Author:Anahi – Page 8 – Maryland Grows

Why Do Pollinators Visit Flowers? Hint: It’s Not Just for Nectar and Pollen

May 13, 2020May 13, 2020Maryland Grows6 Comments

Other than because I think they are pretty, I love looking at plants and their flowers. In fact, one of my pastimes has become figuring where and what is the reward that pollinators get out of their visits to their favorite flowers. You may be now thinking that my pastime is a bit nonsensical, since it is pretty clear that pollinators get pollen and nectar from flowers, so why bother checking? Well, actually, that is only partially true; did you know there’s a myriad of rewards that pollinators can get from their flower visits?

In today’s post I want to tell you a bit about some of those other rewards; the ones that fascinate me so much. Let’s talk about special floral pollination rewards and where you can see them in real life!

We like essential oils, some pollinators like floral oils!

The first time I heard about floral oils my mind was blown in such a way that I became obsessed with them, to the point that now a large part of my research program focuses on them. Floral oils are a reward that many types of plants offer to their favorite pollinators: oil-bees.

But don’t let me get ahead of myself! Floral oils are a special type of oil – different from essential oils – that are produced and presented to pollinators on different parts of the flowers of some plants. Independently of what exactly they look like, all these plants are visited and pollinated in a very specialized way by oil-bees. Unlike honeybees, these oil-bees are solitary and make their nests in the ground. These oils help these bees line their nests to waterproof (!!) and strengthen them. Along with that, they also mix the oils with pollen and feed that ‘pollen ball’ to their larvae.

Macropis oil bee — The whorled yellow loosestrife (left; photo: Eli Sagor) is one of Maryland’s native plants that offers floral oils to their Macropis oil-bees (right; photo: Don Harvey). Note the shiny load of oils and pollen on the hind legs of this Macropis!

Oil flowers are present all around the globe. In our region, they are represented by several species of the yellow loosetrife plant genus Lysimachia. With their floral oil rewards, these loosestrifes sustain the rare oil-bees of the genus Macropis. At the level of the country, most oil-flowers (and their specialized pollinators) are restricted to the Southern USA, where they are visited by the large bee genus Centris. Some of these plants are the wild crapemyrtle, the prairie bur, and the purple pleatleaf.

Hungry? Please, help yourself!

Along with nectar, pollen, and floral oils, food for pollinators can come in many different shapes and forms. In fact, some flowers even offer parts of their flowers to their pollinators. In cases like this, flowers develop special structures – usually around their petals – with the only function of becoming food for pollinators. Flowers providing this type of reward are usually pollinated by beetles, who can use their strong mandibles to chew on and eat the special structures.

One of the coolest examples of the use of this type of reward is our very own sweet shrub, Calycanthus floridus. This spring flowering plant (flowering right now in Maryland!) attracts small beetles that enter the flower and stay there for quite some time. To maintain and support them while they are helping the plant reproduce, the sweet shrub flowers englobes them during parts of their flowering (this is why sometimes these flowers seem to be opening and closing throughout the day) and present small extremely nutritious structures at the base of their petals. It is on these structures that the beetles can feed on to stay strong and healthy while they are on the flowers. If you have one of these flowers in your yard, or happen to see them in one of your walks, take a second to stop and check them; you may get to meet their little beetle friends!

Need a hand taking care of the kids? Here I am!

Some other flowers have established even more intricate relationships with their pollinators, and what they provide is not just food, but also a house! Because in these plants the offered reward is a place for the larvae of these pollinators, these interactions are called ‘nursery pollination’. Here, the pollinator visits the plants, collects pollen, and sometimes even actively places pollen on the flower tip. By doing so, the pollinator makes sure that the plant seeds develop. This is important, because their larvae will need some of them to feed on throughout their development.

yucca moth — Joshua trees (left; photo: Shawn Kinkade) are some of the most iconic plants of the US Southwest. These plants offer a brood site to their super-specialized small moth pollinators (right; photo: Judy Gallagher).

Along with this being the reward we see in a plant we love to eat (figs!), one of the most spectacular examples of the use of this reward is found in an iconic plant of the deserts of the US Southwest, the Joshua tree. Indeed, Joshua trees produce flowers that are visited by a group of moths, the Yucca moths. These moths visit the flowers, collect their pollen, and then literally push it into the flower tip to actively pollinate it. Because the moths lay eggs on the flowers, this assures that the flower develops seeds so the larvae have something to feed on. What is fascinating, though, is that these larvae never eat all the seeds, so this really is a win-win relationship between the plant and the moth.

