Effective Pollinators Research Articles

Effects of honeybee (Apis cerana) visiting behaviour on toxic plant (Tripterygium hypoglaucum) reproduction.

Honeybees play a significant role in the plant–pollinator interactions of many flowering plants. The ecological and evolutionary consequences of plant–pollinator interactions vary by geographic region, and the effects of honeybees on the reproduction of toxic plants have not been well studied. We measured the florescence of toxic plants, the flower-visiting behaviour of honeybees and the effects of pollination on the fertility, weight and moisture content of seeds. The effects of climatic factors on the number of flowers, and the spatial and temporal variation in pollinator visits were evaluated, and the effects of pollinator visits on seed quality were evaluated. Flower visitors were diverse, climatic factors had a great impact on spatio-temporal flowering variation and the number of bee visits was strongly correlated with the spatio-temporal variation in the number of flowers. Honeybees strongly increase the fullness and weight of seeds. Our study demonstrated a good ecological fit between the spatio-temporal variation in the flowering of toxic plants and the general validity of honeybee pollination syndrome in the south of Hengduan Mountains in East Asia. A linear relationship between honeybee visitation and plant reproduction can benefit the stabilization of plant reproduction.

Cacao flower visitation: Low pollen deposition, low fruit set and dominance of herbivores

Abstract Pollination services of cacao are crucial for global chocolate production, yet remain critically understudied, particularly in regions of origin of the species. Notably, uncertainties remain concerning the identity of cacao pollinators, the influence of landscape (forest distance) and management (shade cover) on flower visitation and the role of pollen deposition in limiting fruit set. Here, we aimed to improve understanding of cacao pollination by studying limiting factors of fruit set in Peru, part of the centre of origin of cacao. Flower visitors were sampled with sticky insect glue in 20 cacao agroforests in two biogeographically distinct regions of Peru, across gradients of shade cover and forest distance. Further, we assessed pollen quantities and compared fruit set between naturally and manually pollinated flowers. The most abundant flower visitors were aphids, ants and thrips in the north and thrips, midges and parasitoid wasps in the south of Peru. We present some evidence of increasing visitation rates from medium to high shade (40%–95% canopy closure) in the dry north, and opposite patterns in the semi‐humid south, during the wet season. Natural pollination resulted in remarkably low fruit set rates (2%), and very low pollen deposition. After hand pollination, fruit set more than tripled (7%), but was still low. The diversity and high relative abundances of herbivore flower visitors limit our ability to draw conclusions on the functional role of different flower visitors. The remarkably low fruit set of naturally and even hand pollinated flowers indicates that other unaddressed factors limit cacao fruit production. Such factors could be, amongst others, a lack of effective pollinators, genetic incompatibility or resource limitation. Revealing efficient pollinator species and other causes of low fruit set rates is therefore key to establish location‐specific management strategies and develop high yielding native cacao agroforestry systems in regions of origin of cacao.

Short flowers for long tongues: Functional specialization in a nocturnal pollination network of an asclepiad in long‐tongued hawkmoths

AbstractSince Darwin, very long and narrow floral tubes have been known to represent the main floral morphological feature for specialized long‐tongued hawkmoth pollination. However, specialization may be driven by other contrivances instead of floral tube morphology. Asclepiads are plants with a complex floral morphology where primary hawkmoth pollination had never been described. We detailed here the intricate pollination mechanism of the South American asclepiad Schubertia grandiflora, where functional specialization on long‐tongued hawkmoth pollinators occurs despite the short floral tube of this species. We studied two plant populations in the Brazilian Cerrado and recorded floral visitors using different approaches, such as light‐trapped hawkmoths for pollen analysis, direct field observations, and IR motion‐activated cameras. Finally, using a community‐level approach we applied an ecological network analysis to identify the realized pollinator niche of S. grandiflora among the available niches in the pollinator community. Throughout a period of 17 years, long‐tongued hawkmoths were consistently recorded as the main floral visitors and the only effective pollinators of S. grandiflora. Flowers rely on highly modified corona and gynostegium, and enlarged nectar chambers, to drive visitors and pollination mechanism. Despite its relative short‐tube, network analysis placed S. grandiflora in the module including exclusively long‐tongued hawkmoth pollinators and the most phenotypically specialized sphingophilous plants in the community. These results represent the first example of functional specialization in long‐tongued hawkmoths in an asclepiad species. However, this specialization is uncoupled from the long floral tubes historically associated with the sphingophily syndrome.Abstract in Portuguese is available with online material.

