Long-term monitoring of lipophilic acaricide residues in commercial Swiss beeswax

Colony environment and absence of brood enhance tolerance to a neonicotinoid in winter honey bee workers, Apis mellifera

In eusocial insects, worker longevity is essential to ensure colony survival in brood-free periods. Trade-offs between longevity and other traits may render long-living workers in brood-free periods more susceptible to pesticides compared to short-lived ones. Further, colony environment (e.g., adequate nutrition) may enable workers to better cope with pesticides, yet data comparing long vs. short-living workers and the role of the colony environment for pesticide tolerance are scarce. Here, we show that long-living honey bee workers, Apis mellifera, are less susceptible to the neonicotinoid thiamethoxam than short-lived workers, and that susceptibility was further reduced when workers were acclimatized under colony compared to laboratory conditions. Following an OECD protocol, freshly-emerged workers were exposed to thiamethoxam in summer and winter and either acclimatized within their colony or in the laboratory. Mortality and sucrose consumption were measured daily and revealed that winter workers were significantly less susceptible than summer workers, despite being exposed to higher thiamethoxam dosages due to increased food consumption. Disparencies in fat body activity, which is key for detoxification, may explain why winter bees were less susceptible. Furthermore, colony acclimatization significantly reduced susceptibility towards thiamethoxam in winter workers likely due to enhanced protein nutrition. Brood absence and colony environment seem to govern workers' ability to cope with pesticides, which should be considered in risk assessments. Since honey bee colony losses occur mostly over winter, long-term studies assessing the effects of pesticide exposure on winter bees are required to better understand the underlying mechanisms.

From consumption to excretion: Lithium concentrations in honey bees (Apis mellifera) after lithium chloride application and time-dependent effects on Varroa destructor

BACKGROUND

Owing to its systemic mode-of-action and ease of application, lithium chloride (LiCl) is an ideal varroacide for the control of Varroa destructor infestations in honey bee colonies. To better understand how LiCl functions within a colony, we screened different parts of honey bee anatomy for lithium accumulation. We wanted to elucidate the time-dependent effects of LiCl on V. destructor and its metabolism within honey bees when they were fed continuous LiCl treatments, as well as evaluate potential adverse effects such as accumulation in the hypopharyngeal glands of nurse bees, which could negatively impact queens and larvae.

RESULTS

Cage experiments reveal rapid acaricidal onset, with >95% mite mortality within 48 h of treatment. Bee hemolymph analysis supports these observations, showing a rapid increase in lithium concentration within 12 h of treatment, followed by stabilization at a constant level. Lithium accumulates in the rectum of caged bees (≤475.5 mg kg-1 after 7 days of feeding 50 mm LiCl), reflecting the bees' metabolic and excretion process. Despite concerns about potential accumulation in hypopharyngeal glands, low lithium levels of only 0.52 mg kg-1 suggest minimal risk to the queen and 1st- and 2nd-instar larvae. Cessation of LiCl treatment results in a rapid decline in mite mortality in the first 5 days, which increases again thereafter, resulting in mite mortality of 77-90% after 10 days.

CONCLUSION

These findings help optimize LiCl application in colonies to achieve high Varroa mortality without unwanted adverse effects and provide important baseline data for future registration. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Biomarker responses and lethal dietary doses of tau-fluvalinate and coumaphos in honey bees: Implications for chronic acaricide toxicity

Evidence suggests that acaricide residues, such as tau-fluvalinate and coumaphos, are very prevalent in honey bee colonies worldwide. However, the endpoints and effects of chronic oral exposure to these compounds remain poorly understood. In this study, we calculated LC50 and LDD50 endpoints for coumaphos and tau-fluvalinate, and then evaluated in vivo and in vitro effects on honey bees using different biomarkers. The LDD50 values for coumaphos were 0.539, and for tau-fluvalinate, they were 12.742 in the spring trial and 8.844 in the autumn trial. Chronic exposure to tau-fluvalinate and coumaphos resulted in significant changes in key biomarkers, indicating potential neurotoxicity, xenobiotic biotransformation, and oxidative stress. The Integrated Biomarker Response was stronger for coumaphos than for tau-fluvalinate, supporting their relative lethality. This study highlights the chronic toxicity of these acaricides and presents the first LDD50 values for tau-fluvalinate and coumaphos in honey bees, providing insights into the risks faced by colonies.

