Bumble bees (Bombus terrestris) use time-memory to associate reward with color and time of day

Abstract

Circadian clocks regulate ecologically important complex behaviors in honey bees but it is not clear to what extent these observations can be extended to other species of bees. One key behavior is time-memory allowing foraging bees to precisely time flower visitation to periods of maximal pollen or nectar availability and reducing the costs of arriving at a flower patch at the wrong time. It is unclear whether other bees such as bumble bees, who live in smaller societies and forage over shorter distances than honey bees, can similarly associate a reward with time of day. We trained individually marked bumble bee (Bombus terrestris) workers to forage for sugar syrup in a flight cage with yellow or blue feeders rewarding either during the morning or evening. After a two-weeks training session, we recorded all visitations to colored feeders filled with only water. We repeated this experiment twice, with different colonies. We found that bees tended to show higher foraging activity during the morning and evening training sessions compared to other times during the day. Trained bees were more likely to visit feeders with colors rewarding compared to non-rewarding at the same time of day during the training sessions and with relatively fewer mistakes. Our findings lend credence to the hypothesis that efficient time-memory is not limited to species such as honey bees that evolved sophisticated social foraging behaviors over large distances.