11Animals socially interact during foraging to share information about the quality and location 12 of food sources. The mechanisms of social information transfer during foraging have been 13 mostly studied at the behavioral level, and its underlying neural mechanisms are largely 14 unknown. The fruit fly Drosophila melanogaster has become a model for studying the neural 15 bases of social information transfer, as fruit flies show a rich repertoire of social behaviors 16 and provide a well-developed genetic toolbox to monitor and manipulate neuronal activity. 17 Social information transfer has already been characterized for fruit flies' egg laying, mate 18 choice, foraging and aversive associative learning, however the role of social information 19 transfer on associative odor-food learning during foraging are unknown. Here we present an 20 automated foraging assay for groups of walking flies that allows studying the effect of group 21 size on the formation and expression of associative odor-food memories. We found that 22 inter-fly attraction increases with group size and that groups of flies exhibit extended odor-23 food memory expression, as compared to single or pairs of flies. We discuss possible 24 behavioral and neural mechanisms of this social effect on odor-food memory expression. 25 This study opens up opportunities to investigate how social interactions are relayed in the 26 neural circuitry of learning and memory expression. 27 28

Animals socially interact during foraging and share information about the quality and location of food sources. The mechanisms of social information transfer during foraging have been mostly studied at the behavioral level, and its underlying neural mechanisms are largely unknown. Fruit flies have become a model for studying the neural bases of social information transfer, because they provide a large genetic toolbox to monitor and manipulate neuronal activity, and they show a rich repertoire of social behaviors. Fruit flies aggregate, they use social information for choosing a suitable mating partner and oviposition site, and they show better aversive learning when in groups. However, the effects of social interactions on associative odor-food learning have not yet been investigated. Here, we present an automated learning and memory assay for walking flies that allows the study of the effect of group size on social interactions and on the formation and expression of associative odor-food memories. We found that both inter-fly attraction and the duration of odor-food memory expression increase with group size. This study opens up opportunities to investigate how social interactions during foraging are relayed in the neural circuitry of learning and memory expression.