Evidence for associative learning in newly emerged honey bees (Apis mellifera)

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Abstract
The honey bee is a model organism for studies on the neural substrates of learning and memory. Associative olfactory learning using sucrose rewards is fast and reliable in foragers and older hive bees. However, researchers have so far failed to show any significant learning in newly emerged bees. It is generally argued that in these bees only part of the brain structures important for learning are fully developed. Here we show for the first time that newly emerged honey bees are capable of associative learning, if they are sufficiently responsive to sucrose. Responsiveness to sucrose, which can be measured using the proboscis extension response (PER), increases with age. Newly emerged bees are on average very unresponsive to sucrose. We show that if newly emerged bees displaying a PER to 10% sucrose or lower sucrose concentrations are conditioned to an odour, they show significant associative learning and early long-term memory. Nevertheless, the level of acquisition is still lower than in foragers. The general assumption that newly emerged honey bees are incapable of associative learning must therefore be reconsidered. Further, our study suggests that an age-dependent increase in responsiveness to rewarding stimuli is directly related to the development of early learning abilities. The decisive influence of responsiveness to rewarding stimuli in associative learning of newly emerged bees has far reaching consequences for studies on the development of associative learning capabilities in insects and vertebrates.