Single Visit Pollen Deposition Research Articles

Foraging behavior and pollination efficiency of generalist floral visitors of Leucas aspera (Willd.) link (Lamiaceae)

Pollination services from insects are important for the reproductive success of flowering plants. Measuring the effectiveness of floral visitors provide relative contributions of different insect taxa to pollination services. Here, we tested the efficiency of pollinators visiting flowers of Leucas aspera based on single-visit pollen deposition and visitation frequency. We monitored the visitation behaviors of different insects during the peak flowering seasons. We observed a total of 23 insect taxa representing three orders and eight families, among them 18 floral visitors deposited a significant proportion of pollen grains on the stigma. The flower handling time was significantly higher for most butterfly species relative to bees and flies. The number of flowers and inflorescences visited during each foraging bout varied significantly among pollinators. The proportion of conspecific and heterospecific pollen deposited on the stigma varied significantly among floral visitors. L. aspera was not pollen-limited, and the presence of fruit and seed sets in the pollinator exclusion treatments indicated a self-compatible breeding system. Overall, the findings suggested that the different flower visitors of L. aspera provide complementary pollination services and highlight the importance of having diverse communities of pollinators to ensure successful pollination and reproductive success.

Pollen carryover, pollinator movement, and spatial context impact the delivery of pollination services in apple orchards.

Assessing the relative contributions of different pollinator taxa to pollination services is a central task in both basic eco-evolutionary research and applied conservation and agriculture. To that end, many studies have quantified single-visit pollen deposition and visitation frequency, which together determine a pollinator species' rate of conspecific pollen delivery. However, for plant species that require or benefit from outcrossing, pollination service quality further depends upon the ratio of outcross to self-pollen deposited, which is determined by two additional pollinator traits: pollen carryover and movement patterns among genetically compatible plant individuals. Here, we compare the pollination capacities of managed honey bees, native bumble bees, and native mining bees in apple-a varietally self-incompatible commercial crop-when pollen carryover and pollinator movement patterns are considered. We constructed simulation models of outcross pollen deposition parameterized using empirically measured single-visit pollen deposition, visitation frequency, and probabilities of intertree movement exhibited by each pollinator type, as well as pollen carryover patterns simulated based on parameters reported in the literature. In these models, we also explicitly specified the spatial relationships among cross-compatible trees based on field-realistic orchard layout schemes. We found that estimated pollination service delivery was considerably reduced for all pollinator types when pollen carryover and pollinator movement patterns were considered, as compared to when only single-visit pollen deposition and visitation frequency were considered. We also found that the performance of different pollinator types varied greatly across simulated orchard layout schemes and pollen carryover scenarios, including one instance where bumble and mining bees reversed their relative rankings. In all simulations, native bumble and mining bees outperformed managed honey bees in terms of both outcross pollen delivery per unit time and per flower visited, with disparities being greatest under scenarios of low pollen carryover. We demonstrate the degree to which pollination studies may reach inaccurate conclusions regarding pollination service delivery when pollen carryover and pollinator movement patterns are ignored. Our finding of the strong context dependence of pollination efficiency, even within a single plant-pollinator taxon pair, cautions that future studies in both basic and applied pollination biology should explicitly consider the ecological context in which pollination interactions take place.

Stable pollination service in a generalist high Arctic community despite the warming climate.

Insects provide key pollination services in most terrestrial biomes, but this service depends on a multistep interaction between insect and plant. An insect needs to visit a flower, receive pollen from the anthers, move to another conspecific flower, and finally deposit the pollen on a receptive stigma. Each of these steps may be affected by climate change, and focusing on only one of them (e.g., flower visitation) may miss important signals of change in service provision. In this study, we combine data on visitation, pollen transport, and single-visit pollen deposition to estimate functional outcomes in the high Arctic plant-pollinator network of Zackenberg, Northeast Greenland, a model system for global warming-associated impacts in pollination services. Over two decades of rapid climate warming, we sampled the network repeatedly: in 1996, 1997, 2010, 2011, and 2016. Although the flowering plant and insect communities and their interactions varied substantially between years, as expected based on highly variable Arctic weather, there was no detectable directional change in either the structure of flower-visitor networks or estimated pollen deposition. For flower-visitor networks compiled over a single week, species phenologies caused major within-year variation in network structure despite consistency across years. Weekly networks for the middle of the flowering season emerged as especially important because most pollination service can be expected to be provided by these large, highly nested networks. Our findings suggest that pollination ecosystem service in the high Arctic is remarkably resilient. This resilience may reflect the plasticity of Arctic biota as an adaptation to extreme and unpredictable weather. However, most pollination service was contributed by relatively few fly taxa (Diptera: Spilogona sanctipauli and Drymeia segnis [Muscidae] and species of Rhamphomyia [Empididae]). If these key pollinators are negatively affected by climate change, network structure and the pollination service that depends on it would be seriously compromised.

