Pollinators – Maryland Grows

The Shared History of Wasps and Bees, And How Bees May Have Become Vegetarian

May 13, 2024May 10, 2024Maryland Grows2 Comments

We may have all found ourselves in that situation in which we see an insect on a flower and we wonder whether it is a wasp or a bee, and we may have also seen people panic when they encounter a bee, thinking that it is indeed a wasp. Although the two groups are very distinct and there are several ways of telling them apart (check out this previous post to see how to do it), this difficulty is in part a signature of the shared evolutionary history that the two groups have. In today’s post, I want to tell you about the evolutionary origin of bees, how it is interwoven with that of wasps, and how evolutionary studies can help us understand and explain the diversity of our charismatic bees.

Evolutionary histories and the big family we are all part of

Before jumping into the main topic of this blog, please bear with me so I can give you a bit of context for what I’ll tell you, and so you can fully appreciate the power of the discoveries I will tell you about in just a second. One of the foundations of today’s biology and the way we understand life is that living organisms share a common ancestry and that evolutionary processes such as natural selection, mutations, dispersal, and random processes have led to the establishment of new lineages that can evolve into new species and new groups of organisms. What this means is that all the living organisms we know can be placed in a sort of genealogical tree, where more closely related species and groups appear placed on branches of the trees that are also closer to each other (we call these trees “phylogenies” or “phylogenetic trees”). Also, this means that if we were to take these trees, and we were to follow the evolutionary process “backward” (from the tips to the internal branches; that is, from the present into the past), we would be able to identify branching points, which represent the now extinct ancestors of species we know today.

a diagram of a family tree — A phylogeny can be compared to a genealogical tree we may want to build for our family. In this tree, the most closely related members of our family share recent ancestors (marked with diamonds), but are still connected with more distantly related members of the family with longer branches and other more ancient shared ancestors. In the same way, a phylogeny represents the relationships between species or groups of species, with branches connected by their shared ancestors. Image: University of Iowa

Although this may sound like a biological nerd moment of mine, I hope that you will appreciate the enormity of this principle. This simple concept indicates that each of us and all species that exist on the planet have shared ancestors at some point in our history. We are all related to each other, like a huge family… and as for all families, the study of our history can teach us fun and interesting things about who we are, helping us understand and explain things we observe today. Let me tell you what the study of these phylogenies has taught us about wasps and bees (and their shared history) and why this excuses us in part from not always being able to tell them apart 😉.

Bees and wasps, and the vegetarian wasp

As you may know, bees and wasps are both insects that belong to the order Hymenoptera. Despite the fact that people knew they were related but distinct from each other, it was not until relatively recently that people understood what that relationship was. In fact, because they share a lot of common traits, scientists were for a long time confused about what the most closely related group of Hymenoptera was for bees, wasps, and ants. Some years ago, with the development of new methods that allow for more detailed studies of phylogenies, researchers found strong evidence that ants are a group of organisms that is related but distinct from another group formed by bees and by a particular group of solitary and usually ground-nesting wasps called crabronids. Besides the taxonomic and purely conceptual importance of this discovery, what this meant biologically was on the one hand, that bees are evolutionarily extremely closely related to wasps, to the point that we could consider them “non-carnivorous wasps”. On the other hand, this discovery showed that all bees we know today would have evolved from a wasp-like ancestor that was solitary and ground-nesting, like the crabronids we know today.

a family tree of bees and wasps - showing evolutionary relationships — In 2017, Branstetter and collaborators used phylogenies to demonstrate that all bees and a group of wasps (crabronids) shared a common ancestry, indicating that bees can be considered a type of “vegetarian” wasp. In the figure, the position of the common ancestors is shown with arrows and stars. The main groups are labeled on the left. Image: modified from Branstetter et al., 2017

If you’re like me and find this fun, keep reading because it gets even more fun! 😊 So, after this discovery, the people who work on these topics wanted to know more. For example, can phylogenies tell us more about how the transition from a meat-based diet (wasps are carnivores) to a pollen-based one (bees feed mostly on pollen and nectar) could have happened? To investigate this, researchers ran a similar analysis, but this time considering a lot more species of both bees and crabronids. Constructing phylogenies using genetic information, they figured that when the evolutionary relationships of these groups were studied, it appeared that bees were the most closely related to a particular group of crabronids that is known to predate on thrips (a family called Ammoplanidae).

a closeup of a small black bee — Bees have been shown to be very closely related to a group of tiny wasps in the family Ammoplanidae which are known to hunt on thrips. Photo: CBG Photography Group (CC).