Different landscape features within a simplified agroecosystem support diverse pollinators and their service to crop plants

ContextLandscape simplification is a main driver of insect decline, threatening crop pollination services. Changes in functional features in simplified agroecosystems may impact the abundance of wild pollinators.ObjectivesHere, we studied whether different pollinator groups based on life-history are differentially associated to landscape features, and how this affects crop pollination service delivery.MethodsUsing window traps in a highly simplified agroecosystem, we surveyed pollinator abundances and diversity associated with: (1) bare fence-lines separating pastures (control), (2) conifer hedgerows (3) farm gardens of diverse exotic plant species (4) effluent-ponds, (5) newly established native-plantings, (6) gorse (Ulex europaeus) hedgerows and (7) open water channels across six to twelve dairy farms. We also measured pollination service delivery to potted pak choi (Brassica rapa) plots near features 1–5 on six farms.ResultsPollinators at gardens, native-plantings, and effluent-ponds delivered significantly more pollination service than at bare fence-lines, with flies being more effective pollinators than bees at all features assessed. Taxa delivering the service also differed across features. The native bee Lasioglossum sordidum delivered more pollination at garden and native-planting features than at other features, drone flies (Eristalis tenax) contributed the majority of pollination service at effluent-ponds and bare fence-lines, while calliphorid flies contributed most pollination at conifer hedgerows.ConclusionsConversion of functional features to bare fence-lines negatively affects on-farm pollinator diversity and its service to crop plants. However, farmers can benefit from enhancing features containing diverse plant species that support non-bee and bee species proven to deliver measurable crop pollination services.

Benefits of Insect Pollination in Brassicaceae: A Meta-Analysis of Self-Compatible and Self-Incompatible Crop Species

This paper reviewed the effects of insect pollination on the yield parameters of plants from the family Brassicaceae presenting different breeding systems. Meta-analysis indicates that in both self-compatible and self-incompatible crop species, meta-analysis indicates that seed yield (Y), silique set (SQS), number of siliquae/plant (NSQ), and the number of seeds/silique (NSSQ) increase when plants are insect-pollinated compared to when there is no insect pollination. The weight of seeds (WS), however, increased in self-incompatible species but not in self-compatible ones as a result of insect pollination. Overall, the percentage of studies showing a positive effect of insect pollination on yield parameters was higher in self-incompatible than in self-compatible species. It was shown that the ability of self-compatible species to reproduce does not fully compensate for the loss of yield benefits in the absence of insect pollination. Cultivated Brassicaceae attract a wide variety of pollinators, with honeybees (Apis spp.) such as A. mellifera L., A. cerana F., A. dorsata F., and A. florea F. (Hymenoptera: Apidae); other Apidae, such as bumblebees (Bombus spp.) (Hymenoptera: Apidae); mining bees (Hymenoptera: Andrenidae); sweat bees (Hymenoptera: Halictidae); and hoverflies (Diptera: Syrphidae) constituting the most common ones. The benefits of insect pollination imply that pollinator conservation programs play a key role in maximizing yield in cruciferous crops.

Remarkable floral colour variation in the functionally specialized fly-pollinated iris,Moraea lurida

AbstractSapromyophilous flowers are visited by flies seeking carrion or faeces, and flowers of this guild are typically large, purple or red-brown, often speckled and produce a pungent scent. Flowers of the South African iris Moraea lurida conform to this syndrome, but show considerable variation in colour and pattern. We were intrigued by the floral variation within a single population and investigated floral visitors and the effect of body size on pollen loads and whether different colour forms attracted different pollinator assemblages. We found a diverse array of insect visitors, but Diptera comprised the overwhelming majority, with Calliphoridae considered to be the most important for pollination on the basis of their visitation frequency and pollen loads. Effective pollination appeared to be dependent on large-bodied flies that, unlike smaller flies, fit the entire crawl space between the anthers and petals and thus acted like a key in a lock. Choice experiments revealed that the most important fly pollinators showed no colour preferences, and fly vision modelling showed that flies may not be able to discriminate among the different colour forms. This may lead to relaxed selection on colour. Floral scent was dominated by an unusual mix of aliphatic acids and alcohols, characteristic of mammalian skin products and gut microbiome, probably exploiting the perceptual bias of flies to compounds that typify the mammalian microbiome and fermenting carbohydrates.

