Walter M. Farina

Social learning of floral odours inside the honeybee hive

A honeybee hive serves as an information centre in which communication among bees allows the colony to exploit the most profitable resources in a continuously changing environment. The best-studied communication behaviour in this context is the waggle dance performed by returning foragers, which encodes information about the distance and direction to the food source. It has been suggested that another information cue, floral scents transferred within the hive, is also important for recruitment to food sources, as bee recruits are more strongly attracted to odours previously brought back by foragers in both honeybees and bumble-bees. These observations suggested that honeybees learn the odour from successful foragers before leaving the hive. However, this has never been shown directly and the mechanisms and properties of the learning process remain obscure. We tested the learning and memory of recruited bees in the laboratory using the proboscis extension response (PER) paradigm, and show that recruits indeed learn the nectar odours brought back by foragers by associative learning and retrieve this memory in the PER paradigm. The associative nature of this learning reveals that information was gained during mouth-to-mouth contacts among bees (trophallaxis). Results further suggest that the information is transferred to long-term memory. Associative learning of food odours in a social context may help recruits to find a particular food source faster.

Honeybees learn floral odors while receiving nectar from foragers within the hive

Recent studies showed that nectar odors brought back by honeybee foragers can be learned associatively inside the hive. In the present study, we focused on the learning abilities of bees, which directly interact via trophallaxis with the incoming nectar foragers: the workers that perform nectar-receiving tasks inside the hive. Workers that have received food directly from foragers coming back from a feeder offering either unscented or scented sugar solution [phenylacetaldehyde (PHE) or nonanal diluted] were captured from two observational hives, and their olfactory memories were tested using the proboscis extension response paradigm. Bees that have received scented solution from incoming foragers showed significantly increased response frequencies for the corresponding solution odor in comparison with those that have received unscented solution. No differences in the response frequencies were found between food odors and colonies. The results indicate that first-order receivers learn via trophallaxis the association between the scent and the sugar solution transferred by incoming foragers. The implications of these results should be considered at three levels: the operational cohesion of bees involved in foraging-related tasks, the information propagation inside the hive related to the floral type exploited, and the putative effect of these memories on future preferences for resources.

Informational conflicts created by the waggle dance

The honeybee (Apis mellifera) waggle dance is one of the most intriguing animal communication signals. A dancing bee communicates the location of a profitable food source and its odour. Followers may often experience situations in which dancers indicate an unfamiliar location but carry the scent of a flower species the followers experienced previously at different locations. Food scents often reactivate bees to resume food collection at previously visited food patches. This double function of the dance creates a conflict between the social vector information and the private navigational information. We investigated which kind of information followers with field experience use in this situation and found that followers usually ignored the spatial information encoded by the waggle dance even if they followed a dance thoroughly (five waggle runs or more). They relied on private information about food source locations instead (in 93% of all cases). Furthermore, foragers preferred to follow dancers carrying food odours they knew from previous field trips, independently of the spatial information encoded in the dance. Surprisingly, neither odour identity nor the location indicated by the dancer was an important factor for the reactivation success of a dance. Our results contrast with the assumption that (i) followers usually try to decode the vector information and (ii) dances indicating an unfamiliar location are of little interest to experienced foragers.

Nectar feeding by the ant Camponotus mus: intake rate and crop filling as a function of sucrose concentration

In independent assays, workers of the ant Camponotus mus were conditioned to visit an arena where they found a large drop of sucrose solution of different concentrations, from 5 to 70% weight on weight (w/w). Single ants were allowed to collect the sucrose solution ad libitum, and feeding time, feeding interruptions, crop load, and intake rates were recorded. Feeding time increased exponentially with sucrose concentration, and this relationship was quantitatively described by the increase in viscosity with concentration corresponding to pure sucrose solutions. Ants collecting dilute solutions (5 to 15% w/w) returned to the nest with partial crop loads. Crop filling increased with increasing sucrose concentration, and reached a maximum at 42.6% w/w. Workers collecting highly concentrated solutions (70% w/w) also returned to the nest with a partially-filled crop, as observed for dilute solutions. Nectar intake rate was observed to increase with increasing sucrose concentration in the range 5 to 30% sucrose. It reached a maximum at 30.8%, and declined with increasing sucrose concentration. Results suggest that both sucrose concentration and viscosity of the ingested solution modulate feeding mechanics as well as the workers decision about the load size to be collected before leaving the source.

Food-exchange by foragers in the hive - a means of communication among honey bees ?

Abstract Dancing and trophallactic behaviour of forager honey bees, Apis mellifera ligustica >Spinola, that returned from an automatic feeder with a regulated flow rate of 50% weight-to-weight sucrose solution (range: 0.76–7.65 μl/min) were studied in an observation hive. Behavioural parameters of dancing, such as probability, duration and dance tempo, increased with the nectar flow rate, though with very different response curves among bees. For trophallaxis (i.e. mouth-to-mouth exchange of food), the frequency of giving-contacts and the transfer rate of the nectar increased with the nectar flow rate. After unloading, foragers often approached other nest mates and begged for food before returning to the food source. This behaviour was less frequent at higher nectar flow rates. These results show that the profitability of a food source in terms of nectar flow rate had a quantitative representation in the hive through quantitative changes in trophallactic and dancing behaviour. The role of trophallaxis as a communication channel during recruitment is discussed.

