Bumble Bee (Bombus trifasciatus) pollinator of orchids

 

Bumble Bee (Bombus trifasciatus)

Bombus trifasciatus was one of the common and active forager observed to visit different orchid species during the study period. It forage in both rewarding orchid (Coelogyne and Otochilus species) and also the non-rewarding orchids (Cymbidium species). Coelogyne species was also commonly visited by wasp species and bumble bee due to the presence of sweet exudate. 

The bumble bee were found to forage on the following orchids species 

1. Cymbidium erythraeum Lindl. 

2. Cymbidium hookerianum Lindl. 

The bumble bee was considered the probable pollinator of orchids based on the field observation.

3. Coelogyne longipes Lindl. 

where as it was suggested pollinator for C.lingipes. 

To know more detail on the type of pollinator you can refer to the link  

https://karmabiodiversity.blogspot.com/2022/08/orchids%20pollinator%20.html

Bombus trifasciatus is commonly known as bumble bee that forage on diverse plant families for pollen and nectar. The visitation of B. trifasciatus to Cymbidium species were rarely observe compare to other ornamental flowering plants grown near the orchid species which provided food source. Since Cymbidium species which do not provide any reward to its pollinator, bumble bee might have preferred other rewarding plants. 

The bumble bees were found to take a quick flight visiting 2 to 4 flowers and inserting the body inside the flower to obtain nectar. Since most of the observation were indirect and complete process of pollination was not witnessed, they were classified as probable pollinator. Further studies is therefore essential before confirming or even assuming bumble bee as pollinator of Cymbidium species. However, it was interesting to note that the Cymbidium species use food-fraud mechanism by exhibiting large showy flowers to attract pollinators. Bumble bees were the common visitor to orchids for nectar or deceived to help in pollination.

The transfer of pollinia to stigma was not observed yet the mode of attraction used by the orchid to attract its pollinator can be predicted. The Cymbidium species mentioned above have no nectary reward for the pollinator and attracts the pollinator by food deception mechanism. The pollinator enters inside the flower to explore the base to get nectar and as it exist out from the flower pollinia gets attached on the pollinator’s thoracic region. If a flower does not provide food source they tend to avoid the flower after their first attempt.  This might be one reason that cause this pollinator to forage more on rewarding flowers that the non-rewarding deceptive orchids. Therefore pollinia of the Cymbidium species were mostly found to be carried on scutellum of the pollinator but successful transfer on stigma was not observed.

Images below shows pollinia carried by orchids on their thoracic region and also visiting Coelogyne, Otochilus and Cymbidium.

Pollinators of orchids in Bhutan: The pollinators

Orchids Polllinators

The most common pollinators belongs to order Hymenoptera, Lepidoptera, Diptera, birds (Dodson et al., 1969) and Coleopteran (Dalstrom, Tobgay, & Wangdi, 2015; Lehnebach & Robertson, 2004).  About 60% of the Orchidaceae are said to be pollinated by the bees and wasp, which includes halictid bee, bumble bee, honeybee, carpenter bee and other oil gathering bees (Attri & Kant, 2011). Wasp species such as Vespa, robber flies, carrion flies, butterflies, moths are some of the pollinators which are attracted by the orchids by mimicry or food rewards (Pemberton, 2010). Orthoptera pollinators were also observed in Angraecum cadetti, which was pollinated by raspy cricket (Micheneau et al., 2009).

According to Ackerman (1983), the visitors that remove the pollinarium from the column and carry to another flower of same species can affect the pollination due to the relative position of stigma with respect to anther. Thus the pollinator carrying pollinia is considered as real pollinator of that particular orchid species.  The pollina are deposited on the dorsal part of the insect which is called nototrobic. The deposition can be observed on thorax, legs, mouth, frons and eye of the pollinators. The site of the deposition depend on the morphology of orchid flower and the position of the pollinators entering and exiting the flower. A suitable body surface for pollinia deposition is important since if suitable area is not present the visitor cannot function as pollinator. Such case is seen in bats therefore they have never been observed as the pollinator of orchids (Johnson & Edwards, 1999).

The illustrations above shows the notorobic attachment of pollinia of orchids on it pollinators. the sketch was made from the image taken during the field studies. this images will be given during the up coming blogs on individual pollinators.

The pollinator to be the true pollinators of the orchids need to fulfill the criteria. The criteria includes observing pollinator body coming in contact with the anther, attachment of the pollinia on their body and detachment of the pollinia on the stigma. Based on such observation the pollinators are categorized as confirmed, probable and suggested pollinators. The confirmed pollinators are those that successfully transfer the pollinia to the stigma, probable pollinators are found to attach the pollinia on their body but visitation and deposition on stigma was not reported. The suggested pollinators are carrying or not carrying pollinia but found to visit the inflorescence (Adams & Lawson, 1993).

References

Ackerman, J. D. (1983). Specificity and mutual dependency of orchid-euglossine bee interactions.Botanical Journal of the Linnean Society, 20, 301-314. Retrieved from http://academic.oup.com/biolinnean/article-abstract/20/3/301/2666316

Adams, B. P., & Lawson, D. S. (1993). Pollination in Australian Orchids: A Critical Assessment of The Literature 1882-1992. Australian Journal of Botany, 41(5), 553-575. Retrieved from http://www.publish.ci\siro.au/BT/BT9930553

Attri, L. K., & Kant, R. (2011). Orchid Pollination : An Observation on Pollination-Pollinator Interaction in Cymbidium pendulum (Sw .) Roxb. Current Botany, 2(7), 5-8. Retrieved from http://updatepublishing.com/journal/index.php/cb/article/view/1357

Dalstrom, S., Tobgay, S., & Wangdi, D. (2015). Orchids of Bhutan: An Expected Alleged Natural Vanda Hybrid. Researchgate. Retrieved on 24 August, 2018, from http://www.researchgate.net/profile/Stig_Dalstrom/publication/31344649_Orchids_of_Bhutan_An_expacted_alleged_natural_Vanda_hybrid_pdf

Dodson, C. H., Dressler, R. L., Hills, H. G., Adams, R. M., & Williams, N. H. (1969). Biologically active compounds in orchid fragances. Science, 164, 1243-1249. Retrieved from http://www.researchgate.net/profile/Robert_Dressler/publication/256692263

Johnson, D. S., & Edwards, J. T. (1999). The structure and function of orchid pollinaria. Plant Systematics and Evolution, 222, 243-269. Retrieved from http://link.springer.com/article/10.1007/BF00984105

Lehnebach, C. A., & Robertson, A. W. (2004). Pollination ecology of four epiphytic orchids of New Zealand. Annals of Botany, 93(6), 773-781. doi: 10.1093/aob/mch097

Micheneau, C., Johnson, S. D., & Fay, M. F. (2009). Orchid pollination: from Darwin to the present day. Botanical Journal of the Linnean Society, 161(1), 1-19. doi: 10.1111/j.1095-8339.2009.00995.x

Pemberton, R. W. (2010). Biotic resource needs of specialist orchid pollinators. Botanical Review, 76(2), 275-292. doi: 10.1007/s12229-010-9047-7

Pollinators of orchids in Bhutan: Understanding orchids Pollination