Pollen resource use by managed honey bees and unmanaged wild bees

A bumble bee collecting red pollen
 from an Asphodel

By Boni et al.

Bees play an essential role in maintaining biodiversity, but increasing numbers of managed honey bees, particularly when combined with beekeeping practices that do not adequately consider wild pollinator conservation, may negatively affect wild bees, especially in sensitive ecological contexts.

We investigated the pollen collected by managed honey bees and unmanaged wild bees on three islands of the Tuscan Archipelago National Park (Italy) to better understand how they share floral resources.

Our results showed that honey bees and wild bees shared pollen sources in 58.7% of the comparisons, although the degree of overlap was generally low to moderate, with high overlap occurring in only 16.7% of cases.

Interestingly, higher honey bee densities were associated with lower pollen overlap, suggesting that wild bees may increasingly rely on alternative floral resources, potentially in response to competition with managed honey bees.

Although these findings do not directly demonstrate competition, they highlight the importance of precautionary, low-intensity beekeeping management and further research to better understand these interactions and support wild bee conservation in protected areas.

Read the scientific article in JPE HERE! 

Do nest-departure and nest-return rhythms of bumblebees align with community-level flower visitation patterns?

Bombus lepidus, an alpine bumblebee

by Xu et al.

A Day in the Life of an Alpine Bumblebee

Bumblebees are among the most important pollinators in the world. As they move from flower to flower, they help many wild plants produce seeds and reproduce. On a warm summer day in an alpine meadow covered with flowers, you can often see bumblebees becoming active in the morning, becoming more numerous as the day goes on, and then gradually disappearing in the late afternoon.

But have you ever wondered what happens at the bumblebees' home?

If you are lucky enough to find a bumblebee nest in the wild, you can watch workers leaving the nest to search for flowers and returning later with the food they have collected. This raises an interesting question: Do bumblebees follow the same daily schedule at their nest as they do when visiting flowers?

We became interested in this question while studying pollinators on Yulong Snow Mountain in southwestern China. At high elevations, we noticed that bumblebees and other pollinators were most active at two different times of day—once in the morning and again in the afternoon. Why did this happen? Perhaps the bees were responding to changes in sunlight and temperature. Or perhaps they simply took a break around lunchtime.

To find out, we needed to watch the bees at home.

In 2019, we were fortunate to discover a wild nest of Bombus lepidus, an alpine bumblebee species that has received relatively little scientific attention. Even better, the nest was located between two of our study areas where we were already recording flower visits. This gave us a rare opportunity to follow the bees from their nest to the flowers and back again.

For six days in August, we watched the nest throughout the day. We recorded when worker bees left the nest, when they returned, and whether they were carrying pollen. We then compared these observations with our records of bumblebees visiting flowers in the nearby meadows and forests.

The bees had a surprisingly regular daily routine. They did not simply come and go throughout the day at a steady rate. Instead, there were two clear busy periods: one in the morning and another in the afternoon. We saw a similar pattern among B. lepidus visiting flowers in the surrounding landscape.

However, the timing was not exactly the same. In the morning, flower visits reached their highest level a little later than activity at the nest. In the afternoon, flower visits increased around the same time that many bees were leaving the nest, before many returning bees arrived. One possible explanation is simply that bees need time to fly between their nest and their foraging sites. In other words, what we see at the nest may happen slightly earlier or later than what we see at the flowers.

Life on a high mountain can also change quickly during the day. Temperature, humidity, sunlight, and wind can all change within a few hours. We found that the bees' activity was closely related to conditions around the nest. They were particularly active when the temperature near the nest was around 24°C. Their activity increased as temperatures approached this point but declined when it became warmer. They were also especially active when humidity was around 50–55%.

Interestingly, the bees did not respond to their environment in exactly the same way throughout the day. Their morning activity seemed less affected by changes in weather, while their afternoon activity was more closely linked to changes in temperature, humidity, sunlight, and wind.

We also noticed something unexpected during our six days of observations. The total number of bees leaving and returning to the nest gradually decreased, but a larger proportion of returning bees were carrying pollen. This could mean that the colony was changing how it used its workers over time. Perhaps the flowers available to the bees were changing, or perhaps the colony's needs were changing. We do not yet know the answer because we did not measure these factors directly.

Our observations offer a small but fascinating glimpse into a day in the life of an alpine bumblebee. The bees' movements at their nest and their visits to flowers followed a similar pattern, with busy periods in the morning and afternoon. Weather conditions around the nest also appeared to influence their activity.

