Number Of Flower Visits Research Articles

Home sweet home: Evaluation of native versus exotic plants as resources for insects in urban green spaces

Abstract Insect decline and loss of biodiversity not only affect large‐scale agricultural landscapes, but are increasingly recognized in urban environments. It is undisputed that a greater supply of flowers in urban green spaces can provide insects with more food and habitat. However, it is still controversial whether native wild plants or non‐native ornamental plants and varieties are the right choice. To answer this question we investigated the number of insects interacting with different types of plants: twelve ornamental and six related wild perennials. In this context, the number of flower visitors per plant species and plot was recorded at 10‐minute observation intervals, as well as the feeding damage caused by insect herbivores on the leaves and stems of the study plants. We established 18 plant species in ten independent study plots in the city of Darmstadt, Germany. The plants were six native wild plant species, six ornamental plant species related to the wild plants from the same genus or family and six exotic ornamental plant species from other genera and families than the wild plants. Native insects (wild bees, flies, beetles, wasps) that feed on pollen and nectar visited wild perennials significantly more often (67% of all visits) than related ornamental (24%) and unrelated exotic plants (9%). In contrast, honey bees (Apis mellifera) showed no preferences to any of the three target plant groups and interacted with other plant species than most of the native insects in our study according to analyses of interaction networks. The assessment of leaf damage caused by insect herbivores on the individual plants confirmed a similar and significant difference in the insects' choices. Leaves from wild plants showed the highest herbivory (mean 2.3% of the leaf area), followed by related ornamental plants (0.8%), whereas unrelated exotic plants were hardly consumed (0.1%) by herbivores. Practical implication. Our study shows that in urban green spaces, both flower‐visiting and leaf‐feeding insects are more likely to use native wild plants as a food source than closely related and exotic ornamental plants.

Abiotic conditions affect nectar properties and flower visitation in four herbaceous plant species

Both plant nectar production and insect activity are highly dependent on abiotic environmental conditions. Furthermore, the foraging behaviour of insect pollinators can be affected by nectar properties. In the context of climate change, it is important to understand how plant-pollinator interactions respond to temperature and other abiotic factors. We investigated the effect of natural variation in temperature and solar radiation on nectar quantity (nectar volume) and quality (sucrose concentration and sucrose mass) and on flower visitation rates in four herbaceous plant species (Dictamnus albus, Lamium album, Salvia officinalis, Vincetoxicum hirundinaria) in the Botanical Garden Halle (Germany). Temperature affected nectar properties in all four species. Solar radiation affected nectar quantity and quality in two species, most likely by affecting flower temperature. The number of flower visits was unimodally related to temperature for two species and positively related to solar radiation in another. The variable responses across plant species in the effects of abiotic factors on nectar properties and flower visitation patterns may be due to differences in flower shape and colour, to differences in the composition of flower visitors, or due to other unmeasured extrinsic factors that vary across patches where these species occur. Our study highlights the importance of considering direct and indirect effects of climate factors on pollinator visitation in multiple plant species.

Patterns of pollination interactions at the community level are related to the type and quantity of floral resources

Abstract A fundamental question in community ecology is how the quantity of floral resources affects pollinator activity and how this relates to the structure and robustness of pollination networks. The issue has been mainly addressed at the species level, while at the community level several questions are still open. Using a species‐rich semi‐natural grassland as model ecosystem, we explored the relationship between community‐level quantity of floral resources, the number of flower visits at community level and descriptors of the structure and robustness of pollination networks. To assess whether patterns of pollination interactions were consistent when using different types of floral resources, we measured three types of floral resources, namely the volume of nectar, the number of pollen grains and the number of flowers. Community‐level pollinator visitation rate showed a hump‐shaped relationship with the quantity of floral resources. Results were consistent among models employing different measures of floral resources as independent variables. The relationship between the quantity of floral resources and the structure and robustness of the network was not consistent among different types of floral resources; only intermediate levels of nectar volume were associated with high levels of network robustness. The pattern we found is in contrast with some former studies which reported positive linear relationships between the community‐level visitation rate of pollinators and the quantity of floral resources. Rather, the observed hump‐shaped pattern resembles the relationship previously found between the quantity of floral resources of a given plant species and its visitation rate per flower. Our results highlighted that, by using specific types of floral resources (e.g. the volume of nectar and the number of pollen grains), it is possible to reveal ecological processes that would be masked by using the number of flowers as the sole measure of floral resource. A free Plain Language Summary can be found within the Supporting Information of this article.

