2.2.2.4. Sampling odours at a whole frame scale

Volatiles can be sampled from bees enclosed on a single frame face with a partially-enclosed push-pull airflow system (Fig. 1; Carroll and Duehl, 2012). A metal and glass observation frame is pushed into the wax comb of a colony frame to enclose the bees and materials on the frame face inside. Controlled airflow from the enclosed headspace through a filter trap allows for ventilation of the bees and recovery of most volatile emissions. This approach provides a much more targeted method for in situ sampling of colony volatiles since background odours from most hive materials and outside air are excluded from the collection. 

  1. Weld together the observation frame from metal L-bar material.
    This rectangular frame should precisely fit the inside the inner perimeter of the wooden bars of the colony frame (23.2 cm x 51.1 cm for a standard Langstroth deep) out of 1.91 cm stainless steel or aluminium angle L-bar. The two edges of the L-bar extend perpendicularly down toward the wax comb and outward horizontally as a flat phalange.
  2. To provide access for air and vacuum flow into the enclosure, drill two 0.65 cm diameter port holes through the top edge of the metal frame.
    Drill the holes about 7.70 cm in from the ends of the frame. Position the holes as close to the angle of the metal frame as possible.
  3. Provide a junction (port connector) through the port holes with 4 cm pieces of 0.635 cm outer diameter (OD) Teflon tubing.
    Air and vacuum lines attach to the outside of the port connector and port connector extension tubes attach to the inside of the port connector.
  4. To enclose the bees in the metal frame, cut a piece of 0.47 cm thick piece of rectangular plate glass that extends to the outer edges of the metal frame. 
  5. Form a partial gasket between the glass plate and metal frame of the observation frame by wrapping the perimeter of the glass plate 3 times with 0.635 cm wide Teflon tape. Secure the glass plate to the phalanges of the metal frame with four small (3.75 cm) spring clamps.
  6. Connect air and vacuum lines consisting of 0.635 cm OD flexible Teflon tubing to the outside of the port connectors with slightly larger diameter pieces of Teflon tubing.
  7. To direct flow into the centre of the frame airspace, attach an 11.6 cm long piece of 0.48 cm OD Teflon tubing to the inside of each port connector.
    Orient these slightly curved port connector extension tubes toward the plate glass to avoid contact with the comb (Fig. 3).
  8. The volatile collection system flow rates must be adjusted to final rates with all of the components in place except for the enclosed frame.
    Removal of any part, especially the adsorbent filter traps, alters the resistance of the system to air flow. Likewise, changes in flow in one sampling line affects other sampling lines. Provide a slight excess of air flow (680 ml/min) to vacuum flow (515 ml/min) to ensure that no outside air enters the enclosed frame headspace. Check air and vacuum flow rates against a calibrated flowmeter placed in line after the air flowmeter and between the filter trap and the vacuum flowmeter. 
  9. Remove the adsorbent filter traps
  10. Rinse adsorbent filter traps of residual contaminants 3 times with solvent as previously described in section 2.2.2.3.
  11. Place the cleaned filters into protective tube jackets as previously described in section 2.2.2.3 (Fig. 2).
  12. Select the frame face to be sampled.
    The frame should have completely drawn comb without any major holes or gaps. Small cracks and gaps can be plugged with wax from the colony.
  13. Carefully push the metal frame into the wax comb along the inner perimeter of the wooden colony frame.
    If bees are present, move slowly to avoid crushing them.
  14. Secure the observation frame to the colony frame with four C-clamps.
  15. Remove any bees remaining on the outside of the frames.
    Keep the enclosure out of direct sunlight to avoid overheating the bees.
  16. Transfer the frame quickly to the volatile collection system site (Fig 3) and place the frame on a frame stand to hold the frame upright.
  17. To ventilate the bees, connect one observation frame port connector to the air flow. 
  18. To collect volatiles, attach the filter trap in-line to the vacuum line and the other port connector. Check the air and vacuum flow rates to see that they match the previous settings. Sampling times run from 30 minutes to 12 hours, with 3 hours being sufficient for most odour sources.
  19. End the collection by detaching the filter trap from the vacuum line. 
    Maintain an air flow through the observation frame headspace to keep the bees ventilated until you return them to their colony.
  20. Extract the trapped volatiles from the filter trap with solvent and analyse the samples as previously described in section 2.2.2.1.

 

Fig. 3. Top inside view of assembled observation frame consisting of a (1) metal frame attached to a (2) glass plate by (3) four spring clamps and a Teflon tape gasket (hidden on other side). Air and vacuum enter across the frame through (4) two port connectors and (5) two port connector extension tubes.

figure3

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