To see how this is done, take a look at this video!

yucca moth video — Larvae of the Yucca moths feed on a Joshua tree’s seeds. To make sure that there is something for their larvae to eat, these moths actively pollinate the plants, exchanging a brood site for pollination, and in the process display some of the most fascinating behaviors one can see in pollinators. Check out the video to see it for yourself! Video: University of Nebraska-Lincoln.

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

Gone With The Wind: A Look at Wind Pollination

April 13, 2020Maryland Grows4 Comments

The spring is here, and it seems that all the trees in my neighborhood have finally woken up and entered some sort of tree beauty contest. Some of them, like the cherries, crabapples, and Eastern redbuds have been showing off their beautiful flowers for a while now, and it’s true that they are impressive and that the pollinators are responding to the call. Others, like the oak trees in front of my house are a bit more “introvert” than their showy neighbors and have instead presented their own flowers in a different, less-spectacular but not less-efficient way.

Today’s post is going to be my small honor to the beauty of introverts. Join me in exploring how being low-key in the flower world can be a great strategy for reproducing, and how you can learn how a plant reproduces by paying attention to the shape of its flowers. Let’s talk about wind pollination!

flowering trees — Some of my neighborhood trees are very showy right now, like the crab apple and the redbuds (on the left) around my house, while some others seem to be more “introverted”, like my oak trees (on the right). Photos: crab apple and redbud: A. Espíndola; oak tree: D. Mullen.

What is wind pollination?

Even though when we think of pollination, we usually think of pretty flowers and cute pollinators who come get that sweet nectar, a very large number of plants do not use animal pollination to reproduce. In fact, they instead use wind to disperse their pollen and reach their female counterparts. (See more about how this works in my previous post about plant reproduction.)

In the vast majority of these plants, female and male flowers are either on different plants or on different parts of the same plant, with the male flowers usually grouped in hanging or “grape-like” structures (those catkins!). These elongated structures are extremely fit for their function. Being long and hanging, they are readily shaken by air currents, quickly releasing their pollen into the wind. Once in the air, that pollen will travel sometimes extremely long distances to reach the female flowers, which is facilitated by the pollen grain’s light weight.

oak catkin — *Oak catkins. Photo: Dan Mullen*

Even though this strategy is very efficient in dispersing a lot of pollen over very long distances and avoids the energy cost of having to produce special rewards to attract pollinators, it works best under specific circumstances. For instance, it works best in places that are drier than not (pollen won’t travel well if it rains all the time), and in places that are not so densely inhabited that there is no way for pollen to move or reach the right female flower (a female flower of the same species). These are in fact some of the reasons why wind pollination is so rare in tropical rain forests.

grass pollen — *Wind-pollinated plants can be recognized by their hanging anthers or flowers, like the grass in this photo. Photo H. Rose*

What plants use wind pollination?

This type of pollination mode is present in most conifers and grasses, and in many flowering plants. In fact, I invite you to just look around your house and pay attention to the plants surrounding it. I promise you that if you look carefully on your grasses you will see their tiny hanging anthers, or if you check any hazelnut, willow, birch, or oak tree close to your window or yard you will see the long catkins hanging from the branches. If you can reach them, you should even try gently shaking them and see for yourself how the most minimal movement makes the plant release all that pollen. Oh, and if you like pecan and walnut pies, know that the wonderful nuts these plants produce are actually formed thanks to wind pollination! (Check out my article from last Thanksgiving!)

Is this why all that yellow powder is all over the place in the spring?

Yes! You may have realized that during the spring months, any pond, lake, car, or other surface that is exposed gets completely covered in yellow powder. Virtually all this powder/pollen comes from these wind-pollinated plants. Unfortunately for the plant, the pollen you see will likely not reach a female flower. Luckily for the plants, they do produce a lot (and I mean A LOT) of pollen because pollen production in these plants has evolved to produce sufficient pollen so that enough of it reaches the females.

pollen on water in a rain barrel — *Pollen from wind-pollinated plants ends up on all surfaces, like here in my rain barrel. Note both the yellow layer on the water and on the side of the barrel in the background! Photo: A. Espíndola.*

If pollen is released mostly during the growing season, is this why pollen allergies are seasonal?

