The use of biosensors to assess the health of the bee colony superorganism

Joerg Mayer Exotic Animal, Wildlife and Zoo Animal Medicine Service, Department of Small Animal Medicine and Surgery, College of Veterinary Medicine, University of Georgia, Athens, GA 30602.

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 DVM, MSc

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Introduction

Honeybees are estimated to be responsible for the pollination of approximately 35% of the world's food crops and used for > 90% of global commercial pollination services.1 With the introduction of the new Veterinary Feed Directive for honeybees,2 veterinarians will clearly need to become more involved with the apiary industry and honeybee hobbyist in the management of honeybee colonies. Examining a hive and forming a valid medical opinion about a colony's health require knowledge of the anatomy and physiology of a colony, and specific tools can help veterinarians assess a colony's health status more accurately. Often, the term superorganism is used to describe a population of bees inside a hive because a single bee does not display the range of behaviors for this species (ie, queen and drones for reproduction and workers for brood rearing and foraging). The management tools available for controlling and managing honeybee production greatly advanced when Langstroth patented the modular hive system in 1852.3 To date, the Langstroth system is the most commonly used honeybee management system in the apiary industry and by hobby beekeepers.3 Although small changes to this system have been introduced since its introduction, no important changes in management technology have occurred in the last 160 years of beekeeping. Over 100 years ago, Gates reported the manually obtained hourly temperature of a hive over several days.4 Later, Dunham measured the temperature inside a hive using thermocouples, which was the start of incorporating technological devices for hive management.4 With the miniaturization of sensor technology in recent years, available health data about hives have increased and await exploitation and implementation. Various technological apiary devicesa–g have become commercially available, and their manufacturers have coined the term “the connected hive” to refer to this new industry of apiary devices. Veterinarians can approach the assessment of a hive in ways similar to the assessment of individual animals.

Precision livestock farming refers to the use of principles of control engineering to manage livestock, with the objectives of helping farmers produce food safely and with minimal environmental impact by efficient use of nutrients and reduction of pollutant emissions and of helping farmers identify early signs of poor health.5 The technologies used with precision livestock farming can now be applied to the management of the honeybee superorganism because of recent advances in information technology and sensor miniaturization and commercial access to low-cost hardware and software.5 Many devicesa–g are currently available for obtaining health data of a hive. Reviewing the benefits and drawbacks of all devices is beyond the scope of this article; however, the parameters that the devices measure and their applications for working with the superorganism will be discussed. The aim of this review article is to introduce veterinarians to the various devices and the parameters that they measure such that they can help veterinarians objectively assess the honeybee colony superorganism and provide objective and scientifically based advice on how to manage specific problems.

Colony strength assessment with a thermal imaging camera

Work by Cena and Clark6 in 1972 appears to be the first that included thermography to study insect thermoregulation. However, not until 1983 did scientists report on the use of thermography for the specific study of honeybees.7,8 Technological advances in recent years may now allow beekeepers to purchase small thermal cameras at reasonable prices. A few years ago, cameras were large and expensive. For example, the author purchased a thermal camera in 2006 at a discounted price of $10,000 (US dollars). Now, similar-quality cameras are available for < $400. One drawback of a small, less expensive thermal camera, however, is its lower resolution, which means that the working distance between the camera and the imaged object needs to be short (< 10 m) to obtain useful information. Yet, when working with an entire hive or individual frame of a hive, the observational distance is short, so lower resolution is not an important problem.

The author agrees with other scientists who have concluded that measurements with a thermal camera located approximately 3 to 5 m from a hive results in the most accurate images.9 Maintaining a constant distance from a hive can help reduce the influence of atmospheric factors like water vapor content and uncertainties that may arise from vastly different pixel resolutions, which are seen when the distance from a hive varies between image acquisition.9

A thermal camera can be used to judge the strength of a colony without opening or disturbing the hive (Figures 1 and 2). The heat signature of the superorganism is visible through the wood of the hive, and the temperature inside the hive is usually maintained at 35°C (95°F). This is achieved by vigorous muscle contractions of a majority of bees in the colony. Bees can uncouple their muscles from their wings, and contracting and relaxing the muscles increases their metabolic rate.10 The heat signature of the superorganism is clearly visible because the energy for the control and maintenance of the optimal brood nest temperature is equivalent to continuous power usage of 20 W.10 To get an accurate representative heat signature of a colony, 2 orthogonal images are needed. Two orthogonal images are necessary to accurately assess 3-D objects, similar to the reason for obtaining 2 orthogonal radiographs of the thorax or abdomen of an animal (Figure 3). Two orthogonal images will help to account for situations in which the superorganism has moved to 1 side of the hive. Here, a thermal signature taken from the other side (further away from the superorganism) could misrepresent the strength of the colony as weak because it will appear to have a lower temperature. Conversely, a weak colony could appear healthier if it was situated close to the side from where the image was obtained.

