A test of spatial memory and movement patterns of bumblebees at multiple spatial and temporal scales

Naive bumblebee foragers appear to use movement rules at small spatial and temporal scales, but it is not clear whether these rules determine movement patterns as the scales increase. One strategy for efficient foraging used by bumblebees is near-far search, involving short flights when in good patches of flowers and longer flights when in poor patches. Bumblebees also demonstrate the use of a spatial memory strategy by returning repeatedly to patches of flowers, and even following the same route between flowers, over periods of days. We attempted to determine at what spatial scales bumblebees use spatial memory while foraging within a patch and after how many flower visits spatial memory outweighs near-far search. Bumblebees in the laboratory foraged on a 4 x 4 array of artificial flowers with distances ranging from 10 to 80 cm between flowers in two simple spatial patterns. The proportion of visits to flowers containing a sucrose reward was monitored for either 100 or 400 flower visits in two separate experiments, after which the locations of the rewarding and nonrewarding flowers were interchanged, producing a mirror image. A drop in accuracy after the mirror image switch would indicate that the bees had memorized the location of rewarding flowers. Mirror image tests, and comparisons to a simulation model of near-far search based on actual flight distances, indicate that naive bumblebees used near-far search on flowers 10 cm apart but increasingly used spatial memory as experience and spatial separation increased. Bumblebees thus have multiple tactics available to forage efficiently in different environments.