Again, yes! The plant species that produce seasonal allergies are wind-pollinated, and that is why you have allergies only during the time they are flowering. As a matter of fact, if you have pollen allergies, you may have realized that certain seasons are worse than others, and you may even know what species you are allergic to. Today, there are a lot of tools to know what species are flowering and when you would expect to start having seasonal allergies. For example, check out this online allergy map where you can see what species are releasing pollen in “real-time” across the country and close to your house.

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

Pawpaws: The tropical fruit from our forests

March 9, 2020September 19, 2022Maryland Grows8 Comments

Spring is almost here and now we can start thinking about trees to plant if we did not get to that in the fall. Thinking about trees for my garden, I came back to one I have been considering for a while now — one that gives delicious fruit, is native, makes me think of tropical lands, and is not liked by deer! Today’s post is going to be about a little-known tree that’s native to our region, and whose fruits were apparently one of George Washington’s favorites: pawpaws!

What are pawpaws?

Pawpaws are trees that belong to the same plant family as chirimoyas and custard apples (Annonaceae, the soursoup family; Figure 1). From a botanical perspective, pawpaws are really special because they are the only member of their family adapted to growing outside of the tropics and able to survive our temperate climate.

pawpaw and related fruits — Figure 1 – Pawpaws (left), chirimoyas (top right) and custard apples (bottom right) are all in the same plant family, but pawpaws are the only group adapted to growing in temperate climates.

All pawpaws grow in southeastern North America, but the most common and widespread species is the common pawpaw, Asimina triloba, which is very abundant in our region. The common pawpaw is adapted to growing in well-drained and fertile habitats, such as those found in our forests. I promise you that if you ever walked in a forest in the area, you have seen hundreds of pawpaws growing in groves (Figure 2).

Pawpaw grove — Figure 2 – Pawpaws grow in well-drained fertile soils, and are common in our forests where they often grow in groves. Photo: Katja Schulz.

Why are pawpaws such a “thing”?

Besides being great native trees that grow well in our region, pawpaws have the most delicious fruits. They are considered the largest edible fruits indigenous to the continental United States. The fruits look a bit like a green mango from the outside, but are white/yellow and fleshy in the inside (Figure 3).

pawpaw fruit — Figure 3 – Pawpaw fruits are green on the outside and white and fleshy on the inside. Note the very large seeds. Photo: Elizabeth.

Their flavor is such a delicious one that I always relate it to tropical fruits. People more technical than I am in terms of flavor description say that it is a custard flavor, close to that of bananas, pineapples, and mangos. In any case, believe me when I tell you that these fruits are absolutely delightful and can be eaten fresh, in yogurts, in cakes, as jams, or frozen in ice cream!

Why didn’t I know about this before?

That was my very question the first time I tried them! It turns out that producing pawpaws for selling is not super simple. In fact, the fruits are fragile and thus can’t be transported long distances, which reduces their marketability. This means that pawpaws are usually produced and consumed locally. If you do not happen to know somebody with some trees on their land, you probably never got to try them.

Also, the pawpaw fruit season is relatively short (end of the summer), which means that one has to be in the right place at the right time to eat them. In season, pawpaws can be purchased at local farmers’ markets or on farms. You can also try to find them in the forests of the area, where you will be able to smell the sweet aroma of the fruits while you hike or bike. However, be sure to check property rules; harvesting plant materials from park lands is typically prohibited.

Why are you talking about this now? It’s not pawpaw season yet!

That is correct. However, it is pawpaw planting season now, and soon will be pawpaw pollination season, both needed to actually get the delicious fruits in the summer. So, how to plant and pollinate them?

Pawpaws can be grown from seed, but the simplest way to get one for your land is from a nursery. Several nurseries in the area sell pawpaw trees, and your best choices are those which grow trees that are adapted to your local conditions.

Pawpaws are not hard to grow and can be actually cultivated in your own back or front yard! Further, some counties and cities provide financial support to plant these native trees (see for example, Chesapeake Bay Trust and the Maryland Department of Natural Resources).

Pawpaw trees start producing fruit a couple years after planting. However, fruit production is a bit different from that of other fruits you may be growing. In fact, fruits will form only if there is cross-pollination (see this other post), since a pawpaw is not able to properly self-pollinate. This means that pawpaws need pollinators to produce fruit.

pawpaw flower — Figure 4 – Pawpaw flowers have evolved to attract and trick flies and beetles by looking dark and smelling like ripe fruits, the insects’ preferred food and egg-laying site. With this trick, the plant cross-pollinates their flowers without offering any reward to the pollinators. Photo: Judy Gallagher

Pawpaws are pollinated by flies and sometimes beetles, which the flowers attract with their maroon flowers and their ‘yeasty’ aromas (Figure 4). These scents are known to ‘trick’ the pollinators into visiting the flowers, mimicking the odor of ripe fruits that these insects prefer to feed on or lay their eggs. Flowers then attract these pollen dispersers, who, while visiting the flowers, will cross-pollinate them without their will.