Besides confirming the discoveries of the previous study, this one provided a logical and interesting biological and ecological context for the transition from carnivory to pollinivory in bees. Thrips are a group of insects known to feed on plant materials, often found on flowers, where they feed on pollen. This new study proposed that a possible evolutionary opportunity may have appeared when a lineage of thrip-predating wasps evolved the ability to not only digest thrips meat but also the pollen they contained in their guts (!!). This transition could have set the evolutionary foundations to eventually transition to a diet fully based on pollen, which opened opportunities to the newly emerging lineage to feed on a new dietary resource not already in use by other wasps. If this is true, this transition would have provided an important evolutionary advantage (e.g., reduced competition for food), which would have led to the huge diversification of bees, leading to the extreme diversity we see today.

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!

Waiting on Spring Garden Cleanup to Support Beneficial Insects

April 15, 2024April 15, 2024Maryland Grows1 Comment

With warmer temperatures and spring blossoms we are likely ready to get back into our gardens. Before we get our hands dirty, let’s learn how to support the beneficial insects in our landscapes that are and will be emerging from their overwintering sites. In today’s post we will review some information and tips on how we can support, and not disrupt, the life cycles of beneficial insects like our native bees, when we do any spring garden cleanup or prep.

Plant stems, leaves, and other debris can be home to many beneficial insects during the winter months that are waiting on warmer days before they emerge this spring. Wait as long as you can before removing any plant materials. Photo: M.E. Potter, University of Maryland Extension

Overwintering beneficial insects

Some insects migrate (e.g. Monarch butterfly) to avoid the cold temperatures, but there are many insect species that overwinter (spend the winter months in one of their life stages- egg, larva, nymph, pupae, or adult) in Maryland. Insects like luna moths (Actias luna) who overwinter in the pupal stage in cocoons within leaf litter (see photo below), the great spangled fritillary (Speyeria cybele) who overwinters as caterpillar larvae in leaf litter, bumble bee (Bombus spp.) queens who can overwinter as adults underground, small carpenters bees like Ceratina strenua who overwinter as adults in plant stems, and praying mantids like the Carolina mantis (Stagmomantis carolina) who overwinter in the egg stage as ootheca (an egg case) laid on woody plant stems and other structures. All these examples are of beneficial insects, who provide services like pollination and pest control during their active life stages. This goes to show, even in the cold and quiet winter months, your garden can be full of life!

a luna moth cocoon found in fallen leaves — *Luna moths overwinter as pupae in cocoons made of fallen leaves and silk. In late spring the insect will emerge as an adult moth. Photo: M.J. Raupp, UMD*

When is too early for spring cleaning?

Generally, the longer you can wait the better! Insects do not all emerge at the same time. There are some native bee species that emerge from their overwintering sites as early as March (e.g. some Colletes spp.) and some that typically do not emerge until late May (e.g. Blue-green sweat bees). Due to the changing climate and the diversity of insect life cycles, we unfortunately cannot point to a specific date on the calendar to know all the overwintering insects have emerged from our green spaces. We can look for different cues in our environment to hint at insect emergence.

Before last frost and consecutive warm days

Once we are out of risk of evening frosts and daytime temperatures are consistently above 50°F for several days in a row, many insects will begin to emerge. Otherwise leaf litter and other plant debris are vital for overwintering insects to survive the cooler temperatures. With climate change, and the chances for more drastic temperature changes, fallen plant material becomes even more important for protecting overwintering insect populations. Think of a fallen leaf as a blanket for our beneficial insects!

Looking for spring blooming trees like cherry, peach, or eastern redbuds can clue us in on this year’s seasonal changes and timing when it comes to insect emergence. Once fruit trees have finished blooming, many of our overwintering bees and beneficial insects have likely emerged. Photo: Nancy Lee Adamson, Wild Bee Plantings

Before fruit trees bloom

Many of our fruit trees (along with natives like Eastern redbud and red maple) bloom in early spring, providing nectar and pollen for our early riser pollinators; check out the figure below on native bee and orchard bloom phenology. If you wait for any garden cleanup until these trees have finished blooming (around mid-May), many of our insects will have likely emerged by then. Since phenology (seasonal changes in a plant’s life cycle, such as the timing of bloom) can shift with changing climate conditions, always keep an eye on the trees and blooms around you. A great excuse to get outside and get to know your local plant life.

Before consistent lawn/turf growth

Noticing consistent lawn/turf growth in your area? Cool-season grasses begin their spring growth once soil temperatures are between 50° and 65°F. A general guideline is once lawns need to be mowed it is a good sign it has been warm enough for many of our overwintering insects to emerge. If you have lots of lawn in your space, consider reducing and replacing the lawn with beneficial insect friendly native plants! If you are wondering what you could plant instead, check out Lawn Alternatives. And if you have heard of No-Mow May, check out the Pros and Cons of the No-Mow May Movement and the Controversy Surrounding No Mow May, by Dr. Gail Langellotto.