An easy-to-manage two-entrance honey bee hive system for greenhouse pollination that improves fruit production

An alternative two-entrance hive system demonstrated here is less taxing for the bee colonies. Bees are directed to forage inside the greenhouse when the crop is in flower, and only have access to the outside after anthesis. Consequently, there are no bees in the greenhouse in the afternoon, facilitating crop management. This system allows the farmer to control bee access to the crop without the need for a smoker or protective equipment. Using this system, we compared pollination by honey bees (Apis mellifera) to hand pollination of zucchini squash (Cucurbita pepo) in greenhouses, during two crop seasons. Data included number of flower visits by the bees, fruit production, and the time and consequent labor costs needed to control bee flight direction versus the costs of hand pollination. In the greenhouses with bees, each female flower received a mean of more than 40 bee visits. When eight or more bees visited a flower, the fruits were significantly heavier than with manual pollination (313 versus 232 g, respectively). Total production was increased 41% with bee pollination. Using bee pollination increased profit over 12%, taking into account hive rental and labor costs for hand pollination versus manipulating the hive entrances.

Wind slows play: increasing wind speed reduces flower visiting rate in honey bees

Wind is an understudied environmental variable capable of having profound impacts upon the foraging behaviour of flying organisms. We investigated the effects of wind and temperature on honey bees, Apis mellifera , foraging on two plant varieties, Lavandula x intermedia ‘Grosso’ and Origanum vulgare to determine how wind influences foraging behaviour and whether responses differ between the plant varieties. Fans and an artificial wind break were used to generate wind speeds from 0 to 3.5 m/s with the following behaviours examined in a minute of foraging: number of flower visits, handling time per flower, interflower flight duration and proportion of flowers walked to. Flower movement was quantified using video footage and imageJ tracking software. Bees visited significantly fewer flowers with increasing wind speed on both plant varieties, with an average decrease of 38% between the lowest and highest wind speeds. However, the reduction was significantly steeper when foraging on O. vulgare . The reduction was due to an increase in handling time on both varieties, with interflower flight duration unaffected. Temperature had no effect on flower visit rate for either plant variety. The only behaviour influenced by flower movement was handling time, which was found to increase with flower movement. However, this increase did not result in fewer flower visits. Our results support previous work on artificial flowers which determined that the direct effect of wind on the bee influences foraging efficiency and behaviour more than the indirect effect of flower movement. • The effects of wind on A. mellifera foraging on two plant varieties were tested. • A negative effect of wind on foraging rate differed between plant varieties. • Flower movement did not appear to influence flower visit rate. • Handling time increased with wind speed, causing the reduction in flower visits. • Wind is capable of significantly reducing A. mellifera foraging efficiency.

Disentangling the path of pollinator attraction in temporarily colored flowers

Plants may use different strategies to attract pollinators in long distance (e.g. floral display) and in short distance (e.g. ratio between differentially colored flowers) scales. The Verbenaceae Lantana canescens Kunth is a wide spread species in open sites of the Brazilian Pantanal wetland. Individuals of this generalist species can produce a variable number of open inflorescences with yellow and white flowers that are organized in whorls. In this study we tested the hypothesis that increased floral display (long distance attraction) and the ratio between yellow and white flowers (short distance attraction) enhances the number of pollinator species and individuals. We observed flower visitors and calculated floral parameters in 38 plots of 1 m2 each, that contained a varying number of flowering L. canescens individuals. Non-metric multidimensional scaling and Bray-Curtis distances were used to account for flower visitor composition and the relative visitation rate, respectively. We used a structural equation model to test the power of each predictor variable on the visitation rate and a covariance analysis to disentangle the effect of each independent variable on the frequency of plant-pollinator interactions. We found that the number of flower visitors and the visitation rate increased with increasing number of inflorescences. Disentangling long and short distance attraction indicated that the number of inflorescences (per plot) and the number of yellow flowers (yellowing effect) contributed most to flower visitation at long and short distance, respectively.

