Initial floral visitor identity and foraging time strongly influence blueberry reproductive success

Priority effects occur when the order of species arrival affects subsequent ecological processes. The order that pollinator species visit flowers may affect pollination through a priority effect, whereby the first visitor reduces or modifies the contribution of subsequent visits. We observed floral visitation to blueberry flowers from honeybees, stingless bees or a mixture of both species and investigated how (i) initial visits differed in duration to later visits; and (ii) how visit sequences from different pollinator taxa influenced fruit weight. Stingless bees visited blueberry flowers for significantly longer than honeybees and maintained their floral visit duration, irrespective of the number of preceding visits. In contrast, honeybee visit duration declined significantly with an increasing number of preceding visits. Fruit weight was positively associated with longer floral visit duration by honeybees but not from stingless bee or mixed species visitation. Fruit from mixed species visits were heavier overall than single species visits, because of a strong priority effect. An initial visit by a stingless bee fully pollinated the flower, limiting the pollination contribution of future visitors. However, after an initial honeybee visit, flowers were not fully pollinated and additional visitation had an additive effect upon fruit weight. Blueberries from flowers visited first by stingless bees were 60% heavier than those visited first by honeybees when total floral visitation was short (∼1 min). However, when total visitation time was long (∼ 8 min), blueberry fruit were 24% heavier when initial visits were from honeybees. Our findings highlight that the initial floral visit can have a disproportionate effect on pollination outcomes. Considering priority effects alongside traditional measures of pollinator effectiveness will provide a greater mechanistic understanding of how pollinator communities influence plant reproductive success.     

Contrasting bee foraging in response to resource scale and local habitat management

It is hypothesized that two main factors drive the foraging patterns of native and exotic species: food resource availability and habitat composition. These factors are particularly relevant for native bees and exotic honeybees, essential crop pollinators that are sensitive to floral resources and habitat management, and that have recently exhibited alarming population declines. Mechanisms driving native and exotic bee foraging patterns may critically depend on floral resource availability and habitat composition, yet the impacts of these factors on bee foraging have never been simultaneously analyzed. In a coffee producing region in southern Mexico, we investigated the influence of coffee floral resource levels and habitat management on native and exotic bee foraging. We measured the amount of flowering coffee available at multiple spatial scales within two distinct agroforestry habitat types (high-shade and low-shade coffee) and recorded visits to coffee flowers, documenting bee species, visit duration and visit frequency. We observed a significantly greater number of visits in high-shade coffee habitats than in low-shade coffee habitats for both native and exotic bees. In high-shade coffee habitats, native solitary bee and native social bee visitation decreased significantly in response to increasing floral resource availability, exhibiting a 'dilution effect' at the smallest spatial scale. In contrast, in low-shade coffee habitats, Africanized honeybees exhibited a 'concentration effect', increasing visitation significantly in response to increasing floral resource availability at the largest spatial scale. This study is the first to show that foraging patterns of native bees and exotic honeybees contrast in response to floral resource level and scale and that this response is mediated by the vegetation management of the local habitat.     

The relative importance of birds and bees in the pollination of Metrosideros excelsa (Myrtaceae)

Exclusion experiments were used to assess the effect of different pollinator groups on outcrossing and seed production in Metrosideros excelsa. The main study site was Little Barrier Island, New Zealand where indigenous bird and native solitary bees are the main flower visitors. Our results showed that native birds were more important pollinators of M. excelsa than native bees. Seed production was much higher in open pollination than in two exclusion experiments where either birds were excluded and native bees only had access to flowers, or where all pollinators had been excluded. The number of fertile seeds per capsule was 45% higher after open pollination than in treatments with bee visitation only and 28% higher than in treatments where all flower visitors were excluded. Estimated outcrossing rates were significantly higher (t_m = 0.71) for open pollination in the upper canopy (>4 m above‐ground level) where bird visitation is presumed to be more frequent than for a treatment with native bee access only (t_m = 0.40). Our results also suggest that a large proportion of seeds (66%) arise from autonomous self‐pollination when all pollinators are excluded. In four trees of a modified mainland population with predominantly introduced birds and a mixture of introduced and native bees there was no decrease in seed production for the treatment allowing bee access only, indicating that – in contrast to native bees – honeybees may be more efficient pollinators of M. excelsa. Observation of the foraging behaviour of both groups of bees showed that native bees contact the stigma of flowers less frequently than honeybees. This is likely to be a consequence of their smaller body size relative to honeybees.     

