Monday, September 28, 2009

BUMBLEBEES. Are Some Bumblebees Going the Way of the Dodo?

Who doesn't like a bumblebee? With their plump, fuzzy bodies and striking black and yellow or black and white stripes they easily capture people's hearts, especially when they are seen buzzing around from flower to flower.

What most people don't know is that some species of bumblebees are in decline. We have heard about the plight of its relative, the domestic honey bee; but haven't paid much attention to the situation of this wild cousin. Why should we care? It isn't just because bumblebees are charismatic, but also, and more importantly, because they play key roles in certain ecosystems. So far, we know of only a few species that are showing a reduction in numbers, both in North America and in Europe. It isn't as if all the species of bumblebees were going extinct overnight; fortunately some species are doing well, even in unexpected places such as suburban gardens. But, perhaps we should start paying attention to what is happening now rather than when it is too late. Besides, it is possible that many other species of wild bees are suffering similar declines in their numbers and we have no way to estimate what is happening because we know so little about them.

Here are some of the things that bumblebees do: they pollinate 15% of our food crops, worth about 3 billion dollars; they also pollinate countless wild flowers. Wildflowers are important not just for their beauty, but also for the seeds and berries that they produce. They become food for many species of wildlife, from birds and small rodents to large animals such as bears. Birds don't know what percentage of their food crops are pollinated by bumblebees, but it is possible that for some species is closer to 90% than to 15%. If we are not worried about our own food, we should worry about all the many species of birds and other wildlife that may be suffering because of a reduction on the numbers of wild bumblebees.

Goldfinches and many others owe their food to hard working pollinators such as bumblebees.
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© Beatriz Moisset. 2010

Saturday, September 26, 2009

The Life of a Flower

© Beatriz Moisset
Let us take a simple flower, the simplest you can think of, the one you drew when in Kindergarten. A yellow circle surrounded by petals. It looks like a daisy or a sunflower or an aster or a number of flowers with petals arranged like sun rays and a circle or disk at the center. Well, there is a surprise here; such a flower is far from simple. It has a very complex structure, in fact it isn't just a flower but a whole bunch of tiny flowers. Look at the little parts that comprise that yellow center. What a surprise! Each one looks like a tiny flower all by itself: five petals and a center with little things inside that resemble the center of many other flowers that you have observed at various times. Well, that is exactly what they are. Each one is a flower, called a floret; they are all clustered together.
Each floret contains all flower parts: petals, anthers, stigma
© Beatriz Moisset

You may wonder about the petals that surround this cluster of flowers. Here is the answer: there are two kinds of flowers in this interesting bouquet; only the ones that make the outside rim have petals, the large petals that we see. They are called ray flowers while the ones in the center are called disk flowers. It would be nice if all technical jargon were as obvious as this.
In a newly opened sunflower or helenium, the disk flowers are just like little knobs. The next day the outer line of disk flowers has opened and you can see the sex parts, the pollen and seed producing parts, sticking out. Afterward, each day or so a new row of flowers open. The old ones begin to wilt; they look open and a little dry. Eventually one smaller circle after another opens and passes its prime.
Now let us observe the pollinators that come and visit the flower. They go directly to the freshly opened florets. They have nothing to do with the unopened ones, nor with the wilted ones. They find pollen and nectar only there and they know it. All this goes according to the plans of the flower; this works just right to ensure pollination.

© Beatriz Moisset
One interesting thing is to look at the older flowers that have completed their cycle. The ray petals stay fresh and bright for a few days longer although that flower is no good to pollinators any more and it doesn't need visitors either; right now it is busy growing the seeds that will mature later on.
You may wonder why it continues to look attractive to pollinators. The reason is that a large clump of flowers is more likely to attract pollinators that are passing by than a smaller clump, with many dry blossoms in between. It is like you going shopping; a mall where many stores are closed or vacant is likely to drive you away rather than attract you. Once there, you aim for the store that interests you. Pollinators do the same; they notice the larger displays of flowers than the smaller ones, with the certainty that they will find some food there.
Helenium. The flower on the left is young, only a few florets opened
The one at right is older, most florets are past their prime
© Beatriz Moisset
Such flowers are skilled engineers, and good marketers. They know their clients and how to satisfy their demands, and they get good returns. Other flowers are arranged differently; they use different attractants; their timing varies; but they all know how to maintain a successful partnership with their pollinators.
The clients, on the other hand, know how to use this resource. You can see a bee visiting methodically all the florets and probing them with its long articulated tongue in this video

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© Beatriz Moisset. 2010

Sunday, September 20, 2009

Bugs in the Garden. Hornworm: Friend or Foe? Friend and Foe

Do you grow tomato plants? Who is your worst enemy in that case? Probably the tomato hornworm or the tobacco hornworm. Those fat green caterpillars with a funny looking horn at the rear end, red in the case of tobacco hornworms, blue in tomato hornworms. Besides that minor difference they look very similar; they both attack your precious plants with gusto and grow healthy and vigorous in such a diet. They also feed on tobacco, potato, peppers and other plants of the Nightshade family.

The moths that emerge from those caterpillars after they are done growing and after a period of rest called pupation are called hawk moths or sphinx moths. They are very beautiful, mostly brown and white with orange markings on the sides of their bodies, five in the tomato hornworm and six in the tobacco one; once again not a big difference.

Naturally you hate the worms, fear to find and infestation of them in your garden and would like to exterminate them forever. Fortunately, Nature has provided a few enemies of hornworms that help you in your battle for control but you are very likely not to know them and even accidentally eliminate your little helpers in an effort to combat the worms. So, it is important to know both.

