Pollination of a threatened orchid by an introduced hawk moth species in the tallgrass prairie of North America

The decline of the threatened western prairie fringed orchid (Platanthera praeclara Sheviak and Bowles) is associated with destruction of the tallgrass prairie in North America. The role of pollinators in conservation and recovery is not well understood. We studied interactions with hawk moth pollinators in one of the three remaining metapopulations of P. praeclara. In an experiment, plants exposed to moths showed three signs of visitation that were associated with production of seed capsules. Plants not exposed to moths failed to produce capsules. The signs of visitation were used to estimate visitation rates at field sites over a four-year period. A majority of plants were visited (89%) and most flowers receiving pollen produced a seed capsule (60%). We discovered two new native hawk moth pollinator species, Lintneria eremitus (Hübner) and Hyles lineata (Fabricius), giving a total of five pollinators for this P. praeclara metapopulation. Only one of the five species was found in each of the nine years of trapping. This was the sole non-native pollinator, Hyles euphorbiae L., a Eurasian species introduced to North America to control an invasive weed, leafy spurge (Euphorbia esula L.). Given that plants with a greater diversity of pollinators have reduced risk of extinction, conservation and recovery plans should expand the definition of suitable P. praeclara habitat to include resources required by native pollinators, including the host plants that feed hawk moth larvae and the nectar plants that feed hawk moth adults before and after the nectar provided by P. praeclara.