Original article Age-related foraging behaviour in honey bees under artificial conditions MH Pham-Delègue M Le Métayer, P Douault, C Masson INRA-CNRS (URA 1190), Laboratoire de Neurobiologie Comparée des Invertébrés, 91440 Bures-sur-Yvette, France (Received 31 May 1989; accepted 24 January 1990) Summary — The distribution of foraging among 4 worker groups of different ages was observed in a flight room. Foraging was mostly performed by the oldest workers, who came to forage first and were the most numerous. Workers from the other groups visited the feeding station infrequently until the second half of the observation period, then increased their visits. Regardless of their age group, each individual coming to forage performed a constant average level of activity, despite some vari- ability in the individual scores of visits. These experiments stressed a strong intra-age group interac- tion among a population of potential foragers, and allowed us to record data on both group and indi- vidual strategies. In conjunction with studies performed under natural conditions, our experiments conducted under artificial conditions may contribute to the analysis of some basic parameters of for- aging behaviour. Apis mellifera (ligustica x caucasica) x mellifera / foraging / age effect / division of labour / flight room INTRODUCTION worker population were removed, it was well demonstrated that workers could shift In the normal ontogeny of honey bee from one task to another (Rösch, 1930; Winston tasks, younger workers are devoted to Lindauer, 1961; Kolmes, 1985; hive duties and older workers perform for- and Fergusson, 1985). These efforts, as aging (Rösch, 1925, 1930; Ribbands, well as that of Seeley (1982) who tested 1952; Lindauer, 1953; Sekiguchi and Sak- predictions about the design of the age agami, 1966; Michener, 1974; Seeley, polyethism schedule for labour inside the 1982; Winston and Punnett, 1982; hive, were concerned with the shift of Kolmes, 1985). However, it is known that workers duties. Little time was devoted to there is considerable flexibility in the ages analyzing the division of labour among at which workers shift from hive to field du- workers all performing the task of foraging, ties, depending on internal colony require- except Seeley (1983) who explored divi- ments or external conditions. Through ex- sion of labour between scouts and recruits periments where specific groups of the in honey bee foraging, to determine the * Correspondence and reprints ecological significance of the dance lan- The foraging behaviour was observed on a guage. feeding device (Pham-Delegue and Masson, 1985). This device provided sources of sugar In this paper, we aim to detail the inter- solution associated with a scent. A 50% sucrose group or inter-individual distribution of the solution, known to be highly acceptable to hon- foraging task among a population of ey bees (Waller, 1972), was given as a reward. known age foragers. We have measured The associated scent was geraniol 1 % in paraf- fin oil. Six scented feeders were distributed on a the distribution among groups of foragers slowly rotating device (1/3 rpm). Such a device of closely related ages to assess the de- attracts a high number of foragers which can be gree of flexibility of such a task under con- fed simultaneously. trolled conditions. The experimental device was positioned at 1.50 m from the hive entrance every day be- tween 2 and 4 pm. To maintain the motivation to MATERIALS AND METHODS search for food, at times other than the 2-4 pm period, the honey bees were fed at the same lo- cation with a 50% sucrose solution and a dish of The experiments were conducted under artificial pollen at all times. No additional food was given conditions to control the constitution of the ex- in the hive. perimental colony and to standardize the obser- The device was follow- vation The were carried presented every day procedure. experiments the introduction of the last but the out in a room of 12 m3 vol, as described ing age group, flight by data below with the first Douault (1978). The light intensity was 300 lux reported begin sponta- neous on the device. the observa- with a 12 hr 12 hr The landing Thus, day - night photoperiod. tions started 31 d after the introduction of the was 24 ± 2 °C with 55% relative temperature first of workers in the hive and the The air in the room was renewed group experi- humidity. reg- mental ended 38 d later. ularly (5 times per h). period The observation was as follows: Experiments were conducted with a colony procedure within the each age- of 3-strain hybrid Apis mellifera (ligustica x cau- experimental period, marked bee was collected at its first on casica) x mellifera which produce high honey landing