Recognition of scent marks in solitary bees to avoid previously visited flowers

Knowing how floral visitors forage efficiently among flowers is important to understanding plant-pollinator interactions. When bees search for rewarding flowers, they use several visual cues to detect the available floral resources. In addition to these cues, bees can recognize scent marks, which are olfactory cues left on flowers foraged by previous visitors. This behavior is well known in social bees, such as honeybees and bumblebees. Although solitary bees do not need to give information about which flowers were foraged to conspecifics, several pieces of evidence have indicated the use of scent marks. However, it is unknown whether the behavior is widely used in many different bee species. We investigated whether four different solitary bees, Colletes patellatus (Colletidae), Andrena prostomias (Andrenidae), Osmia orientalis (Megachilidae), and Tetralonia mitsukurii (Apidae), can recognize flowers that have been foraged previously by visitors within 3 min. All four bees showed rejection responses to flowers foraged by conspecifics. However, our results showed that responses to foraged flowers varied among bee species. The tendency of A. prostomias and T. mitsukurii to reject the foraged flowers was pronounced, while in C. patellatus and O. orientalis it was weak. In both A. prostomias and T. mitsukurii, the rejection rate of flowers foraged by conspecifics decreased as the time lag after the last visit increased. Both bees visited the flowers from which pollen or nectar had been artificially removed. We suggest that A. prostomias and T. mitsukurii would recognize scent marks left by previous visitors, while the other two bees would not recognize them so strongly. It is likely that the decision to use scent marks is dependent either on the richness of resources or on the complexity of floral structure.     

Pollinating bees (Hymenoptera: Apiformes) of U.S. alfalfa compared for rates of pod and seed set

Alfalfa (=lucerne) flowers require visiting bees to trip the sexual column, thereby providing pollination and subsequent pod and seed set. Previous studies have compared the pollination values of different bee species solely by the speed with which they handle flowers and the proportion of visited flowers tripped. In this greenhouse study, five species of bees, including the three commercially managed U.S alfalfa pollinators, are likewise compared for their floral tripping frequencies. These bee species are also compared for the pod set and mature seed that results from their single visits to virgin flowers. Regardless of the identity of the pollinating bee, tripped flowers had the same probabilities of pod set and seed set. Thus, differences in the single-visit pollination efficiencies of the various bee species are entirely attributable to the proportion of visited flowers that they trip. Females of the alkali bee, Nomia melanderi Cockerell, and the alfalfa leafcutting bee, Megachile rotundata F, tripped 81 and 78% of visited flowers, respectively. Males of these species are significantly less effective (61 and 51%, respectively), but still significantly superior to the honey bee, Apis mellifera L. (22% of visited flowers tripped). These relationships are supported by field data for tripping frequencies. One candidate pollinator, Osmia sanrafaelae Parker, shows promise (44% tripped), but not the congeneric O. aglaia Sandhouse (13% tripped).     

Influence of functional traits on foraging behaviour and pollination efficiency of wild social and solitary bees visiting coffee (Coffea canephora) flowers in Uganda