Moderate pollination limitation in some entomophilous crops of Europe

Pollination services to crops may be worsening because of declines in farmland pollinators, but the consequences for yields have been uncertain. We therefore investigated pollination limitation in four entomophilous crops (oilseed rape, sunflower, pears and pumpkin) by quantifying the difference in harvestable mass between open-pollinated and saturation-pollinated (hand-pollinated) flowers. We also examined whether pollination limitation in the four crops was associated with the number of flower visits by insects. Across 105 commercial fields in six European countries, the average decrease in harvestable mass due to pollination limitation was 2.8 % (SE = 1.15). Among crops, the highest decreases were in sunflowers (8%) and in one of three oilseed rape production regions (6%). We observed substantial variation among crops in the numbers of insect visits received by flowers, but it did not significantly correspond with the levels of pollination limitation. Our results suggest that yields in these crops were not severely pollination-limited in the regions studied and that other factors besides visitation by pollinators influenced the degree of pollination limitation.

Plant–pollinator interactions along an urbanization gradient from cities and villages to farmland landscapes

AbstractUrbanization affects pollinator diversity and plant–pollinator networks by changing resource availability locally and in the surrounding landscape. We experimentally established (N = 12) standardized plant communities in farmland, villages, and cities to identify the relative role of local and landscape effects on plant–pollinator communities along this urbanization gradient. We found that the number of flower visits by solitary bees, but not bumblebees, was highest in cities and lowest in farmland, with villages being intermediate, whereas syrphid flies exhibited lowest numbers in cities. Villages supported the richest pollinator communities, as they appeared to benefit from both farmland and city communities. Plant–pollinator network metrics such as robustness, interaction evenness, and interaction diversity decreased with increasing urbanization, although local plant richness increased toward urban areas. In conclusion, pollinator communities were most diverse and stable in farmland and village sites, despite the high plant richness in cities. The different composition of pollinator communities along the urbanization gradient suggests considering all three landscape types for conservation schemes.

Importance of Non-Native Honeybees (Apis mellifera) as Flower Visitors to the Hawaiian Tree ‘Ōhi‘a Lehua (Metrosideros polymorpha) Across an Elevation Gradient1

Pollinator populations are in decline worldwide. These declines are likely to impact native Hawaiian species and their interactions. To explore spatial heterogeneity in interactions between a foundational native Hawaiian tree and flower visitors, we examined how flower visitation varied for Metrosideros polymorpha over an elevational gradient, on the Island of Hawai‘i. We conducted a short-term, observational study at sites of high human activity, spanning a 1,500-m elevational gradient. We predicted that native flower visitors would be most important, where importance is defined as the product of the number of flower visitors observed and the number of flowers visited per visitor, at the highest elevations where human impacts have historically been less consistent and human populations are lower. We predicted that non-native bee visitation would be most important at the lowest elevations where human impact is highest. Contrary to our expectations, we found that the non-native honeybee, Apis mellifera, was the most important visitor at both the lowest and highest-elevation sites and second only to native species of Hylaeus bees in visitor importance at mid-elevation sites. We recorded A. mellifera interacting with flowers during 16.3% of all observation blocks and Hylaeus spp. during 9.4% of observation blocks, with all other visitors appearing more rarely. Although this study was short in duration and occurred at only six study sites in disturbed areas, our results suggest that the high importance of A. mellifera as a flower visitor of M. polymorpha is consistent across a range of environmental conditions. Hawai‘i's shifting suite of pollinators may impact gene flow and reproduction for M. polymorpha, a species with immense ecological and cultural importance.

