Journal of Pollination Ecology

Passively crowdsourcing images online for measuring broad-scale fly (Diptera) floral interactions and biodiversity

Evelyn Blakeman — 2023-09-08

Flies (Diptera) represent one of the largest and most important groups of pollinators on the planet; however, little is known about the interactions between flies and flowers compared to well-known pollinators, such as bees. Understanding pollinator assemblages is key to conserving biodiversity and ecosystem services, but monitoring Diptera is time and cost intensive. Using photographs of blooming flowers taken by photographers worldwide and uploaded on internet repositories, we built a dataset of 1,275 images of fly-flower visitations and extracted fly and flower taxonomic information, flower characteristics (shape and color), and fly activity (pollen carrying and foraging). The resulting dataset shows taxonomic and other biases but can still provide an initial overview of factors that affect pollination by Diptera. We identified 22 families of flies, with blow flies (Family Calliphoridae) most represented (29%) and 63 families of flowers, with Asteraceae (42%) and Apiaceae (21%) as the most common. Using logistic regression, we found that the likelihood of flies carrying pollen was determined by the interaction between flower color and shape: pollen-carrying was more likely when elongate cluster flowers were green-yellow. Fly foraging on flowers was determined by flower color: flies were more likely to feed on green-yellow and white flowers. Overall, Syrphidae flies were less likely to forage for nectar than non-Syrphidae, but were more likely to carry pollen. While biases exist in crowdsourced data, we show that data from photographs collected through citizen science offers potentially valuable information for monitoring pollinator-flower interactions and augment our understanding of pollinator ecology in an era of global insect declines.

Comparing levels of geitonogamous visitation by honey bees and other pollinators

Dillon Travis — 2023-07-18

Geitonogamy, the transfer of pollen from one flower to another on the same plant, is often the primary means of self-pollination in flowering plants. For self-compatible plants, self-fertilization may lead to greatly reduced offspring fitness via inbreeding depression. For self-incompatible plants, geitonogamous pollen transfer can result in low seed set, even when stigmatic pollen loads are substantial. For multiple self-compatible, native California plants, we found that honey bees visited more flowers per plant than native insects, and that offspring resulting from pollination by honey bees had reduced fitness relative to those resulting from native insect pollination. Here we investigate whether honey bees generally make more geitonogamous visits than other pollinators using data from a global survey of 41 manuscripts that reported floral visitation data. Compared to the average of all non-honey bee visitors in a plants pollinator assemblage, honey bees visit significantly more flowers per plant, though they do not differ from the non-honey bee visitor with the highest rate of geitonogamous visitation. However, the disparity between rates of geitonogamous visitation by honey bees and non-honey bee visitors is a function of the frequency of honey bees relative to non-honey bee visitors. As honey bees become increasingly numerically dominant, there is a trend for their rates of geitonogamous visitation to increase, accompanied by a significant decline in flowers visited per plant by non-honey bee visitors. While we found that honey bees visited more flowers per plant compared to the average of other visitors, large or eusocial pollinators were as likely as honey bees to be the most geitonogamous visitor.

Observing bees and wasps: Why surveys and monitoring programs are critical and how they can improve our understanding of these beneficial hymenopterans

Jason Graham — 2023-06-07

Flower-visiting bees and wasps (Hymenoptera: Apoidea, Pompiloidea, Scolioidea, Tiphioidea, and Vespoidea) provide essential services in agricultural and urban systems, and ecological functions in natural ecosystems. Understanding the population trends, resource requirements and preferences, ecological challenges, and how to manage these species better requires increased surveys and standardized monitoring efforts for both groups. A monitoring program performed at various scales that provides ecological data is a prerequisite to managing either bees or wasps for conservation or crop pollination purposes. Methods to survey and monitor bees and wasps can be accomplished by a variety of means, depending on the researchers’ aims and goals. Herein, we discuss the importance of 1) evaluating populations of threatened and endangered bee and wasp species, 2) detecting and identifying pollinators of crops, 3) identifying and managing wasp species for use as biological control agents, 4) surveying the ranges of non-native bees and wasps, and 5) utilizing bees and wasps as biological indicators. We also discuss strategies for the selection of surveying and monitoring tools and methodologies best suited to specific goals and situations in beneficial Hymenoptera research. Our hope is that this review will lead to additional bee/wasp survey and monitoring programs and assist researchers with selecting tools and methodologies for the purpose of better understanding these beneficial insects.