Sometimes less is more

Less garden cleanup can have a positive impact on beneficial insect populations! Rethink removing plant debris in certain areas of your landscape. Unless the plant debris comes from a diseased or pest infested plant, leaves, stems, sticks and more can be left, relocated, or reused as wildlife habitat. Your plant debris is some animal’s home! Preliminary data from a study conducted by Max Ferlauto, PhD student in the Burghardt lab, at the University of Maryland, Department of Entomology, shows the number of emerging moths and butterflies are reduced by approximately 67 percent in areas where leaves are removed. If you are removing any plant material, consider relocating the materials to an unmanaged, “habitat area”, or to a compost pile after late spring.

Help fight climate change’s impact on beneficial insects by providing shelter to help insects withstand adverse conditions. Consider leaving and/or adding one or more of the following sources of habitat in your green space this spring!

Leaves
Flower stalks/plant stems
Fallen/removed twigs
Wooden logs
Rocks/rock piles

From “messy” to sustainable

If you are worried about your space looking messy from less spring cleaning, there are ways to get creative to transform your and the public’s view of your conservation areas. An opportunity to personalize your green space with unique and practical “signs of care” (also known as “cues to care”).

Signage

A sign in your green space can not only enhance the look but also help educate others. Why are you leaving the leaves? Let others know by adding a sign about how leaves support native wildlife. Look to local artists and organizations to find a sign that works for your space and could convey a science-based message. You can earn a sign from our Bay-Wise Master Gardener program once your landscape is Bay-Wise certified. To learn more, check out our Bay-Wise program page.

Fencing or edging

Even a short fence or edging can make a space look purposeful and cared for. Edging can be made out of repurposed materials (pebbles, stones, sticks, even glass bottles) or can be purchased from most gardening centers or hardware stores. Think of it as putting a frame around the artwork and beauty that is your garden. For ideas check out, Edging Makes Landscape Beds Pretty, Easy to Keep or Landscape Edging Materials.

Tidy, accessible paths

Ensure any pathways, especially areas around public sidewalks, are clear so all can access and enjoy the space and surrounding area. Cut back overgrown plants that may be blocking or obstructing pathways. If you are working in a community garden, consider the accessibility of your landscape so we may create more inclusive green spaces for all. To learn more about accessible green spaces, check out these pages, Create an Accessible Garden for Those of all Physical Abilities and Gardens Are For Everyone: Ideas for Accessible Gardening.

Additional resources

By Madeline E. Potter, M.S.,Faculty Specialist for Entomology and Integrated Pest Management, University of Maryland Extension

Stem-Nesting Bees in Maryland

March 11, 2024March 8, 2024Maryland GrowsLeave a comment

With their large diversity, bees display a huge variety of nesting preferences. Some bees that are relatively commonly encountered in our region are those that nest in stems. In today’s post, I want to tell you about who they are, their biology, and their preferences when the time comes for them to pick their nesting sites.

Who are the stem-nesting bees in our region?

When we consider bees that nest in stems, we can think about two main groups. In the first group, we have bees that actively dig into pithy stems or wood to build their galleries. In the second group, we have those that use pre-existing cavities in stems and slightly adjust them to accommodate their brood. This difference may seem trivial; at the end of the day, they will all end up in stems, right? Well, that is true to some extent; however, whether we talk about one group or the other will define what actual taxonomic group of bees we’ll be referring to, and a different set of morphological adaptations that allow them to build their nests properly.

In our region both types of bees are present and many of them are relatively common and easily observed in our green spaces.

Stem nesters that dig their nests

In addition to large carpenter bees (Xylocopa), this group includes Halictid bees such as Augochlora and the Apidae Ceratina. Because they all have to dig actively into stems to build their nests inside, all these bees are equipped with very strong mandibles, which have modifications that reinforce them, and strong muscles that allow them to increase the force they can exert on the stems.

a metallic green bee going into a stem nest cavity — Metallic bees are very common in our region. They often can be found emerging or looking for wooden resources to build their nests. Photo: K. Shultz (CC).

Depending on the species, we can find them building nests on different substrates. While Augochlora can often be found building galleries in rotten logs, Ceratina is mostly associated with stems that tend to be a bit hollower, such as those of raspberries and blackberries (you can check out this other post on how to trim those plants to protect their nests), or those of plants of the genus Verbena. In all these cases, the nests have the shape of a gallery, with small cells built consecutively. Each of these cells is carefully built, provisioned with nectar and pollen, populated with one egg, and finally sealed with sawdust or compacted pith.

Stem nesters that use stem cavities that already exist

Several families of bees belong to this group in the Mid-Atlantic. Species of the genus Hylaeus in the family Colletidae are present in our region, and readily nest in hollow stems. Another group that is very commonly seen in our region is that of leaf-cutter bees (Megachilidae). Although this group tends to be more flexible in the types of cavities they will use for building their nests, many species will readily use natural or artificial “stem-like” cavities (these bees are very common in bee hotels).

several bees nesting inside of a plant stem — A small bee commonly seen in bee hotels is that of genus *Hylaeus*, also known as the yellow-faced bees. These bees will readily use small hollow stems and cavities. Photo: R. Cruickshank (CC).

