Flower visitors of Streptocarpus teitensis: implications for conservation of a critically endangered African violet species in Kenya

Effects of ecological factors on the pollination biology and seed production of Salvia daiguii: A critically endangered ornamental species from China

Summary Understanding the relationships between trait diversity, species diversity and ecosystem functioning is essential for sustainable management. For functions comprising two trophic levels, trait matching between interacting partners should also drive functioning. However, the predictive ability of trait diversity and matching is unclear for most functions, particularly for crop pollination, where interacting partners did not necessarily co‐evolve. World‐wide, we collected data on traits of flower visitors and crops, visitation rates to crop flowers per insect species and fruit set in 469 fields of 33 crop systems. Through hierarchical mixed‐effects models, we tested whether flower visitor trait diversity and/or trait matching between flower visitors and crops improve the prediction of crop fruit set (functioning) beyond flower visitor species diversity and abundance. Flower visitor trait diversity was positively related to fruit set, but surprisingly did not explain more variation than flower visitor species diversity. The best prediction of fruit set was obtained by matching traits of flower visitors (body size and mouthpart length) and crops (nectar accessibility of flowers) in addition to flower visitor abundance, species richness and species evenness. Fruit set increased with species richness, and more so in assemblages with high evenness, indicating that additional species of flower visitors contribute more to crop pollination when species abundances are similar. Synthesis and applications. Despite contrasting floral traits for crops world‐wide, only the abundance of a few pollinator species is commonly managed for greater yield. Our results suggest that the identification and enhancement of pollinator species with traits matching those of the focal crop, as well as the enhancement of pollinator richness and evenness, will increase crop yield beyond current practices. Furthermore, we show that field practitioners can predict and manage agroecosystems for pollination services based on knowledge of just a few traits that are known for a wide range of flower visitor species.

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.

The wild tomato (Solanum sisymbriifolium) is a globally distributed shrubby weed with both negative and positive impacts, including its invasive properties and the potential for pharmaceutical and traditional medicinal uses. Despite its ecological significance, the plant's reproductive biology and pollination ecology remain poorly understood. This study aimed to investigate the floral biology, pollination ecology, and plant reproduction of the weed species. Some flower traits, such as flowering intensity, flower display size, and pollen and ovule production, peaked during spring, summer, and the monsoon, while flower longevity and stigmatic receptivity were the longest in winter. The plant species was self-compatible (ISI = 0.02), heavily depended on pollinators (IDP = 0.72), and experienced minimal pollination limitation (D = 0.10) under open-pollination conditions. Flower visitors' traits (e.g., abundance, diversity, and richness) were higher in the spring, summer, and the monsoon, and these were lower in winter. The vital pollination service was provided by Amegilla zonata, Ceratina binghami, Lasioglossum cavernifrons, Nomia (Curvinomia) strigata, Tetragonula pagdeni, Xylocopa aestuans, Xylocopa amethystina, Xylocopa fenestrata, and Xylocopa latipes. Reproductive success, as indicated by fruit and seed set, varied seasonally, being higher during the spring-monsoon period and lower in winter. These findings support effective management of this weed species and help conserve the associated bee populations.

In subtropical dry forest (Chaco Serrano) of Tucuman province, northwestern Argentina, we assessed responses of the flower—visitor assemblage to habitat fragmentation by monitoring insect visits to two spring—flowering tree species and by sampling insects with yellow pan traps. Each of four study sites contained a tract of continuous forest, one large (>2.2 ha) forest fragment, and one small (<1 ha) fragment, with fragments isolated for 5—20 yr preceding the study. During its respective flowering peak each tree species examined, Prosopis nigra (Mimosoideae) and Cercidium australe (Caesalpinoideae), dominated the sites' entomophilous flora. Results indicate that flower—visitor assemblages respond to landscape features on the scale of hectares; specifically, forest fragmentation in the Chaco Serrano leads to an insect flower—visitor fauna increasingly dominated by the exotic honey bee (Apis mellifera). Bees as a group made >90% of observed flower visits to both plant species. The honey bee alone made 82% of all visits to the early—flowering tree species P. nigra and 44% to the later flowering C. australe. Frequency and taxon richness of native flower—visitors at both plant species declined with decreasing forest—fragment size, but frequency of honey bee visits tended to increase in complementary fashion, such that the total frequency of insect visits to flowers of either plant species varied little with fragment size. Frequencies of visits by honey bees and those by native insects were also negatively correlated across individual trees. In both plants, visits by native insects were most consistent (varied the least among plants or over time) in large forest tracts, whereas honey bee visits to C. australe were most consistent in small fragments. In pan trap samples the relative frequency of honey bees increased with decreasing fragment size. Native flower—visitors sampled by pan traps increased in numbers and taxon richness both with increasing patch size and as spring progressed. Thus, fragmentation of the Chaco Serrano appears to (a) affect native flower—visitors adversely and to (b) facilitate honey bees' access to floral resources. It is not clear that these two effects are directly related to each other, however.

