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.