-Bucket Orchid

-Bee Bop - reproduction of the bucket orchid

How does a tropical beauty induce a diminutive beast to airlift sacs of pollen? Writer Eric Hansen takes us on a behind-the-scenes tour of a bucket orchid.

Many orchids have evolved elaborate traps and obstacle courses to attract and capture their insect pollinators. The mechanisms within these flowers are often so daunting that, upon first glance, it is difficult to imagine why insects would visit the flowers once, let alone twice, to complete the process of pollination. For many biologists, from Charles Darwin onward, the insect/flower 

relationships within the family Orchidaceae have been prime examples of co evolution. They also can be seen to exemplify the lighter side of evolutionary fine-tuning, especially as it pertains to the rocky road of insect romance. In the case of Coryathes speciosa, one of the species known as bucket orchids, and its insect pollinator, the male euglossine bee, there is an ardent suitor, tantalizing promises, a noble quest, intoxicating perfumes, deception, dancing, and adventure. This entire scenario is orchestrated by the flower for the sole purpose of fooling an insect into completing the pollination process by transporting pollen from one blossom to another.

Bucket orchids are epiphytes

Bucket orchids are epiphytes (also known as air plants) that sprout on trees in the wet tropical forests of Mexico, Central America, and South America. The flowers grow in clusters, and on the front of each flower are two winglike sepals. Just behind the sepals is a small floral "bucket," which gives the plant its popular name. By the time the flower opens (often with an audible popping sound), two special glands have already started to secrete a liquid that drips into the bottom of the bucket. The flowers now begin to produce a fragrance that proves irresistible to the metallic green male euglossine bee. The fluid dripping into the bucket is not a nectar, nor is it the source of the scent. The droplets serve a different purpose entirely.

Soon after the orchid blooms, male bees, responding to the scent, start to swarm around the flower in a state of great agitation. They hover and try to land, seeking a foothold on the mesochile, a tubular section that connects the bucket to the stem and front of the flower. From the slippery surface of this erect and slightly curving vertical shaft, the excited bees use their front legs to collect a scented wax from just below a bonnet-shaped structure called the hypochile.

The bee uses the hairs on his legs to transfer the aromatic substance to special pockets on his hind legs. He will later use this potion to help him attract females during his courtship dance. Different species of Coryanthes attract different species of bees, because each male bee needs to have a very specific sort of scent. Only after the male bee has collected enough perfume is he ready to fly off in search of a mate.

In a mad rush to get at the limited amount of perfume, many male bees can be attracted to the same orchid flower. The orchid flowers stay in bloom for only a few days, and the eager insects engage in a considerable amount of head butting, shoving with their midlegs, and jostling for position beneath the hypochile. Occasionally one of the bees either loses his footing on the slick surface of the shaft and falls into the bucket, or gets knocked in when his wings collide with a droplet coming from one of the orchid flower's faucet like glands.

-Once within the fluid of the bucket, the bee has only one means of escape:

a narrow tunnel that leads through the front wall of the flower to daylight and freedom. Just at the entrance to this tunnel, on the inside wall of the bucket, is a step that the sodden male uses to climb out of the fluid and into the passageway. He then slowly squeezes and wiggles his way forward. But before he reaches open air, the bee must pass beneath a "twin pack" of pollinia--sacs containing thousands of pollen grains--situated at the roof of the tunnel, on the anther, the male part of the flower.

At a precise moment, the pollen disengages and becomes lodged on the bee's back at the spot where the thorax and abdomen are hinged. By the time the bee has climbed free of the tunnel, the pollen is attached between his wings like a small backpack. Once out, the bee--wet and disoriented--pauses to dry himself on the flower's lateral sepals. His ordeal may have taken as long as forty-five minutes.

In order for Coryanthes speciosa to be pollinated, a bee carrying pollinia must then be lured to another blooming orchid of the same species, fall into the bucket, and negotiate the floral obstacle course a second time (the chances of this happening are remote, and consequently pollination occurs infrequently).

On the bee's visit through the second bucket orchid, a catch mechanism on the roof of the escape tunnel grabs the pollen backpack. By this time, the pollen has dried and diminished in size, so that it fits nicely onto the pistil, the flower's female component. In this way the bucket orchid is pollinated, and with luck a seed pod will eventually form.

The male bee may have been duped  

Freed of his backpack and remembering his own procreative duties, he flies off to a display site, where he dances and launches into an intricate flight and buzz pattern. A heady scent wafts from his hind legs as he performs the fancy footwork. With this kind of action going on, what female bee can possibly resist the temptation to land and get better acquainted?

Author and journalist Eric Hansen ("Bee Bop") has had a long acquaintance with orchids. His father grew these varied, intricate plants, and Hansen's own interest was renewed during extensive travels in the rainforests of Borneo. He is now working on a book about the international trade in rare and endangered species of orchids. Based in northern California, Hansen has recounted his travel experiences in Stranger in the Forest: On Foot Across Borneo (Viking/Penguin, 1989) and Motoring with