Rewarding Flowers Research Articles

Assessing the analytical reliability of traditional and novel sampling methods for the study of flower rewards quality

AbstractPollinator insects are declining worldwide also due to the alteration of their diet which plays a pivotal role in influencing their health status. Despite interspecific and intraspecific diversity in the diet, pollinators completely or partly rely on pollen and nectar as food sources. A precise characterization of the chemical composition of these flower resources represents a key step in the definition of pollinators' nutritional ecology. However, pollen and nectar represent challenging sources to collect and analyze, especially due to their small amounts per flower, and the application of suitable sampling and analysis tools is a pivotal step to perform dedicated studies and comparisons. Here, we compared a recently proposed tool based on a portable vacuum cleaner for floral pollen collection (E‐PoSa, i.e., Electronic Pollen Sampler) with traditional pollen sampling methods (i.e., anther collection and anther sieving) together with the evaluation of different nectar sampling techniques (i.e., centrifugation, microcapillaries, washing, and microrinsing) by looking at the differences in their quantitative recovery as well as their chemical profiling. Pollen and nectar were collected from three model flower species each. Our results demonstrated that different collection methods introduce biases in the nutritional profiling of floral rewards and specifically: (1) underestimation of the pollen protein and lipid content in the anther collection method; (2) reduction in the volume of recovered nectar by centrifugation; (3) overestimation of the glucose content in the nectar collected by flower washing and underestimation of the glucose content by microrinsing; and (4) relevant biases in the phytochemical profiles of pollen and nectar by analyzing the whole anthers and the nectar collected by washing the entire flower. Differences in methods were not directly related to the different productivity of pollen and nectar across species. The final goal of the study is to propose standardized, comparable, and easily accessible strategies for the study of flower resources that ultimately impact on pollinators' nutritional ecology. Acknowledging the potential influences of the sampling techniques and moving toward shared field protocols will advance the comprehension of species interactions, foraging patterns, and pollinators' nutritional needs.

E‐PoSa: A novel and effective tool for sampling pollen directly from flowers

Abstract Pollinator insects are declining worldwide, also due to the alteration of their diet with severe implications on their health status. Pollinators diet relies mainly on flower rewards (i.e. pollen and nectar), and a precise characterization of their chemical composition is crucial in defining pollinators' nutritional ecology. In this context, the pollen represents a challenging source to investigate, especially due to operative challenges during collection operations and to the small amounts produced per flower. Here, we designed and tested a novel, easy‐to‐assemble tool for pollen sampling: E‐PoSa (Electronic Pollen Sampler), based on the use of a portable vacuum cleaner. We compared it with some of the most used sampling methods for pollen (i.e. anthers sieving and sampling of the whole anthers) by looking at the differences in their quantitative recovery and nutritional profile. Its applicability in ecological studies was also corroborated by an assessment of its recovery rate obtained from a panel of wildflower species in an operational environment. The data obtained showed a significantly higher pollen recovery capacity of E‐PoSa compared with the conventional sieving approach and the success in retrieving enough pollen to conduct phytochemical analyses from a broad range of flower morphologies in the field. Our results also demonstrated that high purity pollen can be collected with E‐PoSa and that the device does not introduce any significant variation in the nutritional analysis compared with the conventional sieving. This new sampling approach represents a cheap and easy‐to‐assemble tool encouraging its future use not only in the field of pollen nutrition but also in a wide variety of other contexts related to pollination ecology. Acknowledging the potential influences of the sampling techniques and moving towards shared standardized field protocols will advance the comprehension of species interactions and foraging patterns of pollinators and their nutritional needs.