An on-farm pollination experiment was conducted during the June–August and November–February blooming seasons of 2007 to 2008, in 30 small-scale coffee fields characterised by different habitat and vegetation types. The study was conducted in order to determine the best pollinator groups for coffee in Uganda and to collect relevant field information and determine the pollination efficiency of different bee species. Results indicate that across blooming seasons, coffee flowers were visited by 24–36 bee species. Hypotrigona gribodoi was the most frequent flower visitor, comprising over 60% of 5941 bee-visits recorded. Foraging rate and pollination speed varied among bee species. Solitary bees foraged on more flowers than social bees, but they spent less time per flower visited. Solitary bees visited more coffee trees and fields, but deposited less pollen, whereas social bees visited less trees and coffee fields in the landscape, but deposited more pollen on flowers. Fruit set was of 87%, 64% and 0.9%, respectively, in hand-cross pollination, open pollination and controlled-pollination treatments. Fruit abortion due to self-pollination was insignificant in this study. There was variability in pollination efficiency of different bee species. Pollination efficiency varied more significantly with sociality than with other bee functional traits and was not significantly influenced by tongue length and bee body size. Single-flower visits by social and solitary bees resulted in 89.7% and 68.14% fruit set, respectively. The most efficient bee species was Meliponula ferruginea (98.3%) followed by Meliponula nebulata (97.1%). Thus, very good pollinator species were wild social bees (mainly stingless bees) as opposed to honeybees and solitary bees that were previously reported to be the best pollinators of coffee in Panama and Indonesia. Morphological and anatomical characteristics of the bee pollen storage features may explain the difference in foraging behaviour activities and in pollination efficiency of social and solitary afrotropical bee species visiting lowland coffee in Uganda. In addition, pollination efficiency was influenced by land-use intensity, field management systems and habitat types found in the immediate surroundings of coffee fields, but not by coffee field size, coffee genotypes and mass blooming wild vegetation. It is recommended to farmers to adopt pollinator-friendly conservation and farming practices such as keeping an uncultivated portion (25%–30%) of their farms as pollinator reservoirs, protecting semi-natural habitats found in the vicinity of coffee fields, as well as promoting high on-farm tree cover to benefit a functionally diverse pollinator community.     

Pollinator visitation to mass-flowering courgette and co-flowering wild flowers: Implications for pollination and bee conservation on farms

Managing the complex relationship between pollinators and their habitat requirements is of particular concern to growers of pollinator-dependent crop species, such as courgette (Cucurbita pepo). Naturally occurring wild flowers (i.e. agricultural weeds) offer a free, sustainable, and often underappreciated resource for pollinators, however, they may compete with crop flowers for visits. To understand the extent to which floral resources mediate pollinator visitation to courgette flowers and courgette fields, plant community and pollinator visitation data were collected at two spatial scales: field scale (in margins, and in the cropped area) and farm scale (500 m and 2000 m radii) for nine courgette fields across the UK. Apis mellifera (honeybees) and Bombus spp. (bumblebees) were the only pollinators observed to visit courgette flowers. Bumblebees were significantly more abundant on courgette flowers in fields with a greater species richness of wild flowers in the crop, whilst honeybees were significantly more abundant on courgette flowers in areas with less semi-natural habitat. For both honeybees and bumblebees, their abundance in field margins did not significantly reduce their abundance on courgette flowers, suggesting that wild flowers were not competing with courgette flowers for pollinator visitation. Although solitary bees were not observed to visit courgette flowers, their abundance and species richness in courgette fields were significantly greater with more semi-natural habitat and a greater species richness of wild flowers. Therefore, allowing uncultivated areas around the crop to be colonised by species-rich wild flowers is an effective way of boosting the abundance of bumblebees, which are important visitors to courgette flowers, as well as the abundance and species richness of solitary bees, thereby benefitting pollinator conservation.     

Contribution of native bees and Africanized honey bees (Hymenoptera:Apoidea) to Solanaceae crop pollination in tropical México

In the tropics the contribution of bees as pollinators of important economic indigenous crops remains largely undocumented. We studied the diversity of bee species visiting indigenous tomato (Solanum lycopersicon) and habanero pepper (Capsicum chinense) in subtropical Yucatán, México. The contribution of two native bees, Exomalopsis (E) and Augochloropsis (AG) was compared with that of the introduced Africanized Apis mellífera (HB) for pollinating unvisited flowers in both crops. Apis mellífera and stingless bees were dominant in habanero pepper but solitary bee species were important visitors of tomato. In spite of both crops being autogamic, there was a significant contribution of native bees for pollination of both tomato and habanero pepper. The comparison of fruit weight, number of seeds, and a pollination index based on the latter showed that E and AG were more effective pollinators compared to HB in both crops (ca. Spear’s index of ca. 0.7 vs. 0.35 respectively). In tomato, a further evaluation of the contribution to pollination provided by the three bee species was made using the rate of visits to flowers. Although E and AG were the most efficient pollinators at single flower visits in tomato, none of the three species (including HB) were able to provide single visits to all flowers per unit time to the crop. Our results underline the importance of maintaining diverse assemblages and abundant populations of bee species that can synergically contribute to the productivity of tomato and hot pepper in the Neotropics.     

