The toxic unit approach as a risk indicator in honey bees surveillance programmes: A case of study in Apis mellifera iberiensis

Exploring the effects of the acaricide cyflumetofen on the vital organs of the honey bee Apis mellifera (Hymenoptera: Apidae) workers

Bees are important for maintaining ecosystems, pollinating crops and producing marketable products. In recent years, a decline in bee populations has been reported, with multifactorial causes, including the intensification of pesticide use in agriculture. Among pesticides, cyflumetofen is an insecticide and acaricide used in apple, coffee and citrus crops, whose main pollinator is the honey bee Apis mellifera. Therefore, this bee is a potential target of cyflumetofen during foraging. This study evaluated the histopathological and cytological damage in the midgut, hypopharyngeal glands and fat body of A. mellifera workers exposed to LC50 of cyflumetofen. The midgut epithelium of exposed bees presented cytoplasmic vacuolization, release of vesicles and cell fragments, which indicate autophagy, increased production of digestive enzymes and cell death, respectively. The cytological analysis of the midgut revealed the dilation of the basal labyrinth and the presence of spherocrystals in the digestive cells. The hypopharyngeal glands produced greater amounts of secretion in treated bees, whereas no changes were observed in the fat body. The results indicate that acute exposure to cyflumetofen negatively affect A. mellifera, causing damage to the midgut and changes in the hypopharyngeal glands, which may compromise the survival and foraging of this pollinator.

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.

Building composite indices in the age of big data - Application to honey bee exposure to infectious and parasitic agents

Pollinator insects play a crucial role in maintaining biodiversity and agricultural production worldwide. Yet they are subject to various infectious and parasitic agents (IPAs). To better assess their exposure to IPAs, discriminative and quantitative molecular methods have been developed. These tools produce large datasets that need to be summarised so as to be interpreted. In this paper, we described the calculation of three types of composite indices (numerical, ordinal, nominal) to characterize the honey bee exposure to IPAs in 128 European sites. Our summarizing methods are based on component-based factorial analyses. The indices summarised the dataset of eight IPAs quantified at two sampling times, into synthetic values providing different yet complementary information. Because our dataset included two sampling times, we used Multiple Factor Analysis (MFA) to synthetize the information. More precisely, the numerical and ordinal indices were generated from the first component of MFA, whereas the nominal index used the first main components of MFA combined with a clustering analysis (Hierarchical Clustering on components). The numerical index was easy to calculate and to be used in further statistical analyses. However, it contained only about 20% of the original information. Containing the same amount of original information, the ordinal index was much easier to interpret. These two indices summarised information in a unidimensional manner. Instead, the nominal index summarised information in a multidimensional manner, which retained much more information (94%). In the practical example, the three indices showed an antagonistic relationship between N. ceranae and DWV-B. These indices represented a toolbox where scientists could pick one composite index according to the aim pursued. Indices could be used in further statistical analyses but could also be used by policy makers and public instances to characterize a given sanitary situation at a site level for instance.

Natural Substances, Probiotics, and Synthetic Agents in the Treatment and Prevention of Honeybee Nosemosis

Honeybees are important pollinators, but they are continuously exposed to a variety of fungal and bacterial diseases. One of the various diseases affecting honeybees is nosemosis caused by microsporidia from the Nosema genus. Honeybees are mainly infected through consumption of infected food or faeces containing Nosema spp. spores. Nosemosis causes damage to the middle intestine epithelium, which leads to food absorption disorders and honeybee malnutrition. Fumagillin, i.e., the antibiotic used to treat nosemosis, was withdrawn in 2016 from EU countries. Therefore, researchers have been looking for compounds of both natural and synthetic origin to fight nosemosis. Such compounds should not have a negative impact on bees but is expected to inhibit the disease. Natural compounds tested against nosemosis include, e.g., essential oils (EOs), plant extracts, propolis, and bacterial metabolites, while synthetic substances tested as anti-nosemosis agents are represented by porphyrins, vitamins, antibiotics, phenolic, ascorbic acids, and others. This publication presents an 18-year overview of various studies of a number of natural and synthetic compounds used in the treatment and prevention of nosemosis cited in PubMed, GoogleScholar, and CrossRef.