Land use influences the nutrient concentration and composition of pollen and nectar rewards of wildflowers in human-dominated landscapes

Plant biodiversity is crucial to satisfy the trophic needs of pollinators, mainly through nectar and pollen rewards. However, a few studies have been directed to ascertain the intraspecific variation of chemical features and the nutritional value of nectar and pollen floral rewards in relation to the alteration of landscapes due to human activities. In this study, by using an existing scenario of land use gradients as an open air laboratory, we tested the variation in pollen and nectar nutrient profiles along gradients of urbanization and agriculture intensity, by focusing on sugar, aminoacids of nectar and phytochemicals of pollen from local wild plants. We also highlighted bioactive compounds from plants primary and secondary metabolism due to their importance for insect wellbeing and pollinator health. We surveyed 7 different meadow species foraged by pollinators and common in the main land uses studied. The results indicated that significant variations of nutritional components occur in relation to different land uses, and specifically that the agricultural intensification decreases the sugars and increases the antioxidant content of flower rewards, while the urbanization is positively associated with the total flavonoid content in pollen. These effects are more evident in some species than in others, such as Lotus corniculatus L. (Fabaceae) and Malva sylvestris L. (Malvaceae), as shown by the untargeted metabolomic investigation. This study is crucial for understanding the nutritional landscape quality for pollinators in association to different land uses and sets a base for landscape management and planning of pollinator-friendly strategies by improving the quality of plant rewards to provide benefits to pollinator health in various environmental contexts.

Nitrogen addition affects floral and vegetative traits, reproduction, and pollinator performance in Capsicum annuum L.

It has been demonstrated that nitrogen (N) addition alters flower morphology, floral rewards and pollinator performance. However, little is known about the effects of N addition on plant reproduction, including fruit set and seed set during selfing and outcrossing, floral and vegetative traits, and pollinator performance. We hypothesized that N addition would influence fruit set, seed set in selfed and outcrossed flowers, the relationship between vegetative and flower traits, and pollinator performance. A 2-year pot experiment was conducted in which Capsicum annuum was exposed to three levels of relatively short-term N supply, i.e. 0 g m-2 (no N addition, as a control), 4 g m-2 (4N) and 16 g m-2 (16N), which are equivalent to about 0-, 1- and 4-fold of the peak local N deposition. We measured flower rewards, flower morphology, flowering phenology, as well as pollinator visitation rate, fruit set and seed set by self- and outcross-fertilization of C. annuum. The four levels of N addition increased plant biomass, biomass allocation to flowers, flower size, stigma-anther separation, nectar production and pollen production, resulting in an increase in pollinator visitation and fruit set. Nevertheless, the control and 16 levels of N addition reduced plant biomass, biomass allocation to flowers, flower size and stigma-anther separation, and nectar and pollen production, and consequently decreased pollinator visitation and fruit set. Exclusion of pollinators and hand-pollination experiments revealed that low levels of N addition were associated with high seed set in outcrossed flowers; however, this trend was reversed in flowers grown in the control and 16N treatments. Our results suggest that an optimal level of 4N can enhance the correlation between flower traits, pollinator performance and plant reproduction. Our findings cast new light on the underlying mechanisms of plant-pollinator interactions and plant adaptation to nitrogen deposition.

The role of within-plant variation in nectar production: an experimental approach.

Nectar, a plant reward for pollinators, can be energetically expensive. Hence, a higher investment in nectar production can lead to reduced allocation to other vital functions and/or increased geitonogamous pollination. One possible strategy employed by plants to reduce these costs is to offer variable amounts of nectar among flowers within a plant, to manipulate pollinator behaviour. Using artificial flowers, we tested this hypothesis by examining how pollinator visitation responds to inter- and intra-plant variation in nectar production, assessing how these responses impact the energetic cost per visit. We conducted a 2 × 2 factorial experiment using artificial flowers, with two levels of nectar investment (high and low sugar concentration) and two degrees of intra-plant variation in nectar concentration (coefficient of variation 0 and 20 %). The experimental plants were exposed to visits (number and type) from a captive Bombus impatiens colony, and we recorded the total visitation rate, distinguishing geitonogamous from exogamous visits. Additionally, we calculated two estimators of the energetic cost per visit and examined whether flowers with higher nectar concentrations (richer flowers) attracted more bumblebees. Plants in the variable nectar production treatment (coefficient of variation 20 %) had a greater proportion of flowers visited by pollinators, with higher rates of total, geitonogamous and exogamous visitation, compared with plants with invariable nectar production. When assuming no nectar reabsorption, variable plants incurred a lower cost per visit compared with invariable plants. Moreover, highly rewarding flowers on variable plants had higher rates of pollination visits compared with flowers with few rewards. Intra-plant variation in nectar concentration can represent a mechanism for pollinator manipulation, enabling plants to decrease the energetic costs of the interaction while still ensuring consistent pollinator visitation. However, our findings did not provide support for the hypothesis that intra-plant variation in nectar concentration acts as a mechanism to avoid geitonogamy. Additionally, our results confirmed the hypothesis that increased visitation to variable plants is dependent on the presence of flowers with nectar concentration above the mean.

