Pollen deposition experiments are widely used to study pollination systems in a variety of experimental conditions. However, pollen capture techniques available in the literature have not addressed the possibility of using the same experimental flowers multiple times. This study presents an optimized technique designed for quantifying repeated pollen depositions on the same flowers by floral visitors, using Nicotiana otophora Griseb. (Solanaceae) as a model system. The technique consists of attaching a pollen-trapping surface to the floral stigma, which is made of a thin sheet of transparent plastic covered with different adhesive materials tested (double-sided tape, silicone oil, and glycerin jelly). These materials facilitate the adherence of pollen transported by anthophilous bats and deposited onto the stigmatic surface during floral visits. The main advantage of this protocol is the rapid replacement of the pollen-capture surface, allowing the same flower to be reused multiple times and enabling the documentation of fine-scale temporal variation in pollen deposition during anthesis. To validate the methodology, the efficiency of the three adhesive materials was compared after a single visit per flower by two nectar-feeding bats, Glossophaga soricina or Anoura caudifer (Phyllostomidae). There were no significant differences in pollen capture capacity among the different adhesive materials or between the bat species, demonstrating the robustness of the method, independent of the material used and the floral visitor involved. In addition to providing direct evidence of effective pollination by bats in N. otophora, this methodological approach represents a simple, economical, and field-applicable alternative that does not alter the visitor’s behaviour and is useful for comparative studies of pollination effectiveness.
The study of floral biology is essential for identifying key species to be used in urban gardens. Agastache mexicana (Lamiaceae) is a perennial species native to Mexico, widely studied for its medicinal properties. To evaluate its ecological potential, we characterized its floral biology and recorded the taxonomic and functional diversity of visitors (pollinators, nectar robbers and contact species) in a recently implemented pollinator garden. Over 276 hours of observation, 860 visits were recorded from 66 morpho species, distributed across 12 taxonomic orders. Of these, 57% of the records corresponded to nectar robbers, 26% to pollinators, and 17% to contact species (i.e., animals using the plants for predation, mating, nesting, etc.). A GLMM showed positive effect of ambient temperature and contrasting effects of co-flowering species depending on their location within or between patches, respectively. Visits by pollinators and nectar robbers may be related to the presence of long-lasting inflorescences composed of large tubular nectar rewarding flowers in A. mexicana. According to our results A. mexicana contributes to the attraction of high taxonomic and functional diversity, including mutualistic and antagonistic interactions, highlighting its value for implementation in the design of urban gardens focused on pollinator conservation.
An experimental manipulation of ray florets in Knautia arvensis (Caprifoliaceae) carried out in 2001 originally yielded results that were hard to reconcile with a hypothesis about floral attraction. Reframed as a test of florivory the archived data reveal that cutting ray florets left pollinator visitation and seed set essentially unchanged, but altered plant resource economics. Nectar concentration (and consequently available sugar after accounting for volume) declined under the large cutting treatment, while individual seed weight was consistently lower in the cut inflorescences. Together, these patterns suggest that simulated florivory can leave pollination largely intact yet reduce nectar quality and seed provisioning, producing lighter seeds without reducing seed set. More broadly, the study shows how re-examining archived “inconclusive” experiments through alternative perspectives can generate new ecological insights beyond those originally sought.
Borago officinalis L. is an insect-pollinated crop valued for its seed oil. While described as self-compatible, the extent to which its reproductive success depends on pollinator-mediated cross-pollination and whether it experiences pollen limitation in agricultural settings remain key questions for its sustainable cultivation. We experimentally evaluated the effect of five pollination treatments (natural pollination, autonomous self-pollination, artificial cross-pollination, anemophily, and apomixis) on fruit set and nutlet number in a borage experimental population in the Pampas region of Argentina. Artificial cross-pollination yielded the highest reproductive output, while autonomous self-pollination (including possible geitonogamous pollen transfer) and anemophily produced intermediate and similar results. Artificial cross‑pollination increased fruit set by 284% and nutlet number per fruit by 338% compared to natural pollination, demonstrating strong pollen limitation despite the presence of managed honeybees. Apomixis was negligible. Our findings demonstrate that B. officinalis relies on cross-pollination to maximize reproductive success and that even in the presence of managed honeybees, pollen limitation can significantly reduce yield. This highlights the need to ensure adequate pollinator services for the cultivation of this species.