Brief Pollination Assessment of a Critically Endangered Food-Deceptive Orchid (Cypripedium guttatum) Using a Network Approach.

The translocation of orchids (Orchidaceae) cannot be successful if one is unaware of their effective pollinators and plant–pollinator interactions. Cypripedium guttatum is a generalized food-deceptive orchid, which is highly threatened in the Republic of Korea, thus, requiring immediate translocation actions. Although effective pollinators of the orchid are well known in China, little is known about the pollinators in the Republic of Korea and the ecological context in which the orchid can be successfully pollinated. To briefly assess the pollination of C. guttatum prior to translocation, we conducted a one-month survey of general pollination and the community-wide plant–pollinator network properties. Over 21 h of observation, we found that an effective pollinator of the orchid was the sweat bee Lasioglossum virideglaucum. The network was significantly specialized and modular, but not significantly nested. L. virideglaucum (pollinator) and Arabis gemmifera (plant) were determined to be keystone species, based on network metrics. A total of six network modules were identified and the flower colors of the plant species belonging to the C. guttatum module were purple, white, and yellow. After comparing the daily network patterns, we found that pollination of the orchid was accomplished when various flowering plant species bloom, and the nestedness value was high. This study revealed that high plant and pollinator richness could increase the chance that the deceptive orchid would be pollinated. Our study suggests that the network properties of this food-deceptive orchid community could provide useful insight into understanding the ecologically suitable habitat for the translocation of the highly threatened orchid species C. guttatum.

High flower richness and abundance decrease pollen transfer on individual plants in road verges but increase it in adjacent fields in intensively managed agroecosystems

Road verges can facilitate the movement of pollinators and pollen in intensively managed agroecosystems, reducing the negative impacts of fragmentation (i.e., isolation of wild pollinator communities) and enhancing the pollination service provided to wild plants. To assess the role of road verges in sustaining the pollination service to wild plants, we studied gardens consisting of two plant species arranged within sixteen road verges and their adjacent fields during two consecutive seasons in the Argentine Pampas. We assessed the influence of attributes of road verges on pollination service at different scales: road verges width, species richness of flowering plant, and flower abundance (patch scale), crops and successional pastures (adjacent land use scale), and landscape heterogeneity (landscape scale). We measured the pollination service provided to two species of potted plants (Hirschfeldia incana and Lobularia maritima) in three different ways: visitation rate, conspecific and heterospecific pollen transfer to stigmas, and distance of pollen transfer from a fixed source. The number of conspecific and heterospecific pollen grains deposited on stigmas decreased with an increased abundance of floral units in associated road verges, which is caused by a dilution effect on individual plant pollination. Also, the pollen transfer into adjacent fields decreased with an increased abundance of floral units in the nearby road verges, which is caused by a decrease of pollen spillover into adjacent crop fields. The visitation rate within adjacent fields increased with higher flowering plant species richness in associated road verges. Also, the number of conspecific pollen grains in the road verges adjacent to successional pastures increased with higher flowering plant species richness in road verges, which results in a concentration effect of pollinator visits and pollen transfer into road verges. We conclude that managing flower abundance and increasing flowering plant species richness in road verges are crucial practices for maintaining the pollination service of entomophilous plants in intensively managed agroecosystems.

