Category: educate

Two-spotted longhorn bees (Melissodes bimaculatus) love the city. This important crop pollinator is abundant in urban areas, and lucky for you, this highly distinctive bee is easy to identify. Read on to learn how to spot one in your garden (hint: look on squash and corn) and check out our field ID guide or this species profile on watchingbees.com for ID tips.

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Range

Melissodes bimaculatus can be found across eastern North America, from Texas to Florida, but also as far west as the front range of Colorado. Populations occur to Minnesota and Maine.

Active Period

Two-spotted longhorn bees are active for about six weeks of the growing season—in Massachusetts, from late-June through early August—and produce one generation per year.

Appearance

Two-spotted longhorn bees are about 0.75-1x the size of a honey bee. Males are jet black, with long curly antennae, a cream-colored patch on their face, and thin white hind legs.

Female M. bimaculatus are larger and stockier than males, but with shorter antennae. They have thick brushes of white hairs on their hind legs for carrying pollen (though these hairs can be obscured by orange or yellow pollen). They also have two namesake white spots on the sides of their abdomen, though these spots are often hard to see. Females have have all black faces.

One lookalike to watch out for is the carpenter-mimic leaf-cutter bee (Megachile xylocopoides). This species is found only as far north as southern New Jersey. Females of this species carry pollen beneath their abdomens, not on their legs, and both sexes often hold their wings out at a 45˚ angle while foraging.

Male Behavior

In late-June, males emerge from the ground and patrol patches of flowers in search of females. Male M. bimaculatus are zippy; they speed through the garden, only stopping briefly to sip nectar or rest on a leaf. At night, males sleep on vegetation. They bite twigs or long blades of grass, often two to three feet off the ground, and hang on all night long with their mandibles. Males are highly faithful to particular sleeping perches, and will often sleep near other males. Maybe your garden is home to one of their adorable slumber parties!

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Female Behavior

Females emerge shortly after males and get to work collecting pollen and nectar provisions for their solitary underground nests. Despite their abundance, two-spotted longhorn bees nest in obscurity; few nests have ever been documented. We suspect they nest in sparsely vegetated soils, such as those found on the margin of a garden bed. If you think you’ve found a nest, please reach out!

Floral preferences

The best way to spot M. bimaculatus is to spend time watching your garden in mid summer. Male and females drink nectar from a variety of common vegetable garden plants, including cucumbers, squash, black-eyed susans, oregano, cosmos, purple coneflowers, and zinnias. Females specially like visiting tubular flowers such as wild bergamot (Monarda fistulosa), hoary vervain (Verbena stricta), and mountain mint (Pycnanthemum).

Females collect pollen from a staggering array of plants, including asters like black-eyed susans (Rudbeckia) and cosmos, pumpkins and zucchini (Cucurbita pepo), moss rose (Portulaca grandiflora), rose of sharon (Hibiscus syriaca), and morning glories (Ipomaea purpurea).

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 In addition, while studying M. bimaculatus movement in urban gardens last year, TPI scientists noticed that this species has a curiously strong affinity for corn pollen (Zea mays). This was unexpected since corn flowers have evolved to disperse pollen on the wind, not via insects*. Corn pollen is dry and light, and the flowers produce no nectar, so we figured that M. bimaculatus must have been seeking out corn flowers for pollen. Upon a closer look, we saw a female actively packing corn pollen into her scopae, i.e. the thick hairs on her hind legs. We followed up on our observations by visiting local farms in the area growing corn. Sure enough, M. bimaculatus was on corn flowers in every single field.

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This remarkable association between M. bimaculatus and corn raises many more questions than it answers. Corn is not native to eastern North America—though it has been grown here for thousands of years by native peoples—so which came first? Did M. bimaculatus arrive in this region following widespread trade of corn? Or did M. bimaculatus evolve a local preference for corn pollen since few other flower-visiting insects use this resource? Regardless, we encourage you to look for M. bimaculatus on corn flowers in your garden this year.

Share your findings on iNaturalist or comment on this post! Happy bee watching.

*By collecting pollen from tall male corn flowers, M. bimaculatus is a pollen thief, not a pollinator. M. bimaculatus is not a corn pollinator since it never visits the female flowers of corn plant (the silky ears lower down on the plant), which produce no pollen and offer no nectar.

by Emily Erickson

Spring has finally arrived in the Northeast, and it’s time to start planting your pollinator garden! Perhaps you have already picked out the perfect spot in your yard and started making a list of which plants to purchase. Once you reach the garden center, you may be in awe of the different varieties to choose from. At the same time, you are faced with a familiar dilemma: are all these varieties equally good for pollinators?

What is a cultivar and why should I care?

Unless you are going out of your way to buy your plants from a specialty nursery, chances are you are purchasing a “cultivar,” or a plant that has been bred for desirable traits like the number of petals, flower shape, or flower scent. Plant breeding is not inherently a bad thing: it broadens the diversity of species that you can grow in your garden by improving resilience against pests, drought, or poor soils. As a result, cultivars have become the industry standard. They can be identified by the single quotation marks in the name (ex. Marigold Alumia ‘Flame’).