Morning floral heat as a reward to the pollinators of the Oncocyclus irises

Relationships between flowering plants and their pollinators are usually affected by the amount of reward, mainly pollen or nectar, offered to pollinators by flowers, with these amounts usually positively correlated with floral display. The large Oncocyclus iris flowers, despite being the largest flowers in the East Mediterranean flora, are nectarless and have hidden pollen. No pollinators visit the flowers during daytime, and these flowers are pollinated only by night-sheltering solitary male bees. These iris flowers are partially or fully dark-colored, suggesting that they gather heat by absorbing solar radiation. Here we test the hypothesis that the dark-colored flowers of the Oncocyclus irises offer heat reward to their male solitary bee pollinators. Floral temperature was higher by 2.5°C than ambient air after sunrise. Solitary male bees emerged earlier after sheltering in Oncocyclus flowers than from other experimental shelter types. Pollination tunnels facing east towards the rising sun hosted more male bees than other aspects. We suggest that floral heat reward can explain the evolution of dark floral colors in Oncocyclus irises, mediated by the pollinators’ behavior.     

Errata

In south-eastern Arizona, heterostylous (often trimorphic) populations of Oxalis alpina (Rose) Knuth are visited most commonly by females of the solitary bee Heterosarus bakeri Cockerell. Bees collect pollen from flowers and are presumed to be the major pollinators of O. alpina in this region. Analysis of pollen loads from the corbiculae of H. bakeri suggests that individual bees may specialize temporally on different floral forms. However, the apparent preferential collection of pollen probably results from spatial segregation of morphs and the localized foraging behaviour of bees rather than preference on the part of individual bees for particular stylar forms. As a group, bees appear to visit floral morphs of O. alpina indiscriminately, even though individual bees may have a preponderance of pollen from one morph type. Despite spatial segregation leading to pollinator flights between members of the same incompatibility group, capsule and seed production in populations of O. alpina is high for all forms. Loss of the mid form in some populations cannot be attributed to pollinator preferences for individual style morphs.     

Interaction between oil-collecting bees and seven species of Plantaginaceae

Oil-bee/oil-flower mutualism evolved through multiple gains and losses of the ability to produce floral oil in plants and to collect it in bees. Around 2000 plant species are known to produce floral oils that are collected by roughly 450 bee species, which use them for the construction of nests and for the larval food. The Plantaginaceae contain several Neotropical species that produce floral oils, the main reward offered by these plants. In the genera Angelonia, Basistemon, Monopera and Monttea, mainly associated with Centris bees, the floral oil is produced in trichomes that are located in the inner corolla. The pollinators of a few species in this neotropical clade of Plantaginaceae are known, and the role of flower morphology as well as the requirements from pollinators and the role of other groups of bees in the pollination of these flowers remains unclear. In this paper we provide a list of the flower visitors of seven Plantaginaceae species (six Angelonia species and Basistemon silvaticus) analyzing their behavior to highlight the legitimate pollinators and illustrating little known aspects of flower morphology and oil-collecting apparatuses of the bees. Two general morphological patterns were observed in the Angelonia flowers: deep corolla tube with short lobes, and short corolla tube with long lobes. Corolla tubes of different length result in pollen adherence to different parts of the insect body. The six Angelonia species and B. silvaticus flowers were visited by 25 oil-collecting bee species (10 Centris, 11 Tapinotaspidini and 4 Tetrapedia species), the majority acting as legitimate visitors. The flowers were also visited by illegitimate bee pollinators, which collected pollen but do not transfer it to the female organ. Specialized collectors of Plantaginaceae floral oils present modifications on the first pair of legs, mainly in the basitarsi but also extended to the tarsomeres. The new records of Tapinotaspidini and Centridini species acting as specialized pollinators of Plantaginaceae suggest that there is a geographic variation in the pollinators of the same plant species, and that the evolutionary scenario of the historical relationships between oil-collecting bees and floral oil producing plants is more complex than previously considered.     

