Subjects derived from commercially obtained colonies, housed in a wooden nest-box, connected to a flight arena (a). Bees had never been previously fed in the arena, sucrose solution (50% v/v) having been placed into nest honeypots. Three colonies of number-marked bees were used sequentially.
Figure 1 (a) Demonstrator bees were pinned to four artificial flowers from an array of 12, in a rectangular wooden flight arena with a transparent lid (105×70×30cm) (b) ‘Demonstrators’ were pinned to artificial flowers. (more ...)
The arena contained 12 bicoloured yellow-and-blue artificial flowers, each comprising a dental wick within a glass vial, which held 5
ml of either sucrose solution or water (b
). This sucrose volume is sufficient to fill a bee's nectar stomach. Each flower was scented to encourage visitation (lavender oil, 5
water). Flowers were washed (50% ethanol), dried, refilled and the wick replaced, before subjects entered the arena in both learning and testing phases.
At the beginning of each trial, a bee was selected from those attempting to leave the nest, and allocated to one of four treatment groups: Naive; SC informative; SC redundant; or No SC. Groups were allocated in sequential order, to avoid over-representation of the most motivated foragers (those to leave the colony first) in any one treatment. Each group experienced different conditions during the learning phase, except for the group Naive, which did not participate in this phase.
For bees in the group SC informative, the presence of foraging conspecifics was reliably associated with a sucrose reward. Out of the 12 flowers in the arena, only four contained sucrose, and unrelated dead ‘demonstrator’ bees were pinned in a foraging position to these flowers (a
). Previous work has established that responses to dead, freshly freeze-killed, demonstrators are comparable with those of live foragers (Kawaguchi et al
; Leadbeater & Chittka 2007
). Demonstrators (eight per subject for training and testing) had been frozen to −4°C, then defrosted at room temperature and pin-mounted before use. The remaining flowers provided only water.
For group SC redundant, demonstrators were again pinned to four flowers, but in this case, all 12 flowers were rewarding. Thus, conspecific presence provided no useful information about reward levels.
Bees in group No SC were included as a control, to ensure that any observed difference in behaviour between bees in groups SC informative and SC redundant derived from differences in the value of SC during the learning phase, rather than from the differences in the variance of reward levels experienced by the two groups. These subjects foraged on an identical array to group SC informative, but no demonstrator bees were present. Each subject was allowed to forage alone for five foraging bouts (3–11
min per bout), interspersed with voluntary return visits to the nest-box to offload sucrose solution, during the learning phase.
Testing took place immediately after the learning phase, and tests were identical for every subject. All 12 of the flowers contained only water, and demonstrators were pinned to four arbitrarily chosen flowers. All flower visits completed before the bee attempted to return to the colony were recorded. Since naive bees often ceased foraging when they received no reward, we allowed up to three bouts on the same flowers in group Naive. The total number of visits recorded thus did not differ significantly between groups (Kruskal–Wallis test:
<0.7, mean=11±0.3 (s.e)). A complete dataset was collected from 10 bees in each group—40 bees in total.