Seasonal Variation in the Nectar Sugar Concentration and Nectar Quantity in the Western Prairie Fringed Orchid, Platanthera praeclara (Orchidaceae)

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Abstract The endangered western prairie fringed orchid, Platanthera praeclara, is found in remnant tall grass prairie in the central plains of North America. Platanthera praeclara is pollinated by several species of hawkmoths (Sphingidae) in Canada. There is minimal overlap between the flight period of hawkmoth pollinators and the flowering period of the Canadian orchid population, with orchids normally flowering at the end of the hawkmoth flight period. This study was designed to determine if orchids produce more nectar and higher concentrations of sugars in the nectar at the beginning of the flowering period coinciding with maximal pollinator flight times. As pollinators are nocturnally active, we also determined if orchids produce more nectar or nectar with increased concentrations of sugars during the night versus the daytime. Nectar sugar concentration and the amount of nectar per flower were highest at the beginning of the flowering period, and significantly decreased as the season progressed. Necta...