Honey Bee Environmental Monitoring
Clarence Collison
Human Activities Produce Contaminants
Human activities produce contaminants, the amounts and toxicity of which often exceed the environment’s homeostatic capacity to cleanse itself. Hence, the systematic analysis and monitoring of the environment is increasingly a matter of urgency. Honey bees, thanks to their morphological features, and also bee products are regarded as good indicators of environmental pollution by toxic substances, be these heavy metals, radioactive elements, or persistent organic pollutants such as pesticides. Bees can carry back to the hive many contaminants deposited on utilitarian plants. The pesticides used in agriculture (especially in Spring and Summer when farming activities reach their peak) may not only be the cause of the large-scale mortality of bees but can also get into bee products. The presence of xenobiotics (substances that are foreign to the body or to an ecological system) in these products may impair their quality and properties and put human health at risk (Bargańska et al. 2016).
The honey bee has increasingly been employed to monitor environmental pollution by heavy metals in territorial and urban surveys, pesticides in rural areas and also radionuclide presence in the environment. The bee as a biological indicator possesses several important morphological, ecological and behavioral requisites, and man’s beekeeping assures an unlimited supply. The bee acts as a detector of environmental pollution in two ways, as it signals either via high mortality rates the presence of toxic molecules, or via the residues in honey, pollen and larvae the presence of heavy metals, fungicides and herbicides that are harmless to it (Celli and Maccagnani 2003).
Honey bees have great potential for detecting and monitoring environmental pollution, given their wide-ranging foraging behavior. Previous studies have demonstrated that concentrations of metals in adult honey bees were significantly higher at polluted than at control locations. These studies focused on a limited range of heavy metals and highly contrasting locations, and sampling was rarely repeated over a prolonged period. In this study, the potential of honey bees to detect and monitor metal pollution was further explored by measuring the concentration in adult honey bees of a wide range of trace metals, nine of which were not studied before, at three locations in the Netherlands over a three month period. The specific objective of the study was to assess the spatial and temporal variation in concentration in adult honey bees of Al (Aluminum), As (Arsenic), Cd (Cadmium), Co (Cobalt), Cr (Chromium), Cu (Copper), Li (Lithium), Mn (Manganese), Mo (Molybdenum), Ni (Nickel), Pb (Lead), Sb (Antimony), Se (Selenium), Sn (Tin), Sr (Strontium), Ti (Titanium), V (Vanadium) and Zn (Zinc). In the period of July–September 2006, replicated samples were taken at two week intervals from commercial-type beehives. The metal concentration in micrograms per gram honey bee was determined by inductive coupled plasma–atomic emission spectrometry. Significant differences in concentration between sampling dates per location were found for Al, Cd, Co, Cr, Cu, Mn, Sr, Ti and V, and significant differences in average concentration between locations were found for Co, Sr and V. The results indicate that honey bees can serve to detect temporal and spatial patterns in environmental metal concentrations, even at relatively low levels of pollution (van der Steen et al. 2012).
An experiment was carried out using 12 colonies of honey bees raised in hives located near an extra-urban crossroad. Leita et al. (1996) analyzed the Pb (Lead), Cd (Cadmium) and Zn (Zinc) deposited on the bee’s surfaces and the heavy metal accumulation in the foragers, dead bees, honey products and some environmental markers during nine weeks of the experiment. Results showed a large amount of Zn and Cd on the bee’s surface as a consequence of atmospheric fallout, whereas Pb seems to be either water-extractable and/or likely accumulated in the body of the insect. Dead bees expelled from the hives displayed a progressive accumulation of all heavy metals during the experimental period. Royal jelly and honey contained large amounts of heavy metals. In particular, they found a linear relationship between Cd in the honey and that found in flowers of Trifolium pratense L. (red clover). Results obtained suggested that honey bee products and the examined environmental markers may be considered useful parameters to assess the presence of environmental contaminants, whereas the measurements of heavy metals in the dead bees may be considered a suitable tool also to verify possible dynamics of accumulation of pollutants.