Propagation of olfactory information within the honeybee hive

Transfer of information about food source characteristics within insect societies is essential to colony-foraging success. The food odor communicated within honeybee hives has been shown to be important for food source exploitation. When successful foragers return to the nest and transfer the collected nectar to hive mates through mouth-to-mouth contacts (trophallaxis), potential recruits receiving these samples learn the food odor by associative learning. The food then becomes rapidly distributed among colony members, which is mainly a consequence of the numerous trophallaxes between hive-mates of all ages during food processing. We tested whether the distribution of food among hive mates causes a propagation of olfactory information within the hive. Using the proboscis extension response paradigm, we show that large proportions of bees of the age groups representing the main worker castes, 4 to 9-day-old bees (nurse-aged bees), 12 to 16-day-old bees (food processor-aged bees), and actual foragers (about 17+ day old bees) associatively learn the food odor in the course of processing food that has been collected by only a few foragers. Results further suggest that the information is shared more or less equally between bees of the three age groups. This shows that olfactory information about the flower species exploited by foragers is distributed within the entire colony and is acquired by bees of all age groups, which may influence many behaviors inside and outside the hive.

Trophallaxis in the honeybee, Apis mellifera (L.) as related to the profitability of food sources

Abstract Trophallaxis by honeybees was studied in two series of experiments. Honeybees were fed to satiation with sucrose solutions from 10 to 50% w/w (sugar concentration experiment), or with different amounts of a 50% w/w sucrose solution (crop load experiment). By increasing the concentration of solutions, the transfer rate was increased up to a maximum value for the 30–40% sucrose solution. With increasing crop load, maximum transfer rate was attained for satiated bees. The amount of sucrose transferred during trophallactic contact was related to the amount of sucrose carried in the honey sac for both experimental series. Results are discussed in relation to the foraging and recruiting patterns displayed by foragers.

Standard methods for behavioural studies of Apis mellifera

Summary In this BEEBOOK paper we present a set of established methods for quantifying honey bee behaviour. We start with general methods for preparing bees for behavioural assays. Then we introduce assays for quantifying sensory responsiveness to gustatory, visual and olfactory stimuli. Presentation of more complex behaviours like appetitive and aversive learning under controlled laboratory conditions and learning paradigms under free-flying conditions will allow the reader to investigate a large range of cognitive skills in honey bees. Honey bees are very sensitive to changing temperatures. We therefore present experiments which aim at analysing honey bee locomotion in temperature gradients. The complex flight behaviour of honey bees can be investigated under controlled conditions in the laboratory or with sophisticated technologies like harmonic radar or RFID in the field. These methods will be explained in detail in different sections. Honey bees are model organisms in behavioural biology for their complex yet plastic division of labour. To observe the daily behaviour of individual bees in a colony, classical observation hives are very useful. The setting up and use of typical observation hives will be the focus of another section. The honey bee dance language has important characteristics of a real language and has been the focus of numerous studies. We here discuss the background of the honey bee dance language and describe how it can be studied. Finally, the mating of a honey bee queen with drones is essential to survival of the entire colony. We here give detailed and structured information how the mating behaviour of drones and queens can be observed and experimentally manipulated. The ultimate goal of this chapter is to provide the reader with a comprehensive set of experimental protocols for detailed studies on all aspects of honey bee behaviour including investigation of pesticide and insecticide effects.

Early olfactory experience modifies neural activity in the antennal lobe of a social insect at the adult stage

In the antennal lobe (AL), the first olfactory centre of the insect brain, odorants are represented as spatiotemporal patterns of glomerular activity. Whether and how such patterns are modified in the long term after precocious olfactory experiences (i.e. in the first days of adulthood) remains unknown. To address this question, we used in vivo optical imaging of calcium activity in the antennal lobe of 17‐day‐old honeybees which either experienced an odorant associated with sucrose solution 5–8 days after emergence or were left untreated. In both cases, we imaged neural responses to the learned odor and to three novel odors varying in functional group and carbon‐chain length. Two different odor concentrations were used. We also measured behavioral responses of 17‐day‐old honeybees, treated and untreated, to these stimuli. We show that precocious olfactory experience increased general odor‐induced activity and the number of activated glomeruli in the adult AL, but also affected qualitative odor representations, which appeared shifted in the neural space of treated animals relative to control animals. Such effects were not limited to the experienced odor, but were generalized to other perceptually similar odors. A similar trend was found in behavioral experiments, in which increased responses to the learned odor extended to perceptually similar odors in treated bees. Our results show that early olfactory experiences have long‐lasting effects, reflected in behavioral responses to odorants and concomitant neural activity in the adult olfactory system.

Honeybees assess changes in nectar flow within a single foraging bout

Forager honeybees returning to the hive after a successful foraging trip unload the collected liquid to recipient hivemates through mouth-to-mouth food exchange contacts (trophallaxis). The speed at which the liquid is transferred (unloading rate) from donor to recipient is related to the profitability offered by the recently visited food source. Two of the main characteristics that define food source profitability are the flow of solution delivered by the feeder and the time invested by the forager feeding at the source (feeding time). To investigate which of these two variables is related to unloading rate, we individually trained donor foragers to a regulated-flow feeder that presented changes in the delivered flow of solution within a single foraging bout, while feeding time remained constant. With the range of flows used, bees attained maximum crop loads in all experiments. During the subsequent trophallactic encounter with an unfed recipient hivemate, unloading rate was differentially affected by the changes in flow of solution presented during the previous foraging trip at the source, depending on whether there had been an increase or a decrease of flow rate within that visit. Foragers unloaded at lower rates when they experienced a decrease in flow rate, but did not increase the unloading rate when presented with an increase at the food source. Thus, forager honeybees seem to be able to detect variations in the delivered flow of solution, since they modulate unloading rate in relation to these changes, although decreases in food value seem to be perceptually weighted in relation to increases, independently of the time invested in the food-gathering process.