Insects are essential for the reproduction of pollinator-dependent crops and contribute to the pollination of 87% of wild plants and 75% of the world’s food crops. Understanding pollen flow dynamics between plants and pollinators is thus essential to manage and conserve wild plants and ensure yields are maximized in food crops. However, the determination of pollen transfer in the field is complex and laborious. We developed a field experiment in a pollinator-dependent crop and used high throughput RNA sequencing (RNA-seq) to quantify pollen flow by measuring changes in gene expression between pollination treatments across different apple (Malus domestica Borkh.) cultivars. We tested three potential molecular indicators of successful pollination and validated these results with field data by observing single and multiple visits by honey bees (Apis mellifera) to apple flowers and measured fruit set in a commercial apple orchard. The first indicator of successful outcrossing was revealed via differential gene expression in the cross-pollination treatments after 6 h. The second indicator of successful outcrossing was revealed by the expression of specific genes related to pollen tube formation and defense response at three different time intervals in the stigma and the style following cross-pollination (i.e. after 6, 24, and 48 h). Finally, genotyping variants specific to donor pollen could be detected in cross-pollination treatments, providing a third indicator of successful outcrossing. Field data indicated that one or five flower visits by honey bees were insufficient and at least 10 honey bee flower visits were required to achieve a 25% probability of fruit set under orchard conditions. By combining the genotyping data, the differential expression analysis, and the traditional fruit set field experiments, it was possible to evaluate the pollination effectiveness of honey bee visits under orchards conditions. This is the first time that pollen-stigma-style mRNA expression analysis has been conducted after a pollinator visit (honey bee) to a plant (in vivo apple flowers). This study provides evidence that mRNA sequencing can be used to address complex questions related to stigma–pollen interactions over time in pollination ecology.

Campanula tomentosa, an endemic species, has a limited distribution with a total of 5 populations only in the Western Anatolia Region of Turkey. Research on the reproduction and conservation biology (pollination biology and reproductive success) of the plant was carried out for the first time by us. Within this context, pollen and stigma viability (floral biology), pollination biology, flower visitation, pollinator identification and reproductive success were investigated. The results of the pollen viability test in which 1% TTC (1,2,3-triphenyl tetrazolium chloride) was used indicated that 100% of the pollen grains were viable at the loading stage. In Peroxidase Test Papers and DAB stigma viability tests, the stigmas were completely curled and they were viable during the pollen presentation phase. The main pollination in the plant was realized by Xylocopa valga (Gerstacker, 1872) and Evylaeus setulellus (Strand, 1909). In C. tomentosa, fruit set and seed setting rates were 93.42% and 73.12%, respectively. On the other hand, it was revealed that the total area where it was distributed was 28.7 km2 and that it was classified as endangered.