Lithium chloride treatments in free flying honey bee colonies: efficacy, brood survival, and within-colony distribution

The efficacy of various lithium chloride (LiCl) applications in eradicating the parasitic mite Varroa destructor in honey bee colonies was investigated, with a specific focus on its impact on brood development. In broodless colonies (3 weeks post queen caging), the highest efficacy of 98% was achieved with a 9-day treatment of 2.5 kg of candy spiked with 50 mM LiCl. A shorter 5-day treatment with 2 kg of 50 mM LiCl candy resulted in an efficacy of 78%. In colonies with brood, a repeated short-term application of 4 × 0.5 kg 50 mM LiCl candy yielded an efficacy of 88%. LiCl treatment led to a removal of the first batch of brood reared after release of the queen. However, no long-term effects on colony growth were observed, and the colonies successfully overwintered. Additionally, the study demonstrated that lithium is rapidly distributed among the bees of a colony within 2 days, yet only low concentrations were detected in stored food samples. This suggests that the bees efficiently absorb and distribute lithium within the colony. The harvested honey in the following spring revealed a lithium concentration of 0.1-0.2 mg/kg, which is below naturally occurring lithium levels in honey. Based on these findings, LiCl can be considered an effective and easy-to-apply acaricide in broodless colonies, and even in colonies with brood, it had good efficacy and no long-term effects on colony survival. Further research may be necessary to determine the optimal treatment period for achieving an efficacy over 95%.

Pesticide contamination of beeswax from managed honey bee colonies in New York State

The New York State (NYS) beekeeping industry generated >$11M worth of honey in 2020 and >$300M in pollination services to agriculture annually. Bees are frequently exposed to pesticides through foraging and husbandry practices. Lipophilic pesticides can remain in beeswax for extended periods. We analyzed for pesticides in wax comb samples collected from NYS apiaries at the end of the growing season, comparing residue numbers and concentrations among beekeepers of different operation scales: commercial beekeepers (>300 colonies), sideliners (50-299 colonies), and hobbyists (<50 colonies). We analyzed samples collected from 72 managed honey bee colonies for 92 insecticides, herbicides, and fungicides by liquid chromatography-tandem mass spectrometry. Pesticides were detected in all samples and included 34 fungicides, 33 insecticides, and 22 herbicides. Each wax sample contained 7-35 different residues (x¯ = 17.8 residues). Wax from colonies managed by commercial beekeepers contained the most residues (x¯ = 21.9 residues), hobbyists were second (x¯ = 16.3 residues), and sideliners had the fewest (x¯ = 11.7 residues). Nearly all wax samples (98.6%) contained the pesticide synergist piperonyl butoxide, most samples (86%) contained common varroacides used to control honey bee parasites, including coumaphos and amitraz breakdown products, and 93.1% contained the fungicide difenoconazole. We detected 34 fungicides, 7 of which were found in 50% or more of the samples. We detected 22 herbicides. We found pesticide contamination of beeswax to be common, with commercial beekeepers experiencing the greatest contamination.

Acceptance by Honey Bees of Wax Decontaminated through an Extraction Process with Methanol

Honey bees face serious threats. These include the presence of the Varroa destructor mite in hives, which requires the use of acaricides to control. The constant recycling of old wax exacerbates the problem, and results in the accumulation of residues in the beeswax, which is a problem for the viability of the colony. The same happens with the accumulation of phytosanitary residues. In a previous study, we implemented an efficient wax decontamination method using a batch methanol extraction method. The present study evaluates the acceptance of the decontaminated wax by the bees for comb building, brood, honey and pollen containment. The results show a slight delay in the start of comb building and small changes were observed in the pharmacopoeia of the decontaminated wax compared to the original commercial wax. The slight delay in the acceptance of the decontaminated wax could be due to the loss of some components, such as honey residues, which usually appear in the wax. The addition of bee-attractive substances to the manufacturing process could help to mitigate the delay. The results suggest that the use of decontaminated wax is a good alternative to reduce the concentration of residues in hives.

Quantitation of pesticides in bee bread collected from honey bee colonies in an agricultural environment in Switzerland

