Enhancing pollination of the endangered western prairie fringed orchid (Platanthera praeclara) by sphinx moths (Lepidoptera: Sphingidae) in tall grass prairie in southeastern Manitoba and an examination of orchid nectar production

Abstract

The endangered western prairie fringed orchid, Platanthera praeclara (Sheviak and Bowles), is found in remnant tall grass prairie in southeastern Manitoba, and has a lower level of seed capsule development in comparison to more southern populations in the United States. Pollination of P. praeclara is limited to few select species of sphinx moths, Sphingidae, Lepidoptera, a group that is less abundant in comparison to other lepidopteran families. This study tested the hypothesis that the presence of ultraviolet light sources near orchids would attract more sphinx moths into orchid habitat and increase feeding activity of sphinx moth pollinators, thus increasing seed capsule production. The second part of this study measured orchid nectar quality and quantity during the bloom period and the possible link to pollination success. A significantly larger number of individual flowers and plants developed seed capsules in the ultraviolet light treatment plots (5.13+-0.42% of available flowers; 35.12+-1.74% of total plants) than the control plots (2.78 +- 0.42% of available flowers; 21.76 +- 2.58% of total plants). The intensity of the ultraviolet light treatment may have also had an effect on pollination success. Ultraviolet lights influenced seed capsule production by attracting sphinx moths into experimental plots. Results also indicated that ultraviolet light may be useful to manipulate seed capsule production for other research purposes. Nectar quality and quantity varied considerably during the study. The mean sugar concentration over the sampling season was 23.9+-0.2%; however, values ranged from a low 13% to high of 34%. Nectar sugar concentration decreased by approximately 6% as the flowering period progressed over the season. % of total plants) than the control plots (2.7g + 0.42 %o of available flowers; 2l .7 6 + 2.58 %o of total plants). The intensity of the ultraviolet light treatment may have also had an effect on pollination success.