Pollinator identity and behavior affect pollination in kiwifruit (Actinidia chinensis Planch.).

Many crop plants rely on insect pollination, particularly insect-pollinated crops which are functionally dioecious. These crops require insects to move pollen between separate plants which are functionally male or female. While honey bees are typically considered the most important crop pollinator species, many other insects are known to visit crops but the pollination contribution of the full diversity of these flower visitors is poorly understood. In this study, we examine the role of diverse insect pollinators for two kiwifruit cultivars as model systems for dioecious crops: Actinidia chinensis var. deliciosa ‘Hayward’ (a green-fleshed variety) and A. chinensis var. chinensis ‘Zesy002’ (a gold-fleshed variety). In our round-the-clock insect surveys, we identified that psychodid flies and mosquitoes were the second and third most frequent floral visitors after honey bees (Apis mellifera L), but further work is required to investigate their pollination efficiency. Measures of single-visit pollen deposition identified that several insects, including the bees Leioproctus spp. and Bombus spp. and the flies Helophilus hochstetteri and Eristalis tenax, deposited a similar amount of pollen on flowers as honey bees (Apis mellifera). Due to their long foraging period and high pollen deposition, we recommend the development of strategies to boost populations of Bombus spp., Eristalis tenax and other hover flies, and unmanaged bees for use as synergistic pollinators alongside honey bees.

A generalized bird pollination system in Schotia brachypetala (Fabaceae).

Bird pollination systems are diverse, ranging from narrow-tubed flowers pollinated by specialist nectarivores such as hummingbirds and sunbirds, to relatively open flowers pollinated by opportunistic (i.e. generalist) nectarivores. The role of opportunistic avian nectarivores as pollinators has historically been under-appreciated. A key aspect to understanding the importance of opportunistic birds as pollinators is to investigate how efficiently they transfer pollen among flowers. Here, we document the pollination and breeding systems of Schotia brachypetala, a southern African tree known as the 'weeping boer-bean' on account of its prolific production of dilute hexose-dominated nectar. The cup-shaped flowers of this tree attract a large number of bird species, including both opportunistic and specialist nectarivores. We identified floral visitors using observations and camera traps and quantified the floral traits responsible for animal attraction. We documented the breeding system, used selective pollinator exclusion to test the contribution of birds to fecundity, and performed supplemental pollination to test for pollen limitation. Single-visit pollen deposition trials were undertaken to determine the efficacy of bird pollinators. Controlled hand-pollination experiments showed that S. brachypetala is genetically self-incompatible and therefore dependent on pollinators for seed production. Supplemental hand-pollination experiments showed that natural fecundity is limited by either the amount and/or the quality of pollen on stigmas. Flowers from which birds but not insects were experimentally excluded set fewer seeds than open control flowers. Opportunistic birds deposited more pollen per visit than did specialist sunbirds. We conclude that S. brachypetala has a generalized bird pollination system that mainly involves opportunistic nectarivores.

Larger pollinators deposit more pollen on stigmas across multiple plant species—A meta‐analysis

Abstract Many insect species provide essential pollination services. However, the amount of pollen deposited onto a stigma when visiting a flower (‘single visit pollen deposition’, SVD) can vary greatly among taxa depending on morphological traits of pollinators. Further, SVD is commonly measured using one of two methods (‘static’: waiting for an insect to visit a flower present on plant, and ‘active’: removing the flower and presenting it to a flower visitor) that may also differ in their effectiveness. To gain a more comprehensive understanding of how SVD compares among pollinators, we conducted a hierarchical meta‐analysis using data from 28 studies identified by a systematic review. These contained SVD data for 94 bee and 33 fly taxa (hereafter ‘wild pollinators’), across 30 plant species from which we included 127 observations. In the analysis of each study, we used the western honey bee Apis mellifera as a comparator species. Wild pollinators deposited more pollen onto stigmas per single visit than honeybees, and those with larger body deposited significantly more pollen than smaller ones. Of the two methodological approaches to assess SVD, ‘static’ versus ‘active’, we found no significant difference regarding the amount of deposited pollen. Synthesis and applications. Our meta‐analysis highlights the breadth of wild pollinators that contribute to pollination effectiveness via their delivery of pollen to many crop and non‐crop plant species. However, just 25% of the observations assessed the amount of pollen deposited by fly species. Our findings point to the need to further quantify the pollination effectiveness of non‐bee pollinators as studies have largely focused on managed and wild bee species.