Pesticide contamination of bee products is a widespread phenomenon. Due to its composition, bee bread is affected by both lipophilic and hydrophilic substances. As proof of concept of a monitoring campaign and to better understand the extent of contamination, we developed an analytical method based on a modified QuEChERS extraction, with subsequent separation by liquid chromatography and detection by mass spectrometry. This allowed for the quantitation of 51 agricultural- or beekeeping-associated pesticides in bee bread. The workflow was applied to 60 samples taken biweekly throughout spring to autumn 2022 from five colonies at a Swiss apiary in an agricultural area. In total, 30 pesticides were identified (> LOD), among which 26 pesticides were quantitated. The total number of pesticides detected per colony ranged from 11 to 19. The most prevalent substances (> LOQ) were two neonicotinoid insecticides, acetamiprid and thiacloprid (max. 16 μg/kg and 37 μg/kg, respectively); seven fungicides, azoxystrobin (max. 72 μg/kg), boscalid (max. 50 μg/kg), cyprodinil (max. 1965 μg/kg), difenoconazole (max. 73 μg/kg), mandipropamid (max. 33 μg/kg), pyraclostrobin (max. 8 μg/kg) and trifloxystrobin (max. 38 μg/kg); and two herbicides, prosulfocarb (max. 38 μg/kg) and terbuthylazine (max. 26 μg/kg). The study revealed strong variability in pesticide occurrence and concentrations among colonies sampled at the same site and date. The applied biweekly sampling of bee bread from March to August was shown to be reliable in capturing peak contaminations and revealing the onset of certain pesticides in bee bread. The study provides an adequate practical approach for pesticide monitoring campaigns.

Acaricide residues in beeswax. Implications in honey, brood and honeybee

For beekeeping to be sustainable, the management of colonies for the production of bee products must be economically viable without endangering the lives of bees, and must include acceptable practices such as the treatment of hives with appropriate products. Occasionally, the use of acaricides to treat the hives against varroosis is uncontrolled and can accumulate in the hives, putting the colonies at risk. In this work, a screening of seven acaricides was carried out in different apiaries in Andalusia (Spain). Their distribution in beeswax, brood, honey, and bees from colonies in different surroundings was evaluated at different times. It was found that beeswax was highly contaminated but honey, brood and bees had acceptable levels, below their respective MRL or LD50, after a certain period following varrocide treatments. Acaricides banned for their use against Varroa, such as chlorfenvinphos, cypermethrin and especially acrinathrin, were found in the hives analysed.

Evaluating the Potential of Brood Recapping to Select Varroa destructor (Acari: Varroidae) Resistant Honey Bees (Hymenoptera: Apidae)

Several resistance traits have been proposed to select honey bees (Apis mellifera L.) that can survive in the presence of parasitic mite Varroa destructor (Anderson and Trueman) and enable a more sustainable apiculture. The interest for uncapping-recapping has recently increased following its identification in several naturally surviving honey bee populations, yet the utility of this trait for human-mediated selection is poorly known. Here, we evaluated the repeatability of recapping and its correlations with mite infestation levels, and assessed the expression of the trait in the often neglected drone brood. We also calculated correlations between recapping, mite infertility, and mite fecundity, expressed either at the level of individual brood cells or of the whole colony. Recapping measured in worker brood showed moderate repeatability (ranging between 0.30 and 0.46). Depending on sample, recapping slightly correlated negatively with colony infestation values. Recapping was also measured in drone brood, with values often comparable to recapping in worker brood, but no significant correlations were obtained between castes. At cell level, recapped cells in drone brood (but not in workers) were significantly less infested than nonrecapped cells, whereas in workers (but not in drones), recapped cells hosted mites with significantly lower fecundity. At colony level, with a few exceptions, recapping did not significantly correlate with mite infertility and fecundity, caste, sample, or number of infested cells considered. These results indicate limited possibilities of impeding mite reproduction and possibly mite infestation of honey bee colonies by recapping, which would need to be confirmed on larger, different populations.

Quantitation of 1,4-Dichlorobenzene and Thymol in Beeswax Using Dynamic Headspace Vacuum Transfer in Trap Extraction Prior to Gas Chromatography-Mass Spectrometry

A method based on dynamic headspace vacuum transfer in trap extraction, followed by gas chromatography coupled with a mass spectrometer (DHS-VTT-GC-MS), was validated for the fast quantitation of 1,4-dichlorobenzene (p-dichlorobenzene; PDCB) and thymol residues in beeswax. The quantitation limits (LOQ) were 0.05 mg/kg (PDCB) and 0.25 mg/kg (thymol). Recoveries above 80% were obtained for PDCB concentrations between 0.05 and 10 mg/kg and for thymol concentrations between 0.25 and 200 mg/kg. Analysis of beeswax samples showed a good correlation between the results obtained by DHS-VTT-GC-MS analysis and those of a previous method based on SPE extraction followed by gas chromatography and triple- quadrupole mass spectrometry (GC-MS/MS) (R² = 0.9770 for PDCB and 0.9666 for thymol). However, the sample preparation and chromatography were much shorter using the DHS-VTT-GC-MS method. Forty comb foundations samples produced in Switzerland in 2019 and 2021 were analysed using DHS-VTT-GC-MS. Fourteen samples contained PDCB above the LOQ of 0.05 mg/kg, ranging up to a maximum of 1.53 mg/kg. The mean concentration of the positive samples was 0.22 mg/kg. All samples contained thymol residues ranging between 3.9 and 84.4 mg/kg with mean and median concentrations of 22.7 mg/kg and 17.4 mg/kg. Residue levels of PCDB and thymol in Swiss beeswax were substantially below those measured 20 (PDCB) and 10 (thymol) years ago, respectively.