You can imagine by now that having more than one pawpaw on your land or in the surroundings of your house will increase fruit production. It will then be more likely that the fooled pollinators will have visited another plant and thus carry pollen when they visit your tree.

Alternatively, if you would like to be absolutely sure to get a good pawpaw crop, you can cross-pollinate them by hand. To do that, get a small brush, pick pollen from the anthers of one flower (check the drawing here to find them), and transfer it to the stigma of another. That way you will get to live your best pollinator life! 😊

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

Plant Love & Compatibility: A Valentine’s Tribute to Pollination

February 10, 2020September 19, 2022Maryland Grows14 Comments

February is Valentine’s month, but also that of starting to feel impatient about gardening and all the yummy veggies and fruits that will come through the season. Those two things (Valentine’s, and fruits and veggies) are actually really connected, and in today’s post, we will dive into how that is so.

Valentine’s and fruits and veggies are connected? I don’t get it…

Have you asked yourself how those fruits you see are formed? In fact, this has a lot to do with love (well, plant love) and partner compatibility… quite a bit like Valentine’s couples! Like humans, plants have special organs they use to reproduce, which are all in the flowers (Figure 1).

flower parts — *Figure 1. A flower has all the plant’s reproductive organs.*

When plants reproduce, their offspring are their seeds. Until here all is nice and good, however, a plant’s problem is that because it can’t move, if all the seeds it produces were to just to fall right under it, the mother plant would soon be surrounded by her offspring, which would then compete with each other and herself. To deal with this problem, and because plants are cool, they have evolved some super-smart strategies to help their seeds be dispersed: fruits! (Figure 2)

beans and apples — *Figure 2. Fruits allow plants to disperse their seeds. Some fruits can be fleshy like in apples, or dry like in almonds, while some are able to explode and propel the seeds into the air like in beans.*

In wild plants (and many cultivated ones), the fruit is the packet that will carry or disperse the seeds, and among all fruits, the fleshy ones are actually a ‘bait’ for seed dispersers. In fact, these fleshy parts are usually sweet and nutritious, and thus attract animals that eat this ‘seed packet’ (often along with the seeds). However, because an animal’s digestive system is built the way it is, eating the fruit will usually also mean dispersing the seeds in a different place, when those seeds leave the animal’s body. So, you see, plants having offspring and fruits are directly related, like Valentine’s and my veggies and fruits!

Oooh… so, plants can only make fruit if there has been pollination?

Making a fruit requires a lot of energy from the plant (think about all those sugars and colors that go into that delicious tomato!). This means that it usually is the case that fruits will only form if pollination has happened and seeds have formed. So, if one wants a garden to produce fruits and vegetables, it is very likely that pollination and seed formation will need to happen for it to be productive.

Plants produce seeds and are pollinated in many different ways (see this blog post for examples), but it is pretty common that plants will produce more seeds and larger fruits if they receive pollen from a plant individual that is distantly related. In fact, as for many animals, crossing among too closely-related individuals can lead to genetic diseases and poor health. And this is why pollinators are so important; they allow pollen from different individuals to be transferred among plants of the same species and allow for healthy seeds.

Is this why I sometimes need many similar plants to produce fruit?

Yes! Many groups of plants have developed reproductive strategies that advantage fertilization by pollen from plants that are more distantly related over those from themselves or a very closely-related individual. We say that these plants need cross-pollination for producing seeds (and fruit).

On the other hand, there are some plants that are able to make fruits while receiving pollen from themselves or from closely-related individuals. Because these plants are equally exposed to the health problems associated with producing seeds with a closely-related individual, they have developed other strategies that can help them reduce the occurrence of such an event; for example, their seeds can disperse very long distances.

What are the plants that need cross-pollination?

Apples, pears, almonds, pistachio, some cherries, apricots, figs, and paw-paws are all plants that need to receive pollen from another plant of the same species to make fruits. Further, note that for many of these plants it is not just sufficient to have another plant of the same species; this plant has to be of a different variety and has to be present at a relatively short distance.

Unlike those mentioned above, tomatoes, bell peppers, eggplants, grapes, currants, raspberries, and gooseberries can self-pollinate, and thus do not require other surrounding plants of the same species to produce fruits.