Pollen tube growth from multiple pollinator visits more accurately quantifies pollinator performance and plant reproduction

Pollination services from animals are critical for both crop production and reproduction in wild plant species. Accurately measuring the relative contributions of different animal taxa to pollination service delivery is essential for identifying key pollinators. However, widely used measures of pollinator effectiveness (e.g., single visit pollen deposition) may be inaccurate where plant reproduction is strongly constrained by pollen quality. Here, we test the efficacy of single and multiple pollinator visits for measuring pollinator performance in a model plant species (apple, Malus domestica Borkh) that is strongly limited by pollen quality. We determined pollination success using a suite of measures (pollen deposition, pollen tube growth, fruit and seed set) from single and multiple pollinator visits. We found that pollen deposition from a single pollinator visit seldom resulted in the growth of pollen tubes capable of eliciting ovule fertilisation and never resulted in fruit or seed production. In contrast, multiple pollinator visits frequently initiated the growth of pollen tubes capable of ovule fertilisation and often led to fruit and seed production. Our findings suggest that single visit pollen deposition may provide a poor measure of pollinator performance when linked to reproductive success of plant species that are constrain by pollen quality. Alternatively, pollen tube growth from single and multiple pollinator visits can provide a measure of pollinator performance that is more closely linked to plant reproduction.

Quantifying pollination efficiency of flower-visiting insects and its application in estimating pollination services for common buckwheat

Pollination services provided by managed honey bee and wild pollinators are essential for a range of crops. Pollination services can be measured as species-related services, which can be quantified by the combination of each species’ pollination efficiency and their abundance, as well as harvest-related services, which can be quantified by the pollinator exclusion method. Species-related pollination services are poorly documented and have never been directly compared to harvest-related services. Here, we aimed to quantify the pollination efficiency for common flower-visiting species of common buckwheat (Fagopyrum esculentum) and to scale it up to estimate pollination services. We assessed pollination efficiency by single-visit pollen deposition and visitation rate for common flower-visiting insect species. We monitored the abundance of these species during the entire flowering period across seven sites, where pollinator exclusion treatments were undertaken by caging. In total, we observed 27 flower-visiting species and calculated the pollination efficiency of 17 species. We found that flower-visiting species had different capabilities in transferring compatible pollen grains for two flower morphs and different visitation rates. The estimated pollination efficiency was highest for two honey bee species (Apis mellifera and A. cerana), followed by the hoverfly species (Eristalis tenax), and wasp species (Tiphia vernalis). Species-related pollination services estimated by pollination efficiency and abundance showed a strong positive relationship with harvest-related services, which were estimated by the pollinator exclusion method. Our results suggest that to achieve substantial pollination services for common buckwheat, it is important to maintain sufficient managed honey bees, particularly in areas lacking highly efficient wild pollinators species. Our study also suggests that it is possible to estimate pollination services by scaling up the pollination efficiency of common flower-visiting insects. We provide recommendations for the application of this technique.

Mass-flowering crops have a greater impact than semi-natural habitat on crop pollinators and pollen deposition

ContextMaximising insect pollination of mass-flowering crops is a widely-discussed approach to sustainable agriculture. Management actions can target landscape-scale semi-natural habitat, cropping patterns or field-scale features, but little is known about their relative effectiveness.ObjectiveTo test how landscape composition (area of mass-flowering crops and semi-natural habitat) and field-scale habitat (margins and hedges) affect pollinator species richness, abundance, and pollen deposition within crop fields.MethodsWe surveyed all flower visitors (Diptera, Coleoptera and Hymenoptera) in oilseed rape fields and related them to landscape composition and field features. Flower visitors were classified as bees, non-bee pollinators and brassica specialists. Total pollen deposition by individual taxa was estimated using single visit pollen deposition on stigmas combined with insect abundance.ResultsThe area of mass-flowering crop had a negative effect on the species richness and abundance of bees in fields, but not other flower visitors. The area of semi-natural habitat in the surrounding landscape had a positive effect on bees, but was not as important as the area of mass-flowering crop. Taxonomic richness and abundance varied significantly between years for non-bee pollinators. Greater cover of mass-flowering crops surrounding fields had a negative effect on pollen deposition, but only when non-bee pollinator numbers were reduced.ConclusionsManagement choices that result in landscape homogenisation, such as large areas of mass-flowering crops, may reduce pollination services by reducing the numbers of bees visiting fields. Non-bee insect pollinators may buffer these landscape effects on pollen deposition, and management to support their populations should be considered.

