Pollinator Activity Research Articles

Tree identity and canopy openness mediate oil palm biodiversity enrichment effects on insect herbivory and pollination.

As the extent of oil palm (Elaeis guineensis) cultivation has expanded at the expense of tropical rainforests, enriching conventional large-scale oil palm plantations with native trees has been proposed as a strategy for restoring biodiversity and ecosystem function. However, how tree enrichment affects insect-mediated ecosystem functions is unknown. We investigated impacts on insect herbivory and pollination in the fourth year of a plantation-scale, long-term oil palm biodiversity enrichment experiment in Jambi, Sumatra, Indonesia. Within 48 plots systematically varying in size (25-1600 m2 ) and planted tree species richness (one to six species), we collected response data on vegetation structure, understory insect abundances, and pollinator and herbivore activity on chili plants (Capsicum annuum), which served as indicators of insect-mediated ecosystem functions. We examined the independent effects of plot size, tree species richness, and tree identity on these response variables, using the linear model for random partitions design. The experimental treatments were most associated with vegetation structure: tree identity mattered, as the species Peronema canescens strongly decreased (by approximately one standard deviation) both canopy openness and understory vegetation cover; whereas tree richness only decreased understory flower density. Further, the smallest plots had the lowest understory flower density and richness, presumably because of lower light availability and colonization rates, respectively. Enrichment influenced herbivorous insects and natural enemies in the understory to a lesser extent: both groups had higher abundances in plots with two enrichment species planted, possibly because higher associated tree mortality created more habitat, while herbivores decreased with increasing tree species richness, in line with the resource concentration hypothesis. Linking relationships in structural equation models showed that the negative association between P. canescens and understory vegetation cover was mediated through canopy openness. Likewise, canopy openness mediated increases in herbivore and pollinator insect abundances. Higher pollinator visitation increased phytometer yield, while impacts of insect herbivores on yield were not apparent. Our results demonstrate that even at an early stage, different levels of ecological restoration influence insect-mediated ecosystem functions, mainly through canopy openness. These findings suggest that maintaining some canopy gaps while enrichment plots develop may be beneficial for increasing habitat heterogeneity and insect-mediated ecosystem functions.

Glyphosate-based formulation affects Tetragonisca angustula worker's locomotion, behavior and biology.

Declining bee populations diminish pollination services, damaging plant and agricultural biodiversity. One of the causes of this decline is the use of pesticides. Pesticides with glyphosate as the main active ingredient are among the most used pesticides worldwide, being the most used in Brazil. This study determined the 24 and 48 h LD50 (median lethal dose) of the herbicide's glyphosate-based formulation by ingestion, identified sublethal doses, and investigated its effects on the locomotion and behavior of Tetragonisca angustula workers. The LD50 found indicates that a glyphosate-based formulation is highly toxic to T. angustula. The doses applied, including concentrations found in nature, caused death, motor changes (decreased speed and tremors), excessive self-cleaning, and disorientation (return to light and stop). Although we did not test for pollination effects, we can infer from our results that this formulation can negatively affect the pollination activity of T. angustula. Evaluation of the toxicity and sublethal effects of pesticides on bees contributes to a better understanding of their harmful effects on hives and allows for the development of strategies to reduce these impacts.

B.Y.O. Bees: Managing wild bee biodiversity in urban greenspaces.