Change of Floral Orientation within an Inflorescence Affects Pollinator Behavior and Pollination Efficiency in a Bee-Pollinated Plant,Corydalis sheareri

Vertical raceme or spike inflorescences that are bee-pollinated tend to present their flowers horizontally. Horizontal presentation of flowers is hypothesized to enhance pollinator recognition and pollination precision, and it may also ensure greater consistency of pollinator movement on inflorescences. We tested the hypotheses using bee-pollinated Corydalis sheareri which has erect inflorescences consisting of flowers with horizontal orientation. We altered the orientation of individual flowers and prepared three types of inflorescences: (i) unmanipulated inflorescences with horizontal-facing flowers, (ii) inflorescences with flowers turned upward, and (iii) inflorescences with flowers turned downward. We compared number of inflorescences approached and visited, number of successive probes within an inflorescence, the direction percentage of vertical movement on inflorescences, efficiency of pollen removal and seed production per inflorescence. Deviation from horizontal orientation decreased both approaches and visits by leafcutter bees and bumble bees to inflorescences. Changes in floral orientation increased the proportion of downward movements by leafcutter bees and decreased the consistency of pollinator movement on inflorescences. In addition, pollen removal per visit and seed production per inflorescence also declined with changes of floral orientation. In conclusion, floral orientation seems more or less optimal as regards bee behavior and pollen transfer for Corydalis sheareri. A horizontal orientation may be under selection of pollinators and co-adapt with other aspects of the inflorescence and floral traits.     

Can ants equal honeybees as effective pollinators of the energy crop Jatropha curcas L. under Mediterranean conditions?

Jatropha curcas L. is the subject of many research and breeding programs concerned with its potential as an oil crop for biodiesel production. Despite an increasing amount of information regarding this relatively new crop, pollination requirements of this plant are largely neglected. The aim of the study was to evaluate the relative significance of ants and honeybees as potential pollinators of J. curcas grown under Mediterranean conditions. Jatropha curcas plants bloomed throughout the summer and fall, peaking twice, in early summer and late fall. During this period, the plants were visited by 70 species of insects representing 45 families from seven orders, with most species rarely being observed. Ants and Honeybees were the most common species, accounting for >95% of all flower visits. The foraging behavior of the honeybees followed the pattern of bloom phenology, especially during the summer, and mostly promoted cross‐pollination. Ants on the other hand, mostly promoted self pollination showing no such correlative behavior, reacting often too late to nectar availability, and were highly susceptible to climatic changes. Pollinator exclusion treatments revealed that during summer, fruit and seed sets, as well as seed size and oil and protein contents, were relatively similar for ant and bee‐pollinated flowers. During fall, however, reproductive success of bee‐pollinated flowers was relatively high (66%), while fruit set of ant‐pollinated flowers was significantly reduced from 71 to 11%. In conclusion, while both groups are equal in their pollination effectiveness in the summer, during the fall the honeybees are almost the sole pollinators of the plant. Based on bloom phenology and pollination activity data, the honeybees are responsible for the pollination of more than 80% of the annual reproductive potential of J. curcas, under Mediterranean conditions.     

Floral specialization for different pollinators and divergent use of the same pollinator among co‐occurring Impatiens species (Balsaminaceae) from Southeast Asia

Floral variation among closely related species is thought to often reflect differences in pollination systems. Flowers of the large genus Impatiens are characterized by extensive variation in colour, shape and size and in anther and stigma positioning, but studies of their pollination ecology are scarce and most lack a comparative context. Consequently, the function of floral diversity in Impatiens remains enigmatic. This study documents floral variation and pollination of seven co‐occurring Impatiens spp. in the Southeast Asian diversity hotspot. To assess whether floral trait variation reflects specialization for different pollination systems, we tested whether species depend on pollinators for reproduction, identified animals that visit flowers, determined whether these visitors play a role in pollination and quantified and compared key floral traits, including floral dimensions and nectar characteristics. Experimental exclusion of insects decreased fruit and seed set significantly for all species except I. muscicola, which also received almost no visits from animals. Most species received visits from several animals, including bees, birds, butterflies and hawkmoths, only a subset of which were effective pollinators. Impatiens psittacina, I. kerriae, I. racemosa and I. daraneenae were pollinated by bees, primarily Bombus haemorrhoidalis. Impatiens chiangdaoensis and I. santisukii had bimodal pollination systems which combined bee and lepidopteran pollination. Floral traits differed significantly among species with different pollination systems. Autogamous flowers were small and spurless, and did not produce nectar; bee‐pollinated flowers had short spurs and large floral chambers with a wide entrance; and bimodally bee‐ and lepidopteran‐pollinated species had long spurs and a small floral chamber with a narrow entrance. Nectar‐producing species with different pollination systems did not differ in nectar volume and sugar concentration. Despite the high frequency of bee pollination in co‐occurring species, individuals with a morphology suggestive of hybrid origin were rare. Variation in floral architecture, including various forms of corolla asymmetry, facilitates distinct, species‐specific pollen‐placement on visiting bees. Our results show that floral morphological diversity among Impatiens spp. is associated with both differences in functional pollinator groups and divergent use of the same pollinator. Non‐homologous mechanisms of floral asymmetry are consistent with repeated independent evolution, suggesting that competitive interactions among species with the same pollination system have been an important driver of floral variation among Impatiens spp.     