The family Brassicaceae is agriculturally and economically important. However, ecological knowledge gaps persist for some wild species, even in parts of the world that have broadly well-studied flora, like eastern North America. Knowledge gaps for two eastern North American species, Cardamine concatenata and C. diphylla, are concerning for two reasons. First, these species have known associations with rare, specialist insects. Second, the threat posed by the introduction and spread of noxious invasive confamilial garlic mustard (Alliaria petiolata) within their shared native range. Because C. concatenata and C. diphylla have a short phenological window for seasonal development and reproduction they are at increased risk for mutualism disruption via global change pressures. We aim to evaluate the potential for pollination interference by A. petiolata. We compared pollinator visitation and floral phenology in sympatric wild populations of C. concatenata, C. diphylla, and A. petiolata in northeast Ohio. Pollinator counts and morphotype identifications were recorded during in situ pollinator observations. To supplement morphotype identifications, we collected pollinator specimens and identified them to genus or family in the lab. We found overlap in flowering phenology between A. petiolata and C. diphylla. Fourteen pollinator taxa were observed visiting at least one of the focal plant species; of these, seven taxa were recorded visiting all three plant species. Alliaria petiolata is likely disrupting pollination for the native C. diphylla in our sites because flowering phenology overlaps and pollinator taxa are shared. Future studies should focus on range-wide phenological observation and modelling for all three plant species, and pollen load analysis of native plant stigmas in invaded habitats.
Rapeseed (Brassica napus) can benefit from insect pollination to maximize yield. The Argentine Pampas represent one of the most intensively cultivated regions of the world, characterized by landscape homogenization and a reduced availability of natural habitats for wild pollinators. These conditions provide a unique context to explore the contribution of managed and wild pollinators to rapeseed (Brassica napus) yield under highly intensified agricultural systems. The objective of this study was to evaluate the influence of Apis mellifera and wild insect pollinators on quantitative and qualitative components of rapeseed seed yield in fields of the Argentine Pampas, using a caging experiment. Three pollination treatments were applied: open pollination, pollinator exclusion, and A. mellifera-only. Compared to the exclusion treatment, pollination exclusive by A. mellifera increased crop yield by 33%, whereas open pollination resulted in a 20% increase. These differences in total yield were mainly explained by increases in quantitative components, such as number of seeds per fruit and fruits per plant. Seed physiological quality (ripeness, germination power and vigor) followed the same pattern among treatments. Our findings emphasize the importance of adjusting agricultural practices to promote the conservation of wild pollinators in rapeseed crops, and suggest that supplemental pollination with A. mellifera could serve as a useful tool for enhancing crop production under intensive management systems.
Insect pollinators are important drivers of fruit quality and yield in horticultural systems. The global reduction in wild bee populations has increased the demand for managed honeybees, despite honeybees relatively low pollination efficiency. Here, we assessed how bee communities, bee behaviour, and orchard design in Norwegian apple orchards affects apple pollination success, an important determinant of apple quality. We placed pan and vane traps in 18 apple orchards, in six distinct locations, within the two main apple growing regions in Norway. We also tracked individual bees (honeybees, bumblebees, and solitary bees) throughout the apple flowering season, and recorded their flower handling time, number of flower visits, stigma contact, and movement between apple flowers. Finally, we calculated the seed set rate (ovules developed into seeds / total number of ovules) from 908 harvested apples to estimate pollination success. Our key finding is that pollination success was driven by the abundance of wild bees and overall orchard planting design. We found lower pollination success in block design orchards where a single cultivar is planted continuously over a large area, compared to orchards with an integrated design where compatible cultivars are planted within the orchard. We also found that stigma contact decreased as apple flowering progressed, and that solitary bees visited fewer flowers per foraging event but were potentially more thorough foragers. Our results highlight the importance of promoting wild bees in apple orchards while also ensuring there is compatible pollen in the orchards for optimal pollination.