As cities become more populated and the density of urban development increases, local biodiversity is threatened. Urban greenspaces have the capacity to preserve pollinator biodiversity, but the quality of support they provide depends on greenspace landscape attributes, including the availability of pollinator habitat and foraging resources. Wild native bees provide important pollination services to urban ecosystems, yet relatively little is known about how urban landscape management influences pollinator community composition and diversity. Our study explores how wild bee communities are affected by greenspace and landscape-level features like pollinator management practices, in urban greenspaces in and around Appleton Wisconsin: a mid-sized urban community spanning more than 100 sq. km. We sampled and identified native bees periodically between late-May 2017 and mid-September of 2018 using standardized arrays of pan traps at 15 sites around the city. We classified greenspaces based on their level of development (urban or suburban) and whether they were managed or unmanaged for increasing wild pollinator diversity. We quantified floral species diversity, floral color diversity, tree species diversity, and proximity of sites to open water for each site and used remotely sensed satellite data from both the USGS National Land Cover Database (NLCD) and the Normalized Difference Vegetation Index (NDVI). All variables were tested as potential correlates of wild bee abundance and species richness. Active pollinator management sites supported higher levels of bee abundance and richness. Notably, active greenspace management (e.g. planting native wildflowers) was a stronger correlate of bee abundance and richness than greenspace size and other landscape-level attributes. Within-greenspace attributes such as floral diversity, tree diversity, and proximity to open water contributed positively to both bee abundance and richness. Based on these findings, we suggest that urban greenspaces may be managed more efficiently and cost-effectively by focusing resources on active management by planting wildflowers, removing invasive species, creating nesting habitat, and providing water resources, rather than simply expanding in area.

Flowers of a South African succulent plant predict tomorrow's weather, synchronizing flower opening with pollinator activity

Abstract Day‐to‐day synchrony between flower opening and pollinator activity is important for maximizing plant fitness. A succulent, Bulbine frutescens (L.) Willd., is an ideal model for studying synchrony in response to daily weather as it flowers year‐round. Additionally, it has self‐incompatible flowers that open for just one day, making it essential that flower opening matches pollinator activity. Observations were made on urban plants in California, USA, with validation measurements in the native range in South Africa. Independent observations indicated that flowers open primarily after favourable conditions the previous day, specifically air temperatures above 15°C. Solar radiation was experimentally shown to have limited, but significant effects. Pollinators, mostly bee species, had similar temperature thresholds to flowers. Developmental constraints on flowers were hypothesized to delay opening by a day. Flower bud growth was closely related to temperature, with warm days resulting in sufficient growth for buds to become competent to open the following day. Laboratory experiments demonstrated that competent flowers were suppressed from opening until at least 16 h was accumulated in which temperatures were above 12°C; thus, on many cool days, sufficient development to cause flower opening would only occur a day after favourable weather. Based upon regression models of pollinator and flower response to weather, fitness was estimated as a function of synchrony, over 20 years of weather from California and across the natural range in South Africa. Flowers responding to either the previous day's or current day's weather resulted in similar predicted fitness, with flower response to the current day's weather leading to a slightly higher cost, that is, flowers opened when pollinators would be absent. Multiple temperature responsive constraints on bud growth and development result in delays in flower opening, such that flower opening occurs the day after favourable weather. Given the high correlation between daily temperatures in USA and South African winter‐rainfall environments, behaviour predicting the following day's weather results in high fitness. Many pollinators share similar temperature thresholds for activity, thus diverse plants may have evolved predictive behaviour maximizing daily synchrony between pollinators and flower opening. Read the free Plain Language Summary for this article on the Journal blog.

Active pollination in a functionally dioecious Ficus species: An interplay between pollinator behaviour and floral morphology

Active pollination has evolved four times in brood site pollination mutualisms. When pollination is active, the pollinator's behaviour specifically evolves to ensure flower fertilisation. In functionally dioecious Ficus species, the male figs host pollinating wasp larvae, while wasps cannot breed in the female figs because the styles are longer than the wasp ovipositor. Here we investigate the dioecious Ficus hispida. We show that in male figs, every time the wasp has laid an egg into a pistillate flower, it removes one pollen grain from its pollen pockets and places it on the hypopygium. When the wasp inserts its ovipositor into the next flower, the pollen grain is deposited deep within the style. Each ovipositor insertion results in flower pollination and insect oviposition. Because of systematic pollination of the flowers into which the eggs are laid, the wasp larvae benefit from feeding on fertilised endosperm while no seed are produced. In female figs, after probing a flower, the wasp presents pollination behaviour only every five visits. However, if it does occur, this behaviour lasts longer than in male figs and results in the deposition of on average 10 pollen grains on the hypopygium. The exposed sticky papillae on the stigmatic surface collect pollen from the hypopygium and pollen tubes may grow to neighbouring stigmas, ensuring secondary dispersal and efficient ovule fertilisation. Overall, our study demonstrates that the floral morphology of male figs facilitates precise pollen deposition, beneficial for the wasp progeny, while the floral morphology of female figs compensates for wasp pollination behaviour that is not selected in those figs. We conclude that the morphology of the arena in which interactions with its pollinator are played out is the result of selection on the plant to maximize its male and female fitness. Incidentally, this morphology stabilises the mutualistic interaction.

