Rare plant’s need for native pollinators threatened by invasive plant-pollinator relationship

Chloropyron maritimum ssp. maritimum
visited by Bombus californicus.
Photo: Kylie Etter

By Etter et al.

Many flowering plants need pollinators like bees to reproduce. But when new, non-native plants move into their habitats, they can disturb these important relationships. One rare plant that is reliant on pollinators is Chloropyron maritimum maritimum, which is found in salt marshes in Southern California, USA and Baja California, Mexico. Unfortunately, these marshes are being invaded by a non-native plant called Limonium duriusculum.

To see how this invasion affects the rare plant, we watched which insects visited which flowers, studied the network of plant-pollinator relationships, and tested what happened when L. duriusculum was removed in small areas.

We found that only native bees visited C. maritimum maritimum, and not very often. In contrast, L. duriusculum was mostly visited by two non-native insects, which didn’t once visit the rare plant. Removing L. duriusculum didn’t increase visits to C. maritimum maritimum, but it did make the overall pollination network stronger and more connected.

In the future, we hope to both remove larger areas of the non-native plant and check to see if there are good places nearby for the native bees that visit C. maritimum maritimum to nest. This could help protect the few remaining pollination interactions the rare plant still has.

 

Read the scientific article in JPE!

 

Why Data Quality Matters in Plant–Pollinator Databases

Swamp milkweed with pollinating insects
Photo: Chris Taliga

by Ollerton et al.

Imagine trying to piece together a giant puzzle where each piece represents an interaction between a flower and the insect, bird, bat or other animal that helps it reproduce. In recent years, scientists have gathered millions of these “puzzle pieces” into massive online databases, offering an unprecedented view of how plants and their pollinators connect around the world.

But there’s a catch: not every entry in these databases is equally reliable. Did the researcher actually watch the insect brush pollen against the flower’s stigma? Or did they simply note that the insect visited the blossom and assume pollination happened? Without clues about how each plant–pollinator link was documented, users can’t tell solid evidence from a best guess.

That’s why a growing number of projects are now tagging every interaction with a “data quality badge”—a short note explaining the exact kind of proof behind the record. For example:

•      Direct observation: A scientist observed an animal pollinating a specific flower.
• Pollen analysis: Pollen grains matching that flower were found on the insect’s body.
• Inferred pollinator: The animal regularly visits those flowers and shares similar traits with known pollinators.

Initiatives like the Pollinators of Apocynaceae Database and the Database of Pollinator Interactions (DoPI) have already adopted these quality flags. The upcoming USDA-NRCS PLANTS database is doing the same, and Brazil’s REBIPP network has developed a standardized set of terms—rooted in the global Darwin Core standard—to make sure everyone speaks the same “pollinator language.”

Why is this important? When you know the strength of the evidence behind each plant–pollinator link, you can:

•      Fill in real knowledge gaps with confidence.
• Identify weak spots in our understanding that need more fieldwork.
• Build better conservation plans, targeting the most critical pollinators for at-risk plants.

Ultimately, adding clear data-quality labels turns these massive collections of observations into powerful tools for science, restoration, and education. And that’s good news not only for researchers, but for every garden, farm, and wild ecosystem that depends on diverse and abundant pollinator communities.

Read the scientific article in JPE.

Study on redbud and dogwood trees and their bees

Urban dogwood

by Camilo et al.

Cities often present challenges to natural and seasonal interactions between native pollinator populations and native tree species. In particular, the urban heat island effect may cause native trees to bloom earlier than the emergence of their pollinators. Over a two-year period, we recorded daily temperatures and collected bees as they foraged on two native and spring-flowering tree species (redbud, Cercis canadensis and dogwood Cornus florida) at two urban sites in Saint Louis, Missouri and two woodland sites within 55 kms outside the city limits. As anticipated, the ambient temperatures in the city were higher compared to the exurban sites, and both tree species began blooming earlier in the urban sites. We collected a total of 54 bee species. The diversity of pollen-carrying bees (native and naturalized species) was lower on both tree species at our city sites. The urban redbuds, which were the earliest to bloom, had a lower bee species diversity compared to rural redbuds and urban and rural dogwoods. We caught more pollen-carrying bees on redbud flowers (n = 254) than on dogwood flowers (n = 180). More pollen-carrying bees were captured in rural sites (n = 333) than in urban sites (n = 101). Finally, pollen-carrying female bees (n = 365) outnumbered pollen-carrying males (n = 69) but the percentage of pollen-carrying male to female bees was disproportionately greater on both tree species in our city (redbud, 38%; dogwood 20%) compared to our rural sites (redbud, 12%; dogwood 13%).  Due to urban plantings of mass-flowering but non-native trees and shrubs from Eurasia, bees collected on city dogwoods were more likely to carry the pollen of more than two co-blooming species compared to rural redbuds and dogwoods. Although the flowering period of both tree species always overlapped at urban and rural sites, only 34 out of 434 bees captured were found to carry the pollen of both tree species at the same time.

 

Read the scientific publication in JPE!

Annual diversity of honeybee pollen sources in two pumpkin growing landscapes, Machakos County, Kenya

A honeybee (Apis mellifera scutellata) visiting
the flower of the country mallow (Abutilon
indicum) (Family: Malvaceae)

By Nang’oni et al.

Honey bees (Apis mellifera) play an indispensable role in ecosystems—not only by providing income through hive products but also by pollinating many cultivated crops. Their pollination activities significantly contribute to fruit and seed production, directly enhancing crop yields. As they go about their routine of collecting pollen and nectar, these remarkable insects unintentionally yet effectively support crop production through pollination services.

In our study, we turned our focus to rural farmlands in Machakos County, Kenya, which we categorised into two landscape types: those with low vegetation cover and those with medium vegetation cover. Our objective was to identify the annual sources of pollen that honeybees rely on in these distinct settings, based on colonies strategically placed throughout the study area. To achieve this, we collected pollen samples fortnightly from worker bees returning to their hives over a 14-month period, ensuring we captured the effects of both biophysical and climatic factors across the year. Leveraging these findings, we created a floral calendar for each region, highlighting the predominant pollen sources harvested by the bees.

Our research revealed notable differences between the two landscapes. In areas with low vegetation cover, honeybees predominantly collected pollen from seven plant families, including Asteraceae, Poaceae, Typhaceae, Combretaceae, Acanthaceae, Boraginaceae, and Amaranthaceae. In contrast, bees in areas with medium vegetation cover accessed a more diverse range of pollen sources from ten plant families, such as Asteraceae, Combretaceae, Poaceae, Malvaceae, Fabaceae, Salvadoraceae, Solanaceae, Euphorbiaceae, Liliaceae, and Scrophulariaceae. Interestingly, only four plant families served as major pollen sources for honeybees throughout the year in both landscapes. We also observed a higher diversity of plants providing over 45% of pollen to honeybees in areas with medium vegetation cover compared to those with low vegetation cover. Furthermore, honeybees in low vegetation cover landscapes at any given time collected more than double the amount of pollen from Poaceae and Typhaceae, compared to their counterparts in medium vegetation cover areas.

These findings highlight the ecological variations in forage sources available to honeybees, underscoring the importance of tailored conservation and management strategies. We believe it is essential for land use and management practices in these regions to prioritise the needs of honeybees to sustain livelihoods for beekeepers and farmers alike. At the farm level, we recommend aligning honeybee forage care practices with the developed floral calendars to ensure the effective protection of these vital pollinators.

Read the scientific publication in JPE