Many plants are able to produce fruit by self-pollinating but are far more productive if they are cultivated along with other plants of the same species. This is the case of blueberries, huckleberries, and persimmon.

Finally, some plants, like kiwi, have male and female flowers on different individuals. In these species, although the only fruit-bearing individuals are the female plants, the fruit will only form if a male is present close by.

To help disperse their seeds, some plants have evolved pretty extreme strategies!

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

Serpentine Soils Are Anything But Barren: They Support a Unique Grassland Habitat

December 30, 2019April 19, 2024Maryland Grows3 Comments

I have never been to the African grasslands, where lions, zebras, elephants, and wildebeests seem to be in continuous danger. I have, however, been to a Maryland habitat that few people know about, and that, even though lion-, zebra-, elephant- and wildebeest-less, reminded me strongly of those African savannas.

This habitat I am talking about is the Serpentine Grasslands (or Barrens) of the Eastern United States. If you have never heard of them, fear not! Hopefully, by the end of today’s post, you will know a bit more about them and you’ll even try to go visit the few remains that still exist of this beautiful but endangered habitat of our region.

Serpentine Barren Grassland — *Fig. 1 – The Serpentine Grasslands of Maryland at Soldiers Delight. Photo: U. Weber.*

As you may have guessed from its name, Serpentine Grasslands or Barrens are prairies where the dominant plants are grasses. This is all good, but if they are grasslands, why are they also called Barrens, you may be asking yourself. The answer to that question is what in my opinion makes these habitats so fascinating; something that is also hidden in the other part of their name: “Serpentine”. Indeed, the word Serpentine refers to the type of soil these grasslands are on.

Serpentine soils form on a type of bedrock called serpentinite. This type of rock only exists in places where tectonic plates come into contact, fold, and volcanic activity occurs. This happened in our area about 480 million years ago when the Appalachian Mountains formed. Because of this, there is now an arc of serpentinite present in the Maryland-Pennsylvania area, parallel to the mountains.

Serpentinites are rich in many metals and other compounds that make the soils that form on top of them relatively toxic and unfriendly to many plants. Because not many plants can grow on these soils, not much soil is retained and the ground ends up being rocky. Because of this characteristic, places with these soils are not very fertile, and, when the Europeans arrived in the area, they started referring to them as ‘barren’, since they were not only infertile, they also had no timber on them. However, even though they were referred to as barrens, many plants do grow on these thin soils, and actually, many of Maryland’s rare flower plants and grasses are adapted to grow in this habitat!

Indeed, the Serpentine Grasslands of Maryland and Pennsylvania are some of the unique places where it is possible to find, for example, the rare moss pink, serpentine aster, or the sandplain gerardia (Fig. 3). It is also home to several endangered and rare species of butterflies and moths such as the Dusted or the Cobweb Skipper (Fig. 4).

Even though the plants and butterflies present in this habitat are relatively well-studied, we still know very little about what other organisms live in the grasslands. To remediate this, in my lab at the University of Maryland in College Park, we are working on trying to understand better what species of insects are present in the area.

Plants of the Serpentine Barron — *Fig. 3 – Many rare plants are present in the Serpentine Grasslands of the Eastern US. For example, the moss pink (left; Photo: J. Gallagher) and the sandplain gerardia (right; Photo: A. Espíndola).*

For the moment, we are focusing on insect pollinators, and our first works indicate that the plants growing in these grasslands are pollinated not only by bees but also by hoverflies, showing how important these lesser-known pollinators may be to sustaining a very rare habitat of our region. (Take a look here to learn more about hoverflies as pollinators.)

The Serpentine Grasslands had not always been rare and endangered. Indeed, serpentine soils extended for quite an area in the Maryland-Pennsylvania region. So, what happened to this habitat that made it so rare today? Ecologists and historians can help us with this.

Like many habitats dominated by grasses, Serpentine Grasslands need fire to sustain themselves. In the absence of fire, pines and red cedars from the surrounding areas start establishing in the grasslands and compete with the grasses and all the rare plants, making the once grassland become an encroached pine forest. When the Europeans first arrived in our region, documents said that there were Serpentine Grasslands that extended for at least 130,000 acres. Today, Serpentine Grasslands occupy about 1.6% of that area.

