The Military Orchid and the Bumblebee (2024)

Ryan has nearly finished collating all the records you sent in for the BSBI New Year Plant Hunt, and he and Tim are all set to start on the analyses, but in the meantime - here is something completely different, which Ryan prepared earlier!

The mail-out of New Journal of Botany has been held up by the holidays, although it has now been published on-line (members only, sorry) and we understand that print copies will be mailed out any day now.

But as a pre-Plant Hunt treat (because I knew we would be working him hard over New Year!), I gave Ryan an advance peek at one of the forthcoming NJB papers and he has very kindly prepared this summary for you:

"The process of pollination is essential for both wild plantsand crops to reproduce. In Britain it is mainly insects that pollinate our wildflowersand crops. Without these insects many rare wildflowers are vulnerable to notbeing able to reproduce successfully and are therefore liable to extinction.Pollination usually results in the setting of seeds which allows plants to movegeographically - this is thought to be increasingly important as plants inBritain move northwards in response to warming temperatures and global climatechange. We currently know very littleabout the pollination ecology of some of Britain's rarest plants, even thoughthis knowledge will be essential if we want to anticipate how these plants willrespond to future climate change.

"The Military Orchid (Orchis militaris L.) is one ofBritain's rarest flowering plants and is anecdotally thought to be solelypollinated by small species of solitary bees; honey bees (Apis mellifera) andbumblebees (Bombus spp.) supposedly do not pollinate this orchid species.

However, research presented in the latest issue of New Journal of Botanysuggests that this may not be the case, according to a paper entitled'Bumblebee-mediated pollination of English populations of the Military Orchid (Orchismilitaris): its possible relevance to functional morphology, life history andclimate change'.

"Studies elsewhere in Europe have indicated that the MilitaryOrchid is mainly pollinated by solitary bees and honey bees, so the authors ofthis paper wanted to find out if this was the case in Britain. In Britainvarious people have recorded a wide variety of insect species visiting theflowers of Military Orchids, but until now we did not know which species wereactually pollinating the flowers. In Bateman and Rudall's study they found thatmales of Bombus vestalis (Vestal Cuckoo Bumblebee) and female workers of Bombuspratorum (Early Bumblebee) pollinated the Military Orchids at Homefield Woods.The authors were unable to observe an unequivocal pollination event when Military Orchid pollinaria(a mass of pollen grains) were observed not only stuck to the bumblebees butalso deposited on stigmas. On average, each bumblebee spent a few minutes oneach orchid spike, investigating many flowers on each inflorescence.

"The studysuggests that pollinaria were often deposited on other flowers on the sameflower spike, therefore not exhibiting cross pollination with other plants. Thepollinaria attached to the pollen sacs on the hind legs of B. pratorum and thefaces of both bumblebee species. B. vestalis does not possess pollen sacson the hind legs so pollen is not collected there. The bumblebees were observedtrying to remove the pollinaria from their bodies but no successful attemptswere recorded.

"The study also suggests that most pollinaria were probablydeposited away from the stigma (female receptive organ) of the receptive plantso would not be successful in pollinating the plant. Therefore, although thisstudy shows that it is likely that these two species of bumblebee pollinateMilitary Orchids, this was not proven.

"The paper also suggests that there may be furtherimplications to bumblebee pollination of Military Orchids, as bumblebees werenot observed to visit these flowers frequently in previous studies, suggestingthat this is an increasing phenomenon. This may in turn increase seed set ofthe orchids and expand their local populations. Another bumblebee species, B.hypnorum (Tree Bumblebee), has recently colonised Britain due to climate change.Thisbumblebee has a similar tongue length to those needed to feed on MilitaryOrchids so it is possible that this species may visit these orchids in thefuture. The final implication of this paper is that it shows that pollinariaalso attach to male bumblebees. Usually in pollination studies it is mainlyworker bumblebees that are studied so this research suggests that maybe otherbumblebee castes should be factored into pollination studies.

Many thanks to Ryan for the above and to Richard Bateman for commenting on Ryan's draft and allowing us to publish this summary of his paper. As soon as those Plant Hunt analyses are done, we'll share them with all of you - watch this space!