Some Saxifraga species possess an intraindividual variation of flower symmetry and orientation: flowers with horizontally oriented corolla planes are radially symmetrical, whereas flowers with vertically oriented corolla planes are bilaterally symmetrical. Petal size, petal colouration, sequence of stamen movement, and interpetal angles are induced by gravity and thus correlate with symmetry and orientation. The flower visitors' responses to flower symmetry and orientation were tested in the field with fly-pollinated Saxifraga stellaris and S. cuneifolia. Video analysis of approach and landing behaviour showed that the landing site on the flowers was independent of flower symmetry and orientation. The flower visitors’ body axis, however, was aligned with the flowers’ vertical axis in most cases, since most flies land with their heads facing upwards. The flies' movement on the flower is more constrained in vertically oriented flowers: instead of walking around the protruding carpels, they walk over them. In a lab-based experiment, the deposition of pollen surrogate on stigmas of S. fortunei was tested using Episyrphus balteatus hoverflies that were dusted with pigment particles before a single flower visit. The hoverflies deposited more pigment particles on vertically oriented flowers, irrespective of flower symmetry. It is discussed whether vertically oriented bilaterally symmetrical Saxifraga flowers benefit from the avoidance of self-pollination and reduced pollen clogging. The role of differences in bilateral symmetry among Saxifraga species with regard to the display of floral guides in the upper petals, initiation of stamen movement in the lower stamens, petal length and interpetal angles is discussed in the context of pollination efficiency.
Castilleja grisea, the San Clemente Island paintbrush, is endemic to San Clemente Island (Los Angeles County, California). This bushy hemiparasitic perennial was once threatened by livestock and feral herbivore grazing, but occurrences have increased since island-wide non-native herbivore removal. Recently declassified as a federally endangered species, C. grisea remains state listed (California Rare Plant Rank: 1B.3), and a subset of the population is surveyed annually as part of its post-delisting monitoring plan. We investigated the flower-insect interactions of C. grisea and its neighboring plant community at six locations during early, mid, and late in the flowering season. A total of 23 insect taxa were observed visiting 12 species of plants, with 74% of the floral-visitor taxa observed actively visiting C. grisea flowers. Moreover, plots with blooming C. grisea boasted nearly 50% higher insect species richness than areas where the paintbrush was absent or not flowering. Plant-floral-visitor networks changed over time, becoming significantly less connected and exhibiting lower interaction evenness. Our findings suggest that C. grisea supports a diversity of floral visitors and may be an indicator of habitat health and high plant community diversity. As a potential keystone species, conservation planning and management strategies promoting C. grisea may have far reaching benefits for this island ecosystem.
Optimal foraging theory predicts that pollinators will visit dense floral patches over sparse ones. Understanding how the local abundance of floral resources influences pollinator behaviour is crucial for assessing the effect of floral traits on plant reproduction. In this study, we experimentally investigate the role of plant group size and floral display on pollinator foraging behaviour visiting Moricandia arvensis (Brassicaceae). We performed two field experiments: the first manipulated the number of plants per group (group size), and the second manipulated both the total number of flowers per group (group floral display) and group size. We then recorded the foraging behaviour of pollinators using probability of approaching the group, number of plants visited per group, bout length and floral visitation rate. Group floral display was the primary factor influencing pollinator foraging behaviour, except for the probability of approaching the group, where a significant interaction between group floral display and group size was observed. Specifically, the effect of larger floral displays on attracting pollinators increased disproportionately in larger groups. Because the increase in floral visitation rate due to larger displays was less than the increase in the floral display itself, visitation rate per flower was lower in groups with larger displays than in those with smaller displays. Although pollinator foraging behaviour depended largely on local floral resources, the number of plants per group partially shaped the effect of the group floral display on pollinator attraction and visitation rate. This interaction indicates complex effects of neighbouring floral traits on plant-pollinator interactions, which may have important consequences for mating patterns and plant reproductive success.