These grasslands were managed as hunting grounds by several tribes (Susquehannock, Shawnees, Lenape Delaware), who burned them regularly to maintain the grasses and attract large herbivores to hunt. These tribes had complex systems of rights over these lands, which they shared with neighboring tribes as needed. Records show that these extensive grasslands were extremely rich in fauna. There were myriad birds species (mentioned in some records to ‘have darkened the sky’ when migrating!), wolves, bears, cougars, deer, and buffalo roaming these regions!

European colonizers quickly realized that these grasslands were great land for cattle and hunting, and thus started settling and claiming the native tribes’ lands. However, the new inhabitants did not continue the practice of burning, which led to the habitat starting to degrade and finally becoming less appropriate for cattle and cropping.

Eventually, these lands were relegated as ‘useless’ lands and were thus prime land for building or just reinvaded by pines and other trees, which were used for timber. I sometimes try to imagine what these lands — today just 30 minutes away from my house — may have looked like with those large fascinating animals living right here.

*Fig. 4 – The Serpentine Barrens are the habitat for several rare moth and butterfly species, such as the Dusted Skipper (Photo: A. Wells).*

Today, the Serpentine Barrens are protected and managed with fire in several parts of the state. A large part of these protected lands are not open to the public. However, we are lucky that some places are indeed accessible to the public and can be visited throughout the year.

The largest remnant of Serpentine Grasslands on the Eastern Coast of the US is west of Baltimore, in the Soldiers Delight Natural Environment Area. Another public land where some remains of Serpentine Grasslands are still visible is in Northern Baltimore, at Lake Roland.

I am lucky enough that I can visit and work in these fascinating places. If you have never been to them and would like to see these local jewels, take me up on the invitation and consider hiking some of their trails. The spring and summer are gorgeous on these lands, and who knows, you may be lucky enough to see one of those rare beauties that still live there!

By Anahí Espíndola, Assistant Professor, Department of Entomology, University of Maryland, College Park

Please Pass the Cranberry Sauce and Give Thanks for Pollination

November 25, 2019February 7, 2020Maryland Grows4 Comments

Thanksgiving is a time to gather with loved ones and usually involves first preparing and then ingesting a lot of delicious goodies. Each family has recipes and traditions related to Thanksgiving, and even foreigners (like myself) may join in and create new traditions. Independently of who we are and our origin, the meals we prepare include a number of common foods: cranberries, pumpkins, sweet potatoes, pecans, and potatoes.

For this year’s Thanksgiving, I want to take us on a trip to recognize and thank nature and some of our little winged friends, without whom we would not be sharing all that deliciousness with our loved ones. Plus, after reading this you will know some cool fun facts you can share with others during your Thanksgiving meal!

Cranberry Sauce

Cranberries are the fruits of a plant closely related to blueberries and huckleberries, which all are native to North America. Like blueberries and huckleberries, cranberries need pollinators to produce fruit. The reproductive organs (anthers – where pollen is produced, and carpels – where the ovules are hosted) in a cranberry flower mature at different times, which means that a flower can’t self-pollinate and needs a pollen vector to produce fruit.

As you may know, no pollination means no fruits, and no fruits means no cranberry sauce. Luckily, nature provides and pollinators are around! We know today that several different bees visit cranberry flowers, with bumblebees being some of the best pollinators. Some other wild bees (for example, mining bees, Andrena) also contribute to the pollination of this plant, and honeybees can pollinate as well but not as efficiently as bumblebees and other native bees.

Pumpkin Pie

Pumpkins, squashes, and zucchini are all closely related vegetables that also require pollinators to produce fruit. Unlike cranberries, pumpkin plants produce separate and distinct female and male flowers. Because in these plants the female and male reproductive organs are physically in different parts of the plant, pollination (and thus fruit production) requires a pollen vector. Again, we would have no pumpkin pie if our pollinator friends were not around!

So, who pollinates pumpkins? Pumpkins have very specialized pollinators that do the best job at pollinating. In the US, this specialized pollinator is the squash bee Peponapis, which feeds their larvae a strict diet of squash pollen. Furthermore, unlike many other bees, both the males and females of the squash bee pollinate, since mating happens in the flower. Even though the squash bees are by far the best pollinators of pumpkins, other bees (including honeybees) can occasionally visit and pollinate the flowers… but really it’s these little cuties that we need to thank for all the delicious pumpkin!

Pecan Pie

Like pumpkins, pecan plants can’t automatically self-pollinate and need a pollen vector to produce the yummy nuts we eat. This is not only because their female and male flowers are separated spatially on the plant (like they are for pumpkins); they also flower at different times of the year on the same plant.

