Bumblebees (Bombus spp.) and honeybees, Apis mellifera, both use odour cues
deposited on flowers by previous visitors to improve their foraging effici
ency. Short-lived repellent scents are used to avoid probing flowers that h
ave recently been depleted of nectar and/or pollen, and longer-term attract
ant scents to indicate particularly rewarding flowers. Previous research ha
s indicated that bumblebees avoid flowers recently visited by themselves, c
onspecifics and congeners, while honeybees avoid flowers visited by themsel
ves or conspecifics only. We found that both bumblebees and honeybees also
avoided flowers previously visited by each other when foraging on Melilotus
officinalis, that is, bumblebees avoided flowers recently visited by honey
bees and vice versa. Twenty-four hours after a visit, this effect had worn
off. Honeybees visited flowers that had been visited 24 h previously more o
ften than flowers that had never been visited. The same was not true for bu
mblebees, suggesting that foraging honeybees were also using long-term attr
actant scent marks, whilst bumblebees were not. Flowers previously visited
by conspecifics were repellent to bumblebees and honeybees for ca. 40 min.
During this time, nectar replenished in flowers. Honeybees were previously
thought to use a volatile chemical (2-heptanone) as a repellent forage-mark
ing scent. We suggest that they may be using a less volatile chemical odour
to detect whether flowers have recently been visited, possibly in addition
to 2-heptanone. (C) 2001 The Association for the Study of Animal Behaviour
.