Non-species-specific pollen transfer and double-reward production in euglossine-pollinated Vanilla.

Commonly attributed to orchids, the pollen movement in Vanilla has been associated with food deception and specific plant-pollinator relationships. This study investigated the role of flower rewards and pollinator specificity in the pollen transfer of a widely distributed member to the euglossinophilous Vanilla clade, V.pompona Schiede using data collected from Brazilian populations. These included investigations on morphology, light microscopy and histochemistry, and analysis of flowers scent using GC-MS. The pollinators and the mechanisms of pollination were recorded through focal observations. The yellow flowers of V. pompona are fragrant and offer nectar as reward. The major volatile compound of the V. pompona scent, carvone oxide, shows convergent evolution in Eulaema-pollinated Angiosperms. The pollination system of V. pompona is not species-specific, but its flowers are strongly adapted to pollination by large Eulaema males. Pollination mechanism is based in a combination of perfume collection and nectar seeking. The dogma of a species-specific pollination system based on food deception in Vanilla has been broken with the increase in studies on this Pantropical orchid genus. Here, least three bee species and dual reward-offering are involved in pollen transfer in V.pompona. Visitation frequency of bees collecting perfumes, used in courtship by male euglossines, is higher than in searching for food, as short-lived young euglossine males seem to be more interested in sex than food. A pollination system based on offering both nectar and perfumes as resources is described for the first time in orchids.

Bumblebee flower constancy and pollen diversity over time.

Bees often focus their foraging effort on a few or even a single flower species, even if other equally rewarding flower species are present. Although this phenomenon-called flower constancy-has been widely documented during single foraging trips, it is largely unknown if the behavior persists over longer time periods, especially under field conditions with large temporal variations of resources. We studied the pollen diet of individuals from nine different Bombus terrestris colonies for up to 6 weeks, to investigate flower constancy and pollen diversity of individuals and colonies, and how these change over time. We expected high degrees of flower constancy and foraging consistency over time, based on foraging theory and previous studies. Instead, we found that only 23% of the pollen foraging trips were flower constant. The fraction of constant pollen samples did not change over the study period, although repeatedly sampled individuals that were flower constant once often showed different preferences at other sampling occasions. The similarity of pollen composition in samples collected by the same individuals at different occasions dropped with time. This suggests that the flower preferences change in response to shifting floral resources. The average diversity of pollen from single foraging trips was around 2.5 pollen types, while the colony-level pollen diversity was about three times higher. How rapidly preferences change in response to shifting resources, and if this differs between and within bee species depending on factors such as size, should be the focus of future research.