Parasites, parasitoids, and hive products that are potentially deleterious to wild and commercially raised bumble bees (Bombus spp.) in North America

Elaine Evans — 2023-02-09

Bumble bees are important pollinators for a great diversity of wild and cultivated plants, and in many parts of the world certain species have been found to be in decline, gone locally extinct, or even globally extinct. A large number of symbionts live on, in, or with these social bees. We give an overview of what is known about bumble bee ecto-symbionts and parasitoids. We provide information on assessment of risks posed by select bumble bee symbionts and methods for their detection, quantification, and control. In addition, we assess honey bee hive products such as pollen and wax that are used in commercial bumble bee production, and highlight key risks and knowledge gaps. Knowledge of these potential threats to native pollinators is important and they need to be managed in the context of national and international commercial trade in bumble bees to prevent pest introduction and pathogen spillover that can threaten native bees.

Endosymbionts that threaten commercially raised and wild bumble bees (Bombus spp.)

Laura Figueroa — 2023-02-07

Bumble bees (Bombus spp.) are important pollinators for both wild and agriculturally managed plants. We give an overview of what is known about the diverse community of internal potentially deleterious bumble bee symbionts, including viruses, bacteria, protozoans, fungi, and nematodes, as well as methods for their detection, quantification, and control. We also provide information on assessment of risk for select bumble bee symbionts and highlight key knowledge gaps. This information is crucial for ongoing efforts to establish parasite-free programs for future commerce in bumble bees for crop pollination, and to mitigate the problems with pathogen spillover to wild populations.

An evidence-based rationale for a North American commercial bumble bee clean stock certification program

James Strange — 2023-01-24

The commercial production and subsequent movement of bumble bees for pollination of agricultural field and greenhouse crops is a growing industry in North America and globally. Concerns have been raised about the impacts of pathogen spillover from managed bees to wild pollinators, including from commercial bumble bees. We recommend development of a program to mitigate disease risk in commercial bumble bee production, which will in turn reduce disease stressors on wild pollinators and other insects. We provide recommendations for the components of a clean stock program with specific best management practices for rearing commercial bumble bees including related products such as wax, pollen, and nesting material.

Pollenkitt is associated with the collectability of Malvoideae pollen for corbiculate bees

Sabine Konzmann — 2023-05-23

Pollen grains of Malvoideae (Malvaceae) which corbiculate bees cannot collect constitute a floral filter that excludes pollen-collecting bumble bees and honey bees from exploiting pollen resources. Although large, spiny pollen grains are in fact harder to compact for collection by corbiculate bees, pollen morphology (e.g., grain diameter, spine length) is not by itself a reliable indicator of pollen collectability. In this study, we discovered that two Malvoideae species, Anoda cristata and Malope trifida, possess large, spiny pollen grains that can be groomed and collected by corbiculate bees. To gain insight into the underlying cause of collectability of Malvoideae pollen, we tested pollen adhesion to bumble bee setae and found that significantly less of the collectable pollen grains of A. cristata and M. trifida adhere to bees’ setae compared to uncollectable pollen grains of Hibiscus trionum. As the primary mediator of pollen adhesion is pollenkitt, a viscous lipid-rich substance covering pollen of zoophilous plants, we examined the surface of uncollectable and collectable Malvoideae pollen using cryo-SEM. Fresh pollen grains were abundantly covered with pollenkitt that also coated the long spines and formed liquid bridges between the grains. Washing pollen with hexane removed all pollenkitt, whereas washing pollen with water only removed pollenkitt on the collectable pollen grains of M. trifida, but not the uncollectable pollen grains of Hibiscus syriacus. We hypothesise that pollenkitt composition differs between Malvoideae species with uncollectable and collectable pollen. Specific pollenkitt properties might elicit excessive viscidity which affects adhesion to insect visitors but prevents pollen collection by corbiculate bees.

Floral scent and pollination of the invasive plant Coreopsis lanceolata in Japan

Muhammad Arifin — 2023-05-05

The invasive plant Coreopsis lanceolata threatens ecosystems in Japan by competing for resources with native plants. This species is self-incompatible and requires pollinator agents for seed production; however, it is known to produce many seeds. Here, we document the pollination biology and plant-pollinator interactions that facilitate seed production of C. lanceolata in the introduced range. Results revealed that C. lanceolata attracted a wide array of floral visitors comprising 60 species from 20 families. Although most floral visitors could be potential pollinators, the functional groups of halictid bees appeared to be the most important pollinators of C. lanceolata in terms of visitation frequency and the ability to carry pollen. The floral scent emission of C. lanceolata consists predominantly of monoterpenes, sesquiterpenes, and benzenoids. Furthermore, the mean seed set was nearly 30% of the ovule mean. Our study confirmed that in the introduced range in Japan, C. lanceolata is integrated into the local pollinator community, especially with the functional group of halictid bees involved in the reproductive success.

