This study provides evidence for the effect of long-term exposure of chlorantraniliprole on the survivorship and locomotor activity of honey bees. Bees receiving a more field-relevant short-term exposure survived and moved similarly to untreated bees, reiterating the relative safety of chlorantraniliprole exposure to adult honey bees at recommended label concentrations. © 2020 Society of Chemical Industry.

Pollutants and Their Interaction with Diseases of Social Hymenoptera

Many insect species, including social insects, are currently declining in abundance and diversity. Pollutants such as pesticides, heavy metals, or airborne fine particulate matter from agricultural and industrial sources are among the factors driving this decline. While these pollutants can have direct detrimental effects, they can also result in negative interactive effects when social insects are simultaneously exposed to multiple stressors. For example, sublethal effects of pollutants can increase the disease susceptibility of social insects, and thereby jeopardize their survival. Here we review how pesticides, heavy metals, or airborne fine particulate matter interact with social insect physiology and especially the insects’ immune system. We then give an overview of the current knowledge of the interactive effects of these pollutants with pathogens or parasites. While the effects of pesticide exposure on social insects and their interactions with pathogens have been relatively well studied, the effects of other pollutants, such as heavy metals in soil or fine particulate matter from combustion, vehicular transport, agriculture, and coal mining are still largely unknown. We therefore provide an overview of urgently needed knowledge in order to mitigate the decline of social insects.

Terpenoid-Induced Feeding Deterrence and Antennal Response of Honey Bees

Multiple interacting stressors negatively affect the survival and productivity of managed honey bee colonies. Pesticides remain a primary concern for beekeepers, as even sublethal exposures can reduce bee immunocompetence, impair navigation, and reduce social communication. Pollinator protection focuses on pesticide application guidelines; however, a more active protection strategy is needed. One possible approach is the use of feeding deterrents that can be delivered as an additive during pesticide application. The goal of this study was to validate a laboratory assay designed to rapidly screen compounds for behavioral changes related to feeding or feeding deterrence. The results of this investigation demonstrated that the synthetic Nasonov pheromone and its terpenoid constituents citral, nerol, and geraniol could alter feeding behavior in a laboratory assay. Additionally, electroantennogram assays revealed that these terpenoids elicited some response in the antennae; however, only a synthetic Nasonov pheromone, citral, and geraniol elicited responses that differed significantly from control and vehicle detections.

Defining Pollinator Health: A Holistic Approach Based on Ecological, Genetic, and Physiological Factors

Evidence for global bee population declines has catalyzed a rapidly evolving area of research that aims to identify the causal factors and to effectively assess the status of pollinator populations. The term pollinator health emerged through efforts to understand causes of bee decline and colony losses, but it lacks a formal definition. In this review, we propose a definition for pollinator health and synthesize the available literature on the application of standardized biomarkers to assess health at the individual, colony, and population levels. We focus on biomarkers in honey bees, a model species, but extrapolate the potential application of these approaches to monitor the health status of wild bee populations. Biomarker-guided health measures can inform beekeeper management decisions, wild bee conservation efforts, and environmental policies. We conclude by addressing challenges to pollinator health from a One Health perspective that emphasizes the interplay between environmental quality and human, animal, and bee health.

A two-year monitoring of pesticide hazard in-hive: High honey bee mortality rates during insecticide poisoning episodes in apiaries located near agricultural settings

Pesticide residues in beebread, live and dead honey bees, together with honey bee death rate were monitored from June 2016 to June 2018 in three apiaries, located near agricultural settings and in wildlands. Dead honey bees were only collected and analyzed when significant mortality episodes occurred and pesticide content in beeswax of each experimental apiary was evaluated at the beginning of the study. Samples were extracted by a modified QuEChERS procedure and screened for pesticides residues by liquid chromatography mass spectrometry (LC-MS/MS). Pesticide hazard in the samples was evaluated through the hazard quotient approach (HQ). Beebread was widely contaminated with coumaphos and amitraz degradate 2, 4-dimethylphenylformamide (DMF), miticides detected in 94 and 97% of samples respectively. However, insecticides sprayed during citrus bloom like chlorpyrifos (up to 167 ng g ^-1) and dimethoate (up to 34 ng g ^-1) were the main responsible of the relevant pesticide hazard in this matrix. Pesticide levels in live bees were mostly residual, and pesticide hazard was low. Beeswax of the apiaries, contaminated by miticides, revealed a low pesticide hazard to honey bee colonies. Acute mortality episodes occurred only in the two apiaries located near agricultural settings. Dead bees collected during these episodes revealed high levels (up to 2700 ng g ^-1) of chlorpyrifos, dimethoate, omethoate and imidacloprid. HQ calculated in dead bees exceeded up to 37 times the threshold value considered as elevated hazard to honey bee health.

Deformed wing virus type A, a major honey bee pathogen, is vectored by the mite Varroa destructor in a non-propagative manner

Honey bees, the primary managed insect pollinator, suffer considerable losses due to Deformed wing virus (DWV), an RNA virus vectored by the mite Varroa destructor. Mite vectoring has resulted in the emergence of virulent DWV variants. The basis for such changes in DWV is poorly understood. Most importantly, it remains unclear whether replication of DWV occurs in the mite. In this study, we exposed Varroa mites to DWV type A via feeding on artificially infected honey bees. A significant, 357-fold increase in DWV load was observed in these mites after 2 days. However, after 8 additional days of passage on honey bee pupae with low viral loads, the DWV load dropped by 29-fold. This decrease significantly reduced the mites’ ability to transmit DWV to honey bees. Notably, negative-strand DWV RNA, which could indicate viral replication, was detected only in mites collected from pupae with high DWV levels but not in the passaged mites. We also found that Varroa mites contain honey bee mRNAs, consistent with the acquisition of honey bee cells which would additionally contain DWV replication complexes with negative-strand DWV RNA. We propose that transmission of DWV type A by Varroa mites occurs in a non-propagative manner.

Chlorothalonil Exposure Alters Virus Susceptibility and Markers of Immunity, Nutrition, and Development in Honey Bees

Chlorothalonil is a broad spectrum chloronitrile fungicide that has been identified as one of the most common pesticide contaminants found in managed honey bees (Hymenoptera: Apidae: Apis mellifera L.), their food stores, and the hive environment. While not acutely toxic to honey bees, several studies have identified potential sublethal effects, especially in larvae, but comprehensive information regarding the impact of chlorothalonil on adults is lacking. The goal of this study was to investigate the effects of exposure to a field relevant level of chlorothalonil on honey bee antiviral immunity and biochemical markers of general and social immunity, as well as macronutrient markers of nutrition and morphological markers of growth and development. Chlorothalonil exposure was found to have an effect on 1) honey bee resistance and/or tolerance to viral infection by decreasing the survival of bees following a viral challenge, 2) social immunity, by increasing the level of glucose oxidase activity, 3) nutrition, by decreasing levels of total carbohydrate and protein, and 4) development, by decreasing the total body weight, head width, and wing length of adult nurse and forager bees. Although more research is required to better understand how chlorothalonil interacts with bee physiology to increase mortality associated with viral infections, this study clearly illustrates the sublethal effects of chlorothalonil exposure on bee immunity, nutrition, and development.