Environmental and agronomic determinants of hairy vetch (Vicia villosa Roth) seed yield in rainfed temperate agroecosystems

Vicia villosa Roth, commonly named hairy vetch (HV), is one of the most promising cover crop (CC) legumes, commonly included in strategies aimed at increasing agriculture sustainability. Due to the generally low yield, the availability of commercial seed is often limited. The objective of this study was to identify management and key weather factors governing the variation in HV seed yield. The study comprises a database of 96 fields dedicated to HV seed production distributed in the Pampas region of Argentina, under a wide range of soil and weather conditions. Among the wide range studied, it was found that only poorly drained soils reduced HV seed yield. Crop protection practices, through the application of insecticide plus fungicide, and the axial threshing harvest system were the most important management tools determining high HV seed yield (> 600 kg ha−1). The inclusion of honey bees (HB) as pollinators did not significantly increase the seed yield, which might be due to alternative pollinator activity coming from neighbouring fields. A boundary function showed that an annual precipitation of 680 ± 243 mm and a sowing date during late autumn-early winter appeared to be sufficient to maximise seed yield under rainfed conditions. On the other hand, heat stress (>30 °C) during flowering and seed filling constrained the seed yield. A simplified crop model was developed to explain the effect of the most important factors on the seed yield. Crop management practices that increased the photosynthetic activity, such as foliar protection, were associated with increased seed yield.

Nano Aerial Vehicles for Tree Pollination

Currently, Unmanned Aerial Vehicles (UAVs) are considered in the development of various applications in agriculture, which has led to the expansion of the agricultural UAV market. However, Nano Aerial Vehicles (NAVs) are still underutilised in agriculture. NAVs are characterised by a maximum wing length of 15 centimetres and a weight of fewer than 50 g. Due to their physical characteristics, NAVs have the advantage of being able to approach and perform tasks with more precision than conventional UAVs, making them suitable for precision agriculture. This work aims to contribute to an open-source solution known as Nano Aerial Bee (NAB) to enable further research and development on the use of NAVs in an agricultural context. The purpose of NAB is to mimic and assist bees in the context of pollination. We designed this open-source solution by taking into account the existing state-of-the-art solution and the requirements of pollination activities. This paper presents the relevant background and work carried out in this area by analysing papers on the topic of NAVs. The development of this prototype is rather complex given the interactions between the different hardware components and the need to achieve autonomous flight capable of pollination. We adequately describe and discuss these challenges in this work. Besides the open-source NAB solution, we train three different versions of YOLO (YOLOv5, YOLOv7, and YOLOR) on an original dataset (Flower Detection Dataset) containing 206 images of a group of eight flowers and a public dataset (TensorFlow Flower Dataset), which must be annotated (TensorFlow Flower Detection Dataset). The results of the models trained on the Flower Detection Dataset are shown to be satisfactory, with YOLOv7 and YOLOR achieving the best performance, with 98% precision, 99% recall, and 98% F1 score. The performance of these models is evaluated using the TensorFlow Flower Detection Dataset to test their robustness. The three YOLO models are also trained on the TensorFlow Flower Detection Dataset to better understand the results. In this case, YOLOR is shown to obtain the most promising results, with 84% precision, 80% recall, and 82% F1 score. The results obtained using the Flower Detection Dataset are used for NAB guidance for the detection of the relative position in an image, which defines the NAB execute command.

