FORAGING BY HONEYBEES ON CARDUUS-ACANTHOIDES - PATTERN AND EFFICIENCY

1. The relationship between the fluctuation in total quantity of sugar available in the nectar of Carduus acanthoides inflorescences and the foraging behaviour of honeybees Apis mellifera ligustica was studied in a patch under natural conditions. 2. Every day, three inflorescence populations coexisted, one for each day of the inflorescence life-span. The maximum availability of sugar occurred in second-day capitula from 12.00 to 15.00 hours. 3. Bee arrivals at the patch were positively correlated with the total availability of sugar as determined by sampling. 4. Bees responded to variation in the availability of sugar by visiting the inflorescence stage that was most rewarding at that time of day. Early in the morning, when the frequency of visits was low, the bees worked the third-day capitula, which were the best available choice at that time. Similarly, beginning at 12.00 hours, bees switched to second-day capitula. At the end of the day, some bees switched to third-day capitula where a slightly superior quantity of sugar could be obtained from a small number of florets although other bees continued to work the second-day capitula. 5. Individual bees switched to another inflorescence stage after a high proportion of their visits to a small number of capitula of one kind had provided a low reward. 6. The number of florets visited per minute per bee varied throughout the day and was positively correlated with the availability of sugar.