While cultivars are great for people, they are not always great for pollinators. Native plants and their pollinators share a long evolutionary history, and many flowers have evolved particular traits that signal honest advertisements of a high quality food resources. For instance, the smell and color of wild geranium tell a bee that that nectar and pollen awaits and the dark lines on the petals help them to quickly locate their meal.

In contrast, cultivars have been removed from evolutionary history with insects; humans have bred cultivars in labs and greenhouses to meet our aesthetic preferences. And sometimes, by selecting for traits that we deem impressive, we inadvertently produce plants that broadcast false advertising. Recent work, including my PhD research,  has demonstrated how cultivars—even ones that look quite visually similar—can vary dramatically in the abundance and diversity of insects that they are able to support^1–6, so it’s important to choose carefully.

5 tips for choosing better cultivars

But, how do you choose? Ideally, all ornamental cultivars would scored for pollinator attractiveness to help guide customers to select high-value plants for their flower gardens. A metric like this doesn’t yet exist, however, so we’ve distilled down some basic guidelines that you can use to identify the best plants for flower-visiting insects!

1. Avoid doubled flowers

Double-flowered varieties are those that have been selected for extra petals, such as in many roses, impatiens, chrysanthemums, and carnations. Often, this doubling comes at a cost: the reproductive florets (where pollen and nectar are produced) are converted to petals, meaning the flower no longer feeds pollinators! And, even if the plant is still capable of producing rewards, doubling often obstructs visitor access to those resources⁶. So, while doubled varieties are interesting to look at, they are best left on the shelves.

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2. Choose perennials and ‘nativars’

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Recently, the commercial plant industry has shifted towards producing more cultivars of perennial plants, including many native species, or ‘Nativars’.⁷ These varieties are often rewarding to grow since they come back every year once established and they require less maintenance overall. My research found that many native and non-native perennial cultivars can be highly attractive to flower-visiting insects in the field. I even observed several rare and specialized species foraging on nativars! Some of the best pollinator-friendly nativars are also easy to find:

• Oenothera ‘Fireworks’
• Echinacea ‘Magnus’
• Rudbeckia ‘Herbstonne’
• Solidago ‘Fireworks’
• Agastache ‘Blue Fortune’
• Eupatorium ‘Gateway’

For tips on which native plants to source for your garden, check out TPI planting guides!

3. Choose cultivars that resemble wild types

A general guideline for selecting the best ornamentals is to go for cultivars that look most like the wild types. Of course, this is a subjective criterion, and there are many traits that we cannot readily perceive (such as scent or nutrition) that can influence plant attractiveness to pollinators. Still, in my research I found that pollinator attraction to the herbaceous perennial Catmint (Nepeta)—of which purple is the primary color found in the wild (Catmint is native to the Caucasus region)—was highest for purple compared to white cultivars. In other words, the less derived, the better!

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4. Check the label

A major concern with ornamental flowers is the use of pesticides, particularly systemic neonicotinoids, during production. These pesticides can end up in the pollen and nectar treated plants and can have lethal and sublethal effects on visiting pollinators. Before you purchase a plant from the nursery, check the label to see if it has been treated with neonicotinoids!⁸

5. See for yourself!

One of the best ways to find ornamental cultivars that are attractive to pollinators is to walk through the garden center and notice which plants seem to be either getting the most pollinator visits or are visited by many different species! This will open your eyes to all the different pollinators that call our yards home and the wide array of plants that they like to use.

References

1.  Garbuzov, M. & Ratnieks, F. L. W. W. Quantifying variation among garden plants in attractiveness to bees and other flower-visiting insects. Funct. Ecol. 28, 364–374 (2014).
2. Erickson, E., Patch, H. M. & Grozinger, C. M. Herbaceous perennial ornamental plants can support complex pollinator communities. Sci. Rep. 11, 17352 (2021).
3. Erickson, E. et al. More than meets the eye? The role of annual ornamental flowers in supporting pollinators. Environ. Entomol. 49, 178–188 (2020).
4. Rollings, R. & Goulson, D. Quantifying the attractiveness of garden flowers for pollinators. J. Insect Conserv. 23, 803–817 (2019).
5. Marquardt, M. et al. Evaluation of the importance of ornamental plants for pollinators in urban and suburban areas in Stuttgart, Germany. Urban Ecosyst. 24, 811–825 (2021).
6.  Corbet, S. A. et al. Native or exotic? Double or single? Evaluating plants for pollinator-friendly gardens. Ann. Bot. 87, 219–232 (2001).
7.   Criley, R. A. Native fashion. Acta Hortic. 1167, 1–10 (2017).
8.   Erickson, E. et al. Complex floral traits shape pollinator attraction to ornamental plants. In Review.