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We developed an experimental system for monitoring multiple bumble bees foraging on electric artificial flowers with a known rate of nectar secretion, by combining LED (Light Emitting Diode) based detection technology and RFID (Radio Frequency Identification) based identification technology. Using data on 2 workers of Bombus impatiens that were tagged with small chips and allowed to forage on these flowers in a cage, we demonstrate that our system is capable of tracking movement patterns, reward history, and foraging performance of individuals at large spatial scales.
Monitoring System
Monitoring System
The entire system is comprised of both instrumentation and software. The RFID reader, IR detector and the Feeder make up the instrumentation, while the Data logger is implemented via software. The RFID reader and IR detector are electronic sub-systems that serve as inputs to the PC. The Feeder is a mechanical system whose only function is to provide each station with a steady stream of nectar. The Data logger is a software system that runs on the PC, and gathers data based on the inputs from the RFID reader and IR detector.
Design
Design
The design of the IR detector consists of an infrared LED, and a photo-transistor that work together as an optocouple. The requirements for the optocouple pair were to have a threshold value to compare against, in order to determine whether or not a bee was at the feeder.
It was decided that for ease of use, to have the threshold permanently fixed in hardware, and leave only the light source intensity adjustable. This would permit flexibility in the system to compensate for lab environment lighting conditions, tolerances in the electronic components and, variances brought up in the construction of each module. Essentially, it allows a technician to calibrate it.
The hardware threshold was set high enough so that direct sunlight would register as a blocked beam. This prevents the sun from falsely indicated a permanently vacant feeder. The technician had to compensate by turning up the intensity of the IR LED to bias the system by holding the output of the photo-transistor above the threshold.
Control Box
Control Box
The IR detectors are all connected to a central control box, where the main power source for the IR system is connected and the intensities of the IR LEDs are adjusted. The control box also serves as a means to connect the hardware to the PC via a digital input/output card (DIO Card). The control box receives the analog signal from the photo-transistor and converts it to the appropriate electrical levels that the DIO Card requires. All circuitry other than the IR LED and the photo-transistor are contained centrally in the control box.
Synchronization
Synchronization
The RFID readers communicate with software via the USB. Due to the design of the USB protocols each reader is assigned an ID in an unpredictable manner. This means that every time the system is started, the readers loose sync with their associated IR detector.
The system is calibrated using a setup routine. The technician has to block a single IR detector and provide that RFID with a tag to read. Once the software routine detects the block signal it cycles through all the readers one at a time until a tag is read. When a reader is found that responds with a tag number, that reader is assigned to the IR detector that initiated that search cycle. The technician continues this for each and every flower in the field.
Communication
Communication
Once calibrated, the software receives the signal form the hardware by reading data from RAM, which is mapped to a known address by the DIO card. The software checks for any change in data at that location. If the change indicates that a bee has arrived at that location, the software issues the command to the RFID reader at that location to power up its antenna and to take a reading. When a change occurs that indicated that the bee has vacated the feeder, the flower location, the arrival time, the departure time, and the RFID tag number is logged to a data file. The software graphically displays when there is a bee is at a flower, and its RFID tag number once read.
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