Pollen Transfer Research Articles

Goldilocks’ quarter-hectare urban farm: An agent-based model for improved pollination of community gardens and small-holder farms

Industrial agriculture’s expansive monocultures contrast against community farms of diverse crops in small allotments constrained by urban regulations. These human-controlled differences in scale, arrangement and crop diversity, may differently impact insect foraging and pollination. The relationship between human management and insect pollination is under-explored, especially regarding the implications of insect flower constancy–the tendency of insects to favour visits to a single rewarding flower species during a foraging bout. Although high flower-constancy is associated with reliable pollen transport, its impact on pollination depends also on planting regimes, the vicinity of neighbouring crops, weeds and wildflowers. This study explores the potential pollination impacts of insect flower constancy, heterospecific pollen transfer, and human-dictated crop patch size, using an agent-based model of insect pollinators foraging from two flowering plant species. Highly constant pollinators were most effective in the smallest patches when heterospecific pollen transfer was an issue. As patch size increased, pollination rates improved overall, but less constant insects produced better pollination rates for intermediate sized areas because they rapidly switched preferences between flower species. As patch size increased further, the influence of flower constancy on pollination rates was reduced. Study results suggest that typical community farms containing small single-crop patches operated by independent growers within an allotment, may be better pollinated if operated collaboratively to increase single-crop patch size. Crop patches needn’t be large homogeneous agricultural monocultures, but neither should they be so small and heterogeneous as to inhibit pollination. We found a “Goldilocks zone” around 11m x 11m to be a good compromise for pollination, regardless of the level of flower constancy in local insects. As climate and human land use increasingly impact insect populations, the relationships between pollination systems, growers and policy makers must be continually examined to safeguard food supplies and native ecosystems.

Defensive mutualists affect outcross pollen transfer and male fitness in their host plant

Ant guards can increase plant fitness by deterring herbivores, but they may also reduce it by interfering with pollination. While ant impacts on herbivory have been well‐studied, much less is known about their impacts on pollinators and associated consequences for plant pollination, particularly pollen transfer dynamics and outcrossing/selfing rates. We used field experiments to quantify the effect of ant guards on pollinator community composition, frequency and duration of flower visits, and cascading effects on outcrossing pollen transfer and pollen exports in Turnera velutina (Passifloraceae). Although ant patrolling did not affect pollinator community composition or visitation frequency, it decreased flower visit duration and the time pollinators spent foraging inside flowers. Such behavioural changes resulted in reduced pollen deposition on stigmas, decreased pollen exports (a proxy for male fitness) and significantly doubled outcross pollen transfer. This study contributes to our understanding of how non‐pollinator mutualists can shape plant reproductive processes. We discuss the downstream effects that variation in biotic defences, such as rewards for guarding ants, can have on plant pollen transfer patterns and fitness.In conclusion, guarding ants influence pollen transfer patterns in Turnera velutina, increasing outcrossing in a self‐compatible species at the cost of male fitness. We show how non‐pollinators, such as defensive ant mutualists, can shape plant reproductive traits and discuss the consequences these interactions may have for plant mating systems.

Pollen transfer and patterns of reproductive success in pure and mixed populations of nectariferous Platanthera bifolia and P. chlorantha (Orchidaceae).

Plant species evolution is driven by many factors that have different roles in space and time. Using different field and laboratory methods, we studied reproductive patterns and their determinants in pure and mixed P. bifolia and P. chlorantha populations in different habitats. We also considered the probability of hybridisation between these two species and the role of intra-population processes in maintaining species integrity. Generally, we found a high level of reproductive success in both Platantherans. In both species, male (MRS) and female (FRS) reproductive success depended on floral display, and male reproductive success additionally on population structure. The flower traits were only weakly related to reproductive success. Moths’ assemblages varied spatially and temporally, and their diversity and numbers were correlated with MRS in the year, when their abundance was markedly lower. Analysis of patterns of pollen transfer showed that pollen was transported up to 25 m (average 8.2 ± 4.83 m) and showed gene exchange between these two Platanthera species. The germination level of both species was significantly lower than seed viability, although P. bifolia seed germinated with higher frequency than P. chlorantha seeds. We noted differences in viability and germination of seeds developed as an effect of experimental interspecies crossings and those developed from natural pollination. The presence of intermediate ecotypes together with observations of spontaneous interspecies crosses in the field and viability of seeds produced in interspecies crossing suggest that both pre- and postzygotic reproductive barriers are not complete and do not prevent hybrid production.