We were especially fortunate to find a natural nest of Bombus lepidus, because wild bumblebee nests are difficult to find and observe. Our study involved only one colony, so we cannot yet say whether all B. lepidus colonies behave in the same way. More observations of different nests, in different seasons and mountain environments, will help us understand how these remarkable bees organize their daily lives—and how their daily routines shape pollination in alpine ecosystems.

Read the scientific article in JPE HERE! 

Unexpected pollinators of highbush blueberry

Bumblebee (left) and ant (right) in blueberry flowers

By Castro et al.

Highbush blueberry, a pollinator-dependent crop, attracts a wide range of insects, including managed honeybees, wild bees, and hoverflies. But not every visitor is equally effective. Blueberry flowers can be challenging for pollinators: their shape limits access to nectar and pollen, while their poricidal anthers release pollen more efficiently when vibrated, a process known as buzz pollination. Visitors also differ in how they forage and how much pollen they carry and deposit. 

We monitored visitors to the highbush blueberry cultivar ‘Duke’ and found a surprise: most visits came from the ant Formica rufibarbis, followed closely by the bumblebee Bombus terrestris. To compare their effectiveness, we allowed individual insects to visit previously bagged flowers, then measured the pollen they deposited. Only Formica rufibarbis and Bombus terrestris visited flowers during this experiment.

Bumblebees deposited significantly more pollen tetrads than ants, and the flowers they visited developed more pollen tubes. Even so, unbagged flowers exposed to open pollination developed more pollen tubes than flowers visited just once by a bumblebee. This suggests that repeat visits by bumblebees, contributions from other pollinators, or both may increase pollen deposition.

Ants were less effective blueberry pollinators because they deposit less pollen and may promote self-fertilization. Yet when flying pollinators are scarce, for example, during unfavorable weather or early in the flowering season, large numbers of ants could still make a valuable contribution to the pollination of this crop.

Read the scientific article in JPE here!

The role of native bees in Avocado pollination

A native bee on an Avocado flower

by Pérez-Giraldo et al.

Much of the food we eat exists because of bees. As they visit flowers, they carry pollen, which allows plants, such as avocado trees, to produce fruit. But what about native bees? Unlike honey bees, they are mostly solitary and come in an incredible variety of sizes, shapes and colours. Yet, we still know very little about their role in producing crops such as avocados. To learn more, we studied two avocado orchards in central Chile. We asked two questions: First, do trees closer to native forests or shrublands receive more visits from native bees? Second, we asked which bees, depending on their body size, carry more pollen available for pollination and contribute more to fruit production. In 2018, we observed 20 trees in each orchard located between six and 72 meters from natural vegetation. Additionally, in 2018 and 2019, we covered selected trees to control which bees could visit their flowers. This allowed us to compare the amount of fruit produced under each treatment.

What did we discover? The distance from the forest did not affect bee visits or the amount of pollen available for pollination. For a bee, 72 meters is a short flight. However, body size did matter. Small and medium-sized bees carried more pollen for pollination than large bees -that is, they had more pollen on their bodies, ready to be deposited on the next flowers they visited. This was not because they visited more flowers, but rather, because each bee carried more pollen. The fruit results were surprising: flowers visited by medium-sized bees, as well as self-pollinated flowers, produced almost as many avocados as flowers open to all visitors, though the fruit was not heavier. Small bees produced fewer avocados, but the fruit was larger and heavier, though this varied by year. Why does this matter? No single group of bees performed in every respect. Some contribute to the quantity of fruit, while others influence its size and weight. That is why diversity is key. The greater the variety of bees, the better the harvest. Protecting the natural vegetation around orchards and safeguarding our native bees means protecting food production.

Read the scientific article in JPE here!

 

Self-incompatibility of U.S. Great Basin Sphaeralcea (Malvaceae) and regional prevalence, pollination efficacy, and floral infidelity of their oligolectic Diadasia bees

Diadasia bee on Sphaeralcea flower

By Cane & Love

Globemallows (Sphaeralcea species) are widely adapted in rangeland restoration across basins of the western United States, yet little was known about how breeding biology and pollination affect seed production in the genus. We studied three common species to determine their reliance on outcrossing, document the prevalence of different bees that visit them across sagebrush‑steppe habitats, and evaluate the pollination performance of the specialist bee, Diadasia diminuta.

