Floral Scent Attraction in Geonoma macrostachys, an Understorey Palm of the Amazonian Rain Forest

Abstract

The flowers of Geonoma macrostachys, a monoecious, neotropical, understorey palm, produce a strong floral scent and are visited by beetles, flies, and bees. To study the importance of floral scent in the attraction of insects to G. macrostachys, a biotest with natural scented and non-scented inflorescence models was set up in the field. Variation in floral scent composition was studied diurnally as well as between staminate and pistillate flowers and individuals. Floral scent was collected using headspace methods and was analysed by combined gas chromatography-mass spectrometry. The natural scented inflorescence models attracted significantly (p<0.0001) more insects than the non-scented models. Although the total amount of floral scent produced decreased steadily during the daily flowering, individual compounds showed three patterns of variation: a steady decrease, an increase during the morning followed by a steady decrease, and an increase during the morning and midday followed by a steady decrease. The variation in chemical composition of the floral scent of staminate and pistillate flowers on the same individual was as large as it was between all pistillate and staminate samples and individuals investigated. The diurnal variation in floral scent production and composition is hypothesized to be related to a daily variation in the visiting fauna. Due to floral scent collection on both staminate and pistillate flowers male euglossine bees are regarded as potentially important pollinators of G. macrostachys. However. G. macrostachys rely partly on a deceptive pollination strategy, since, for all visitors except male euglossine bees the pistillate flowers contain no reward.