Varietal and seasonal differences in the effects of commercial bumblebees on fruit quality in strawberry crops

Both wild and managed pollinators significantly contribute to global food production by providing pollination services to crops. Colonies of commercially-reared honey bees and bumblebees are two of the largest groups of managed pollinators. Bumblebees in particular are increasingly used on soft fruit crops, such as strawberry, an economically important crop globally. Despite the use of commercial bumblebees in strawberry crops, there is little quantitative evidence that they provide a benefit to farmers. Given the negative impacts that commercial colonies can have on wild bee populations, it is vital that the benefits of commercial bumblebees are quantified, so reasoned management decisions can be made that provide maximum benefit to both farmers and wild bees. In this study, commercial colonies of the UK native subspecies Bombus terrestris audax were placed into June-bearer (flowering March-April, varieties ‘Malling Centenary’ and ‘Flair’) and everbearer (flowering May-June) strawberry polytunnels on a soft-fruit farm in the south east of England, and opened and closed at weekly intervals. The flower-visiting assemblage inside polytunnels was quantified, and fruit was harvested and quality assessed. In the June-bearer variety Malling Centenary, the presence of commercial bumblebees increased the amount of high commercial grade fruit by 25%. In contrast, no benefit of commercial bees on pollination or fruit quality was observed in the June-bearer variety Flair and the everbearer crop. The increase in quality of fruit in the Malling Centenary crop may be driven by the higher B. terrestris audax flower visitation rates seen in this crop in combination with varietal differences in pollination dependency. The number of flower visits by wild pollinators was not a well-supported predictor of strawberry quality, thus the benefit they provide in this system remains to be elucidated. The results presented here suggest that commercial bumblebees can greatly increase the quality and subsequent value of a strawberry crop, when deployed on a suitable variety at a time when wild pollinator numbers are low. However, the results also raise the possibility that commercial colonies do not always provide the benefits to strawberry crops that they are thought to. For growers to make informed decisions on commercial bumblebee use, further research is required into the effect of commercial bumblebees on the major strawberry varieties, in different locations and seasons. This study is an important step in gaining this understanding.

Fragmentation of nest and foraging habitat affects time budgets of solitary bees, their fitness and pollination services, depending on traits: Results from an individual-based model.

Solitary bees are important but declining wild pollinators. During daily foraging in agricultural landscapes, they encounter a mosaic of patches with nest and foraging habitat and unsuitable matrix. It is insufficiently clear how spatial allocation of nesting and foraging resources and foraging traits of bees affect their daily foraging performance. We investigated potential brood cell construction (as proxy of fitness), number of visited flowers, foraging habitat visitation and foraging distance (pollination proxies) with the model SOLBEE (simulating pollen transport by solitary bees, tested and validated in an earlier study), for landscapes varying in landscape fragmentation and spatial allocation of nesting and foraging resources. Simulated bees varied in body size and nesting preference. We aimed to understand effects of landscape fragmentation and bee traits on bee fitness and the pollination services bees provide, as well as interactions between them, and the general consequences it has to our understanding of the system. This broad scope gives multiple key results. 1) Body size determines fitness more than landscape fragmentation, with large bees building fewer brood cells. High pollen requirements for large bees and the related high time budgets for visiting many flowers may not compensate for faster flight speeds and short handling times on flowers, giving them overall a disadvantage compared to small bees. 2) Nest preference does affect distribution of bees over the landscape, with cavity-nesting bees being restricted to nesting along field edges, which inevitably leads to performance reductions. Fragmentation mitigates this for cavity-nesting bees through increased edge habitat. 3) Landscape fragmentation alone had a relatively small effect on all responses. Instead, the local ratio of nest to foraging habitat affected bee fitness positively through reduced local competition. The spatial coverage of pollination increases steeply in response to this ratio for all bee sizes. The nest to foraging habitat ratio, a strong habitat proxy incorporating fragmentation could be a promising and practical measure for comparing landscape suitability for pollinators. 4) The number of flower visits was hardly affected by resource allocation, but predominantly by bee size. 5) In landscapes with the highest visitation coverage, bees flew least far, suggesting that these pollination proxies are subject to a trade-off between either longer pollen transport distances or a better pollination coverage, linked to how nests are distributed over the landscape rather than being affected by bee size.