To be pollinated, the female flowers of a pecan plant need to receive pollen from the male flowers of another plant which is flowering at the same time. For this reason, pecan flowers need a vector of pollination, which here is not an insect but the wind! Pecan flowers are indeed adapted to wind pollination, displaying hanging bunches that shake with the wind, releasing and catching a lot of the pollen in the air.

Sweet Potatoes

The part of the sweet potato plant that we eat during Thanksgiving is the tubers, which are roots. And since what we eat is not a fruit, pollinators have no role to play for this Thanksgiving ingredient… at least not directly. But the sweet potato plant still needs pollinators to produce seed and breed, because their flowers are unable to be successfully pollinated by the same flower’s pollen.

Pollinators are then really important for the successful maintenance of the genetic diversity of this plant. Sweet potatoes belong to the morning glory family, and as its name suggests, flower in the morning hours. They are pollinated by many different types of bees (from large bumblebees and carpenter bees to smaller bees such as sweat bees), which visit the flowers for nectar and pollen.

Mashed Potatoes

As for sweet potatoes, the part of the potato plant we eat is not the fruits but the tubers. Pollinators are not needed for obtaining these tubers, but the plant requires pollinators to be able to breed and maintain genetic diversity. Since they are in the same family (the nightshades), potato flowers look similar to those of tomatoes and eggplants.

Like in those other vegetables, pollinator visits, and more specifically something called ‘buzz pollination,’ needs to occur for successful pollination. In this type of pollination, the insect visits the flower and buzzes loudly, which shakes the flower, releasing the pollen, which they then transfer to a different flower during their next visits. Among these buzzy bees, bumblebees and mining bees (Andrena) are very efficient at pollinating potatoes.

[VIDEO: Buzz pollination of a bumblebee on a potato flower. Note how the pollen is released from the anthers — the four yellow long organs — and sticks to the bee abdomen where the stigma — the female flower organ in the middle of the flower — rubs the bee abdomen where it collects the pollen and gets pollinated. Video by thyreodon.]

Happy Thanksgiving!

By Anahí Espíndola, Assistant Professor, Department of Entomology, University of Maryland, College Park

Where are all the pollinators?

October 25, 2019November 11, 2022Maryland Grows5 Comments

Yard in the fall with leaves on the ground — *Leaving fallen leaves, plant twigs, and wood in your landscape can help pollinators survive the winter.* Photo: Anahí Espíndola

Even though I love the heat of summer, I have to admit that fall makes me happy in a different way. I like the trees that turn into beautiful colors, the crisp air, quiet nights, and the days that slowly become shorter and make me want to drink tea and eat cookies. There is however one thing that makes me a little sad about fall, and it’s that all those beautiful pollinators I love so much are now gone! But are they? Actually, have you ever asked yourself where pollinators go in the fall? Well, thanks for asking — today is your lucky day! In today’s blog post we will talk about what happens to pollinators in the fall, and what we can all do to continue helping them during this quiet time.

When the season reaches an end, pollinators find themselves in a hard spot. They could hopefully collect food (nectar, pollen, etc.) during the spring and summer, but now all the flowers are gone and decisions need to be made if they are to survive until next year. When the season reaches an end, pollinators have basically two options to make sure they or their progeny survive until the next season: migrate for the winter, or stay and protect themselves against the cold.

How to Help Pollinators in the Fall

#1 – Let them go!

Some famous pollinators migrate. You may be familiar with the impressive and beautiful Monarch butterfly migration, which happens every year, and which allows Monarch populations that are far North reach latitudes where the climatic conditions are more benevolent to their survival. Other less famous pollinator migrations are those of hummingbirds, which also migrate to less harsh conditions at the beginning of the fall.

The best thing to do to help migratory pollinators is to help them migrate! This may sound a bit counterintuitive but providing plant resources for migrant pollinators for too long can be a bad idea, because that may make them stay in the region for longer, expose them to parasites for longer, and not reach their final destinations in time.

Let’s take the Monarchs as an example. Monarch caterpillars feed on milkweed, and there are both native and non-native species of milkweed they can develop on (Figure 1).