Stem-nesting bees (Hylaeus) were observed in a raspberry cane on May 10, 2023, in Montgomery County, MD. Video: Christa Carignan, University of Maryland Extension

Because these groups do not need to actively dig into wood to build their nests, their mandibles are not as developed as those of the other group of bees I presented above. A common characteristic of all these bees is that they have relatively long and slender bodies, which is believed to allow them to move with more ease in relatively small cavities. It is also for this reason that specialists think that all these species transport pollen either internally or on the lower part of their abdomens (instead of on their legs, for example); this reduces their “width” and allows them to fit into cavities that may otherwise be too narrow. Another characteristic of this group of bees is that they often line their brood cells with special materials, such as leaves, petals, resins, or mud. This means that building these nests is a lot of work!

leaf-cutter bee carrying a leaf piece to a nest — Leaf-cutter bees of genus *Megachile* are also very commonly seen in bee hotels and nesting in cavities around our homes. Here, *M. centuncularis*, brings leaf cuttings to line the nest in a cavity offered in a bee hotel. Photo: B. Plank (CC).

Although bees (and most insects) are generally negatively affected by urbanization, this group of bees appears to benefit from their interactions with humans. Unlike ground-nesting bees which are very negatively affected by land development and urbanization, it seems that stem-nesting bees can easily use many cavities created by humans, such as those appearing in buildings, walls, fences, and gardens.

Read more: This Year, Host Bees in Your Garden

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

Anahí also writes an award-winning 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!

Help us improve the Maryland Grows Blog! Please complete our brief survey to give us your feedback and let us know about your interests.

A Little-Known Group of Pollinators: Beetles!

February 12, 2024February 12, 2024Maryland GrowsLeave a comment

As we mentioned in previous posts, when we think about pollinators, we tend to think of butterflies and bees, but rarely about the super important hoverflies or other groups of organisms. In today’s post, I want to tell you about another of those little-known pollinator groups; let’s talk about beetles that act as pollinators!

Beetles: “hard-shelled” pollinators

From a taxonomic perspective, beetles are a group of insects that belong to the Order Coleoptera. Among other important characteristics, they are recognized by their extremely well-protected body, in particular by structures called “elytra”, which provide a very hard cover to their wings (the wings are placed under the elytra). Generally, beetles have mouth parts that are adapted to chewing, which means that they have large mandibles that allow them to break their food. You may be wondering why I am talking about these structures in a pollination post… well, as for all pollinators, the shape and function of a pollinator define what they do (and don’t do). Let’s see how this affects our pollinating beetles.

a black and yellow beetle on a purple flower — Beetles are common flower visitors, with some of them being very effective pollinators. Because of their very well-protected bodies (see elytra covering the “back” of this beetle), they often spend a lot of time on flowers, where they feed on pollen, nectar, and floral parts. In this picture, we can see a cetoin scarab beetle with prominent elytra and a very hairy body that helps them transport pollen grains between flowers. Photo: C. J. Sharp (CC).

In the case of beetles, the fact that they are well protected by those elytra makes them more “confident.” That “hard shell” provides a great deal of protection against predation by other arthropods, which in turn makes them generally more “chill” in their visits to flowers. Unlike butterflies, bees, or hoverflies, beetles tend to move little within and between flowers, taking all their time to get the resources they need from them. For this reason, they are often considered as more generalist and inconsistent pollinators than their less-protected counterparts.

The shape of their mouths and their feeding habits also affect their efficiency as pollinators. In fact, beetle visits to flowers tend to be relatively destructive because they are attracted to them by their floral tissues, including in some cases pollen and the ovaries! In this respect, beetles tend to visit flowers to feed on them, which in some cases can lead to floral destruction. So, given this, are beetles good pollinators or just flower herbivores?

Beetles as pollinators

Among all the many different groups of beetles, some of them are considered to be particularly good pollinators. Specifically, these belong to the beetle families known as soldier (family Cantharidae) and longhorn (family Cerambycidae) beetles, families that depend on floral resources for their survival at least at one stage of their development. Other families such as scarabs can also be strongly associated with flowers for their survival. In all these groups, the beetles in question have clear adaptations that make them good agents of pollen transfer. For example, we observe different parts of their bodies covered with abundant hairs. This improves pollen transport and thus increases their ability to effectively cross-pollinate the flowers they visit.

a beetle with pollen grains on its head — Beetles that are good at transporting pollen have hairier bodies that can carry pollen grains, like this cantharid beetle that got its face covered in pollen while visiting these flowers. Note the yellow “powder” – pollen – that covers part of the beetle body and take a look at the large mandibles the beetle uses to feed on floral parts. Photo: J. Tann (CC).