Insect camera traps are a rapidly developing technology for automated insect monitoring. However, little has been reported on improving the attractants used for daytime flying insects on such cameras. This study compares the attractiveness of 3D-printed artificial flowers with traditional attractants (pan traps and coloured paper squares). We hypothesised that artificial flowers would attract higher insect abundance and diversity by more accurately mimicking flowers, and additionally examined colour preference and landing duration. Artificial flowers, dry pan traps and paper squares, painted in UV-induced fluorescent yellow, white, or blue paint, were filmed simultaneously to observe wild insect behavioural responses (landings and approaches). The results indicate an overall preference for artificial flowers over traditional attractants, and colour preferences for blue and yellow. Analysed by group, hoverflies preferred landing on artificial flowers over the other attractants. Bumblebees preferred approaching artificial flowers, and 'small insects' preferred landing and approaching artificial flowers over the other attractants. 'Other flies' preferred landing on pan traps and paper over artificial flowers. Hoverflies, 'small insects', wasps, and 'solitary bees' responded more to yellow than the other colours, while bumblebees responded more to blue. Analysis of landing probability broadly mirrored these attractant preferences. Landing duration showed limited effects across groups, though 'small insects' spent longer on artificial flowers and pan traps than paper, and hoverflies spent longer on yellow than the other colours. These results suggest artificial flowers could offer an efficient attractant for insect camera traps as they attracted higher abundances of key pollinating insects (hoverflies and bumblebees) without reducing attraction rates for other insect groups (excluding 'other flies').
Plant–pollinator interactions are essential to the functioning of natural and agricultural ecosystems. Although the volume of available data on these interactions is steadily increasing, their utility for integrative studies is limited by heterogeneity in data formats and poor documentation. The WorldFAIR project aimed to improve data interoperability and promote the adoption of the FAIR (Findable, Accessible, Interoperable, Reusable) principles. In this study, we evaluated the effectiveness of two standardisation approaches (manual and semi-automated) applied to five datasets with varying levels of cleanliness, complexity, and structure. Our results show that for small datasets (fewer than 637 records), the manual method is more suitable, while for larger datasets, the semi-automated approach—based on tools such as OpenRefine—is more efficient after an initial learning curve. Additionally, we compiled a list of common issues encountered during the standardisation process and suggested possible solutions. This study aims to guide those interested in applying FAIR principles to ecological interaction data, supporting the planning and decision-making process when choosing the most suitable approach.
Depending on species and season, tree canopies can provide floral resources in abundance. However, researchers often do not consider these resources when sampling bee communities, because they are difficult to access. While observer-based methods, such as hand-netting along transects, are often used for collecting bees from near-ground resources like wildflower strips, flight interception traps (FITs), such as aerial Malaise traps (AMTs) and window interception traps (WITs), can be used for collecting bees from elevated resources like flowering canopies. We assessed the suitability of WITs and AMTs for sampling bees from flowering canopies. We sampled canopies of four different tree taxa (Salix, Malus, Robinia, Tilia) in Braunschweig, Germany, between March and June 2024. In total, we collected 395 bee individuals, including 247 honeybees. Sampled communities comprised ten genera and showed marked differences in the ratio of honeybee and wild bee individuals. In Salix trees, wild bees were more abundant than honeybees, whereas in Tilia trees and especially Robinia trees, honeybees outnumbered wild bees. The collectors above the interception surface of both WITs and AMTs collected no bees. This was surprising, because we expected bees to move upwards upon flight interception, as they do in ground-based Malaise traps. We conducted a systematic literature search in the WoS to compare our findings to previous studies using WITs and AMTs for sampling bees. To our knowledge, our study is the first to show that collectors above the interception surface are generally inefficient when sampling bees with WITs and AMTs. Our study provides methodological advice for future researchers seeking to sample pollinators in tree canopies.
