Planning your garden to support specialized pollinators

Looking out my window, as the ground is covered with snow and I am getting ready for another snowstorm coming tonight, it seems ironic that I have been spending many hours these days ordering seeds and planning my garden. While I am thankful that the winter brings some rest to the soil in my garden, planning this season brings me happy memories of the scents and buzzes in my yard during the growing days… which reminds me that I should also plan for my little buzzing pollinator friends when I plan what to grow this season. In today’s blog, I want to chat about how we can plan for many types of pollinators, with a special focus on planning for specialists and not just for generalist pollinators.

Specialist pollinators – never heard of them?

As we mentioned in a previous post, pollinators visit plants to feed on nectar and/or to collect pollen to feed themselves or their offspring. However, pollen is not just there for pollinators to feed on; pollen is central to plant reproduction, so plants tend to make it both attractive to pollinators but hard to digest. For this reason, and in order to be able to properly digest the pollen, pollinators are often specialized in their pollen choices. This is because being able to digest the compounds that plants add to their pollen to make them hard to eat requires some level of adaptation, which often involves a trade-off with the ability to eat anything. There are, of course, many levels of specialization, and, while many pollinators feed on many plant families, others are more specialized than that, and feed on only specific plant genera or even species! For us gardeners, this means that if we want to support many different pollinators, we need to make sure that we are also providing for those very specialized pollinators as well!

Luckily for us, the floral choices and pollen specialization is known to some extent for Maryland and Eastern USA bees (see this site to learn more). For this reason, we know that many specialized bees in our region are also rare or uncommon… another reason to try to provide resources for them!

Who are pollen specialists in our region?

Many known pollen specialist bees in our region belong to bee genera Andrena, Colletes, Osmia, and Melissodes, which have many species considered rare or uncommon in Maryland and Mid-Atlantic.

Andrena

Many of these ground-nesting mining bees are specialized on different plant groups, such as the sunflower family Asteraceae and the heather family Ericaceae, as well as genera Salix, Phacelia, and Rhododendron.

Adrena bee on geranium flower
While many Andrena of our region specialize on Asteraceae and Ericaceae, the lovely A. distans specialize on Geranium flowers. Photo: M. Veit.

Colletes

Also known as the cellophane bees because of the polyester-type secretion they use to line their nests, Colletes is a genus of ground-nesting bees that can sometimes nest communally (this is, all in the same patch). Several of its species specialize on pollen of the sunflower family Asteraceae, and plant genera such as Physalis and Vaccinium.

Colletes bee
Many species of this genus, Colletes, are specialized on plants of the sunflower family, like C. simulans, which feeds only on goldenrods. Photo: M. Veit.

Osmia

Several native species of this group of mason bees are found in our region, and those specialized on pollen resources visit mostly one of the following plant genera: Cirsium, Vaccinium and Penstemon.

Osmia bee on a sunflower
The small mason bee Osmia texana specialized on flowers of the sunflower family, like the one in this picture, feeding on the sunflower genus Helianthus. Photo: M. Veit.

Melissodes

This group of bees are also known as long-horned bees due to their very long-antennae. In our region, several species are considered specialized in their pollen choices. While their vast majority are specialized on plants of the sunflower family Asteraceae, one species specializes on the pickerelweed Pontederia, an aquatic plant of our region.

How to support pollen-specialist bees?

A simple approach we can take to support pollen-specialists is to make sure that we provide floral resources that they can use. As we could see in the previous section, most of our specialized bees use Asteraceae, such as goldenrods Solidago, wild sunflowers Helianthus, American Asters Symphyotrichum and coneflowers Rudbeckia. Planting native species of these plants is thus a great way to provide resources to these pollen-specialists.

Several other species in our region are also specialized on genus Vaccinium and Rhododendron, and for that reason, planting native species of these plant genera can be a great way to support these bees, all while enjoying their lovely flowers (e.g., in Rhododendron, the Azalea genus) and delicious fruits (e.g., in Vaccinium, the genus of blue- and huckleberries!).

If you’re now itching to get some of these plants, here and here are useful lists of places where one can acquire seeds and/or starts/pots of these wonderful plants. And if you’re interested in getting seeds for these plants, hurry up; most people are doing the same right now and many species may already be sold out!

By Anahí Espíndola, Assistant Professor, Department of Entomology, University of Maryland, College Park. See more posts by Anahí.

Anahí also writes an Extension Blog in Spanish! Check it out here, extensionesp.umd.edu, and please share and spread the word to your Spanish-speaking friends and colleagues in Maryland. ¡Bienvenidos a Extensión en Español!

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