People and bees have a long and mutually beneficial history. Ancient cave paintings in Spain depict a woman harvesting honey. The Egyptians moved bees on barges up and down the Nile. Originating near current-day Afghanistan, one species of honey bee, Apis mellifera, now lives all over the world, with the exception of the Antarctic and far Arctic regions. In every community and country, bees are kept for the honey and wax that they produce, and for the crops that they pollinate. Honey bees have recently received considerable attention as an innovative method to detect a variety of explosives, landmines and UXO.
Passive Sampling
More than 30 years ago, we at the University of Montana (UM) began sending out bees to explore and sample environments of interest, as a way of collecting and mapping data over large areas within a two-to-four-km radius of the hive.
A honey bee’s body has branched hairs that develop a static electricity charge, making them an extremely effective collector of chemical and biological particles, including pollutants, biological warfare agents and explosives. They also inhale large quantities of air and bring back water for evaporative cooling of the hive. As such, bees sample all media (air, soil, water and vegetation) and all chemical forms (gaseous, liquid and particulate).
With proper colony placement and sampling, gradient maps of the distribution of chemical or biological materials can be produced. This approach has been described in numerous studies and publications, with statistical mapping of large areas first described in Science, 1985.
Time of year, spatial distribution of the colonies, and component of the hive to be sampled all must be considered before an appropriate sampling plan can be developed and carried out.
Given an appropriate sampling design, bees can quickly provide samples of materials in the vicinity of each hive, since the foragers from each colony will make tens to hundreds of thousands of foraging forays or flights each day, with each forager returning to its home hive by nightfall. This passive collection to determine environmental presence of chemical and biological threats can provide an initial survey of landscapes. It generally identifies regions where materials of concern can be found and, with appropriate re-location of hives and re-sampling, can help narrow down the search to areas of a few hundred meters.
Active Training and Search
For several years, researchers at the University of Montana been refining the ability to condition or train bees to go to “odors of interest.” Bees have an acute sense of smell and can be trained to find explosives, bombs and landmines, as well as other chemicals of interest, including drugs and even decomposing bodies.
Defense Advanced Research Project Agency’s (DARPA’s) Controlled Biological and Biomimetic Systems Program commissioned researchers at the University of Montana to develop the methods and equipment necessary to condition bees to pass rigorous blind field trials. This research was conducted at Southwest Research Institute in San Antonio, Texas. Sandia National Laboratories (SNL) and the Air Force Research Laboratory (AFRL) collaborated, providing specific expertise in explosives and signal processing, respectively.
The researchers observed that bees behaved like a very fine-tuned, nearly ideal detector at vapor levels higher than 10 pptr (parts per trillion) from 2.4-dinitrotoulene (2.4-DNT) mixed in sand. Bees consistently detected DNT targets generating 50–80 pptr vapor. Under moist conditions, this dropped to about 30 pptr. AFRL predicted that with sufficient numbers of bees, the detection threshold could go even lower.
Bees are trained in much the same way as dogs, using traditional operant conditioning methods. The reward is food, which is associated with the odor of the chemical of interest.
Bees indicate the presence of an odor by the numbers of bees following vapor plumes toward and over the source or target. We have observed that bees detect the vapor plume several meters from the source, then navigate up the plume to the source. Numbers of bees over odor sources are integrated over time and compared to those over the rest of the area.
There is convincing evidence that bees can reliably find explosives’ vapors at levels reported to occur in landmine fields. Tests were conducted to determine whether conditioned honey bees can be used to locate buried landmines and explosives. MSU and NOAA joined in with the Light Detection and Ranging (LIDAR) technology in further trials.
UM’s earlier trials had demonstrated that honey bees can be trained to efficiently and accurately locate explosives signatures in the environment. However, it was difficult to track bees and determine precisely where the targets are located. Video equipment is not practical due to its limited resolution and range. In addition, it is often unsafe to set up cameras within a minefield.
LIDAR is a remote sensing technique that uses laser light in much the same way that sonar uses sound or radar uses radio waves. Laser light pulses are transmitted over the area where bees are trained to fly. Some of the laser light that strikes the bees is scattered back to a detector collocated with the laser. The time between the outgoing laser pulse and the return signal is used to measure the distance from the bees to the LIDAR. By using a narrow laser beam and scanning this beam over time, one can produce an accurate map of the location of the bees. Since LIDAR can provide both the range and the coordinates of the bees over targets, the location of buried munitions can be mapped for subsequent removal.