Propolis Contra Pharmacological Interventions in Bees

In addition to wax, propolis is a mixture of resins, terpenes, and etheric and aromatic oils. This composition supports its very strong biochemical activity that affects bee health. Bee colonies are externally exposed to the activity of other different pharmacologically active substances and toxic agents used in beekeeping procedures, veterinary interventions, and the environment. Even if free form common diseases, they may suffer from parasites or toxins. In any such case the abundance and variety of honeyflow, besides proper therapy, is crucial for the maintenance of bee health. Propolis itself cannot be considered as food but can be considered as micro-nutrients for bees. This is due to the fact that some of its compounds may penetrate different bee products, and this way be consumed by bees and their larvae, while stored in the hive. This perspective shows propolis as natural agent reducing the toxicity of pyrethroid acaricides, stimulating production of detoxification enzymes, enhancing the action of antibiotics, and increasing expression of genes that encode proteins responsible for detoxication. The aim of this review is to summarize current data on the possible impact on veterinary public health of the introduction into propolis of residues of pharmacological agents approved in the EU for use in the treatment of bee colonies and their environment.

Use of Thymol in Nosema ceranae Control and Health Improvement of Infected Honey Bees

Simple Summary

In the European Union, there is no registered product for the control of the honey bee endoparasite Nosema ceranae. Thus, researchers are looking for options for Nosema treatment. The aim of this study was to investigate the effect of a natural essential-oil ingredient (thymol) derived from Thymus vulgaris on honey bees infected with N. ceranae. Thymol exerted certain positive effects (increasing bee survival, immunity, and antioxidative protection), as well as positively affecting the spore loads in Nosema-infected bees. However, when applied to Nosema-free bees, thymol caused certain health disorders; therefore, beekeepers should be careful with its use.

Abstract

Nosema ceranae is the most widespread microsporidian species which infects the honey bees of Apis mellifera by causing the weakening of their colonies and a decline in their productive and reproductive capacities. The only registered product for its control is the antibiotic fumagillin; however, in the European Union, there is no formulation registered for use in beekeeping. Thymol (3-hydroxy-p-cymene) is a natural essential-oil ingredient derived from Thymus vulgaris, which has been used in Varroa control for decades. The aim of this study was to investigate the effect of thymol supplementation on the expression of immune-related genes and the parameters of oxidative stress and bee survival, as well as spore loads in bees infected with the microsporidian parasite N. ceranae. The results reveal mostly positive effects of thymol on health (increasing levels of immune-related genes and values of oxidative stress parameters, and decreasing Nosema spore loads) when applied to Nosema-infected bees. Moreover, supplementation with thymol did not induce negative effects in Nosema-infected bees. However, our results indicate that in Nosema-free bees, thymol itself could cause certain disorders (affecting bee survival, decreasing oxidative capacity, and downregulation of some immune-related gene expressions), showing that one should be careful with preventive, uncontrolled, and excessive use of thymol. Thus, further research is needed to reveal the effect of this phytogenic supplement on the immunity of uninfected bees.

Evaluation of pesticide residues in commercial Swiss beeswax collected in 2019 using ultra-high performance liquid chromatographic analysis