Further, although these beetles tend to still feed on floral parts, they are usually much less destructive than their more generalist cousins. They often feed on specific flower parts (instead of on all the floral sections), leaving the central reproductive structures (e.g., the ovaries) intact, and thus allowing plant reproduction. These beetles are also often more specialized in their floral choices, preferring a small range of plant groups (usually one or a few species within the same plant genus), and moving more readily between flowers. Combined, all of this means these beetles can not only carry a lot of pollen (they are hairy) but also move it from flower to flower more effectively and do not destroy completely the flowers they visit.

A cool beetle pollination example

Beetle pollination is a very understudied topic in temperate regions such as Maryland, and we are still learning a lot about it. It is thus not surprising that the number of examples from our region is not super high. Let’s talk about one of them that happens to be relatively well-studied elsewhere but that also occurs in North America.

yellow and black soldier beetle on a magnolia flower — Beetles are considered some of the most important pollinators of species of the genus *Magnolia.* Here, a long-horned (Cerambycid) beetle on a *Magnolia grandiflora* flower. Photo: D. Hill (CC).

An example of beetle pollination of native plants that are also present in our region is that of Magnolia flowers. Although most of our knowledge on the pollination of this plant genus comes from studies done on species outside of North America, there are a couple of reports of floral visitors in several of our local species. From elsewhere, we know that these trees display flowers that appear to be particularly attractive to beetles: they are white, easily accessible, offer a lot of pollen, are fragrant, and in some cases even produce heat! In many of these species, the flowers appear to attract scarab beetles, which, once landed on the flowers, feed on the petals, mate, and then actively move between flowers and cross-pollinate. In North America, some studies like this one and this other one (in PDF) have found a wide variety of beetles attracted to our native species. Many of these beetles are very small and visit Magnolia flowers to feed on them, mate, and spend the night protected within the flowers.

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Floral Supplements Support Ecosystem Services in Our Green Spaces

January 9, 2024Maryland Grows2 Comments

Winter is a good season to plan for spring. In today’s post, we want to tell you a bit about a type of planting that one can consider. This planting will boost the stability of our green spaces, turning them into havens of biodiversity. Let’s talk about floral supplementation and floral supplements.

a row of yellow flowers — Example of a floral supplementation in the form of a flower strip (e.g., “pollinator strip”) in a Mid-Atlantic agroecosystem. Photo: K. Evans.

What are floral supplements?

Floral supplements are semi-natural habitats that are added to green spaces and are designed to concentrate a large amount of plant resources into a small area. By including a mixture of herbaceous or woody flowering plant species, floral supplements provide food and habitat to local wildlife. This increase in floral resources correlates to local increases in the number of insect and other animal species and their abundance, which results in the improvement of ecosystem services in the area. Common examples include pollination, pest suppression, nutrient (re)cycling, soil conservation, and improvements in water provision and quality.

skipper on a flower — Hairstreak butterfly collecting nectar (left); a leafcutter bee using yellow bits of partridge pea flowers to line the interior of their nest (center); early spring andrenid bee returning to her underground nest in May. Photos: K. Evans.

inside of a stem looking at a leaf-cutter bee nest — Hairstreak butterfly collecting nectar (left); a leafcutter bee using yellow bits of partridge pea flowers to line the interior of their nest (center); early spring andrenid bee returning to her underground nest in May. Photos: K. Evans.

While supplements formed of mainly herbaceous flowering plants offer great nectar, pollen, and nesting resources to insects that act as pollinators and pest control agents, other plants can also be used to create floral supplements. In particular, woody plants and shrubs can provide valuable food and cover for various songbirds and small mammals. The benefits of floral supplementation go beyond supporting insects, birds, and mammals. In fact, these plant additions also have been shown to assist with weed suppression and to reduce soil erosion, while permanent woody plantings (e.g., hedgerows) can also serve as windbreaks.

hedgerow along a road — Hedgerows are coming into leaf along a road in the spring. Photo: McEnnerney/Alamy.

Nowadays, floral supplements can be found nearly everywhere, from home gardens to roadsides, and croplands to city greenspaces, and are commonly referred to as “pollinator strips” or “conservation strips”. Generally, floral supplements are primarily implemented as a conservation initiative to support wildlife and arthropod biodiversity, particularly in floristically impoverished areas such as agricultural monocultures and urban environments.