Flower size affects bee species visitation pattern on flowers with poricidal anthers across pollination studies

Flower size is a crucial trait for pollinator attraction. In flowers with poricidal anthers, the plant constraints the pollinator's access to the flower's rewards by enclosing pollen grains in poricidal anthers. The pollen is only released by mechanical vibrations applied mainly by bee species during buzz pollination. Although buzz-pollinated flowers exhibit a large size variation across species, their influence over patterns of flower visitation by different pollinator species remains to be elucidated. To fill such gap, we asked how flower size influences flower visitor assemblage, especially bees, across plant species and how flower size is related to body size and vibrating behavior of the most frequent bee species. We hypothesized that the assemblage of animals, especially bees, visiting larger flowers have higher taxonomic and functional diversity than smaller flowers, and the most frequent bee species visiting larger flowers have larger body size and a mandatory vibrating behavior. To test this hypothesis, we conducted a systematic review of pollination studies that reported patterns of flower visitation in plant species with poricidal anthers, describing the relationship between flower size and flower visitor metrics. We found that large-flowered species were visited by three times more species than small-flowered species, including vibrating and non-vibrating bee species. Unlike our expectations, non-vibrating bees were largely absent from small-flowered species. The most frequent bee species visiting flowers, irrespective of flower size, exhibited vibrating behavior. The most frequent bee species visiting large flowers were twice the body size of those visiting small flowers, highlighting a morphological match between flowers and pollinators. Although larger flowers are more susceptible to interactions with exploiters, reproductive success should be favored owing to the higher probability of their interaction with vibrating, large-bodied bee species. Still, a reduction in flower size probably prevents interactions with non-vibrating bees, while favoring vibrating small-bodied bee species.

Evidence of floral rewards in Brasiliorchis supports the convergent evolution of food-hairs in Maxillariinae.

Angiosperms distributed over a large geographical area may display considerable phenotypic variation that can be recognized at morphological and micromorphological levels. Here, we investigate the pollination biology and the presence of floral rewards in Brazilian populations of the widely distributed orchid, Brasiliorchis picta. Based on the new data presented here this study investigates the evolution of floral rewards in Maxillariinae, and tests for the occurrence of convergent evolution of food-hairs in this subtribe. Micromorphological and histochemical analyses of the labellar tissues were conducted, together with chemical analysis of fragrance and experiments involving the use of chemical baits. The evolution of floral rewards in Maxillariinae were addressed. Microscopy revealed that B. picta offers food-hairs as a reward. Fragrance is produced by abaxially located labellar epidermal papillae. The main compound present in our samples (2-phenylethanol) also occurs in the aggregation pheromone produced by the mandible glands of pollinators, Meliponini bees. Our analyses indicate a high diversity of flower rewards and pollinators displayed by members of Maxillariinae, and support that edible trichomes evolved independently five times in the subtribe. The high diversity of floral rewards and pollinators displayed by members of Maxillariinae suggests that different pollinator pressures are involved in the evolution of this neotropical subtribe. In addition, the offering of food-hairs, which are generally infrequently encountered in Orchidaceae, arose by convergent evolution in Maxillariinae.

Changes in Florets’ Vertical Direction within Inflorescence Affects Pollinator Behavior, and Fitness in Trifolium repens

Ecological interactions between flowers and pollinators greatly affect the reproductive success. To facilitate these interactions, many flowers are known to display their attractive qualities, such as scent emission, flower rewards and floral vertical direction, in a rhythmic fashion. However, less is known about how plants regulate the relationship between these flower traits to adapt to pollinator visiting behavior and increase reproduction success. Here we investigated the adaptive significance of the flower bending from erect to downward in Trifolium repens. We observed the flowering dynamic characteristics (changes of vertical direction of florets, flowering number, pollen grain numbers, pollen viability and stigma receptivity over time after blossom) and the factors affecting the rate of flower bending in T. repens. Then we altered the vertical direction of florets in inflorescence of different types (upright and downward), and compared the pollinator behaviors and female reproductive success. Our results showed that florets opened sequentially in inflorescence, and then bend downwards slowly after flowering. The bending speed of florets was mainly influenced by pollination, and bending angle increased with the prolongation of flowering time, while the pollen germination rate, stigma receptivity and nectar secretion has a rhythm of “low-high-low” during the whole period with the time going. The visiting frequency of all the four species of pollinators on upward flowers was significantly higher than that of downward flowers, and they especially prefer to visit flowers with a bending angle of 30°–60°, when the flowers was exactly of the highest flower rewards (nectar secretion and number of pollen grains), stigma receptivity and pollen germination rate. The seed set ratio and fruit set ratio of upward flowers were significantly higher than downward flowers, but significantly lower than unmanipulated flowers. Our results indicated that the T. repens could increase female and male fitness by accurate pollination. The most suitable flower angle saves pollinators’ visiting energy and enables them to obtain the highest nectar rewards. This coordination between plants and pollinators maximizes the interests of them, which is a crucial factor in initiating specialized plant-pollinator relationships.