Fishing for flies: testing the efficacy of “stink stations” for promoting blow flies as pollinators in mango orchards

Jonathan Finch — 2023-03-21

Pollinator communities are composed of diverse groups of insects, with radically different life histories and resource needs. Blow flies are known to visit a variety of economically important crop plants. Larval blow flies develop by feeding on decaying animals. Some fruit growers are known to place carrion on farms during the flowering season to attract adult blow flies (Calliphoridae). However, the efficacy of these “stink stations” has not been tested. We conducted a series of experiments to determine: 1) if stink stations promote the abundance of blow flies in mango orchards (Mangifera indica L.), 2) if any increases in the abundance of flies acts to promote pollination and fruit set in Australian mango orchards. Farms with stink stations had approximately three times more flies than control farms. However, the increased abundance of blow flies did not result in increased fruit set. Although stink stations increased the abundance of blow flies, we found no evidence that their use improves mango yield. This may be due to pollination saturation by a highly abundant native hover fly, Mesembrius bengalensis (Syrphidae), during our study. We hypothesize that stink stations may only be beneficial in years or regions where other pollinators are less abundant.

Pollen biology and reproductive ecology of selected paleotropical Dendrobiums and its commercial hybrids

Rumalie de Silva — 2023-02-23

Understanding the reproductive biology is of great importance in the development of novel hybrids in ornamental plants. Pollen fitness-related traits are crucial for the pollination success in any plant species including dendrobiums. The aim of the study was to determine and compare the fitness traits of ten commercial Dendrobium hybrids and two indigenous Dendrobium species, D. crumenatum and D. anosmum found in Sri Lanka. We measured pollen viability, pollen germinability, and fruit production after controlled pollination. The effect of storage temperature on D. crumenatum pollen viability was evaluated to establish a suitable pollen storage method to improve future breeding programmes, as the flowering of dendrobiums is seasonal. The reproductive ecology of selected dendrobiums was studied by the observations of visits of natural pollinators and by assessing floral morphology to predict their potential pollinators. Six commercial hybrids had non-viable pollen while D. crumenatum showed the highest pollen germinability under both in vivo and in vitro conditions. Ninety percent of the commercial hybrids failed in vitro pollen germination whereas under in vivo conditions 50% were successful. Self-incompatibility in D. crumenatum was observed in both hand-pollination and under natural pollination. Pollen of D. crumenatum can be stored for two weeks at 9°C maintaining viability and germinability. Selected dendrobiums have shown adaptations to melittophily, suggesting the pollination by bees. Findings indicated a reduction of male fitness in most of the commercial Dendrobium hybrids and a higher fruit set is seen in selfing than cross-pollination. The present study provides information for developing conservation strategies and future hybridization programmes in paleotropical dendrobiums.

Genotype and environment effects on sunflower nectar and their relationships to crop pollination

Jarrad Prasifka — 2023-02-16

Whether caused by genotype (G) or environment (E), floral trait variation has consequences for plants and their pollinators. Cultivated sunflower is a model system to explore floral trait variation; though sunflowers are bred to self-pollinate, benefits of pollination by bees remain substantial. To better understand sunflower-pollinator interactions, experiments were conducted to: (i) examine genotype and environment effects on nectar quantity and quality under controlled conditions, and (ii) assess effects of bags used for pollinator exclusion on nectar quantity, quality and bee foraging in a field environment. Contrasting temperature treatments (28°C, 21°C, 28°C / 16°C) reveal environment effects or G × E interactions for nectar volume (µl / floret), concentration (°Brix), and sugar composition (% sucrose). Bags used to exclude sunflower pollinators resulted in nectar volumes greater than plants with unrestricted access for bees (= open-pollination), and in ≈ 5-fold increased visitation by wild bees after bags were removed. Differences in bee visits to plants that were previously bagged versus plants never bagged decreased over the 2 h following bag removal. Though genetic variation in sunflower nectar is affected by the environment and G × E interactions, improving pollination via plant breeding still appears feasible. Future research on intraspecific variation in pollen rewards could be helpful, especially because pollen has received little research compared to nectar. For research with nectar or pollen, it seems desirable to measure floral rewards with methods that don’t rely on pollinator exclusion (bags or cages), which should provide more realistic data on what pollinators experience while foraging.