Penn State Pollinator Webinar Series: "Bee nutritional ecology: from flowers to landscapes" (Christina Grozinger)

Posted: June 30, 2020

Animal mediated pollination supports nearly 90% of plant species. Animals also gain nutritional benefits from this process. Bees collect pollen from flowering plants to feed to their offspring, and thus bee and flowering plant species have coevolved to benefit both species involved.

The nutritional rewards provided by these plants have evolved alongside bees and thus provide bees with a balanced diet. Many plants have also evolved specific "advertisements" such as size, color, scents, and shape to attract bees. However, oftentimes humans focus too much on these "advertisements" instead of the nutritional benefits of the plants. In this Webinar, Dr. Grozinger, a professor of entomology and the director of the Center for Pollinator Research at Penn State, answers four major questions that people should consider when developing a garden or habitat to support pollinators. The goal is to create both beautiful and ecologically functional landscapes, by seeing landscapes through the eyes of pollinators.

The first question that one should ask is, "what are the most nutritious flowers for bees"? Nectar is the main source of carbohydrates for bees, while pollen provides protein and lipids. Anthony Vaudo, a former Ph.D. student at Penn State, demonstrated that protein:lipid ratios in pollen varied greatly across plant species, and that there also seems to be variation in the preferred ratios for the three different bee species used in his study (press release). This suggests that different bee species may prefer to forage on different plant species due to their different nutritional needs. Thus, it is important to include a diversity of plant species, which span a range of pollen protein:lipid ratios, in your planting schemes.

In the next question, Dr. Grozinger discusses the strategies we can use to identify the most nutritious and attractive flowering plant cultivars and species for pollinators. Here Dr. Grozinger presents three research studies, which use observations of pollinators visiting selected plant stocks in field plots, observations of pollinators visiting plants growing in forests, and studies using DNA barcoding to identify the species of plants from which honey bees are collecting pollen. We first look at Emily Erickson's research which specifically focuses on the role of ornamental plants in supporting pollinator populations (press release). Ornamental plants are often the result of long breeding programs by people, not pollinators, and thus nutritional rewards may have been uncoupled from "floral advertisements", resulting in stocks that cannot support diverse pollinator species. Emily evaluated 25 annual and 25 perennial cultivars. She found that overall perennial cultivars attracted greater abundance and diversity of pollinator species than annual cultivars, and there was substantial variation among cultivars. Of the stocks Emily evaluated, she recommends plants such as Catmints, Black Eyed Susans, Hyssops, and Cone Flowers. We then look at Doug Sponsler's research evaluating the preferred plant species for honey bees in urban areas, specifically Philadelphia (press release). Doug found that honey bees exhibited preferences for different plants throughout the seasons. In spring they collected pollen from trees, in summer they preferred herbaceous plants, and during late summer and fall, they mostly foraged on woody shrubs and vines. A third study by Codey Mathis (a recent graduate from Indiana University of Pennsylvania) focused on habitat ecology of native pollinator communities within early successional deciduous forests of the central Appalachian mountains. Her research found that native pollinators were also supported by a varied plant community that changed throughout the growing season. In early to mid summer naive pollinators preferred small shrubs, brambles, and forbs. In late summer to early fall they tended to forage on brambles, forbs, and devil's walking stick. In mid-fall, the pollinators preferred goldenrods and asters. Overall, the results of these studies demonstrate that the flowering plant species that provide the best nutrition for pollinators varies with the type of pollinator, the season, and the location.

The third question is, "how do we use this information to design pollinator habitats?" Bees and other pollinators require a large diversity of plants that bloom throughout the growing season, and these plants need to provide good quality and quantity of both pollen and nectar. One way to achieve this is to incorporate a diversity of types of plants (trees, shrubs, herbaceous species) that have flowers with varied shapes, colors, and scents. Bees also need a lot of flowering plants to be attracted from a distance, and to have enough food to sustain them, so planting as many flowering plants as possible is best. It is best to choose native plant species, since these are more likely to provide the resources needed for pollinators than exotic, ornamental, or invasive species. Furthermore, since wild bees nest in soil, wood, and cavities, these habitats need to be available to support these populations. Finally, the overall landscape context needs to be considered: if a garden is a very small oasis in a large area that does not support pollinator populations, it will likely not be able to attract many species.

The last question Dr. Grozinger tackles is, "how do we know if our landscapes are good for bees?" Fortunately, there are multiple readily available resources that can help answer this question. On the Center for Pollinator Research website, there is a link to a guide that allows you to score your gardens, farms, or yards to determine if they provide sufficient floral resources and nesting habitat for bees. To study the landscape at a larger scale, you can go to the Beescape website. This site will show the nesting resource index, floral resource index, and the insecticide toxicity index in any area across the US. Beewinterwise is another great tool that can help understand the survival rates of bees throughout the winter, based on local weather conditions. At the moment this tool only has information on Pennsylvania, but Dr. Grozinger encourages others to add their honey bee colony winter survival data to Beescape to improve and expand their models.

Links to these sites and others are listed below! To learn even more about maintaining pollinator health there are many additional resources available through the Center for Pollinator Research website, the Pollinators' Garden at the Arboretum at Penn State, and the PSU Sustainability Institute Frost Entomological Museum at Penn State. You can also learn more by signing up for the other Webinars in this pollination series!

Written by Ashley Moak

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