The selfing syndrome and beyond: diverse evolutionary consequences of mating system transitions in plants.

The shift from outcrossing to self-fertilization (selfing) is considered one of the most prevalent evolutionary transitions in flowering plants. Selfing species tend to share similar reproductive traits in morphology and function, and such a set of traits is called the 'selfing syndrome'. Although the genetic basis of the selfing syndrome has been of great interest to evolutionary biologists, knowledge of the causative genes or mutations was limited until recently. Thanks to advances in population genomic methodologies combined with high-throughput sequencing technologies, several studies have successfully unravelled the molecular and genetic basis for evolution of the selfing syndrome in Capsella, Arabidopsis, Solanum and other genera. Here we first introduce recent research examples that have explored the loci, genes and mutations responsible for the selfing syndrome traits, such as reductions in petal size or in pollen production, that are mainly relevant to pre-pollination processes. Second, we review the relationship between the evolution of selfing and interspecific pollen transfer, highlighting the findings of post-pollination reproductive barriers at the molecular level. We then discuss the emerging view of patterns in evolution of the selfing syndrome, such as the pervasive involvement of loss-of-function mutations and the relative importance of selection versus neutral degradation. This article is part of the theme issue 'Genetic basis of adaptation and speciation: from loci to causative mutations'.

Effects of heterospecific pollen on stigma behavior in Campsis radicans: Causes and consequences.

Pollinator sharing of co-flowering plants may result in interspecific pollen receipt with a fitness cost. However, the underlying factors that determine the effects of heterospecific pollen (HP) are not fully understood. Moreover, the cost of stigma closure induced by HP may be more severe for plants with special touch-sensitive stigmas than for plants with non-touch-sensitive stigmas. Very few studies have assessed HP effects on stigma behavior. We conducted hand-pollination experiments with 10 HP donors to estimate HP effects on stigma behavior and stigmatic pollen germination in Campsis radicans (Bignoniaceae) at low and high pollen loads. We assessed the role of phylogenetic distance between donor and recipient, pollen size, and pollen aperture number in mediating HP effects. Additionally, we observed pollen tube growth to determine the conspecific pollen-tube-growth advantage. Stigma behavior differed significantly with HP of different species. Pollen load increased, while pollen size decreased, the percentage of permanent closure and stigmatic germination of HP. Stigmatic HP germination increased with increasing aperture number. However, HP effects did not depend on phylogenetic distance. In addition, conspecific pollen had a pollen-tube-growth advantage over HP. Our results provide a good basis for understanding the stigma-pollen recognition process of plant taxa with touch-sensitive stigmas. We concluded that certain flowering traits drive the HP effects on the post-pollination period. To better understand the impact of pollinator sharing and interspecific pollen transfer on plant evolution, we highlight the importance of evaluating more factors that determine HP effects at the community level.

Self-compatibility provides little reproductive assurance in the summer-flowering Aloe reitzii var. reitzii

Floral adaptations, notably floral design and display, enable plants to govern their mating opportunities through pollinator attraction and pollen dispersal. However, large floral displays, together with multiple simultaneously open flowers in an hermaphroditic plant, increase the potential for geitonogamous self-pollination. Many angiosperms have evolved self-incompatibility that prevents self-fertilization, instead requiring outcrossing by pollen vectors for successful seed set. We investigated the reliance of the summer-flowering Aloe reitzii var. reitzii on pollinators for reproduction and by using controlled hand-pollination experiments to determine whether Aloe reitzii var. reitzii is self-compatible. Contrary to most aloes, Aloe reitzii var. reitzii is shown here to be partially self-compatible, but reliant on pollinators to transfer pollen between flowers within the same raceme or plant, as well as to other plants. Aloe reitzii var. reitzii appears incapable of autonomous self-pollination and pollinator-mediated geitonogamy causes reduced fecundity in Aloe reitzii var. reitzii. However, hand-selfed treatments produced viable seeds capable of germinating, suggesting that the partial self-compatibility in Aloe reitzii var. reitzii does provide some reproductive advantage and may have evolved due to its restricted distribution and increasing population fragmentation – possibly due to anthropogenic change.