Pollination disruption by European honeybees in the Australian bird-pollinated shrubGrevillea barklyana (Proteaceae)

European honeybees (Apis mellifera) were less efficient pollinators ofGrevillea barklyana than nectar-feeding birds. Nectar-collecting honeybees did not contact reproductive parts of flowers. Pollen-collecting honeybees preferentially visited malestage flowers but rarely visited female-stage flowers. Fruit set on caged inflorescences that allowed access to honeybees but excluded birds was reduced by more than 50% compared to inflorescences that were visited by both types of visitors. Further, fruit set on caged inflorescences was less than on bagged inflorescences that excluded both birds and honeybees, indicating that pollen removal by bees decreased opportunities for delayed autonomous selfing in the absence of birds. Although fruit set was not pollen-limited at the study site, pollen removal by honeybees would decrease fruit set in small populations where birds are scarce. In addition, pollen removal by honeybees would reduce opportunities for outcrossing and reproductive success through male function. Although honeybees have been in Australia for insufficient time to have exerted selection on floral traits, evolutionary shifts in response to these animals are likely to occur in the future.     

Bees assess pollen returns while sonicating Solanum flowers

Summary Can bees accurately gauge accumulating bodily pollen as they harvest pollen from flowers? Several recent reports conclude that bees fail to assess pollen harvest rates when foraging for nectar and pollen. A native nightshade (Solanum elaeagnifolium Cavanilles) that is visited exclusively for pollen by both solitary and social bees (eg. Ptiloglossa and Bombus) was studied in SE Arizona and SW New Mexico. The flowers have no nectaries. Two experiments were deployed that eliminated pollen feedback to the bees by experimentally manipulating flowers prior to bee visits. The two methods were 1) plugging poricidal anthers with glue and 2) emptying anthers of pollen by vibration prior to bee visitation. Both experiments demonstrated that bees directly assess pollen harvest on a flower-by-flower basis, and significantly tailor their handling times, number of vibratile buzzes per flower and grooming bouts according to the ongoing harvest on a given flower. In comparison to experimental flowers, floral handling times were extended for both Bombus and Ptiloglossa on virgin flowers. Greater numbers of intrafloral buzzes and numbers of times bees groomed pollen and packed it into their scopae while still on the flower were also more frequent at virgin versus experimental flowers. Flowers with glued andreocia received uniformly brief visits from Bombus and Ptiloglossa with fewer sonications and virtually no bouts of grooming. Curtailed handling with few buzzes and grooms also characterized visits to our manually harvested flowers wherein pollen was artificially depleted. Sonicating bees respond positively to pollen-feedback while harvesting from individual flowers, and therefore we expect them to adjust their harvesting tempo according to the currency of available pollen (standing crop) within Solanum floral patches.     

Specialised protagonists in a plant–pollinator interaction: the pollination of Blumenbachia insignis (Loasaceae)

• Analyses of resource presentation, floral morphology and pollinator behaviour are essential for understanding specialised plant‐pollinator systems. We investigated whether foraging by individual bee pollinators fits the floral morphology and functioning of Blumenbachia insignis, whose flowers are characterised by a nectar scale‐staminode complex and pollen release by thigmonastic stamen movements.
• We described pollen and nectar presentation, analysed the breeding system and the foraging strategy of bee pollinators. We determined the nectar production pattern and documented variations in the longevity of floral phases and stigmatic pollen loads of pollinator‐visited and unvisited flowers.
• Bicolletes indigoticus (Colletidae) was the sole pollinator with females revisiting flowers in staminate and pistillate phases at short intervals, guaranteeing cross‐pollen flow. Nectar stored in the nectar scale‐staminode complex had a high sugar concentration and was produced continuously in minute amounts (~0.09 μl·h^?1). Pushing the scales outward, bees took up nectar, triggering stamen movements and accelerating pollen presentation. Experimental simulation of this nectar uptake increased the number of moved stamens per hour by a factor of four. Flowers visited by pollinators received six‐fold more pollen on the stigma than unvisited flowers, had shortened staminate and pistillate phases and increased fruit and seed set.
• Flower handling and foraging by Bicolletes indigoticus were consonant with the complex flower morphology and functioning of Blumenbachia insignis. Continuous nectar production in minute quantities but at high sugar concentration influences the pollen foraging of the bees. Partitioning of resources lead to absolute flower fidelity and stereotyped foraging behaviour by the sole effective oligolectic bee pollinator.