Evaluation of morphological traits of flowers and crossing possibility of haskap (Lonicera L.) cultivars depending on their origin

BACKGROUND: Haskap (Lonicera L.) is as a new perspective berry species for growing in temperate region climate. According to nowadays knowledge haskap is absolutely self-sterile species hence the studies on pollination mode are required. OBJECTIVE: The aim was to evaluate new haskap cultivars of Canadian and Russian origin in terms of their matching for cross-pollination. METHODS: The overlapping of flowering time of cultivars for mutual cross pollination was selected. The effectiveness of pollination was assessed: in terms of pollen tube overgrowth through the pistil tissue and the quality of set fruit. RESULTS: The Russian cultivars bloomed much earlier than the Canadian cultivars. The stigma is most receptive in the freshly open flower stage and directly after the anther burst. The minimum qualitatively acceptable weight of a berry is 1 g, which corresponds to the formation of about 6 seeds in the fruit. The most compatible pairs of cultivars were: ‘Aurora’בJugana’, ‘Aurora’בSinij Utes’ and ‘Aurora’בVostorg’. CONCLUSION: The Russian cultivars bloomed much earlier than the Canadian cultivars, the stigma is most receptive in the freshly open flower, minimum qualitatively acceptable weight of berry is 1 g (what represents 6 seeds in fruit), best mutual pollinating cultivars are the cultivars within the same breeding group (Russian x Russian and Canadian x Canadian)

Habitat effects on reproductive phenotype, pollinator behavior, fecundity, and mating outcomes of a bumble bee-pollinated herb.

PremiseFecundity and mating outcomes commonly differ among plant populations occupying contrasting environments. If self‐pollination occurs primarily among flowers within plants, contrasting reproductive outcomes among populations must reflect environmental effects on plant‐pollinator interactions. Specifically, local conditions could affect features of plant phenotypes that influence pollinator behavior, in turn modifying plant reproductive outcomes.MethodsWe compared phenotypes, pollinator abundance and behavior, and female fecundity and mating in two meadow populations and two forest populations of Aconitum kusnezoffii within 3 km of each other. Mating outcomes were assessed using microsatellites.ResultsMeadow plants generally produced more, shorter ramets with more, larger flowers, but less nectar per flower than forest plants. These differences likely largely represent phenotypic plasticity. Individual bumble bees visited more flowers on forest plants, likely because the more abundant bees in the meadows depleted nectar availability, as indicated by briefer visits to individual flowers. Despite similar fruit set in both habitats, forest plants set more seeds per fruit. Nevertheless, meadow plants produced more seeds overall, owing to sevenfold greater flower production. Consistent with individual bees visiting fewer flowers on meadow plants, more of their seeds were outcrossed. However, the outcrossed seeds of forest plants included more male mates.ConclusionsReproductive outcomes can vary among populations of animal‐pollinated plants as a result of differences in the availability of effective pollinators and environmental effects on plant phenotypes, and their functional consequences for pollinator behavior that governs pollen dispersal.

Intraspecific independent evolution of floral spur length in response to local flower visitor size in Japanese Aquilegia in different mountain regions.

Geographic differences in floral traits may reflect geographic differences in effective pollinator assemblages. Independent local adaptation to pollinator assemblages in multiple regions would be expected to cause parallel floral trait evolution, although sufficient evidence for this is still lacking. Knowing the intraspecific evolutionary history of floral traits will reveal events that occur in the early stages of trait diversification. In this study, we investigated the relationship between flower spur length and pollinator size in 16 populations of Aquilegia buergeriana var. buergeriana distributed in four mountain regions in the Japanese Alps. We also examined the genetic relationship between yellow‐ and red‐flowered individuals, to see if color differences caused genetic differentiation by pollinator isolation. Genetic relationships among 16 populations were analyzed based on genome‐wide single‐nucleotide polymorphisms. Even among populations within the same mountain region, pollinator size varied widely, and the average spur length of A. buergeriana var. buergeriana in each population was strongly related to the average visitor size of that population. Genetic relatedness between populations was not related to the similarity of spur length between populations; rather, it was related to the geographic proximity of populations in each mountain region. Our results indicate that spur length in each population evolved independently of the population genetic structure but in parallel in response to local flower visitor size in different mountain regions. Further, yellow‐ and red‐flowered individuals of A. buergeriana var. buergeriana were not genetically differentiated. Unlike other Aquilegia species in Europe and America visited by hummingbirds and hawkmoths, the Japanese Aquilegia species is consistently visited by bumblebees. As a result, genetic isolation by flower color may not have occurred.

Stingless Bees Pollination Increases Fruit Formation of Strawberry (Fragaria x annanassa Duch) and Melon (Cucumis melo L.).