Fruit Set and Single Visit Stigma Pollen Deposition by Managed Bumble Bees and Wild Bees in Citrullus lanatus (Cucurbitales: Cucurbitaceae).

Pollinators provide essential services for watermelon, Citrullus lanatus (Thunb.; Cucurbitales: Cucurbitaceae). Managed bumble bees, Bombus impatiens (Cresson; Hymenoptera: Apidae), have been shown to be a useful watermelon pollinator in some areas. However, the exact contribution bumble bees make to watermelon pollination and how their contribution compares to that of other bees is unclear. We used large cages (5.4 × 2.5 × 2.4 m) to confine bumble bee hives to watermelon plants and compared fruit set in those cages to cages containing watermelons but no pollinators, and to open areas of field next to cages (allows all pollinators). We also collected data on single visit pollen deposition onto watermelon stigmas by managed bumble bees, honey bees, and wild bees. Overall, more fruit formed within the open cages than in cages of the other two treatment groups. B. impatiens and Melissodes spp. deposited the most pollen onto watermelon stigmas per visit, but all bee species observed visiting watermelon flowers were capable of depositing ample pollen to watermelon stigmas. Although B. impatiens did deposit large quantities of pollen to stigmas, they were not common within the field (i.e., outside the cages) as they were readily drawn to flowering plants outside of the watermelon field. Overall, bumble bees can successfully pollinate watermelon, but may be useful in greenhouses or high tunnels where watermelon flowers have no competition from other flowering plants that could draw bumble bees away from watermelon.

Contrasting Pollination Efficiency and Effectiveness among Flower Visitors of Malva Sylvestris, Borago Officinalis and Onobrychis Viciifolia

Biotic pollination is an important factor for ecosystem functioning and provides a substantial ecosystem service to human food security. Not all flower visitors are pollinators, however, and pollinators differ in their pollination performances. In this study, we determined the efficiencies of flower visitors to the plant species Malva sylvestris , Borago officinalis and Onobrychis viciifolia by analysing stigmatic pollen deposition. We further calculated pollinator effectiveness by scaling up single-visit pollen deposition using visitation frequency. Flower-visitor groups differed in their efficiencies at the single-visit level and not all of them deposited more pollen compared to unvisited stigmas. Bumblebees tended to be most efficient in depositing pollen per single visit across the three plant species. Due to the by far highest visitation frequencies, Apis mellifera showed the highest effectiveness in depositing pollen per hour for M. sylvestris and B. officinalis , but not for O. viciifolia , for which the Bombus lapidarius complex was both the most frequent and the most effective pollinator group. Hence, the most frequent flower visitors were most effective in our study. For non-dominant pollinator groups, however, visitation frequencies contributed disproportionally to pollinator effectiveness. Thus, combining pollen deposition per single-visit with visitation frequency is necessary to reveal true pollinator performance and to better understand flower-visitor interactions. PLEASE NOTE: Supplementary files to this article can be found in the left menu of this website.

Contrasting pollination efficiency and effectiveness among flower visitors of <i>Malva sylvestris, Borago officinalis</i> and <i>Onobrychis viciifolia</i>

Biotic pollination is an important factor for ecosystem functioning and provides a substantial ecosystem service to human food security. Not all flower visitors are pollinators, however, and pollinators differ in their pollination performances. In this study, we determined the efficiencies of flower visitors to the plant species Malva sylvestris, Borago officinalis and Onobrychis viciifolia by analysing stigmatic pollen deposition. We further calculated pollinator effectiveness by scaling up single-visit pollen deposition using visitation frequency. Flower-visitor groups differed in their efficiencies at the single-visit level and not all of them deposited more pollen compared to unvisited stigmas. Bumblebees tended to be most efficient in depositing pollen per single visit across the three plant species. Due to the by far highest visitation frequencies, Apis mellifera showed the highest effectiveness in depositing pollen per hour for M. sylvestris and B. officinalis, but not for O. viciifolia, for which the Bombus lapidarius complex was both the most frequent and the most effective pollinator group. Hence, the most frequent flower visitors were most effective in our study. For non-dominant pollinator groups, however, visitation frequencies contributed disproportionally to pollinator effectiveness. Thus, combining pollen deposition per single-visit with visitation frequency is necessary to reveal true pollinator performance and to better understand flower-visitor interactions.

Hairiness: the missing link between pollinators and pollination.

