Surfing the Internet can often be a fruitless endeavour, but occasionally
one crashes into something that makes one take notice. And thus I stumbled upon
information concerning the pollination of Cymbidium floribundum (= C. pumilum), something which I had not read about before and which does not appear to have
been mentioned in the English-language, hobbyist, orchid literature. This page was updated on 11 May 2009.
© 2003-2011 Greig Russell
There is a whole biological discipline called Chemical Ecology which revolves around semiochemicals, something I have only come upon recently, although there has been an international society devoted to this field in existence for some 20 years. Semiochemicals are defined as chemical substances produced by an organism and used in communication with or to modify the behavior of another organism. The first part of the word semiochemical is derived from a Greek word sema, which can be transliterated as sema and means a sign or signal. The same root is used in the word semaphore; which also has to do with signals. Pheromones are a special group of semiochemicals which are released by an organism and modify the behavior of another organism of the same species. If you have ever owned a bitch in season; you will understand the term pheromone.
The very complex and ordered life of a colony of bees is to a large extent under the control of a series of pheromones. Queen bee substance is one of the best known of these pheromones. It is produced by the queen and gets her the special attention she requires, it also excites the drones and suppresses development of ovaries in the workers. Other pheromones are involved in foraging, swarming, alarm, etc.
Cymbidium floribundum does not have a scent that can be detected by humans; however there is some evidence that it must have some sort of scent-producing mechanism. The closely related C. suavissimum is strongly scented (as the name suggests) and hybrids of C. floribundum such as C. Oriental Legend (x C. Babylon) have been reported to have some fragrant clones; something I have also observed in C. Beenak Rose (x C. Hamsey). Cymbidium floribundum does in fact produce volatile compounds and when these are characterised, they are found to be identical to substances produced in the pheromone-producing head glands of the Japanese Honeybee (Apis cerana japonica).
The genus Apis contains a handful of species, one being the Western Honeybee (A. mellifera) with many subspecies ranging naturally through Europe, Africa and Western Asia (and widely introduced to other parts of the world). The other few species of the genus are native to Eastern Asia, one of them being the aforementioned A. cerana which also has many subspecies. The Japanese honeybee has been kept for honey production in Japan since at least the seventeenth century, the western honeybee having been introduced there in the latter half of the nineteenth century.
The volatile semiochemicals produced by Cymbidium floribundum correspond to the bee pheromones apparently associated with foraging and swarming and are powerful enough to cause even drones (a noticeably lazy lot) to exhibit foraging behavior at the flower and it seems possible that the drones in fact are responsible for carrying out the pollinations. Should the bees swarm during the flowering season of C. floribundum, the entire swarm settles on open spikes of the orchid. The pheromones of the western honeybee, although similar to those of Apis cerana, are sufficiently different to allow the former to ignore the orchid and not to be involved in its pollination at all.
It has been reported that Japanese honeybees respond to plants of the alba variety of Cymbidium floribundum in the same way as they respond to typical plants. It would seem therefore that tepal colour in this species is not important to the pollinator as a long-range cue. The tepals therefore assume a safe, cryptic, brown colour, so as not to attract plant-eating enemies. The light-coloured lip serves as a short-range cue which helps the bees to align themselves into a position which would allow for pollen collection and deposition.
For more information see Michio Sugahara's superb website on the Japanese Honeybee at http://homepage3.nifty.com/jhb/english/index.htm. See also the relevent abstract of the presentation by Hiromi Sasagawa and Shigeru Matsuyama from the 15th Annual Meeting of the International Society of Chemical Ecology at http://www.chemecol.org/meetings/98/o-36.html. Another abstract from the same authors as well as Takahisa Suzuki is also available from the Meeting of the previous year at http://www.chemecol.org/meetings/97/C-6-2.html.
The spike-formation in Cymbidium floribundum is interesting, in that the spikes are formed early and persist for a long period as small nubs, until some stimulus causes them to elongate rapidly and flower. Often, under my growing conditions, this stimulus never comes and the nubs just wither. For this species to be successful, it must time its flowering by using the same stimuli that promote either the swarming or drone production of hives of Apis cerana japonica. So by studying bees, perhaps we can better learn how to flower our plants of C. floribundum.
This page was updated on 11 May 2009.
© 2003-2011 Greig Russell