Stingless bees (Apidae: Meliponini) are distributed in tropical and subtropical areas in the world. Stingless bees are potential pollinator to increase yield of various crops species. We measured the pollination effectiveness of stingless bees, i.e., Tetragonula laeviceps in strawberry (Fragaria x annanassa) and Heterotrigona itama in melon (Cucumis melo) in the greenhouse. Pollination effectiveness of stingless bees were measured based on their visiting activities, i.e., foraging rate and flower handling time using focal sampling method. Measurements of fruit set consist of the number of fruits per plant, the number of normal and abnormal fruits, and the size and weight of fruits. Results showed that visiting activity of T. laeviceps in strawberry flowers ranged 2.33–2.73 flowers/3 min, while H. itama in melon flowers ranged 1.77–7.12 flower/3 min. Peak activities of H. itama in melon (7.12 flowers/3 min) occurred at 9.00 a.m. to 10.00 a.m., while T. laeviceps in strawberry (2.73 flowers/3 min) occurred at 11.00 a.m. to 12.00 p.m. Pollination by T. laeviceps increased 78.9% of fruit formation and reduced 16.7% of abnormal fruits of strawberry. In melon, ratio between female and male flowers was 0.03. The number of fruits produced in melon with T. itama (6.1 fruits/plant) was higher than in open field (2.6 fruits/plant) and control plants (no pollination) (0.2 fruits/plant). Pollination by H. itama increased fruit formation of melon.

Supplemental bee pollination effect on the productivity of soybean grown in a low yield potential condition

Brazil is the leading soybean producing country in the world, and soybean is the major crop of Brazilian agriculture, spread over 36 million hectares during the 2020/21 season, producing almost 125 million tons. The honey bee, Apis mellifera Linnaeus, 1758 (Hymenoptera: Apidae), and other bees are known as soybean flowers visitors, being potential pollinators of the crop, normally resulting in higher soybean yields. Over the last ten years, it has been observed an increasing interest of both beekeepers and soybean growers, to place honey bee colonies close to soybean fields, using the crop as a forage source. In the majority of the reports of soybeans growers, an increase of the soybean yield was observed when following this practice, while a small number claimed no yield modification. The purpose of the present work was to study the effect of visits of individuals of A. mellifera to soybean flowers and the consequent pollination on soybean productivity, when there is a constraint to the expression of the potential crop yield. The experiments were set up in Londrina, Brazil, during the 2016/17 and 2019/20 crop seasons, in areas with known sub superficial compaction layers, preventing soybean roots from deepening in the soil, therefore restricting the absorption of water and nutrients by the plants. Treatments consisted of 1) open plots, resembling a typical grower field with free access of bees; 2) a caged plot with an A. mellifera beehive inside, and 3) a caged plot with no bees or any other potential pollinating insect inside. Results indicated no yield differences due to the pollination of soybean flowers by the bees, compared to the treatment with the absence of bee visit. Among the yield components, only pods with 1 or 2 seeds were lower on caged plots with bees on the 1st experiment. No differences were detected for all others observed parameters on 1st and for all components on 2nd experiments. Observations of the honey bee behavior demonstrated that only 27.9% of the bee visits to soybean flowers resulted in nectar hoarding, with a time lapse of 4.52 seconds for a visit to a single flower. When a flower was only tested (72.1%), without nectar collection, the average time of a honey bee visit was 1.38 seconds. New studies should be performed to verify if other biotic or abiotic stresses that depress soybean yield also prevent the expression of the benefit of bees’ pollination to soybean yield.

Reproductive biology of an endangered lithophytic shrub and implications for its conservation