Habitat quality and surrounding landscape structures influence wild bee occurrence in perennial wildflower strips

Perennial wildflower strips (WFS) are known to have positive effects on wild bees in intensively used agricultural landscapes. Little knowledge exists, however, about the drivers of wild bee occurrence and if Red List species also profit from this agri-environmental scheme (AES). Therefore, we studied wild bees on transects along 20 four- to five-year-old WFS and in 10 cereal fields without AES (CONTROL sites) in differently structured landscapes across Saxony-Anhalt (Germany). In addition to local site parameters, we measured parameters of landscape structure in a 1 km radius of the WFS and CONTROL sites. The overall species richness of wild bees (125 species in total, 23 on average), including numerous specialist and Red List species, indicates a high attractiveness of perennial WFS sown with 30 native forbs. In CONTROL fields, 11 bee species (on average only one) were found.The species richness and abundance of wild bees were positively affected by local site conditions of the WFS and CONTROL sites, such as the overall number of sown and spontaneous forbs, the amount of flower rewards of sown forbs available to pollinators (Pollinator Feeding Index), and negatively by the cover of grasses. Therefore, seed mixtures of future AES should comprise a high diversity of wildflower species relevant as pollen sources for wild bees. The share of Red List wild bee species was strongly influenced by the landscape context and increased e.g. with Shannon landscape diversity and the availability of non-forest woody habitats and water bodies in the 1 km surroundings. These results suggest that besides the establishment of high-diversity WFS, semi-natural habitat structures have to be promoted to preserve rare wild bees especially in structurally simple agricultural landscapes.

Association of flower color with pollen reward may explain increased bumblebee visitation to the Scotch broom yellow morph

Given that pollinators usually visit flowers for hidden rewards, they need to rely on floral traits that indicate reward status (“honest signals”). However, the relationship between pollination, honest signals, and floral rewards is little documented in natural conditions. The Scotch broom (Cytisus scoparius) is an invasive shrub with polymorphism in the color of its flowers that can be yellow, orange, or red. In three areas dominated by the Scotch broom, we described the abundance of the floral morphs and estimated bumblebee (Bombus terrestris) visitation rate. We examined whether bumblebee visitation to the floral morphs was related to pollen reward. We collected flowers and classified their stamens according to their function: reward or pollen export. Then, we measured anther size and estimated pollen quantity. The yellow morph was more abundant and more visited by bumblebees than the orange and red morphs. The yellow flowers did indeed offer more pollen than the other morphs and this occurred only for rewarding anthers, suggesting that bumblebees could use yellow color as an honest signal to visit the most rewarding flowers. We discuss whether innate and/or learned preferences of bumblebees can explain why the yellow morph is more visited, pollinated, and abundant, while the other morphs are maintained at a lower frequency. This is one of the few field works that shows that variation in intra-specific floral traits is associated with variation in floral reward and pollinator visitation rate, helping to understand the foraging preferences of pollinators and the coexistence of floral morphs in nature. Clinical trials registration: Not applicable.