a feeder and labelled with a num- yields under natural conditions (Fresnaye et al, individually 1974; Comuet and Fresnaye, 1979), and which bered tag according to its rank of landing. Every 15 min, the and of the is known to exhibit a high level of foraging under identity (colour number) artificial conditions (Pham-Delegue et al, 1984). foragers on the device was recorded, up to 8 re- cordings per observation day. Experiments were The colony was first constituted of unknown carried out daily, with several days of disruption, winter worker and later age bees, replaced by leading to 22 d of observations. Mortality was workers: a old with a age-marked 2-year queen noted every observation day by collecting dead cluster of 150 worker bees of unknown age bees on the floor of the flight room. were first introduced in the experimental hive (21 x 21.5 x 27 cm), set with 5 empty combs and 1 comb filled with food; these escort bees RESULTS were later removed when arriving at the feeding device. Four samples of new born worker bees were successively introduced, leading to a the the % cu- range of 4 groups of workers differing in age by During experimental period 14 d from the first group introduced to the pre- mulative mortality per group according to ceeding one: group I (400 individuals), group II age (ie number of dead workers, including (310 individuals) introduced 3 d later, group III foragers and non-foragers, versus the ini- (440 individuals) introduced 5 d later than group tial number of workers x 100), increased II, IV introduced 6 d later group (800 individuals) of the all than group III. Each age group was identified by similarly; regardless group, points a different coloured spot painted on the thorax fitted with a curve (y = 0.71 exp (0.07 x)), of the workers. with a highly significant level of correlation (r = 0.97,82 df). Until 35 d old, mortality spectively, for the oldest foragers from was of 0-5%; between 35-70 d old, mor- groups I, II, III, IV. The statistical compari- tality increased linearly from 5-65%. son of the proportions, within the common age-range when the 4 groups were Since the mortality was approximately present (from 33-57 day old), showed that equivalent in every group, it did not affect the foraging activity was significantly high- the foraging activity differentially among er in group I than in the other groups (2- each this was group. Thus, activity report- tailed, signed ranks Mann-Whitney test, ed as the of new daily percentage foragers P < 0.01); the activity in group II was lower number of new is cumulated (the foragers than in group IV (P < 0.05). The highest observation versus the initial every day) proportion of foragers from group I number of workers (eg, 400 in group I), as reached the value of 30% workers dedicat- a function of age (fig 1). The age when the ed to foraging at the end of the experi- first member of a its first group performed ment; bees from the 3 other groups were foraging trip was, respectively, 32, 33, 28, involved in foraging with maximum values 18 day old for groups I, II, III and IV. Work- of 11-13%; group II being the least repre- ers from group IV was recorded simultane- sented. At the end of the experiment, ously; workers from groups II and III ap- groups I and II, whose foragers were the peared at the third observation day. At the oldest, reached a steady state, while the end of the experiment, workers were still number of foragers was still increasing foraging at an age of 71, 68, 63, 57 day re- among groups III and IV. Consistent with the fact that foragers 80 (17th observation day), 106 (17th ob- from group I were the most numerous, servation day), respectively, for groups I, they were the most active until the 10th II, III, IV. observation day (performing more than 75% of the visits), and were then progres- Considering the individual activity ac- sively replaced by the other groups, to a fi- cording to age group, by reporting the nal level of 16.3% visits in group I, 14.2% number of visits per observation day as a in group II, 25.5% in group III, 43% in function of particular individuals performing group IV, at the 22nd observation day. The these visits (fig 2), no difference appeared highest number of visits was 245 (6th ob- between the groups. Globally, the number servation day), 63 (16th observation day), of visits was positively correlated with the number of individuals (r = 0.93, 86 df, P < servation days when each individual came 0.001; y = 4.74 x - 1.17). Thus, each indi- to forage (fig 3). Over 22 observation days, vidual performed the same average num- 19 foragers were observed only once and ber of 4.74 visits per observation day, did not come on the following observation whatever group it came from.