The origin of floral supplementation

The concept of floral supplementation has roots in agriculture. For example, the use of companion plantings and flowering margins in and around crops has been long known to enhance biological control by boosting natural enemies of crop pests, such as predatory bugs and beetles, and parasitic wasps. In this respect, the addition of these plants to the agroecosystem has been recognized as a strategy to improve pest control with lower pesticide inputs.

spider on a flower — Spiders (left) are important natural enemies of pests, such as this crab spider lurking on a black-eyed Susan. Floral supplementation also supports the presence of other pest control agents, such as this samurai wasp, *Trissolcus japonicus*, parasitizing brown marmorated stink bug eggs. Photos: K. Evans; S. Athanas.

samurai wasp parasitizing brown marmorated stink bug eggs — Spiders (left) are important natural enemies of pests, such as this crab spider lurking on a black-eyed Susan. Floral supplementation also supports the presence of other pest control agents, such as this samurai wasp, *Trissolcus japonicus*, parasitizing brown marmorated stink bug eggs. Photos: K. Evans; S. Athanas.

Today, the concept has expanded in conjunction with aesthetic and conservation initiatives. For example, the Beautification Act of 1965 encouraged roadside wildflower plantings, and actions such as establishing pollinator gardens and defining no-mow months increase floral resources for pollinators. The USDA also offers conservation programs for monarchs and other pollinators by encouraging farmers and ranchers to plant pollinator-friendly wildflowers, shrubs, and trees (https://www.nrcs.usda.gov/).

No Mow April — No Mow initiatives promote not mowing the lawn to allow early spring flowers to grow and bloom, thus providing food for early spring insects.

How to start with floral supplements?

Although there is not a hard definition for what constitutes a floral supplement, guidelines have been proposed by government and conservation societies including the Xerces Society and the USDA. What species to plant ultimately depends on the location and purpose of the supplement. For example, recommended species to plant for upland or grassland habitats will be different than those for wetter habitats. Generally, however, regionally native or naturalized species are often recommended to sustain more native animal diversity than exotic species. In fact, because most ornamental plants used for aesthetic purposes are often non-native, they tend to offer unsuitable or no resources to the local animal communities. Further, even among native species, regional varieties (i.e., local ecotypes) are often preferred because they are better adapted to the local climates, growing conditions, and living communities.

milkweed in a field — Flower plantings can sometimes support specific pollinators, such as monarch butterflies. Examples of this are roadside and field margin milkweed plantings (left) and the participation of cities in the Monarch City Certification Program. Photo: Bill Hubick, Maryland Biodiversity Project.

Monarch City signs — Flower plantings can sometimes support specific pollinators, such as monarch butterflies. Examples of this are roadside and field margin milkweed plantings (left) and the participation of cities in the Monarch City Certification Program. Photo: Bill Hubick, Maryland Biodiversity Project.

Another aspect to consider when starting or creating floral supplements is the diversity of plants used. In fact, diversity is a common theme for floral supplements: one seeks to obtain a high diversity in flower color, flower shape, and bloom times. For example, the best supplements contain a mixture of annuals, perennials, and woody plants that bloom at different times throughout the growing season to ensure that floral resources will be sustained over time. Further, including flowers with diverse shapes, colors, and sizes facilitates access to nectar and pollen for arthropods with different mouth and body shapes.

Although one can try to do it by oneself, designing a floral supplement can be tedious and sometimes overwhelming. Luckily, federal agencies, seed companies, and local nurseries have mixes available for certain habitat types and regions, that one can order directly.

To learn more visit:

USDA, Natural Resources Conservation Service

Xerces Society in the Northeast

Pollinator Partnership

Site preparation guidelines for pollinator gardens (PDF)

By Katy Ciola Evans, Ph.D. student in the Espíndola Lab, University of Maryland Department of Entomology. View her website to learn more about her research.

How Do We Study Pollination?

December 11, 2023December 11, 2023Maryland GrowsLeave a comment

Pollination is such a buzzword right now, and a lot is said about pollination and pollinators. However, how do people learn about pollination and pollinators? How do people know who the pollinators are and how pollination works? Because I happen to do research on pollination, I wanted to use this opportunity to share with you some insights into how pollination is studied, what it teaches us about plants and their reproduction, and how this connects with the things we hear about pollination.

What are we studying when we study pollination?

As we mentioned in previous posts, pollination is basically how plants reproduce. Generally, pollination involves the deposition of pollen grains on the female organs of a plant, which in many cases leads to ovule fertilization and often the production of seeds and sometimes fruits. So, when we study pollination, what we are studying is the reproductive strategies of plants. If we think about plants and the many different ways they have to reproduce, it may be simple to imagine all the different aspects one can try to understand about pollination. Here I will present a couple.

The reproductive strategy of plants – selfing, crossing, or both?