Nectar Production and Spectrum of Insect Visitors in Six Varieties of Highbush Blueberry (Vaccinium corymbosum L.) in SE Poland

Abstract The attractiveness of plants to pollinators depends strongly on flower rewards, especially nectar and pollen. Nectar mass, sugar concentration, and sugar mass are known to influence the spectrum and abundance of insect visitors. Respective data on nectar secretion in highbush blueberry ( Vaccinium corymbosum ) under the climatic conditions of Poland are scarce. This study was conducted in 2002–2005 to assess flower abundance, nectar production, and insect visitors in six varieties of V. corymbosum in Niemce, SE Poland. Flower abundance ranged from 1.63 ± 0.64 (‘Darrow’) to 4.07 ± 0.95 in thousands of flowers per shrub (‘Northland’). Nectar mass, sugar concentration, and nectar sugar mass increased with flower age, peaking between the sixth and ninth day. Significant differences in nectar characteristics occurred between years and between varieties. ‘Bluecrop’ and ‘Darrow’ produced the largest nectar mass (19.08 ± 7.09 and 16.60 ± 8.31 mg nectar per flower, respectively) and nectar sugar mass per flower (6.39 ± 1.52 and 5.76 ± 1.51 mg sugar per flower, respectively). The estimated sugar yield in the studied V. corymbosum varieties ranged from 9.4 ± 3.3 to 20.7 ± 3.8 g sugar per shrub (‘Croatan’ and ‘Bluecrop,’ respectively). Regarding insect visitors, only honey bees and bumble bees were observed. Honey bees comprised 81%–98% of the total number of observed insect visitors. Highbush blueberry, due to abundant blooming and high per-flower sugar yield, is thus a good source of nectar sugars for honey bees.

Do visual traits honestly signal floral rewards at community level?

Abstract The high variability observed in floral traits has been interpreted as resulting from the adaptation of plants to pollinators, as the latter present innate preferences for specific floral traits and impose selection over them. However, some pollinators such as bees can learn to associate floral signals with rewards, thus increasing floral constancy on more rewarding flowers. The integration of all these rewards and cues is markedly important at community level, where co‐flowering species compete for pollinators. In order to verify the honesty of the above‐mentioned signals, we examined the association between floral visual signals (size, colour, symmetry and floral display) and rewards (pollen and nectar) for 98 species in a Mediterranean community. The associations between floral traits were analysed considering the phylogenetic relationship between the different species. Flower colour, size, pollen volume or amount of sucrose exhibited no phylogenetic signal, which suggests an adaptive evolution in response to different conditions in the pollinator community. Flower size was seen to constitute the most honest signal for pollinators, as this was significantly associated with quantities of pollen and nectar. In contrast, nectar concentration was observed to be positively associated with chromatic contrast. We detected no relationship between flower shape and rewards, on the one hand, nor between flower display and rewards, on the other. Our study unequivocally demonstrates the correlation between rewards and the visual signals perceived by bees, the most effective pollinators in the Mediterranean Basin. In the community studied, bees employed flower size at longer distances and chromatic contrast at shorter distances to predict rewards. The limited number of studies existing in this sense indicates that this kind of association appears to be community specific.

Pollinator parasites and the evolution of floral traits.

The main selective force driving floral evolution and diversity is plant–pollinator interactions. Pollinators use floral signals and indirect cues to assess flower reward, and the ensuing flower choice has major implications for plant fitness. While many pollinator behaviors have been described, the impact of parasites on pollinator foraging decisions and plant–pollinator interactions have been largely overlooked. Growing evidence of the transmission of parasites through the shared‐use of flowers by pollinators demonstrate the importance of behavioral immunity (altered behaviors that enhance parasite resistance) to pollinator health. During foraging bouts, pollinators can protect themselves against parasites through self‐medication, disease avoidance, and grooming. Recent studies have documented immune behaviors in foraging pollinators, as well as the impacts of such behaviors on flower visitation. Because pollinator parasites can affect flower choice and pollen dispersal, they may ultimately impact flower fitness. Here, we discuss how pollinator immune behaviors and floral traits may affect the presence and transmission of pollinator parasites, as well as how pollinator parasites, through these immune behaviors, can impact plant–pollinator interactions. We further discuss how pollinator immune behaviors can impact plant fitness, and how floral traits may adapt to optimize plant fitness in response to pollinator parasites. We propose future research directions to assess the role of pollinator parasites in plant–pollinator interactions and evolution, and we propose better integration of the role of pollinator parasites into research related to pollinator optimal foraging theory, floral diversity and agricultural practices.

