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Flowers act as multisensory billboards to pollinators by using a range of sensory modalities such as visual patterns and scents. Different floral organs release differing compositions and quantities of the volatiles contributing to floral scent, suggesting that scent may be patterned within flowers. Early experiments suggested that pollinators can distinguish between the scents of differing floral regions, but little is known about how these potential scent patterns might influence pollinators.We show that bumblebees can learn different spatial patterns of the same scent, and that they are better at learning to distinguish between flowers when the scent pattern corresponds to a matching visual pattern. Surprisingly, once bees have learnt the spatial arrangement of a scent pattern, they subsequently prefer to visit novel unscented flowers that have an identical arrangement of visual marks, suggesting that multimodal floral signals may exploit the mechanisms by which learnt information is stored by the bee. [ABSTRACT FROM AUTHOR]

Background: Bumblebees use information provided inadvertently by conspecifics when deciding between different flower foraging options. Such social learning might be explained by relatively simple associative learning mechanism: the bee may learn to associate conspecifics with nectar or pollen reward through previous experience of foraging jointly. However, in some studies, observers were guided by choices of ‘demonstrators’ viewed through a screen, so no reward was given to the observers at the time of seeing other bees’ flowers choice and no demonstrator bee was present at the moment of decision. This behaviour, referred to observational conditioning, implies an additional associative step as the positive value of conspecific is transferred to the associated flower. Here we explore the role of demonstrator movement, and the distance between observers and demonstrators that is required for observation conditioning to take place. Methodology/Principal Findings: We identify the conditions under which observational conditioning occurs in the widespread European species Bombus terrestris. The presence of artificial demonstrator bees leads to a significant change in individual colour preference toward the indicated colour if demonstrators were moving and observation distance was limited (15 cm), suggesting that observational conditioning could only influence relatively short-range foraging decisions. In addition, the movement of demonstrators is a crucial factor for observational conditioning, either due to the more life-like appearance of moving artificial bees or an enhanced detectability of moving demonstrators, and an increased efficiency at directing attention to the indicated flower colour. Conclusion: Bumblebees possess the capacity to learn the quality of a flower by distal observation of other foragers’ choices. This confirms that social learning in bees involves more advanced processes than simple associative learning, and indicates that observational conditioning might be widespread in pollinating insects, raising intriguing questions for the underlying mechanisms as well as the spread of social information in pollinator-plant interactions. [ABSTRACT FROM AUTHOR]

In the absence of predators, pollinators can often maximize their foraging success by visiting the most rewarding flowers. However, if predators use those highly rewarding flowers to locate their prey, pollinators may benefit from changing their foraging preferences to accept less rewarding flowers. Previous studies have shown that some predators, such as crab spiders, indeed hunt preferentially on the most pollinator-attractive flowers. In order to determine whether predation risk can alter pollinator preferences, we conducted laboratory experiments on the foraging behavior of bumble bees ( Bombus impatiens) when predation risk was associated with a particular reward level (measured here as sugar concentration). Bees foraged in arenas containing a choice of a high-reward and a low-reward artificial flower. On a bee's first foraging trip, it was either lightly squeezed with forceps, to simulate a crab spider attack, or was allowed to forage safely. The foragers' subsequent visits were recorded for between 1 and 4 h without any further simulated attacks. Compared to bees that foraged safely, bees that experienced a simulated attack on a low-reward artificial flower had reduced foraging activity. However, bees attacked on a high-reward artificial flower were more likely to visit low-reward artificial flowers on subsequent foraging trips. Forager body size, which is thought to affect vulnerability to capture by predators, did not have an effect on response to an attack. Predation risk can thus alter pollinator foraging behavior in ways that influence the number and reward level of flowers that are visited. [ABSTRACT FROM AUTHOR]

Plants often attract pollinators with floral displays composed of visual, olfactory, tactile and gustatory stimuli. Since pollinators' responses to each of these stimuli are usually studied independently, the question of why plants produce multi-component floral displays remains relatively unexplored. Here we used signal detection theory to test the hypothesis that complex displays reduce a pollinator's uncertainty about the floral signal. Specifically, we asked whether one component of the floral display, scent, improved a bee's certainty about the value of another component, color hue. We first trained two groups of bumble bees (Bombus impatiens Cresson) to discriminate between rewarding and unrewarding artificial flowers of slightly different hues in the presence vs absence of scent. In a test phase, we presented these bees with a gradient of floral hues and assessed their ability to identify the hue rewarded during training. We interpreted the extent to which bees' preferences were biased away from the unrewarding hue (`peak shift') as an indicator of uncertainty in color discrimination. Our data show that the presence of an olfactory signal reduces uncertainty regarding color: not only was color learning facilitated on scented flowers but also bees showed a lower amount of peak shift in the presence of scent. We explore potential mechanisms by which scent might reduce uncertainty about color, and discuss the broader significance of our results for our understanding of signal evolution. [ABSTRACT FROM AUTHOR]