Theoretical Advances in the Ecology and Evolution of Mutualistic Interactions – Review of a Symposium (SYMP 14) Organized at ESA + CSEE 2022 Joint Meeting

Theoretical Advances in the Ecology and Evolution of Mutualistic Interactions – Review of a Symposium (<scp>SYMP</scp> 14) Organized at <scp>ESA</scp> + <scp>CSEE</scp> 2022 Joint Meeting

The role of floral traits in community assembly processes at high elevations in the Himalayas

Abstract There is a common agreement that, to maximise our understanding of trait‐based community assembly, traits related to different organs should be considered as they relate to different ecological niche axes. Floral traits, in particular, have been suggested to play an important role in the plant community assembly along with environmental gradients as they determine reproductive success, one of the key functions in plants. However, the role of floral traits in community assembly research remains largely unverified empirically. Using a large and novel dataset on plant traits and plant communities, we analysed the variability of six floral traits of 139 herbaceous species in 21 sites located along an elevation gradient (2000–4000 m) in the western Himalayas. The variability of floral traits along the gradient was analysed using community‐weighted mean (CWM) trait values and functional diversities (FDs) calculated for each study community. The CWMs showed that with increasing elevation, flowering began later, and flowers tended to be larger with decreasing specific flower area (SFA). Along with the convergence in the onset of flowering and SFA (i.e. lower FD at high‐elevation sites), these patterns suggest that abiotic filtering and plant–pollinator interactions could affect the floral trait composition of the communities. Most likely, increasing low‐temperature stress towards high‐elevation sites selected for late‐flowering species that produce flowers with larger display areas. The low abundance and activity of pollinators at high elevation could also explain why these traits were selected in the communities studied. Delayed flowering with increasing elevation might facilitate the phenological overlap of plants and their pollinators, as pollinator activity at higher elevation peaks in the second half of the vegetation period. The dominance of a species with low SFA and larger display area in high‐altitude communities could be attributable to increased flower longevity and attraction of pollinators, respectively, to maximise pollination success under pollinator scarcity. Synthesis. Our study provides empirical support for the recent argument that floral traits contribute considerably to the assembly of plant communities along environmental gradients. Thus, such traits should be included in community assembly research as they represent key ecological functions for reproduction.

Moth community among apples during bloom in Northwest Arkansas: likely pollinators and activity periods.

Apples are a fruit crop of economic and nutritional importance that require cross-pollination primarily by insects for sustainable production. It was recently demonstrated that nocturnal pollinators can contribute as much to apple pollination as diurnal pollinators. However, information concerning nocturnal pollinator identity, activity periods, and community composition in apples is lacking, which limits research expansion. To address this knowledge gap, nocturnal moths in an apple orchard were surveyed during apple bloom from 2018 to 2020 using blacklight traps, with samples collected hourly to delineate moth activity. Observations during the same periods were made to identify moths visiting apple flowers, whose capture data were then compared to other captured moth species to provide useful information concerning community composition during apple bloom. Blacklight surveys yielded 1,087 moths representing at least 68 species from 12 families, wherein 15 species from five families were observed visiting apple flowers. Captured moths were most abundant and diverse in the first two hours after sunset. Most captured moth species did not visit flowers and are likely not associated with apple pollination. However, moth species that were observed visiting flowers were the most abundant overall and most diverse by hour in surveys. Data indicate a rich moth community present among apple orchards during bloom and identify likely moth pollinators of apples. Though more research is required to establish the precise relationships between moth pollination and apples, the information provided here allows for targeted efforts to do so.

Pollination ecology of the early-spring-blooming dioecious shrub Eurya japonica (Pentaphylacaceae)

While the majority of angiosperm plants have hermaphrodite flowers, where a single pollinator visit can achieve both pollen removal and deposition, 5%–6% of angiosperms, including zoophilous species, are dioecious, necessitating pollen transport from male plants to females. As such, dioecy is considered less adaptive under low-temperature conditions that tend to restrict or lower potential pollinator activity. Interestingly, however, a number of dioecious, zoophilous plants such as Eurya japonica Thunb. (Pentaphylacaceae) bloom in low-temperature seasons. This study made a quantitative assessment of flower visitors/pollinators of E. japonica blooming in early spring in central Japan. A total of 15 families in 4 orders of insects were recorded on both pistillate and staminate flowers of E. japonica, of which Diptera (Empididae and Chironomidae, in particular) and Hymenoptera were predominant regardless of site/year. Hymenopteran visitors were more active at higher temperatures, while dipterans were observed even at low temperatures. The fruiting rate and the number of seeds were greater at the site where dipteran visitors were more abundant. The present study suggests that the system of multi-taxa, Diptera-dominated pollination may play an important role in the reproductive ecology of dioecious plant species, in particular those flowering at low temperatures.