Tropical Milkweed — *Figure 1 – Monarchs can develop on many species of milkweed. Non-native milkweed such as the tropical milkweed (*Asclepias curassavica; *left) can hinder their migration. Favoring native milkweed species (such as the common milkweed; right) is a way to help Monarchs stay safe in the winter.*

The native milkweeds naturally start drying out by the end of summer. This changes the chemistry of the plant and “tells” the caterpillars that the end of the season is coming. This is one of the triggers for the caterpillars to start transforming into adult butterflies. Without that trigger from the host plant, the caterpillars continue feeding. This is what happens when they develop on non-native milkweeds that stay green for longer. In fact, caterpillars that develop on those non-native species become adults later in the season, and when they finally emerge, it is too late in the season and they are unable to migrate and make it to the next spring. One of the best ways to protect these migrants is to let them finish their natural cycle and leave in time (I know it’s hard to see them leave!), which in the case of Monarchs requires favoring planting native milkweeds over their non-native counterparts.

#2 – Let them diapause!

Most of the pollinators in our region, however, are adapted to spend the winter right here. Where are they? As I mentioned in another blog post, the vast majority of pollinators in our area are insects. Insects can’t move, fly, or feed if the temperatures are too low. To deal with very low temperatures, insects in temperate regions like ours enter a physiological stage called diapause.

During this stage, the insect physiological rate is reduced and all development is put in a pause until conditions are more favorable. Even though we usually think about these stages when the season comes to an end for us (the fall), it is interesting to note that many of our pollinators reach this stage at the beginning of the summer and they maintain it until the following spring. The practical consequence of this is that if we want to protect pollinators, we don’t just need to provide food for them; we also need to make sure that wherever they decide to spend their diapause is safe from disturbances.

So, how to do this? First, it’s important to realize that each pollinator species enters diapause at different times and places and at different developmental stages (e.g., larva, pupa, adults). Our native bees diapause in nests (solitary or communal), which can be built in different places, depending on the species. The majority of our native bees are ground-nesting bees and they can enter diapause as early as the beginning of the summer and as late as the fall. For nesting, these bees usually prefer loose soils such as those that are sandy or rocky (Figure 2). Making sure that we are not disturbing the ground in places where we see nests will be key for them to survive until the following year. Practically speaking, this means that if you see bees digging holes in the ground of your garden, you may not want to till that part of it.

Ground nesting bees — *Figure 2 – The Rufous-Chested Cellophane Bee* (Colletes thoracicus) establishes nests in the ground. They can be identified by the mounds left around their entrances. These bees are solitary and non-aggressive, so if you see them nest, don’t disturb that area and rejoice in the bees’ return next spring! Photo by CsabaVadasz.

The second most common place for bee nesting is in cavities. These cavities can be plant twigs and branches, cracks in rocks or walls, or even, in some regions of the world, empty snail shells! If you would like to help these bees in your garden or yards, just leave the remains of all your dry plants through the winter. Chances are that some bees have chosen your dry plants as a place to set their nest (Figure 3). These bees also are the ones that like nesting in homemade bee hotels, and it is really fun to see them emerge early in the spring from the little tubes.

Bees nesting in twigs — *Figure 3 – Some bees nest in twigs and branches, like these nimble Ceratina Bees* (Ceratina strenua) which have chosen a raspberry branch as a perfect place to raise their progeny. Waiting until the spring to clean your dry raspberry branches is a good way to keep these bees protected throughout the winter. Photo by Terry Miesle.

Other bees prefer to build their nest completely above ground. You may have seen little mud “amphoras” or other structures made of little rocks that hang from walls. If you see these nests close to your house, try to not disturb them and keep an eye on them next spring!

Other pollinators, like moths and butterflies, diapause in leaf litter, on wood, or in the ground. They usually do so by enveloping themselves in dry leaves, by digging themselves in the ground, or by attaching their chrysalis onto sticks and branches (Figure 4). To protect these pollinators, you can leave parts of your yard or garden soil undisturbed, keeping at least some of your dry leaves on the soil.

Black swallowtail butterfly chrysalis and polyphemus moth cocoon — Figure 4 – Some moths and caterpillars diapause in cocoons, such as this Black Swallowtail (left; photo: Megan McCarty) or this Polyphemus moth (right; photo: Leckie Seabrooke). Note how the moth has enveloped itself in dry leaves.

Finally, some moths and butterflies diapause as adults, hiding in wall cracks or small orifices. In these cases, it can be hard to spot them before it’s too late. To avoid that, you can observe around your garden or yard (and around the house) to try to find them. This way, you will know what places you should not disturb when you are doing yard or garden work.

For more information on this topic, check out Where Do Maryland’s Butterflies Overwinter? and Bewitching Butterflies and Moths with Fall and Winter Habitat.

By Anahí Espíndola, Assistant Professor, Department of Entomology, University of Maryland, College Park