Unlike us humans, many plants can self-pollinate. This means that the species that can do this can technically accept pollen from their own flower and use it to fertilize their own ovules. The consequence of this is that plants that can self-pollinate do not necessarily need pollen from another individual to produce offspring. This may seem like a nerdy technicality of mine, but the ability or not of a plant to self can have a lot of wide-ranging consequences. From an evolutionary perspective, this can affect the genetic diversity in a species or group of species, which can define whether a species can adapt or not to certain conditions, among other things. This can also have consequences for food production and plant breeding; if a plant cannot self, several stocks need to be present in a field for it to be able to produce fruit. This for example happens to some varieties of cherries, where more than one tree needs to be planted in an orchard for the plants to produce fruit.

reproductive parts of flowers — To test for plant reproductive strategies, researchers can perform controlled crossing experiments, which follow generally what is presented in this figure. Image: University of Waikato.

To understand whether a plant species can self, a basic experiment can be done. In this experiment, one creates groups of plants of the same species that will be pollinated following different methods. By comparing the number of seeds produced by each method, one can infer how the plant reproduces. In its simplest forms, one of these experimental groups of plants is manually selfed, which usually involves removing all anthers from a flower and then manually depositing pollen from the same plant on its stigma. In another group, plants are crossed using pollen from another plant. The flowers and potentially fruits of both groups of plants are then left to develop, and once fruit/seed maturity is reached, one counts the number of fruits and seeds per group of plants. If the two groups present significantly different numbers of fruits or seeds, then we can infer whether the plant is able or not to self.

Who pollinates a plant?

Imagine that we figured that a plant requires cross-pollination. Now, a question we may want to ask is how the pollen of one flower can get to the stigma of another flower. Again, this is not just a biologist niche question; this has practical and evolutionary consequences. For example, if a plant is wind or water-pollinated, it will be able to produce offspring in the absence of animal pollinators. Alternatively, if a plant needs animal pollinators, then their absence can lead to the plant’s inability to sustain its population over time. In a food production world, plants that need animal pollinators will benefit from the presence of those pollinators, leading to higher fruit or crop production when more pollinators are present (this is the case of, for example, almonds and strawberries).

To study this, scientists have a large palette of methods. Here are some. One of them involves observation of the flowers in question. For example, one can assume that a flower that produces nectar or that has special color markings aimed at directing pollinators when they visit a flower will be more likely pollinated by animal pollinators than one that does not offer any floral rewards in exchange for flower visitation. Similarly, the general floral shape gives clues about how it may be pollinated. Flowers pollinated by animals tend to have specific shapes that improve pollen deposition by animal visits, while those pollinated by abiotic factors are usually droopy or displayed in very humid areas.

markings on flowers only visible with UV light — Flowers that can look “plain” to us may have special colorations that only pollinators can see, like this black-eyed Susan, which shows its floral markings that can be seen only under UV light (a wavelength many insects can see). Observing markings or “signs” on flowers indicates that the plant may use animals for pollen dispersal and transfer. Photo: A. Davidhazy.

As said before, observations are a huge part of studying pollination and the identity of pollinators of a plant. This generally also entails spending hours upon hours over several seasons carefully observing and sometimes capturing any floral visitor and potential pollinator of a plant population. This requires patience and focus, and careful recording of the abundance, frequency, and identity of any flower visitor. This also often requires hours of identification of captured floral visitors, often under the microscope (given that most floral visitors are often insects), and through the use of taxonomic keys or the consultation of experts of specific taxonomic groups.

a man in a field using an insect sweep net — One way to understand what pollinates a plant involves hours of focused observation of flowers and capture of the animals seen visiting them. Photo: A. Espíndola.

fluroescent dyes are used to track movement of pollen by pollinators — Fluorescent dyes can be used to track the movement of pollinators and the potential for pollen transfer. Photo: Huais et al., 2022.

Along with these hours of observing and describing what is being seen, other more “manipulative” approaches exist. For example, many scientists try to understand who visits a flower by marking flowers with powdery dyes and then seeing if any animal seen visiting the flowers becomes colored with the dyes. More “technological” approaches use high-resolution cameras and artificial intelligence (AI) methods, as well as DNA sequencing to identify the presence and species identity of pollen grains on animals seen or suspected of visiting flowers.

Want Flowers Next Year? Here Are Some Pollinator-friendly Plants to Plant This Fall

October 9, 2023September 22, 2023Maryland GrowsLeave a comment

Although the end of the summer/early fall may seem like an odd time to think about planting, don’t be fooled! This is actually prime time to allow plants to establish and grow strong for next spring. In fact, planting in the early fall gives time for plants to establish their root system, acclimate to the new conditions, and be ready to grow as soon as the spring conditions become ideal for them to develop. In today’s post, I want to present a couple of very neat plants that can be planted now to bloom and provide resources for next spring’s pollinators. And because these are some plants that are just close to my heart, let me try to convince you to add some (or all! 😊) of these to your green spaces, so you can enjoy them next year. Let’s talk about mountain mints, beardtongues, and Culver’s roots.