The potential use of honey as an indicator in mineral prospecting and environmental contamination studies has been investigated. Silver, Cd, Cu and Pb levels are reported in honeys collected throughout the U.K. The elemental content of honeys was investigated in relation to that in the soils collected from within the foraging area. For samples collected over two seasons the following concentrations were found: Ag < 0.1 to 6.5 ng g-1 (d.w.); Cd < 0.3 to 300 ng g-1; Cu 35 to 6510 ng g-1; Pb < 2 to 200 ng g-1. Considerable spatial and seasonal fluctuations were apparent. No correlations were observed between honey and soil concentrations for either Cu or Pb. It is concluded that the low concentrations of heavy metals in honey and their inherent variability (due to differences in floral source, foraging range, entrapment of atmospheric particulates on the flower, etc.) detract from the reliable use of honey as a monitoring tool (Jones 1967).
Environmental Sampling
Arsenic can be toxic to living organisms, depending not only on the concentration, but also its chemical form. The aim of this study was to determine arsenic concentrations and perform arsenic speciation analysis for the first time in honey bees, to evaluate their potential as biomonitors. Highest arsenic concentrations were determined in the vicinity of coal fired thermal power plants (367 µg kg−1), followed by an urban region (213 µg kg−1), with much lower concentrations in an industrial city (28.8 µg kg−1) and rural areas (41 µg kg−1). Until now, honey bees have never been used to study different arsenic species in the environment. For this reason, four extraction procedures were tested: water, hot water at 90°C, 20% methanol, and 1% formic acid. Water at 90°C was able to extract more than 90% of the total arsenic from honey bee samples. Inorganic arsenic (the sum of arsenite and arsenate) accounted for 95% of arsenic species in bees from three locations, except the industrial city, where it represented only 80% of arsenic species, while 15% was present as DMA (dimethylarsinic acid) (Zarić et al. 2022).
Three beehive matrices, sampled in eighteen apiaries from West France, were analyzed for the presence of lead (Pb). Samples were collected during four different periods in both 2008 and 2009. Honey was the matrix least contaminated by Pb (min = 0.004 μg g−1; max = 0.378 μg g−1; mean = 0.047 μg g−1). The contamination of bees (min = 0.001 μg g−1; max = 1.869 μg g−1; mean = 0.223 μg g−1) and pollen (min = 0.004 μg g−1; max = 0.798 μg g−1; mean = 0.240 μg g−1) showed similar levels and temporal variations but bees seemed to be more sensitive bringing out the peaks of Pb contamination. Apiaries in urban and hedgerow landscapes appeared more contaminated than apiaries in cultivated and island landscapes. Sampling period had a significant effect on Pb contamination with higher Pb concentrations determined in dry seasons (Lambert et al. 2012).
Due to their extensive use in both agricultural and non-agricultural applications, pesticides are a major source of environmental contamination. Honey bee colonies are proven sentinels of these and other contaminants, as they come into contact with them during their foraging activities. However, active sampling strategies involve a negative impact on these organisms and, in most cases, the need of analyzing multiple heterogeneous matrices. Conversely, the APIStrip-based passive sampling is innocuous for the bees and allows for long-term monitorings using the same colony. The versatility of the sorbent Tenax, included in the APIStrip composition, ensures that comprehensive information regarding the contaminants inside the beehive will be obtained in one single matrix. In the present study, 180 APIStrips were placed in nine apiaries distributed in Denmark throughout a six-month sampling period (10 subsequent samplings, April to September 2020). Seventy-five pesticide residues were detected (out of a 428-pesticide scope), boscalid and azoxystrobin being the most frequently detected compounds. There were significant variations in the finding of the sampling sites in terms of detections, pesticide diversity and average concentration. A relative indicator of the potential risk of pesticide exposure for the honey bees was calculated for each sampling site (Murcia-Morales et al. 2021).