In my doctoral research, I combined a literature review with field experiments to investigate the pollination ecology of cocoa, the third largest export commodity worldwide. The aim of my work was to elucidate the potential of ecological intensification, through pollination services, for increasing yields and improving farmer income in the region of Napu Valley, in Central Sulawesi, Indonesia. I divided my doctoral dissertation into four chapters, formatted as peer-reviewed scientific manuscripts. In Chapter I, I compiled all available scientific literature from the past 65 years to elaborate an exhaustive review on the neglected role of cocoa pollination. In Chapter II, I report the results of my field studies to quantify the relative importance of landscape, farm, and plant performance, as well as soil organic litter for species richness and abundance of cocoa flower visitors. In Chapter III, I present results of a large-scale hand pollination experiment and contrast the contribution of pesticide and fertilizer uses with that of pollination on fruit set and yield for improving farmer income. Finally, in Chapter IV, I present recommendations on how to translate gene-editing technologies from the laboratory to the farm, expanding the scope to three perennial crops: cocoa, citrus, and coffee. My findings in Chapter I and II provide evidence that mainly ants and to a lower extend dipterans are the main flower visitors of cocoa. This suggests that neglected ants may play a larger direct and indirect role in cocoa pollination than previously acknowledged. Multi-strata vegetation surrounding the farms (e.g. forests, agroforests), the shade provided by the tree canopy cover in the farm, and the amount of tree flowers are the main factors explaining flower-visitor species richness and abundance. Contrary to my initial hypothesis, increased amounts of soil litter in my experimental approach did not affect flower visitors. In Chapter III, the hand pollination experiments show that pollination, and not pesticides or fertilizers, is the main driver of fruit set and yields. Moreover, I found that hand pollinating 13% of cocoa flowers in a tree increases yields by 51%, and hand pollination of all flowers (100% of flowers/tree) by 260%. These yield increases have a direct effect on farmer livelihoods as their income increases by 69%, 50% and 85% at the local (study region), regional (Central Sulawesi) and national (Indonesia) level. Finally, in Chapter IV, I give comprehensive recommendations on how to integrate innovative gene editing technologies with traditional ecological intensification strategies, such as pollination services and grafting. These recommendations aim to bridge the gap between lab and farm implementation. In conclusion, I found that pollination services play a major role for increasing cocoa yields. While I prove that hand pollination can increase yield notably, it is still highly labor intensive. Thus, a well-structured working plan and the creation of innovative pollination tools are needed to reduce the implementation costs. On the other hand, natural pollination by enhancing flower visitation through management adjustments at the landscape and farm level should become an ecological alternative to hand pollination, but future studies need to detect the still hidden identity of pollinators and their ecology. The results from my work suggest that the preservation of multi-strata vegetation in the surroundings and high canopy cover enhances flower visitor populations and flower visitation, and this presumably improves yields. As litter amount did not appear to affect pollinator species’ richness and abundance, further studies should focus on soil litter quality rather than quantity. Finally, I argue that in the future cocoa stakeholders need to find alternative management practices to agrochemical intensification. These practices should successfully integrate ecological, such as pollination services, and promising gene editing approaches for increasing cocoa production sustainably, improve farmer livelihoods, and preserve biodiversity in times of climate change.

Pongamia pinnata, is an important biodiesel plant in India. The seed is an economic part of the plant used for extraction of biodiesel. The reproductive biology of P. pinnata is important for determining barriers in setting pods. The study has been carried out at Central Agroforestry Research Institute, Jhansi, India, during 2017–2019. The observations were made on the floral biology and pollinator activity in P. pinnata for 2 years. Anthesis was noticed between 0800 and 1000 h with peak anthesis between 0800 and 0830 h. Flower longevity was only 1 day. Pollen dehiscence occurred 1–2 h before anthesis. Pollen remained viable throughout the day with maximum germination (96.15%) coinciding anthesis time. Whereas, maximum pollen tube length (0.54 ± 0.10) was observed during 1000 h. Stigma remained receptive for 8 h after anthesis, the maximum receptivity was noticed 2 h after anthesis (82% of pollen germination) and it was coinciding the time where maximum pollen tube length recorded. The style was longer than stamens, indicating that the flower appeared to be adapted for cross-pollination. There were 13 flower visitors recorded, of which Megachile species were more abundant compared to Apis, Xylocopa species and, other flower visitors. The pollinator exclusion experiment was conducted to assess the role of flower visitors on pollination and fruit set. No pod set was noticed in the absence of insect pollinators. Whereas, in an open-pollinated condition, pod set ranged between 15 to 18%.