Urban grassland restorations have reduced plant fitness but not pollinator limitation

Native grasslands worldwide have been greatly reduced due to anthropogenic activities. Grassland restoration efforts strive to increase biodiversity and ecosystem services of these habitats, but often fall short of management goals. This is especially true for small-scale restoration efforts in urban areas, which face unique challenges including increased surface temperatures, increased pollution, decreased habitat connectivity, and decreased pollinator availability. In 2019–2020, we conducted a seed-addition field experiment in four restoration sites near Louisville, KY USA to examine how urbanization influenced survival, growth, and reproduction of a common native forb, Chamaecrista fasciculata. We also conducted observations twice per week to characterize the active pollinator community in each site. We found that plants in urban restoration sites had reduced growth, flowering period, and reproduction compared to those in rural restoration sites. However, pollination rates (visits/flower) in urban sites did not differ from those in rural sites, and urban sites even tended to have greater pollinator effectiveness (seeds/flower) than rural sites. Our results suggest that pollination services are adequate in urban restorations, but that other factors associated with urbanization, such as increased drought stress, can reduce growth and fitness of native plants. Further work is needed to better characterize environmental stresses associated with urban grassland restoration in order to minimize fitness effects on target plant species.

Brassica plants promote Apis mellifera visitation to Japanese apricot in cold conditions

Floral resource enhancements are widely used to boost insect pollination in various crops. The Japanese apricot, a winter-flowering fruit crop, requires mid-winter pollination. However, cold weather can restrict pollinator activity. In this study, we explored the use of Brassica plants, which bloom fully during the Japanese apricot blossom period, as additional flower resources to promote honey bee visitation. We sowed Brassica rapa and used existing feral Brassica plants as additional floral resources to compare the honey bee visitation frequency, visitation behavior, and the number of pollen grains on the stigmas of Japanese apricot flowers with those of the control group. The visitation of the managed honey bee (Apis mellifera) to the Japanese apricot flowers was studied at temperatures below 15 ºC. Under such cold conditions, Brassica flowers increased A. mellifera visitation in both the experimental and commercial orchards. Brassica-rich orchards exhibited clear positive effects of flower resources. Observations of flower-visiting behavior and pollen grains on the stigmas suggest that the increased honey bee visitation to Japanese apricot flowers was not caused by spillover from the Brassica flowers. The flower resources did not increase the number of pollen grains on the Japanese apricot stigmas irrespective of the increase in the number of honey bee visits. Fruit production instability caused by cold weather is a major issue in the agricultural management of commercially cultivated Japanese apricot. The findings suggest that Brassica plants can solve pollination-related problems in Japanese apricot orchards. In addition, Brassica plants are easy to grow, do not have common pests with Japanese apricot, and are beneficial for both apiarists and farmers. Therefore, Brassica plants are a promising floral resource for use in Japanese apricot orchards.

Citizen science initiatives increase pollinator activity in private gardens and green spaces

Wild insect pollinators are essential to cultivated and natural ecosystems globally. Today, many pollinator species are declining. One reason is a general lack of flowering habitats at landscape scales. However, urban areas, including private gardens, may provide flowers, and constitute beneficial habitats for pollinators. Here, we evaluate the ecological outcomes of a citizen science campaign run by the Swedish Society for Nature Conservation (SSNC) (called “Operation: Save the bees”), encouraging citizens to incorporate interventions beneficial to wild pollinators (garden meadows, flower plantings, and bee hotels) in their gardens. Data on insect observations and flowering plants were collected through online questionnaires at the end of the growing season. In total, we received 3,758 responses for the three interventions. We found that participants were more likely to observe many pollinators (as opposed to few or none) in more species rich garden meadows, and in larger and older plantings. The surrounding environment also affected pollinator abundance: fewer pollinators were observed in plantings in dense urban areas. Direct counts of pollinators during 10-min surveys correlated strongly to the simplistic abundance assessment (none, few, or many insects seen over the summer season). Bee hotel occupancy was positively related to local flower availability and bee hotel age. Smaller nest holes (&amp;lt;10 mm) were more occupied than larger holes (11–15 mm) and hotels in rural gardens and natural/semi-natural sites were more occupied than those in urban gardens. This study demonstrates that flower-rich private gardens provide integral habitat for wild pollinators and that citizen science programs can provide a tool for implementing and evaluating conservation practices. However, longer lasting commitment resulting in older interventions are preferable and should be encouraged in future campaigns.