The breeding system of Hyacinthoides non-scripta (Asparagaceae): assessing the role of geitonogamy with captive pollinators

Background and aims – In self-incompatible species, geitonogamous pollen deposition can result in stigma clogging, with negative effects on cross-fertilisation and subsequently reduced fruit and seed set. In this work, using laboratory and field experiments with pollinators in captivity, we describe the reproductive system of Hyacinthoides non-scripta and analyse the effect of the different mechanisms of pollen transfer, trying to quantify the effect of geitonogamy on the reproductive success of the species. Material and methods – Using laboratory and field experiments with pollinators in captivity we evaluated the effect of the different types of pollen transfer. Key results – The results show that H. non-scripta is a self-incompatible species and the pollen tubes in autogamous and geitonogamous pollination are rejected at the base of the style. In the field experiments, the presence of geitonogamous pollen on the stigma did not prevent subsequent fertilization by xenogamous pollen, but it reduced seed production. Conclusion – This study provides evidence that natural rates of geitonogamy significantly reduce female fitness in plants with large numbers of flowers per inflorescence and show how experiments with captive pollinators can help quantify the intensity of this effect.

Sexual deception of maleBradysia(Diptera: Sciaridae) by floral odour and morphological cues inPterostylis(Orchidaceae)

AbstractSexually deceptive orchids exploit the innate sexual preferences of their male insect pollinators to achieve pollen transfer. Although floral volatiles are critical for pollinator attraction in sexually deceptive systems, floral morphology is also expected to exploit the sexual preferences of the pollinator. Here, we investigate the pollination of the Australian orchid Pterostylis cycnocephala. We confirm that male fungus gnats of a single undescribed Bradysia sp. (Diptera, Sciaridae) act as pollinators and display sexual behaviour on flowers, including wing fanning, abdomen curling and genitalic clasping of the prominent labellum appendage. Gnats only triggered the labellum and became trapped in the flower after attempting pseudocopulation with the appendage, a process necessary for pollen removal and deposition. Male gnats located flowers hidden from view, suggesting long-range attraction is primarily due to floral odour. However, male gnats displayed reduced copulatory behaviour when the labellum was absent and when the labellum appendage was inaccessible, suggesting that appropriate morphology may be required to elicit the copulatory behaviour needed for pollination. Our study is the first detailed investigation of sexual deception of male Sciaridae in Australian orchids and represents an example of convergent evolution with some Neotropical Lepanthes orchids, which also sexually deceive male Bradysia.

Biomonitoring via DNA metabarcoding and light microscopy of bee pollen in rainforest transformation landscapes of Sumatra

BackgroundIntense conversion of tropical forests into agricultural systems contributes to habitat loss and the decline of ecosystem functions. Plant-pollinator interactions buffer the process of forest fragmentation, ensuring gene flow across isolated patches of forests by pollen transfer. In this study, we identified the composition of pollen grains stored in pot-pollen of stingless bees, Tetragonula laeviceps, via dual-locus DNA metabarcoding (ITS2 and rbcL) and light microscopy, and compared the taxonomic coverage of pollen sampled in distinct land-use systems categorized in four levels of management intensity (forest, shrub, rubber, and oil palm) for landscape characterization.ResultsPlant composition differed significantly between DNA metabarcoding and light microscopy. The overlap in the plant families identified via light microscopy and DNA metabarcoding techniques was low and ranged from 22.6 to 27.8%. Taxonomic assignments showed a dominance of pollen from bee-pollinated plants, including oil-bearing crops such as the introduced species Elaeis guineensis (Arecaceae) as one of the predominant taxa in the pollen samples across all four land-use types. Native plant families Moraceae, Euphorbiaceae, and Cannabaceae appeared in high proportion in the analyzed pollen material. One-way ANOVA (p > 0.05), PERMANOVA (R² values range from 0.14003 to 0.17684, for all tests p-value > 0.5), and NMDS (stress values ranging from 0.1515 to 0.1859) indicated a lack of differentiation between the species composition and diversity of pollen type in the four distinct land-use types, supporting the influx of pollen from adjacent areas.ConclusionsStingless bees collected pollen from a variety of agricultural crops, weeds, and wild plants. Plant composition detected at the family level from the pollen samples likely reflects the plant composition at the landscape level rather than the plot level. In our study, the plant diversity in pollen from colonies installed in land-use systems with distinct levels of forest transformation was highly homogeneous, reflecting a large influx of pollen transported by stingless bees through distinct land-use types. Dual-locus approach applied in metabarcoding studies and visual pollen identification showed great differences in the detection of the plant community, therefore a combination of both methods is recommended for performing biodiversity assessments via pollen identification.

