Journal of Pollination Ecology

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.

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.

Spatio-temporal differences in pollinator species richness, abundance and conservation status in a Mediterranean island

Pau Enric Serra Marin — 2022-12-23

Although the Mediterranean basin is a hotspot of pollinator diversity, little is still known about how such diversity is distributed in the region and about its conservation status. This study contributes to filling this information gap by studying pollinator diversity parameters in one of the main Mediterranean islands, Mallorca, and further evaluating their conservation category according to the IUCN criteria. We focus on three communities, two coastal and one mountain shrubland, which we have studied for several years. For each community, we obtained the following variables: (1) Shannon diversity (H'), (2) Pielou's index (J'), (3) Number of pollinators per plant (L_p), (4) Flower visitation rate (FVR), (5) Specialisation index (d') and (6) Normalised degree of pollinators, i.e. the number of plants visited per pollinator species relative to the total number of plant species in the community (ND). All pollinators were categorised into functional groups to test for differences in such variables among them. Differences across communities, years and functional groups were tested through GLMMs. The three communities showed differences in pollinator species composition, species richness and diversity. Pollinator diversity also varied with time, especially in the coastal community, which suffered a major disturbance during one of the study years. Regardless of the functional group, the pollinator specialisation degree seems context-dependent. Native and endemic species might disappear in the short term if appropriate management measures are not taken to narrow down the threats to pollinator populations. Further research is urgently needed to assess most insect pollinators' conservation status in the Mediterranean before such rich diversity is lost forever.

Pollen accumulation on hawkmoths varies substantially among moth-pollinated flowers

Gordon Smith — 2022-12-23

Using the pollen loads carried by floral visitors to infer their floral visitation behavior is a powerful technique to explore the foraging of wild pollinators. Interpreting these pollen records, however, requires assumptions about the underlying pollen dynamics. To compare visitor foraging across flower species, the most important assumption is that pollen is picked up and retained on the visitor at similar rates. Given differences in pollen presentation traits such as grain number or stickiness even among flowers with similar morphologies, however, the generality of this assumption is unclear. We investigated pollen accumulation on the hawkmoth Manduca sexta, testing the degree to which accumulation differed among flower species and how pollen stickiness affected this accumulation. In no-choice floral visitation assays to six plant species visited by long-tongued hawkmoths in the wild, M. sexta individuals were allowed to visit flowers 1, 2, or 5 times, after which the pollen on their proboscises was removed and counted. We found that the six plant species varied orders of magnitude in the number of pollen grains deposited on the moths, with some placing thousands of grains after a single visit and other placing none after five. Plant species with sticky pollen adhesion mechanisms placed more pollen on the moths and had relatively less pollen accumulation over successive visits than non-sticky plants. Intriguingly, moths carried fewer pollen grains after 5 visits than after 2 visits, suggesting that both sticky and non-sticky pollen was lost during foraging. Together, our results suggest that interpretation of pollen load data should be made cautiously, especially when comparing across plant species.

The importance of soil and vegetation characteristics for establishing ground-nesting bee aggregations

Konstantinos Tsiolis — 2022-11-15

Most bee species are ground-nesters, yet knowledge on the nesting behaviour of this diverse group remains sparse. Evidence on the effectiveness of ground-nesting bee species as crop pollinators is growing, but there is limited information on their nesting habits and preferences and how to manage habitats to enhance populations on farms. In this study, artificially prepared plots of bare soil were constructed with the aim to attract ground-nesting bees to nest in a commercial orchard in Kent, UK. Nine soil parameters were measured to determine their preferred soil properties: hydraulic conductivity, soil compaction, soil moisture, soil temperature, soil stoniness, soil organic matter, soil root biomass, soil texture and vegetation cover. Eighteen non-parasitic ground-nesting bee species (7 Andrena, 9 Lasioglossum, 1 Halictus and 1 Colletes spp.) were recorded in the study plots. Soil stoniness and soil temperature at 10cm depth were positively correlated, and vegetation cover and hydraulic conductivity were negatively correlated with the number of ground-nesting bees on the plots. We show that artificially created habitats can be exploited for nesting by several ground-nesting bee species. This study’s findings can inform management practices to enhance ground-nesting bee populations in agricultural and urban areas.

