Age-related sampling of food sources in unsuccessful foraging bumblebees [Hymenoptera: Apidae: Bombus]

Naive Bombus terrestris (Linnaeus 1758) bumblebees that failed to learn to handle feeders of sucrose solution were examined for sampling frequency and duration until they stopped their feeding attempts. The number of sample-bouts [attempts to feed], the duration of each sample-bout, and the time between subsequent sample-bouts [pauses] were measured. The question was whether the age and cohort of the unsuccessful bees correlated with their feeder-sampling behaviour. Younger bees sampled the feeders more frequently, but stayed a shorter time during each sample-bout, than older bees. The duration of each separate pause was longer for older bees than for younger bees. The total sampling-time before giving up tended to be higher for the older bees. Bee cohort, and colony size at the time of observation, did not affect sampling frequency and duration in the unsuccessful foragers. For all bees, subsequent sample-bouts decreased in duration, while the duration of each subsequent pause increased. This was possibly due to negative reinforcement by the unsuccessful samples. The higher sampling frequency of the younger bees may be considered part of a first orientation and learning process of handling of food sources. The longer durations of sample-bouts and pauses in the older workers may reflect the effects of senescence on foraging behaviour.