Bees, dust and hard objects produce a back-scatter signal that is larger than the typical atmosphere. It is possible to discriminate different objects with fluorescence LIDAR, but the bees for these tests, the density of bees over the minefield were compared to an adjacent control area. Other insects may have been detected, but their numbers were small compared to those of the bees.
SNL also conducted vapor plume and soil sampling, followed by chemical analysis for explosives, to verify bee localization of mined areas. A NOAA LIDAR system that swept the field every 26 seconds. Bee conditioning was accomplished using a new, pressurized, digitally-controlled (hands-off) bee conditioning system.
The objectives for the Ft. Leonard Wood tests were to:
1. Show that area reduction (i.e., discrimination of mined versus unmined areas) can be performed by conditioned bees
2. Show that bees can locate individual mines or at least small clusters of mines
3. Demonstrate that LIDAR can be used as an effective tool for mapping density (numbers) of conditioned bees focused on explosive vapors emitted from buried mines
Results of Ft. Leonard Wood Bee Trials
All of the data forms (LIDAR, video, visual counts) indicate that area reduction, identification, and ranking (strength of the plume source) could be determined using bees.
The following are some results of the trials:
1. LIDAR was able to detect individual bees at long ranges of hundreds of meters. Fixed and scan modes were tested and proved capable of providing bee location and range data within a few centimeters’ resolution.
2. Video and visual counts showed that bees found both individual mines and clusters of mines within the test area.
3. Preliminary chemical analyses results indicate that numbers of bees correlate with plume concentrations. Ten of 12 vapor sources identified by the initial chemical analysis have already been detected by a partial data set of bee counts (based on only four days of the data). The contour maps of the landmine field, based on the visual and partial video counts of bees and on the cumulative results of three different chemical sampling methods illustrate the degree of localization that was achieved.
4. In the designated, unmined, blank or control area, the LIDAR detected a concentration of bees over a spot in front of the minefield. When that spot was later sampled, it was found to be contaminated with TNT, 2.4-DNT and 4-amino DNT.
5. The pressurized conditioning system worked flawlessly, and Missouri bees conditioned as readily as any of the bees that we have previously worked with in Montana and Texas.
The bees also made a surprise detection of a contaminated site where none was expected. This example proves the importance of combining a high-resolution tracking system such as LIDAR with properly conditioned bees as a system for detecting explosives or residues.
Limitations and Agricultural Benefits
Bees do not fly at night, during heavy rain or wind, or when temperatures drop to near or below freezing. As such, the use of bees is seasonal in temperate climates. Bees are active year-round in tropical regions.
Bees have several advantages in addition to their keen sense of smell and wide area coverage:
1. Bees can be conditioned and put into use in one to two days.
2. Local bees and beekeepers are used.
3. Overall costs are far lower than for dog teams.
4. Bees are essential to re-vitalizing agriculture in war-torn countries.
Whether the beekeeper uses sophisticated equipment or keeps bees in a hollow log is of little consequence. It is the knowledge of the beekeeper about his or her bees and area that is important. Beekeepers can be trained to use micro-processor controlled food delivery and conditioning systems or a decidedly simpler system, using mine-contaminated soils, conditioning syrup and a squirt bottle. If necessary, binoculars or simple video cameras suspended from a boom or wire can provide short-distance (within yards) observations of bees.
A critical humanitarian demining issue is the amount of arable land that has been mined; putting agricultural fields back into production is a major objective. War often disrupts and sometimes destroys bees, beehives and beekeeping. The first step in economic development often focuses on re-establishing beekeeping, since bees are essential to the pollination of many crops and agricultural productivity. Use of honey bees for humanitarian demining addresses both issues—clearing of croplands and restoring of beekeeping and agriculture.
Acknowledgements:
Science, 1985, Issue 1
DARPA
Space and Naval Systems Center, San Diego, CA.
Special thanks to Lee Spangler, MSU; Jim Wilson, NOAA; and Larry Hall and Joe Browning, SKE
References
“Pollution Monitoring of Puget Sound with Honey Bees.” Science. 227:632–634, 1995.
“Honey Bees: Estimating the Environmental Impact of Chemicals.” Taylor and Francis, New York, 2002.
“Vehicle Bomb Detection Video.” Online video: http://beekeeper.dbs.umt.edu/bees/videos. September 2001.
“Alternatives for Landmine Detection.” MacDonald, et al. Online document: http://www.rand.org/publications/MR/MR1608/. January 2003.
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