Consequences of pollinator availability and effectiveness for pollen transfer in a gynodioecious seed crop system

Riley Waytes — 2022-09-26

Pollinator availability and effectiveness are important considerations in plant systems that depend on insect transfer of pollen. In mixed-flower systems (such as dioecious or gynodioecious systems), pollinators may distinguish between morphs, a behaviour which could have negative implications if it leads to reduced cross-pollination. We examined pollinator visitation, response, and effectiveness in hybrid canola seed production, a gynodioecious crop, to understand how pollinator behaviour contributes to cross-pollination between ‘male’ (hermaphroditic) and ‘female’ (male-sterile) morphs. The pollinator types found in these fields differ in visitation rate, size, and pollen load, factors that may affect pollen transfer between plants. The willingness of pollinators to move between male and female flowers can also affect pollen deposition. We used an interview bouquet to present unvisited female inflorescences to different pollinator types visiting male and female flowers to understand behavioural responses to floral morphs and the factors that contribute to better pollination effectiveness. Managed pollinators (honey and leafcutter bees) were far more abundant than wild pollinators in this system. Bees foraging on male flowers were less likely to accept a proffered female flower than those foraging on female flowers. Pollen deposition on stigmas was influenced by pollinator type (female leafcutter bees were the most effective) and increased with time spent on a flower. Pollinators transferring from a male flower to a female flower deposited more pollen than those that originated on female flowers, emphasizing the importance of transfer between male and female morphs. Surprisingly, pollinators carrying more pollen transferred less pollen to recipient stigmas.

Pollination ecology and breeding system of the tropical tree Guaiacum sanctum on two Caribbean islands with contrasting pollinator assemblages

Jose J. Fumero-Caban — 2022-09-21

Insular pollination systems are more extinction-prone and vulnerable to invasive species than mainland ones. They often have plants with reproductive mechanisms allowing for self-compatibility and low species-rich communities of pollinators. Here, we document different reproductive traits of the tropical tree Guaiacum sanctum on two insular populations with contrasting pollinator assemblages: Guánica in Puerto Rico with alien honeybees and Mona Island where honeybees do not occur. Using field observations and pollination experiments, we evaluated pollinator species richness, visitation rates, breeding system, and the fitness of selfed- vs. crossed-progenies. We found that flowers are pollinated by insects on both islands, but while the species richness of pollinators was higher on Mona, the visitation rates were considerably higher in Guánica where trees are almost exclusively visited by the introduced Apis mellifera. Flowers are not apomictic, and autogamy is negligible indicating that pollinators are required to set fruits. Outcrossing yielded nearly twice the number of fruits and seeds than selfing and these differences were consistent between populations, which might reflect early acting inbreeding depression, partial self-incompatibility, or differences in resource allocation between selfed and outcrossed fruits. Our combined results suggest that the substantial reduction in pollinator visitors in areas dominated by A. mellifera may add an additional level of vulnerability to these threatened populations. Although reproductive fitness is higher in Guánica, mostly due to the pollination services provided by A. mellifera, this population may be more susceptible to environmental changes and large-scale disturbances affecting pollinator abundance given the reduced diversity of flower visitors.

