Overnight memory retention of foraging skills by bumblebees is imperfect

Newly emerged bees learn to forage more efficiently as they gain experience. To test the hypothesis that foraging efficiency would increase as bees gain experience during the day, but would decrease after a night, owing to loss of memory, naive Bombus terrestris bumblebees were allowed to forage on two clusters of artificial flowers of unequal profitabilities during 3 consecutive days. Nectar intake rate, percentage of visits to the more profitable cluster, probing time and time intervals between visits were computed as measures of the bees' foraging efficiency. Nectar intake rates increased significantly during the day, and decreased partially but significantly after a night. They varied greatly between bees. The bees did not show a preference for one of the clusters at the onset of the experiment, and none consistently increased their visits to the more profitable cluster during single observation days. Most individuals did not visit the higher-reward cluster exclusively by the end of the third day. However, visits to the higher-reward cluster did increase significantly when the first day of observation was compared with the third day. Preference for the higher-reward cluster increased after the first night but decreased significantly after the second night. Probing time and inter-visit intervals decreased significantly during observation days, and increased significantly after a night. The results indicate that bees learn to approach and probe flowers faster, as they gain experience, during a foraging day, but that these skills are partially forgotten overnight. Patch preference is formed more slowly. Once formed, it is also weakened overnight. Such partial forgetting may aid the bee in reacting quickly to overnight changes in resource profitability by modifying flower choices and handling techniques.