Figure 1
Figure 1

Image captured with a thermal camera with the heat signature of a cluster of bees inside a hive at a lower temperature (8°C [46.7°F]) than at the core.

Citation: Journal of the American Veterinary Medical Association 258, 5; 10.2460/javma.258.5.471

Figure 2
Figure 2

Photograph of a cluster of bees and the corresponding image captured with a thermal camera of the heat signature of a hive that has a core temperature of 39°C (102.3°F).

Citation: Journal of the American Veterinary Medical Association 258, 5; 10.2460/javma.258.5.471

Figure 3
Figure 3

Orthogonal images of a hive captured with a thermal camera.

Citation: Journal of the American Veterinary Medical Association 258, 5; 10.2460/javma.258.5.471

Besides assessing overall colony health, a thermal camera may identify other abnormalities, such as a rodent intruder, a common problem in wintertime (Figure 4). Generally, the best results have been obtained just before sunrise with clear skies and calm air.9 During the day, direct solar heating causes the thermal signature emanating from the hive interior to become difficult or impossible to assess.9 Knowledge of the proper use of a thermal camera is essential because user errors are possible, including loss of details because of an inappropriate distance between the camera and hive or the camera not being adjusted to the environmental temperature.

Figure 4
Figure 4

Image captured with a thermal camera of the heat signature of a bee colony and a separate isolated heat signature that is often a signature of a rodent seeking shelter in a hive during the winter.

Citation: Journal of the American Veterinary Medical Association 258, 5; 10.2460/javma.258.5.471

Colony health assessment with a hive weight scale

Just as body weight is one of the first and most essential data points collected for vertebrate veterinary patients, the weight of the hive can provide insight into the health of the hive over time (Figure 5). In the spring when the colony is foraging and collecting nectar and pollen and the queen is laying eggs, the weight of the hive should increase (vs other seasons; Figure 6). Then, its weight should decrease in the fall and winter as stored food is converted into thermal energy to keep the hive at the optimal temperature. Variations in hive weight can also provide data about individual events, such as hive robbing (ie, bees raid another hive and take honey to their hive) or swarming (ie, a colony splits into 2 and half of the colony leaves with the old queen). Monitoring of weight trends may greatly help with hive management, such as whether to remove or add food sources (eg, sugar syrup) to the colony. If a colony is below its optimal weight in the fall or winter, this finding can alert the beekeeper to pay special attention to that hive and support it with additional energy resources as needed. Persistent weight loss may indicate a problem with the colony or cessation of nectar flow that requires feeding of the colony.

Figure 5
Figure 5

Photograph of a hive with a hive scale.

Citation: Journal of the American Veterinary Medical Association 258, 5; 10.2460/javma.258.5.471

Figure 6
Figure 6

Output obtained from a hive scale that documents a slow increase in hive weight, suggestive of colony growth or nectar flow.

Citation: Journal of the American Veterinary Medical Association 258, 5; 10.2460/javma.258.5.471

Because of the numerous types of hives, a standardized reference for hive weights such that veterinarians can locate “normal” weights for the hive being examined is not available. Instead, the application of a hive scalea–c,e–g should be used to monitor the weight of a hive over time and determine whether any trend of weight gain or loss is evident.

Hive microclimate assessment with a temperature and humidity probe

A colony around the brood maintains its core temperature at 35°C, and small deviations in temperature have been shown to have a long-lasting effect on a colony's health.11 Broods raised at suboptimal temperatures are more susceptible to certain pesticides as adults.11 The colony assigns special “heater bees” to thermoregulate the colony, such that they bring water to cool the hive through evaporation or beat their wings to generate heat to warm the hive. If the temperature suddenly drops, it may indicate loss of the queen, thereby resulting in no brood production. Temperature trends can provide an early warning of a problem, well before the colony's size appears smaller or the colony appears weaker. Temperature can also be used to monitor a weak or starter colony to determine whether the space in the hive is too large for the bees to adequately thermoregulate (Figures 7 and 8). In this situation, reducing hive volume (removal of a super) may allow for better thermoregulation. When the temperature of the hive is too hot, bees will beard (ie, congregate on the outside surface of the hive), such that the hive could be ventilated in an attempt at cooling it. Although bearding is easy to observe, a weak colony, which cannot maintain an optimal temperature, will not display any obvious signs to facilitate the diagnosis of suboptimal hive temperature.