Evaluating the effects of observation period, floral density, and weather conditions on the consistency and accuracy of timed pollinator counts

Neil Mahon — 2022-09-14

Insect pollinators are experiencing substantial declines as a result of habitat loss, agricultural intensification, invasive pests, and climate change. To investigate factors causing pollinator declines, evaluate the success of conservation measures, and institute long-term monitoring schemes, it is essential to validate and standardize pollinator sampling techniques. This study investigated how sampling duration, weather conditions, and abundance of floral resources influenced the results of timed pollinator counts by repeatedly sampling the same pollinator assemblage in an Irish meadow. The likelihood of detection of Apis mellifera, Bombus spp, solitary bees, and Syrphidae was strongly associated with the density of floral units or floral cover in the observation plot. Also, even though protocol criteria restricted pollinator counts to the middle of the day and benevolent weather, pollinator counts were strongly influenced by factors such as cloud cover, light levels, wind speed and relative humidity. Increasing the duration of the timed counts from 5-minutes to 30-minutes considerably increased the probability of detection of each pollinator group. Additionally, the perceived diversity of the pollinator assemblage at the meadow was markedly affected by sampling duration and floral abundance. To improve the consistency or comparability of studies using timed pollinator counts, we recommend that criteria are set restricting surveys to narrow ranges of weather conditions and floral density when possible. Additionally, pollinator field investigations or monitoring programs would benefit from a systematic evaluation of how erroneous non-detection of target taxa can be reduced to acceptable levels by modifying sampling duration.

Stem-nesting Hymenoptera in Irish farmland: empirical evaluation of artificial trap nests as tools for fundamental research and pollinator conservation

Simon Hodge — 2022-08-03

Insect pollinators are suffering global declines, necessitating the evaluation and development of methods for long-term monitoring and applied field research. Accordingly, this study evaluated the use of trap nests (“bee hotels”) as tools for investigating the ecology of cavity nesting Hymenoptera within Irish agricultural landscapes. Three trap nests consisting of 110 mm diameter plastic pipe containing 100 cardboard nest tubes of varying diameter were placed at eight apple orchards and eight oilseed rape sites and left in the field for five months. Sealed nest tubes occurred at 15 of the 16 sites, and in 77% of the 48 nests. However, only 7% of the 4800 individual nest tubes were sealed, and only 4% produced cavity-nesting Hymenoptera. Three cavity nesting bee species (Hylaeus communis, Osmia bicornis, Megachile versicolor) and two solitary wasp species (Ancistrocerus trifasciatus, A. parietinus) emerged from nest tubes. There were significant differences among species in terms of emergence date and the diameter of nest tubes from which they emerged, the latter allowing the calculation of niche width and niche overlap, and informing choice of tube size in future studies/conservation efforts. Trap nests, therefore, offer a valuable tool for fundamental ecological research and a model system for investigating interactions between stem-nesting species within their wider ecological networks. The ability of trap nests to actually increase farmland pollinator abundance and diversity as part of agri-environment schemes requires additional investigation. However, used in sufficient numbers, these trap nests provide valuable biogeographical data for cavity nesting Hymenoptera and offer a viable means for long term monitoring of these species in Irish farmland.

What are the plant reproductive consequences of losing a nectar robber?

Trevor Ledbetter — 2022-08-03

Pollinator declines worldwide are detrimental for plants. Given the negative effects that antagonisitc visitors, including nectar robbers, can sometimes inflict, might declines in their populations instead confer benefits? During the 1970s, reproductive biology of the Colorado columbine, Aquilegia caerulea (Ranunculaceae), was documented near Gothic, Colorado. At that time, Bombus occidentalis, the Western Bumble bee, was one of its many pollinators, but more commonly acted as its only known nectar robber. Bombus occidentalis abundance has declined precipitously throughout the Western USA since the 1970s. In 2016, we documented floral visitors at sites near those used in the original survey. We then experimentally quantified the effects of nectar robbing, allowing us to estimate the reproductive consequences of losing B. occidentalis. We also quantified the potential pollination services of muscid flies (Muscidae, Diptera). The floral visitor community was dramatically different in 2016 compared to the 1970s. Bombus occidentalis was infrequently observed, and nectar robbing was negligible. Our experiments suggested that a high level of nectar robbing would lead to significantly reduced fruit set, although not seeds per fruit. Fly visits to flowers were dramatically higher in 2016 compared to the 1970s. In the absence of bumble bees, muscid flies significantly reduced fruit set below the self-pollination rate. The negative effect of the increase in these flies likely outweighed any positive effects A. caerulea experienced from the absence of its nectar robber. Although the field observations were conducted in a single year, when interpreted in combination with our manipulative experiments, they suggest how A. caerulea may fare in a changing visitation landscape.