Climate warming shifts the time interval between flowering and leaf unfolding depending on the warming period.

The timing of flowering (FL) and leaf unfolding (LU) determine plants' reproduction and vegetative growth. Global warming has substantially advanced FL and LU of temperate and boreal plants, but their responses to warming differ, which may influence the time interval between FL and LU (∆LU-FL), thereby impacting plant fitness and intraspecific physiological processes. Based on twigs collected from two flowering-first tree species, Populus tomentosa and Amygdalus triloba, we conducted a manipulative experiment to investigate the effects of winter chilling, spring warming and photoperiod on the ∆LU-FL. We found that photoperiod did not affect the ∆LU-FL of Amygdalus triloba, but shortened ∆LU-FL by 5.1 d of Populus tomentosa. Interestingly, spring warming and winter chilling oppositely affected the ∆LU-FL of both species. Specifically, low chilling accumulation extended the ∆LU-FL by 3.8 and 9.4 d for Populus tomentosa and Amygdalus triloba, but spring warming shortened the ∆LU-FL by 4.1 and 0.2 d °C-1. Our results indicate that climate warming will decrease or increase the ∆LU-FL depending on the warming periods, i.e., spring or winter. The shifted time interval between flowering and leaf unfolding may have ecological effects including affecting pollen transfer efficiency and alter the structure and functioning of terrestrial ecosystem.

A COMMUNITY-WIDE DESCRIPTION AND KEY OF POLLEN FROM CO-FLOWERING PLANTS OF THE SERPENTINE SEEPS OF THE MCLAUGHLIN NATURAL RESERVE, LAKE COUNTY, CA

Pollen morphology is species-specific and its identification can inform many different research objectives, including those focused on understanding pollinator niche breadth, pollen transfer dynamics, and factors driving plant community composition. Community-wide characterization of pollen can thus accelerate research on plant-pollinator interactions on both contemporary and historical time frames. Here we present descriptions, a dichotomous key, and reference set of light microscopy images of pollen from 70 species in 28 families of co-flowering plants growing in and around serpentine seeps at the McLaughlin Natural Reserve in Lake County, CA. This represents a reference and a tool for the study of species interactions in this unique biodiversity hotspot.

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.

Increasing pollen production at high latitudes across animal‐pollinated flowering plants

AbstractAimPlant reliance on animal mutualists is expected to decrease with latitude owing to increasing environmental instability. As a consequence, more erratic animal pollination in the temperate zones than in the tropics could translate into lower efficiency in pollen transfer, and thus increasing pollen wastage. Despite the relevance of this hypothesis for plant reproductive evolution, the implications of a proposed latitudinal gradient in pollinator reliability for pollen and ovule production, traits directly affecting seed siring and seed set, respectively, remain unresolved.LocationGlobal.Time period1971–2020.Major taxa studiedAngiospermae.MethodsBased on a bibliographic survey and our own data, we collated a dataset with information on pollen production (P) and ovule number (O) per flower from 419 studies, including a total of 1,392 animal‐pollinated angiosperm species from 141 families distributed worldwide and sampled between the equator and 68.35° latitude. Using phylogenetic general linear mixed models, we investigated latitudinal variation in P and O. We also tested a latitudinal effect on several ancillary plant traits associated with a plant’s mating system and pollinator specialization that might confound any latitudinal effect on gamete production.ResultsP but not O was positively associated with latitude, a trend that even became stronger after including the latitudinally varying ancillary traits (i.e., growth form, flower size, flower symmetry and number of pollinator orders). The latitudinal effect on P was more pronounced among species producing large flowers, a trait that could be linked to self‐incompatibility and thus outcrossing. A weak phylogenetic patterning of P also indicates high evolvability potential of this trait, which may have an effect on both male and female plant fitness.Main conclusionsEven though a latitudinal trend in pollinator reliability still awaits direct testing, the observed latitudinal increase in P across angiosperms can be interpreted as an evolutionary consequence of an increasingly unpredictable pollination environment.