The status of pollinating insects is of international concern, but knowledge of the magnitude and extent of declines is limited by a lack of systematic monitoring. Standardized protocols are urgently needed, alongside a better understanding of how different methods and recorders (data collectors) influence estimates of pollinator abundance and diversity. We compared two common methods for sampling wild pollinating insects (solitary bees, bumblebees and hoverflies), pan traps and transects, in surveys of 1 km countryside squares (agricultural and semi‐natural habitats) and flowering crop fields across Great Britain, including the influence of local floral resources (nectar sugar availability or crop flower density) on the insects sampled. Further, we compared the performance of recorders with differing expertise (non‐specialist research staff, taxonomic experts and non‐expert volunteers) in applying methods. Pan traps and transects produced compositionally distinct samples of pollinator communities. In the wider countryside, pan traps sampled more species of solitary bee and hoverfly. In flowering crops, transects recorded a greater number of individual bumblebees, but fewer species. Across all taxonomic groups and countryside and crop samples, transects generally had lower rates of species accumulation per individual collected than pan traps. This demonstrates that differences between methods in estimating richness are not due to sampling effort alone. However, recorders possessing greater taxonomic expertise can produce species accumulation data from transects that are almost commensurate with pan trapping. The abundance and species richness of pollinators (except solitary bees) on transects in the wider countryside was positively related to the availability of estimated nectar sugar. In crops, pollinator abundance responses to flower densities were idiosyncratic according to crop type, but overall the response was positive and negative for transects and pan traps, respectively. Given these taxonomic and context‐specific differences in method performance, we assess their suitability for monitoring pollinating insect communities and pollination services. We discuss the relevance of these findings within the context of achieving standardized, large‐scale monitoring of pollinating insects.

Specialization of a plant on a particular pollinator may not evolve if co-pollinators are effective and abundant. This is particularly evident if fruit set is resource limited and cannot be increased above the levels produced by the actions of co-pollinators. The pollinating seed-consuming interaction between senita cacti and senita moths in the Sonoran Desert presents a paradox because it exhibits many traits resembling those of the highly specialized yucca/yucca moth system, but also involves co-pollinators. For 6years, we studied how contributions of nocturnal senita moths and diurnal co-pollinating bees to fruit set depended on resource and pollen limitation, time of flower closing, and the onset and phenology of flowering. Fruit set was typically resource limited. Fruit set of flowers exposed only to senita moths was not different from resource-limited fruit set of control flowers. When only co-pollinating bees were allowed to visit flowers, however, fruit set became pollen limited. Only in one year when fruit set was pollen limited were bees able to increase fruit set beyond the level resulting from senita moth pollination. High temperatures commonly induced flowers to close before sunrise so that diurnal bees were unable to visit flowers. This was particularly important from 1998 to 2000, when flowering did not begin until late in spring when temperatures were already high enough to induce flowers to close before sunrise. Bees were typically functionally redundant with senita moths; excluding bees from visiting flowers did not alter fruit set. Nevertheless, extreme specialization of floral traits to exclude co-pollinators has not evolved in senita, possibly because there are times when bees do increase fruit set. This can occur when senita moths are rare, fruit set is pollen limited, cool temperatures prevent flowers from closing before sunrise, and flowering begins early in spring.

