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Monday, December 28, 2009

POLLINATORS. Robbers and thieves

Some flowers allow only specialized pollinators. They place their nectar out of the reach of most visitors and only those with a long enough tongue can reach it. Such is the case of the bee balm or monarda; a flower visited by hummingbird moths and bumblebees
A hummingbird moth unfurls its long tongue and sticks it inside the equally long throat of a bee balm flower.

The tongue of a bumblebee isn't as long as that of moths or butterflies, but by burying itself into the flower this visitor can reach the store of nectar without difficulty.
These visitors approach the flower the "legitimate" way, meaning that they touch the pollen carrying parts and also the female parts of the flower by entering it this way. When they do so they carry pollen from some flowers to others and accomplish pollination. Everybody benefits; the insects get nourishment and the flowers are pollinated. However this flower's strategy may backfire when clever and lazy flower visitors take a shortcut and steal the nectar. One very common robber is the carpenter bee; with its powerful jaws it can easily slash through a flower's tissues. Here a female carpenter bee is opening the throat of a bee balm flower. When this bee goes directly to the nectar bypassing the sexual parts of the flower it doesn't pick up or carry pollen. As a consequence, it doesn't help the flower at all.
A carpenter bee stealing some nectar
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© Beatriz Moisset. 2010

Wednesday, December 16, 2009

DECEITFUL FLOWERS. Lady slipper

In most cases the relationship between flowers and their pollinators is a wonderful partnership in which everybody wins; but there are exceptions. In some cases, insects exploit flowers and take their offerings without returning the favor and in other cases it is the flowers that exploit their visitors.
Many orchids use a wide range of deceptions; some, such as the lady slippers, engage in a rather innocuous deceit that only causes the insect a minor inconvenience. This flower has a very peculiar shape, with the lower petal expanded into a bag. The purpose of this bag is to act as a temporary trap.

The drawings show a flower cut through the middle to illustrate what happens.
It is not known exactly what the attractant is, but it is powerful enough that several kinds of bees come to the flower seduced by its appeal.
The bee perches on the edge of the sac and often loses its footing and falls inside; once there it struggles to get out but the inside is slippery and the curled lip of the bag makes it hard to get out. Fortunately for the bee there is a escape route.
Toward the back of the flower there is a ladder made of hairs that leads to a tunnel. There is a sort of skylight at the end of it to guide the disoriented bee, so even though the passage is narrow the bee strives tenaciously headed toward the light. In doing so it rubs its body against the pollen sacs, called pollinia, which get glued to its back.
Once outside the bee flies away; its little brain can remember the unhappy experience long enough to travel some distance from the plant that it has just visited. But most likely, it will repeat this adventure when it finds another lady slipper some time later. At this point it will leave behind the pollinia that it has been carrying inadvertently, performing pollination of the lady slipper and getting no reward for its labor.

Sunday, December 6, 2009

Hummingbird Moths. Where do They go in Winter?

Not all moths fly at night; some choose to do it during the day. One of them is the hummingbird moth, so called because it looks and flies and even hums like a diminutive version of a hummingbird when hovering in front of flowers. Just like their feathered namesakes hummingbird moths love long throated flowers, such as bee balm or horse mint. But unlike them, they don’t migrate south when the cold weather arrives. They resort to a different strategy to survive the harsh weather and lack of food.

Like all moths and butterflies they have a complex life cycle with dramatic transformations, called metamorphosis. The distinctive stages are called egg, larva or caterpillar, pupa and adult or imago. The one you are most familiar with is the adult, that colorful flying marvel; the other stages are wingless and prefer to remain out of sight and out of danger. The larva’s job is to eat almost non-stop and to grow; the pupa goes through a resting period and later through a tremendous remodeling job where all the parts are transformed to turn into the active, winged creature which we see during the summer. The flying adult’s whole purpose is to find a mate and to start the next generation; for that they need nourishment, nectar, which they find in flowers.

It is in the resting state of pupa that they choose to spend the winter. After the caterpillar reaches full size feeding on any of its favorite plants, such as hawthorn, black cherry or wild rose, it drops to the ground. There it spins a loose cocoon that lies partially buried under the leaf litter. Leaf litter is very important to this species; it provides some protection against the winter weather and against predators. When birds or squirrels go through leaf litter, scattering it here and there, they may very well be looking for one of these nutritious morsels.

If the pupa survives these attacks, it will complete its metamorphosis and emerge as a winged adult next spring, when nectar-laden flowers are blooming again.

Moths as Pollinators
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© Beatriz Moisset. 2010