14.3. Determining sucrose acceptance thresholds in the field
By reducing the concentration of sucrose in the feeder, one can determine under free-flying conditions at which concentration an individual bee gives up foraging for sucrose. This concentration can be defined as the sucrose acceptance threshold of an individual.
1. Mark approximately 50 foragers visiting an artificial sucrose feeder on their abdomen or thorax (see section 2.3.).
2. Reduce the concentration in the feeder logarithmically in 20-min steps (30 % → 10 % → 3 %; Fig. 37C).
3. Record for each individual marked bee the number of visits to each presented concentration.
4. After testing bees at each concentration for 20 min, assign each individual to one of two groups: (1) Bees accepting sucrose concentrations of 30 % (w/w), but do not accept lower concentrations; (2) Bees accepting concentrations down to 3 % (w/w).
When you train the two groups of bees in the field (see section 14.4.), you will notice that bees accepting only high sucrose concentrations (group 1) will perform poorly, while bees accepting low sucrose concentrations (group 2) will learn very well, even if the sucrose concentration used as reward is not very high.