Effects of habitat loss on the plant–flower visitor network structure of a dune community

Pollination is a valuable ecosystem service, and plant–pollinator interactions in particular are known to play a crucial role in conservation and ecosystem functioning. These mutualisms, like other ecological interactions, are currently threatened by different drivers of global change, mainly habitat loss, fragmentation, or modification of its quality. Most studies so far have focused on the impact of such disturbances on particular species interactions and we thus need more empirical evidence on the responses at a community‐level. Here we evaluated how habitat loss influenced the pattern of interactions between plants and their flower visitors in a coastal dune marshland community. Using data from four years (2008–2011), we assessed the effect of a large disturbance in the area (occurring in 2010) that represented the loss of more than 50% of the vegetation cover. We found a considerable decrease in species richness and abundance of flower visitors, which resulted in a lower number of interactions after the disturbance. Not all functional groups, however, responded similarly. Contrary to the expected from previous findings, bees and wasps were less negatively influenced than beetles, flies and ants, possibly due to their higher movement capacity. Species interactions in the community were more specialized after habitat loss, resulting in a lower level of network nestedness and a higher modularity. At a species level, the number of flower visitors per plant decreased after the disturbance, and plants were visited by less abundant flower visitors. Our findings lead us to predict that the overall plant–flower visitor network became less robust and resilient to future perturbations. However, the fact that each functional group responds distinctly to disturbances makes it more difficult to foresee the final consequences on community composition and ecosystem functioning.

Effects of competition and climate on a crop pollinator community

Abstract Plant-pollinator interactions are ubiquitous in nature where both wild and domesticated pollinators interact with wild plant communities and entomophilous crops. Honeybees are important pollinators in many crop systems, but recent declines in honeybee stocks in Europe and the US have caused concern about the sustainability of crop systems solely depending on honeybees. In addition, several studies have shown that honeybees might negatively affect native pollinator populations, bumblebees in particular. Here we have studied flower visitation to two raspberry farms and surrounding wildflower communities in SE Norway. Bumblebees were excluded from the raspberry field by means of exploitative competition from honeybees ( > 97% of flower visits in the raspberry fields were conducted by honeybees). More than 55% of the visits recorded in wild plant communities surrounding the farms were conducted by bumblebees, showing that bumblebees were present in the system. Pollinator taxa were affected differently by temperature; honeybee visits showed a unimodal relationship with maximum flower visitation activity at a temperature of 24.1 °C, while flower visits by bumblebees showed a positive, linear relationship with temperature. The effect of temperature was much weaker for bumblebees than for honeybees (∼2.2% of the variation was explained by temperature, compared to ∼46% for honeybees). Farming practice affected flower visitation, as flowers within growing tunnels received fewer visits. However, the number of flower visits, also within the growing tunnels, was far above what other studies have shown to be sufficient for optimal pollination in raspberry. We conclude that the raspberry fields were sufficiently pollinated by honeybees but that the system should be considered vulnerable as it is solely dependent on this particular pollinator species. The honeybees were sensitive to ambient temperature suggesting that they might suffer more from future climate change than bumblebees.

Dose‐dependent effects of nectar alkaloids in a montane plant–pollinator community

SummaryAlthough secondary metabolites are prevalent in floral nectar, the ecological consequences for pollinators and pollination remain relatively unexplored. While often deterrent to pollinators at high concentrations, secondary metabolite concentrations in nectar tend to be much lower than secondary metabolite concentrations in leaves and flowers; yet, they may still affect the maintenance of pollination mutualisms.Delphinium barbeyi, a common montane herb, contains norditerpene alkaloids in its nectar but at concentrations that are substantially lower than those found in its leaves or flowers. By manipulating nectar alkaloid concentrations in the field and laboratory, we assessed the degree to which varying concentrations of alkaloids in nectar influenced pollinator behaviour and activity and plant reproduction.In the field, nectar alkaloids significantly reduced both the number of flower visits and the time spent per flower by free‐flying bumblebee pollinators, but we only observed effects at alkaloid concentrations 50 times that of natural nectar. When we supplementedD. barbeyinectar with alkaloids at concentrations almost 15 times that of natural nectar, we found no evidence for direct or pollinator‐mediated indirect effects on female plant reproduction.In the laboratory, the direct consumptive effects of nectar alkaloids on bumblebee pollinators were also concentration dependent. Bumblebees exhibited reduced mobility and vigour but only at alkaloid concentrations more than 25 times higher than those found in natural nectar.Synthesis. We found that nectar alkaloids have dose‐dependent effects on pollinator behaviour and activity. While concentrations of nectar alkaloids rivalling those found in leaves would negatively affect pollinator behaviour and pollination services, the natural concentrations of nectar alkaloids inD. barbeyihave no negative direct or pollinator‐mediated indirect effects on plant reproduction. These results provide experimental insight into the dose‐dependent ecological consequences of nectar secondary metabolites for pollinators and pollination, suggesting that low nectar alkaloid concentrations incurred no ecological costs forD. barbeyi.