Occasionally you find a hornworm all covered with white little oval things that you might mistake for eggs. Those are not eggs at all; they are your friends. It is fascinating to learn how they got there, although I must warn you: be prepared for some gore.

There is a tiny wasp, so small that if you drop a handful of them on a white piece of paper they look like the marks you could make with a regular pen, no bigger than some scribbles. This wasp lays its eggs inside the body of a caterpillar. The poor thing feels the prick and goes back to eating and growing for a while, without knowing that it is doomed. Eventually it becomes lethargic and later catatonic. It stops moving but continues to cling to the stem of one of your tomato plants.

In the interim the wasp’s eggs have turned into minute grubs that start doing a lot of eating and growing of their own at the expense of the caterpillar. When they are fully grown, something out of the movie “Alien” takes place. Remember a scene, early in the movie? An astronaut, that had suffered an encounter with the alien creature, seems fully recovered. Then, all of the sudden, he screams and writhes in pain. A blood covered hideous creature, a parasite, the alien in question, bursts out of his chest and scurries away. They must have gotten the idea from the parasitic wasp.

The full grown grubs emerge from the body of the caterpillar after making little holes. They cling to the body for safety, and spin cocoons around themselves. By then the caterpillar is too far gone to care. The wasp’s larvae need a period of repose inside their cocoons to turn into winged adults. They emerge in a few days ready to go and infest another caterpillar. I told you that it wasn’t pretty!

But it works to your benefit. Be thankful to the wasps that keep the population of hornworms down and prevent serious damage to your tomato plants. Hold the pesticides! You don’t want to kill these friends of yours along with your enemies.

There is still another twist to this story. As I said, the unwanted pest that devours your plants turns into a handsome moth. The transformation is so complete that people even end up calling it by a different name; in the case of the tobacco hornworm it becomes the Carolina sphinx moth. It flies at night visiting flowers such as morning glories, sweet potatoes, Nicotiana, etc. in search of nectar. It hovers on front of them, unfurls its long tongue and drinks deeply. In doing so it pollinates them. It has gone from foe to friend, from tomato destroyer to pollinator. We have to think twice about our desire to eliminate the hornworm entirely. Perhaps Nature works best by keeping a delicate balance by means of parasites.

Thursday, September 17, 2009

THE WEB OF LIFE. The Bear, the Waxwing and the Bee

You may be wondering what bears, waxwings and bees have in common. We'll get to that later.

Let us start with a black bear, the formidable resident of forests and broad spaces. An encounter with one of them can be an unforgettable experience. It is surprising to realize that an animal built up with such powerful claws and jaws is seldom a hunter; in fact perhaps only 10 or 15 percent of its diet consists of animal matter and a good part of that is carrion or insects. So, what does a bear eat? With great versatility it finds a wide range of plant food in the course of the year. In early spring, fresh out of hibernation it may find skunk cabbage to its liking as well as sprouts from plants in the pea family, horsetails and sedges. Later in the season it will find the growing cow parsnips and dandelions, as well as flowers of several kinds. It may supplement this vegetarian diet with some animal protein, from caterpillars to the occasional newborn elk; but still about 80 percent of the summer diet is vegetable. In the fall, it is the time to feast on berries; blueberries, raspberries and everything in between. It can devour enormous quantities of this food because it needs to fatten for the long winter ahead. It is hard to believe that such diet can become many pounds of fat in the short period of a couple of months.

And now for cedar waxwings, those attractive birds that are so much fun to watch. They are especially interesting when they are engaging in their peculiar tradition of passing berries from one to another. Cedar waxwings eat an assortment of berries through the year. In summer, when they are raising young, they enrich their diet with insects; but berries are the main staple of their diet.

Finally, let us talk about bees. Let us make it clear that I am not referring to the domestic honeybee but to any of the numerous native bees and bumblebees that feed on pollen and nectar of wild flowers. If we want to be more specific we can choose the blueberry bee. This industrious little bee is very specialized on the pollen it chooses to feed her family. It goes almost exclusively to blueberry flowers. When doing so it carries some pollen from flower to flower and from plant to plant, providing the plant an invaluable service, pollination. Once the flowers are pollinated they can start setting seeds and developing fruits.

Now, you see the link between bees and birds such as the cedar waxwing and larger animals such as the black bear. They feed on the berries that have been pollinated by the bees or, in the case of the bear, on other plant parts that also require pollination to multiply.

Experts on pollination remind us frequently that one third of our food comes to us courtesy of pollinators; most fruits and vegetables require the services of these little go-betweens, most of them bees. What they forget to mention is the large number of other species that also depend on pollinators for a good part of their diet. The bear and the waxwing are just two examples of a very long list that intertwines the little bees with the more visible birds and mammals.

Another twist in this intricate web, the bear and the waxwing digest the berries but not the seeds. So they end up dropping them farther from the mother plant and surrounded with an amount of excellent fertilizer. So, the pollinator, in turn, also depends on the seed dispersers.

But the final, and perhaps most marvelous twist, is that the plants, so dependent on pollinators and seed dispersers are actually making use of them. They are very skilled in attracting their attention and supplying their needs, either with rich pollen and nectar or with juicy, nutritious fruits. At the same time, they make sure that not all the pollen gets eaten and that the seeds can safely go through the intestines of the berry gluttons.
Thus the web is complete: flowering plants need the pollinators and the seed dispersers; bees need the flowers and the seed dispersers and, finally, bears and birds need the plants and the pollinators. When you walk through the woods or the meadows, think about this invisible web and what it is doing to make everything possible.

Bear feeding: BearDiet

Cedar waxwing feeding: Appalachian Mountain Club: Bird of a Feather...