Byron N Van Nest

Abstract: Honey bee foragers form time-memories that enable them to match their foraging activity to the time of day when a particular food source is most productive. Persistent foragers show food-anticipatory activity by making reconnaissance flights to the previously productive food source and may continue to inspect it for several days. In contrast, reticent foragers do not investigate the source but wait for confirmation from returning persistent foragers. To determine how persistent and reticent foragers might contribute to the colony�s ability to rapidly reallocate foragers among sources, we trained foragers to collect sucrose from a feeder at a restricted time of day for several days and then observed their behavior for three consecutive days during which the feeder was empty. In two separate trials, video monitoring of the hive entrance during unrewarded test days in parallel with observing reconnaissance visits to the feeder revealed a high level of activity, in both persistent and reticent foragers, thought to be directed at other food sources. This �extracurricular� activity showed a high degree of temporal overlap with reconnaissance visits to the feeder. In some cases, inspection flights to the unrewarded feeder were made within the same trip to an extracurricular source, indicating that honey bees have the ability to manage at least two different time memories despite coincidence with respect to time of day. The results have major implications for understanding flower fidelity throughout the day, flower constancy within individual foraging excursions, and the sophisticated cognitive management of spatiotemporal memories in honey bees.

Abstract: Forager honey bees exhibit a robust time-memory, based on an endogenous circadian clock, enabling them to schedule their flights to coincide with the nectar presentation of known food sources. They retain this time-memory for several consecutive days even in the absence of nectar rewards. Recent work has identified two classes of forager: �persistent� foragers that reconnoiter a known food source to ascertain its status and �reticent� foragers that apparently wait in the hive for a waggle dance confirming source availability. Surprisingly, a foraging group contains 40�90% persistent foragers, depending on experience at the source. What is the benefit in sending so many foragers to investigate a source when only a few foragers are required to reactivate the entire group? We used an agent-based software model to test the energetics underlying several different ratios of persistent and reticent individuals in the foraging group while varying six ecological factors: forager group size, source distance, source sucrose concentration, source availability in hours, number of days the source is known to the colony, and the rate at which new unemployed foragers appear on the dance floor. Our model demonstrates two primary explanations. First, a large number of persistent foragers is needed to ensure that at least some foragers will reconnoiter their source early in its availability, thus enabling the group to effectively exploit the source. Second, the cost of a reconnaissance flight is negligible compared to even a single successful foraging trip.

Abstract: The honey bee time-memory enables foragers to remember the time and place of a previously encountered food source, allowing them to match their behavior to daily floral rhythms of nectar and pollen presentations in nature. This phenomenon is well known but has been examined almost exclusively with artificial food sources. As a first step in understanding how the time-memory becomes established under natural conditions, we examined nectar secretion patterns in flowers of the squash Cucurbita pepo. Under greenhouse conditions, squash flowers exhibit consistent diel changes in nectar volume and concentration through anthesis. These temporal patterns are robust, persisting under simulated drought conditions in the greenhouse as well as in the field. In the presence of active pollinators, diel patterns are evident but with highly variable, severely reduced volumes. The potential consequences of these factors for acquisition of the time-memory are discussed.

Abstract: Classical experiments demonstrated that honey bee foragers trained to collect food at virtually any time of day will return to that food source on subsequent days with a remarkable degree of temporal accuracy. This versatile time-memory, based on an endogenous circadian clock, presumably enables foragers to schedule their reconnaissance flights to best take advantage of the daily rhythms of nectar and pollen availability in different species of flowers. It is commonly believed that the time-memory rapidly extinguishes if not reinforced daily, thus enabling foragers to switch quickly from relatively poor sources to more productive ones. On the other hand, it is also commonly thought that extinction of the time-memory is slow enough to permit foragers to �remember� the food source over a day or two of bad weather. What exactly is the time-course of time-memory extinction? In a series of field experiments, we determined that the level of food-anticipatory activity (FAA) directed at a food source is not rapidly extinguished and, furthermore, the time-course of extinction is dependent upon the amount of experience accumulated by the forager at that source. We also found that FAA is prolonged in response to inclement weather, indicating that time-memory extinction is not a simple decay function but is responsive to environmental changes. These results provide insights into the adaptability of FAA under natural conditions.

Abstract: Honey bees can form distinct spatiotemporal memories that allow them to return repeatedly to different food sources at different times of day. Although it is becoming increasingly clear that different behavioral states are associated with different profiles of brain gene expression, it is not known whether this relationship extends to states that are as dynamic and specific as those associated with foraging-related spatiotemporal memories. We tested this hypothesis by training different groups of foragers from the same colony to collect sucrose solution from one of two artificial feeders; each feeder was in a different location and had sucrose available at a different time, either in the morning or afternoon. Bees from both training groups were collected at both the morning and afternoon training times to result in one set of bees that was undergoing stereotypical food anticipatory behavior and another that was inactive for each time of day. Between the two groups with the different spatiotemporal memories, microarray analysis revealed that 1329 genes were differentially expressed in the brains of honey bees. Many of these genes also varied with time of day, time of training or state of food anticipation. Some of these genes are known to be involved in a variety of biological processes, including metabolism and behavior. These results indicate that distinct spatiotemporal foraging memories in honey bees are associated with distinct neurogenomic signatures, and the decomposition of these signatures into sets of genes that are also influenced by time or activity state hints at the modular composition of this complex neurogenomic phenotype.

Abstract: Classical experiments on honey bee time-memory showed that foragers trained to collect food at a fixed time of day return the following day with a remarkable degree of time-accuracy. A series of field experiments revealed that not all foragers return to a food source on unrewarded test days. Rather, there exist two subgroups: �persistent� foragers reconnoiter the source; �reticent� foragers wait in the hive for confirmation of source availability. A forager�s probability of being persistent is dependent both on the amount of experience it has had at the source and the environmental conditions present, but the probability is surprisingly high (0.4�0.9). Agent-based simulation of foraging behavior indicated these high levels of persistence represent an energetically optimal strategy, which is likely a compromise solution to an ever-changing environment. Time-memory, with its accompanying anticipation, enables foragers to improve time-accuracy, quickly reactivating the foraging group to more efficiently exploit a food source.