First national survey of residues of active substances in honeybee apiaries across Spain between 2012 and 2016

This nationwide monitoring aimed to investigate the prevalence of residues of plant protection products (PPPs) and veterinary medicine products (VMPs) based on random selection of apiaries of Apis mellifera. For a three-year period (2012, 2013 and 2016), this study targeted 306 PPPs, VMPs and other active substances in 442 samples of bee bread honeycomb (BBHC) and 89 samples of honeybees collected from up to 177 apiaries. The results indicate that honeybees were most often exposed to residues of coumaphos, tau-fluvalinate, chlorfenvinphos, and acrinathrin, with a prevalence from a maximum of 98.8% to 49.4% in BBHC samples. Residues of coumaphos, tau-fluvalinate, amitraz (DMF + DMPF), carbendazim and orthophenylphenol were also frequently detected, from a maximum of 55.1% to 13.5% of the honeybee samples. Neonicotinoid residues, namely clothianidin and thiamethoxam, whose outdoor uses in crops are completely banned in EU, were not detected. Imidacloprid was found in 3.4% to 13.3% of samples during 2013 and 2016, respectively. Imidacloprid exceeded its acute toxicity (LD₅₀) value for honey bees in two samples of BBHC. Fipronil was detected in 0.5% of the samples during 2013. The diversity of active substances found (% of different residues analyzed) ranged from 33.9% to 37.2% in BBHC from 2012, 2013 to 2016, and was of 26.5% in honeybees in 2016. In at least 54% of the samples, the total residue load was in the range of 200 to 1500 μg·kg^-1. Up to 50% of BBHC samples were positive for one or two residues. No toxic residues for honeybees were detected in up to 88.8% of bee samples. This systematic surveillance of active substances assisted the evaluation of which target pesticides to look for and provided support to the competent authorities in the bee health decision-making.

Evaluating the chronic effect of two varroacides using multiple biomarkers and an integrated biological response index

There is mounting evidence that acaricides are among the most prevalent medicinal compounds in honey bee hive matrices worldwide. According to OCDE guideline No. 245 chronic lethal concentration of tau-fluvalinate (at concentrations ranging from 77.5 to 523.18 ppm), coumaphos (59.8 ppm) and dimethoate (0.7 ppm) were determined. The activity of the biomarkers acetylcholinesterase (AChE), carboxylesterase (CbE), glutathione S-transferase (GST), catalase (CAT) and malondialdehyde (MDA) was analysed and as they are implicated in neurotoxicity, biotransformation and antioxidant defences, these values were combined into an integrated biomarker response (IBR). There was enhanced AChE, CAT and GST activity in honey bees exposed to tau-fluvalinate, while dimethoate inhibited AChE activity. Both dimethoate and coumaphos inhibited CbE activity but they enhanced CAT activity and MDA formation. Our results highlight how these biomarkers may serve to reveal honey bee exposure to commonly used acaricides.

Study of pyrethroid resistance mutations in populations of Varroa destructor across Spain

The Varroa destructor mite is a serious worldwide pest of honeybees that is usually controlled with pyrethroid-based acaricides. However, the intensive use of these substances over the past decades has led to the development of resistance in these mites. Here, Varroa samples collected between 2006 and 2021 from apiaries across Spain were studied to evaluate the presence of mutations producing pyrethroid resistance, particularly those in the gene encoding the voltage-gated sodium channel (VGSC). Genotyping of the IIS4-IIS5 region of this gene detected the L925V (Leucine 'CTG' to valine 'GTG') mutation at position 925 and confirmed the presence of the M918L (Methionine 'ATG' to Leucine 'TTG') mutation at position 918 in these Spanish Varroa mites. Interestingly, the M918L mutation was always found in combination with L925V, both of which were always homozygous. Over and above the high frequency of pyrethroid-resistant mutations in Spanish Varroa populations, this apparently recent association of the M918L and L925V point mutations is a combination that appears to trigger greater resistance than that produced by L925V alone.

The Role of Nosema ceranae (Microsporidia: Nosematidae) in Honey Bee Colony Losses and Current Insights on Treatment

Honeybee populations have locally and temporally declined in the last few years because of both biotic and abiotic factors. Among the latter, one of the most important reasons is infection by the microsporidia Nosema ceranae, which is the etiological agent of type C nosemosis. This species was first described in Asian honeybees (Apis cerana). Nowadays, domestic honeybees (Apis mellifera) worldwide are also becoming infected due to globalization. Type C nosemosis can be asymptomatic or can cause important damage to bees, such as changes in temporal polyethism, energy and oxidative stress, immunity loss, and decreased average life expectancy. It causes drastic reductions in workers, numbers of broods, and honey production, finally leading to colony loss. Common treatment is based on fumagillin, an antibiotic with side effects and relatively poor efficiency, which is banned in the European Union. Natural products, probiotics, food supplements, nutraceuticals, and other veterinary drugs are currently under study and might represent alternative treatments. Prophylaxis and management of affected colonies are essential to control the disease. While N. ceranae is one potential cause of bee losses in a colony, other factors must also be considered, especially synergies between microsporidia and the use of insecticides.