BackgroundFunctional traits are the primary biotic component driving organism influence on ecosystem functions; in consequence, traits are widely used in ecological research. However, most animal trait-based studies use easy-to-measure characteristics of species that are at best only weakly associated with functions. Animal-mediated pollination is a key ecosystem function and is likely to be influenced by pollinator traits, but to date no one has identified functional traits that are simple to measure and have good predictive power.MethodsHere, we show that a simple, easy to measure trait (hairiness) can predict pollinator effectiveness with high accuracy. We used a novel image analysis method to calculate entropy values for insect body surfaces as a measure of hairiness. We evaluated the power of our method for predicting pollinator effectiveness by regressing pollinator hairiness (entropy) against single visit pollen deposition (SVD) and pollen loads on insects. We used linear models and AICC model selection to determine which body regions were the best predictors of SVD and pollen load.ResultsWe found that hairiness can be used as a robust proxy of SVD. The best models for predicting SVD for the flower species Brassica rapa and Actinidia deliciosa were hairiness on the face and thorax as predictors (R2 = 0.98 and 0.91 respectively). The best model for predicting pollen load for B. rapa was hairiness on the face (R2 = 0.81).DiscussionWe suggest that the match between pollinator body region hairiness and plant reproductive structure morphology is a powerful predictor of pollinator effectiveness. We show that pollinator hairiness is strongly linked to pollination—an important ecosystem function, and provide a rigorous and time-efficient method for measuring hairiness. Identifying and accurately measuring key traits that drive ecosystem processes is critical as global change increasingly alters ecological communities, and subsequently, ecosystem functions worldwide.

Comparing the performance of native and managed pollinators of Haskap (Lonicera caerulea: Caprifoliaceae), an emerging fruit crop

Fruit set in many crops is dependent on pollinating insects, but the pollination performance of floral visitors can vary tremendously among taxa. Apis mellifera L. is the primary managed pollinator used for most crops, but alternative managed bee species or wild pollinators may be more effective and efficient pollinators. In this study, we compared the performance of A. mellifera to commercial Osmia lignaria Say and wild Bombus spp. as pollinators of Haskap (Lonicera caerulea L.), an early flowering fruit crop grown in northern regions of North America, Europe, and Asia. We conducted field experiments that compared single visit pollen deposition (SVD), foraging behaviour, and pollen load composition among the three taxa. We found that individual Bombus spp. had the highest SVD levels, visited the most flowers per time interval, had high floral constancy, and could tolerate the colder temperatures often experienced during Haskap flowering. Apis mellifera had the lowest SVD levels, spent three times as long per flower as Bombus spp., and were not active during cooler temperatures. However, their potential for high densities in good weather and their affinity for Haskap suggest that as a colony they are important for Haskap pollination. Osmia lignaria rarely visited Haskap when alternative forage such as willow (Salix) was available and therefore contributed very little to Haskap pollination. These results emphasize the economic importance of wild bees in agro-ecosystems, and we conclude that pollination in Haskap orchards can be optimized by providing year-round forage and nesting habitat for wild Bombus spp., in addition to pollination by A. mellifera.

Performance of Apis mellifera, Bombus impatiens, and Peponapis pruinosa (Hymenoptera: Apidae) as Pollinators of Pumpkin

Pollination services of pumpkin, Cucurbita pepo L., provided by the European honey bee, Apis mellifera L., were compared with two native bee species, the common eastern bumble bee, Bombus impatiens (Cresson), and Peponapis pruinosa Say, in New York from 2008 to 2010. Performance of each species was determined by comparing single-visit pollen deposition, percentage of visits that contacted the stigma, flower-handling time, fruit and seed set, and fruit weight per number of visits. Fruit yield from small fields (0.6 ha) supplemented with commercial B. impatiens colonies was compared with yield from those not supplemented. A. mellifera spent nearly 2 and 3 times longer foraging on each pistillate flower compared with B. impatiens and P. pruinosa, respectively. A. mellifera also visited pistillate flowers 10-20 times more frequently than B. impatiens and P. pruinosa, respectively. Yet, B. impatiens deposited 3 times more pollen grains per stigma and contacted stigmas significantly more often than either A. mellifera or P. pruinosa. Fruit set and weight from flowers visited four to eight times by B. impatiens were similar to those from open-pollinated flowers, whereas flowers pollinated by A. mellifera and P. pruinosa produced fewer fruit and smaller fruit compared with those from open-pollinated flowers. Fields supplemented with B. impatiens produced significantly more pumpkins per plant than nonsupplemented fields. B. impatiens was a better pollinator of pumpkin than P. pruinosa and should be considered as a promising alternative to A. mellifera for pollinating this crop.