Temporal and spatial niche complementarity in sunflower pollinator communities and pollination function

One of the most invoked mechanisms mediating the positive effect of pollinator diversity on plant reproduction is pollinator's niche complementarity (i.e. partitioning of resource use by different pollinator species). However, the influence of spatial and temporal pollinator's niche complementarity on crop pollination function is rarely tested. We investigated the influence of spatial and temporal niche complementary in explaining sunflower crop production by comparing pollination activity at the edge and centre of crop fields and over the day. We found weaker evidence for spatial niche complementarity than for temporal niche complementarity in pollinator visitation rates. Only the visitation rate of hoverflies slightly differed between the centre and the edge of the fields. Nevertheless, we observed no differences in seed weight between the edge and the centre of the fields, but interestingly, plants allowed to be pollinated only by small-sized pollinators experienced a decline in seed production with distance from the edge. Pollinators did show complementary peak activity periods throughout the day, with Bombus terrestris and honeybees preferring to forage early in the day and at cooler temperatures than B. lapidarius and solitary bees. Unexpectedly, only morning- and only afternoon-pollinated plants produced similar seed weights, but these were higher than in all-day exposed plants. These findings indicate that sunflower fields shelter a small number of complementary pollinator species groups, which become rapidly redundant as diversity increases. Overall, we show that temporal and spatial niche complementarity effects on yield can unfold in unexpected ways, which are hard to predict without testing for the specific mechanisms.

Weather conditions affect pollinator activity, fruit set rate, and yield in Japanese apricot

Japanese apricot blooms in mid-winter, and thus severe weather conditions, including low temperatures, sometimes limit pollinator activity and consequently decrease fruit set rate and yield. Plant physiology is also affected by weather conditions. In this study, we aimed to evaluate the effect of pollinator activity on fruit set rate and yield, in comparison with the effects of meteorological factors. First, we conducted field experiments in 2021 and 2022 at Wakayama prefecture. The results showed that honey bee visitation increased as ambient temperature increased. Fruit set rate also increased under warm conditions when Japanese apricot was naturally pollinated by honey bees. In contrast, hand-pollinated flowers were not affected by ambient temperature. These results revealed that low temperature during the flowering period decreased pollinator visitation but did not affect plant fertilization ability. To compare pollinator activity with meteorological factors over a long period, including the pre- and post-flowering periods, we used a state-space model describing the time series of fruit set rate. The model using fruit set rate data and meteorological records over 15 years (2007–2021) at the Japanese Apricot Laboratory showed that the pre-blossom temperature and number of days suitable for pollination significantly affected the fruit set rate. Another model for the time series of fruit yield using the fruit yield records over 46 years (1976–2021) in Wakayama prefecture showed that fruit yield was affected by number of suitable pollination days, pre-blossom temperature, and sunshine duration before harvest. Moreover, the introduction of Western honey bees into orchards had considerable effects on fruit yield. These results indicate that pollinator activity (which is responsive to weather conditions) and pre-blossom temperature have a significant influence on fruit set rate and yield in Japanese apricot.