Occurrence of Pesticide Residues in Spanish Honey Measured by QuEChERS Method Followed by Liquid and Gas Chromatography-Tandem Mass Spectrometry

In the current study, the QuEChERS extraction method with slight modifications, followed by liquid and gas chromatography–tandem mass spectrometry, was applied for the determination of 399 pesticide residues in 91 raw honey samples from northeastern Spain. The quality control procedure established in Document No. SANTE/12682/2019 was successfully followed: the responses in reagent blank and blank honey samples were below 30% of the reporting limit (0.01 mg kg⁻¹) for all analysed compounds, the correlation coefficients (R²) were higher than 0.99 in most calibration curves, the deviation of back-calculated concentration from the true concentration was below ±20% (using the standard of 50 μg L⁻¹ concentration), and the recoveries of spiked samples on matrix were within the range of 70–120% for almost all analytes. Only chlorfenvinphos (2–7.8 ng/g) and coumaphos (8.8–37 ng/g) were detected in 13 samples, and neither were observed to exceed their maximum residue limits (MRLs). Dietary risk assessment for pesticide residues in honey above their lowest calibrated level (LCL) was performed, and two different age groups, adults and infants, were considered as populations at risk. The contribution of honey lay far below the acceptable daily intake (ADI) for both pesticide residues. Therefore, according to our results, honey is unlikely to pose concerns for consumer health in terms of its contribution to dietary long-term exposure. However, to maintain the level of compliance, pesticide residues in honey should be continuously monitored.

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.

A Case Report of Chronic Stress in Honey Bee Colonies Induced by Pathogens and Acaricide Residues

In this case report, we analyze the possible causes of the poor health status of a professional Apis mellifera iberiensis apiary located in Gajanejos (Guadalajara, Spain). Several factors that potentially favor colony collapse were identified, including Nosema ceranae infection, alone or in combination with other factors (e.g., BQCV and DWV infection), and the accumulation of acaricides commonly used to control Varroa destructor in the beebread (coumaphos and tau-fluvalinate). Based on the levels of residues, the average toxic unit estimated for the apiary suggests a possible increase in vulnerability to infection by N. ceranae due to the presence of high levels of acaricides and the unusual climatic conditions of the year of the collapse event. These data highlight the importance of evaluating these factors in future monitoring programs, as well as the need to adopt adequate preventive measures as part of national and international welfare programs aimed at guaranteeing the health and fitness of bees.

The countryside or the city: Which environment is better for the honeybee?

For a number of years, the decline of honeybee (Apis mellifera) in North America and Europe has been the subject of much debate. Among the many factors proposed by hundreds of studies to explain this phenomenon is the hypothesis that agricultural activities using pesticides contribute to the weakness of bee colonies. Moreover, while urban beekeeping is presently booming in several cities, we do not know if this environment is more beneficial for bees than the typical, rural area. In the summer of 2018, we sampled honeybees (foragers and larvae) in rural (Laurentians) and urban (city of Montreal) areas and compared them using the following biomarkers: carotenoids, retinoids, α-tocopherol, metallothionein-like proteins (MTLPs), lipid peroxidation, triglycerides, acetylcholinesterase activity (AChE) and proteins. Pesticides, pharmaceuticals and personal care products (PPCPs) and metals were also quantified in honeybees' tissues. Our result revealed that, globally, urban foragers had higher levels of insecticides and PPCPs and that metals were in greater concentrations in urban larvae. Compared to rural foragers, urban foragers had higher concentrations of MTLPs, triglycerides, protein and AChE activity. The multifactorial analysis confirmed that insecticides, some metals and PPCPs were the most influential components in the contaminant‒biomarker relationships for both foragers and larvae.

Assessing the resistance to acaricides in Varroa destructor from several Spanish locations

Varroosis is the disease caused by the ectoparasitic mite Varroa destructor, one of the most destructive diseases of honeybees. In Spain, there is great concern because there are many therapeutic failures after acaricide treatments intended to control varroosis outbreaks. In some of these cases it is not clear whether such failures are due to the evolution of resistance. Therefore, it is of high interest the development of methodologies to test the level of resistance in mite populations. In this work, a simple bioassay methodology was used to test whether some reports on low efficacy in different regions of Spain were in fact related to reduced Varroa sensitivity to the most used acaricides. This bioassay proved to be very effective in evaluating the presence of mites that survive after being exposed to acaricides. In the samples tested, the mortality caused by coumaphos ranged from 2 to 89%; for tau-fluvalinate, it ranged from 5 to 96%. On the other hand, amitraz caused 100% mortality in all cases. These results suggest the presence of Varroa resistant to coumaphos and fluvalinate in most of the apiaries sampled, even in those where these active ingredients were not used in the last years. The bioassay technique presented here, either alone or in combination with other molecular tools, could be useful in detecting mite populations with different sensitivity to acaricides, which is of vital interest in selecting the best management and/or acaricide strategy to control the parasite in apiaries.