Honey bee health is compromised by complex interactions between multiple stressors, among which pesticides play a major role. To better understand the extent of honey bee colonies’ exposure to pesticides in time and space, Tosi et al. (2018) conducted a survey by collecting corbicular pollen from returning honey bee foragers in 53 Italian apiaries during the active beekeeping season of three subsequent years (2012-2014). Of 554 pollen samples analyzed for pesticide residues, 62% contained at least one pesticide. The overall rate of multi-residual samples (38%) was higher than the rate of single pesticide samples (24%), reaching a maximum of seven pesticides per sample (1%). Over three years, 18 different pesticides were detected (10 fungicides and eight insecticides) out of 66 analyzed. Pesticide concentrations reached the level of concern for bee health (Hazard Quotient (HQ) higher than 1000) at least once in 13% of the apiaries and exceeded the thresholds of safety for human dietary intake (Acute Reference Dose (ARfD), the Acceptable Daily Intake (ADI), and the Maximum Residue Limit (MRL)) in 39% of the analyses. The pesticide which was most frequently detected was the insecticide chlorpyrifos (30% of the samples overall, exceeding ARfD, ADI, or MRL in 99% of the positive ones), followed by the fungicides mandipropamid (19%), metalaxyl (16%), spiroxamine (15%) and the neonicotinoid insecticide imidacloprid (12%). Imidacloprid had also the highest HQ level (5054, with 12% of its positive samples with HQ higher than 1000). This three year survey provides further insights on the contamination caused by agricultural pesticide use on honey bee colonies. Bee-collected pollen is shown to be a valuable tool for environmental monitoring, and for the detection of illegal uses of pesticides.
Monitoring the environment for pollution, pesticides and pathogens is crucial for protecting human, agriculture and overall ecosystem health. Diverse strategies ranging from physical sensors to sentinel species have been used for environmental monitoring. The European honey bee is a globally managed pollinator that can serve as a continuous biomonitoring species. During foraging, honey bees are exposed to contaminants and pathogens and carry them to their hives where they can be detected and quantified. Although individual bees are vulnerable to environmental stressors, the honey bee colony as a whole is more resilient and can accumulate contaminants or respond to them without collapsing. This allows for long-term monitoring of the colony to map contaminants in a geographical area and study ecotoxicology gradients over space and time. (Cunningham et al. 2022).
Environmental DNA (eDNA), defined as DNA extracted from environmental- or organismal-related specimens or matrixes, has been proposed as a powerful tool to detect and monitor cryptic, elusive, or invasive organisms, including parasites and many other pathogens that might be difficult to sample or to identify. Ribani et al. (2020) recently demonstrated that honey constitutes an easily accessible source of eDNA. In this study, they extracted DNA from 102 honey samples (74 from Italy and 28 from 17 other countries of all continents) and tested the presence of DNA of nine honey bee pathogens and parasites (Paenibacillus larvae (AFB), Melissococcus plutonius (EFB), Nosema apis, Nosema ceranae (Nosema Diseases), Ascosphaera apis (Chalkbrood), Lotmaria passim (Trypanosome Parasite), Acarapis woodi (Tracheal Mite), Varroa destructor (Varroa Mite), and Tropilaelaps spp., (Parasitic Mite)) using qualitative PCR assays. All honey samples contained DNA from V. destructor, confirming the widespread diffusion of this mite. None of the samples gave positive amplifications for N. apis, A. woodi, and Tropilaelaps spp. M. plutonius was detected in 87% of the samples, whereas the other pathogens were detected in 43% to 57% of all samples. The frequency of Italian samples positive for P. larvae was significantly lower (49%) than in all other countries (79%). The co-occurrence of positive samples for L. passim and A. apis with N. ceranae was significant. This study demonstrated that honey eDNA can be useful to establish monitoring tools to evaluate the sanitary status of honey bee populations.
Nucleus colonies (nucs) of 4,500 honey bees were evaluated as an alternative to full-size colonies for monitoring pollution impacts. Fifty nucs were deployed at five sites along a transect on Vashon Island, Washington. This provided a gradient of exposure to arsenic and cadmium from industrial sources. After 40 days, statistically significant differences were observed among sites for mean mass and numbers of bees (P ≤ 0.01), honey yield (P ≤ 0.07), and arsenic and cadmium content of forager bees (P ≤ 0.001) (Bromenshenk et al. 1991).
References
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Clarence Collison is an Emeritus Professor of Entomology and Department Head Emeritus of Entomology and Plant Pathology at Mississippi State University, Mississippi State, MS.