Urban green spaces have gained importance in view of growing urbanization; however, limited research exists on the interactions of native plants with the local fauna, particularly comparing protected natural areas vs. recreated ones. To help fill this gap, the floral biology and pollination of Abutilon grandifolium (Malvaceae) were studied in an Ecological Reserve and in a square where the local environment had been recreated with native plants, both located in Ciudad Autónoma de Buenos Aires, Argentina. A. grandifolium was self-compatible. The flowers presented typical traits associated with biotic pollination (ornamented pollen, conspicuous perianth and rewards), particularly melittophily (diurnal anthesis, nectar, yellow-orange coloration and pleasant odour). At both sites, the most frequent visitors were Apis mellifera and halictid bees, collecting nectar and/or pollen. While visits from the former were predominantly illegitimate, halictids mostly performed legitimate visits. Occasional visitors included the bees Xylocopa sp. and Bombus pauloensis, syrphid flies and, more rarely, beetles. Large quantities of A. grandifolium pollen were found on all bee species, in positions compatible with an effective transfer to the stigmas, indicating that they likely pollinate when accessing flowers legitimately. In contrast, flies and beetles would be mainly pollen and nectar thieves. In general, the identity, frequency and activity of the floral visitors were similar at both sites, with species richness even higher in the square; suggesting that restored native plantings can support functional pollination processes in urban green spaces.
Response to Krahner et al. (2025) Build the EU Pollinator Monitoring Scheme on robust evidence. Journal of Pollination Ecology 38(13): 183-185. https://doi.org/10.26786/1920-7603(2025)846 (this issue)
Pollination syndromes describe convergent floral traits linked to specific pollinator groups. While conceptually useful, the application of this framework to diverse insect assemblages, such as Diptera, remains challenging due to their functional heterogeneity. Recent studies have therefore proposed narrowing dipteran pollination into more precise syndromes. In this context, preliminary field observations of flower visitors to Succisella microcephala suggest a potential case of specialisation towards tachinid flies. Despite its generalist-like floral morphology, S. microcephala exhibits geographic variation in corolla colour and contrasting pigmentation between the corolla tube and lobes. Field observations revealed that populations with darker, more contrasting, flowers were predominantly visited by tachinid flies, which were particularly abundant at higher elevation sites, where Deschampsia cespitosa, an important food plant for moth larvae – the main larval hosts of tachinids – was also abundant. These observations suggest a potential adaptive relationship between floral pigmentation and tachinid attraction. Comparative evidence from other European taxa (e.g., Neotinea ustulata) further supports the hypothesis of shared, visually mediated traits favouring tachinid attraction and pollination. Additionally, the proximity between flowering and fruiting structures, and the striking resemblance between the dark red immature diaspores of S. microcephala and the similarly pigmented globular floral structures in plants associated with tachinid pollination, raise the novel possibility of diaspore-mediated pollinator attraction. Here, we suggest that dark colour structures may be associated with tachinid pollination and tachinid flies may act as potential drivers of an as-yet undescribed pollination syndrome. Succisella microcephala represents a promising system to investigate the potential convergence of floral and diaspore traits under pollinator-driven selection and tachinid sensory ecology.