Pollination Biology and Seed Production of a Federally Endangered Perennial, Echinacea laevigata (Asteraceae∶Heliantheae)

Abstract Pollination biology and factors affecting reproductive success of the federally endangered Echinacea laevigata (coneflower) were studied in one large and five small populations. Insect visitor exclusion from flowering heads and pollination treatments showed that seed production was 10x higher in open-pollinated treatments compared to bagged flowers that were not pollinated and 20x higher than flower heads receiving self pollen suggesting that cross-pollination was responsible for most seed production. Peak flowering occurred the 2nd–4th wk of Jun. 2004 and the large population contributed 50–68% of the flowering individuals in its plant community. During this period, Bombus (Apidae, bumblebees), Hesperiidae (skippers), and Megachile (Megachilidae, leaf-cutter bees) accounted for 73%, 12%, and 11% of the observed visits to coneflower, respectively. Species richness of coneflower flower visitors and number of flower visits was lower in each small population than in the large population. However, co...

Flower-visiting insect communities on two closely related Rhododendron species flowering in different seasons

To determine the effects of flowering season on the community structure and dynamics of flower visitors, I examined annual and hourly variation in flower-visiting insects on two Rhododendron species in a deciduous secondary forest in central Japan. Rhododendron reticulatum flowers from late March to mid-April, whereas R. macrosepalum flowers from late April to late May. Bagged and hand-pollination experiments indicated that outcrossing by flower visitors was important for the pollination of both R. reticulatum and R. macrosepalum. Pollinator and pollen limitation were detected in both Rhododendron species, although the extent of both differed between the two species. The flowers of both Rhododendron species were visited by insects of diverse taxa, including Hymenoptera, Diptera and Lepidoptera. The composition of flower visitors differed between R. reticulatum and R. macrosepalum, although a few species visited both of them. The beefly Bombyliusmajor (Diptera: Bombyliidae) most frequently visited R. reticulatum, whereas the bumblebee Bombusardensardens (Hymenoptera: Apidae) most frequently visited R. macrosepalum. Hourly changes in the number of flower visitors also differed between R. reticulatum and R. macrosepalum; insects visited R. reticulatum flowers less frequently in the morning than in the afternoon, whereas insect visitations to R. macrosepalum flowers did not differ between morning and afternoon. Differences in both insect community structure and hourly changes of visitations between the two Rhododendron species occurred annually and may be related to the life history of the abundant visitor species as well as flowering phenology.

Space-dependent effects of floral abundance on flower visitors

Previous studies have shown that floral abundance is an important trait to attract flower visitors. However, few studies considered the spatial effects of flower abundance on flower visitors. In this paper, we examined and discussed the relationship between floral abundance and number of flower visitors in three spatial scales.

Alternative pollinator taxa are equally efficient but not as effective as the honeybee in a mass flowering crop

