7.8.2. Feeding a liquid test substance to individual adult workers in the laboratory
Individual feeding is used when specific, known quantities of test substance are required to be ingested by individual workers. Although precise, individual feeding can be extremely time-consuming and may inadvertently limit sample size.
The easiest way to orally feed workers liquid test substances individually is to provide a micropipette filled with a known quantity of test substance to an individual as detailed below. A specific quantity (i.e. the same volume for each experimental worker) between 3-10 µl should be provided. This will ensure that all workers can easily consume the same volume of homogeneously mixed test substance.
- Because some workers may not feed, it is appropriate to starve more individuals than will be required for the experiments. Pre-trials testing starvation times and test substance consumption will help determine how many workers will be needed.
- Remove a starved individual worker from its cage using a forceps by gently grasping a leg. Refer to Human et al., (2013) in the BEEBOOK paper discussing miscellaneous methods for details on how to handle adult honey bees.
- Gently grasp the wings together at their base using the thumb and index finger so that her mouthparts are exposed (i.e. wings facing down) and her stinger is pointing away from your body (Fig. 23).
- Vortex the food test substance for 5 seconds.
- Feed a specific volume (i.e. a volume between 3-10 µl) of liquid test substance to the worker using a micropipette, which allows for a precise volume to be administered. Place the end of the loaded pipette tip in front of the individual’s mouthparts or beneath the mandibles in front of the maxillae and create a small droplet at the open end of the pipette tip to promote feeding (Fig. 23). Additionally, the pipette tip can be gently placed against an antenna when the honey bee is reluctant to feed.
- Provide the remaining test substance by depressing the pipette plunger gently to ensure that nothing spills when the individual begins to feed. Discard the individual and start over using a new worker if she does not consume all of the test substance within one minute.
- Place the fed worker in an appropriate cage (section 5) with food (section 7) maintained under proper incubator conditions (section 6).
- If needed, isolate the worker for
20-30 minutes to observe regurgitation or to ensure that none of the test
substance is passed to another worker via trophallaxis. Isolation is not
required when individually feeding queens and drones because they are not food
providers (Crailsheim, 1998), and therefore will not discard the test substance
to another individual. Orally transmitted pathogens take fewer than 15 minutes
to enter the ventriculus after ingestion (Kellner and Jacobs, 1978; Verbeke et al. 1984).
typically less efficient, individuals withheld in isolation cages, such those
shown in Figs. 17 and 18, can also be fed a test substance using a micropipette,
and may minimize the handling of honey bees.
Fig. 23. A worker honey bee being individually fed using a micropipette. Note that the individual is held by gently squeezing its wings between the index finger and thumb, and that the distal part of the abdomen is pointed in such a way that the honey bee cannot sting the handler.