1. Most pollination biologists have used the collective pollinator visits to a plant as the measure of its pollinator attraction. However, we know very little about how many returns by the same individuals compose these visits, and how far each visitor travels after leaving the plant. Such behavioural aspects of individual pollinators are essential to understand the patterns of pollen flow among plants. 2. We observed plant visits by tagged bumble bees Bombus diversus in a field population of Cirsium purpuratum. By dissecting the collective visitation data into visits made by individual foragers, we addressed how ‘visitor density’ (number of individuals that visited a plant per 2 h) and ‘individual visitation rate’ (number of visits made by each individual per 2 h) are related to floral display size (number of flowering heads on a plant) and local flower density (number of flowering heads on neighbouring plants). We also tracked individual bees to determine how display size and local flower density of a plant influences its relative position in a bee's foraging area. 3. Plants attracted both regular visitors (bees that visited a plant more than three times per 2 h) and occasional visitors (bees that visited a plant fewer than four times per 2 h). Densities of both types of visitors increased with floral display size, whereas only occasional visitor's density increased with local flower density. 4. Individual bees preferred to visit central plants within their own foraging areas, plants with larger displays, and plants with lower local flower density. However, these preferences were independent from one another. Plants with large displays were not necessarily chosen by a bee as the centre of its own foraging area. On the other hand, plants with high local flower density were often located near the centre of a bee's foraging area. 5. The observed pollinator movements have implications for pollen flow in the plant population. Plants with larger displays probably experience greater mate diversity by attracting more occasional visitors, but they also assure matings with particular plants by increasing returns from regular visitors. [ABSTRACT FROM AUTHOR]

Pollinators collect resources that are patchy, since flowers are usually aggregated on several spatial scales. Empirical studies have established that pollinators almost invariably visit a smaller proportion of flowers as patch size increases. This has not been adequately explained. Here I present data on the payoff curve achieved by bumblebees, Bombus lapidarius, when visiting patches containing different numbers of inflorescences, and use the marginal value theorem to predict the optimum duration of stay within patches. The data demonstrate that visiting a declining proportion of inflorescences as patch size increases is an optimal strategy, if we assume that bees are attempting to maximise their rate of reward acquisition. I argue that this occurs because searching for the remaining unvisited inflorescences is easier in a small patch. On large patches, bees visited more inflorescences per patch than predicted (although still visiting a declining proportion). I suggest that this may occur because bees are using simple departure rules which result in near-optimal behaviour. I show that a departure rule based on two successive encounters with empty inflorescences closely predicts observed behaviour. [ABSTRACT FROM AUTHOR]

Pollinators often sequentially visit 1 flower type while bypassing other equally rewarding flower types, behavior known as flower constancy. One explanation for flower constancy is that pollinators use the search image of a specific flower type to efficiently find flowers because they are often cryptic. The so-called search image hypothesis predicts that temporal specialization to 1 flower type by an individual pollinator declines as flower conspicuousness increases because if flowers are conspicuous, pollinators can divide their attention among different flower types. To test this prediction, we investigated visitation sequences of individual bumble bees (Bombus ignitus) to a patch of blue and yellow artificial flowers. We used different flower sizes and interflower distances as independent determinants of flower visual size and noisiness of the background and, thus, of flower crypsis. Flower color selectivity and flower search time decreased and subsequently increased with visual size of the nearest flowers, with a minimum of approximately 15° of the visual angle. Within-bout constancy, measured as the tendency of flying to the same flower types in succession compared with the expectation of a given flower selectivity within a bout, increased with visual size of the nearest flowers. Flower selectivity and within-bout constancy did not differ among arrays that shared the same floral visual angle, indicating that visual size, rather than flight distance or flower size itself, had a substantial effect on flower choices. Our results suggest that flower visual size and background noisiness affect flower crypsis and constancy, providing support for the search image hypothesis.We experimentally show that small flower sizes and background noisiness increase short-time flower specialization by bumble bees. This is in agreement with the food searching behavior of some vertebrates that limit their search to one type of inconspicuous food while ignoring other types that provide similar benefit. Our findings indicate that this behavior, termed search image foraging, affects flower choices by bees and suggest a universal tendency to form search images in food seeking animals. [ABSTRACT FROM PUBLISHER]