Spontaneous colour preferences and colour learning in the fruit-feeding butterfly, Mycalesis mineus

Spontaneous colour preferences have been extensively studied in flower-visiting insects and such preferences exhibited by inexperienced flower-visiting insects are proposed to be adaptive by guiding them to the most rewarding flowers. Thus, spontaneous preferences are hypothesised to reflect the floral reward properties of the habitats in which these insects evolved. However, little is known about colour preferences in non-flower-visiting insects, and the ecological significance of such preferences. We investigated spontaneous colour preferences in the context of feeding and colour learning in the obligate fruit-feeding satyrine butterfly Mycalesis mineus. We report that M. mineus has true colour vision and naive butterflies, both males and females, did not prefer any colour in the absence of olfactory cues in a four-colour test array. Interestingly, females preferred yellow in the presence of food odour, indicating the modulatory effect of olfactory cues on spontaneous colour preferences. Further, when yellow was replaced with orange, female preference shifted to red, demonstrating the influence of colour combinations used in the test. We also report that M. mineus females rapidly learn to associate colour, both the preferred yellow and the non-preferred blue, with fermented banana as reward. Thus, for the first time, we report spontaneous colour preferences and colour learning in a non-flower-visiting butterfly. We also demonstrate that the colour preferences are sexually dimorphic in M. mineus and argue that multimodal stimuli are important for foraging decisions in fruit-feeding butterflies. Spontaneous colour preferences exhibited by naive flower-visiting insects are thought to reflect sensory biases and are hypothesised to be adaptive as they guide insects to rewarding flowers. However, such colour preferences in non-flower-visiting insects and their adaptive significance remain unclear. We demonstrate that Mycalesis mineus, a fruit-feeding butterfly, has true colour vision and exhibits spontaneous colour preferences and these preferences are sexually dimorphic. We also demonstrate that colour preferences are modulated by olfactory cues and are influenced by colour combinations presented in tests. We also report that female butterflies rapidly learn to associate colour with rewards. Our results demonstrate that naive fruit-feeding butterflies rely on both visual and olfactory modalities and depend on spontaneous and learnt behaviours while making foraging decisions.

Predator and floral traits change pollinator behaviour, with consequences for plant fitness

1. Flower‐dwelling predators may interfere in plant–pollinator interactions through changes in pollinator behaviour, leading to a reduction in pollination services. Although the context‐dependency of tri‐trophic interactions is often acknowledged, the relative contribution of predator, pollinator and flower traits in shaping pollinator behaviour has been rarely studied simultaneously.2. Pollinators' responses to predation risk were evaluated using artificial spiders on Alstroemeria aurea flowers in order to experimentally test whether predator traits (colour and size) and nectar availability affect their behaviour and plant fitness.3. Regarding the predator's traits, both sizes of artificial spiders used were similarly rejected, but spider colour was detected differently. In particular, red and black artificial spiders were more strongly rejected than the rest. In turn, nectar availability increased the time spent in the inflorescences, yet most pollinators rejected flowers with artificial spiders independently of nectar availability. Furthermore, responses to artificial spider colour and nectar availability varied significantly between dipterans and hymenopterans. Finally, artificial spiders reduced seed set and fruit weight of plants owing to changes in the behaviour of the most efficient pollinators.4. It was shown that poorly studied predator traits such as colour and size may affect pollinator behaviour in different ways among taxa. In addition, feeding necessity in a rich‐resource environment was a weaker selecting force than predation risk. Hence, it is argued here that trade‐offs between predation and flower reward may arise depending on predator detection, relationship between pollinator and predator size, and resource availability in the ecosystem with consequences for plant fitness.