     

Intersexual mimicry and flowering phenology facilitate pollination in a dioecious habitat specialist species, <Emphasis Type="Italic">Myristica fatua</Emphasis> (Myristicaceae)

Myristica fatua is a dioecious specialist species restricted to the endangered, freshwater Myristica swamp forests in the Western Ghats, India. Earlier studies have alluded to pollination by deception in members of the Myristica genus, and thus we examined the pollination ecology comprising floral biology, flower production, flower visitors, and reproductive success in M. fatua and inferred the potential strategies that could permit such deception in this habitat specialist tree. Male flowers provide pollen rewards for an extended period of time while female flowers are rewardless and both sexes are visited by generalist insects, mainly by honeybees and stingless bees. Bee visits were significantly more frequent and longer on male than on female flowers as bees collected pollen from male flowers. We found that flower production patterns create a preponderance of males compared to females in the swamp populations. Using a model of honeybee color vision, we found the distance between the color loci of male and female flowers and based on minimum visual angle subtended by these flowers, we suggest that the two floral sexes cannot be discriminated by bees. Bees are likely deceived by the perceptual similarity of rewardless female flowers to pollen-offering male flowers and pollination is the consequence of foraging errors made by pollinators that encounter largely male–rarely female flower mosaics as they forage among clump-distributed M. fatua trees in the swamp habitat.     

Pollination in Turnera subulata (Turneraceae): Unilateral reproductive dependence of the narrowly oligolectic bee Protomeliturga turnerae (Hymenoptera, Andrenidae)

Turnera subulata Smith (Turneraceae) is a subshrub with distylic flowers, common as a ruderal plant in NE-Brazil. We studied the pollination biology of a population in João Pessoa, Paraíba, paying attention to effective pollinators and characteristics of short- and long-style morphs. The flowers attracted insects of 28 species, predominantely bees. Several bee species were observed to be effective pollinators, including highly eusocial species, polylectic solitary species (Centris and Xylocopa) and 1 oligolectic species, Protomeliturga turnerae (Andrenidae, Panurginae). The latter species shows reproductive dependency on T. subulata. The plant species, on the other hand, does not depend on this specialized bee, as reproductive success was also guaranteed by the other polylectic flower visitors. Floral characteristics of both floral morphs are discussed with respect to pollination biology.     

Pollination biology in Roepera (Zygophyllaceae): How flower structure and shape influence foraging activity

The foraging behavior of bees is a complex phenomenon that depends on numerous physical features of flowers. Of particular importance are accessibility of floral rewards, floral proportions, symmetry and orientation. The flowers of Roepera are characterized by the presence of staminal scales (SS), which play an important role in nectar protection. We studied two species of Roepera with different symmetry and flower orientation, which are mainly visited by honeybees (Apis mellifera). We aimed to show how the foraging behavior of honey bees is affected by the function of SS, floral symmetry and orientation. The foraging behavior was documented by video photography. Handling time, access to nectar, percentage of pollen/nectar foraging, percentage of pollen contact and pollen deposition site on the honey bee's body were assessed. The morphometric features of the honey bees and flowers were analyzed. We found that the SS restricted pollinator access to nectar. Our results indicated consistency of visitation patterns in zygomorphic, laterally oriented flowers of R. fuscata versus random patterns in actinomorphic, diversely oriented flowers of R. leptopetala. The relative proportions of SS and proboscis length appear to be crucial for the success of pollinators. The directionality of the honey bees' movement, together with the different positioning of reproductive organs, plays an important role in the accuracy of pollen transfer and pollination efficiency.