Progresses of the international community to understand sunflower–pollinator interactions through multiscale approaches

The first web conference on sunflower–pollinator interactions gathered the international community around a major topic for sunflower productivity and ecosystemic biodiversity. Insect-mediated pollination is important for increasing sunflower seed yield, but is dependent on environmental factors. Climate change can impact sunflower-pollinator interactions by influencing both plant and pollinator behavior. Natural or artificially elevated ambient temperatures appear to accelerate floret development and advance the timing of pollen presentation to coincide with pollinator activities. Drought showed no major effect on morphological traits such anther or corolla length, but dramatically reduced nectar and pollen productions. Flavonol-glycoside conjugates lower head transpiration thereby mitigating deleterious effects of abiotic stresses. Wild pollinators show fine scale preferences among sunflower varieties, likely due to the different resource focus of wild and managed honeybees. Agricultural practices such as planting flower strips to provide nesting sites for wild pollinators, or supplementing crop plots with hives, can have a positive effect on insect-mediated pollination efficiency and ensure optimal yields. All together, recent results on sunflower–pollinator interactions pave the way to develop varieties and corresponding cropping systems more favorable to pollinator biodiversity while maintaining high yields in the context of climate change.

Foraging activities of major bee pollinators in Momordica cymbalaria Hook (Fenzl.)

Foraging activities of major bee pollinators in Momordica cymbalaria Hook (Fenzl.)

Insect pollinator diversity and their foraging behaviour in Radish, Raphanus sativus L.

Radish is a cross-pollinated crop and honey bees are essential for its pollination. In the present investigation, the diversity and abundance of insect pollinators and additionally their visitation rate and frequency were also studied during 2019 and 2020. The foraging observations were noted at 08:00–10:00 hours (early morning foraging activity), 10:00-12:00 hours (late morning foraging activity), 12:00-14:00 hours (noon foraging activity), and 14:00-16:00 hours (afternoon foraging activity). The results revealed that nine species of bees, five flies, three butterflies, and three wasps species visited the flowers of radish during the study period. Apis florea, Apis mellifera, and Apis dorsata were the dominant pollinator species with 132-201, 110-130, and 90-115 individuals, respectively during the study duration. The maximum foraging activity of the dominant pollinators was observed at 14:00 hrs followed by 12:00 hrs whereas the minimum foraging activity was recorded in the early morning hours at 08:00. The frequency of floral visitors varied greatly, with A. florea (14.50-15.80 visits/flower/5 min) being the most frequent, followed by A. mellifera (9.80-11.00 visits/flower/5 min) and A. dorsata (8.30–9.40 visits/flower/5 min) in both seasons. Similarly, A. florea had statistically higher visitation rate (26.93–27.40 flowers visited/min) followed by A. mellifera (15.93–16.00 flowers visited/min) and A. dorsata (12.62-15.13 flowers visited/min). The findings suggested that A. florea, A. mellifera, and A. dorsata may be efficient radish pollinators. Therefore, on a commercial scale, these three species can be effectively used to increase crop yields.

Spatio-Temporal Variations in Pollen Limitation and Floral Traits of an Alpine Lousewort (Pedicularis rhinanthoides) in Relation to Pollinator Availability.

Populations of the same plant species living in different locations but flowering at different times may vary in pollinator availability and floral traits. However, the spatial and temporal links between floral traits and pollination are rarely included in single studies. In this study, three populations of an alpine lousewort, Pedicularis rhinanthoides Schrenk subsp. tibetica (Bonati) Tsoong, were surveyed to detect the variations in floral traits and pollinator activity. We hypothesized that floral divergence was spatio-temporally correlated with pollen limitation (PL) in relation to pollinators. Sampled plants from each population were divided into three groups, according to flowering stage: early, peak, and late. Pollen-supplementation experiments and investigations into pollinators, reproductive success, and floral traits were conducted on the plants from the different flowering stages and across the populations. Our results showed that the extent of PL varies across populations and among flowering stages. Populations in which more pollinators were recorded displayed a lower extent of PL. Furthermore, the temporal differences in PL showed a similar pattern for the three populations; the plants from the peak flowering stage suffered slighter PL than those from the other two stages. Nevertheless, some of the floral traits displayed similar spatial and temporal patterns to the PL, while the others only varied among the populations spatially. The results indicated that the performance of floral traits in a particular spatial-temporal situation shows they are well adapted to the corresponding pollination environment, which might help plants to optimize their reproductive fitness under different abiotic factors.