Pollination deficits can compromise fruit yield and quality and have been reported in several fruit crops. It is unknown whether there is a pollination deficit in the production of Korla fragrant pear, Pyrus sinkiangensis, in China, and if so, whether this deficit can be mitigated by the use of managed honeybees (Apis mellifera). We assessed insect communities, flower visitation, pollination deficit and honeybee contribution to pear pollination in Korla fragrant pear orchards in Xinjiang, China. Insect communities were monitored using colored pan traps, and pollination deficit was assessed by comparing fruit set with open pollination to that with hand pollination in orchards without beehives from 2018 to 2021. The contribution of honeybees to pollination was assessed by comparing flower visitation, fruit set and fruit quality in pear orchards with and without beehives in 2020 and 2021. In orchards without beehives, wild bees (72%) were the dominant pollinator group in pan traps, followed by honeybees (15%), moths, hoverflies, butterflies and wasps (Vespidae). Fruit set in these orchards was much lower with open pollination (8 ± 2%) than with hand pollination (74 ± 4%). When comparing pollination in orchards with and without beehives in 2020 and 2021, we found that honeybees were responsible for most of the flower visits in orchards with (96%) and without beehives (66%). Wild bees were responsible for 1% and 6% of flower visits in orchards with and without beehives, respectively. Fruit set was significantly higher in orchards with beehives (38 ± 9%) than in orchards without beehives (12 ± 3%), while fruit set and sugar content were positively associated with pollinator visitation rate. The findings reveal a large pollination deficit in Korla fragrant pear orchards, and show that this deficit can be mitigated using managed honeybees.

Biotic and environmental conditions could affect the plant-flower visitor dynamics and, consequently, the fruit set in angiosperms. The aims of this study were: 1) to test the effect of microenvironment on activity of flower visitors in a population of Astrophytum myriostigma and 2) to describe the plant-flower visitor network’s structure. Data were recorded during two synchronous flowerings. The effect of microenvironment on flower visitors’ activity was tested through generalized linear models, and the interaction network structure was described. Frequency and duration of visits were mainly affected by atmospheric pressure and dew point. There were fewer flower visitors on plants located close to nurses and rocks. The interaction network topology tends to have a nested structure. Due to pollinators’ decline, these findings help understand the drivers limiting the flower visitors’ activity. The interactions between flower visitors and plants could be affected by atmospheric pressure alterations triggered by climate change.

Family farms can benefit from the presence of a diverse set of native pollinators and associated pollination services. In the present study we assessed the effect of flower visitor richness and visitation rate by honeybees and native insects on mandarin production (Citrus reticulata `Criolla´), in ten citrus family farms located in the Dry Chaco region of northwest Argentina. An exclusion experiment was conducted to explore how pollinators influence the fruit set and quality of `Criolla´ mandarin. The influence of features such as local richness and abundance of flowering plants, farm size, and surrounding natural/semi-natural habitats in the diversity of flower visitors was also evaluated. Fruit set in open pollination branches was three times higher than in bagged branches, where flower visitors were excluded. Moreover, the mandarin fruit set increased with a higher native visitation rate, and mandarin quality (fruit weight and size) decreased with a higher honeybee visitation rate. Flower visitor diversity was higher in farmlands with a greater proportion of surrounding natural and semi-natural habitats. Our results demonstrate the negative effects of excessive honeybee visitation on citrus fruit quality and highlight the importance of native pollinators and natural habitat conservation to increase the fruit set and quality of mandarin in family farms.

Species of Apocynaceae are pollinated by a diverse assemblage of animals. Here we report the first record of specialized cockroach pollination in the family, involving an endangered climbing vine species, Vincetoxicum hainanense in China. Experiments were designed to provide direct proof of cockroach pollination and compare the effectiveness of other flower visitors. We investigated the reproductive biology, pollination ecology, pollinaria removal, pollinia insertion, and fruit set following single visits by the most common insects. In addition, we reviewed reports of cockroaches as pollinators of other plants and analyzed the known pollination systems in Vincetoxicum in a phylogenetic context. The small, pale green flowers of V. hainanense opened during the night. The flowers were not autogamous, but were self-compatible. Flower visitors included beetles, flies, ants and bush crickets, but the most effective pollinator was the cockroach Blattella bisignata, the only visitor that carried pollen between plants. Less frequent and effective pollinators are ants and Carabidae. Plants in this genus are predominantly pollinated by flies, moths and wasps. Globally, only 11 plant species are known to be cockroach-pollinated. Because their range of floral features encompass similarities and differences, defining a "cockroach pollination syndrome" is difficult. One commonality is that flowers are often visited by insects other than cockroaches, such as beetles, that vary in their significance as pollinators. Cockroach pollination is undoubtedly more widespread than previously thought and requires further attention.