Figure 7
Figure 7

–Output of a sensor that monitors temperature (top) and relative humidity (bottom) of a newly started colony. Note the decrease in temperature to below the normal (optimal) zone, indicating that the colony was weak and could not adequately thermoregulate.

Citation: Journal of the American Veterinary Medical Association 258, 5; 10.2460/javma.258.5.471

Figure 8
Figure 8

–Output of a sensor that monitors temperature (top) and relative humidity (bottom) of a weak colony, which was enhanced by adding 1.4 kg (3.1 lb) of bees into the hive (arrow). Note that the large fluctuations of temperature and relative humidity stop after the addition of bees, indicating that the colony was able to manage its environment.

Citation: Journal of the American Veterinary Medical Association 258, 5; 10.2460/javma.258.5.471

Hive humidity is also an important parameter to monitor because studies12,13 show that abnormal levels of humidity greatly affect colony health. Relative humidity of a hive is usually maintained between 50% and 60% to ensure that the brood hatches appropriately. Relative humidity outside of this range significantly reduces the number of hatched eggs.13 Also, abnormal relative humidity often leads to chronic problems of the hive. For example, a hive with high relative humidity can attract pests, such as fungi, snails, or pill bugs or other pest insects, into the hive.

Several temperature and humidity probesa–g are commercially available. Although the manufacturers of some probes claim that their probes work with any hive type, some probes have restrictions that make them less useful. Regardless of the probe used, the author strongly advises to follow the manufacturer's recommendations for probe placement in the hive because inaccurate placement may affect a probe's sensitivity and reliability.

Colony activity and health status assessment with bioacoustics

The bioacoustics of certain sounds are used to help recognize behavioral or production problems in many species, such that a particular acoustic frequency produced by an animal equates to its health status.14 Likewise, honeybees produce various sounds to communicate among each other in the colony.1 Studies1,15 reveal that the health status and activity of a colony can be determined through analysis of a hive's acoustic characteristics. In 1967, a change in acoustic frequency prior to and during swarming was described.16 However, not until the recent (2008) modernization and miniaturization of high-tech sensor probes with microphones was acquisition of longitudinal sound recordings inside a hive possible, to document and predict swarming.17 Researchers noted that with an increase in activity in the hive, as seen with swarming, the frequency shifted from a range of 100 to 300 Hz to a range of 500 to 600 Hz.17 The sound change was the result of an intense flitting of the bees' wings, which also caused a drop of temperature from 35°C to 33°C (91.4°F).17 This shift in acoustic frequency, together with the temperature drop, can be used to predict swarming, enabling preventive action and possibly avoidance of honey or economic loss.17 A queen also emits a specific sound, described as a tooting and quacking,18 that can be used to determine whether a queen is present.

Several smartphone apps are currently available that can be used to record the sound of the hive, such that the sound could be reviewed to characterize the status of the colony and, if the sound indicates a problem, help with determining differential diagnoses (Supplementary Figure S1, available at: avmajournals.avma.org/doi/suppl/10.2460/javma.258.5.471). Other acoustic in-hive monitorsc,d,g are commercially available. Research to determine which devices are available and may work best for their purposes is encouraged because some devices may not be available in all countries.

Summary

Precision livestock farming can be optimally applied to honeybee colonies, especially with the introduction of new technology into an area in which traditional management has been used with no or few objective technological tools. As 1 author10 commented, “the employment of heat-sensitive cameras, in particular, coupled with patient behavioral observation and careful manipulation of bees and bee colonies, have provided entirely new perspectives, the consequences of which are far from being fully appreciated.” As with traditional farm animals, precision livestock farming as relates to honeybee management involves the use of sensors for the measurement of temperature and relative humidity and recording of activity and sounds, as discussed, plus other parameters. All data can be analyzed and included in modeling and prediction techniques.5 Technological advances may help veterinarians provide a more complete and accurate assessment of a hive when an apiarist requests professional advice. Technological devicesa–g should always be used in conjunction with knowledge of hives and hands-on assessment, but devices can enhance a veterinarian's capability to evaluate a honeybee colony's superorganism.

Acknowledgments

The author declares that there were no conflicts of interest.

The authors thank the Georgia Beekeeper's Association and the office of the Dean of the Veterinary College and the Department of Small Animal Medicine and Surgery, College of Veterinary Medicine, University of Georgia, for funding and maintaining the teaching hives.

Footnotes

a.

Solutionbee LLC, Raleigh, NC.

b.

BroodMinder, Stoughton, Wisc.

c.

Arnia, Newcastle, England.

d.

OSBeehives Inc, Broomfield, Colo.

e.

HiveGenie, Montgomery, Tex.

f.

GoBuzzR, Lakewood, Calif.

g.

Flir Systems Inc, Wilsonville, Ore.

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