Distinguishing signals and cues: bumblebees use general footprints to generate adaptive behaviour at flowers and nest

Chemicals used in communication are divided into signals and cues. Signals are moulded by natural selection to carry specific meanings in specific contexts. Cues, on the other hand, have not been moulded by natural selection to carry specific information for intended receivers. Distinguishing between these two modes of information transfer is difficult when animals do not perform obvious secretion behaviours. Although a number of insects have been suspected of leaving cues at food sites and nest entrances, studies have not attempted to experimentally distinguish between cues and signals. Here, we examine the chemical composition of the scent marks left by the bumblebee Bombus terrestris at food sites and compare it to those found at a neutral location. If bees are depositing a cue, we expect the same chemicals to be found at both sites, but if they deposit a signal we only expect to find the scent marks at the food site. We were also interested in identifying the chemicals left at the nest entrance to determine if they differed from those used to mark food sites. We find that bees deposit the same chemicals at food, nest and neutral sites. Therefore, bumblebees leave behind general chemical footprints everywhere they walk and we propose that they learn to use these footprints in a manner that ultimately enhances their fitness, for example, to improve their foraging efficiency and locate their nest. Experimentally, distinguishing these two modes of information transfer is crucial for understanding how they interact to shape animal behaviour and what chemical bouquets are under natural selection.