xMany assays employ the excellent learning capacities of honey bees under controlled laboratory conditions (see sections 4-6), where a single bee is restrained in a holder. Although these conditions are very helpful for specific analyses, for some questions like the behaviour of the honey bee in the social context or behavioural adaptations to environmental issues, a more natural learning situation is required. Honey bee foragers typically associate the characteristics of a food source with its location. Therefore, a learning situation is required which rewards the bee in the field. In the last century, several appetitive conditioning protocols were used to train free-flying bees in the field to different sensory cues like odours and colours (von Frisch, 1919; Menzel, 1967; Waller et al., 1973; Greggers and Menzel, 1993), visual patterns and geometrical forms (Hertz, 1935; Giurfa and Menzel, 1997; Giurfa et al., 1999; Horridge, 2000) or varying tactile cues (Martin, 1965; Erber et al., 1998). The learning performance of a bee is strongly connected to the selection and combination of the sensory stimuli used. Bees, for example, learn odours faster and more reliably than colours (von Frisch, 1967; Kriston, 1973; Couvillon and Bitterman, 1988). Visual cues can be perceived at a much further distance than odours and tactile cues need a direct physical contact to be learned.
The majority of appetitive learning protocols uses sucrose as a reward. Several studies on PER-learning in the laboratory showed that the sucrose concentration of the reward and the individual responsiveness to sucrose strongly correlate with the learning performance in honey bees (see Scheiner et al., 1999, 2003, 2004, 2005). Bees that received a high-concentrated sucrose solution as reward learned faster than bees receiving a low sucrose concentration. Bees with high responsiveness to sucrose performed better than bees with low responsiveness. Similar rules between responsiveness to sucrose and appetitive learning performance in bees can be found under free-flying conditions in the field (Mujagic et al., 2010). Bees accepting low sucrose concentrations from a feeder also show a significant better appetitive learning performance than bees accepting only high-concentrated sucrose solutions. The sucrose acceptance threshold of a bee is a reliable measure of its responsiveness to sucrose in the field and can be employed to select bees for training (von Frisch, 1927; Mujagic and Erber, 2009).