Narrow-leaved Mountain Mint – Pycnanthemum tenuifolium

As its name may let you infer, this is a plant that belongs to the mint family (Lamiaceae) and, as a mint, it is very aromatic. The genus is native and restricted only to northern North America, and we are lucky to count several species within Maryland’s native flora. As is the case for most Lamiaceae, mountain mints do not only present beautiful flowers; they have been used traditionally as a food seasoning and in medicinal teas to treat colds, coughs, and fever by many Native American tribes. Although some species are currently protected in the state, some are common, one of which being the narrow-leaved mountain mint (P. tenuifolium) I want to introduce you to.

*(Left)* The plant establishes very well in sunny areas where it displays its clusters of white flowers. Photo: SB_Johnny (CC). *(Right)* The delicate flowers of the mountain mint attract a very large diversity of pollinators, such as this Pearl Crescent butterfly. Photo: S. Cadwell (CC)

white flowers of mountain mint with a butterfly visiting for nectar — *(Left)* The plant establishes very well in sunny areas where it displays its clusters of white flowers. Photo: SB_Johnny (CC). *(Right)* The delicate flowers of the mountain mint attract a very large diversity of pollinators, such as this Pearl Crescent butterfly. Photo: S. Cadwell (CC)

This plant is a favorite of mine because it is relatively tall (~ 3-4ft), makes a lot of flowers, attracts a bunch of insects, and tolerates conditions that many other plants don’t like. As is the case for all mountain mints, the flowers of this plant are clustered, and in this species, the flowers are white and bloom in the summer. The plants attract a very large variety of insects and for that reason are one of the recommended plants by the Xerces Society for supporting pollinators in our area. Bees of all sizes, beetles, butterflies, wasps, flies, and hoverflies… nobody can resist this beauty! And to top it all, this plant grows great in full sun and even in relatively dry conditions, which makes it a great one to plant close to roads or in those areas of our green spaces where other more water-needy plants may not do so great.

Hairy Beardtongue – Penstemon hirsutus

I have to say that I have a weakness for Penstemons specifically and plants of the whole family they belong to (the figwort family; Scrophulariaceae) generally. Their complex flowers always get to me, and plants of the genus Penstemon are to me one of those that I can look at and marvel at forever. So, this is one of the first ones I want to grow every time I can… maybe I’ll convince you to plant it too?

The genus Penstemon is almost restricted to North America, where they represent one of the largest groups of native plants on the continent. They are characterized by having tubular flowers, and their coloration varies by species, going from white, to pink, purple, red, and blue. Although there are a few species native to Maryland, and several can be grown, I want to talk a bit about the hairy beardtongue, P. hirsutus (but also check out the foxglove beartongue, P. digitalis!).

pink-lavender flowers of hairy beardtongue — *(Left)* Hairy beardtongue plants display a large number of tubular flowers. Photo: K. Woods (CC). *(Right)* The tubular flowers of hairy beardtongue provide nectar and pollen to a variety of pollinators, such as bumblebees, other bees, hoverflies, and butterflies. Photo: A. Espíndola

lavender flower with a bee — *(Left)* Hairy beardtongue plants display a large number of tubular flowers. Photo: K. Woods (CC). *(Right)* The tubular flowers of hairy beardtongue provide nectar and pollen to a variety of pollinators, such as bumblebees, other bees, hoverflies, and butterflies. Photo: A. Espíndola

The flowers of this species are multicolored, with purple tubes tipped with yellow and white. The flowers are visited by bees (including bumblebees), hummingbirds, and butterflies, and have been described to support the adults of the Baltimore checkerspot, our state insect! The plant itself is not overly tall (~2-3ft) and makes a lot of flowers. They prefer drier conditions and full sun to some shade and will bloom in the late spring/early summer.

Culver’s Root – Veronicastrum virginicum

I feel that plants with small white flowers (like this one) are often kind of forgotten, to the benefit of showier and more colorful flowers. However, Culver’s root is a little gem native to our region that any local interested in supporting pollinators should consider having around.

Belonging to the Plantain family (Plantaginaceae), the genus counts only a couple of species, one of which is the only North American native: Culver’s root (V. virginicum). Like all members of the genus, this species presents its white flowers arranged in long spikes. This species will become taller over the years, reaching 4-5 feet at full maturity. They prefer sunny to shadier spots, where sufficient moisture is present (e.g., wood edges).

The flowers mature sequentially, and because there are so many flowers in their long spikes, a single plant is likely to flower for weeks. Besides its sustained floral display, this plant is super interesting and important for pollinators because it happens to flower at a time when few other plants flower in our region (July-August). Their white flowers attract and provide food for bees, butterflies, wasps, and (hover)flies.

spiky white flowers of culver's root — Once established, Culver’s root can reach 4-5 feet in height, displaying their long spikes of white flowers. Photo: E. Enking (CC)