BackgroundPlants in cliff habitats may evolve specific reproductive strategies to cope with harsh environments, and unraveling these reproductive characteristics can improve our understanding of survival strategies and lithophyte evolution. This understanding is especially important for efforts to protect rare and endemic plants. Here, we investigated the reproductive biology of Lonicera oblata, an endangered lithophytic shrub that is scattered in highly fragmented and isolated cliff habitats of the Taihang and Yan mountains in North China.ResultsFlowers of L. oblata are herkogamous and protandrous, characteristics that can prevent autogamy at the single-flower level, and insects are necessary for pollination. The outcrossing index, pollen/ovule ratio, and the results of hand pollination were measured and all revealed a mixed mating system for L. oblata, that combines cross-fertilization and partial self-fertilization. The floral traits of L. oblata of zygomorphic and brightly yellowish corolla, heavy fragrance, and rich nectar, suggest an entomophilous pollination system. Sweat bees were observed as the most effective pollinators but their visiting frequencies were not high. Pollen limitation may limit the reproductive success of L. oblata.ConclusionsWe determined the reproductive characteristics of L. oblata, a critically endangered species endemic to cliffs in North China, providing insight into its endangerment and suggesting conservation strategies. L. oblata has highly pollinator-dependent self-fertilization as part of a mixed mating system. Floral features such as low-flowering synchrony, asynchronous anthers dehiscence, and high duration of stigma receptivity, improve pollination efficiency in the case of low pollinator service. Our work provides reference information to understand the survival strategies and conservation of L. oblata and other lithophytes.

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

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

Nocturnal emission and post‐pollination change of floral scent in the leafflower tree, Glochidion rubrum, exclusively pollinated by seed‐parasitic leafflower moths

AbstractMany insect‐pollinated plants use floral scent signals to attract and guide the effective pollinators, and temporal patterns of their floral scent emission may be tuned to respond to the pollinator's activity and pollination status. In the intimate nursery pollination mutualism between monoecious Glochidion trees (Phyllanthaceae) and Epicephala moths (Gracillariidae), floral scent signals mediate species‐specific interactions and influence the moth's efficient pollen‐collecting and pollen‐depositing behaviors on male and female flowers, respectively. We tested the hypotheses that both sexes of flowers of Epicephala‐pollinated Glochidion rubrum exhibit a diel pattern of scent emission matching the activity period of the nocturnally active pollinator, and that female flowers change the chemical signal after pollination to reduce further visits and oviposition by the pollinator. We investigated the diel change of floral scent emissions during two consecutive days and the influence of pollination on the floral scent by conducting hand‐pollinations in the field. The total scent emission of male and female flowers was higher at night than in the day, which would be expected from the nocturnal visitations of Epicephala moths. Some compounds exhibited a clear nocturnal emission rhythm. Hand‐pollination experiments revealed that emission of two compounds, nerolidol and eugenol, drastically decreased in pollinated flowers, suggesting that these compounds may function as key attractants for the pollinator; however, the total scent emission of the female flower was not influenced by hand‐pollination. The pattern of the floral scent emission of G. rubrum may be optimized to attract nocturnal pollinators and reduce oviposition.

Strongly unbalanced gender attractiveness in a dioecious mass flowering tropical tree pollinated by stingless bees.

In dioecious, bee-pollinated tree species, male and female flowers offer different resources. It is unclear how this unbalanced quantity and quality of floral resources affects flower visits and pollen transfer to female flowers. We asked, what characteristics of flowering and dynamics of resource production by trees favour flights of bees between male and female trees. We quantified the floral resources produced by individual flowers and entire trees of Myracrodruon urundeuva (Anacardiaceae), measured pollen flow to female flowers, fruit set of naturally pollinated flowers and determined the effective pollinators. Crown volume of male trees was four-fold, flower number 15-fold and nectar volume 60 times higher than in female trees. While ~70% of male flowers opened in the morning, ~70% of female flowers opened in the afternoon. Fruit set was 27%. Stingless bee species were the main pollinators, while honeybees were common only on male flowers. Strongly unbalanced production of floral resources, high potential lifespan of female flowers and anticipated opening of male flowers favour pollinator movement and pollen deposition on female flowers, albeit low (0.003% of pollen that reached stigmas), but sufficient to produce thousands of fruits per tree. Besides being an astonishing pollen and nectar source for numerous social bee species, only a few of them were effective pollinators. Our quantitative approach to floral resource production of each gender provides new insights, such as the proportion of resources allocated to each gender and the corresponding behaviour of flower visitors, for understanding the reproductive strategy of dioecious tropical mass-flowering trees.