Impact of flower rewards on phytophagous insects: importance of pollen and nectar for the development of the pollen beetle (Brassicogethes aeneus)

Entomophilous plants reward pollinators with provision of nutrient-rich foods such as pollen and nectar. These rewards contain compounds that are essential to insect development and can be used by pollinators as well as herbivorous insects. The pollen beetle (Brassicogethes aeneus, syn. Meligethes aeneus) whose larvae develop in oilseed rape flowers (Brassica napus) is known to feed on pollen. Previous studies already showed the importance of pollen on the development of this insect but it seems that other resource, such as nectar, could also be used. The purpose of this study was to assess the respective roles of pollen and nectar on pollen beetle development. We tested their role with behavioural and developmental experiments using flowers where the presence and absence of nectar and pollen varied. Larvae, irrespective of their instar, fed both on anthers and nectar. Nectar did not influence larval development or adult survival while pollen influenced development by increasing both larval and adult weight. However, pollen did not affect larval or adult survival nor development time. These results indicate that pollen beetle larvae are adapted to deal with various diets and can complete their development without pollen or nectar.

Temperature and water stress affect plant-pollinator interactions in Borago officinalis (Boraginaceae).

Climate change alters the abiotic constraints faced by plants, including increasing temperature and water stress. These changes may affect flower development and production of flower rewards, thus altering plant–pollinator interactions. Here, we investigated the consequences of increased temperature and water stress on plant growth, floral biology, flower‐reward production, and insect visitation of a widespread bee‐visited species, Borago officinalis. Plants were grown for 5 weeks under three temperature regimes (21, 24, and 27°C) and two watering regimes (well‐watered and water‐stressed). Plant growth was more affected by temperature rise than water stress, and the reproductive growth was affected by both stresses. Vegetative traits were stimulated at 24°C, but impaired at 27°C. Flower development was mainly affected by water stress, which decreased flower number (15 ± 2 flowers/plant in well‐watered plants vs. 8 ± 1 flowers/plant under water stress). Flowers had a reduced corolla surface under temperature rise and water stress (3.8 ± 0.5 cm2 in well‐watered plants at 21°C vs. 2.2 ± 0.1 cm2 in water‐stressed plants at 27°C). Both constraints reduced flower‐reward production. Nectar sugar content decreased from 3.9 ± 0.3 mg/flower in the well‐watered plants at 21°C to 1.3 ± 0.4 mg/flower in the water‐stressed plants at 27°C. Total pollen quantity was not affected, but pollen viability decreased from 79 ± 4% in the well‐watered plants at 21°C to 25 ± 9% in the water‐stressed plants at 27°C. Flowers in the well‐watered plants at 21°C received at least twice as many bumblebee visits compared with the other treatments. In conclusion, floral modifications induced by abiotic stresses related to climate change affect insect behavior and alter plant–pollinator interactions.

An analysis of the energetic reward offered by field bean (Vicia faba) flowers: Nectar, pollen, and operative force.

Global consumption of crops with a yield that is dependent on animal pollinators is growing, with greater areas planted each year. However, the floral traits that influence pollinator visitation are not usually the focus of breeding programmes, and therefore, it is likely that yield improvements may be made by optimizing floral traits to enhance pollinator visitation rates. We investigated the variation present in the floral reward of the bee‐pollinated crop Vicia faba (field bean). We examined the genetic potential for breeding flowers with a greater reward into current commercial varieties and used bee behavioral experiments to gain insight into the optimal nectar concentration to maximize bee preference. There was a large range of variation in the amount of pollen and nectar reward of flowers in the genotypes investigated. Bee behavioral experiments using nectar sugar concentrations found in V. faba lines suggest that Bombus terrestris prefers 55% w/w sugar solution over 40% w/w, but has no preference between 55% w/w and 68% w/w sugar solution. We provide a first indication of the force required to open V. faba flowers. Our results provide a valuable starting point toward breeding for varieties with optimized floral reward. Field studies are now needed to verify whether the genetic potential for breeding more rewarding flowers can translate into higher yield and yield stability.