Settling velocity and pollination dynamics in Diarrhena obovata, a grass of temperate forest edges and understories

Phillip Klahs — 2022-07-12

Pollen from a naturally occurring population of the forest grass species Diarrhena obovata was successfully captured in a series of pollen traps to understand the timing of anthesis and the dispersal mechanics of wind pollination in an example of the flowering plant family Poaceae. Scanning electron microscopy was used to identify the pollen surface ornamentation as microechinate-areolate. The spherical grains have a diameter of 38.74 μm. The settling velocity calculated by Stoke’s Law was 4.48 cm s^-1, but physical measurement by drop tower experiments resulted in 3.77 ± 0.15 cm s^-1 (sd). The surface ornamentation observed in D. obovata pollen is not expected to alter drag forces considerably but the reduction of settling velocity may be a result of species-specific pollen grain density. In forest grasses an improvement in settling velocity may be adaptive in overcoming dispersal constraints in an environment where trees obstruct wind speeds and create more turbulence.

By land and by tree: Pollinator taxa diversity of terrestrial and epiphytic orchids

Haleigh Ray — 2022-10-26

There are approximately 30,000 species in the family Orchidaceae, with some species growing terrestrially and others growing as epiphytes. Though the pollination biology of many of these species is not well known, there has been a diversity of taxa recorded as orchid pollinators. Insects, birds, and even a record of a mammal species have been documented as successful pollinators, while some orchids are able to reproduce without the use of a pollen vector. The goal of this review is to provide an overview of orchid pollination tactics, with references to more specific studies of each, and to analyze a large subset of publications to determine differences in pollinator taxa and specificity between epiphytic and terrestrial orchid genera.

This review examines pollination data from over 400 orchid species, including 74 epiphytic and 83 terrestrial orchid genera. Two pollinator taxa, Coleoptera and Hymenoptera (Class: Insecta), were found to pollinate significantly more terrestrial than epiphytic orchid genera, while other taxa showed no significant differences. Hymenoptera were the dominant taxa of pollinator in regards to the overall number of species recorded; however, based on species interaction webs that were built, the Lepidoptera (Class: Insecta) have stronger interactions with the orchid species they pollinate, suggesting a more specific relationship between the two.

Pollinator-flower interactions in gardens during the COVID-19 pandemic lockdown of 2020

Jeff Ollerton — 2022-07-27

During the main COVID-19 global pandemic lockdown period of 2020 an impromptu set of pollination ecologists came together via social media and personal contacts to carry out standardised surveys of the flower visits and plants in gardens. The surveys involved 67 rural, suburban and urban gardens, of various sizes, ranging from 61.18° North in Norway to 37.96° South in Australia, resulting in a data set of 25,174 rows, with each row being a unique interaction record for that date/site/plant species, and comprising almost 47,000 visits to flowers, as well as records of flowers that were not visited by pollinators, for over 1,000 species and varieties belonging to more than 460 genera and 96 plant families. The more than 650 species of flower visitors belong to 12 orders of invertebrates and four of vertebrates. In this first publication from the project, we present a brief description of the data and make it freely available for any researchers to use in the future, the only restriction being that they cite this paper in the first instance. The data generated from these global surveys will provide scientific evidence to help us understand the role that private gardens (in urban, rural and suburban areas) can play in conserving insect pollinators and identify management actions to enhance their potential.

Beyond Botany: In appreciation of the life and contributions of Dini Eisikowitch (1936 – 2022)

Amots Dafni — 2022-09-30

Professor Dan Eisikowitch (Dini), one of the greatest researchers in 10 pollination and botany, has passed away (1936-2022). Dini died on 19 July, 2022 at 11 the age of 86. An obituary.