Thrifty flowers

Pollen is a valuable commodity. The less pollen needed, the more energy is left for other functions. Flowers resort to several strategies to economize on pollen. Some use a method called explosive pollination, others resort to buzz pollination. Both methods are well illustrated by official state flowers.

Mountain laurel in bloom. © Beatriz Moisset

Explosive Pollination of Mountain Laurels

Mountain laurel (Kalmia latifolia), Pennsylvania’s and Connecticut's state flower, has a singular way to ensure that its insect visitors carry pollen to other flowers of its species. The unopened blossoms present little knobs which give them a funny look. Their function becomes apparent when the flower opens. They are pockets that hold the anthers trapped. Anthers are the part of the flower that produces male cells, pollen.

Mountain laurel flower before an insect's visit.  © Beatriz Moisset

Flower tripped by an insect. © Beatriz Moisset

In most flowers the anthers are free and exposed to spread their pollen at the slightest touch of a flower visitor. The mountain laurel has a different strategy. The pollen is well protected against rain and wind; but, when a pollinator lands on the flower searching for nectar, the weight acts as a trigger, causing the taut stem of the anther to spring. The anther hits the pollinator gently on the back and gives it a dusting of pollen.

This method allows mountain laurel flowers to produce only a moderate amount of pollen because most of it ends up where it is intended, on the body of a pollinator, rather than being wasted in other ways.

Connecticut: Mountain laurel

Pennsylvania: Mountain laurel

Explosive Pollination of Pea-like Flowers

Texas Bluebonnet. Wikicommons © Jacopo Werther

Other flowers encase both the pollen-producing parts and the female parts, or stigma, into a sheath. Some members of the pea family, Fabaceae, have flowers that resemble a butterfly, this is why this subfamily is called Papilionoideae, papilio meaning butterfly. The top petal is large and shaped as the sail of a ship and is called the banner. Two side petals are called wings, and the bottom two petals are merged into one forming a sheath that encloses both the anthers and the stigma. This structure looks like the keel of a boat and it is so called.

Structure of a papilionoid flower. Wikicommons. © David Richfield

When a pollinator lands on a blossom, its weight triggers a mechanism causing the keel to spread open and the anthers and stigma jump up out of the enclosure. This is called tripping. The insect has to be heavy enough to cause such reaction. Some bumble bees are pros at this task; honey bees, on the other hand, dislike being pounced upon. After a few times, they learn to sneak around and steal the nectar through a small opening at the base of the keel. Only novices perform pollination. Once they learn this trick no more pollen is transferred to the stigmas. Nevertheless managed honey bees are widely used to pollinate alfalfa and clover. Bee hives provide a large labor force that makes up for this deficiency. Some bumble bees, especially the short-tongued species, are also inclined to a little larceny. However, they are generally considered highly competent pollinators of alfalfa and clover.

Clover, another papilionoid flower. © Beatriz Moisset

Texas’ bluebonnet (Lupinus) and Vermont’s red clover (Trifolium pratense) need to be tripped. Six species of lupines, all of them called bluebonnets because of their appearance, live in Texas. All six of them are considered the state flower. The red clover, Vermont’s state flower, on the other hand, is not a native plant. It is an important crop used to feed livestock.

Texas: Bluebonnet

Vermont: Red Clover

Buzz Pollination or the Salt Shaker Technique

Other flowers make the pollinators work for pollen in a different way. Interestingly enough, honey bees never learned how to do the job I will describe, but native bumble bees and numerous species of bees are real pros.

Azalea Andrena bee pollinating azalea. Observe the pores at the tips of the anthers. © Beatriz Moisset

In most flowers the pollen is made available to pollinators as soon as it is ripe. The anther splits open. We all have seen the golden dust many flowers have. If we touch it, it sticks to our fingers. Rhododendrons and azaleas do something else. They keep the pollen enclosed inside the anther. It can only come out through a small opening at the tip. Several other native flowers, like tomato and blueberry have a similar characteristic.

In order to extract it, the bee has to cling to the anther and give it a good shake. It accomplishes this by vibrating its flight muscles while keeping the wings still; it is like running the car engine in neutral. Pollen comes in clouds and clings to the body of the pollinator. Later, the bee proceeds to package its loot in the little baskets of the hind legs.

Buzz pollination of azalea. Video. © Beatriz Moisset

Two states have official flowers that exemplify this method of pollination, Washington has chosen the Coast Rhododendron (Rhododendron macrophyllum) and West Virginia has another species of Rhododendron (Rhododendron maximum). Georgia’s official wildflower, azalea (Rhododendron prunifolium), follows the same system of pollination; its official flower is the rose; but, fortunately, they decided to honor a native plant in addition to a non-native flower.

Georgia (official wildflower): Azalea

Washington: Coast Rhododendron

West Virginia: Rhododendron

Other plants select their pollinator clientele through other methods. Some hide the nectar rather than the pollen. A different set of skills are needed to deal with these flowers as we'll see in the next post.

References

Pollination of mountain laurel

Image illustrating the parts of a Papilionoid flower

Red clover pollination (also alfalfa)

Legume pollination

Bluebonnet pollination

List of articles
Beginners Guide to Pollinators and Other Flower Visitors

© Beatriz Moisset. 2015

Don't Underestimate the Native Pollinators

Honey bee and several native bees on flowers of fruit trees

© Beatriz Moisset

 The concern for honey bees has exploded in recent years. A day doesn't go by without a new article on the media or comments on numerous nature blogs. Some are agonized cries of help with words such as: Save the bees to save our food supply! Honey bees are going extinct, we are next! Almost completely lost in the shuffle are native pollinators, namely the 4,000 species of bees in the US.

