Movements of floral parts and roles of the tooth on the column wall of &lt;i&gt;Bulbophyllum praetervisum&lt;/i&gt; (Orchidaceae) flower in pollination by Dacini fruit flies (Diptera: Tephritidae)

Keng Hong Tan,Lin Tze Tan

doi:10.26786/1920-7603(2018)19

Abstract

Bulbophyllum is the largest genus of the orchid family, with about 2000 species that are mainly pollinated by flies. Flowers of many Bulbophyllum species under the Sections Sestochilos and Beccariana specifically attract Dacini fruit flies, Bactrocera and Zeugodacus species, as pollinators. Non-nectar producing and non-resupinate solitary flowers of Bu. pratervisum emit specific and pleasant floral fragrances to specifically attract and reward male fruit flies. Slippery surfaces on their lateral sepals aid in pollination. Although pollinia removal by male fruit flies has been observed frequently, deposition of pollinia to complete pollination (by two males of Ba. albistrigata and Z. caudatus) has only been observed recently. Field observations show two previously unreported movements of floral parts – a) petals and medial sepal during daily closing and reopening of flowers, and b) the spring-loaded and hinged lip during removal and deposition of pollinia by a male fruit fly. Additionally, a third (novel) movement has been observed, either when the flower closes for the night to protect the stigma, or after a fly has deposited the pollinia onto the stigma, the 'acute tooth' on each column wall folds inwards specifically to secure the newly deposited pollinia.

Highlights

Orchids have fascinating pollination mechanisms (Baker, H.G. 1963, Jersakova et al 2006, Lord & Russell 2002, Tan & Nishida 2013), frequently including display and deception
Since there is no published report on either the movements of floral parts or the role of the floral tooth on each column lateral wall (CLW), we describe and discuss a) three movements shown by different sets of floral parts to ensure successful pollination from blooming until just before fertilisation, and b) the roles of the tooth on each CLW in Bu. praetervisum flowers
It was necessary to perform artificial pollination to study movements of CLW and its acute tooth to confirm our observation after the witnessing the two natural depositions of pollinia

Summary

Introduction

Orchids have fascinating pollination mechanisms (Baker, H.G. 1963, Jersakova et al 2006, Lord & Russell 2002, Tan & Nishida 2013), frequently including display (via bright colour) and deception (via fragrance/odour). This species was reported to be pollinated by tephritid fruit flies – namely Ba. albistrigata (Radian & Padmarsari 2012), the actual deposition of pollinia onto the stigma was not observed. Flowers of Bu. praetervisum release mainly RK while those of Bu. macranthum release zingerone (except a chemotype from Philippines) to attract males of certain Bactrocera and Zeugodacus species for pollination (Nakahira et al 2018).

Results

Conclusion