Colour similarity to flowering neighbours promotes pollinator visits, pollen receipt and maternal fitness

While co-flowering plants often compete for pollination through pollinator visits and pollen transfer, recent studies reveal potential for the facilitation of pollination. Pollination may be promoted when similarities in the floral traits of co-flowering species enhance pollinator visitation and seed set. Floral similarity, however, could also lead to heterospecific pollen transfer, creating a fitness trade-off that is seldom explored empirically.Here we construct experimental communities of Oxalis to investigate the trade-off between enhanced visitation and heterospecific pollen receipt, which can impact seed set at varying relative plant abundance. Our experimental communities comprise O. purpurea that is matched or mismatched to congeners in flower colour at low and high relative plant abundance. We investigate the consequences of colour overlap for pollinator visitation and the receipt of conspecific, heterospecific, and mixed pollen loads, and assess seed set in natural plots.Flower colour similarity increases visitation by shared pollinators at both low and high relative abundance when O. purpurea occurs in matched flower colour communities. The receipt of pollen analogues from conspecifics is also greater at both abundances when neighbours are matched in floral colour. Although conspecific pollen in matched communities is mostly delivered in mixed pollen loads, hand pollinations confirm the receipt of mixed pollen carries no fitness costs for seed production. Consequently, plants in natural populations plots of O. purpurea experiences increase maternal fitness when growing in matching flower colour communities.We demonstrate a positive net effect of flower colour similarity, relative to flower colour dissimilarity, that can facilitate plant reproduction. Through field experiments we systematically test previously observed patterns of clustered flower colour assembly in Oxalis communities to provide a comprehensive assessment of facilitative co-flowering interactions.

Settling moths are the vital component of pollination in Himalayan ecosystem of North-East India, pollen transfer network approach revealed

Majority of the pollination related studies are based on the diurnal pollinators, and the nocturnal pollinators received less scientific attention. We reveal the significance of settling moths in pollination of angiosperm families in Himalayan ecosystem of North-East India. The refined and novel method of pollen extraction from the proboscides provides a more robust assessment of the pollen carrying capacity. The study is based on one of the largest data sets (140 pollen transporter moth species (PTMS)), with interpretation based on seasonal as well as altitudinal data. In the present study about 65% moths (91 species) carried sufficient quantities of pollen grains to be considered as potential pollinators (PPMS). Teliphasa sp. (Crambidae) and Cuculia sp. (Noctuidae) are found to carry the highest quantity of pollen. We found pollen grains of 21 plant families and the abundant pollen are from Betulaceae, Fabaceae, Rosaceae and Ericaceae. Species composition of PTMS and PPMS in pre-monsoon, monsoon, and post-monsoon revealed the dominance of Geometridae. Maximum diversity of PTMS and PPMS is found from 2000 to 2500 m altitude. The nocturnal pollen transfer network matrices exhibited high degree of selectivity (H2ʹ = 0.86).

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.

The role of adult noctuid moths (Lepidoptera: Noctuidae) and their food plants in a nocturnal pollen-transport network on a Mediterranean island

Noctuidae belong to one of the largest families of night-flying Lepidoptera. However, despite being among the most common nocturnal flower-visitors, they have seldom been included in pollination networks. Similarly, the current knowledge on food plants used by adults is rather scarce. In this article, we build the first moth–plant pollen transfer network in the Balearic archipelago. We aim to increase the knowledge of which plants are used as food resources by adult Noctuidae, assess how specific or generalist nocturnal pollinators and their food plants are and establish the first baseline information on adult Noctuidae–plant interactions on the archipelago and the Mediterranean. 20.7% of the adult Noctuidae in our samplings carried pollen and were therefore potentially involved in nocturnal pollination. The family Ericaceae, and especially Arbutus unedo, was a key food resource for our moth community, with 46% of the total recorded interactions belonging to this plant. Overall, both plants and moths in our system behaved in a generalist way. Niche overlap was larger in moths than in plants, suggesting that the functional role that moth species take in our system is more redundant than that taken by plants. Robustness values suggest that the network functionality would not collapse despite the extinction of a few species.Implications for insect conservationDetecting flower preferences and the role of nocturnal insects on pollination will allow understanding of ecosystem functionality and will be crucial for conservation of both moths and organisms that depend on them.

