Flower constancy and memory dynamics in bumblebees (Hymenoptera: Apidae: Bombus)

Abstract

Flower visitors of several taxa (including bees, butterflies and hoverflies) are known to move preferentially between flowers of the same species, while neglecting other equally rewarding flower species. Darwin proposed memory limitations as a potential mechanistic explanation for this flower constancy behaviour. This reanalysis of a previously published dataset, relating a real-time sequential analysis of bumblebee flower choices to the distance distribution between flowers in a natural meadow, shows that Darwin was right in an unexpected way. Bees (Bombus spp) can learn how to extract rewards from several flower species, and switching between flower species does not compromise their handling efficiency (ie flower handling times do not increase following a species switch). However, bees do lose time flying between flowers. If a flower is encountered within a short time (0-2 secs) after the last flower visit, it is likely to be visited only if it is the same species. After longer intervals (3-6 secs), bees are more likely to switch to visiting different flower species. Thus, flower constancy is in part an effect based on comparing incoming stimuli (the flowers a bee detects in flight) with a transient form of short-term (working) memory, which holds the signal of the last visited flower. The relative weighting of working and reference memory changes as time passes following a flower visit. This results in a low probability of retrieving the memory for a different flower species (from that just visited) within a short time interval after the most recent flower visit (0-2 secs). This probability rises as the signal of the last visited flower fades from working memory (>2 secs).