VIRGINIA TURFGRASS JOURNAL: Margaret J. Couvillon, Ph.D., Assistant Professor of Pollinator Biology and Ecology, Department of Entomology, Virginia Tech

Ornamental Plant Choice Impacts the Abundance and Diversity of Insect Pollinators in Gardens

This article is based upon the following peer-reviewed study: MC Palmersheim, R Schürch, ME O’Rourke, J Slezak, and MJ Couvillon. “If You Grow It, They Will Come: Ornamental Plants Impact the Abundance and Diversity of Pollinators and Other Flower-Visiting Insects in Gardens.” Horticulturae 8, no. 11 (2022): 1068.

Plants are mostly stationary. Although they can move a little bit, growing upwards and outwards, these movements are small, slow, and generally insufficient for finding a mate, especially if you want to reproduce sexually every year. Sexual reproduction helps maintain genetic diversity in a population and is a winning strategy. Therefore, over millions of years of co-evolution, plants have solved this sessile challenge by developing close relationships with some animals to serve as the vectors to transport pollen, the male sex cells. That close relationship is pollination, and about 88% of all flowering plants need that animal-assist to make the magic happen (Ollerton, Winfree & Tarrant 2011). Of the animals that participate in pollination, insects are by far the most consequential. If we line up the plants, both wild and agricultural, that need pollination services, our heavy lifters are insects, such as bees, butterflies, and flies. Therefore, while birds and bats are also valuable in this process, there is a critical need for the contribution of insect pollinators (Klein et al. 2007; Ollerton 2021).

The large role of insects in plant reproduction makes their recently recorded declines even more alarming: insects in general, and pollinators in particular, are decreasing in numbers (abundance) and species richness (diversity) (Hallmann et al. 2017; Sánchez-Bayo & Wyckhuys 2019). These declines have been precipitous, upwards to 75% by some measures, and likely a reflection of the larger threats to wildlife in general that humans have bequeathed to our world. For insect pollinators, of course, their declines have direct consequences on our global food security, as 75% of food crops need insect pollination services (Klein et al. 2007).

Both wild and managed insect pollinators, like honey bees, face challenges from pesticides, pests, pathogens, and poor nutrition, where a lack of abundant, diverse flowers in a landscape can have direct and indirect negative consequences on insects (Goulson et al. 2015). Media and popular press coverage has been wide: everyone wants to feed hungry pollinators. One activity that is immensely popular among concerned citizens is to establish a pollinator garden, where ornamentals are planted with the express purpose of feeding pollinators. Groups ranging from schools to libraries to museums to private individuals are frequently approaching perceived experts (i.e., an Assistant Professor of Pollinator Biology) for advice on what plants to use. When I started receiving such phone calls in 2017, I realized that all I could do was direct people to existing plant recommendation lists. I quickly realized, however, that a non-specialist gardener, such as myself, might experience barriers against making informed choices about plants for pollinators. For example, recommendations from organizations like the Xerces Society publish lists that appear based on expert opinion but lack empirical backing and/or do not cite sources. There are also inconsistencies among plant recommendations, where there is very little overlap, even within regions (Garbuzov & Ratnieks 2014a). Sometimes recommendations are too general, even if we know that different cultivars might vary in as much as tenfold in their attractiveness to insects (Garbuzov & Ratnieks ...