Moths can transfer pollen between flowers under experimental conditions

To be considered an effective pollinator, a floral visitor must not only be able to remove pollen but also transfer this pollen to a receptive conspecific stigma. While studies of diurnal pollination are commonplace, our understanding of the effectiveness of nocturnal pollinators is limited largely because of the difficulties of doing these studies at night. As a result of this, the way in which moths transfer pollen between flowers has been understudied globally, despite many authors suggesting they could be significant contributors to pollination.

Mutual complementarity among diverse pollinators as a mechanism underlying open insect pollination in Japanese pear orchards

AbstractCultivated Japanese pear varieties, mostly showing self‐incompatibility, require pollen transfer from other varieties. To elucidate the underlying mechanisms of open Japanese pear insect pollination, we first collected flower‐visiting insects using plastic vials and sticky traps in orchards located at different regions in Japan. Results showed that insects assigned to the families Andrenidae (Hymenoptera), Apidae (Hymenoptera), Halictidae (Hymenoptera), Syrphidae (Diptera) and Empididae (Diptera) are abundant in the orchards. Second, we restricted the flower‐visiting insects to access Japanese pear flowers using bags with mesh sizes of 0, 2 and 3.5 mm. Results indicated that insects which allowed to pass through bags with 3.5‐mm mesh size but not through bags with 2‐mm mesh size contribute primarily to pollination, represented as the fruit‐set ratio and seed number. Third, we measured head and thorax widths of the flower‐visiting insects and counted pollen grains on their body surfaces to estimate their pollination potential. Results indicated that insects assigned to the families Andrenidae, Halictidae, Syrphidae, Bibionidae (Diptera) and Muscidae (Diptera), including species with both widths smaller than 3.5 mm, harbour large quantities of Pyrus pollen grains, in addition to Apis mellifera (Apidae) with both widths greater than 3.5 mm. Consequently, the families Andrenidae, Apidae, Halictidae and Syrphidae might be the most important insect families for Japanese pear pollination. However, species identification of the flower‐visiting insects showed no common key species that contribute remarkably to pollination services other than A. mellifera. Consecutive insect collection using plastic vials and sticky traps demonstrated that compositions of the flower‐visiting insects are fluctuating continuously in the orchards. Nevertheless, year‐to‐year fluctuation of the fruit‐set ratio was less pronounced in open‐pollinated orchards than in hand‐pollinated orchards. These results suggest that mutual complementation among diverse pollinator species might be the mechanism underlying open Japanese pear insect pollination.

Flower pollination algorithm with pollinator attraction

The Flower Pollination Algorithm (FPA) is a highly efficient optimization algorithm that is inspired by the evolution process of flowering plants. In the present study, a modified version of FPA is proposed accounting for an additional feature of flower pollination in nature that is the so-called pollinator attraction. Pollinator attraction represents the natural tendency of flower species to evolve in order to attract pollinators by using their colour, shape and scent as well as nutritious rewards. To reflect this evolution mechanism, the proposed FPA variant with Pollinator Attraction (FPAPA) provides fitter flowers of the population with higher probabilities of achieving pollen transfer via biotic pollination than other flowers. FPAPA is tested against a set of 28 benchmark mathematical functions, defined in IEEE-CEC’13 for real-parameter single-objective optimization problems, as well as structural optimization problems. Numerical experiments show that the modified FPA represents a statistically significant improvement upon the original FPA and that it can outperform other state-of-the-art optimization algorithms offering better and more robust optimal solutions. Additional research is suggested to combine FPAPA with other modified and hybridized versions of FPA to further increase its performance in challenging optimization problems.