Breakdown of Self-Incompatibility in Citrus by Temperature Stress, Bud Pollination and Polyploidization

Self-incompatibility (SI) is present in around half of all species of flowering plants. SI limits endogamy and contributes to increased genetic diversity. SI is a very important trait in citrus because, when coupled with parthenocarpy, it allows seedless fruit production. Otherwise, SI is an impediment to genetic studies and breeding programs. Temperature stress, bud pollination and polyploidization can induce the breakdown of the SI mechanism in several species. In this work, we investigated how the SI mechanism can be broken down in two self-incompatible diploid citrus genotypes: ‘Fortune’ mandarin and ‘Clemenules’ clementine. The influence of temperature stress on the SI mechanism was assessed in self-pollinated flowers of ‘Fortune’ mandarins subjected to 2 temperature regimes (10 °C and 30 °C), whereas the bud pollination effect was investigated in the same genotype and in ‘Clemenules’ clementines cultivated under field conditions. The tetraploid ‘Clemenules’ clementine cultivated under field conditions was used to study if tetraploidization can bypass the SI reaction. Histological observations of pollen tube growth and seed production in self-pollinated flowers were used to evaluate the breakdown of SI, while the genetic analysis with SSR and SNP markers confirmed that all recovered plants were zygotic and had been originated by selfing. Our results confirm that the SI reaction can be surpassed by temperature stress, bud pollination and tetraploidy. To our knowledge, this is the first report in citrus in which the SI reaction breakdown by these three different strategies is demonstrated by molecular markers.

Ants are effective pollinators of common buckwheat Fagopyrum esculentum

Abstract Proper management of wild pollinators of agricultural crops requires identification of effective pollinator species. Although non‐bee pollinators are gaining increasing attention, small ground‐dwelling insects such as ants are often deemed ineffective. However, our previous study found a positive correlation between ant visitations to flowers and seed set in the distylous crop common buckwheat, suggesting a potential role of ants as effective pollinators. In this study, we aimed to confirm the effectiveness of ant pollination by conducting ant‐exclusion experiments in the field. In addition, as evidence that ants can transfer pollen, we also counted the number of pollen grains attached to the body surface of two abundant flower‐visiting ant species, Formica japonica and Camponotus japonicus. Under the ant‐exclusion treatment, the buckwheat plants showed a significant reduction (30% on average) in seed set compared with control plants, and this effect was consistent across both flower morphs (pin and thrum) and two seasons (summer and autumn). Moreover, pollen grains of each flower morph were found on both ant species visiting both types of flower, suggesting a potential contribution to seed set in buckwheat. The results of this study suggest that ants may be an underappreciated pollinator of common buckwheat.

Wild bees are less abundant but show better pollination behaviour for sweet cherry than managed pollinators

AbstractPollinating insects provide pollination services to many crop species, including sweet cherry (Prunus avium L.), and this can be delivered by both managed and wild pollinators. Managed pollinators are often used to pollinate a range of fruit crops, but increasingly the role of wild insects is being studied. However, the importance of pollinator species depends on their relative abundance and pollination effectiveness, which depends on their foraging activity and their variability throughout the day. In this study, insect visitors of blossoms were observed in commercial sweet cherry orchards to explore abundance, diversity and pollination foraging behaviour of different insect pollinator groups throughout the day. A total of 1,174 pollinators from 31 different species were recorded visiting cherry blossoms over 2 years, of which 71.0% of total visits were by managed pollinators (western honeybee, Apis mellifera L. and buff‐tailed bumblebee, Bombus terrestris L.) compared to 29.0% by wild pollinators. On average, solitary bees visited a sweet cherry blossom for the longest duration (20.7 (±2.0 SE) seconds), whereas wild queen bumblebees visited the greatest number of flowers per minute (mean of 19.0 (±1.3 SE)). As both these pollinator groups contacted cherry stigmas more often and moved more frequently between tree rows than managed bees and hoverflies, they are more likely to facilitate cross‐pollination. The different pollinator groups also showed variation in behavioural parameters throughout the day, but less variation was recorded when all pollinator groups were considered altogether. This suggests diverse pollinator communities might be expected to provide a more stable pollination service to sweet cherry. This study demonstrates that whilst cherry blossoms were more frequently visited by managed pollinators, wild solitary bee and bumblebee behaviours are likely to be more effective at enhancing pollination in sweet cherry orchards, which, in turn, might lead to increased yields.