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

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.