The aim of this study was to determine residue levels of pesticides in Swiss commercial beeswax. Foundation samples were collected in 2019 from nine commercial manufacturers for analysis of 21 pesticides using ultra-high performance liquid chromatography. Individual samples showed the variability and residue ranges and pooled samples represented the average annual residue values of the Swiss production. In total, 17 pesticides were identified and 13 pesticides were quantified. They included 13 acaricides and/or insecticides, two fungicides as well as a synergist and a repellent. The means calculated from individual samples were similar to the average annual residue values for most tested pesticides. Mean values of 401, 236, 106 and 3 μg·kg^-1 were obtained for the beekeeping-associated contaminants coumaphos, tau-fluvalinate, bromopropylate and N-(2,4-Dimethylphenyl)-formamide (DMF; breakdown product of amitraz), respectively. For the other pesticides, the mean values were 203 μg·kg^-1 (synergist piperonyl butoxide), 120 μg·kg^-1 (repellent N,N-Diethyl-3-methylbenzamide, DEET), 19 μg·kg^-1 (chlorfenvinphos) and 4 μg·kg^-1 ((E)-fenpyroximate), while the means for acrinathrin, azoxystrobin, bendiocarb, boscalid, chlorpyrifos, flumethrin, permethrin, propoxur and thiacloprid were below the limit of quantification (< LOQ). Individual samples contained from seven to 14 pesticides. The ranges of values for coumaphos and piperonyl butoxide (from 14 to 4270 μg·kg^-1; from 6 to 1555 μg·kg^-1, respectively) were larger as compared to the ranges of values for DEET and tau-fluvalinate (from < LOQ to 585 μg·kg^-1; from 16 to 572 μg·kg^-1, respectively). In conclusion, the most prominent contaminants were the pesticides coumaphos and tau-fluvalinate, which are both acaricides with previous authorization for beekeeping in Switzerland, followed by piperonyl butoxide, a synergist to enhance the effect of insecticides.

An in vitro model for assessing the toxicity of pesticides in beeswax on honey bee larvae

While many studies have examined residue levels in beeswax, little is known about the levels that pose a risk for honey bee development. In an in vitro study, we aimed to assess the toxicity of pesticides in wax for worker larvae using coumaphos as a model substance. First, we reared larvae in beeswax with the aim to correlate the larval toxicity to the corresponding levels of coumaphos in beeswax. In a second step, we tested to which extent coumaphos migrates from the beeswax into the larval diet and if such dietary levels are toxic to larvae. We observed dose-related toxicity when larvae were exposed to coumaphos concentrations in beeswax from 30 to 100 mg/kg. The lethal concentration in 50% of the individuals (LC₅₀) was calculated to be 55.9 mg/kg, while the no observed effect concentration (NOEC) for exposure of larvae to coumaphos in wax was 20 mg/kg. Additional test series without larvae allowed to assess the migration of coumaphos from the beeswax into the diet. The resulting dietary coumaphos concentrations were four to five times lower than the initial concentrations in wax. In accordance, the LC₅₀ for chronic exposure of larvae to coumaphos in the diet was 12.5 mg/kg, which was 4.5 times lower than the LC₅₀ obtained for wax exposure. Finally, a coumaphos level of 20 mg/kg in wax led to a dietary concentration of 3.9 mg/kg that was close to the NOEC of 3 mg/kg obtained in the diet. In conclusion, both experimental approaches suggest that coumaphos concentrations of up to 20 mg/kg in wax are non-lethal.

Review of harmful chemical pollutants of environmental origin in honey and bee products

Honey is a natural food with many pro-health properties, which comprises a wide variety of valuable ingredients. It can also be the source of chemical contaminants of environmental origin, including POPs that can contribute to adverse health effects to human. Monitoring the degree of pollution of honey/bee products with hazardous chemicals is important from a nutraceutical point of view. In the present work, overview of recent literature data on chemical pollutants in honey/bee products originating from the environment was performed. Their MLs, MRLs and EDI were discussed. It can be concluded that huge amount of research concerned on the presence of TMs and pesticides in honey. Most of the studies have shown that honey/bee products sampled from urban and industrialized areas were more contaminated than these sampled from ecological and rural locations. More pollutants were usually detected in propolis and bee pollen than in honey. Based on their research and regulations, authors stated, that most of the toxic pollutants of environmental origin in honey/bee products are at levels that do not pose a threat to the health of the potential consumer. The greatest concern relates to pesticides and TMs, because in some research MLs in individual samples were highly exceeded.

Varroa destructor from the Laboratory to the Field: Control, Biocontrol and IPM Perspectives-A Review

Varroa destructor is a real challenger for beekeepers and scientists: fragile out of the hive, tenacious inside a bee colony. From all the research done on the topic, we have learned that a better understanding of this organism in its relationship with the bee but also for itself is necessary. Its biology relies mostly on semiochemicals for reproduction, nutrition, or orientation. Many treatments have been developed over the years based on hard or soft acaricides or even on biocontrol techniques. To date, no real sustainable solution exists to reduce the pressure of the mite without creating resistances or harming honeybees. Consequently, the development of alternative disruptive tools against the parasitic life cycle remains open. It requires the combination of both laboratory and field results through a holistic approach based on health biomarkers. Here, we advocate for a more integrative vision of V. destructor research, where in vitro and field studies are more systematically compared and compiled. Therefore, after a brief state-of-the-art about the mite's life cycle, we discuss what has been done and what can be done from the laboratory to the field against V. destructor through an integrative approach.