Summary 1. The honeybee Apis mellifera is currently in decline worldwide because of the combined impacts of Colony Collapse Disorder and the Varroa destructor mite. In order to gain a balanced perspective of the importance of both wild and managed pollination services, it is essential to compare these services directly, a priori, within a cropping landscape. This process will determine the capacity of other flower visitors to act as honeybee replacements. 2. In a highly modified New Zealand agricultural landscape, we compared the pollination services provided by managed honeybees to unmanaged pollinator taxa (including flies) within a Brassica rapa var. chinensis mass flowering crop. 3. We evaluate overall pollinator effectiveness by separating the pollination service into two components: efficiency (i.e. per visit pollen deposition) and visit rate (i.e. pollinator abundance per available flower and the number of flower visits per minute). 4. We observed 31 species attending flowers of B. rapa. In addition to A. mellifera, seven insect species visited flowers frequently. These were three other bees (Lasioglossum sordidum, Bombus terrestris and Leioproctus sp.) and four flies (Dilophus nigrostigma, Melanostoma fasciatum, Melangyna novae‐zelandiae and Eristalis tenax). 5. Two bee species, Bombus terrestris and Leioproctus sp. and one fly, Eristalis tenax were as efficient as the honeybee and as effective (in terms of rate of flower visitation). A higher honeybee abundance, however, resulted in it being the more effective pollinator overall. 6. Synthesis and applications. Alternative land management practices that increase the population sizes of unmanaged pollinator taxa to levels resulting in visitation frequencies as high as A. mellifera, have the potential to replace services provided by the honeybee. This will require a thorough investigation of each taxon’s intrinsic biology and a change in land management practices to ensure year round refuge, feeding, nesting and other resource requirements of pollinator taxa are met.

A test of the effect of floral color change on pollination effectiveness using artificial inflorescences visited by bumblebees

Floral color change has been recognized as a pollination strategy, but its relative effectiveness has been evaluated insufficiently with respect to other floral traits. In this study, effects of floral color change on the visitation pattern of bumblebees were empirically assessed using artificial flowers. Four inflorescence types were postulated as strategies of flowering behavior: type 1 has no retention of old flowers, resulting in a small display size; type 2 retains old flowers without nectar production; type 3 retains old flowers with nectar; and type 4 retains color-changed old flowers without nectar. Effects of these treatments varied depending on both the total display size (single versus multiple inflorescences) and the pattern of flower-opening. In the single inflorescence experiment, a large floral display due to the retention of old flowers (types 2-4) enhanced pollinator attraction, and the number of flower visits per stay decreased with color change (type 4), suggesting a decrease in geitonogamous pollination. Type-4 plants also reduced the foraging time of bees in comparison with type-2 plants. In the multiple inflorescence experiment, the retention of old flowers did not contribute to pollinator attraction. When flowering occurred sequentially within inflorescences, type-4 plants successfully decreased the number of visits and the foraging time in comparison with type-2 plants. In contrast, floral color change did not influence the number of visits, and it extended the foraging time when flowering occurred simultaneously within inflorescences but the opening of inflorescences progressed sequentially within a plant. Therefore, the effectiveness of floral color change is highly susceptible to the display size and flowering pattern within plants, and this may limit the versatility of the color change strategy in nature.

Significance of nectar distribution for bumblebee behaviour within inflorescences, with reference to inflorescence architecture and display size

:Because pollinator behaviour within plants affects the mating outcomes of animal-pollinated plants, plants may regulate the pollinator behaviour by controlling floral design and display to maximize pollination efficiency. We assessed how extent of the display size, inflorescence architecture, and nectar distribution within inflorescences alter bumblebee behaviour (number of flowers visited, time of stay, and nectar intake efficiency) under controlled conditions using artificial inflorescences. The effect of display size on bumblebee attraction was also measured. Eighteen types of artificial inflorescences, two display sizes (large and small) × three architectures (panicle, umbel, and raceme) × three nectar distributions (constant nectar content in every flower, gradual changes in nectar content, and random distribution of empty and rewarded flowers) were visited by bumblebees. The mean nectar amount per flower was set as 3 μL in 2003 and 1 μL in 2004. Although the inflorescence architecture had little effect on bumblebee behaviour, the random nectar distribution decreased the number of successive flower visits (both 3 μL and 1 μL) and staying time (only 3 μL) during a single visit and increased the foraging efficiency (both 3 μL and 1 μL). These features may contribute to decreases in the geitonogamous pollination and pollen loss during pollinator movements. Display size did not influence the attraction of bumblebees in this study. Our results suggest that nectar distribution within inflorescences can be a strategy for efficient pollination by manipulating pollinator behaviour.