All three globemallows produced substantially more capsules and seeds when flowers received pollen from other plants rather than self‑pollen. Field surveys showed that a diverse assemblage of solitary, ground‑nesting bees visit globemallow flowers, with D. diminuta consistently the most abundant species. Single visits by female D. diminuta deposited enough pollen to achieve full seed set. The bees readily established in newly planted restoration plots, even where wild globemallow populations were distant. Although D. diminuta specializes on Sphaeralcea, foraging females frequently moved between species in mixed plantings, behavior consistent with the natural hybridization common in this genus.

Read the scientific article in JPE here

Who visits forest bramble flowers, and when? What camera traps reveal about pollinators in the woods

A bumblebee on a bramble flower

by Bonneau-Chloup et al.

Forest understories are the scene of everyday interactions between plants and insects, yet we know surprisingly little about who visits forest flowers, when they do it, and if they are sensitive to the very local microclimate. Most pollinator research focuses on open meadows or crops, leaving forest flower-visitor communities largely overlooked, even though forests host some specialized insects and may represent a refuge for more generalist wild pollinators in increasingly farmed or urbanised landscapes.

To fill this gap, we set up a non-invasive video monitoring system on bramble flowers (Rubus fruticosus agg., a common forest-edge shrub) across four patches of the Fontainebleau forest, near Paris. Over 369 hours of footage, we recorded every insect that visited the flowers, day and night, without ever touching or trapping a single one.

We counted 3,636 visits from 17 different types of visitors. Ants turned out to be the most frequent guests, accounting for nearly half of all visits, followed by ordinary flies, then bees, hoverflies, and moths/butterflies together. Each group had its own daily rhythm: most insects were busiest from late morning to late afternoon, but ants were more active at dusk and dawn, and some flies and hoverflies showed two separate activity peaks in a single day. A few visitors, including some beetles and grasshoppers, lingered on a single flower for over an hour, while bumblebees and hoverflies typically stayed just a few seconds. Interestingly, sunlight and temperature had only a limited effect on which insects showed up, flies and ants were less active in bright light, and flies also foraged faster as it got warmer, but most other visitors carried on regardless of the microclimate.

Overall, our results suggest that forest flower visitors avoid competing with each other mainly by using the flowers at different times of day. Beyond the ecological findings, this study shows that filming brambles with cameras is a simple, low-cost, and environmental-friendly way to study forest flower visitors, one that can run continuously, day and night, and could be used to track forest pollinator communities more widely in the future.

 

Read the scientific article in JPE here! 

Pollination services of managed common eastern bumble bees (Bombus impatiens) in seedless watermelon (Citrullus lanatus)

Common eastern bumble bees: A) at the entrance of a commercial colony and 
B) visiting a watermelon flower.

By Mateos-Fierro et al.

Pollinator-dependent crops rely on pollinating insects for successful pollination and thereby achieving commercial yields. Seedless watermelon (Citrullus lanatus) is particularly dependent on insect pollination, as pollinators must transfer pollen from pollen-donor plants. While pollen transfer can be provided for free by wild pollinators, these gratis pollination services are typically insufficient. As a result, growers use managed pollinators. The western honey bee (Apis mellifera) has historically been the only managed species employed, but recently, growers have also supplemented with bumble bees, such as the common eastern bumble bee (Bombus impatiens). However, adding a second managed pollinator entails a greater investment, which may not pay off, particularly since the role of managed bumble bees in seedless watermelon production is uncertain.

In this study, we investigated the pollination contribution of managed bumble bees by combining field observations and experiments. Field observations were conducted in commercial seedless watermelon fields; all fields were stocked with honey bees, but only some were also supplemented with bumble bees. We recorded the number of flower visits and the behaviour of different pollinator groups. Additionally, we conducted a powder tracing experiment in which we sprayed fluorescent powder into the bumble bee colonies so that they would leave traces on flowers. Finally, we analysed pollen collected from bumble bees and their colonies to explore what percentage of the pollen belonged to watermelon.

Our field observations revealed that bumble bees were infrequent visitors to watermelon flowers. Supplementing fields with managed bumble bees did not increase watermelon visits across the entire field, but visits increased locally, within 10 m around their colonies. Additionally, managed bumble bee presence in the fields influenced other pollinators’ behaviours, but this differed across pollinator groups. Small solitary bees were, in general, more affected. The powder tracing experiment indicated little managed bumble bee activity, with only 1.5% of flowers showing powder traces, whereas the pollen analysis revealed that watermelon pollen made up only 2.9% of the pollen collected by bumble bees.

These data suggest that stocking fields with managed bumble bees may not increase visits to watermelon flowers and therefore may not be important contributors to watermelon pollination. However, their direct contribution to yield and whether an increase in stocking rate can increase visits to flowers have yet to be explored.

Read the scientific article in JPE