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Spiranthes spiralis - pollination

Posted by
Johan Dierckx (Wijnegem, Belgium) on 8 September 2010 in Plant & Nature and Portfolio.

Series: European Terrestial Orchids

I promissed yesterday the story of pollination of this orchid species.
The flowers are pollinated by bumblebees. When the flower opens the longboat-shaped rostellum lies close to the lip at the bottom of the tubular flower with the sticky viscidium facing downwards. In this position the rostellum blocks access to the stigma so that the flower cannot be self-pollinated. A bumblebee lands on the lip and inserts its proboscis in search of the nectar that is produced at its base. There is just enough room for the proboscis to reach the nectaries but in the process it pushes past the rostellum, and the pollinia are attached to the proboscis by the fast-drying flue of the viscidium. The bee moves on, carrying the pollinia with it. This can be seen in the image above: two pair of pollinia are attached to the proboscis of this bumblebee (Bombus lapidarius).
Over the following 24 hours or so the column and the lip move apart, creating enough space for a visiting bumblebee to insert its proboscis, with the pollinia attached, into the flower, where they rub against the stigma (which is now exposed and has become much stickier). The pollinia are brittle and break off in small pieces. A single bumblebee can pollinate several flowers. Due to the 24-hour interval, older flowers are always pollinated with pollinia from a younger flower. The lowest flower in a spike open first and, as bumblebees work upward from the bottom of a spike (i.e. from older to younger flowers), they visit the older flowers first and cannot pollinate them with pollinia taken from the same spike. In this way cross-pollination is virtually guaranteed. The mechanism is efficient and seed is set by almost all flowers.

Image: Zuid-Holland (NL) - 03/09/2010

Canon EOS 400D 1/200 second F/5.6 ISO 200 150 mm

© Johan Dierckx

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marc battault from clermont ferrand, France

magnifique cette capture ,elle est en plein travail !!!
amitiés !!

8 Sep 2010 4:24pm

@marc battault: Thanks Marc. There are not many images where you can see this action... so I'm happy I could make some. Greetz!

Marleen from Doesburg, Netherlands

Geweldig dat je de bestuiving van deze zeldzame bloemen hebt kunnen vastleggen! Zal vast wel een lang en geduldig wachten aan vooraf zijn gegaan...;-)

8 Sep 2010 6:41pm

@Marleen: Inderdaad lang en geduldig wachten op de hommel maar dan .... op tijd van amper 5 seconden bezocht deze hommel de volledige bloem op de voorgrond en de volledige bloem in het middenplan... Ik kon een reeks van 9 beelden maken die het hele bezoek in kaart brengen.. maar tijd om mooi te kadreren en dergelijke heb je dan absoluut niet. Ontzettend snel zijn die hommels ... De afbeelding van vandaag is de tweede uit het reeksje, omdat je hier mooi de stuifmeelklompjes kan zien die op de "tong" van de hommel gekleefd zijn. Het volgende moment zat ze al op de volgende bloem. Het is indrukwekkend om het voor je ogen door een macrolens te kunnen bekijken. Natuur zit zo wonderlijk in mekaar ...

Veronique from Sarrouilles, France

very interesting et great macto

8 Sep 2010 8:10pm

@Veronique: The shot itself is not realy my best image ever, but the documentary value of this one is very large. There are not many images to document the polination on the species. So I thought it was interesting enough to display. Greetz, Veronique !

Dutçh from Chicagoland, United States

Nature can be so fragile, everything is timing. I'm looking at the bee and it is all black? No yellow at all or is that the angle. All our bumble bees have some form of yellow on them.

9 Sep 2010 2:52am

@Dutçh: Red-tailed bumblebees (Bombus lapidarius) are mostly coloured black, the hind-quarters are auburn red though. Due to the shooting-angle it is very hard to see this in this particular image (I have some more images where it can be seen more clearly but there the pollinia are not visible like in this one). When you look very carefully it can be seen in the corner between the dried leaf, the stem and the flower.
Speaking about timing ... this bumblebee visited the entire front spike and the one just behind in only 5 seconds... I have a 9- image series of this visit in which this one is the 2nd. Reading about this pollination takes much longer than the actual visit :-)

daniela scharnowski from Berlin, Germany

What´s this - a square format? Oo Here? ;D Just kidding - I know how difficult it can be to bring out the scene you´ve got in mind by cropping..... though I´m not to happy with the very centered crop - nevertheless an amazingly good capture!!

9 Sep 2010 6:34am

@daniela scharnowski: I know it is very centered and that is not my favorite compo too but ... It all happened just so incredibly fast that there was just no time to frame properly. This is one of the very few images I made with AF turned on (I normally use MF). I only used the center-focus spot following the tongue of the bee to get the pollinia sharp and hoped to get enough from the entire scene. In 5 seconds I made 9 images documenting the entire visit on the first and second spike...

KriKridesign from Cully, Switzerland

priceless...looks sweet, make me want to touch!

9 Sep 2010 3:19pm

@KriKridesign: Be carefull ... bumblebees do sting ... Auch :)

Loner from Wörgl, Austria

Schöne Dokumentation - danke für die ausführliche Beschreibung !

9 Sep 2010 5:06pm

@Loner: It was just so wonderfull to see in real this pollination mechanism I only did know from books. And I am very happy I was able to document this with a series of images.

Julie Brown from Indianapolis, United States

Now that is an interesting process! I assume that the pollinia stuck to the proboscis does not interfere with the bee's ability to nectar? Nice detail on the flowers. As for the square crop-it works for me! :) So, really, did I influence you to use a square crop?

11 Sep 2010 1:18pm

@Julie Brown: The pollinia do not interfere with the ability to nectar but obviously the bee likes to get rid of those as soon as possible. I think it is one of the reasons they visit several flowering-spikes in sequense. I was able to follow different bumblebees during the pollination-job and the never visited other flower species between the visits of these orchids ! Just from one spike to the other - dozens in sequense (mostly till I lost track ... ). There were also other bumblebees (same species!), visiting other flowers species present on the site, but those did not touch any of the orchids.... I just don't have a good reason for this different behaviour ... "to be solved" :-) (And yess - it is definitely your influence that made me decide to use this square crops on my images - I never did that before ... - the pano-crops you like to use will follow when apropriate to the image)

Julie Brown from Indianapolis, United States

I am definitely flattered that you would be influenced by my photos. I am inspired to take my macro images up a few notches by the example you set with the lovely light and detail that you always managed to create.

12 Sep 2010 1:54am

@Julie Brown: That is the purpose of this site - getting inspired with each-others work ... Isn't it ?

Demo from Villeneuve d, Croatia

I had not seen this picture, it is really impressive!
details are fantastic and Your description was very rewarding again ;)

29 Nov 2010 8:51pm

Canon EOS 400D
1/200 second
F/5.6
ISO 200
150 mm

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