Flowers display remarkable diversity, much of which is shaped by interactions with pollinators. While various floral traits are considered adaptations to pollination, the function of many morphological features remains untested. In buzz-pollinated species, where bees use vibrations to extract pollen, anther morphology is diverse and can influence pollen removal and transfer. Poricidal anthers, common in these species, sometimes bear spur-like projections. These spurs are hypothesized to aid pollen release, but this has not been experimentally tested. Here, we investigated the function of anther spurs in Vaccinium myrtillus (Ericaceae). Using a laboratory setup, we conducted two complementary experiments: one where Bombus terrestris bumblebees foraged on flowers, and another applying 1 s artificial vibrations to mimic bee buzzes. We compared pollen release between flowers with intact anther spurs and those where spurs had been removed. Bumblebees produced vibrations during 90% of visits, irrespective of spur presence. Buzzing visits were shorter (21.70 ± 24 s; mean ± SD) and removed more pollen (60 ± 29%) than non-buzzing visits, which were three times longer (63.79 ± 70.45 s) but removed 23 ± 43% of pollen. Artificial 1 s buzzes removed an average of 23% of pollen. Spur removal increased pollen release in both the bee (54% to 60%) and the artificial buzzing experiment (18% to 28%). Our results suggest that anther spurs in V. myrtillus potentially act as a pollen-dispensing mechanism, but this effect depends on bee behaviour and visit duration. Further studies could explore other roles the spur has in interactions with non-buzzing visitors, such as regulating pollen release when visitors collect nectar.
Due to shared evolutionary history, native pollinator diversity and coexistence is promoted by niche partitioning and behavioural differences between species. Introduced insect species, however, have potential to compete with wild pollinators and negatively affect native insect populations. Honeybee (Apis mellifera) is an introduced pollinator species in northern Europe and may affect native pollinator populations negatively. Diversity in plant communities also promotes variation in the associated pollinator communities. Diversity of a community encompasses not only species diversity but includes within species variation as well. Within species, genetic diversity could promote insect coexistence and affect competitive interactions between pollinator insects. In this study, we measured floral visitation rates in female and hermaphrodite Geranium sylvaticum genotypes in the presence and absence of a beehive (Apis mellifera) in an experimental field located in Central Finland. We show that competition with honeybees reduced visitation rates by bumblebees, but not by other native pollinator groups. Furthermore, bumblebees preferred some plant genotypes in the absence of the honeybees, but not in the presence of honeybees. Overall, bumblebees preferred females over hermaphrodite plants, but honeybees showed no such preference. Our study links the native pollinators and genetically diverse plant populations, and sheds light on the competition between pollinator insects.
Plant-pollinator interactions affect the quantity and identity of pollen delivered to stigmas, influencing plant genetics and fitness. Here, we test the pollen competition hypothesis, which predicts that competition among pollen grains yields higher-quality offspring, by hand-pollinating Allium stellatum with pollen from one, two, or three donors while controlling pollen load size. We germinated seeds and assessed seed and seedling traits using generalised linear mixed-effects models. We found that flowers that received pollen loads with a greater number of donors had slower growing seedlings but also had a greater proportion of seeds that successfully germinated. These results provide mixed support for the pollen competition hypothesis, in that greater donor diversity leads to higher female reproductive success, but with a possible trade-off in progeny vigour. Pollen donor diversity thus affects reproductive outcomes and should be considered when examining how pollinators influence plant population dynamics.
Pollinators play a vital role in most terrestrial ecosystems, supporting wild plant communities and enhancing agricultural yields. However, despite their ecological and economic importance, they have been experiencing an alarming decline over the past decades. The Mediterranean region, known for harboring highly diverse communities of plants and pollinators, is particularly vulnerable due to intense anthropogenic pressures. Furthermore, the ecological roles of many floral visitors remain poorly understood, hindering conservation efforts. In response, in recent years, growing attention has been directed toward the contribution that citizens can give in support of pollinator research. An increasing number of projects have adopted a Citizen Science approach to enable large-scale data collection. The LIFE 4 Pollinators project (LIFE18/GIE/IT/000755) “Involving people to protect wild bees and other pollinators in the Mediterranean” aims to promote the conservation of pollinating insects and entomophilous plants across the Mediterranean region by fostering progressive changes in human practices that threaten wild pollinators. In addition to the implementation of several actions to raise awareness, the project launched a web platform to collect photographic records of flower–insect interaction from the public. The platform is expected to remain active for at least ten years, during which we encourage continuing record submissions by interested bodies. With this data paper we are making the current dataset freely accessible to anyone, committing to periodic online updates.