Most of the public is unaware that native pollinators could supply a substantial amount of crop pollination. In many instances one or another native bee or an entire cadre of them results in more efficient pollination than that of honey bees. Here are a few examples:

In an apple orchard, 250 orchard mason bees can do as much as 15,000 to 20,000 honey bees. Squash bees are early risers and are likely to do more pollination of pumpkins and squash than the late arrivals—honey bees and bumble bees. The Southeastern blueberry bee, Habropoda laboriosa, is capable of pollinating $20 worth of blueberries in her lifetime. Many native bees work in wetter or colder weather than honey bees. The alkali bee and the non-native alfalfa leaf cutter bee pollinate a higher percentage of visited flowers than honey bees do. Some small orchards and vegetable fields get most of their pollination done by native bees.

Many native bees practice buzz pollination,

needed by tomatoes and other crops

© Beatriz Moisset

All and all according to some studies, native bees provide $3 billion worth of pollination to agriculture, while honey bees' contribution is valued at $15-18 billion. If we put native bees to work, we could reverse these proportions. Perhaps the best way out of the so-called honey bee crisis is to find the way to take better advantage of the other bees. How difficult would that be?

A hundred years ago native bees played an important role on crop pollination. As far back as seventy or eighty years, several authors noticed that bumble bee and solitary bee populations were dropping. This loss was most noticeable in larger farms where sometimes fruit or vegetable yield suffered by the absence of pollinators. Nobody seemed terribly concerned as long as the honey bee could be brought into service. Some observers knew that native bees were more efficient in many cases, but felt that the ease with which honey bees can be managed compensated for this drawback.

Some native bees are just as efficient as honey bees

at pollinating fruit trees

© Beatriz Moisset

Intensive farming grew as did the need for pesticides, and beehives started to be transported long distances and in large numbers to do their duty. It was the birth of the pollination industry involving beekeeping practices far removed from what would be considered natural. It shouldn't surprise us that such an unsustainable system is causing troubles for honey bees.

Can we bring native pollinators back after they continued to lose ground for the past century? Are there enough left around to take over the task of pollinating our crops? Even without statistics, we can be sure that only a tiny fraction of the previous populations remains. Perhaps, some species are precariously hanging on the verge of extinction or have already disappeared.

Dead solitary bee © Beatriz Moisset

No species takes the road to extinction willingly. Every creature, large or small, fights tooth and nail, or mandible and tarsal claw as the case may be, to stay alive and procreate. A few years ago, an entomologist found a miner bee's nest in a flower pot in his backyard. Another bee expert encountered a rare species of bee, regarded close to extinction, in the very heart of Washington DC, in a butterfly garden at the Washington Mall. With remarkable tenacity, these little survivors had managed to find just enough resources and shelter to raise their families in the middle of the concrete jungle.

We should not give up hope. Native pollinator populations can be brought back to the levels of yesteryear; perhaps then they can resume pollinating the crops that feed us.

Pollinators. © Beatriz Moisset.

Update, April, 2014. I followed some published reports when I said "native bees provide $3 billion worth of pollination to agriculture, while honey bees' contribution is valued at $15-18 billion." However this may be shortchanging native pollinators. Perhaps they do a lot more. A publication by Claire Kremen states that in California  native pollinators are responsible for $2.4 billions and honey bees for $3.9 billions. In other words, in that state native pollinators are responsible for almost 40% of all agricultural pollination. I will keep searching the truth.


List of articles

One Bite our of Three

Will We all Die if Honey Bees Disappear?

Bring Back the Native Pollinators! We need them more than Ever

Wild pollinators worth up to $2.4billion to farmers, study finds

Reversing threats to native pollinatorcommunities and services

Beginners Guide to Pollinators and Other Flower Visitors

© Beatriz Moisset. 2014 

Buzz Pollination of Fabaceae Flowers

Flower of Senna. Observe the pores at the tip of the anthers

© Beatriz Moisset

It is interesting how several families of plants have evolved anthers that require buzz pollination, also called sonication, independently of each other. The organ that contains the pollen or anther of most flowers splits open when the pollen is ripe, making it available to the flower visitor. Buzz pollinated flowers do it differently. The anther remains closed, except for a pore at its tip. The only way to extract the pollen is by shaking the anther with just the right kind of vibration. Bumble bees are pros at doing this. Honey bees never developed the technique.

Close-up of the anthers © Beatriz Moisset

We are most familiar with the members of the tomato and potato family, Solanaceae. So much so, that some gardeners resort to a tuning fork or just an electric toothbrush to ensure pollination of the tomato flowers. Seeing pollen fly from the anthers during this process is a sight worth seeing. Another family with members that require buzz pollination is the Ericaceae; Blueberries, cranberries, azaleas and rhododendrons use this process.

Senna plant. © Beatriz Moisset

Perhaps, it is less known that some members of the pea family, Fabaceae, in the Caesalpinioideae subfamily also resort to this process. The genera Senna and Cassia, belong to this group. Recently I observed a bumble bee visiting the bright yellow flowers of a Cassia and was able to record the buzzing. The sound is unmistakable, quite different from the buzzing of flying. Watch the video of bumble bee on Senna and pay attention to the sound. You can compare it to that of a bumble bee pollinating an azalea.

Bumble bee, probably the common bumble bee. © Beatriz Moisset

List of Articles

Beginners Guide to Pollinators and Other Flower Visitor

© Beatriz Moisset. 2013