Popular perennial flowering plants can attract various pollinator mixtures

UNIVERSITY PARK, Pa .– Popular species of perennial flowering plants vary widely in their appeal to pollinators, but homeowners and landscape managers who select certain perennial cultivars can support a diverse community of pollinators in their own backyards, according to a new study from a team of researchers at Penn State.

Insect pollinators are essential in agriculture and natural ecosystems, but these pollinators have experienced a decline in the world’s population, largely due to a loss of flowering plants in their landscapes, on which they depend for food.

“We know that green spaces such as parks and gardens in many human-modified landscapes have the potential to support very rich pollinator communities, including rare or vulnerable species,” said lead author study Emily Erickson, postdoctoral researcher in entomology at the College of Agricultural Sciences. . “However, urban and suburban pollinator communities tend to lack the diversity they need to be resilient to new disturbances.”

Erickson noted that many studies have shown that increasing the availability of attractive flowering plants is one of the most effective and accessible ways to increase pollinator diversity in cityscapes. “But a key challenge,” she said, “is to identify combinations of plant species that can support and design a diverse and therefore more stable pollinator community.”

Co-author Christina Grozinger, Publius Vergilius Maro professor of entomology and director of Penn State’s Center for Pollinator Research, explained that in urban and suburban areas, people often select varieties of ornamental plants for their gardens because of their appearance and their growth patterns.

“Many of these varieties were developed by breeders to appeal to consumers rather than pollinators,” said Grozinger, who also heads the Insect Biodiversity Center at the Huck Institutes of the Life Sciences. “There was concern that these plant varieties would no longer be attractive to pollinators.

“Cultivars are bred for variation in characteristics such as structure, color, size and duration of flowering, all of which are known to influence pollinator attraction,” she said. “We also know, from previous studies, that closely related cultivars can vary widely in their attractiveness to pollinators.”

To help optimize the ecological value of urban and suburban green spaces and develop specific recommendations for home gardeners and landscapers, researchers studied 25 cultivars from five plant genera: Agastache (giant hyssop, hummingbird mint); Echinacea (echinacea); Nepeta (cat mint); Rudbeckia (Susanna with black eyes); and Salvia (sage) – which a recent USDA grower survey indicated to be commercially popular in the North American floriculture market. They assessed each variety’s attractiveness to pollinators throughout the growing season for two years at two sites, each of which previously housed a diverse community of pollinators.

Researchers have found that Rudbeckia ‘Herbstonne’ is one of the perennial flowering varieties that attract a large number of visits from pollinators, like this monarch butterfly.

“We have discovered that these plants can attract bees, flies, butterflies and beetles, including many rare and vulnerable bee species,” said co-author Harland Patch, assistant professor of entomology and research. director of pollinator programming at the Penn State Arboretum. “But some cultivars are more attractive than others. A garden of the six most attractive plant cultivars will attract nearly 80 species of bees, while a garden of the six least attractive cultivars will attract only 20 species of bee. bees. “

The results of the study, published recently in the journal Scientific Reports, revealed that the giant hyssop Agastache ‘Blue Fortune’ received the most pollinating visitors. Other varieties with greater visitor abundance were Agastache ‘Foeniculum’ and ‘Black Adder’, Nepeta ‘Faassenii’ and ‘Walker’s Low’ and Rudbeckia ‘Triloba’ and ‘Herbstonne’. Many of these same varieties have also attracted the greatest diversity of bee species, including rare and vulnerable ones.

Echinacea Echinacea purpurea ‘Magnus’ received the fewest pollinator visits. In fact, the five cultivars of Echinacea as a whole had lower visitation rates.

The total abundance and diversity of visiting bees of different plant genera varied with the seasons. The researchers noted that pollinator species vary around the time of year they emerge and seek food sources.

“As a result, a complete habitat for pollinators will include flowering plants with overlapping flowering times to ensure constant availability of food resources,” said Erickson, who added that plant diversity in the landscape was also correlated. to the abundance and diversity of pollinating visitors. “Although cultivars of some genera, such as Salvia and Nepeta, are not very attractive overall, they can play an important role in providing food resources early in the season, especially when combined with d ‘other high flowering spring resources such as flowering trees. “

The researchers point out that plants with larger flowers, such as cultivars of Rudbeckia and Agastache, can support many species of bees, including some rare ones. Therefore, these varieties are candidates to be planted in multiples and should be given priority when planting a pollinator garden.

“Other species with relatively small flower arrangements that are less attractive to pollinators, such as cultivars of Salvia and Echinacea, can be planted more sparingly while contributing to the overall floral diversity and abundance of the plant. landscape, ”said Grozinger. “An understanding of this relationship between ecological function, plant attractiveness and flower display size can be applied to garden design, especially in areas where space is limited. “

A grant from the Specialty Crops Research Initiative of the National Institute of Food and Agriculture of the United States Department of Agriculture supported this work.

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