Floral Phenylpropanoid Cocktail and Architecture of Bulbophyllum vinaceum Orchid in Attracting Fruit Flies for Pollination

Abstract

It is widely believed that most orchid flowers attract insects by using deception or chemical rewards in the form of nectar. Flowers of Bulbophyllum vinaceum produce a large array of phenylpropanoids that lure tephritid fruit fly males and also act as floral reward, which the flies subsequently convert to pheromone components. The major floral volatile components identified are methyl eugenol (ME), trans-coniferyl alcohol (CF), 2-allyl-4,5-dimethoxphenol (DMP), and trans-3,4-dimethoxycinnamyl acetate, whereas the minor components are eugenol, euasarone, trans-3,4-dimethoxy cinnamyl alcohol, and cis-coniferyl alcohol. Among the various floral parts, the lip (which is held in a closed position up against the sexual organs) has the highest concentration of the major compounds. An attracted male fly normally lands on one of the petals before climbing up onto and forcing the "spring loaded" floral lip into the open position, hence exposing the floral sexual organs. The architecture and location of chemical attractants of the lip compel the fly to align itself along the lip's longitudinal axis in a precise manner. As the fly laps up the compounds and moves towards the base of the lip, it passes the point of imbalance causing the lip to spring back to its normal closed position. The fly is catapulted headfirst into the column cavity, and its dorsum strikes the protruding sticky base of the hamulus and adheres to it. The momentum of the fly and the structural morphology of the long stiff hamulus act to pry out the pollinia from its anther cover. Hence, the pollinarium (pollinia + hamulus) is detached from the flower and adhered to the fly's dorsum. In this unique mutualistic association, both species receive direct reproductive benefits--the flower's pollinarium is transported for cross pollination, and the fly is offered a bouquet of phenylpropanoids (synomone) that it consumes, converts, and/or sequesters as sex pheromonal components, thus enhancing sexual attraction and mating success.

Methyl Eugenol: Its Occurrence, Distribution, and Role in Nature, Especially in Relation to Insect Behavior and Pollination

“…dorsalis with one or two Ba . unimacula in the highlands of Sabah (Tan et al 2006). An attracted male fly normally lands on one of the petals before climbing onto and forcing the “spring loaded” floral lip that has the highest concentration of the phenylpropanoids, into the open position.…”

Chemical ecology of insect–plant interactions: ecological significance of plant secondary metabolites

“…The orchid flower seems to endow the male flies not only with precursor attractant (44) but also intact pheromone (45 and 46), although the complete pollinator spectrum and actual role of such a multi-component system of attractant volatiles is unclear. 81) Another fruit fly orchid, Bulbophyllum apertum releases raspberry ketone (RK, 49) in its fragrance to attract several RK-sensitive Bactrocera species such as the melon fly, B. cucubitae.…”

Comparison of phenylpropanoid volatiles in male rectal pheromone gland after methyl eugenol consumption, and molecular phylogenetic relationship of four global pest fruit fly species: Bactrocera invadens, B. dorsalis, B. correcta and B. zonata

“…In the wild, native males actively seek and ingest ME from natural sources (Tan 2009;Tan et al 2002Tan et al , 2006. There are ca.…”